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No. 1
CONTENTS
Shenghua Zhu, Yonghui Bai, Lunjing Yan, Qiaoling Hao
Fan Li, Characteristics and synergistic effects of copyrolysis of Yining coal and poplar sawdust .......................... 1
Jasmina Gubić, Jelena Tomić, Aleksandra Torbica, Mirela
Iličić, Tatjana Tasić, Ljubiša Šarić, Sanja Popović,
Characterization of several milk proteins in domestic
balkan donkey breed during lactation, using lab-on-a-chip capillary electrophoresis ................................................ 9
Seyed Ali Alavi Fazel, Goharshad Hosseyni, Experimental
investigation on partial pool boiling heat transfer in
pure liquids ........................................................................... 17
Marija Ilić, Franz-Hubert Haegel, Vesna Pavelkić, Dragan
Zlatanović, Snežana Nikolić-Mandić, Aleksandar Lolić,
Zoran Nedić, The Influence of alkyl polyglucosides
(and highly ethoxylated alcohol boosters) on the phase
behavior of a water/toluene/technical alkyl polyethoxylate microemulsion system ........................................ 27
V. Sangeetha, V. Sivakumar, biogas production from
synthetic sago wastewater by anaerobic digestion:
optimization and treatment ................................................... 33
Muhammad Imran Ahmad, Muhammad Sajjad, Irfan Ahmed
Khan, Amina Durrani, Ali Ahmed Durrani, Saeed Gul,
Asmat Ullah, Sustainable production of blended
cement in Pakistan through addition of natural
pozzolana ............................................................................. 41
Yuehao Luo, Robert Smith, Lork Green, Exploring instantaneous micro-imprinting technology on semi-cured
epoxy resin coating based on relationship between
forming precision and curing degree .................................... 47
Zorana Boltić, Mića Jovanović, Slobodan Petrović, Vojislav
Božanić, Marina Mihajlović, Continuous improvement
concepts as a link between quality assurance and
implementation of cleaner production – Case study in
the generic pharmaceutical industry .................................... 55
Aleksandar Golubović, Ivana Veljković, Maja Šćepanović,
Mirjana Grujić-Brojčin, Nataša Tomić, Dušan Mijin,
Biljana Babić, Influence of some sol-gel synthesis
parameters of mesoporous TiO2 on photocatalytic
degradation of pollutants ....................................................... 65
Mehdi Asadollahzadeh, Shahrokh Shahhosseini, Meisam
Torab-Mostaedi, Ahad Ghaemi, The effects of operating parameters on stage efficiency in an oldshuerushton column ..................................................................... 75
CONTENTS Continued
Xiaolei Li, Chunying Zhu, Gas–liquid mass transfer with
instantaneous chemical reaction in a slurry bubble
column containing fine reactant particles ............................. 85
Jelena Popović, Goran Radenković, Jovanka Gašić, Slavoljub Živković, Aleksandar Mitić, Marija Nikolić, Radomir Barac, The examination of sensitivity to corrosion
of nickel-titanium and stainless steel endodontic
instruments in tooth root canal irrigating solutions ............... 95
O.S. Glavaški, S.D. Petrović, V.N. Rajaković-Ognjanović,
T.M. Zeremski, A.M. Dugandžić, D.Ž. Mijin, Photodegradation of dimethenamid-P in deionised and ground
water ...................................................................................... 101
Sonja V. Smiljanić, Snežana R. Grujić, Mihajlo B. Tošić,
Vladimir D. Živanović, Srđan D. Matijašević, Jelena D.
Nikolić, Vladimir S. Topalović, Effect of La2O3 on the
structure and the properties of strontium borate
glasses ............................................................................... 111
Marija Šljivić-Ivanović, Aleksandra Milenković, Mihajlo Jović,
Slavko Dimović, Ana Mraković, Ivana Smičiklas, NI(II)
immobilization by bio-apatite materials: Appraisal of
chemical, thermal and combined treatments ..................... 117
Activities of the Association of Chemical Engineers of Serbia are supported by:
- Ministry of Education, Science and Technological Development, Republic of Serbia
- Hemofarm Koncern AD, Vršac, Serbia
- Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia
- Faculty of Technology, University of Novi Sad, Novi Sad, Serbia
- Faculty of Technology, University of Niš, Leskovac, Serbia
- Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Belgrade, Serbia
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
SHENGHUA ZHU
YONGHUI BAI
LUNJING YAN
QIAOLING HAO
FAN LI
State Key Laboratory Breeding
Base of Coal Science and
Technology Co-founded by Shanxi
Province and the Ministry of
Science and Technology, Taiyuan
University of Technology, Taiyuan,
China
SCIENTIFIC PAPER
UDC 66.092-977-922(510):622.33
DOI 10.2298/CICEQ141125012Z
CI&CEQ
CHARACTERISTICS AND SYNERGISTIC
EFFECTS OF CO-PYROLYSIS OF YINING
COAL AND POPLAR SAWDUST
Article Highlights
• Co-pyrolysis characteristics of a Chinese coal and poplar sawdust were studied
• Gas product yields of co-pyrolysis shows notable increase than that of separate pyrolysis
• The synergistic effect is contributed mainly by the ash in the poplar sawdust
Abstract
Co-processing of biomass and coal is perceived as a way to enhance the
energy utilization by virtue of the integrated and interactive effects between
different types of carbonaceous fuels. The purpose of this study was to investigate the co-pyrolysis characteristics of Yining coal and poplar sawdust, and to
determine whether there is any synergistic effect in pyrolytic product yields.
The coal was blended with sawdust at mass ratios of 9:1, 7:3, 5:5, 3:7 and 1:9.
The change of char yields, maximum weight loss rate and the corresponding
temperature of different coal/sawdust blends during pyrolysis were compared
by thermogravimetric analysis (TG). The total tar yields during pyrolysis of separate coal and sawdust, as well as their blends, were acquired from the low
temperature aluminum retort distillation test. From the comparison of experimental and theoretical values of the char yields from TG and tar yields from
carbonization test, it was observed that co-pyrolysis of coal/sawdust blends
produced less char and tar than the total amount produced by separate coal
and sawdust pyrolysis. The different product distribution suggested that there
was synergy effect in gas product yields. The co-pyrolysis of demineralized
and devolatilized sawdust with coal indicated that the ash in the sawdust was
the main contributor to the synergistic effect.
Keywords: co-pyrolysis, poplar sawdust, aluminum retort carbonization,
synergies.
To face the severe situation of fossil fuel supply
shortage and environmental pollution, biomass energy
has become a global interest and seen wide application in partly replacing coal in gasification process.
As a renewable energy source, rational utilization of
biomass can effectively solve the problem of energy
shortage [1-5]. Co-pyrolysis, as the preliminary process of co-gasification, plays a crucial role in determining gas product distributions and char structure,
Correspondence: F. Li, State Key Laboratory Breeding Base of
Coal Science and Technology Co-founded by Shanxi Province
and the Ministry of Science and Technology, Taiyuan University
of Technology, Taiyuan 030024, China.
E-mail: lifan66@hotmail.com
Paper received: 25 November, 2014
Paper revised: 27 April, 2015
Paper accepted: 29 April, 2015
which is of vital importance to gasification reactivity.
Therefore, it is necessary to understand the interactions between coal and biomass, the change in pyrolysis characteristic and possible synergistic effects of
coal–biomass blending [6-10].
Although co-processing has become a widely
accepted practice all over the world, the research
results published about synergies still do not have
agreeable conclusions.
Some research results showed that the synergistic effect is dependent on the extent of contact
between fuel particles, and the synergy is more likely
to happen when pyrolysis is carried out on a fixed-bed
reactor than on a fluidized-bed or drop tube reactor
[11,12], while other scholars [13] revealed the lack of
synergistic effects on pyrolytic products yields as well
1
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
as gas composition from pyrolysis of coal/sawdust
blends under both low heating rate in a fixed-bed
reactor and high heating rate in a drop-tube reactor.
Kastanaki et al. also confirmed that the co-pyrolysis of
coal/biomass blends did not have substantial interaction in the solid phase [14]. Masnadi et al. performed switch-grass and coal co-pyrolysis in a thermogravimetric analysis and no significant interaction
between coal and biomass were observed during co-pyrolysis [4]. On the contrary, some researchers [15-18] found an obvious synergy on the overall weight
loss yield and characteristics of pyrolysis products
during the co-pyrolysis of coal and other feedstock,
including oil residue and biomass. Krerkkaiwan et al.
researched co-pyrolysis of coal and biomass using a
drop tube fixed reactor. The results showed that the
biomass has a significant influence not only on the
magnitude of the synergetic effect during the co-pyrolysis but also on the reactivity of the resultant chars
[19]. However, the authors did not consider the interactions between the volatile and coal char, so the
results they got has important dependency on the volatile. Previous study shows that the volatile-char interactions can affect almost every aspect of low-rank
fuel gasification and pyrolysis [20]. Therefore, the
synergies in co-pyrolysis of biomass and coal are still
not clear. Further and more detailed researches are
needed.
Considering that the type of blending fuels was
a major factor that triggers the synergy [21], a typical
Chinese coal and biomass, which have striking difference in volatile content and ash content, were selected as the experimental sample. In this study, the
pyrolysis characteristics and the char yields of the
coal, sawdust and their mixtures were investigated
using TG analyzer, and low temperature aluminum
retort distillation test were carried out to compare the
tar yields of coal, sawdust and their mixture. The synergy during co-pyrolysis was examined by comparing
the theoretical and experimental data. To further
understand the conditions that lead to synergy,
demineralized sawdust (DASA) and devolatilized
sawdust (DVSA) were prepared, and then added to
coal to appraisal whether one of them in biomass is
the main contributor to the synergy.
EXPERIMENTAL
Preparation of raw materials
Chinese bituminous coal from Yining (YN) and
poplar sawdust (SA) were used in this study. The YN
was drawn and manually crushed using a pestle and
a mortar, while the SA was crushed using a grinder.
2
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
Crushed samples were sieved and only particles
between the sizes of 0.074–0.154 mm were used to
run the TG and aluminum retort carbonization test.
The specific particle diameter is consistent with those
produced in practical milling systems used in pulverization units [22]. In our previous study [23], the particle size less than 0.125 mm was found to be able to
eliminate the effects of mass and heat transfer limitations. The mixture of YN and SA (SA-YN) was made
by mechanically blending them together in different
proportions, aSA-bYN means that the mass ratio of
SA to YN is a:b. The addition of biomass to coal has
important influence on the pyrolysis product distribution. In order to comprehensively investigate copyrolysis characteristics, five blending rates ranging
from pure coal to pure biomass in 20 wt.% increments
were chosen in this study. Moreover, the blending
rates are similar to those typically used in industryscale co-firing trails. The ultimate and proximate analyses of the samples were shown in Table 1. The ultimate analysis of the coal was determined following
the Chinese National Standard GB/T 476-2008 for
carbon, hydrogen and nitrogen, and GB/T 214-2007
for sulfur [24,25]. The proximate analysis of the coal
was measured following the Chinese National Standard GB/T 212-2008 for moisture (Mad), ash (Ad) and
volatile matter (Vdaf) [26].
It can be seen that the SA had high content of
volatile and low content of ash, while YN had a
relatively low content of volatile and high content of
ash.
Table 1. Ultimate and proximate analysis data of YN and SA
(wt.%); ad: air-dried basis; daf: dry and ash-free basis; *: by difference
Sample
Ultimate analysis
Cad
Had
O*ad
Nad
Proximate analysis
St,ad
Mad
Vdaf
Ad
YN
58.99 3.28 18.37 0.96 0.36 12.61 33.80
6.21
SA
49.01 2.69 40.50 0.72 0.01
0.41
6.69
82.94
Preparation of DASA and DVSA
First, the pretreatment of raw sawdust in acid
was conducted by the ratio of 1 g:20 mL of HCl solution (37 wt.% HCl was diluted in 1:1 proportion),
soaking for 24 h at room temperature and stirring
continuously using a magnetic stirrer. Then, the HCl-washed sample was blended with hydrofluoric acid
(HF) at a ratio of 1 g to 12.5 mL to prepare the demineralized sawdust sample, soaking for 24 h at room
temperature and stirring continuously using a magnetic stirrer. Finally, the demineralized sawdust sample
was obtained after oven drying to constant weight at
60 °C for 14 h. As to the preparation of DVSA, the
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
sawdust was first pyrolyzed in a high-temperature silicon carbide furnace from room temperature to 800
°C with a heating rate of 10 °C/min in argon atmosphere and had a residence time of 20 min, then the
sample was cooled to room temperature in Ar atmosphere, the residual solid was the DVSA.
Pyrolysis experiments in TG
The TG experiments were performed in the
thermogravimetric analyzer (NETZSCH STA449F3),
the maximum temperature error of the measurement
is ±1 °C and the mass precision is 1 μg. Approximately 10 mg initial sample was fed into the Al2O3 plate
and heated from room temperature to 1000 °C at a
constant heating rate of 10 °C/min under argon atmosphere at a constant flow rate of 50 mL/min. At least 3
repetitions were conducted to ensure the reproducibility of the experiments and accuracy of the data.
The maximum mass loss standard deviation was 3%.
Test of low temperature distillation by aluminum retort
To obtain the tar yields of coal, sawdust and
their mixture during pyrolysis, tests of low temperature distillation by aluminum retort were performed
according to China Standard GB/T 480-2010, “Test of
low temperature distillation of coal by aluminum
retort” [27]. First, 20 g coal sample was packed in
aluminum retort. Then, in the temperature range of
260–510 °C, it was heated with a heating rate of
5 °C/min and it was held at the final temperature for
20 min. After the distillation experiment, the tar, pyrolysis water, char and gas yields were measured. All
the experiments were replicated at least three times
to make sure that the results were reproducible; the
maximum standard deviation in tar yield was 5%.
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
Data processing methods
Theoretical calculation of co-pyrolysis yields of
tar and char
In order to investigate whether interactions
existed between the coal and sawdust, the theoretical
and experimental value of pyrolysis products were
compared. The theoretical value was given by the
following equation:
MT = xMSA + (1-x)MYN
(1)
where MSA is the tar or char yield during single sawdust pyrolysis or aluminum retort carbonization test,
MYN is the tar or char yield during single coal pyrolysis
or aluminum retort carbonization test, MT is the theoretical value of char yield during co-pyrolysis or tar
yield during aluminum retort carbonization test, and x
is the mass fraction of sawdust in solid feed mixture.
RESULTS AND DISCUSSION
TG analysis of the pyrolysis of coal, sawdust and
coal/sawdust blends
Figure 1 shows the weight and the derivative
weight change profiles for coal and sawdust as a
function of temperature. TG/DTG curves of them at a
heating rate of 10 °C/min suggest that both the thermal decomposition and mass loss of poplar sawdust
and Yining coal have three steps during pyrolysis, but
the temperature of the maximum degradation rate
(Tmax) of each step are rather different.
The first stage of YN pyrolysis occurs between
33 and 250 °C, while sawdust pyrolysis occurs
between 33 and 185 °C. A minor mass decay was
observed, this is due to the release of H2O and some
100
0
80
-2
TG / %
SA
40
-4
YN
20
DTG / %/min
60
-6
0
0
200
400
600
800
-8
1000
Temperature / oC
Figure 1. TG/DTG curves of SA and YN at a heating rate of 10 °C/min.
3
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
from 0.96 to 7.22%/min with increasing SA content in
the SA-YN, which means the SA-YN has higher pyrolysis reactivity and the addition of SA could promote
the overall evolution rate of volatile matters.
Char and tar yields
Figure 3 shows the theoretical and experimental
value of char yields of five different mixtures with the
YN:SA rates spanning from 9:1 to 1:9 in 20 wt.%
increments during co-pyrolysis. With increasing SA
addition from 10 to 90%, the experimental and predicted char yields all had a remarkable decrease, the
former was from 32.58 to 5.73% and the latter was
from 45.87 to 8.96%, which was caused by the increase in the absolute amount of high volatile SA
(82.49, daf). Moreover, it is obvious that the experimental char yield of any kind YN-SA is always lower
than the predicted value, the maximum and minimum
differences are 13.28 and 3.23%, respectively, and
the addition of SA have inhibiting effect on pyrolysis
Maximum weight loss rate
Tmax
6
420
400
5
380
Tmax, oC
Maximum weight loss rate, %/min
absorbing gases such as CH4, CO2 and N2. The
greatest fraction of mass loss of sawdust occurs in
the second step, in the temperature range of 250445 °C, which is attributed to the drastic thermal
decomposition of SA, the maximum devolatilization
rate is 7.22%/min and the Tmax is 378 °C. The third
stage covers a wide temperature range from 445 °C
to the final temperature and a slight weight loss was
observed, which was associated with the degradation
of heavier chemical structures in the SA matrix [28].
Figure 1 shows that the profile trend of YN is
similar to that of SA, but different in some pyrolysis
characteristic parameters, especially the Tmax and the
maximum mass loss rate. A more detailed analysis of
the parameters (see Figure 2) suggests that the Tmax
and the maximum mass loss rates of SA-YN with
different ratio, YN and SA varied from each other. The
Tmax for SA-YN was lower than either of the two pure
samples and the maximum weight loss rate shifted
7
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
4
3
360
2
340
1
320
YN
9:1
7:3
5:5
3:7
SA
Proportion of coal to poplar sawdust in the blending sample
Figure 2. Pyrolysis characteristic parameters of different coal/sawdust blending.
100
Difference
Theoretical value of char yield
Experimental value of char yield
Char yields(%)
80
60
40
20
0
9:1
7:3
5:5
3:7
1:9
Proportion of coal to poplar sawdust in the blending sample
Figure 3. Theoretical and experimental value for char yields of different coal/sawdust blending during co-pyrolysis.
4
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
char yield and promotion effect on gas product formation.
As is known, the gas yield was the summation of
un-condensed light gases and condensed volatile
matter (coal tar) at room temperature and pressure.
Therefore, to have a more detailed analysis of SA
addition on tar yields, low temperature aluminum
retort distillation tests of YN, SA, and YN-SA were
conducted respectively. Figure 4 shows 7YN-3SA and
9YN-1SA as examples for interpretation of the difference of experimental and predicted values of tar
yields during distillation test. The tar yield of SA alone
pyrolysis is much higher than that of YN pyrolysis, the
experimental values of tar during 7YN-3SA and 9YN-1SA distillation are 6.41 and 3.26%, and 0.43 and
1.38% lower than the predicted values, which means
that SA has an inhibiting effect on tar yields during copyrolysis, i.e., co-pyrolysis of SA and YN could have
synergistic effects on gas product yields.
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
Synergy analysis
Pyrolysis behavior of SA, DASA and DVSA
Considering co-pyrolysis of SA and YN could
have synergistic effects on gas product yields, the
contribution of ash and volatile in the SA on synergistic effect was investigated. The pyrolysis behavior
of DASA and DVSA were analyzed first. Figure 5
shows the comparison of the TG and DTG curves of
SA, DASA and DVSA. It suggests that the DVSA did
not have an obvious mass loss until the pyrolysis
temperature surpassed 750 °C. The final mass decay
accounts for 39% of DVSA, far below the final value
of SA (92%). It reveals the differences of pyrolysis
behavior of SA and DASA, the onset and final volatile
evolution temperature of DASA was shifted to the
higher and lower temperature, respectively, the volatile release rate of DASA was much higher than that
of SA, and the release time of volatile was shortened.
14
Tar yields / %
12
10
8
6
4
2
0
0
YN
2
SA
M 7:3
M 9:1
4
T 7:3
6
T9:1
Figure 4. Theoretical and experimental value for tar yields of different samples during low temperature aluminum retort distillation (where
T7:3 and M7:3 are the experimental and theoretical value of 7YN-3SA).
100
TG/%
80
60
DASATG
40
DVSATG
SATG
20
0
0
DTG/%/min
-4
DASADTG
SADTG
-8
DVSADTG
-12
-16
0
200
400
600
800
1000
o
Temperature/ C
Figure 5. TG and DTG profiles comparisons between SA, DVSA and DASA.
5
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
It may suggest that the DASA has a larger surface
area and more active sites, which could accelerate
the releasing of volatile. In addition, the alkali/alkaline
earth metals in the SA have important influence on
the pyrolysis reactivity, which could make the pyrolysis reaction happen at lower temperature [28,29]. As
shown in Figure 5, the maximum volatile release rate
of DASA was 16%/min, while the max volatile release
rate of SA was 7%/min.
Co-pyrolysis behavior of YN, DASA and DVSA
Figure 6 gives the comparison of co-pyrolysis
behaviors of YN, DASA and DVSA. The whole pyrolysis process could be divided into three stages, the
first stage occurred between 26 and 200 °C, a faster
H2O release rate and larger amount of 3SA-7YN was
observed than that of 3DASA-7YN due to that DASA
was dried for 24 h after it was prepared. The second
stage was in the temperature range of 200–400 °C
and the strongest weight loss observed was attributed
to the active thermal decomposition of the raw feeds,
the maximum mass loss rate of 3DASA-7YN was
2.68%/min higher than that of 3SA-7YN. It may be
that the ash in the SA had obvious effects on the
synergy. The third stage appeared between 400–1000
°C. As it was also shown in Figure 1, the temperature
range of 400–600 °C was the most drastic mass loss
interval of YN, but the DTG curve of 3SA-7YN in this
temperature range only had slight difference compared with that of 3DASA-7YN.
Compared to the co-pyrolysis curves of 3SA7YN and 3DVSA-7YN, it is clear that the pyrolysis
behaviors of them are quite different. The DTG profile
of 3DVSA-7YN had a remarkable mass loss peak
when the pyrolysis temperature was higher than 680
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
°C, which, however, was not observed in the DTG
curve of 3SA-7YN. Table 2 illustrates the experimental and predicted values of the final mass loss fraction
of 3SA-7YN, 3DVSA-7YN and 3DASA-7YN at terminal pyrolysis temperature of 1000 °C. Since the experimental values are higher than the respective theoretical ones, it may be concluded that the synergy
effect between YN and SA on gas product yields was
observed. Compared with 3DVSA-7YN and 3DASA-7YN, it is obvious that the ash in the SA could widen
the difference between experimental and theoretical
value, suggesting that the ash in the SA was the main
contributor to the synergy between SA and YN. The
demineralized coal and coal-containing fuel blends
along with the demineralized and devolatilized biomass components will be tested in the future.
Table 2. Experimental and predicted values (%) of the final
mass loss fraction of 3SA-7YN, 3DVSA-7YN and 3DASA-7YN
under terminal pyrolysis temperature of 1000 °C
Value
3SA-7YN
3DVSA-7YN
3DASA-7YN
Experimental
41.2
56.8
40.1
Predicted
26.1
40.4
33.8
CONCLUSIONS
In this research, experiments were conducted by
TGA and low temperature aluminum retort distillation
to study the changes in pyrolysis characteristic
parameters and possible synergistic effects of coal–
biomass blending during pyrolysis. The following conclusions can be drawn from the results:
The degradation of poplar sawdust and Yining
coal had three stages in pyrolysis temperature ranging from room temperature to 1000 °C and the tem-
100
TG/%
80
60
3SA-7YNTG
3DASA-7YNTG
40
3DVSA-7YNTG
20
0
DTG/%/min
0
-2
3SA-7YNDTG
3DASA-7YNDTG
-4
3DVSA-7YNDTG
-6
0
200
400
600
800
1000
o
Temperature/ C
Figure 6. Co-pyrolysis behavior of 3SA-7YN, 3DASA-7YN and 3DVSA-7YN.
6
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
peratures of the maximum weight loss rate of each
stage were rather different. The Tmax for SA-YN was
lower than either of the two pure samples and the
maximum weight loss rate shifted from 0.96 to
7.22%/min with the increase of the SA content in the
SA-YN. It indicated that the SA-YN had higher pyrolysis reactivity and the addition of SA could promote
the overall evolution rate of the volatile matters.
The addition of SA had inhibiting effect on char
and tar yields during pyrolysis and supportive effect
on gas product formation. Co-pyrolysis of SA and YN
had synergistic effects on gas product yields.
The volatile matter during SA pyrolysis only had
slight influence on synergy, while the ash in the SA
was the critical factor that led to the synergistic effects
on gas product yields.
Acknowledgements
The authors gratefully acknowledge the financial
support from Shanxi Coal Based Key Scientific and
Technological Project (No. MH2014-02) and National
Natural Science Foundation (21176166).
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7
S. ZHU et al.: CHARACTERISTICS AND SYNERGISTIC EFFECTS OF…
SHENGHUA ZHU
YONGHUI BAI
LUNJING YAN
QIAOLING HAO
FAN LI
State Key Laboratory Breeding
Base of Coal Science and
Technology Co-founded by Shanxi
Province and the Ministry of
Science and Technology, Taiyuan
University of Technology, Taiyuan,
China
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 1−8 (2016)
KARAKTERISTIKE I SINERGIJSKI EFEKAT
PIROLIZE UGLJA YINING I PILJEVINE TOPOLE
Procesiranje biomase i uglja predstavlja način za poboljšanje korišćenja energije na
osnovu integrisanih i interaktivnih efekata između različitih vrsta ugljeničnih goriva. Cilj
ovog istraživanja je analiza pirolitičkih karakteristika uglja iz Jininga (Yining, Kina) i piljevine topole, kao i da se utvrdi postojanje sinergiijskog efekta u prinosima pirolitičkih proizvoda. Ugalj je pomešan sa piljevinom u masenim odnosima 9:1, 7:3, 5:5, 3:7 i 1:9. Promena prinosa čađi, maksimalna brzina gubitka mase i odgovarajuća temperatura različitih
mešavina ugalj/piljevina tokom pirolize su upoređeni termogravimetrijskom analizom (TG).
Destilacijom u aluminijumskoj retorti na niskoj temperaturi određen isu ukupni prinosi
katrana za vreme pirolize uglja, piljevine i njihovih mešavina. Poređenjem eksperimentalnih i teorijskih vrednosti prinosa čađi iz TG analize i prinosa katrana iz ispitivanja karbonizacije uočeno je da ko-piroliza mešavine ugalj/piljevina proizvodi manje čađi i katrana od
ukupnih količina proizvedeni u odvojenim procesima pirolize uglja i piljevine. Različita distribucija proizvoda ukazuje na sinergistički efekat u prinosu gasovitih proizvoda. Piroliza
demineralizovane i devolatilizovane piljevine sa ugljem pokazuje da pepeo iz piljevine daje
najveći doprinos sinergističkom efektu.
Ključne reči: Piroliza, piljevina topole, karbonizacija u aluminjimuskoj retorti, sinergija.
8
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 9−15 (2016)
JASMINA GUBIĆ1
JELENA TOMIĆ1
ALEKSANDRA TORBICA1
MIRELA ILIČIĆ2
TATJANA TASIĆ1
LJUBIŠA ŠARIĆ1
SANJA POPOVIĆ1
1
Institute of Food Technology,
University of Novi Sad, Novi Sad,
Serbia
2
Faculty of Technology, University
of Novi Sad, Novi Sad, Serbia
SCIENTIFIC PAPER
UDC 637.12’618(497):543.545.2
DOI 10.2298/CICEQ150105013G
CI&CEQ
CHARACTERIZATION OF SEVERAL MILK
PROTEINS IN DOMESTIC BALKAN DONKEY
BREED DURING LACTATION, USING LAB-ON-A-CHIP CAPILLARY ELECTROPHORESIS
Article Highlights
th
• Protein profile of domestic Balkan donkey milk during lactation period to the 280 day
were determined
• Donkey’s milk protein profiles were determined by applying lab-on-a-chip electrophoresis
• Domestic Balkan donkey milk was found to be low in casein content
• Lysozyme, lactoferrin and immunoglobulins were identified
• Balkan donkey milk represents a rich source of high nutritive components
Abstract
Domestic Balkan donkey (Equus asinus asinus) is a native donkey breed, primarily found in the northern and eastern regions of Serbia. The objective of the
study was to analyze proteins of Domestic Balkan donkey milk during the lactation period (from the 45th to the 280th day) by applying lab-on-a-chip electrophoresis. The chip-based separations were performed on the Agilent 2100
Bioanalyzer in combination with the Protein 80 Plus lab chip kit. The protein
content of domestic Balkan donkey milk during the lactation period of 280 days
ranged from 1.40 to 1.92% and the content of αs1-casein, αs2-casein, β-casein, α-, β-lactoglobulin, lysozyme, lactoferrin and serum albumin was relatively
quantified. Lysozyme (1040-2970 mg/L), α-lactalbumin 12 kDa (1990-2730
mg/L) and α-lactalbumin 17.7 kDa (2240-3090 mg/L) were found to be the proteins with the highest relative concentrations.
Keywords: donkey milk, protein, lab-on-a-chip electrophoresis.
Over the past decades donkey milk has been
less studied compared to ruminant milk, but in the last
few years, interest in donkey milk has considerably
increased among the scientific community of Europe.
Donkey milk has been successfully used in clinical
studies, with children who suffer from cow’s milk protein allergy (CMPA), and has good palatability [1,2].
Its composition is more similar to human milk than
ruminant milk, however. It has a relatively low lipid
content and adequate lipid integration is needed for
toddlers’ diet [3,4]. Other types of milk, such as
mare’s [5], have been proposed as a substitute for
Correspondence: Ja. Gubić, Institute of Food Technology,
University of Novi Sad, Bulevar cara Lazara 1, 21000 Novi Sad,
Serbia.
E-mail: jasmina.gubic@fins.uns.ac.rs
Paper received: 5 January, 2015
Paper revised: 29 April, 2015
Paper accepted: 8 May, 2015
human milk, but scarce information is available regarding the use of donkey milk for this purpose.
Domestic Balkan donkey is a native breed, primarily found in the northern and eastern regions of
Serbia, with about 1000 subjects reared [6,7]. The
population of this breed is nowadays reduced to a
very low number. Therefore, it is very important to
preserve the breed and to increase the number of
animals, in order to achieve milk production in significant amounts. FAO – the organization of food and
agriculture – has initiated and recommended activities
for the mentioned breed protection. Specific milk
characteristics and parameters are the effect of the
keeping conditions and pasture feeding, climate, as
well as the race [8]. Donkey milk has been traditionally used in Serbia as a natural remedy for the treatment of asthma and bronchitis. Considering this fact,
there has recently been a growing demand for donkey
milk in the Serbian market [9].
9
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
Donkey milk has a lower protein content than
other ruminant milk ranging from 13 to 28 g/L, while
proteomic profile is quite similar to human milk
[10,11]. Protein content varies considerably among
species and is influenced by breed, stage of lactation,
feeding, climate, parity, season, and udder health
status [12]. The content of casein in donkey milk
ranges from 6.4 to 10.3 g/kg of total protein content.
Generally, casein present in different types of milk
consists of four genetic fractions: αs1-, αs2-, β- and
k-casein [13]. Guo et al. [14] reported that the content
of whey proteins in donkey milk is within the range
from 4.9 to 8.0 g/kg of total protein. According to the
research by Cunsolo et al. [15], considerable differences can exist between the primary structure of donkey and bovine αs1-casein, which could be related to
the previously demonstrated low allergenic properties
of donkey milk and could contribute to its better
human tolerance.
The basic whey proteins in donkey milk are
β-lactoglobulin, α-lactalbumin, immunoglobulins, blood
serum albumins, lactoferrin and lysozyme [16,17].
The β-lactoglobulin is present in donkey milk as a
monomer whereas this protein is a dimer in ruminant
milk [11] and has better digestibility in newborns due
to higher digestibility and absorption of soluble monomer proteins [18,19]. Furthermore, there is a possibility of utilization of low-cost protein in formulations
for infant feeding [20].
Donkey milk contains several antimicrobial components, including lactoferrin, lactoperoxidase and
lysozyme [14,21]. Šarić et al. [9] investigated the antibacterial properties and the protein profile of raw milk
from the native Serbian donkey breed with an emphasis on the lysozymes and lactoferrin. The average
lysozyme content of 1.0 mg/mL determined is considerably higher compared to the milk of other species
[13,16].
SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel) electrophoresis analysis is a commonly
used method for protein separation, which is also
widely applied to donkey milk analysis. Salimei et al.
[13] and Guo et al. [14] have, using this method, concluded that whey proteins such as β-lactoglobulin,
lysozyme and α-lactalbumin are the most abundant in
donkey milk originating from Italian breeds, and lactoferrin, serum albumin and immunoglobulins were
found to be minor protein components.
Criscione et al. [22] used mass spectrometry
and high performance liquid chromatography to characterize IEF patterns. The authors reported the absence of αs1-casein in some individual cases and the
presence of αs2-casein in all donkey milk samples.
10
Chem. Ind. Chem. Eng. Q. 22 (1) 9−15 (2016)
Polidori et al. [11] analyzed donkey milk proteins
using two-dimensional electrophoresis (2-DE) followed by N-terminal analysis and found and determined β-caseins with molecular weights ranging from
33.10 to 33.74 kDa and from 31.15 to 32.15 kDa and
lower.
Since literature data on use of donkey milk in
human nutrition and its changes during lactation is
very limited, the main objective of this study was to
characterize several of the proteins of domestic Balkan donkey milk during the lactation period from the
45th to the 280th day. Moreover, the aim of this study
was to evaluate the nutritional value of domestic Balkan donkey milk from the protein point of view, by
applying lab-on-a-chip electrophoresis. Deep knowledge of the protein composition and variability could
be beneficial for a more appropriate use in infant
feeding.
MATERIALS AND METHODS
Sample collection
The research on domestic Balkan donkeys, a
native breed, was conducted in the Special Nature
Reserve Zasavica [23]. Zasavica is located in the
north-west region of Serbia and is currently home for
a herd of more than 150 female donkeys. Donkey milk
samples were individually collected from 10 female
domestic Balkan donkeys, after parturition from spring
(April) to winter (January) season, on the 45th, 60th,
80th, 100th, 125th, 150th, 170th, 200th, 230th and 280th
day of lactation. From June to early October the animals in the grassland of Zasavica reservation were
reared outdoors on pasture, where they had the possibility to consume meadow plants. During other
months of the year, donkeys were reared indoors, in a
covered area, and they were fed with corn and corn
stalks, while hay was available ad libitum. From April
to June the way of feeding changed substantially.
Corn and fresh water clover were given to the animals
before milking. Donkeys had access to water ad libitum.
The animals were manually milked twice a day,
at 7:00 am and 3:00 pm, 120 min after separating
foals from their mothers. During milking, foals remained in visual and tactile contact with their mothers.
Milk was completely removed from both udders. Each
individual raw milk sample was collected into glass
flasks and stored in an ice box at 4 °C. For each day
of sampling, which is 10 days in total, 10 individual
samples were collected twice (morning and evening)
for a total of 200 samples.
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
Protein determination
Chem. Ind. Chem. Eng. Q. 22 (1) 9−15 (2016)
RESULTS AND DISCUSSION
Total protein concentration was measured
through nitrogen determination. Total nitrogen was
determined by the application of ISO standard
method [24]. A nitrogen conversion factor of 6.38 was
used for the calculation of the protein content of milk
samples.
Electrophoretic analysis
The proteins of donkey milk were separated and
quantitated using lab-on-a-chip electrophoresis technique based on their molecular mass in comparison
with the marker protein ladder [25]. Sample preparation was carried out according to Tidona et al. [26]
with minor modifications. Milk samples were diluted in
1:1.5 (V/V) ratio, sample: buffer (0.125 M Tris-HCl,
4% SDS, 2% glycerol, 2% β-mercaptoethanol, pH
6.8) and heated at 100 °C for 5 min.
The chip-based separations were performed
using Agilent 2100 bioanalyzer (Agilent Technologies,
Santa Clara, CA, USA) in combination with the Protein 80 Plus lab chip kit and the dedicated Protein 80
software assay on 2100 expert software. Chips were
prepared according to the protocol provided by the
Protein 80 lab chip kit. The Protein 80 ladder (1.6, 3.5,
6.5, 15, 28, 46, 63 and 95 kDa) and the internal
markers were used as reference for sizing and relative quantification. According to Živančev et al. [27]
values of LOD and LOQ for the proteins in the analyzed solutions were 5.4 and 8.4 ng/μL, respectively.
Statistical analysis
The one way ANOVA analysis and Duncan post
hoc test were performed to assess data differences
between various samples using Statistical software
version 12 (STAT SOFT Inc., 2013, USA). The data
means were considered to be significantly different at
P < 0.05.
Protein content of domestic Balkan donkey milk
during the lactation period of 280 days is shown in
Table 1.
The protein content reached the highest value of
1.92% on the 60th day of the lactation stage. Afterwards, the concentration decreased until the end of
the lactation period when it reached the value of
1.40%. The protein content in Domestic Balkan donkey milk is in agreement with others studies on Italian
donkey breeds – Martina Franca, Ragusana and
Amiata [4,13,28,29].
Figure 1a and b shows the molecular weight (in
kDa) of the bands present at the beginning and at the
end of the lactation period. The proteins were determined based on the literature data [11,21,22] by comparison of molecular weights and relative concentrations.
The bands of basic casein proteins that have
been discovered have molecular weights ∼30.3 kDa
(αs1-casein) and ∼26.7–27.0 kDa (αs2-casein). The
findings showed two bands with 16-16.7 and 34.5–35.0 kDa for β-casein in donkey milk. The results of
electrophoresis showed a pattern similar to that reported in the literature [11,13,16]. The chip-based separation profiles of soluble proteins of donkey milk
quantified α-lactalbumin with approximate molecular
weight of 12 and 17.7 kDa. β-lactoglobulin and serum
albumin molecular weights in whey protein fraction
were around 19.6 and 66.0 kDa, respectively.
Major antimicrobial proteins determined in donkey milk were immunoglobulin (Mr 37-38 kDa), lactoferrin (Mr 74-78 kDa) and lysozyme (Mr 14.7-15.0
kDa). The results obtained in this research are similar
to those obtained by other authors [11,21,22].
The concentrations of several protein fractions
in Balkan donkey milk during the lactation period are
shown in Figure 2. The trend for αs1-casein content
Table 1. Protein content of domestic Balkan donkey milk (total n = 200) during the lactation period of 280 days; results are given as
mean ± standard deviation;*p < 0.05; ns - not significant
Time of milk sampling, day
Protein (nitrogen×6.38), %
Significance level
45
1.83 ± 0.12
*
60
1.92 ± 0.20
*
80
1.73 ± 0.23
*
100
1.70 ± 0.28
*
125
1.64 ± 0.30
*
150
1.62 ± 0.19
*
170
1.49 ± 0.28
ns
200
1.50 ± 0.19
ns
230
1.45 ± 0.19
*
280
1.40 ± 0.20
*
11
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
CI&CEQ 22 (1) 9−15 (2016)
(a)
(b)
th
Figure 1. a) Gel-like image of samples taken on the 45 and the 280th day; b) electropherogram of samples taken from the 45th until
the280th day of the lactation stage.
showed a high variability and ranged from 1160 to
730 mg/L, whereas αs2-casein content ranged from
110 to 74 mg/L. The content of αs1-casein began to
decline significantly from the 60th day until the 150th
day, compared to αs2-casein whose content started
decreasing after the 150th day and continued until the
end of the lactation period. Trend variations for αs1casein content throughout the lactation period were
related to the change in total protein content. During
the lactation period, the values of αs2-casein did not
change significantly until the 150th day, and followed
the same pattern from the 170th to the 230th day
12
(P < 0.05). However, the β-casein content (P < 0.05)
decreased significantly (84 to 13 mg/L) from the
beginning to the end of the lactation period.
The content of α-lactalbumin was 2730 mg/L in
the early and 2240 mg/L in the late lactation stage,
which is very similar to the content found in human
milk (2200 mg/L) [16]. The α-lactalbumin content
showed a significant increase four months after parturition and reached values of 2450 to 3090 mg/L,
after which the content decreased and remained quite
stable until the end of the lactation period. The concentration of β-lactoglobulin varied from 139 to 263
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
CI&CEQ 22 (1) 9−15 (2016)
Figure 2. Trend of the concentration (mg/L) of several proteins fractions in Balkan donkey milk during the lactation period.
mg/L. β-Lactoglobulin concentration decreased significantly (P < 0.05) after the 60th day and also after
the 150th day of lactation. Though β-lactoglobulin is
generally resistant to gastro-intestinal enzymes, in a
simulated in vitro digestion of donkey milk 70% of the
β-lactoglobulin was digested, which is the amount
twice as high compared to the bovine counterpart
[30,31]. Also, equine β-lactoglobulin was digested significantly faster compared to bovine and caprine
β-lactoglobulin [31]. The serum albumin content (113-238 mg/L) showed a tendency towards stabilization
during the mid-lactation period.
High concentrations of lysozyme were quantified
in Balkan donkey milk, in which it ranged from 1040 to
2970 mg/L. The lysozyme content was stable during
different stages of lactation and significantly decreased (P < 0.05) after the 150th day. Donkey milk is
known to be a rich source of lysozyme (1000 mg/L)
[16] and has a significantly higher content of lysozyme than human milk (400 mg/L) and bovine milk
(130 mg/L), while being quite similar to that in equine
milk (400-1000 mg/L) [29,32]. Lysozyme inhibits the
growth of a large number of gram positive bacteria.
Šarić et al. [9] investigated the antibacterial properties
and the protein profile of raw milk from the native
donkey Serbian breed with an emphasis on the lysozyme and lactoferrin contents. Lysozyme and α-lactalbumin showed high resistance to human gastric
and duodenal juices as already reported for raw
equine, cow and human milk [30,31]. In our study,
-lactalbumin was the dominant protein fraction of
donkey milk, while immunoglobulin and lactoferrin
were minor components. The lactoferrin content (87–
–13 mg/L) decreased significantly from the beginning
to the end of the lactation period, and showed similar
trend as β-casein. The immunoglobulin had an increasing trend, reaching the climax on the 100th day
(88.3 mg/L) and decreasing thereafter. The high content of protective antimicrobial compounds in donkey
milk taken from the early and middle lactation period
suggested its beneficial impact on gut health and
immune defense system.
13
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
Chem. Ind. Chem. Eng. Q. 22 (1) 9−15 (2016)
CONCLUSIONS
[9]
Lj. Šarić, B. Šarić, A. Mandić, A. Torbica, J. Tomić, D.
Cvetković, Đ. Okanović, Int. Dairy J. 25 (2012) 142-146
Lab-on-a-chip capillary electrophoresis could be
applied to the relative quantification of several milk
proteins. αs1-casein, αs2-casein, β-casein, α-lactalbumin, β-lactoglobulin, lysozyme, lactoferrin and
serum albumin were relatively quantified, with the
highest relative concentration of lysozyme and α-lactalbumin. The concentration of all determined proteins
decreased during the lactation period. The minimum
significant changes were observed for αs2-casein,
lysozyme and β-lactoglobulin. It can be concluded
that Balkan donkey milk represents a source of antibacterical proteins such as lysozyme and highly digestible proteins such as whey protein, α-lactalbumin
and lactoferrin.
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Acknowledgments
This paper is part of the research work on the
project III46012 financed by the Ministry of Education,
Science and Technological Development of the Republic of Serbia. We would like to thank Mr Slobodan
Simić and Nikola Nilić (Special Nature Reserve
Zasavica, Serbia) for milk samples and great cooperation.
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conservation, report 2007/2008, Monitoring Institute for
Rare Breeds and Seeds in Europe/SAVE Foundation: St
Gallen, Switzerland.
S. Stojanović, PhD Thesis, University of Novi Sad, Novi
Sad, 2012, p. 25 (in Serbian)
[20]
M. Friedman, J. Agric. Food Chem. 44 (1996) 6-29
[21]
F. Nazzaro, P. Orlando, F. Fratianni, R. Coppola, Open
Food Sci. J. 4 (2010) 43-47
[22]
A. Criscione, V. Cunsolo, S. Bordonaro, A. M. Guastella,
R. Saletti, A. Zuccaro, Int. Dairy J. 19 (2009) 190-197
[23]
http://www.zasavica.org.rs/en/o-magarcima/
11 May 2011)
[24]
ISO Standard 8968-1:2001 (E) (2001)
[25]
S.G. Anema, Int. Dairy J. 19 (2009) 198-204
[26]
F. Tidona, C. Sekse, A. Criscione, M. Jacobsen, S. Bordonaro, D. Marletta. G.E. Vegarud, Int. Dairy J. 21 (2011)
158-165
[27]
D.R. Živančev, B.G. Nikolovski, A.M. Torbica, J.S.
Mastilović, N.H. Đukić, Chem. Ind. Chem. Eng. Q. 19
(2013) 553-561
[28]
C. Giosuè, M. Alabiso, G. Russo, M.L. Alicata, C. Torrisi,
Anim. 2 (2008) 1491-1495
[29]
A. Alabiso, C. Giosuè, M.L. Alicata, F. Mazza, G.
Iannolino, Anim. 3 (2008) 543-547
[30]
R.A.E. Inglingstad, T.G. Devold, E.K. Eriksen, H. Holm,
M. Jacobsen, K.H. Liland, E.O. Rukke, G.E. Vegarud,
Dairy Sci. Tech. 90 (2010) 549-560
[31]
F. Tidona, A. Criscione, T.G. Devold, S. Bordonaro, D.M.
Gerd, E. Vegarud, Int. Dairy J. 35 (2014) 57-62
[32]
R. Floris, I. Recio, B. Berkhout, S. Visser, Curr. Pharm.
Des. 9 (2003) 1257-127.
(accessed
J. GUBIĆ et al.: CHARACTERIZATION OF SEVERAL MILK PROTEINS…
JASMINA GUBIĆ1
JELENA TOMIĆ1
ALEKSANDRA TORBICA1
MIRELA ILIČIĆ2
TATJANA TASIĆ1
LJUBIŠA ŠARIĆ1
SANJA POPOVIĆ1
1
Naučni institut za prehrambene
tehnologije, Univerzitet u Novom Sadu,
Bulevar cara Lazara 1, 21000 Novi
Sad, Srbija
2
Tehnološki fakultet, Univerzitet u
Novom Sadu, Bulevar cara Lazara 1,
21000 Novi Sad, Srbija
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 9−15 (2016)
KARAKTERIZACIJA NEKOLIKO PROTEINA MLEKA
RASE DOMAĆI BALKANSKI MAGARAC TOKOM
LAKTACIJE, UPOTREBOM LAB-ON-A-CHIP
KAPILARNE ELEKTROFOREZE
Domaći balkanski magarac (Equus asinus asinus) je autohtona rasa, primarno nađena u
severnom i istočnom regionu Srbije. Cilj rada je bio da se analiziraju proteini mleka
domaćeg balkanskog magarca tokom laktacije primenom Lab-on-a-Chip elektroforeze.
Razdvajanje na čipu izvršeno je korišćenjem uređaja Agilent 2100 bioanalyzer u kombinaciji sa Protein 80 Plus Lab Chip kitom. Sadržaj proteina mleka domaćeg balkanskog
magarca tokom laktacionog perioda od 280. dana kretao se od 1,40 do 1,92% i sadržaj
αs1-kazeina, αs2-kazeina, β-kazeina, α-laktalbumina, β-laktoglobulina, lizozima, laktoferina i serum albumina je relativno kvantifikovan. Lizozim (1040-2970 mg/L), α-laktalbumin 12 kDa (1990-2730 mg/L) i α-laktalbumin 17,7 kDa (2240-3090 mg/L) su proteini
koji su nađeni u relativno visokim koncentracijama.
Ključne reči: magareće mleko, protein, lab-on-a-chip elektroforeza.
15
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
SEYED ALI ALAVI FAZEL
GOHARSHAD HOSSEYNI
Department of chemical
engineering, college of chemistry
and chemical engineering,
Mahshahr Branch, Islamic Azad
University, Mahshahr, Iran
SCIENTIFIC PAPER
UDC 66:544.355-145.13
DOI 10.2298/CICEQ150213014F
CI&CEQ
EXPERIMENTAL INVESTIGATION ON
PARTIAL POOL BOILING HEAT TRANSFER IN
PURE LIQUIDS
Article Highlights
• Boiling heat transfer increases with increasing surface roughness
• The bubble shape and oscillating characteristics determined the boiling heat transfer
coefficient
• Eotvos and Roshko numbers are related to boiling heat transfer coefficient
Abstract
Saturated partial pool boiling heat transfer on a horizontal rod heater was investigated experimentally. The boiling liquids included water and ethanol. The heating section was made from various materials including SS316, copper, aluminum
and brass. Experiments were performed at several degrees of surface roughness
ranging between 30 and 360 µm average vertical deviation. The boiling heat
transfer coefficient, bubble departing diameter and frequency, and nucleation site
density were measured. The data have been compared to major existing correlations. It was found that experimental data do not match with major correlations in
the entire range of experiments with acceptable accuracy. The boiling heat transfer area was divided in two complementary areas, the induced forced convection
area and the boiling affected area. Based on two dimensionless groups, including
Eötvös and Roshko numbers, a semi-empirical model is proposed for prediction
of the boiling heat transfer coefficient. It is shown that the proposed model
provides improved performance in prediction of the boiling heat transfer coefficient in comparison with to existing correlations.
Keywords: induced force convection, pool boiling, surface roughness,
heat transfer coefficient.
The nucleate pool boiling phenomenon is widely
applied in many engineering processes. The heat
transfer mechanism from the surface to the boiling
fluid is known to be a very complicated phenomenon.
Design, operation and optimization of the involved
equipment require precise prediction of the boiling
heat transfer coefficient. There has been a lot of
research on pool boiling over the past few decades.
However, the mechanism of pool boiling heat transfer
is still not completely understood. This is because of
the intense complexity of three interconnected heterogeneous parameters: 1) bubble departing diameter,
2) bubble departing frequency, and 3) nucleation site
Correspondence: S. Ali Alavi Fazel, Department of chemical
engineering, college of chemistry and chemical engineering,
Mahshahr Branch, Islamic Azad University, Mahshahr, Iran.
E-mail: alavifazel@gmail.com
Paper received: 13 February, 2015
Paper revised: 17 April, 2015
Paper accepted: 8 May, 2015
density. In addition, the structures of boiling heat
transfer surface are usually very complex and contain
nucleation cavities with various shapes and sizes.
This information is not completely available for every
given heating surface.
In this investigation, the experimental data
covers a wide range of heating surfaces characteristics and liquids physical properties. Water and ethanol have been selected as the boiling liquids. The
cylindrical heating surfaces were made by various
metals including SS316, copper, aluminum and brass.
Each surface has been sanded with several grades to
provide various degrees of roughness. Note that the
roughness is defined as the arithmetic average of the
vertical deviations of the surface.
The experimental data have been compared to
major existing correlations. It is shown that the existing correlations cannot predict the boiling heat transfer coefficient with a satisfactory accuracy. Some of
17
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
the existing correlations may agree well with present
experimental data in some limited degrees of roughness; however the deviations between present experimental data and existing correlations exceed 50%
absolute average error (A.A.E.) in some other degrees of roughness. In this investigation, a new semiempirical model is presented to predict the boiling
heat transfer coefficient with A.A.E. of 11% at full
range of roughness degrees, which is much less than
the A.A.E. of the existing correlations and is within
maximum expected uncertainty of the experimental
procedure.
McNelly [1] has proposed one of the first empirical correlations for prediction of pool boiling heat
transfer coefficient. In this correlation, the physical
characteristics of heating surface are not involved.
Rohsenow [2] has proposed an empirical correlation
based on the bubble agitation mechanism. In this
correlation, the boiling fluid is assumed to be single
phase. In the Rohsenow [2] correlation, the Nusselt
number is empirically correlated to Prandtl and Reynolds numbers. Mostinski [3] has ignored the surface
effects and applied the principle of corresponding
states to pool boiling heat transfer. In this correlation,
the experimental data are correlated to the reduced
pressure and critical pressure of boiling liquid. In this
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
correlation, many tuning parameters have been implemented and additionally the physical properties of
heating surface are totally ignored. Stephan and
Abdelsalam [4] proposed four specific correlations
applying a statistical multiple regression technique to
the following liquid classes: water, organics, refrigerants and cryogenics. In these correlations, the bubble
diameter is estimated by Fritz [5] correlation. Cooper
[6] proposed a new reduced pressure form of pool
boiling heat transfer correlation including the roughness of the boiling surface. Gorenflo [7] has proposed
an empirical correlation based on the reduced pressure of the boiling liquid. In this correlation, the surface roughness is also included. Application of the
Gorenflo [7] correlation requires the specific reference
heat flux, qo and also reference boiling heat transfer
coefficient, α0. Vinayak and Balakrishnan [8] and also
Alavi Fazel, Jamialahmadi and Safekordi [9] have
also a wide-ranging survey on some other correlations. In Table 1, the major existing correlations
have been summarized.
Modeling of problems with stochastic roughness
is very difficult due to the complicated interactions
between bubbles and surface. This problem has been
reviewed by McHale and Garimella [10]. Also the
problem of surface topography is investigated by
Table 1. A summary of major existing correlations
Author
Correlation
McNelly [1]
 qC
l
 Ahfg

α = 0.225 
Rohsenow [2]
 C ΔT
 l
 hfg
Mostinski [3]
q 

A
0.7
α = bPc0.69 
Stephan and Abdelsalam [4]
k
α = 0.23  l
d
Cooper [6]
Gorenflo [7]
α = α 0FqFPFWRFWM
Boyko and Kruzhiline [25]
18
α=
 q /A
; Fq = 
 (q / A )
0

31.4P
c 0.2
Mw 0.1T
c0.9
k
α = 0.082  l
l
0.17
 Pk l 


 σ 
0.31
2 /15
1.2
P 
P
 +  P
P
 c
 c
+ 
0.674
 ρv 
 
 ρl 
0.297
( −logPr )
0.12 − 0.443Ra
 R a0 

 Ra 
Nishikawa [24]



  qd 



  AkT
l s 
FWR = 
0.69
 ρl

− 1

 ρv




q /A
σ


 = C sf 
 μ lhfg  g ( ρl − ρ v ) 




 P
1.8 
  Pc

α = 55Pr




h d 2 
 fg 
 α 
 l2 
−0.55




0.33
Prl

 ; b = 3.75E-5 SIUnit 




0.371
 α 2 ρl 
 l 
 σ d 
Mw −0.55 (q / A )
0.35
 ( ρl − ρ v ) 


ρl


−1.73
0.67
n

 ;


n = 0.9 − 0.3Pr 0.3 ; Fp = 1.2Pr 0.27 + 2.5Pr +
 k l ρC
l pl
; FWM = 
 k 0 ρ 0C p0

( 8R a )
10



0.5
0.33
(
0.2 1− pr
1/ 4




; q 0 / A = 20
Pr
1 − Pr
kW
m2
0.8
) p r0.23q / A
; Rp = 0.125 μm
0.9
(1− 0.99pr )
  hfgq / A  ρ v


  gTsk l  ρl − ρ v

 
 
0.7
T C σP
 s l
 hfg2 ρ 2 l
v





0.33


σ
; l= 

−
g
ρ
ρ

v)
 ( l
0.5
;
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
Jabardo [11] and more recently by Moita, Teodori and
Moreira [12].
EXPERIMENTAL
Apparatus
The boiling vessel contained 35 L of test liquid.
This volume was sufficient to provide pool boiling
conditions. The vessel was thermally insulated to
minimize the heat loss. The temperature of the system was constantly monitored and regulated to saturation point. The vessel was equipped with a rod
heater, which includes four thermocouples, embedded parallel to the heating surface. The input AC
electrical power to the rod heater was adjustable by a
variable electrical transformer. This transformer converts the input AC voltage of 220 V into any selectable voltage between 0-240 V. The electrical input
power to the rod heater is calculated by the product of
electrical voltage, current and cosine of the difference
between electrical voltage and current. A schematic
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
of the rod heater is shown in Figure 1.
The heating surface temperature was calculated
by the integrated form of Fourier’s conduction equation in cylindrical coordinates. In this investigation,
several rod heaters have been produced from different metals, including stainless steel 316 (SS316),
copper, aluminum and brass. These metals have
been selected based on: 1) ease of metalworking, 2)
providing a wide range of physical properties and 3)
availability of the physical properties in the literature.
Because the bubble dynamics and boiling heat transfer coefficient are strongly affected by surface roughness, the surfaces of the heaters were sanded to
provide various degrees of roughness. Roughness is
generally quantified by the vertical deviations of a real
surface from its ideal form. There are many definitions
for surface roughness. In this research, the roughness Ra, is defined as the arithmetic average of the
vertical deviations. Figure 2 presents a typical
measured value of surface roughness.
Figure 1. A schematic of the rod heater.
Figure 2. A typical value of surface roughness.
19
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
In this investigation, water and ethanol have
been chosen as the boiling liquids, based on: 1) the
availability of the physical properties, 2) covering a
wide range of physical properties and 3) non-toxic
properties.
Procedure
Initially, the entire system was cleaned by circulating and draining the boiling liquid through the
vessel, after which the test solution was introduced.
The pressure of the system was kept at about 10 kPa
(abs.) for an hour by a vacuum pump to degas the
boiling liquid. The temperature of the system was
then raised to the saturation temperature, and the
electrical voltage was supplied to the rod heater up to
the maximum value. After reaching steady state, the
surface temperature was recorded. Then, the electrical voltage was decreased in various intervals and
the recordings were repeated in each interval after
steady-state accomplishment. Note that the decreasing path of heat flux was to prevent a hysteresis
effect. Each experiment took about five minutes to
reach a steady state at any specific condition. The
wall temperature was calculated based on the recorded temperatures of the thermocouples inside the
rod heater. The distance between thermocouples location and surface was 0.5 mm, which was introduced
in the integrated form of the Fourier conduction law in
cylindrical coordinates. In addition, the thermal conductivities of individual heating materials were introduced in the Fourier conduction law. The arithmetic
averages of four thermocouples were assigned to the
actual wall temperature. Note that the measured temperatures from the four measuring points were approximately correspondent within ±0.2 K. Some runs
were repeated twice to ensure the reproducibility of
the experiments. The physical properties of liquid and
heating surface were evaluated at bulk and wall temperature, respectively.
To measure the bubble diameter, photographs
of the heating surface have been captured at high
speed at each heat flux. The diameters of 20 bubbles
were measured and the arithmetic averages were
calculated. To measure the bubble departing frequency and nucleation site density, high speed video
recording (1000 fps) was performed at each condition. The slow motion of the recordings was analyzed and the nucleation sites were counted and
divided to project area. In addition, the bubble frequencies of the nucleation sits were counted and the
arithmetic averages were calculated. A Casio EX-FH25 camera was used to record the visual information. The effective resolution of the mentioned
20
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
camera is 10.1 megapixels and the shutter speed is
1/2000 s. These values were sufficient to provide a
sharp and clear image from the heating surface.
A summary of surface characteristics and boiling
fluid at various degrees of roughness are presented in
Table 2. The measured values of the cosine of contact angle between boiling liquid and surface, which
describes the wettability characteristics, are presented in Table 3. Note that the contact angle slightly
varies upon variation of surface temperature; the
mentioned table presents the average values. The
static contact angles are measured when droplet is
standing on the surface and the three-phase boundary is not moving. To measure the static contact
angle, a droplet of specific liquid was placed on the
particular metallic surface. Then, the image of the
drop was captured using a digital camera, which was
equipped with a micro-lens to magnify the subject.
The experimental static contact angle was then
defined by fitting the tangent line on the liquid-solid
contact point. Note that because of the hysteresis
effect, the static contact angle has a spectrum of
contact angles ranging from advancing (maximal), to
the receding (minimal) contact angle. The equilibrium
contact angle is somewhere between those values,
and was calculated by the Tadmor correlation [13].
Table 2. The experimented degrees of roughness at various
boiling fluids and surfaces
Fluid
Aluminum
Water
1.9×10 m 3.0×10 m 3.0×10 m
-4
Brass
-5
-4
-5
Stainless steel 316
-6
2.5×10 m
-4
3.5×10 m
-5
Copper
1.4×10 m
-4
3.6×10 m
-5
-5
Ethanol 3.0×10 m 3.0×10 m 3.0×10 m
-4
Not tested
-4
1.9×10 m
-4
3.5×10 m
1.4×10 m
-4
3.6×10 m
Table 3. The measured values of the cosine of contact angle
between boiling liquid and surface
Fluid
Aluminum
Brass
Copper
Water
0.738
0.623
0.435
Stainless steel 316
0.813
Ethanol
0.902
0.901
0.922
Not tested
Experimental uncertainty
The resolution of the voltmeter, ammeter and
the millivolt meter used in the present study was ±1 V,
±0.1 A and ±0.01 mV respectively. The uncertainty in
the measurement of temperature is ±0.2 K. The propagation error of the four parallel thermocouples,
which are provided to measure the surface temperature, was estimated to (4×0.2)/4 = 0.2 K, which is
equal to 0.2/100 = 0.002 or 0.2% at boiling point of
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
pure water. The maximum propagation error of heat
flux in terms of fractional uncertainty is estimated to:
q 
Δ 
 ΔI
A
=
q 
 I
Δ 
 A best value
  ΔV   0.1   1 
 +  V  =  1.1  +  50  = 0.11
 
 
 

Note that the heat flux is calculated by the
products of electrical voltage and current divided to
the heating area of the rod heater. It is considered
that the heating area was accurate enough to ignore
from error analysis. The standard deviation of measured bubble diameters and bubble frequencies for
water at 25 kW/m2 was typically equal to 0.00009 mm
and 2 Hz, respectively. This means that the uncertainty for measured bubble diameter and bubble frequency would be about 0.00009/0.002 = 4.5% for a
bubble with 2 mm in diameter and 2/100 = 2% for
bubble frequency of 100 Hz. The nucleation sites
were visually counted by the slow motion playback of
the recorded videos without any significant degree of
uncertainty.
Experimental results
The raw numerical values of heat flux versus
degree of superheat are presented in Figure 3. It can
be inferred that the boiling heat transfer coefficient
increases with increasing the degree of superheat at
any constant condition. In addition, the boiling heat
transfer coefficient increases with increasing the surface roughness at any constant condition. This is
because of the enhancement in nucleation site density.
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
The performances of major existing correlation
are presented in Figure 4. The numerical comparisons show that for water/SS316, water/brass and
ethanol/SS316, the Mostinski [3] correlation has the
best performance with 11, 24 and 11% absolute average error (A.A.E.), respectively, while the mentioned
correlation has about 56% A.A.E. for Water/Cu and
Ethanol/Cu boiling systems. For water/Cu, ethanol/
/brass, ethanol/Al and ethanol/Cu, the correlation proposed by Stephan and Abdelsalam [4] has the best
agreement with experimental data with 44, 16, 14 and
34% absolute average error respectively, while the
mention correlation has more than 60% A.A.E. for
water/SS316 boiling system at the average experimented roughness and heat fluxes. These deviations
are large because of the experimental basis of the
existing correlations.
To cross-check the validity of the derived model,
an independent dataset was collected [14]. The mentioned dataset consists of water, acetone, ethyl acetate, 2-propanol, methanol and ethanol at the boiling
liquid. The heating section was pure copper with
smooth texture. To quantify the impact of various
physical properties on boiling heat transfer coefficient,
the sensitivity analysis was performed by arranging
the following equation:
α = ρlg0 ρ vg1hfgg2C lg3 μlg4σ g5k lg6 ρsg7C sg8k sg9
(1)
By using the genetic algorithm, the vector G =
= [g0,g1,…,g9], which represents the exponents of Eq.
(1), is found equal to:
G = [0.46, − 0.86, − 0.39,0.78, − 0.16,0.24, − 0.32, − 0.26, − 0.10,0.37, − 0.10,0.38]
(2)
Figure 3. The raw numerical values of heat flux versus degree of superheat.
21
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
CI&CEQ 22 (0) 000−000 (2016)
Q = qA = q c Ac + q b Ab
(7)
By combining Eqs. (4), (5) and (7) the heat flow
rate can be calculated as:
Q = qA = α b Ab ΔT + α c Ac ΔT
(8)
Assuming the affected areas by spherical bubbles are equal to the projected area of the bubbles, Ab
can be calculated by:
Ab N π 2
= β d
A A 4
Figure 3. The raw numerical values of heat flux versus degree
of superheat.
Modeling
According to Newton’s cooling law, the heat
transfer is proportional to the area and the thermal
driving force, i.e.:
qA = α A ΔT
(3)
In the presence of bubbles on the heating surface, the heating area can be divided by two complementary zones: 1) Ab, the area that is affected by
bubbles and 2) Ac, the convective heat transfer area,
as designated in Figure 5. Each zone has the
individual magnitude of heat transfer, i.e.:
q c Ac = α c Ac ΔT
(4)
and:
q b Ab = α b Ab ΔT
(5)
where the subscripts “c” and ”b” stand for “convection”
and “bubble affected” areas, respectively. Openly, the
following equation is already established:
A Ac Ab
=
+
=1
A A A
(6)
where N/A is the nucleation site density. In the
aforementioned equation, β is the ratio of area of
influence to projected area of bubble at departure.
Judd and Hwang [15] have matched their predicted
heat fluxes with experimental data and reported that
β = 1.8. Some other investigators, such as Han and
Griffith [16], postulated that β = 4. In this investigation,
it is found that the parameter β depends on the shape
and the oscillating behavior of the departing bubble.
Clift, Grace and Weber [17] proposed that the bubble
shapes can be describes by the dimensionless Eötvös number. In addition, because the dimensionless
Roshko number describes the oscillating nature of the
rising bubbles, here it is postulated that the parameter
β should be a function of both Ro and Eö. By regression analysis it is found that:
β = 22−4 Ro .Eö
Summing up Eqs. (4) and (5) yields:
22
(10)
where:
Eö =
( ρl − ρv ) gd 2
(11)
σ
and:
Ro =
fd 2
μl / ρl
(12)
Figure 6 describes the relation between the
aforementioned dimensionless groups. Combining
Eqs. (8) and (9) yields:
α = α c + (α b − α c ) β
Figure 5. Dividing the boiling heat transfer area in the modeling.
(9)
N πd 2
A 4
(13)
where α is the total heat transfer coefficient, αc is the
convective heat transfer coefficient and αb is the heat
transfer coefficient in the bubble affected area (all in
W m-2 K-1).
When a bubble is develops on a heating surface, the heat transfer coefficient through the bubble
stem, αb can be predicted by the correlation proposed
by Mikic and Rohsenow [18]. The heat transfer
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
mechanism is substantiated to be transient conduction around nucleation sites. The heat transfer coefficient is calculated by:
age absolute error of 14% for the entire systems. The
Stephan correlation [21] is an experimental correlation with the following mathematical form:
αb = 2 π k l ρC
l plf
  Ja 2 100000 
d = 0.25 1 + 


Ar 
  Pr 
(14)
0.5
2σ
g ( ρl − ρ v )
(18)
To predict the nucleation site density, the correlation proposed by Xiao, Jiang, Zheng, Chen and Liu
[22] is recommended:
N
−6
= 7.8125e-29 (1 − cosφ ) R c,min
A
(19)
In the aforementioned correlation, the minimum
cavity radius is calculated by:

R c,min =
2

Figure 6. The ratio of area of influence to projected area of
bubble at departure as a function of the products of Roshko
number and Eötvös number.
The convective heat transfer coefficient, αc can
be calculated by the equation proposed by Churchill
and Bernstein [19], which is applicable to forced convection around the horizontal cylinders:
Nu OD = 0.3 +
+
1/2
0.62Re OD
Pr 1/3
1 + ( 0.4 / Pr )2/3 


1/ 4
5/8
  Re

OD 
1 + 
 
  282000  
4/5
(15)
where the dimensionless Reynolds number is calculated based on the upward terminal velocity of
bubbles, uT. The upward terminal velocity can be
calculated by:
uT =
4 d ρl − ρ v
g
3 C d ρl
(16)
and the drag coefficient, Cd, is already calculated by
Ishii and Zuber [20]:
Cd =
24
Re d
(
1 + 0.1Re d0.75
)
(17)
Note that to find the terminal velocity, Eqs. (16)
and (17) should be calculated iteratively, because the
Reynolds number is already a function of the terminal
velocity.
To predict the bubble departing diameter, many
correlations have been compared to experimental
data. It is found that the Stephan correlation [21] has
the best agreement with experimental data with aver-

 θ  4ζ c 2 
δ  θs
− 1− s  −
1−

c1
θw
δθ w 
 θw 


(20)

where:
ζ=
2σTsat
(21)
ρ vhfg
1 + cos ϕ
sin ϕ
(22)
c 2 = 1 + cos ϕ
(23)
c1 =
where ϕ is the contact angle of the fluid and the
heater material. The boundary layer thickness can be
calculated by dividing the liquid thermal conductivity
to the natural convection heat transfer coefficient:
δ=
kl
αNC
(24)
To calculate the bubble departing frequency, the
experimental correlation proposed by Zuber [23] is
recommended:
 σ g ( ρl − ρ v ) 
fd = 0.59 

ρl2


0.25
(25)
Note that in the modeling of the present data,
the experimental values of nucleation site density,
bubble departing frequency and diameter are used.
MODEL VALIDATION
The performance of the new model is compared
to experimental data, as presented in Figure 7. It is
found that 95% of the data points are matching within
±11% absolute average error with experimental data.
Note that the value of ±11% is calculated as the max-
23
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
imum expected uncertainty. To revalidate the new
model, an independent dataset [14] have been compared to the new model as presented in Figure 8. It is
shown that about 90% of the data points are matching
within ±20% absolute average error with experimental
data. It is important to note that the new model is very
sensitive to three key parameter including nucleation
site density, bubble departing frequency and diameter. In evaluating the performance of the new model
by the independent dataset [14], the three aforementioned parameters were estimated by existing correlation introduced by Eqs. (18), (19) and (25). In the
mentioned reference [14], these values are not reported.
Figure 7. The predicted values of heat flux versus the
experimental values of present study.
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
CONCLUSION
In this investigation, saturated nucleate pool
boiling heat transfer was studied experimentally for
two boiling liquids – water and ethanol. Several heating elements were made and tested with different
metals including copper, aluminum, brass and SS316
with various degrees of roughness. The measured
data includes boiling heat transfer coefficient, nucleation site density, bubble departing diameter, as
well as bubble departing frequency. The experimental
heat fluxes were limited to 100 kW m-2 to be able to
measure the visual information of the boiling phenomenon. It was found that bubble departure frequency,
diameter and nucleation site density are three key-parameters in determining the boiling heat transfer
coefficient. Furthermore, the ratio of area of influence
to projected area of bubble at departure can be correlated to the products of two dimensionless groups,
Roshko and Eötvös numbers. The Roshko number
describes the oscillating nature of bubble dynamics,
while the Eötvös number characterizes the shape of
bubbles.
It was shown that by dividing the heating surface
to two complementary areas, one is directly influenced by bubbles and the other is free from bubbles
effects; the boiling heat transfer is predictable. A new
semi-empirical model was proposed to predict the
boiling heat transfer coefficient.
Acknowledgment
The author is thankful to department of chemical
engineering, college of chemistry and chemical engineering, Mahshahr Branch, Islamic Azad University,
Mahshahr, Iran for financial support of research project entitled “Pool boiling heat transfer in pure liquids”.
NOMENCLATURE
Figure 8. The predicted values of heat flux versus the
experimental values from independent investigation.
24
A
Ar
b
c1
c2
Cd
C
Csf
d
Eö
f
Fp
Fq
FWM
FWR
g
area, m-2
Archimedes number
constant (see Mostinski correlation)
constant, see Eq.(22)
constant, see Eq.(23)
drag coefficient
heat capacity, J kg-1 K-1
constant, see Rohsenow correlation
bubble diameter, m
Eötvös number
bubble departing frequency, Hz
see Gorenflo correlation
see Gorenflo correlation
see Gorenflo correlation
see Gorenflo correlation
acceleration of gravity, N kg-1
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
hfg
Ja
k
Mw
N
P
Pr
Pr
q
Re
Ro
Ra
T
uT
specific heat of vaporization, J kg-1
Jakob number
thermal conductivity, W m-1 K-1
molecular weight, g mol-1
number of nucleation sites
pressure, Pa
Prandtl number
reduced pressure
heat flux, W/m2
Reynolds number
Roshko number
absolute roughness, m
temperature, K
terminal velocity, m s-1
Subscripts
0
b
c
l
NC
OD
s
v
w
reference
boiling
convection or critical
liquid
natural convection
outside diameter
saturated or solid
vapor
wall
Greek symbols
heat transfer coefficient, W m-2 K-1
thermal diffusivity, m2 s-1
the ratio of area of influence to projected
area of bubble at departure
boundary layer thickness, m
δ
ζ
see Eq. (21)
θs
D-value of Ts-T∞
D-value of Tw-T∞
θw
ρ
density, kg m-3
σ
surface tension, N m-1
contact angle – see Eq. (19), (22) and (23)
ϕ
α
αl
β
REFERENCES
[1]
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
[2]
W.M. Rohsenow, Trans. ASME 74 (1952) 969-976
[3]
I.L.Mostinski, Teploenergetika 4 (1963) 66
[4]
K. Stephan, K. Abdelsalam, Int. J. Heat Mass Transfer 23
(1980) 73–87
[5]
W. Fritz, Phys. Z. 36 (1953) 379–384
[6]
M.G. Cooper, Adv. Heat Transfer 16 (1984) 157-239
[7]
D. Gorenflo, VDI Heat Atlas. (1993)
[8]
R. Vinayak Rao, A.R. Balakrishnan, Exp. Therm. Fluid
Sci. 29 (2004) 87–103
[9]
S.A. Alavi Fazel, M. Jamialahmadi, A.A. Safekordi, Iran.
J. Chem. Chem. Eng. 27(3) (2008) 135–150
[10]
J.P. McHale, S.V. Garimella, Int. J. Multiphase Flow 36
(2010) 249-260
[11]
J.M. Saiz Jabardo, Open Transp. Phenom. J. 2 (2010)
24-34
[12]
A.S. Moita, E.Teodori, A.L.N. Moreira, Int. J. Heat fluid
flow 52 (2015) 50-63
[13]
R. Tadmor, Langmuir 20(18) (2004) 7659-7664
[14]
S. Matthew, Ph.D. Thesis, Michigan State University,
1988
[15]
R.L. Judd, K.S. Hwang, J. Heat Transfer 98 (1976) 623–
-629
[16]
C.Y. Han, P. Griffith, MIT Press Energy Lab. Ser. (1962)
1-76
[17]
R. Clift, M.E. Grace, Bubbles Drops and Particles, Academic Press, New York, 1978, p. 26
[18]
B.B. Mikic, W.M. Rohsenow, J. Heat Transfer 91 (1969)
245–250
[19]
S.W. Churchill, M. Bernstein, Trans. ASME 99 (1977)
300–306
[20]
M. Ishii, N. Zuber, AIChE J. 25 (1979) 843–855
[21]
K. Stephan, Ph.D. Thesis, University of Auckland,
Auckland 1992
[22]
B. Xiao, G. Jiang, D. Zheng, L. Chen, B. Liu, Res. J. Appl.
Sci., Eng. Technol. 6(4) (2013) 587-592
[23]
N. Zuber, Appl. Mech. Rev. 17 (1964) 663-672
[24]
K. Nishikawa, Y. Fujita, H. Ohta, S. Hidaka, in Proceedth
ings of the 7 International Heat Transfer Conference,
München, Germany, 4, 1982, pp. 1–66
[25]
L.D. Boyko, G.N. Kruzhilin, Int. J. Heat Mass Transfer 10
(1967) 361.
M.J. McNelly, J. Imp. Coll. Chem. Soc. 7 (1953) 18–34
25
S. ALI ALAVI FAZEL, G. HOSSEYNI: EXPERIMENTAL INVESTIGATION…
SEYED ALI ALAVI FAZEL
GOHARSHAD HOSSEYNI
Department of chemical
engineering, college of chemistry
and chemical engineering,
Mahshahr Branch, Islamic Azad
University, Mahshahr, Iran
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 17−26 (2016)
EKSPERIMENTALNA ISTRAŽIVANJA PRENOSA
TOPLOTE PRI DELIMIČNOM KLJUČANJU
ZASIĆENIH ČISTIH TEČNOSTI
Prenos toplote pri delimičnom zasićenom ključanju je eksperimentalno ispitivan u sudu sa
horizontalnim grejačem oblika šipke. Ispitivanje je uključilo vodu i etanol. Sekcija za grejanje je napravljena od različitih materijala: SS316, bakar, aluminijum i mesing. Eksperimenti su izvršene sa površinama čiji stepen hrapavosti meren srednjom vertikalnom devijacijom u opsegu između 30 i 360 μm. Ispitivani su koeficijent prenosa toplote, prečnik i
učestalost otkidanja mehura, kao i gustina nukleacionih mesta. Podaci su poređeni sa
glavnim postojećim korelacijama. Pokazano je da se eksperimentalni podaci ne poklapaju
sa prihvatljivom tačnošću sa glavnim korelacijama u celom opsegu eksperimentlnih
uslova. U ovom radu, oblast prenosa toplote pri ključanju je podeljen u dve komplementarne podoblasti: izazvane prinudne konvekcije i oblasti pod uticajem ključanja. Za koefijent prenosa toplote predložen je polu-empirijski model koji uključuje dva bezdimenziona
kriterijuma, Etvesov i Roškov kriterijum. Pokazano je da predloženi model nudi poboljšane
performanse u predviđanju koeficijenta prenosa toplote u poređenju sa postojećim korelacijama.
Ključne reči: indukovana prinudna konvekcija, ključanje zasićene tečnosti, hrapavost površine, koeficijent prenosa toplote.
26
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 27−32 (2016)
MARIJA ILIĆ1
FRANZ-HUBERT HAEGEL2
VESNA PAVELKIĆ3
DRAGAN ZLATANOVIĆ4
SNEŽANA NIKOLIĆ-MANDIĆ5
ALEKSANDAR LOLIĆ5
ZORAN NEDIĆ6
CI&CEQ
THE INFLUENCE OF ALKYL POLYGLUCOSIDES (AND HIGHLY ETHOXYLATED
ALCOHOL BOOSTERS) ON THE PHASE
BEHAVIOR OF A WATER/TOLUENE/
/TECHNICAL ALKYL POLYETHOXYLATE
MICROEMULSION SYSTEM
1
Faculty of Mining and Geology,
University of Belgrade, Belgrade,
Serbia
2
Forschungszentrum Jülich, Institut
für Bio- und Geowissenschaften,
IBG-3 Agrosphäre, Jülich,
Germany
3
Institut of Chemistry, Technology
and Metallurgy, University of
Belgrade, Belgrade, Serbia
4
Innovation Center Faculty of
Mechanical Engineering, University
of Belgrade, Belgrade, Serbia
5
Faculty of Chemistry, University of
Belgrade, Belgrade, Serbia
6
Faculty of Physical Chemistry,
University of Belgrade, Belgrade,
Serbia
Article Highlights
• Addition of sugar surfactant to system of water/tolune/Lutensol ON 50 was investigated
• Sugar surfactant shifts the phase behavior to lower temperature
• Microemulsion of water/tolune/Lutensol ON 50 and alcohol ethoxylate C18E100 was
investigated
• Strongly hydrophilic C18E100 shifted the one phase region to higher temperature
Abstract
UDC 547.533:66:544
The influence of additives (alkyl polyglucoside, Glucopon 600 CS UP and alcohol ethoxylate C18E100) on the behavior of the water/toluene/Lutensol ON 50
(technical oxoalcohol, i-C10E5) microemulsion system as a function of temperature and composition has been investigated. The phase behavior of the microemulsions was determined by vertical sections through the Gibbs phase prism
(fish-like phase diagrams). Alkyl polyglucoside shifts the one phase region to
lower temperatures compared with water/toluene/Lutensol ON 50 mixtures.
This is contrary to the expectation, considering the extreme hydrophilic nature
of the sugar headgroup. The addition of hydrophilic alcohol ethoxylate
(C18E100) to the water/toluene/Lutensol ON 50 system increases the solubilization capacity of the surfactant, even if the co-surfactant is used in small quantities, and shifts the one-phase region to higher temperature by a few °C.
DOI 10.2298/CICEQ141105015I
Keywords: microemulsion, toluene, alkyl polyglucoside, oxoalcohol
ethoxylate, efficiency booster, “fish” diagrams.
SCIENTIFIC PAPER
Microemulsions are thermodynamically stable
optically isotropic mixtures, consisting of two immiscible components, oil and water, made miscible by a
third component, the surfactant. They may contain
additives such as salt or alcohol. The properties of
ternary nonionic surfactant/water/oil microemulsions
are very interesting scientifically and technically. A
convenient way to study these systems is to measure
the phase behavior at constant oil/water ratios as a
function of temperature, T, and surfactant mass
fraction, γ.
Correspondence: M. Ilić, Faculty of Mining and Geology, University of Belgrade, Djušina 7, 11000 Belgrade, Serbia.
E-mail: marija.ilic@rgf.bg.ac.rs
Paper received: 5 November, 2014
Paper revised: 13 May, 2015
Paper accepted: 20 May, 2015
The stability of microemulsions over a large temperature range and low surfactant concentration is
required for technical applications. Some investigations [1,2] show that the use of surfactants with longer
hydrophobic units reduces the amount of surfactant
needed for microemulsification due to the increasing
efficiency of the surfactant. Adding suitable additives
such as sugar surfactants and nonionic alcohol
ethoxylates received much attention in recent years. It
was found that the addition of a small amount of
polymer with amphiphilic properties to the microemulsion system increases the efficiency of the surfactant
[3-10]. Alcohol ethoxylate surfactants are widely used
for microemulsion applications. The phase behavior
with respect to the length of the hydrocarbon tails and
the number of ethylene oxide (EO) units depends on
the purity of alcohol ethoxylates. The structure of the
27
M. ILIĆ et al.: THE INFLUENCE OF ALKYL POLYGLUCOSIDES…
hydrocarbon tail of the surfactant strongly influences
the microemulsion behavior [11,12]. Technical grade
alcohol ethoxylates usually contain mixtures of different alcohols and often exhibit a distribution over a
large range of ethoxylation degrees.
In recent years, alkyl polyglucosides, a class of
sugar surfactants, have received considerable interest as nonionic surfactants because of their excellent
biodegradability, ease of manufacture from renewable
resources, such as sugar and vegetable oil feedstocks [13], and potential use in a large number of
industrial applications [14-19]. One potential use of
sugar surfactants is in microemulsion formulations.
Making microemulsions with alkyl polyglucosides is
difficult owing to the low surfactant solubility in many
classes of oils. Fundamentally, it is of substantial
interest to form microemulsions with sugar surfactant
as co-surfactant or to form sugar surfactant-based
microemulsions using co-surfactant.
Alkyl polyglucosides, abbreviated as CmGn, represent complex mixtures [20] where m is the number
of carbon atoms in the hydrocarbon chain and n is the
average number of glucose units in the hydrophilic
headgroup. The nonionic surfactants, n-alkyl polyglycol ethers (CiEj) are typically used. These surfactants contain i carbon atoms in the hydrophobic
alkyl chain and j ethoxy units in the hydrophilic headgroup. The phase behavior of microemulsion systems
containing alkyl polyglucoside has been studied by
some authors [21-23].
In the last decades, a lot of papers were published concerning many aspects of polymers in microemulsions, such as solubilization efficiency boosting
by amphiphilic polymers in microemulsions [24-26].
The influence of various polymers on the phase equilibrium of microemulsions containing nonionic surfactant, water and oil, has also been studied. It was found
that water-soluble polymers expelled into the coexistent water phase cause the coexistence of the lamellar
phase with water, which does not appear in the absence of polymer [27].
In this work, we studied the phase behavior of
Lutensol ON 50-based microemulsions after addition
of alkyl polyglucoside Glucopon 600 CS UP as a cosurfactant or a hydrophilic alcohol ethoxylate (C18E100)
as an efficiency booster [28].
Chem. Ind. Chem. Eng. Q. 22 (1) 27−32 (2016)
ance (HLB) of 13.8, according to Griffin [29]. Lutensol
ON 50 (C10 oxoalcohol polyethoxylate with an average of 5 ethylene oxide units, i-C10E5) is a commercial
nonionic surfactant of BASF AG, Ludwigshafen (Germany). It has a HLB of 11.5 (technical information
sheet of BASF).
Glucopon 600 CS UP alkyl polyglucoside (alkyl
chain containing 10 to 16 carbon atoms, and an average number of glucose units of 1.4) is a commercial
nonionic sugar surfactant containing 51% active matter and 49 mass% water (technical information sheet
of Cognis, Monheim, Germany). The alcohol ethoxylate C18E100 was synthesized under argon using a high
vacuum line by Frank et al. [28] in the laboratory of
JCNS-1 at Forschungszentrum, Jülich. Water was
deionized and twice distilled.
Phase diagram determination
Kahlweit et al. [30,31] introduced a way of studying the phase behavior of ternary or quaternary mixtures. A procedure to obtain an overview of the
phases is to draw the phase diagram at a constant
oil/water ratio as a function of temperature, T, and
surfactant mass fraction, γ. The phase boundaries
resemble the shape of a fish. Typically, temperature-composition phase diagrams obtained for a 1/1 mass
ratio of oil and water show a one-phase microemulsion at relatively high surfactant concentration. At
lower surfactant concentration a three-phase body
exists consisting of a middle-phase microemulsion in
equilibrium with excess phases of oil and water,
surrounded by two-phase regions illustrated as 2Φ
and 2Φ . When a surfactant is mainly dissolved in
water and two phases consist of a surfactant-rich
water (lower) phase in equilibrium with an excess oil
phase, the region is denoted as 2φ. At high temperature a nonionic surfactant is more soluble in oil and
forms a surfactant-rich oil (upper) phase in equilibrium
with an excess water phase denoted 2Φ (Figure 1).
MATERIALS AND METHODS
Toluene (purity 99% by GC) was purchased
from Merck Schuchardt (Germany). Octaethylene glycol decylether (C10E8, octaethyleneoxide decylether)
with purity higher than 98% (GC) was purchased from
Fluka (Germany). It has a hydrophilic-lipophilic bal-
28
Figure 1. Schematic “fish cut” phase diagram of a nonionic
microemulsion with equal water to oil proportions as a function
of surfactant concentration.
M. ILIĆ et al.: THE INFLUENCE OF ALKYL POLYGLUCOSIDES…
The convenient variables are the temperature
and the following composition variables (pressure is
always kept constant) – the mass fraction of oil in the
mixture of water and oil:
α = mB /(mA + mB)
Chem. Ind. Chem. Eng. Q. 22 (1) 27−32 (2016)
branched i-C10E5 (Lutensol ON 50) in order to find the
composition and temperature of optimum solubilization (Figure 2).
(1)
The mass fraction of surfactant in the mixture of all
three components in ternary mixtures:
γ = mC/(mA + mB + mC)
(2)
or:
γ = (mC + mD)/(mA + mB + mC + mD)
(3)
when two surfactants or mixtures of surfactant and
co-surfactant are used. In this case, the mass fraction
of one of the surface-active components (δ) in the
mixture is defined as:
δ = mC/(mC + mD)
(4)
where the capital indices A, B, C, D refer to the components, water, oil, surfactant and co-surfactant, respectively.
The so-called γ -point, where the three-phase
body meets the one-phase region, defines the minimum mass fraction of surfactant needed to solubilize
water and oil and is a measure for the efficiency of the
surfactant. The corresponding temperature, T , is a
measure for the phase inversion temperature (PIT).
The phase diagrams were recorded by successively adding water and oil to the initial water-oil-surfactant mixture. The samples were prepared by weighing appropriate amounts of components (1:1 ratio of
oil to water) on 0.1 mg precision scales in the order
surfactant, toluene, water to suppress intermediate
formation of liquid crystals. The mass fraction of the
surfactant (or surfactant/additive) is calculated with
Eqs. (2) or (3) and the mass fraction of the additive in
the surfactant /additive mixture with Eq. (4).
Samples were weighed into test tubes, which
were immediately sealed (glass stoppers) and put into
a thermostated water bath with temperature control
up to 0.2 °C. In the thermostated bath, the mixtures
were stirred with small magnetic stirrers to ensure
complete mixing of the components at the given temperature. After equilibrium was established, the
occurring phases were characterized by visual inspection between crossed polarizers.
RESULTS AND DISCUSSION
The pseudo-binary phase diagrams of microemulsion systems were determined at equal mass
fractions of water and toluene (α = 0.5) for two nonionic surfactants, pure linear C10E8 and technical
Figure 2. Phase diagrams of water/toluene/C10E8 and
water/toluene/Lutensol ON 50 at equal mass fractions
of water and toluene (α = 0.5).
The phase boundaries of the system with C10E8
meet at γ = 0.123, T = 24.9 °C. Beyond that point, a
single homogeneous phase appears, when the mass
fraction of surfactant γ is further increased. Thus, this
point where the three-phase (3φ) and one-phase
regions (1φ) meet represents the lowest surfactant
concentration needed to solubilize equal masses of
the two immiscible components, water and toluene. At
lower temperatures the microemulsion coexists with
excess oil (denoted by 2Φ). At higher temperatures
the microemulsion coexists with excess water ( 2Φ ).
This system exhibits a strong tendency to form liquid
crystals. Its phase diagram shows a large area of
liquid crystals (LC) surrounded by microemulsion
(regions 1φ and 1φ*). These results are very similar to
those reported for the same system with equal volume fraction φ of water and toluene, i.e., lower mass
fraction α of oil (α ≈ 0.465). In that case, the “fishtail
point” was found at γ = 0.114 and T = 24.34 °C [32].
Owing to the lower density difference of toluene and
water compared to alkane systems, the samples
exhibit somewhat slower phase separation. The
bicontinuous microemulsion containing water, toluene
and C10E8 also shows some unusual behavior at low
temperatures. Shear-induced birefringence was observed between crossed polarizers in the region
denoted 1φ* while stirring the sample.
For the water/toluene/Lutensol ON 50 system,
the determination of the point of optimum solubilization of equal masses of water and toluene failed. At
high γ values, a single homogeneous phase (1φ) was
29
M. ILIĆ et al.: THE INFLUENCE OF ALKYL POLYGLUCOSIDES…
found in a temperature range similar to that of the
C10E8 system, but with considerably higher surfactant
content needed for mutual solubilization of both water
and toluene. The shape of the “fishtail” is also not
symmetrical with respect to temperature. This behavior
is typical for technical surfactants with a distribution of
more or less hydrophobic components due to different
degrees of ethoxylation [10]. In contrast to the system
with linear C10E8, no liquid crystals are found within
the region of the bicontinuous microemulsion (1φ)
indicating a less rigid structure of the surfactant layer
at the interface between the oil and the water micro-phases. Approaching the composition of optimum
soulubilization of equal masses of water and toluene,
samples with the branched technical surfactant
needed very long and sometimes extremely long
times for equilibration after agitation or temperature
changes. They show delayed visible phase separation and the phase boundaries to the two-phase
regions determined visually are diverging.
Using the ternary mixtures water/toluene/Lutensol ON 50 as a base case, the role of added substances, sugar surfactant and hydrophilic alcohol
ethoxylate on the phase behavior is explored.
Effect of alkyl polyglucoside (Glucopon 600 CS UP):
Phase behavior as a function of δ
Figure 3 shows the temperature-composition
phase diagram at mass fraction α = 0.5 for the quaternary system water/toluene/Lutensol ON 50/Glucopon
600 CS UP for varying fractions of sugar surfactant, δ
(0.05, 0.10 or 0.20).
Figure 3. Temperature-composition phase diagram at water to
toluene mass fraction α = 0.5 for the system
water/toluene/Lutensol ON 50 with added sugar surfactant,
Glucopon 600 CS UP , for varying mass fractions of sugar
surfactant, δ (.05, 0.10 or 0.20).
30
Chem. Ind. Chem. Eng. Q. 22 (1) 27−32 (2016)
The water/toluene/Lutensol ON 50 “fish” (δ = 0)
is shown for reference in Figure 3. As can be seen,
with the addition of CmGn, the homogeneous microemulsion region (“fish tail” with the phase sequence
2Φ-1- 2Φ ) becomes wider and the efficiency of the
surfactant mixture increases slightly.
With increasing δ, the “fish tail” unexpectedly
moves downward on the temperature scale despite
the hydrophilic nature of the sugar surfactant. The
efficiency of the surfactant mixture increases with
increasing δ. In these quaternary systems the location
of γ is not determined because, in contradiction to
many other microemulsion systems, equilibration for
the system water/toluene/Lutensol ON 50 was particularly slow near the point of optimum solubilization
for the investigated ternary mixture (see Figure 1).
Effect of hydrophilic alcohol ethoxylate
The effect of small amounts of hydrophilic alcohol ethoxylate C18E100, on the location and width of
the one-phase region was investigated.
Figure 4 shows phase diagrams for the
water/toluene/Lutensol ON 50 system with and
without addition of C18E100. In this presentation the oil
mass fraction is α = 0.5 and the mass fraction of
additive is δ = 0.01. Compared with the system
without additive, the one-phase region with additive is
shifted to higher temperature. This effect can be
explained by the large hydrophilic moiety of C18E100.
For higher content of C18E100, formation of liquid
crystals was observed, which makes the system
unsuitable for many applications (data not shown).
Figure 4. Temperature-composition phase diagram at water to
toluene mass fraction α = 0.5 of the water/toluene/Lutensol ON
50 system with C18E100 as additive (mass fraction δ = 0.01).
M. ILIĆ et al.: THE INFLUENCE OF ALKYL POLYGLUCOSIDES…
CONCLUSIONS
We have studied the phase behavior of water/
/toluene/Lutensol ON 50/Glucopon 600 CS UP and
water/toluene/Lutensol ON 50/C18E100 mixtures as a
function of temperature and composition. Both additives lead to improved solubilization and shift the onephase region to lower surfactant content near to the
values obtained for pure C10E8.
The addition of the alkyl polyglucoside, Glucopon 600 CS UP, to the ternary water/toluene/Lutensol
ON 50 system additionally shifts the phase behavior
to lower temperature. This behavior is unexpected,
because the sugar surfactant is absolutely insoluble
in toluene and should act as a hydrophilic surfactant.
It should rather increase the temperature for the onephase region. No formation of liquid crystals was observed by the addition of Glucopon 600 CS UP. The
microemulsion consisting of water, toluene, Lutensol
ON 50 and alcohol ethoxylate C18E100 as an additive
also increases the efficiency of the surfactant system,
but shifts the one-phase region to higher temperature,
as expected. The formation of liquid crystals at higher
content of C18E100, however, makes this additive less
suitable. These findings make the sugar surfactant a
better choice for improving the ternary system water/
/toluene/Lutensol ON 50 with respect to applications.
Alkyl polyglucosides are also preferable because of
their outstanding ecological and biological properties.
Chem. Ind. Chem. Eng. Q. 22 (1) 27−32 (2016)
[2]
K. Holmberg, B. Jönsson, B. Kronberg, B. Lindman,
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A. Kabalnov, U. Olsson, K. Thuresson, H. Wennerström,
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Matter 13 (2001) 9055-9074
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T. Sottmann, R. Strey, in Fundamentals of Interface and
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[11]
K.R. Wormuth, S. Zushma, Langmuir 7 (1991) 2048-2053
[12]
C. Frank, H. Frielinghaus, J. Allgaier, H. Prast, Langmuir
23 (2007) 6526-6535
[13]
K. Hill, in Alkyl Polyglucosides: Technology, Properties
and Applications, K. Hill, W. von Rybinski, G. Stoll (Eds.),
VCH, New York, 1997, pp. 1-7
[14]
D. Geetha, R. Tyagi, Tenside, Surfactants Deterg. 49
(2012) 417-427
[15]
M. Haeger, K. Holmberg, Tetrahedron Lett. 41 (2000)
1245-1248
[16]
A. Stradner, B. Mayer, T. Sottmann, A. Hermetter, O.
Glatter, J. Phys. Chem., B 103 (1999) 6680-6689
[17]
I.F. Uchegbu, S.P. Vyas, Int. J. Pharm. 172 (1998) 33-70
[18]
R. Schwering, D. Ghosh, R. Strey, T. Sottmann, J. Chem.
Eng. Data 60 (2015) 124-136
[19]
K. Hill, W. von Rybinski, G. Stoll, Alkyl Polyglucosides:
Technology, Properties and Applications, VCH, New
York, 1997
[20]
C. Stubenrauch, Curr. Opin. Colloid Interface Sci. 6
(2001) 160-170
[21]
L.D. Ryan, E.W. Kaler, Colloids Surfaces, A 176 (2001)
69-83
[22]
K. Fukuda, U. Olsson, M. Ueno, Colloids Surfaces, B 20
(2001) 129-135
[23]
J.L. Chai, Y.T. Wu , X.Q. Li, B. Yang, L.S. Chen, S.C.
Shang, J.J. Lu, J. Chem. Eng. Data 56 (2011) 48-52
[24]
T. Sottmann, Curr. Opin. Colloid Interface Sci. 7 (2002)
57-65
[25]
D. Byelov, H. Frielinghaus, O. Holderer, J. Allgaier, D.
Richter, Langmuir 20 (2004) 10433-10443
Nomenclature
CiEj
CmGn
EO
HLB
T
T
γ
n-alkyl polyglycol ethers
alkyl polyglucosides
ethylene oxide units
hydrophile-lipophile balance
temperature
phase inversion temperature
surfactant mass fraction
Acknowledgments
The authors thank the Ministry of Education,
Science and Technological Development of the
Republic of Serbia for financial support under project
number 172051, D. Richter and J. Allgaier (JCNS-1),
Forschungszentrum, Jülich, for providing experimental equipment and the synthesis of C18E100. Lutensol
ON 50 was a gift from BASF. Glucopon 600 CS UP
was a gift from Cognis. M. Ilić further thanks DAAD
(Germany) for a scholarship.
REFERENCES
[1]
I.D. Morrison, S. Ross, Colloidal Dispersions: Suspensions, Emulsions and Foams, Wiley, New York, 2002
31
M. ILIĆ et al.: THE INFLUENCE OF ALKYL POLYGLUCOSIDES…
[26]
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[29]
W.C. Griffin, J. Soc. Cosmet. Chem. 1(5) (1949) 311-326
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(1985) 654-668
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A. Kabalnov, U. Olsson, H. Wennerström, Langmuir 10
(1994) 2159-2169
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M. Kahlweit, R. Strey, P. Firman, D. Haase, Langmuir 1
(1985) 281-288
[28]
C. Frank, H. Frielinghaus, J. Allgaier, D. Richter, Langmuir 24 (2008) 6036-6043
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S. Burauer, T. Sottmann, R. Strey, Tenside, Surfactants
Deterg. 37 (2000) 8-16.
MARIJA ILIĆ1
FRANZ-HUBERT HAEGEL2
VESNA PAVELKIĆ3
DRAGAN ZLATANOVIĆ4
SNEŽANA NIKOLIĆ-MANDIĆ5
ALEKSANDAR LOLIĆ5
ZORAN NEDIĆ6
1
Faculty of Mining and Geology,
University of Belgrade, Belgrade,
Serbia
2
Forschungszentrum Jülich, Institut
für Bio- und Geowissenschaften,
IBG-3 Agrosphäre, Jülich,
Germany
3
Institut of Chemistry, Technology
and Metallurgy, University of
Belgrade, Belgrade, Serbia
4
Innovation Center Faculty of
Mechanical Engineering,
University of Belgrade, Belgrade,
Serbia
5
Faculty of Chemistry, University of
Belgrade, Belgrade, Serbia
6
Faculty of Physical Chemistry,
University of Belgrade, Belgrade,
Serbia
NAUČNI RAD
32
UTICAJ ALKILPOLIGLUKOSIDA (I ALKOHOLA
VISOKOG STEPENA ETOKSILACIJE U ULOZI
POJAČIVAČA) NA FAZNO PONAŠANJE
MIKROEMULZIONOG SISTEMA
VODA/TOLUOL/TEHNIČKI ALKIL POLIETOKSILAT
Ispitivan je uticaj aditiva (alkil poliglukosida, Glukopon 600 CS UP, i alkohol-etoksilata
C18E100) na fazno ponašanje mikroemulzionog sistema voda/toluol/lutensol ON 50 (tehnički
oksoalkohol, i-C10E5) u funkciji temperature i sastava sistema. Za određivanje faznog
ponašanja u mikroemulziji korišćeni su vertikalni preseci Gibbs-ovih faznih prizmi (dijagrami oblika tela ribe). Jednofazni region sistema voda/toluol/Lutensol ON 50 dodatkom
alkil poliglukozida se pomera ka nižim temperaturama. Ovakvo ponašanje je suprotno očekivanom, polazeći od izrazito hidrofilne prirode glave molekula površinski aktivnog šećera.
Dodatak malih količina hidrofilnog alcohol etoksilata (C18E100) sistemu voda/toluol/Lutensol
ON 50, povecava kapacitet rastvaranja površinski aktivne supstance i pomera jednofazni
region sistema ka višim temperaturama.
Ključne reči: mikroemulzija, toluol, alkil poliglukozid, oksoalkohol etoksilat, aditiv-pojačivač, “riba” dijagram.
Available on line at
Association of the Chemical Engineers of Serbia AChE
Chemical Industry & Chemical Engineering Quarterly
www.ache.org.rs/CICEQ
Chem. Ind. Chem. Eng. Q. 22 (1) 33−39 (2016)
V. SANGEETHA1
V. SIVAKUMAR2
1
Department of Food Technology,
Kongu Engineering College,
Perundurai, Tamil Nadu, India
2
Department of Chemical
Engineering, Alagappa College of
Technology Campus, Anna
University, Chennai, India
SCIENTIFIC PAPER
UDC 662.756.3:628.3
DOI 10.2298/CICEQ140612016S
CI&CEQ
BIOGAS PRODUCTION FROM SYNTHETIC
SAGO WASTEWATER BY ANAEROBIC
DIGESTION: OPTIMIZATION AND
TREATMENT
Article Highlights
• Optimization for biogas yield was conducted using response surface methodology
• Mixed culture from sago industry sludge can produce effective biogas
• The optimum condition for biogas production and COD removal was at pH 7 and
32 °C
2
• Adequacy of the model shows R value for COD removal and biogas production was
0.9943 and 0.9880, respectively
•
Abstract
Sago processing industries generate a voluminous amount of wastewater with
extremely high concentration of organic pollutants, resulting in water pollution.
Anaerobic digestion was employed for reduction of COD and maximization of
biogas production using synthetic sago wastewater by batch process. Mixed
culture obtained from sago industry sludge was used as a source for microorganisms. Response surface methodology was used to optimise the variables,
such as pH, initial BOD, temperature and retention time. Statistical results
were assessed with various descriptives, such as p-value, lack of fit (F-test),
coefficient of R2 determination, and adequate precision values. Pareto analysis
of variance revealed that the coefficients of determination value (R2) of COD
and BOD removal and biogas production were 0.994, 0.993 and 0.988, respectively. The optimum condition in which maximum COD removal (81.85%),
BOD removal (91.61%) and biogas production of 99.4 ml/day were achieved
was at pH 7 with an initial BOD of 1374 mg/l, and with the retention time of 10
days at 32 °C.
Keywords: anaerobic digestion, synthetic sago wastewater, biogas production, chemical oxygen demand, optimisation.
Sago, the common edible starch processed from
the tubers of cassava (Mannihotesculenta) is one of
the major tuber crops grown in more than 80
countries in the humid tropics. In the southern part of
India, particularly in Tamil Nadu, there are about 800
small-scale units of sago industries discharging about
40,000 to 50,000 L of sago wastewater and 15 to 30 t
of sludge per unit per day [1,2]. Sago processing
industries generates two types of wastewater; one
resulting from the washing and peeling of cassava in
Correspondence: V. Sivakumar, Department of Chemical Engineering, Alagappa College of Technology Campus, Anna University, Chennai, India.
E-mail: drvsivakumar@yahoo.com
Paper received: 12 June, 2014
Paper revised: 13 April, 2015
Paper accepted: 25 May, 2015
a rotary drum with low chemical oxygen demand
(COD) and the other from the extraction process
which owns a high contaminating load of COD and
biochemical oxygen demand (BOD). Hence, large
quantities of processed water up to 15 m3/t of fresh
cassava root are converted into wastewater, which
must be treated before its release into the environment. The amount of water used to produce one ton
of starch ranges from 10-30 m3 and repeated washing
improves the starch quality [3].
Due to stringent environment protection regulations, it is necessary for the processing industry to
treat wastewater [4]. Hence, it has become mandatory for these units to treat the wastewater for safe
discharge. There is ample space for an effective and
complete treatment system which will ensure a safe
33
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
effluent standard limit and hidden energy recovery in
the form of biogas before the disposal [1]. Viewing the
socio-economic profile of small-scale industrial farming operations, it is necessary to develop a suitable
low-cost treatment method for treatment of sago
wastewater [3]. Physical and chemical methods of
treating the sago wastewater have been unpredictable due to the problem of sludge disposal. Biological
methods are classified into two types: aerobic processes [5-7], which have limited applicability due to
aeration cost [8,9], and anaerobic processes at high
treatment rate such as anaerobic filter [10], hybrid
UASB [11], anaerobic rotating biological contactor
[12] and fluidized bed [1] systems.
From previous literature, it is found that most of
the researchers successfully used anaerobic processes for treatment of sago wastewater [11-13]. Various anaerobic treatment techniques, including conventional method, pave way for sustainable environment [14-18]. Anaerobic treatment has an advantage
of degrading concentrated waste and producing significantly less sludge [4]. Because of variations in
process variables, anaerobic treatment processes are
rare at the industrial scale and easily unstable under
certain circumstances. Therefore, the model has been
developed to optimize the treatment process for COD
removal, BOD removal and biogas production, as
functions of the following operating variables: pH, initial BOD, temperature and retention time. Response
surface methodology (RSM), a mathematical (statistical) technique, is commonly used for developing,
analysing, optimizing, and understanding performance of complex variables in an efficient mode. Recently, it has been successfully applied to different
wastewater treatment for achieving optimization using
experimental designs [19-25]. The advantage of using
RSM is the reduction in the number of experiments,
compared to a full experimental design at the same
level [26].
The objective of the present work is to study the
treatment of COD and BOD removal and biogas production in anaerobic digestion of synthetic sago
wastewater, and also optimizing the effect of the process variables such as pH (4-8), initial BOD
concentration (798–1702 mg/L), temperature (26–34
°C) and retention time (4–12 days) using RSM. A full
factorial Central Composite Design (CCD) was employed for the optimisation of process variables.
Chem. Ind. Chem. Eng. Q. 22 (1) 33−39 (2016)
MATERIALS AND METHODS
Sago wastewater
Preparation of synthetic sago wastewater was
reported elsewhere [27] and the physicochemical
characteristics of the synthetic sago wastewater were
analysed as per standards of American Public Health
Association (APHA) [28]. The characteristics of the
wastewater were pH: 6.8, COD: 2286 mg/L, BOD:
840 mg/L, TDS: 1237 mg/L, TSS: 537 mg/L, VS: 610
mg/L and VSS: 1015 mg/L.
Experimental setup and procedure
The experiment was carried out in a batch reactor of 1 L capacity (Figure 1) for different time intervals (4-12 days). Mixed sludge from sago industry
was used as inoculum (10 vol.%) containing methanogenic bacteria of Methanosarcina, Methanococcoides, Methanoplanus and Methanospirillum. The
pH was adjusted by 1 M HCl or 1 M NaOH using a pH
meter (1283286 Eutech Instruments, Singapore).
Initial BOD was varied from 798 to 1702 mg/L by
adding sago powder and temperature was adjusted
from 26 to 34 °C with the help of a water bath. The
samples were taken for analysis of COD by the open
reflux method and for BOD by the standard dilution
technique according to APHA [28] and also for biogas
production [13].
Figure 1. Experimental setup.
Experimental design
Four factors and five levels of rotatable CCD
were carried out with 30 experimental runs. Twenty
four experiments were augmented with six replicates
at the design centre to evaluate the pure error. Each
variable was varied from 5 levels and the relationship
between the coded and actual values are described
as follows:
xi =
34
(Xi − X o )
ΔX i
(1)
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
where xi and Xi are the dimensionless and actual
values of the independent variable i, Xo is the actual
value of the independent variable at the centre point
and ΔXi is the step change of Xi corresponding to the
unit variation of the dimensionless value. The variables and its levels are designated as –2, –1, 0, +1 and
+2. The second order polynomial equation was used
to describe the effect of independent variables in
terms of linear, quadratic and interactions:
Y = β o + β1X 1 + β 2 X 2 + β3 X 3 + β 4 X 4 + β12 X 1X 2 +
+ β13 X 1X 3 + β14 X 1X 4 + + β 23 X 2 X 3 + β 24 X 2 X 4 +
Chem. Ind. Chem. Eng. Q. 22 (1) 33−39 (2016)
COD Removal (Y1) = −513.15 + 15.10 X 1 +
0.061X 2 + 23.152 X 3 + 10.289 X 4 + 0 .009 X 1X 2 +
+2.539 X 1X 3 − 1.062 X 1X 4 + 0.003 X 2 X 3 −
(3)
2
1
−0.0007 X 2 X 4 + 0.165 X 3 X 4 − 6.94 X −
−0.00008 X 22 − 0.669 X 32 − 0.322 X 42
BOD Removal (Y 2 ) = −1418.08 + 55.88 X 1 +
0.21X 2 + 67.62 X 3 + 23.68 X 4 + 0.007 X 1X 2
+1.52 X 1X 3 − 0.115 X 1X 4 + 0.0004 X 2 X 3 +
(2)
+ β34 X 3 X 4 + β11X 12 + β 22 X 22 + β33 X 32 + β 44 X 42
where Y is predicted response, βo is constant coefficient, β1, β2, β3 and β4 are linear coefficients, β11, β22,
β33 and β44 are quadratic coefficients, β12, β13, β14, β23,
β24 and β34 are cross-products coefficients, and X1, X2,
X3 and X4 are input variables (pH, initial BOD,
temperature and retention time).The data obtained
from the response surface methodology on COD
removal and BOD removal and biogas production
was subjected to the ANOVA.
The quality of the fit polynomial model was
stated by the coefficient of determination (R2),
adjusted R2, and its statistical significance was determined by F test. The individual effect of each variable
as well as the effect of the interaction were determined, and numerical optimisation was performed to
determine the optimal solution (maximum COD removal, BOD removal and biogas production).
RESULTS AND DISCUSSION
Statistical analysis and fitting of second order
polynomial equation
Several factors influence the removal of COD
and biogas production from the synthetic sago wastewater, but initial BOD, pH, temperature and retention
time play important roles.
The response COD, BOD and biogas were measured for different runs according to the design matrix
carried out based on the design of experiment and the
values for random runs are shown in Table 1. CCD
seeks to minimise the integral of the prediction variable across the design space. Experimental results
were analysed, approximating the function of COD
and BOD removal and biogas production. The regression equations (3)–(5) shown below are obtained after
the ANOVA:
2
1
(4)
2
2
+0.003 X 2 X 4 − 0.46 X 3 X 4 − 8.14 X − 0.001X −
−1.82 X 32 − 0.66 X 42
Biogas production (Y 3 ) = −2497.74 + 91.60 X 1 +
+0.45 X 2 + 117.33 X 3 + 35.29 X 4 + 0.01X 1X 2
+1.02 X 1X 3 + 0.52 X 1X 4 - 0.0007 X 2 X 3 −
2
1
(5)
2
2
0.002 X 2 X 4 − 0.20 X 3 X 4 − 9.91X − 0.0018 X −
−1.96 X 32 − 1.64 X 42
To check the estimated regression equation for
the goodness of fit, Fishers F-test was employed and
the multiple correlation coefficients R2 was calculated
[21]. The ANOVA results showed the significant response models with highest (p < 0.05) R2 value of
0.994, 0.993 and 0.988 for removal of COD, BOD and
biogas production, respectively. The two different
tests, such as sequential model sum of squares and
model summary statistics are used to decide the adequacy of various models. prob > F values for the
quadratic model were less than 0.0001, while the
maximum adjusted R2 value and predicted R2 value
were found to be 0.989 and 0.970 for COD removal.
Even though the cubic model was found to be aliased, prob > F values were greater than 0.05. Therefore, the quadratic model was chosen for further analysis. Adeq Precision measures the signal-to-noise
ratio; typically a ratio greater than 4 is desirable.
Thus, signal-to-noise ratios of 56.422, 47.407 and
31.701 for removal of COD, BOD and biogas production, respectively, indicate an adequate signal,
and this model can be used to navigate the design
space. The result indicates that the process variables
are significant factors that affect the response variables. The interacting terms significant for removal of
COD, BOD and biogas production are shown in Table 2.
Effect of independent variables on % COD and %
BOD removal
The polynomial equation framed for the above
analysis was expressed as three-dimensional surface
plots to visualise individual and interactive outcome of
factors on the response within the design range.
According to the quadratic model X1, X2, X3 and X4
35
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
CI&CEQ 22 (1) 33−39 (2016)
Table 1. The design of experiment and response for random runs of anaerobic digestion
pH
Int. BOD
T
t
COD Removal, %
BOD Removal, %
X1
X2
X3
X4
Yexp
Ypre
Yexp
Ypre
Yexp
Ypre
1
7
1024
28
10
45.38
47.93
64.62
66.62
72.3
72
2
6
1702
30
8
50.83
49.73
60.81
60.81
54.1
56.26
3
6
798
30
8
43.83
44.22
54.55
54.87
42.6
45.75
4
5
1476
28
6
25.27
26.57
35.27
35.38
26.5
25.54
5
7
1024
28
6
43.24
41.49
55.65
54.54
55.9
52.32
6
6
1250
26
8
38.64
37.8
52.24
51.69
46
45.5
7
6
1250
30
8
63.55
63.95
78.79
81.31
84.6
88.9
8
5
1024
28
6
29.61
30.34
38.08
39.41
21.6
22.37
9
6
1250
30
4
46.02
47.41
56.92
58.4
43.6
48.51
10
8
1250
30
8
56.9
57.23
70.9
72.79
83.1
90
11
4
1250
30
8
16.1
15.06
26.26
24.69
10.1
8.51
Run
Biogas production, ml/day
12
6
1250
34
8
68.52
68.66
72.23
73.1
63.6
69.41
13
7
1024
32
6
62.33
62.62
76.9
74.66
73.6
70.72
14
5
1476
32
10
48.72
49.96
56
56.36
43.6
42.94
15
7
1476
28
6
46.6
45.78
58.33
57.07
65.3
64.67
16
6
1250
30
8
65.21
63.95
80.41
81.31
89.6
88.9
17
5
1476
32
6
34.98
33.65
45.63
44.06
35.1
34.33
18
6
1250
30
8
64.35
63.95
82.56
81.31
90.1
88.9
19
5
1024
28
10
46.36
45.28
54.4
52.41
37.4
37.87
20
7
1024
32
10
73.52
71.71
80.2
79.34
90.4
87.12
21
7
1476
28
10
50.4
50.94
76.8
75.83
82.6
80.72
22
5
1024
32
6
32.2
31.15
47.1
47.32
34.9
32.54
23
6
1250
30
8
64.2
63.95
81.54
81.31
90
88.9
24
6
1250
30
12
72.25
70.16
83.94
82.78
76.4
76.8
25
5
1024
32
10
46.7
48.74
51.25
52.94
45.2
44.77
26
6
1250
30
8
62.5
63.95
82.54
81.31
88.6
88.9
27
7
1476
32
6
72.6
73.17
76.69
77.94
86.4
81.69
28
7
1476
32
10
80.5
80.99
90.21
89.31
96.3
94.47
29
5
1476
28
10
39.3
40.23
52.4
55.07
35.6
37.42
30
6
1250
30
8
63.86
63.95
82.01
81.31
90.5
88.9
Table 2. ANOVA of the second order polynomial equation for COD and BOD removal and biogas production
Source
df
COD Removal, %
BOD Removal, %
Biogas production, ml/day
Coefficient
p-Value
Coefficient
p-Value
Coefficient
p-Value
estimate
Prob > F
estimate
Prob > F
estimate
Prob > F
Model
14
7184.55
< 0.0001
8093.31
< 0.0001
18091.68
< 0.0001
X1
1
2667.67
< 0.0001
3469.21
< 0.0001
9959.30
< 0.0001
X2
1
45.46
0.0010
52.96
0.0018
165.90
0.0043
X3
1
1428.36
< 0.0001
687.05
< 0.0001
858.01
< 0.0001
X4
1
776.46
< 0.0001
891.45
< 0.0001
1199.92
< 0.0001
X1×X2
1
64.92
0.0002
42.87
0.0040
84.18
0.0303
X1×X3
1
412.80
< 0.0001
148.66
< 0.0001
67.65
0.0487
X1×X4
1
72.21
0.0001
0.86
0.6373
17.43
0.2934
X2×X3
1
39.28
0.0018
0.57
0.6999
1.89
0.7249
X2×X4
1
1.63
0.4515
44.72
0.0034
13.14
0.3595
X3×X4
1
7.04
0.1293
54.58
0.0016
10.73
0.4065
X12
1
1324.67
< 0.0001
1818.38
< 0.0001
2694.50
< 0.0001
36
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
Chem. Ind. Chem. Eng. Q. 22 (1) 33−39 (2016)
Table 2. Continued
COD Removal, %
Source
df
BOD Removal, %
Biogas production, ml/day
Coefficient
p-Value
Coefficient
p-Value
Coefficient
p-Value
estimate
Prob > F
estimate
Prob > F
estimate
Prob > F
< 0.0001
X22
1
493.56
< 0.0001
944.20
< 0.0001
2461.88
X32
1
196.93
< 0.0001
613.25
< 0.0001
1695.16
< 0.0001
X42
1
45.70
0.0010
196.96
< 0.0001
1180.88
< 0.0001
Residual
15
40.96
Lack of fit
10
36.87
Pure error
5
4.08
55.74
0.0549
are the important factors determining Y1 and Y2. The
results shown in Figures 2 and 3 indicate that at pH 7,
COD and BOD removal are 81.85 and 91.16%, respectively. In mixed sludge, methane producing bacteria are sensitive to mesosphilic temperature range;
the graph shows that at 32 °C removal of COD and
BOD were achieved at a maximum. Further increase
in temperature is not significant in COD removal and
also the production of bio gas decreases. Retention
time less than 4 days is insufficient for a stable digestion because initial volatile fatty acid concentration
was high in the wastewater. After 8-10 days there is a
decrease in volatile fatty acid which leads to high
COD removal [29]. Therefore, increase in retention
time increases the COD removal [1,13]. Similarly, increase in retention time increases the BOD removal
due to reduction in organic content of the wastewater
caused by anaerobic digestion.
44.96
10.78
220.55
0.2159
196.27
0.0683
24.28
Figure 3. Effect of temperature and retention time on BOD
removal (%) at optimum pH and initial BOD.
Effect of independent variables on biogas production
Figure 2. Effect of temperature and retention time on COD
removal (%) at optimum pH and initial BOD.
Biological decomposition of organic wastes
results in biogas production. The variation in parameters such as pH, initial BOD, temperature and
retention time are significant factors affecting the
growth of microbes during anaerobic digestion. From
Figure 4 it is observed clearly that an increase in
retention time proportionately increases the biogas
production, which further indicates that a maximum of
99.4 ml/day of the biogas was recovered at optimum
condition. Anaerobic digestion can take place at
either mesophilic or thermophilic temperatures. Even
small changes in temperature from 32–34 °C have
been shown to reduce the biogas production rate.
Hence, mixed sludge was suitable for biogas recovery
in the mesophilic temperature in which anaerobes are
active at 32 °C. pH is an important parameter for
anaerobic digestion. The suitable pH range for
methane producing bacteria is 6.8–7.2. The pH range
of 5.5–6.5 is suitable for acetogenic bacteria. The pH
is maintained with a methanogenic range to prevent
the predominance of the acid forming bacteria [4].
37
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
From the results, it was found that the optimum pH is
7 for biogas production.
Chem. Ind. Chem. Eng. Q. 22 (1) 33−39 (2016)
thetic sago wastewater using anaerobic digestion is
very effective and the operating variables highly influence the response variables. Hence, this study was
a unique attempt to optimise the treatment and production of effective biogas using anaerobic digestion
treatment. The RSM model helped to identify the
most significant operating factors and the optimum
levels with minimum effort and time.
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Figure 4. Effect of temperature and retention time on biogas
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Optimization of experimental conditions
The optimum region was identified by considering the maximum removal of COD, BOD and biogas
production. The optimized process conditions obtained
at pH 7, initial BOD 1374 mg/L, temperature 32 °C
and a retention time of 10 days showed a maximum
COD and BOD removal of 81.85 and 91.16%, respectively, and maximum biogas production of 99.4
ml/day with a desirability of 0.991. The results
obtained at 10 days of retention time show higher BOD
removal, COD removal and biogas production [2].
CONCLUSION
In the present study, anaerobic digestion methodology has been employed for reduction of COD and
biogas production under optimal condition. The RSM
based CCD was shown to be useful for the design of
experiments to investigate the effect of the four
estimated parameters (pH, initial BOD, temperature
and retention time) on the response parameters
(COD and BOD removal and biogas production). The
results showed good agreement between experimental and predicted values. Based on the ANOVA table,
the coefficient of determination (R2) values of 0.994
and 0.988 indicate the adequacy of the model for
COD removal and biogas production, respectively.
Maximum COD reduction and biogas production was
achieved at a pH value of 7, initial BOD of 1374 mg/L,
temperature of 32 °C and with the retention time of 10
days. It was identified from this study that COD reduction and biogas production in the treatment of syn-
38
V. SANGEETHA, V. SIVAKUMAR: BIOGAS PRODUCTION…
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L. Appels, J. Baeyens, J. Degrève, R. Dewil, Prog.
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239271, doi: 10.1100/2012/239271
V. SANGEETHA1
2
V. SIVAKUMAR
1
Department of Food Technology,
Kongu Engineering College,
Perundurai, Tamil Nadu, India
2
Department of Chemical
Engineering, Alagappa College of
Technology Campus, Anna
University, Chennai, India
NAUČNI RAD
PROIZVODNJA BIOGASA IZ VEŠTAČKIH
OTPADNIH VODA IZ PROIZVODNJE SKROBNOG
BRAŠNA PALME SAGO ANAEROBNOM
DIGESTIJOM: OPTIMIZACIJA I TRETMAN
Prerađivačka industrija skrobnog brašna palme sago stvara veliku količinu otpadnih voda
sa izuzetno visokom koncentracijom organskih zagađivača, što dovodi do zagađenja vode.
Za redukciju HPK i maksimalnu proizvodnju biogasa korišćena je anaerobna digestija
veštačkih otpadnih voda iz industrije skrobnog brašna šaržnim postupkom. Mešana kultura
dobijena iz mulja industrije skrobnog brašna je korišćeno kao izvor mikroorganizma.
Metodologija odzivne površine je korišćena za optimizaciju faktora procesa, kao što su:
pH, početna vrednost BPK, temperatura i vreme zadržavanja. Statistički rezultati su ocenjeni preko p vrednosti, odstupanja (F-test), koeficijenta determinacije R2 i adekvatne preciznosti. Pareto analiza varijansi je pokazala da koeficijenti determinacije (R2) za smanjenje HKP i BPK i proizvodnju biogasa iznose 0,994, 0,993 i 0,988, redom. Optimalni
uslovi pri kojima je postignuto maksimalno uklanjanje HPK (81,85%) i BOD uklanjanje
(91,61%) i proizvodnju biogasa (99,4 ml po danu) su: pH 7, početni BPK 1374 mg/l, vreme
zadržavanja 10 dana i temperatura 32 °C.
Ključne reči: anaerobna digestija, veštačka optadna voda iz proizvodnje skrobnog brašna, produkcija biogasa, hemijska potrošnja kiseonika, optimizacija.
39
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 41−45 (2016)
MUHAMMAD IMRAN AHMAD1
MUHAMMAD SAJJAD1
IRFAN AHMED KHAN2
AMINA DURRANI2
ALI AHMED DURRANI1
SAEED GUL1
ASMAT ULLAH1
1
Department of Chemical
Engineering, University of
Engineering and Technology,
Peshawar, Pakistan
2
Qadir Enterprises, Peshawar,
Pakistan
SCIENTIFIC PAPER
UDC 666.94(549.1)
DOI 10.2298/CICEQ141012017A
CI&CEQ
SUSTAINABLE PRODUCTION OF BLENDED
CEMENT IN PAKISTAN THROUGH ADDITION
OF NATURAL POZZOLANA
Article Highlights
• Ordinary Portland cement is partially substituted with rhyolite to reduce cost
• Blended cements employing rhyolite are demonstrated to possess satisfactory compressive strength
• Inter-grinding of rhyolite and clinker to produce blended cement shows reduced
energy consumption
Abstract
In this work, pozzolana deposits of district Swabi, Pakistan were investigated
for partial substitution of Portland cement along with limestone filler. The cement samples were mixed in different proportions and tested for compressive
strength at 7 and 28 days. The strength activity index (SAI) for 10% pozzolana,
and 5% limestone blend at 7 and 28 days was 75.5 and 85.0% satisfying the
minimum SAI limit of ASTM C618. 22% natural pozzolana and 5% limestone
were interground with clinker and gypsum in a laboratory ball mill to compare
the power consumption with ordinary Portland cement (OPC) (95% clinker and
5% gypsum). The ternary blended cement took less time to reach the same
fineness level as OPC due to soft pozzolana and high grade lime stone, indicating that intergrinding may reduce overall power consumption. Blended cement production using natural pozzolana and limestone may reduce the energy
consumption and greenhouse gas emissions.
Keywords: ternary blended cement, natural pozzolana, limestone filler,
cement production.
Natural pozzolans have been employed in civil
works since ancient times [1]. The addition of natural
volcanic rocks to cement or to concrete mixes results
in improving chemical and physical properties such as
reduction in heat release when mixed with water,
good ultimate compressive strength, low permeability,
high resistance to sulphates and chloride attacks, and
reduced alkali-silica reaction [2]. Addition of limestone
as a filler increases the early strength development in
concrete; however, chloride ion diffusion may also
increase depending upon the blending ratio. A careful
choice of additives and their blending ratios may yield
cements with enhanced performances. Cement production may become more sustainable by addition of
Correspondence: M. Imran Ahmad, Department of Chemical
Engineering, University of Engineering and Technology, Peshawar, Pakistan.
E-mail: Imran.Ahmad@nwfpuet.edu.pk
Paper received: 12 October, 2014
Paper revised: 12 October, 2014
Paper accepted: 1 June, 2015
cementitious materials in the process resulting in reduction in fuel consumption required for clinker formation, CO2 emissions, as well as enhanced durability
and life cycle performance of the concrete structures
[3].
The addition of natural pozzolans to form blended
cements has been investigated extensively by
researchers previously demonstrating benefits in reduction of energy consumption, green house gas emissions, and cost [4-7]. The addition of natural pozzolans is constrained due to increase in hydration
requirements and decrease in early strength development [8]. Blending of cement with natural pozzolans
and others additives offers the advantage of exploiting characteristic of various materials while compensating for disadvantageous features [9-14]. Blended
cements are also produced on a commercial scale,
for example in Algeria, using natural pozzolana and
limestone [15].
41
M. IMRAN AHMAD et al.: SUSTAINABLE PRODUCTION OF BLENDED CEMENT…
Natural pozzolans are known to react with the
calcium hydroxide formed during the reaction of ordinary Portland cement with water. The reaction of
silica component of pozzolana with calcium hydroxide
is relatively slow, and produces calcium silicate hydrates. The addition of pozzolana also results in increase of cementitious aluminates resulting from the
reaction of alumina component of pozzolana with
calcium hydroxide and sulphate ions [16-19].
This research work attempts to explore the production of blended cements in Pakistan through addition of natural pozzolana for sustainable growth of the
cement, and construction sector. Natural pozzolana
deposits are available in different areas of KPK,
Pakistan such as in Karak, Mohmand agency, Swabi
and Swat. Bentonite deposits of Karak district have
been investigated for partial substitution of ordinary
Portland cement in mortars and concrete [20].
In this paper the natural pozzolana deposits of
Swabi are investigated for production of ternary
blended cement. Pozzolana deposits are located in
Gohatee, on both sides of Swabi-Mardan road as
extrusive rocks, i.e., during geological transformation
Chem. Ind. Chem. Eng. Q. 22 (1) 41−45 (2016)
these extruded to the ground surface. The estimated
quantity of deposit above ground level is 9.2 million
tons, while the quantity below ground level needs to
be estimated after proper drilling. The pozzolana
deposits of Swabi are whitish in color without any
significant variation in size and composition [21].
MATERIAL AND METHODS
Pozzolana samples were collected and tested
for chemical, mineralogical composition, using XRF,
XRD, and other properties essential to determine
feasibility of use as cementitious material. Ordinary
Portland cement (OPC) was used with natural pozzolana from Swabi, Pakistan and high grade limestone
(consisting of more than 95% calcium carbonate)
from the quarry of Askari Cement, Nizampur, Pakistan. The chemical composition of OPC, natural pozzolana, and limestone employed in this work are
shown in Table 1. It may be observed from Table 1
that the minimum requirement of oxides as per ASTM
C618, i.e., the sum of silica, alumina, and iron oxides
content should be greater than 70%, for natural poz-
Table 1. Chemical composition (%) of the cement, pozzolana and limestone employed in experiments
Material
SiO2
Al2O3
Fe2O3
CaO
MgO
K2O
N2O
SO3
Cement
20.5
4.89
4.49
61.41
1.65
0.95
0.22
3.59
Pozzolana
70.61
11.97
0.69
1.95
0.61
4.06
0.0
0.09
Limestone
5.25
1.4
1.2
53.0
0.8
0.05
0.03
0.01
Figure 1. X-ray diffractogram of natural pozzolana.
42
M. IMRAN AHMAD et al.: SUSTAINABLE PRODUCTION OF BLENDED CEMENT…
zolana is satisfied. The mineralogical composition of
natural pozzolana is shown in Figure 1. The mineralogical composition as determined by X-ray diffraction
bears similarity with the mineralogical composition of
a natural pozzolana reported previously [15].
Pozzolana sample was also tested for loss on
ignition using BS–FLS–2011–04 standard. The loss on
ignition was 1.15%, satisfying the maximum of 10%
specification of ASTM C618. It was concluded based
on the loss on ignition that natural pozzolana under
consideration could be mixed with clinker or cement
without any drying through external heat source.
The formulation of blended cement was varied
by substitution of ordinary Portland cement with pozzolana ranging from 5 to 22%, while the limestone
content was maintained constant at 5%. Ordinary
Portland cement used was from Askari Cement Ltd.,
Nizampur, Pakistan, with fineness of 289.3 m2/kg and
residue of 10% on 45 μm. Pozzolana and limestone
were separately ground to 370 m2/kg and then mixed
with ordinary Portland cement in specified ratios, as
shown in Table 2. Mortar cubes were casted and
tested for compressive strength at 7 and 28 days.
Mortar cubes were prepared using 1:3 ratio of cement
and sand, taking 200 g of cement and 600 g of sand.
Cube dimensions were 70.1 mm×70.1 mm×70.1 mm.
Curing of cubes was carried out at 27±2 °C water
temperature in curing tank until the day of testing.
Table 3 presents the composition, loss on ignition,
specific surface area, i.e., Blaine and residue of various blends.
Strength activity index (SAI) was calculated for
all the blends to test for minimum specification of 75%
as per ASTM C618. The strength activity index is
defined as [22]:
SAI =
100 A
B
(1)
where A = average compressive strength of the
blended cement mortar cubes and B = average compressive strength of the cement mortar cubes without
any substitution.
The effect of pozzolana substitution on power
consumption was investigated by grinding clinker,
pozzolana, high grade limestone and gypsum mix,
and compared with grinding of clinker and gypsum in
a laboratory ball mill. The ball mill consisted of a
single chamber manufactured by Wuxi Building Material Instrument & Machinery Co, China. The laboratory ball mill had a diameter of 560 mm and length of
520 mm. The feed size was less than 30 mm as per
the mill requirement. The installed motor was 1.5 kW
Chem. Ind. Chem. Eng. Q. 22 (1) 41−45 (2016)
while total quantity of grinding media was of 96 kg.
Media sizes were 72 (12.56 kg), 63 (21.7 kg), 49
(22.06 kg) and 39 mm (10.64 kg). The dimensions of
the cylinders were 27 mm, length 37 mm (17.17 kg),
and diameter 25 mm, length 31 mm (11.87 kg). The
feed quantity was 5 kg. The ball mill was drained at
regular time intervals for sieve analysis using 600, 90
and 45 μm mesh as well as for Blaine fineness. Insoluble residue (IR) was determined by the BS–FLS–
20051–04 standard.
RESULTS AND DISCUSSION
The chemical composition of ordinary Portland
cement, pozzolana, and limestone employed in this
work is shown in Table 1.
It may be observed from Table 1 that the minimum requirement of oxides as per ASTM C618, i.e.,
the sum of silica, alumina, and iron oxides content
should be greater than 70%, for natural pozzolana is
satisfied. The compressive strength (MPa) at 7 and
28 days of various blends is shown in Table 2.
Table 2. Compressive strength of tested composite cement mortars
Cement Pozzolana Limestone
%
%
%
100
0
0
Compressive strength, MPa
7 days
28 days
54.7
61.8
90
5
5
44.3
58.3
85
10
5
41.3
52.5
80
15
5
40.0
49.6
73
22
5
37.1
48.3
The strength activity index calculated using Eq.
(1) for various blends at 7 and 28 days is shown in
Figure 2.
It may be observed from Table 2 and Figure 2
that increasing the weight percentage of pozzolana
above 10% while maintaining limestone percentage
fixed at 5% resulted in violation of the ASTM C618
specification, i.e., below the specified limit of 75%.
Alternatively, it may be noted that substitution of more
than 15% of ordinary Portland cement, using pozzolana and limestone, in cement mortars resulted in significant loss of compressive strength at 7 days. The
two blends (80/15/5 and 73/22/5) with significant loss
of compressive strength at 7 days show a recovery of
strength between 7 and 28 days, as shown by the
satisfactory SAI value at 28 days. All the cement composite mortars showed an increase in compressive
strength after 7 days indicating that between 7 and 28
days both the OPC hydration and pozzolanic hydration reactions contributed to strength development.
The reduction in early strength development is char-
43
M. IMRAN AHMAD et al.: SUSTAINABLE PRODUCTION OF BLENDED CEMENT…
Chem. Ind. Chem. Eng. Q. 22 (1) 41−45 (2016)
Figure 2. Strength activity indices for composite cement mortars after 7 and 28 days.
acteristic to use of natural pozzolans due to the need
for longer duration of moist-curing. However, this
shortcoming is partially addressed by addition of limestone filler, which accelerates the reactions in cement
pastes and mortars [15].
The chemical composition and physical properties such as Blaine fineness and residue are
shown in Table 3.
loying a mix of clinker 68%, pozzolana 22%, limestone 5% and gypsum 5% and compared with the
grinding to produce OPC, i.e., clinker 95% and gypsum 5%. The specific surface area obtained after
regular time intervals for the ternary blended cement
and OPC are shown in Table 4.
Table 3. Chemical composition (%) and physical properties of
blended cement composites
Grinding time, min
Table 4 Grinding test for OPC and blended cement
2
Component
OPC/Pozzolana/Limestone blend
Blaine fineness, m /kg
OPC
Blended cement
10
163.3
245.8
15
183.8
301.9
100/0/0
90/5/5
85/10/5
80/15/5
73/22/5
20
239.5
363.4
SiO2
20.5
22.84
25.65
28.22
32.48
25
275.3
408.5
Al2O3
4.89
5.21
5.79
6.3
7.15
Fe2O3
4.49
4.43
4.5
4.56
4.68
CaO
61.41
58.56
55.17
51.39
45.88
MgO
1.65
1.47
1.22
1.00
0.62
K2O
0.95
1.06
1.20
1.32
1.51
N2O
0.22
0.22
0.23
0.23
0.23
SO3
3.59
3.26
3.09
2.88
2.54
LOI
2.12
3.74
3.52
3.67
3.69
It may be observed from Table 4 that blended
cement was easier to grind compared to OPC due to
reduced percentage of clinker in blended cement. The
grinding tests indicate that inter-grinding of pozzolana
and limestone with clinker and gypsum in the cement
mill may reduce the power consumption required to
achieve the specified fineness for cement.
CONCLUSIONS
Physical properties
Blaine fine2
ness, m /kg
289.3
330.6
335.6
342.2
361.2
Residue, %
8.50
10.80
12.60
14.40
15.40
It may be observed from Table 2 that the substitution of OPC with pozzolana and limestone results
in reduction in early strength development. However,
the specific surface area, i.e., Blaine fineness increases, indicating that pozzolana is a relatively soft
additive. The partial substitution of OPC with pozzolana and limestone may also result in further saving in
energy consumption through reduction in power consumption requirement in the cement mill for grinding
of clinker and gypsum. The grinding test for blended
cement was carried out in a laboratory ball mill emp-
44
In this paper, partial substitution of ordinary
Portland cement with natural pozzolana from the
Swabi district and limestone was investigated for production of ternary blended cement in Pakistan. Pozzolana percentage was varied from 5 to 22%, to
substitute OPC, while maintaining a fixed percentage
of limestone. It is concluded based on the results of
compressive strength at 7 and 28 days that up to 15%
OPC may be substituted with 10% pozzolana and 5%
limestone in cement composites. The use of ternary
blended cement composites in civil works would need
further investigation to determine the long term strength
development, i.e., after 28 days, as well durability
through sulphate resistance, and permeability tests.
M. IMRAN AHMAD et al.: SUSTAINABLE PRODUCTION OF BLENDED CEMENT…
The power consumption required in the cement
mill was inferred through investigation on a laboratory
ball mill indicating that intergrinding of pozzolana and
limestone with clinker and gypsum may reduce the
overall power consumption of cement production.
Chem. Ind. Chem. Eng. Q. 22 (1) 41−45 (2016)
[9]
J. Bai, B. Sabir, S. Wild, J.M. Kinuthia, Mag. Concr. Res.
52(2) (2000) 153-162
[10]
R. Bleszynski, R.D. Hooton, M.D.A. Thomas, C.A.
Rogers, ACI Mater. J. 99(5) (2002) 499-508
[11]
M.F. Carrasco, G. Menendez, V. Bonavetti, E.F. Irassar,
Cem. Concr. Res. 35(7) (2005) 1324-1331
Acknowledgement
[12]
The support of Askari Cement, Nizampur, Pakistan is acknowledged for providing assistance in testing of composition and properties of samples.
J.M. Khatib, J.J. Hibbert, Constr. Build. Mater. 19(6)
(2005) 460-472
[13]
Z. Li, Z. Ding, Cem. Concr. Res. 33(4) (2003) 579-584
[14]
G. Menendez, V. Bonavetti, E.F. Irassar, Cem. Concr.
Compos. 25(1) (2003) 61-67
REFERENCES
[15]
M. Ghrici, S. Kenai, M. Said-Mansour, Cem. Concr.
Compos. 29 (2007) 542-549
[1]
S.H. Kosmatka, B. Kerkhoff, W.C. Panarese, N.F. Macleod, R.J. McGrath, Design and Control of Concrete Mixth
ture, 7 ed., Portland Cement Association, Skokie, IL,
2002
[16]
V.L. Bonavetti, V.F. Rahhal, E.F. Irassar, Cem. Concr.
Res. 31(6) (2001), 853-859
[17]
M. Heikal, H. El-Didamony, M.S. Morsy, Cem. Concr.
Res. 30(12) (2000) 1827-1834
[2]
ACI, ACI Mater. J. 91(4) (1994), 410-426
[18]
[3]
P.K. Mehta, ACI SP-178, Farmington Hills, MI, 1998, pp.
1-25
G. Kakali, S. Tsivilis, E. Aggeli, M. Bati, Cem. Concr. Res.
30(7) (2000) 1073-1077
[19]
A.M. Neville, Properties of Concrete, 3
Harlow, 1981
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ed.,. Pearson,
[4]
P.K. Mehta, Cem. Concr. Res. 11 (1981) 507-518
[5]
F. Massazza, Cem. Concr. Compos. 15(4) (1993) 185-–214
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A. Tagnit-Hamou, N. Pertove, K. Luk, ACI Mater. J.
100(1) (2003) 73-78
J. Mirza, M. Riaz, A. Naseer, F. Rehman, A.N. Khan, Q.
Ali, Appl. Clay Sci. 45 (2009), 220-226
[21]
[7]
L. Turanli, B. Uzal, F. Bektas, Cem. Concr. Res. 35
(2005) 1106-1111
A.H. Kazmi, S.G. Abbas, Metallogeny and Mineral
Deposits of Pakistan, Orient Petroleum Inc., Islamabad,
2001
[8]
B. Uzal, L. Turanli, Cem. Concr. Compos. 34 (2012) 101–109
[22]
ASTM, Standard Specification for Coal Fly Ash and Raw
or Calcined Natural Pozzolan for Use in Concrete. C618-08a. ASTM International, West Conshohocken, PA,
2008.
MUHAMMAD IMRAN AHMAD1
MUHAMMAD SAJJAD1
IRFAN AHMED KHAN2
AMINA DURRANI2
ALI AHMED DURRANI1
SAEED GUL1
ASMAT ULLAH1
1
Department of Chemical
Engineering, University of
Engineering and Technology,
Peshawar, Pakistan
2
Qadir Enterprises, Peshawar,
Pakistan
NAUČNI RAD
ODRŽIVA PROIZVODNJA CEMENTNE MEŠAVINE
IZ PAKISTANA UZ DODATAK PRIRODNOG
PUCOLANA
U ovom radu istraživana su nalazišta pucolana u oblasti Svabi (Swabi, Pakistan), radi
parcijalne zamene portland cementa uz dodatak krečnjaka kao punioca. Komponente su
mešane u različitim odnosima, a uzorci betona su testirani na pritisnu čvrstoću posle 7 i 28
dana. Indeks pritisne čvrstoće (SAI) za mešavine od 10% pucolana i 5% krečnjaka posle 7
i 28 dana bio je 75,5 i 85,0%, redom, što zadovoljava minimalnu SAI granicu prema ASTM
C618. Smeša sa 22% prirodnog pucolana i 5% krečnjaka je samlevena sa klinkerom i
gipsom u laboratorijskom kugličnom mlinu radi poređenja potrošnje energije sa običnim
portland cementom (OPC) (95% klinkera i 5% gipsa). Trojnoj cementnoj mešavini je trebalo manje vremena da se postigne ista finoća kao OPC zbog prisustva mekih faza pucolana i visokog udela krečnjaka, što pokazuje da je moguće smanjiti ukupnu potrošnju energije. Evidentno da proizvodnja cemente mešavine, koristeći prirodni pucolan i krečnjak,
može da smanji potrošnju energije i emisiju gasova staklene bašte.
Ključne reči: trojna cementna mešavina, prirodni pucolan, krečnjački punioc,
proizvodnja cementa.
45
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
YUEHAO LUO1
ROBERT SMITH2
LORK GREEN3
1
School of Engineering and
Applied Science, The George
Washington University,
Washington D.C., USA
2
College of Applied Sciences and
Technology, Ball State University,
Muncie, IN, USA
3
School of Engineering, Boston
University, Boston, MA, USA
SCIENTIFIC PAPER
UDC 678.686:544:66
DOI 10.2298/CICEQ150119018L
CI&CEQ
EXPLORING INSTANTANEOUS MICRO-IMPRINTING TECHNOLOGY ON SEMI-CURED EPOXY RESIN COATING BASED
ON RELATIONSHIP BETWEEN FORMING
PRECISION AND CURING DEGREE
Article Highlights
• Micro-dimple imprinting method is explored and adopted
• Relationship between plastic deformation capacity and curing degree is investigated
• Instantaneous micro-imprinting method is exploited
• Forming precision of instantaneous micro-imprinting can surpass 90%
Abstract
Nano/micro-imprinting technology based on polymer material coating has
attracted increased attention throughout the world in the past several decades,
and it is at present progressively developing into a hot topic, in which how to
improve the manufacturing efficiency is becoming the urgent issue to be
resolved. Polymer’s curing process is exactly complicated and sophisticated,
which involves simultaneously performing physical and chemical changes,
when the curing reaction reaches certain level, the system will abruptly transform into insoluble, non-melting gel with rapidly increased viscosity and rigidity,
which can generate fixed deformation under persistent external pressure. In
this paper, the plastic deformation capacity of epoxy resin in the curing process
is investigated by the micro-dimple imprinting experiment, and the relationship
between forming precision and curing degree is ascertained adopting the DSC
(differential scanning calorimetry) method. In addition, the instantaneous
micro-imprinting technology based on the micro-grooves is explored, and the
experimental results indicate that the forming precision can surpass 90%. The
paper will establish a novel avenue for application of the nano/micro imprinting
technology into practical engineering.
Keywords: polymer material, semi-cured, DSC, micro-imprinting,micro
grooves, forming precision.
Entering the 21st century, with the increasingly
serious energy crisis and climate warming, saving
energy and reducing emission of greenhouse gases
has turned into an important issue, in which lowering
the friction force on the contact surfaces between
moving objects can take a critical role. For protecting
surfaces from corrosion and obtaining the smoothness, polymer coatings have been widely exploited in
Correspondence: Y. Luo, School of Engineering and Applied
Science, The George Washington University, Washington D. C.,
20052, USA.
E-mail: luoyuehao1985@163.com; luoyuehao@gwu.edu
Paper received: 19 January, 2015
Paper revised: 18 May, 2015
Paper accepted: 13 June, 2015
fluid engineering applications, such as natural gas
pipelines, navigation, agriculture, industry, airplanes,
everyday life, etc. [1-3]. It has been illustrated that
bio-inspired micro-structured morphology has the
apparent drag-reducing effect in turbulence with
smooth skin as baseline [4, 5]. Expanding the applications of bio-inspired drag-reducing technology to
coating surfaces is an effective way to reduce friction
force and conserve resources. Traditional imprinting
methods with micro-textures have been explored and
investigated comprehensively; however, for the purpose of holding the perfect forming effect, long duration with persistent external pressure is imperative
[6]. This can lower the manufacturing efficiency and
restrict the practical engineering applications; there-
47
Y. LUO et al.: EXPLORING INSTANTANEOUS MICRO-IMPRINTING…
fore, new and feasible manufacturing ways should be
researched further.
For the current nano/micro imprinting methods,
the time-points exerting pressure on semi-cured coatings are not concentrated into the short time-zone [7-9], and the consequence is that the duration should
be very long to maintain the high forming precision.
Reducing the duration for improving the manufacturing efficiency has thus developed into an urgent
problem. If the duration could be condensed into the
time of polymer padding into the hollows of the mold,
while obtaining satisfactory forming precision after
curing, the manufacturing efficiency will improve
greatly with good machining quality. Therefore, ascertaining the most appropriate time-points to exert instantaneous pressure on the semi-cured coating in the
curing process is a critical issue. In this article, the
relationship between forming precision and curing
degree is investigated by the micro-dimple imprinting
experiment, and the instantaneous micro imprinting
technology is preliminarily explored adopting the
micro-grooved mol. The results show that when the
curing degree is located into 0.8-0.9, the coating has
the best plastic deformation capacity, and forming
precision can be more than 90%.
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
MATERIALS AND METHODS
Curing of epoxy resin
The curing and cross-linking mechanism of thermosetting epoxy resin is very complex and intricate.
The chemical kinetics and physical interactions both
exist in the curing process [10-12], which has so far
not been understood thoroughly. The phenomenological method is the most popular and commonly
adopted in studying epoxy resins. The following semiempirical formula, which has laid the basic foundation
to investigate the curing mechanism of epoxy resin,
has been applied widely [13]:
dα
 E 
= A0 exp  − a  (1 − α )n
dt
 RT 
where: α is the curing degree, t is the duration time,
A0 is the frequency factor, Ea is the activation energy,
R is the universal gas constant, T is the absolute
temperature, and n is the reaction cardinal number.
The epoxy resin used in this paper (AW-01
epoxy resin) can be cured completely at temperature
higher than 30 °C. SEM images of the epoxy resin
coating at curing temperatures 40-100 °C are shown
in Figure 1a-d. It can be seen that the internal structure of the epoxy resin cured at 45 °C is more meti-
Figure 1. SEM images and wear scars of epoxy resin coating curing at different temperatures.
48
(1)
Y. LUO et al.: EXPLORING INSTANTANEOUS MICRO-IMPRINTING…
culous than that cured at 95 °C. In order to validate
the wear property, wearing experiments were conducted on an SRV machine (produced in Germany).
The schematic drawing and key parts of the tester are
shown in Figures 2 and 3. In the experiment, the force
exerted on the smooth steel ball was 25 N, the stroke
of the rectilinear reciprocating movement was set as
1.6 mm, the frequency was 15 Hz, and the wear scars
corresponding with the internal structures are illustrated in Figures 1a-1d. It can be concluded that with
decreasing curing temperature, the width of wear
scars drops from 2.51 to 1.87 mm, which implies that
the anti-wear property of epoxy resin is gradually improved. Additionally, finer structures can enable better
mechanical and chemical properties, such as anti-corrosion, tensile strength, anti-acid, hardness, roughness, etc. [14-16]. Therefore, the curing temperature
of 45 °C was used in this paper.
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
Micro-dimple imprinting
To ascertain the plastic deformation capacity of
epoxy resin at different time-points, the micro-dimple
imprinting experiment is designed and as shown in
Figure 4. The system was comprised of parallel light,
coating sample, substrate, convex lens imaging system, displaying screen, rigid probe, etc.
The basic steps of the micro-dimple imprinting
experiment are as follows: 1) exerting instantaneous
displacement on the semi-cured coating surface by
the rigid probe; 2) epoxy resin coating gradually
becomes cured; 3) measuring the depth of microdimple by the precise scanning method. The forming
precision of the imprinting experiment is defined as
the ratio of depth of micro-dimple and instantaneous
displacement. The feeding displacement of rigid
probe can be exactly exerted by the screw rotation
with the precision of 1 μm. In the experiment, the
epoxy resin is covered on the plat aluminum substrate
by the airless spraying method, and the depth of
liquid film is 300 µm, which can be measured by the
liquid film gauge, as shown in Figure 5. The threedimensional morphology and parameters on cured
epoxy resin coating can be obtained by the highly
precise scanning, as shown in Figure 6a-c.
Figure 2. Schematic drawing of wearing testing experiment.
Figure 5. Measuring the depth of epoxy resin liquid film.
The obtained results from experiments in which
the curing temperature is fixed at 45 °C and duration
is varied are displayed in Table 1. It can be concluded
that with increasing duration, the forming precision
Figure 3. Key parts of SRV wearing tester.
Figure 4. Schematic diagram of micro-dimple imprinting method.
49
Y. LUO et al.: EXPLORING INSTANTANEOUS MICRO-IMPRINTING…
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
Figure 6. Three-dimensional morphologies on cured epoxy resin coating.
Table 1. Results of micro-dimple imprinting experiments; T = 45 °C
Duration, min
Depth of dimple, μm Forming precision, %
Duration, min
Depth of dimple, μm Forming precision, %
100
145.2
72.6
114
180.8
90.4
102
156.2
78.1
115
180.6
90.3
105
172.2
86.1
117
180.4
90.2
107
174.2
87.1
118
180.2
90.1
110
179.8
89.9
119
180.0
90.0
111
180.4
90.2
120
179.0
89.5
112
181.2
90.6
121
176.6
88.3
113
182.2
91.1
122
176.0
88.0
first increases and then decreases gradually. Moreover, the maximum of forming precision can be
greater than 90%.
Differential scanning calorimetry (DSC)
For studying the properties and characteristics
of epoxy resin system more comprehensively, the
kinetics of the curing reaction were monitored by a
differential scanning calorimeter (DSC) and investigated by the constant heating method, which is an
important basis of composite materials forming technology and can supply the basic theoretical foundation [18-22].
DSC is the most popular phenomenological
method to explore and investigate the curing kinematics of epoxy resin, which mainly involves two
operation models: isothermal DSC and dynamic DSC
[23,24]. The isothermal DSC can obtain the reaction
heat at some certain temperature, the dynamic DSC
can obtain the reaction heat (ΔHtotal) or the residual
reaction heat (ΔHres). In addition, the glass transition
temperature can be measured by the shift of the
baseline. The isothermal DSC experiment was conducted at 45 °C.
RESULTS AND DISCUSION
Relationship between different parameters
When the forming precision is greater than 90%,
it can be regarded as the best plastic deformation
50
capacity. The relationship between forming precision,
curing degree and heat flow is shown in Figure 7,
indicating that the best plastic deformation corresponds to the curing degree (α) range of 0.8-0.9.
Furthermore, with increasing curing degree, the forming precision first increases and reaches a maximum,
and then decreases. The measured hardness of
semi-cured coating fitting to exert the external pressure varied from 68-72 HA (Figure 8).
Exploration on instantaneous micro-imprinting
technology
Bio-inspired micro-structured surfaces have an
apparent drag reduction effect in turbulent flowing
conditions [25-29], and have extensively been put into
application in fluid engineering [30, 31]. However, the
practical applications are limited by the manufacturing
efficiency to some extent. The instantaneous microimprinting technology with micro-grooved mold is preliminarily exploited to improve the manufacturing efficiency according the aforementioned conclusion. If
the operating time is not enough, the polymer will not
fill the hollows of the mold completely [32]. Meanwhile, if the operating time is too long, the imprinting
efficiency will be affected and restricted. The equation
for shortest duration required for filling the hollows
completely has been derived by Heyderman [33]:
tf =
η0S 2 1
1
(
− )
2P hf2 h02
(2)
Y. LUO et al.: EXPLORING INSTANTANEOUS MICRO-IMPRINTING…
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
Figure 7. Relationship between heat flow rate, forming precision and curing degree.
where tf is the duration, η0 is the viscosity of polymer,
S is area of pattern, P is the pressure, h0 is the height
of the pattern before imprinting, and hf is the height of
pattern after imprinting. When the curing degree of
epoxy resin is 0.8-0.9, the duration tf is 0.25-0.35 s.
In the experiments, the operating time was
about 1 s, which was greater than the filling time and
much less than that of available imprinting. The
images of micro-grooved mold and cured micro-structured coating morphology are shown in Figure 9a and
b, and the cross section curves are illustrated in
Figure 10a and b. It can be seen that the depth and
semi-width of micro-grooved mold were 41.4 and 95.3
µm, and those of the coating surface were 38.3 and
95.3 µm, respectively. From the forming precision
analysis (Figure 11), it can be concluded that the
forming errors only exist in the vertical direction (forming precision can be more than 90%, 38.3/414×100 =
= 92.5%), and there is no error in the horizontal direction.
Figure 8. Measuring the hardness of semi-cured epoxy resin.
Figure 9. Three-dimensional morphology of micro-grooved model and imprinted coating.
51
Y. LUO et al.: EXPLORING INSTANTANEOUS MICRO-IMPRINTING…
Chem. Ind. Chem. Eng. Q. 22 (1) 47−53 (2016)
Figure 10. Cross section curves of micro-grooves and morphology on imprinted coating.
Figure 11. Forming precision analysis of instantaneous micro-imprinting technology.
CONCLUSIONS
REFERENCES
In this paper, the relationship between plastic
deformation capacity and curing degree was investigated by the micro-dimple imprinting experiment,
and the following conclusions can be drawn:
1) When the curing degree is located in the
range of 0.8-0.9, the forming precision can be greater
than 90% and the epoxy resin has the best plastic
deformation capacity.
2) The relationships between forming precision,
curing degree and heat flow rate are ascertained for
the first time. With increasing curing degree, the forming precision first increases and reaches a maximum,
and then decreases.
3) The instantaneous micro-imprinting technology adopting the micro-grooved template was preliminarily explored, and the experimental results showed
that it has good forming effect and quality. The forming precision in the horizontal direction is about 100%,
and the forming precision in the vertical direction is
greater than 90%.
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YUEHAO LUO1
ROBERT SMITH2
LORK GREEN3
1
School of Engineering and
Applied Science, The George
Washington University,
Washington D.C., USA
2
College of Applied Sciences and
Technology, Ball State University,
Muncie, IN, USA
3
School of Engineering, Boston
University, Boston, MA, USA
NAUČNI RAD
ISTRAŽIVANJE TEHNOLOGIJE TRENTUNOG
MIKRO-ŠTAMPANJA NA POLUOČVRSLIM
PREMAZIMA EPOKSI SMOLA ZASNOVANIM
NA ZAVISNOSTI IZMEĐU PRECIZNOSTI
OBLIKOVANJA I STEPENA OČVTŠĆAVANJA
Tehnologija nano/mikro-štampanja baziranim na premazima polimernih materijala privlači
sve veću pažnju širom sveta u poslednjih nekoliko decenija, da bi danas postala top tema
u kojoj je kako poboljšati efikasnost proizvodnje urgentan problem koji treba rešiti. Proces
očvršćavanja polimera je komplikovan i sofisticiran postupak, koji uključuje istovremeno
obavljanje fizičkih i hemijskih promena. Kada reakcija očvršćavanja dostigne određeni
nivo, sistem se naglo transformiše u nerastvorljiv i netopljiv gel sa naglo povećanim viskozitetom i rigidnošću, koji mogu da dovedu do stalne deformacije pod stalnim spoljašnim
pritiskom. U ovom radu, kapacitet plastične deformacije epoksidne smole u procesu očvršćavanja je praćen utiskivanjem mikro-otisaka, a odnos između preciznosti oblikovanja i
stepena očvršćavanja je utvrđen metodom diferencijalne skaning kalorimetrije. Pored toga,
proučavana je i tehnologija trenutnog mikro-štampanja zasnovana na pravljenju mikro-otisaka, a eksperimentalni rezultati ukazuju da preciznost oblikovanja može biti preko 90%.
Rad utvrđuje novi put primene tehnologije nano/mikro štampanja u praktičnom inženjerstvu.
Ključne reči: polimerni material, semi-čvršćavanje, diferencijalna skaning kalorimetrija; mikri-štampanje, mikro-otisci, preciznost oblikovanja
53
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 55−64 (2016)
ZORANA BOLTIĆ1
MIĆA JOVANOVIĆ2
SLOBODAN PETROVIĆ2
VOJISLAV BOŽANIĆ3
MARINA MIHAJLOVIĆ4
1
Hemofarm A.D, Vršac, Serbia
2
Faculty of Technology and
Metallurgy, University of Belgrade,
Belgrade, Serbia
3
Faculty of Organizational
Sciences, Belgrade, Serbia
4
Innovation Centre of the Faculty of
Technology and Metallurgy,
University of Belgrade, Belgrade,
Serbia
SCIENTIFIC PAPER
UDC 615:66:338.45
DOI 10.2298/CICEQ150430019B
CI&CEQ
CONTINUOUS IMPROVEMENT CONCEPTS AS
A LINK BETWEEN QUALITY ASSURANCE AND
IMPLEMENTATION OF CLEANER
PRODUCTION – CASE STUDY IN THE
GENERIC PHARMACEUTICAL INDUSTRY
Article Highlights
• CI as a relationship between QA and CP implementation in the generic pharmaceutial
industry
• Application of Lean and Six Sigma tools for process improvement and link to other
known concepts
• Evaluation of the production systems in terms of CI, considering both quality and efficiency
Abstract
The subject and the research objective presented in this article is establishing
of the relationship between quality assurance and implementation of cleaner
production in the generic pharmaceutical industry through the comprehensive
concept of continuous improvement. This is mostly related to application of
Lean and Six Sigma tools and techniques for process improvement and their
link to other known concepts used in the industrial environment, especially
manufacturing of generic pharmaceutical products from which two representative case studies were selected for comparative analysis, also considering
relevant regulatory requirements in the field of quality management, as well as
appropriate quality standards. Although the methodology discussed in this
conceptual and practice oriented article is strongly related to chemical engineering, the focus is mainly on process industry, i.e., production systems,
rather than any specific technological process itself. The scope of this research
is an engineering approach to evaluation of the production systems in terms of
continuous improvement concepts application, considering both quality
aspects and efficiency of such systems.
Keywords: quality assurance, cleaner production, pharmaceutical industry, continuous improvement, lean, six sigma.
The present article is based on the application of
specific continuous improvement techniques on
relevant performance measures (PM) of different processes in the pharmaceutical industry and evaluation
of their effectiveness in the actual industrial environment [1,2]. The processes that are studied in this
work are related to design and operation of the equipment, as well as to the flow of the manufacturing
Correspondence: M. Jovanović, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade,
Serbia.
E-mail: mica@tmf.bg.ac.rs
Paper received: 30 April, 2015
Paper revised: 17 June, 2015
Paper accepted: 15 November, 2015
process of the products under consideration, but also
to quality systems relevant for production of pharmaceuticals. This implies optimization techniques of process design versus treatment processes (including
techno-economic analysis) with the aim of introducing
cleaner process technologies and how it relates to the
improvement of the quality systems as well. Continuous improvement techniques also represent a part
of chemical engineering, but in the sense of process
industry, i.e. in the area of production systems, rather
than any individual technological process. An original
and novel approach is applied to the evaluation of
industrial processes, as well as a new industrial engineering methodology and its application in practice is
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Chem. Ind. Chem. Eng. Q. 22 (1) 55−64 (2016)
studied through the evaluation of the production systems, which are determined both by their capacities
and quality aspects. The scope is therefore the processes in the generic pharmaceutical industry, which,
as such, has certain specificities that have to be considered when evaluating the applicability of certain
techniques in the area of continuous improvement.
Pharmaceutical industry is involved in development, production and marketing of drugs, i.e., pharmaceutical products approved by relevant regulatory
authorities. Pharmaceutical companies can have their
own research and development – originators, i.e.,
innovators, or produce generic drugs – products bioequivalent to the innovator’s, i.e., comprising the
same medicinal or therapeutic substances as the original drug. Pharmaceutical companies based on their
own development made a significant progress in
treatment of numerous diseases, but increasing
healthcare costs over time also resulted in the increased use of generic drugs with certain advantages
over more expensive original drugs, especially among
the poorer population of patients. Because of this,
generic pharmaceutical production represents a significant portion of the world pharmaceutical industry.
Either based on its own development or generic,
pharmaceutical industry is regulated through numerous laws and regulations in the area of patenting,
testing and ensuring safety and efficiency of drugs,
i.e., product release to the market.
The aim of this work is to evaluate the relationship between process performance measurement
with key indicators of success on the company level
and the concept of introducing cleaner production
principles in the generic pharmaceutical industry,
linked to the continuous improvement programs.
effectively make decisions. Selection of the appropriate key performance indicators, as well as measurement methodologies, represents a critical factor for
the success of measurement and analysis procedures.
In the new philosophy of sustainability, the concept of sustainable development is replaced with the
term sustainable success, as a result of the organization's ability to achieve and maintain long-term
goals, and this is the main novelty in revised standard
ISO 9004: 2009 [3] in relation to the second revision
of this standard [4]. ISO 9001 [5] specifies the requirements for the quality management system and is
focused on its effectiveness in complying with customer requirements. ISO 9004 gives additional guidance for the organizations willing to move further than
these requirements, to solving the needs and expectations of all interested parties and their satisfaction
through systematic and continuous performance improvement. Therefore, it represents a powerful tool for
the management, and the sustainable success of the
organization is developed through its capability to
satisfy needs and expectations imposed by its customers and other interested parties in a balanced way
and over a long period of time. Self-assessment is
used to identify areas for improvement and innovation, establish priorities and develop action plans
aimed at sustainable success. The results of the
organization's evaluation according to ISO 9004 may
represent a valuable input for management review as
required by ISO 9001 (i.e., for information review from
monitoring, measurement and analysis, as stipulated
in ISO 9004:2009), but this self-assessment process
also has a certain potential to be a learning tool
enabling the improved involvement of interested parties whose needs and expectations have to be properly understood, as the key element of the organization's maturity model.
Cleaner production and eco-efficiency are part
of the consideration in the area of the environment, as
prescribed by the social responsibility standard.
These are the strategies for satisfaction of human
needs through more efficient utilization of resources
and producing less pollution and waste. Significant
focus is to introduce the improvements at the source
instead at the end of process or activity. Cleaner and
safer production, as well as eco-efficiency approaches
include also the improvement of the sustainable practice, introducing new technologies or processes with
lower consumption of material and energy (i.e., utilization of its renewable resources) and rationalization
of water consumption. Cleaner production assumes
elimination or safe management of toxic and hazard-
THEORETICAL PART
It is a well known fact that pharmaceutical production is one of the most regulated industrial sectors
and that quality is the key factor that determines each
manufacturing system, including product characteristics, its appearance, duration, maintenance, but also
its supply and relevant documentation. For the purpose of achieving sustainable success, the organizations regularly measure, analyse and review their
performance, including evaluating the progress in
achieving planned results compared to their mission,
vision, policies, strategy and goals on all levels and in
all relevant processes and functions in the organization. Measurement and process analysis is used to
track this progress, gather and have all the necessary
information available to evaluate performance and
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ous materials/wastes, as well as improvement of the
products and services projects. Cleaner production in
general represents a contemporary approach in preventing the creation of pollution that provided the
greatest contributions in the production sector, especially in industry [6].
Six Sigma approach to continuous improvement
uses the methodology known as DMAIC (Define,
Measure, Analyze, Improve, Control) for process improvement from beginning to end [7]. In each of these
phases, appropriate tools are being used, such as
project plan, SIPOC (Supplier, Input, Process, Output,
Customer), process mapping and different team management techniques in the define phase, measurement system analysis, histogram and Pareto in measure, FMEA (Failure Mode and Effects Analysis),
“5 whys” and fishbone diagram for cause-and-effect
analysis, statistic process control and control charts in
the control phase of the implemented improvements.
According to well known statistical principles,
sigma represents a Greek letter for standard deviation
showing how much the measured results are distant
from the average of the observed set of data, i.e.,
representing a measure of process variability and its
capability to work without errors and as little variation
as possible. Measures are necessary in order to
determine whether the process of interest is stable
and predictable, as well as how much variation is present [8]. Six Sigma means that the interval between
both upper and lower limit of the process specification
and the average of the results obtained from that
actual process is 6 standard deviations. This number
of standard deviations is inversely proportional to the
probability of defects and in fact illustrates how much
of the obtained results is within the interval required
by the customer, i.e. increasing the sigma level of the
process decreases the cost and increases productivity and customer satisfaction. In order to state that a
process is “sigma” it is not allowed to have more than
3.4 defects per million opportunities [9], therefore six
sigma virtually represents a measure of quality practically aiming for perfection. ISO/TR 10017:2003 also
provides guidance on the selection of appropriate statistical techniques that may be useful to an organization in developing, implementing, maintaining and
improving a quality management system in compliance with ISO 9001 [10].
Lean, on the other hand, is a concept originating
from Toyota in the 1950s and representing a common
sense and practical approach to solving problems
with the focus on identifying and eliminating waste
from the process. Over the years, Toyota started a
global transformation in almost all industry sectors in
accordance with Lean philosophy in the area of
manufacturing and supply chain [11]. There are seven
common forms of waste, namely: transport, inventory,
movement, waiting, over-production, over-processing
and defects, and one of the tools introduced by the
Lean methodology is Kaizen (Ky = change and Zen =
= for the better, generally being translated as continuous improvement through solving problems).
Kaizen is a quick, intensive look at the process with
the aim of improvement. It gathers customers, suppliers, support and people performing the work, where
the latter is key for its success. The actual process is
observed and waste identified and eliminated through
establishing a new process but as a continuous effort
rather than reaching perfection in one step. Production system established in Toyota is the starting basis
for numerous literature sources in this field, including
The Machine That Changed the World: The Story of
Lean Production [12] and Lean Thinking [13].
The international conference on harmonisation
of technical requirements for registration of pharmaceuticals for human use (ICH) in its guidance Q10
[14] describes one comprehensive model for an
effective pharmaceutical quality system that is based
on International Organization for Standardization
(ISO) quality concepts, includes applicable good
manufacturing practice (GMP) regulations, and complements ICH “Q8 Pharmaceutical Development” and
ICH “Q9 Quality Risk Management.” ICH Q10 is a
model for a pharmaceutical quality system that can be
implemented throughout the different stages of a product lifecycle. Much of the content of ICH Q10 applicable to manufacturing sites is currently specified by
regional GMP requirements. Implementation of ICH
Q10 throughout the product lifecycle should facilitate
innovation and continual improvement and strengthen
the link between pharmaceutical development and
manufacturing activities.
In this work, the selected criteria used to determine the existence of either Lean or Six Sigma approach (or both) in the case studies subject to evaluation
are as follows: 1) data based approach/performance
measurement, 2) link to the customer, 3) proactive
thinking and 4) tools and techniques. Additionally, the
link between the processes subject to relevant case
studies (quality assurance – QA and cleaner production – CP) was analyzed against relevant regulatory
requirements and quality standards.
CASE STUDY
Starting hypotheses are based on the importance of measurement as the key element to control,
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manage and improve processes on one side and the
link of continuous improvement to the cleaner production concept in the industrial environment on the
other. Performance measurement represents the basis
of most continuous improvement programs, enabling
for example the implementation of cleaner production
step by step, using appropriate tools and techniques.
This is especially true for generic pharmaceutical
industry where it is necessary to change technological
procedures in a highly regulated environment in contrast to minimizing harmful effects of the production
processes in the end-of-pipe approach.
Therefore, the scope of this study is to evaluate
the following:
• Performance measurement system represents the comparison of the current values with the
predefined objectives and enables feedback to the
participants in the process - this approach should
result in the improvement of the quality management
system and continual adjusting of the performance
measures.
• Implementation of the continuous improvement program based on process performance measurement leads to decreased costs related to different
forms of waste, i.e., redundant engagement of
resources.
• Efficient elimination of waste from the processes with positive effects on quality, environment,
working conditions and social responsibility at the
same time, can be accomplished through a unique
approach of the continuous improvement program
implementation, introducing step by step improvements in individual areas.
This evaluation is performed using the examples
of quality assurance processes [1] as the case study
CS I, and dealing with volatile organic compounds
(VOCs) emissions, as one of the challenges for the
implementation of cleaner production in the generic
pharmaceutical industry [2], as the case study CS II.
Description of the analyzed case studies
CS I in the area of quality assurance was aimed
to evaluate the implementation of the modern
approach based on measures and key performance
indicators in a pharmaceutical company using the
example of the delivery time improvement through
decreasing the number of deviations and time spent
on unnecessary investigations. Problems subject to
the analysis were identified in both cases based on
relevant information and data available in the industrial information system related to actual processes,
and appropriate corrective actions and suggested
improvements were implemented through the described improvement projects. Results were discussed
relative to the previously established objectives: in the
area of quality assurance, significant decrease of total
number of deviations was shown – more than 50% [1].
On the other hand, as CS II for introducing the
cleaner production principles into the processes
within the generic pharmaceutical industry, the case
of tablets coating was selected, as one of the most
common and widely used operation in the pharmaceutical production in general. The conclusion was
made that the option of preventing pollution through
modifying the formulation has a significant advantage
both considering financial benefits and minimization
of waste, i.e. negative impact on the environment [2].
Data based approach/Performance measurement
In CS I, methods used for gathering the information related to key performance indicators (KPI) are
selected as feasible and appropriate for the organization, which is also one of the requirements in ISO
9004:2009 (Figure 1). On the other hand, the KPI is
Figure 1. Main characteristics of the key indicators, performance measures and data analysis performed.
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selected to enable its quantification and make feasible to the organization to set measurable goals,
identify, monitor and predict trends and implement
corrective, preventive and improvement measures, as
needed. It is important to ensure that measurable and
reliable information are available for the implementation of these corrective actions when the performance is not in compliance with the previously established goals.
As efficient utilization of resources is also one of
the requirements that need to be assured by the
management system, it is shown in the CS II that the
processes are established to monitor and optimize
these resources in order to ensure their effective and
efficient use. Therefore, the organization continually
measures their current utilization to identify opportunities for the improvement in this area. In addition,
the environmental impact was measured as part of
continual monitoring to enable the organization to
identify and implement the appropriate risk management in this area.
Organization performance measurement thus
represents an important source of data for a systematic approach to evaluation of the available information to assure that this information serves as a basis
for making important decisions. Improvement, innovations and learning can be applied on products, processes and technology, as well as on organizational
structures, management systems, infrastructure and
work environment and the basis for this is the capability of the organization to draw conclusions based
on relevant data analysis. One of the key benefits of
continuous improvement, besides improving performance through enhanced capability of the organization
and harmonizing the improvement activity at all
levels, in accordance with its strategic orientation, is
the adaptability, i.e., flexibility to respond fast enough
to opportunities, mostly in terms of increased competitiveness on the market.
Security management within the supply chain for
which the KPI is selected for evaluation in CS I is
related to numerous other business aspects, and relevant requirements covering these management systems are defined in ISO 28001:2007 [15]. According
to this standard, the supply chain represents the interlinked ensemble of resources and processes beginning with the source of raw materials, through product
and/or services supplied to the end user by means of
different kinds of transport. The system of supply
chain managements in the CS I is also subject to continuous improvement.
Cleaner production as a concept evaluated in
CS II can be indirectly linked to the population of
pharmaceutical industry customers through sustainable development taking care of limited environmental capacity to receive a specific quantity of
waste, mostly related to industrial pollution. The relationship between the elements of procurement, production and the consumers in a broader sense is
shown implying the need to develop preventive activities through the product life cycle. This is additionally supported by the fact that cleaner production represents an application of the comprehensive preventive strategy of environmental protection on the production processes, products and services with the
aim to increase overall efficiency and decrease health
and environmental risks (UNEP), meaning preservation of resources, water and energy, reduced application of toxic and hazardous raw materials and reduced quantities and toxicity of all emissions and
wastes at the source of the production process instead of the End-of-Pipe technologies (Figure 3).
Cleaner production does require significant
changes in the organization and its processes. This
Link to the customer
In the CS I the selected KPI is decomposed as a
performance indicator in relevant functions and levels
in the organization to support reaching the higher
level objectives in line with the strategy and corporate
policies (Figure 2).
Strategic goals
Management Review
Business
Strategy
Key Performance
Indicators
Processes
Continuous Improvement
Performance
measures
Figure 2. Link between strategic goals, key indicators and
performance measures.
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Figure 3. Example of EOP – a typical adsorption process for VOCs [16].
can be accomplished through an approach that can
bring benefits to all interested parties, which is also
shown based on the techno-economic analysis performed as part of CS II.
Proactive thinking
Processes and their relationships, as shown in
CS I, are regularly reviewed and appropriate actions
are taken for their improvement. In the course of
planning and management of these processes, the
organization's environment was considered and analyzed, mostly taking into account relevant regulatory
and other requirements. The planning process
according CS I considers the established needs of the
organization to develop or apply new process characteristics as an added value, which at the same time
represents one of the requirements of ISO 9004:2009.
In CS II, the focus is on process optimization
and new technologies. When it comes to the infrastructure which is planned, enabled and managed by
the organization in an efficient and effective manner,
appropriate attention is also given to safety and protection, the elements of this infrastructure linked to
production processes, as well as its impact on the
working environment, overall efficiency, costs and
capacities. At the same time, working environment is
evaluated in accordance with applicable laws and
other regulations in the field of environmental, health
and safety management. Therefore, technological
opportunities were considered in CS II to improve organization performance in different areas, including
product realization and interaction with interested
parties. It is shown that the organization is also
considering the integration of the environmental aspects in the design and product development, as well
as developing the specific processes to minimize the
60
identified risk in the field of environmental management. Furthermore, cleaner production is by its definition a proactive approach to dealing with the environmental impact of the processes in all industries.
Using prevention in formulating environmental protection policy is also required according to ISO
140001 [17] and cleaner production completely supports this concept complying with the organization's
practices for environmental management systems in
achieving the common objectives to continually implement the improvements. Živković et al. have done a
case study for the Oil Refinery Belgrade that confirmed an improvement of environmental performances using the ISO 14001 standard [18].
Tools and techniques
Pareto diagrams were used in CS I as a tool to
focus attention to problems offering the greatest
potential for improvement. This technique is based on
the rule that 20% of causes lead to 80% of problems
(Pareto principle). Fishbone diagram or root cause
analysis was also applied in this study (CS 1) representing a visual description of individual contributions to a certain problem. The fish head represents a
problem to be solved while the bones serve to picture
the root causes classified in 4–6 main categories: materials, methods, people, machines, the environment
and measurement. Additional categories or further
classifications within individual categories are also
possible depending on their importance.
Suitable working environment, as a combination
of human and physical factors, assumes also maximum efficiency and minimization of waste, which is
one of the key principles of Lean manufacturing and
the basis of the CS II at the same time. Furthermore,
cleaner production focuses on the root causes of
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Chem. Ind. Chem. Eng. Q. 22 (1) 55−64 (2016)
problems related to the environment and not the
consequences, which is one of the main goals in the
six sigma analyze phase of the improvement process.
financial benefits. As a result, a natural link is developed between the environmental goals and improvement projects initiated to increase productivity,
achieve better yields, implement savings in materials
and decrease the cost of waste management. Therefore, cleaner production becomes an important element of the comprehensive strategy of performance
improvement and efficiency increase through the
application of production concepts in accordance with
Lean principles.
Based on the studied facts, as well as numerous
literature findings in this area, but also with regards to
practical experience in management of the quality
assurance processes and pharmaceutical production
in general, it is obvious that the continuous improvement programs can be considered as the link
between establishing sustainable process performance measurement systems and implementation of
cleaner production in the pharmaceutical industry
(Figure 4).
Requirements for the Pharmaceutical Quality
System are stipulated in ICH Q10 [14] and related to
quality assurance processes as described in Good
Manufacturing Practice. Performance measures eva-
RESULTS AND DISCUSSION
Results of the two case studies analysis against
pre-defined criteria are summarized in Table 1.
Additionally linked to CI through regulations and
quality standards (a–e are referred in Table 1):
a. ISO 9004 requirements;
b. ICH Q10 and GMP requirements;
c. System of ecological management;
d. ISO 140001 focus on prevention;
e. Similar to PDCA in ISO 9001.
Linking the objectives in the field of environmental protection with improved productivity, material
savings and decreased cost of handling and waste
management, cleaner production is imposed as an
inseparable part of the overall strategy to improve
performances and increase total efficiency. Environmental protection aspects may be regarded as an
important motivation factor to come to innovative solutions leading to both safety increase and significant
Table 1. Comparative analysis against the suggested Continuous Improvement Criteria
Continuous Improvement (CI)
Criteria
Data based approach/
Performance measurement
Customer orientation
Proactive thinking
CS I related to QA processes
CS II related to CP
a
data gathered to support the selected KPI
b
Monitoring and optimization of resources
PMs established in relevant functions
Measuring the environmental impact
KPI and PMs link to strategy to achieve flexibility in
terms of market requirements through KPI
selection for supply chain management
Indirectly through sustainable development
Regular review of processes and measures for
their improvement
c
Techno-economic analysis
Focus on optimization and new technologies
Evaluation against applicable laws and regulations
Integration of environmental aspects in design and
d
Product development
Tools and techniques
Pareto
Lean manufacturing
Fishbone
Kaizen philosophy
e
Figure 4. Continuous improvements as the link between quality assurance and cleaner production principles.
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luation in terms of quality management processes is
one of the key activities required for achieving the
continuous improvement as one of the most important
requirements of the Pharmaceutical Quality System
given in ICH Q10. At the same time, system of ecological management, as one of the cleaner production
elements, is also an instrument to recognize and
solve environmental problems based on the continuous improvement concepts. Implementation of the
Q10 model should facilitate continual improvement, in
order to identify and implement appropriate product
quality improvements, process improvements, variability reduction, innovations, and pharmaceutical
quality system enhancements, thereby increasing the
ability to fulfill a pharmaceutical manufacturer’s own
quality needs consistently. Quality risk management
represents a logical path adopted by an organization
that has successfully implemented the basics
required by ISO 9001, as it provides broader focus on
the quality management system through a wider
model based on processes. It relates to needs and
expectations of all interested parties and gives instructions for systematic and continual improvement of
overall performance of an organization. Additionally,
ISO 9004 also comprises broader requirements for
management of the resources and their efficient use,
which again brings performance measurement within
the quality system in relation to cleaner production
principles through the concept of continuous improvement (Figure 5).
It is clear that in both case studies the focus was
on the contemporary requirements of the ICH Q10
Figure 5. The link between performance measurement and cleaner production through the concept of CI.
can be useful for identifying and prioritizing areas for
continual improvement.
The results of the performed study may also be
summarized are follows:
• single methodology for improvement of quality management and industrial processes through
continual monitoring and control of relevant performance measures;
• correlation between different regulatory
requirements for pharmaceutical industry to enable
compliance through implementation of a single concept of continuous improvement;
• dissemination of continuous improvement
philosophy and knowledge in the area of integrated
environmental and quality management, as well as
safety, all in accordance with the main principles and
key aspects of social responsibility.
Performance measurement plays the key role in
the area of quality management, providing insight in
parts of the process where change and improvement
is required, necessary feedback as the basis for
further improvements, as well as relevant information
for analysis and evaluation of the achieved performance. When it comes to models based on Total Quality Management (TQM), process management and
customer orientation are regarded as the key factors
for implementation. On the other hand, new ISO 9004
62
related to establishing the process performance
indicators in critical areas within the Pharmaceutical
Quality System and implementation of the continuous
improvement concept in general, leading to evaluation of the overall organization performance through
ISO 9004 and enhanced model based on processes,
as well as taking into consideration the needs and
expectations of all interested parties, which defines
the CI as a common term both for quality management and cleaner production principles.
CONCLUSION
Measures and KPIs represent an important
element of the CI concept, which on the other hand
plays the key role in the modern Quality Management
System (QMS) of the pharmaceutical company. The
appropriate application of the process performance
measurement system actually means measuring the
current values of the specific parameters against the
objectives and providing the feedback to relevant
participants in the process. This approach should lead
to the continuous improvement of the QMS, as well as
performance measures in various processes, including sustainable environmental protection.
Applying the appropriate Lean and Six Sigma
tools and techniques, further significant problems
Z. BOLTIĆ et al.: CONTINUOUS IMPROVEMENT CONCEPTS…
categories can be identified to be gradually solved
leading to completely eliminating, e.g., an entire class
of deviations or environmental impacts when it comes
to harmful emissions for example. Additionally, links
and precise correlations can be determined between
such performance measures managed locally and
higher level objectives and the analysis can be expanded to other processes supporting these objectives. In this regard, the approach and concept of
application of appropriate tools and analysis methods
shown and developed in this work may be readily
used in all similar improvement projects through different areas of the quality system and generic pharmaceutical production.
Chem. Ind. Chem. Eng. Q. 22 (1) 55−64 (2016)
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from the World's Greatest Manufacturer, McGraw-Hill,
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Acknowledgements
The authors are grateful to the Ministry of Science and Technological Development of the Republic
of Serbia for the support (project TR 34009).
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Z. BOLTIĆ et al.: CONTINUOUS IMPROVEMENT CONCEPTS…
ZORANA BOLTIĆ1
MIĆA JOVANOVIĆ2
SLOBODAN PETROVIĆ2
VOJISLAV BOŽANIĆ3
MARINA MIHAJLOVIĆ4
1
Hemofarm A.D, Beogradski put
b.b, 26300 Vršac, Srbija
2
Tehnoško-metalurški fakultet,
Univerzitet u Beogradu,
Karnegijeva 4, 11000 Beograd,
Srbija
3
Fakultet organizacionih nauka,
Jove Ilića 154, 11000 Beograd,
Srbija
4
Inovacioni centar Tehnološko-metalurškog fakulteta, Univerzitet
u Beogradu, Karnegijeva 4, 11000
Beograd, Srbija
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 55−64 (2016)
KONCEPTI KONTINUIRANOG UNAPREĐENJA KAO
VEZA IZMEĐU OBEZBEĐENJA KVALITETA I
UVOĐENJA ČISTIJE PROIZVODNJE – STUDIJA
SLUČAJA U GENERIČKOJ FARMACEUTSKOJ
INDUSTRIJI
Predmet i cilj istraživanja koje je predstavljeno u ovom radu jeste uspostavljanje veze
između obezbeđenja kvaliteta i uvođenja čistije proizvodnje u generičkoj farmaceutskoj
industriji kroz sveobuhvatni koncept kontinuiranog unapređenja. Ovo se u najvećoj meri
odnosi na primenu “lean” i “šest sigma” alata i tehnika za unapređenje procesa i njihovu
povezanost sa drugim poznatim konceptima koji se koriste u industrijskom okruženju, a
posebno proizvodnji generičkih farmaceutskih proizvoda, gde su za potrebe komparativne
analize odabrane dve reprezentativne studije slučaja, uzimajući u obzir i relevantne regulatorne zahteve u oblasti menadžmenta kvalitetom, kao i odgovarajuće standarde kvaliteta.
Iako je metodologija razmatrana u ovoj konceptualnoj i praktičnoj studiji usko povezana sa
hemijskim inženjerstvom, akcenat je u najvećoj meri stavljen na procesnu industriju,
odnosno proizvodne sisteme, pre nego na pojedinačne tehnološke procese. U tom smislu,
predmet ovog istraživanja jeste inženjerski pristup evaluaciji proizvodnih sistema u pogledu primene koncepta kontinuiranog unapređenja, uzimajući u obzir kako aspekte kvaliteta, tako i efikasnost tih sistema.
Ključne reči: obezbeđenje kvaliteta, čistija proizvodnja, farmaceutska industrija,
kontinuirano unapređenje, “lean”, “šest sigma”.
64
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
ALEKSANDAR GOLUBOVIĆ1
IVANA VELJKOVIĆ2
MAJA ŠĆEPANOVIĆ1
MIRJANA GRUJIĆ-BROJČIN1
NATAŠA TOMIĆ1
DUŠAN MIJIN3
BILJANA BABIĆ4
1
Institute of Physics, University of
Belgrade, Belgrade, Serbia
2
Institute for Multidisciplinary
Research, University of Belgrade,
Belgrade, Serbia
3
Faculty of Technology and
Metallurgy, University of Belgrade,
Belgrade, Serbia
4
Institute of Nuclear Sciences
“Vinča”, University of Belgrade,
Belgrade, Serbia
SCIENTIFIC PAPER
UDC 54:66:544.526.5
DOI 10.2298/CICEQ150110020G
CI&CEQ
INFLUENCE OF SOME SOL-GEL SYNTHESIS
PARAMETERS OF MESOPOROUS TIO2 ON
PHOTOCATALYTIC DEGRADATION OF
POLLUTANTS
Article Highlights
• Anatase nanopowders were synthesized by sol–gel method using tetrabutyl titanate as
precursor
• XRPD data showed slight growth of crystallites in synthesized samples (from 24 to 35
nm)
• Raman scattering data confirmed the anatase as dominant TiO2 phase
• The BET showed that specific surface area was greater at the lower temperature of
calcination
• Photodegradations were comparable with Degussa P25 for C.I. Reactive Orange 16
and phenol
Abstract
Titanium dioxide (TiO2) nanopowders were produced by sol-gel technique from
tetrabutyl titanate as a precursor by varying some parameters of the sol-gel
synthesis, such as temperature (500 and 550 °C) and the duration of
calcination (1.5, 2 and 2.5 h). X-ray powder diffraction (XRPD) results have
shown that all synthesized nanopowders were dominantly in the anatase
phase, with the presence of a small amount of rutile in samples calcined at 550
°C. According to the results obtained by the Williamson-Hall method, the anatase crystallite size was increased with the duration of the calcination (from 24
to 29 nm in samples calcined at lower temperature, and from 30 to 35 nm in
samples calcined at higher temperature). The analysis of the shift and linewidth of the most intensive anatase Eg Raman mode confirmed the XRPD
results. The analysis of pore structure from nitrogen sorption experimental data
described all samples as mesoporous, with mean pore diameters in the range
of 5-8 nm. Nanopowder properties have been related to the photocatalytic
activity, tested in degradation of the textile dye (C.I. Reactive Orange 16), carbofuran and phenol.
Keywords: nanostructures, anatase, X-ray diffraction, Raman scattering.
Photocatalysis is a well-known process mostly
employed to degrade or transform organic and inorganic compounds, and the kinetics depend on catalyst
surface area, availability of active sites, pore sizes,
number and nature of trapped sites, as well as on
adsorption/desorption characteristics. TiO2 is an
important photocatalyst mainly because of its strong
oxidizing power, non-toxicity and long-term photostaCorrespondence: A. Golubović, Institute of Physics, University of
Belgrade, Pregrevica 118, 11080 Belgrade, Serbia.
E-mail: golubovic@ipb.ac.rs
Paper received: 10 January, 2015
Paper revised: 7 April, 2015
Paper accepted: 30 June, 2015
bility. Nanocrystalline TiO2 is essentially a cheap and
biocompatible wide band-gap semiconductor with an
involving photogenerated holes and photocatalytic
capabilities for organic pollutants [1-3]. Namely, many
organic compounds can be decomposed in aqueous
solution in the presence of TiO2 powders or coatings
illuminated with near ultraviolet (UV) or visible light.
The structural, morphological, optical and photocatalytic properties of TiO2 nanocrystals are strongly
dependent on the synthesis process [4,5]. Among the
various synthesis methods, the sol-gel method has
recently attracted a lot of attention, since it is simple
and cost-effective way of producing nanostructured
anatase TiO2 with tailored properties.
65
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
Many factors influence photocatalytic reactivity
of TiO2 which is documented by numerous publications in the last decades [6-11]. Generally, anatase
is considered a desirable phase for photocatalysis
application as it shows higher activity then rutile [8,12–13]. However, a mixture of anatase and rutile with a
sintered interface, like commercial TiO2 (Degusa
P25), is claimed to be more active then pure anatase
[14-17]. In order to obtain the highest performance,
the main challenge is the synthesis of preferably
nanocrystalline anatase TiO2 that enables a balance
between major influencing parameters: crystal structure, surface hydroxylation and crystallinity.
The sol-gel process represents a flexible chemical route to synthesize various high-performance
nanostructured ceramic materials with controlled
internal morphology and chemistry. Materials with
designed internal nanostructure (entirely interconnected open nanoporosity, hierarchical, fractal or
nanocrystalline solid network) and various possible
chemical compositions (from organic to inorganic) can
be obtained in large range of shapes (finely divided
nanopowders, nanoparticles, thin and thick films,
fibers, granular beds and monolithic materials). The
sol-gel process is a solution-based technique, where
the material structure is created through chemical
reactions in the liquid state, giving the high flexibility
of the process for easy application.
The photocatalytic efficiency of TiO2 powder
heavily depends on its microstructure and physical
properties, which are in turn determined by the preparation conditions. Among these, the presence of
mesopores gives rise to a large surface area, which
offers abundant interaction sites with external molecules [18]. The photocatalytic process involves the
separation of the electron-hole charge pair, their
transport and trapping to/at the surface, and, finally,
their reaction with the desired molecules. These processes always compete with the charge pair recombination. The nanostructure significantly affects these
elemental processes based on several reasons. Apart
from a high surface-to-volume ratio, which must be
beneficial for all chemical processes, the first factor is
the quantum confinement and improved reduction/
/oxidation power. The second factor is the practical
absence of band bending and the consequent easier
access of both charged particles to the surface [19].
TiO2 nanopowders are very efficient compounds
for the photodegradation of many pollutants [20,21].
In our investigations, we made a focus on degradation of organic pollutants having different chemical
structure. Namely, a textile dye (C.I. Reactive Orange
16) [22,23], an insecticide (carbofuran [2,24-26]) and
66
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
a phenol [27,28]. The commercial TiO2 (Degussa
P25) was applied in a number of photodegradation
processes of pollutants, and we wanted to synthesize
TiO2 nanopowders using various parameters of synthesis and to compare the photocatalytic properties of
such prepared catalysts. The mechanism of the
photodegradation process is not completely defined,
as many parameters are involved. According to this,
our manuscript is a contribution in understanding of
such a complex process. To the best of our knowledge, this study is original and it was not found in the
literature.
Several methods of characterization, such as
XRPD, Brunauer-Emmett-Teller (BET) measurements, and Raman scattering were employed in this
study to correlate structural and morphological properties of synthesized TiO2 nanopowders and their
photocatalytic activity under UV light irradiation.
EXPERIMENTAL
Synthesis
The TiO2 nanocrystals were prepared by a solgel method. All of the reagents were of analytical
grade and were obtained from commercial sources
and used without further purification. Tetrabutyl
titanate (99%, Acros Organics, Belgium) was used as
the precursor of titania, hydrochloride acid (36.2%,
Zorka, Serbia) as the catalyst, ethanol (96%, denatured, Carlo Erba, Italy) as the solvent, and distilled
water for hydrolysis. pH of the solution was 7. The
reagent molar ratio was Ti(OBu)4:HCl:EtOH:H2O =
= 1:0.3:15:4 according to [29], which enabled obtaining a stable gel. The process of gelation was carried
out at 4 °C, where appropriate amounts of Ti(OBu)4,
HCl and EtOH were stirred one hour by magnetic stirrer. After that, an appropriate amount of distilled water
was added in the mixture due to hydrolysis and formation of the gel. This gel was “aged” (the process of
polycondensation) for two hours, the wet gels were
dried at 80 °C, and then calcinated at 500 and 550 °C
for 1.5, 2 and 2.5 h, to obtain TiO2 nanocrystals. The
heating and the cooling rates were 135 °C/h. According to the calcination conditions (various temperature
of calcinations and duration of the calcinations), synthesized samples were labeled as: T500/1.5, T500/2,
T500/2.5, T550/1.5, T550/2 and T550/2.5.
Characterization methods
Generally, instrumental broadening is negligible
in the case of low crystallinity samples. Broadening of
the peaks because of low crystallinity is dominant.
These are fundamentals of X-ray powder analysis.
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
Structural analysis of prepared samples was done by
XRPD on an Ital Structures APD2000 diffractometer,
using CuKα radiation (λ = 1.5406 Å), angular range:
20°< 2θ < 90°. Data were collected at every 0.01° in
the 20-90° 2θ using a counting time of 80 s/step. MDI
Jade 5.0 software was used for calculation of the
structural and microstructural parameters. The Williamson-Hall method [30] was applied for the determination of average microstrain and the mean crystallite sizes, <D>, of the prepared samples. The
obtained values were compared to the mean crystallite sizes calculated by the Scherrer formula [31].
The Scheerer formula is an estimate of crystallite size
calculated from FWHM of all diffractions collected
during measurement.
Raman scattering measurements was performed in the backscattering geometry at room temperature in air, using Jobin-Yvon T64000 triple spectrometer, equipped with a confocal microscope and a
nitrogen-cooled coupled device detector. The spectra,
excited by 514.5 nm line of Ar+/Kr+ laser with output
power less than 5 mW to avoid local heating due to
laser irradiation, was recorded with high spectral
resolution of about 0.7 cm-1.
The porous structure of anatase samples is
evaluated from adsorption/desorption isotherms of N2
at –196 °C, using the gravimetric McBain method. The
main parameters of the porosity, such as specific
surface area and pore volume, have been estimated
by BET method from αs-plot [32]. The pore size distribution was estimated from hysteresis sorption data
by the Barret-Joyner-Halenda (BJH) method [33].
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
Orange 16), 6.86×10-4 M (carbofuran), 4×10-4M (phenol), respectively. Upon preparation of the solution,
agitation was applied in dark by continuous stirring
(magnetic stirrer) at 400 rpm to keep the suspension
homogenous for 90 min. Then, the lamp was
switched on and the suspension sampled after appropriate times of irradiation. The concentration of pollutants was determined after centrifugation of a sample
on Mini Spin Eppendorf at 12000 rpm by a UV-Vis
spectrophotometer (Shimadzu 1700) at appropriate
wavelength.
RESULTS AND DISCUSSION
XRPD measurements
The XRPD measurement confirmed that sol-gel
synthesis resulted with preparation of anatase modification of TiO2, which is clearly indicated with the
main anatase reflection at 2θ ≈ 25° (JCPDS card no.
21-1272). The samples calcinated at 500 °C were
found to be phase-pure anatase (Figure 1), with crystallite sizes growing with increasing calcination time
(Table 1), while the samples calcinated at 550 °C
have small amount of rutile impurities, which are
confirmed by small peaks at 2θ ≈ 27° in Figure 1
(JCPDS, card no. 21-1276). The presence of rutile in
calcined anatase samples can be caused both by pH
value and the temperature of the calcination [34]. In
our case, the small amount of rutile in samples
calcined at 550 °C is caused by the temperature of
the calcination as pH value is the same (pH 7).
Measurements of photocatalytic activity
UV irradiation of a suspension (an appropriate
amounts of pollutant and TiO2 powder as the catalyst)
was performed in an open flask (100 ml volume) with
an Osram Ultra-Vitalux® 300 W (UV-A) lamp placed
50 cm from the surface of the solution. The light
intensity was 40 mW cm–2, and it was measured on
the Amprobe Solar-100, Solar Power meter, BehaAmprobe, GmbH. The textile dye, C.I. Reactive
Orange 16, was obtained from the company Bezema,
Switzerland, as a gift (commercial name Bezaktiv
Orange V-3R) and used without futher purification.
Carbofuran (99.2 %) was obtained from FMC, USA.
Phenol, p.a. grade, was purchased from Fluka. The
photodegradation of organic pollutants was studied by
preparing a solution containing known concentration
of organic and appropriate amount of TiO2. In a
typical experiment, 25 ml of a solution was used, the
quantity of TiO2 was 50 mg, whereas the pollutants
solution molarities were 8.1×10-5 M (C.I. Reactive
Figure 1. The XRPD patterns of TiO2 samples, where rutile
diffraction is denoted by “R”.
67
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
Table 1. The unit cell parameters and unit cell volume, together with average crystallite size, <D>, of anatase and microstrain obtained
by Scherrer and Williamson-Hall methods
Sample
Calcination conditions
Unit cell parameters
Scherrer method
Williamson-Hall method
Temperature, °C
Time, h
a and c in Å, V in Å3
<D> / nm
<D> / nm
Microstrain, %
T500/1.5
500
1.5
a = 3.784(3)
c = 9.53(0)
V = 136.4(8)
15
24
0.301
T500/2
500
2.0
a = 3.789(9)
c = 9.52(1)
V = 136.7(5)
18
28
0.231
T500/2.5
500
2.5
a = 3.789(2)
c = 9.50(3)
V = 136.4(5)
19
29
0.247
T550/1.5
550
1.5
a = 3.789(1)
c = 9.51(5)
V = 136.6(1)
24
30
0.108
T550/2
550
2.0
a = 3.788(7)
c = 9.51(4)
V = 136.5(7)
28
33
0.077
T550/2.5
550
2.5
a = 3.789(1)
c = 9.53(4)
V = 136.8(9)
30
35
0.085
According to the Scherrer formula, the crystallite
size for samples calcinated at lower temperature has
been estimated in the range from 15 to 19 nm, while
the samples calcinated at higher temperature have
higher crystallinity, with crystallite size in the range
from 24 to 30 nm, while for these estimated by Williamson-Hall method were in the range from 24 to 29
nm for lower temperature and from 30 to 35 nm for
higher temperature. The analysis of XRPD data by
the Williamson-Hall method has shown higher microstrain value in the samples calcinated at 500 °C
compared to the samples calcinated at 550 °C. In all
futher discussion, values of crystalline size evaluated
by the Williamson-Hall method were used.
Raman scattering measurements
The Raman spectra of all synthesized nanopowders are dominated by anatase Raman modes
[35,36]: Eg(1) (∼143 cm−1), Eg(2) (∼199 cm−1), B1g (∼399
cm−1), A1g+B1g (∼518 cm−1), and Eg(3) (∼639 cm−1), as
can be seen from the spectrum of two chosen
samples shown in Figure 2. The most intensive
Raman Eg(1) mode is positioned between 142.8 and
143.5 cm-1, with linewidths from 9 to 11.5 cm-1. The
dependence of Raman shift on linewidth of this mode
is shown in Figure 3. The Eg(1) Raman modes in the
samples T500/1.5, T500/2 and T500/2.5, calcined at lower
temperature (500 °C), are more shifted and more
broadened then the mode in samples calcined at
higher temperature (550 °C). Having in mind the relatively large crystallite size in all samples registered
68
Figure 2. The Raman spectra of samples T500/1.5 and T550/2.5. The
experimental spectra (circles) are fitted by the sum of
Lorentzians (thin lines). Anatas modes are denoted by “A”
and rutile by “R”.
by XRPD (24-35 nm), slight shift and broadening
relative to bulk anatase [33] may rather be ascribed to
defects and disorder in anatase crystal structure, than
to the phonon confinement effects. The smaller linewidth and the Raman shift of Degussa P25 compared
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
to the series of obtained samples can be explained as
the least deffective and disordered anatase structure.
Figure 3. The experimental dependence of Raman shift on
linewidth for the most intensive Eg(1) mode of synthesized
anatase samples and Degussa P25.
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
T550/2 the porosity was very small (the pore concentration is within experimental error). The mean pore
diameters obtained by BET and BJH method are in
good agreement. The pore size distribution for synthesized anatase samples and Degussa P25,
obtained by BJH method, are shown in Figure 4. It
could be seen that in the rows T500/1.5, T500/2, T500/2.5
and T550/1.5, T550/2, T550/2.5 value of specific surface area
had the highest value for the first member, lowest for
the second and close to the first for the third member.
The explanation for this tendency lies in the fact that
the pores tranformed during the time of calcination.
The tendency of microstrain in Table 1 was in accordance with the tendency of a pore evolution. Also, the
pores in the samples calcined at 500 °C (mean pore
diameter around 5-6 nm) are smaller than those in the
samples calcined at higher temperature (7-8 nm), as
can be seen in Table 2. From Figure 4 can be also
Some additional Raman features, detected in
the sample T550/2.5 shown in Figure 2, can be ascribed
to the rutile modes [37] Eg (∼445 cm-1) and A1g (∼609
cm-1). The Raman modes related to the brookite
phase [38] in the synthesized samples were not detected.
Porosity
To investigate the effects of synthesis conditions
parameters on the adsorption abilities and pore structure of TiO2 samples, the nitrogen sorption isotherms
measurements have been carried out. The specific
surface area, pore volume and mean pore diameter
calculated from both BET and BJH are listed in Table
2. The samples calcined at 500 °C (samples T500/1.5,
T500/2 and T500/2.5) are obviously more porous than
those calcined at 550 °C (samples T550/1.5 and T550/2.5).
Note that the parameters of porosity, determined from
the αs-plots [16,39], suggest that the samples are fully
mesoporous (Smeso = SBET), whereas in the sample
Figure 4. The pore size distribution for synthesized anatase
sample and Degussa P25 obtained by BJH method.
Table 2. The porous properties of synthesized anatase samples, as well as Degussa P25: specific surface areas (SBET, SBJH), pore
volumes (Vp, Vt), and mean pore diameters ( DBET , DBJH ) obtained by BET and BJH methods, respectively
Sample
T500/1.5
SBET = Smeso, in m2/g
Vp / cm3 g–1
DBET / nm
SBJH / m2 g–1
Vt / cm3 g–1
DBJH / nm
52
0.1063
5.3
52.0
0.1025
5.1
T500/2
33
0.0757
5.9
34.2
0.0777
5.9
T500/2.5
45
0.0922
5.3
45.9
0.0903
5.1
T550/1.5
18
0.0580
8.3
18.5
0.0599
8.3
T550/2
2
–
–
–
–
–
T550/2.5
17
0.0454
6.9
18.3
0.0504
7.1
Degussa P25
13
0.0244
7.5
11.6
0.0214
7.4
69
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
seen that the pore distribution of Degussa 25 was
almost uniform (except for the largest value of about 9
nm) and that could be the crucial fact why Degussa
25 was the powerful tool for the photocatalytic degradation.
Photocatalytic activity
The photocatalytic activity of synthesized catalyst was studied using three representatives of organic pollutants: C.I. Reactive Orange 16 (textile dye),
carbofuran (pesticide) and phenol. The samples were
(after mixting with pollutants, sorption and UV irradiation) withdrawn and analyzed on a UV-Vis spectrophotometer at 492.5 nm for C.I. Reactive Orange 16,
277 nm for carbofuran and 270 nm for phenol. The
time after the agitation 90 min in dark is denoted as 0,
and these concentrations are denoted as c0. The
reactions were performed using Degussa P25 TiO2
for comparison. The results are shown in Figure 5.
In Figure 5a, the effectiveness of synthesized
TiO2 catalysts in photodegradation reaction of (C.I.
Reactive Orange 16) is presented. In comparison to
Degussa P25, the catalyst T500/1.5 showed almost the
same photodegradation effectiveness (99 and 98%
after 90 min of UV irradiation, respectively), while the
others samples, except T550/1.5, showed similarly good
photodegradation effectiveness. The photodegradation efficiency can be determined as:
Efficiency = 100
c0 − c
c0
where c0 is the initial concentration of pollutant sol-
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
ution and c is the concentration after irradiation with
UV light. The efficiencies of the studied TiO2 catalysts
as well as the observed pseudo first reaction rate
constants were presented in Table 3. The main difference between Degussa P25 and synthesized catalysts is the reaction rate as a result of pore distribution uniformity.
In case of carbofuran, Degussa P25 showed
higher photodegradation efficiency than all synthesized samples (98% of carbofuran was photodegraded after 90 min). After 150 min of UV irradiation,
the highest photodegradation efficiency was obtained
by samples T500/1.5 (75%), whereas the lowest efficiency were observed for the samples T550/1.5 and
T550/2.5 (both 49%). The obtained results are in accordance with the pore distribution influence on the reaction rate. Photocatalitic degradation of carbofuran
using synthesized of TiO2 series and Degussa P25 as
catalysts are presented in Figure 5b. Here, one can
observe that the photocatalytic reaction rate is highest
when Degussa P25 is used, while the differences
between synthesized catalysts are much less pronounced. As given above, the observed reaction rate
might be the result of the mean pore diameter range,
and the combination of specific surface area and
mean pore diameter.
Phenol [40] was also subjected to photodegradation using synthesized catalysts and the results
are shown in Figure 5c. It appears that TiO2 (both
synthesized and Degussa P25) is able to remove
phenol too, but it requires more time, since the concentrations continuously decrease. After 150 min of
Figure 5. The kinetics of degradation of: a) C.I. Reactive Orange 16, b) carbofuran and c) phenol, under UV irradiation monitored in the
presence of synthesized TiO2 samples and Degussa P25.
70
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
Table 3. The efficiency, %, of the studied TiO2 catalysts as well as the observed pseudo-first reaction rate constants
Time, min
Catalyst
P-25
T500/1.5
T500/2
T500/2.5
T550/1.5
T550/2
T550/2.5
RO16
0
0
0
0
0
0
0
0
30
72
40
34
25
33
42
32
60
98
61
62
63
60
71
63
90
99
96
98
95
85
97
95
0.0546
0.0287
0.0335
0.0271
0.0189
0.0322
0.0271
k / min
-1
Carbofuran
0
0
0
0
0
0
0
0
30
38
1
1
1
1
1
1
60
82
4
4
3
2
4
2
90
98
17
10
10
9
15
5
120
48
29
32
21
36
19
150
75
63
68
49
68
49
0.0372
0.0062
0.0041
0.0027
0.0028
0.0049
0.0027
0
0
0
0
0
0
0
0
30
14
1
6
5
4
2
0
60
24
10
10
19
14
13
1
k / min-1
Phenol
90
32
23
23
23
14
19
16
120
41
38
38
33
23
34
32
54
52
52
45
46
44
34
0.0048
0.004
0.004
0.0035
0.003
0.0033
0.0025
150
k / min
-1
UV irradiation, Degussa P25 degraded 54%, almost
the same value as for T500/1.5 and T500/2 (52%). Other
samples (T500/2.5, T550/1.5 and T550/2) degraded about
45% and T550/2.5 showed the worst result (34%).
Obtained photodegradation result for Degussa P25 is
in accordance with results from de la Cruz Romero et
al. [3] where phenol was not 100% photodegraded
even with the UV irradiation of 10 h (only 60% under
similar experimental conditions).
One would expect that the smaller molecule,
phenol, can easily access the internal surface of
Degussa sample giving higher degradation rate in
comparison to other two organic pollutants. Namely, if
only size of the molecule is important, than the
reaction rate order would be: phenol > carbofuran >
> RO16. On the contrary, the rate order is inverse,
RO16 being most reactive. The main reason for such
reaction rate is due to the different mechanisms of
degradation and different part of molecules involved.
If only one molecule is concerned, then the influence
of the catalyst is more complex. Not only the mean
pore diameter is important, but also the combination
of specific surface area and mean pore diameter,
giving Degussa an advantage when voluminous
molecules are concerned.
CONCLUSIONS
The structural and morphological properties of
TiO2 powders were intentionally varied by the temperature and duration of the calcination. The analysis
of XRPD data showed that rising of temperature and
extending the duration of the calcination caused slight
growth of crystallites in synthesized samples (from 24
to 35 nm), which was confirmed by Raman scattering.
It was also noticed that the most intensive Raman Eg
mode in the samples calcined at higher temperature
(550 °C) is less broadened and blueshifted than in the
samples calcined at 500 °C, pointing to less deffective
and disordered anatase structure. The BET analysis
showed that the greatest specific surface area was in
the sample calcined for 1.5 h at 550 °C (T550/1.5). The
samples calcined at 500 °C displayed higher photocatalytic activity in the degradation in comparison with
the samples calcined at 550 °C. The results of photodegradation of C.I. Reactive Orange 16 for the
sample calcined 2 h at 500 °C (sample T500/2) was
comparable with Degussa P25. The samples calcined
for 1.5 and 2 h at the same temperature (samples
T500/1.5 and T500/2) showed comparable efficiency with
Degussa P25 in photodegradation of phenol, while in
71
A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
photodegradation of carbofuran Degussa P25 showed
superior photocatalytic properties.
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
[18]
W. Li, X. Guo, Y. Zhu, Y. Hui, K. Kanamori, K. Nakanishi,
J. Sol-Gel Sci. Technol. 67 (2013) 639-645
[19]
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J. A. Rodriguez, Chem. Rev. 104 (2004) 4063-4104
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Hashib, Water Air Soil Pollut. 215 (2011) 3-29
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C.-Y. Chen, Water Air Soil Pollut. 202 (2009) 335-342
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This work was financially supported by the
Serbian Ministry of Education, Science and Technological Development, Projects No. III45018 and
ON171032, as well as SASA project F-134.
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A. GOLUBOVIĆ et al.: INFLUENCE OF SOME SOL-GEL SYNTHESIS…
ALEKSANDAR GOLUBOVIĆ1
IVANA VELJKOVIĆ2
MAJA ŠĆEPANOVIĆ1
MIRJANA GRUJIĆ-BROJČIN1
NATAŠA TOMIĆ1
DUŠAN MIJIN3
BILJANA BABIĆ4
1
Institut za fiziku, Univerzitet u
Beogradu, Pregrevica 118, 11080
Beograd, Srbija
2
Institut za multidisciplinarna
istraživanja, Univerzite u
Beogradu, Kneza Višeslava 1,
11000 Beograd, Srbija
3
Tehnološko-metalurški fakultet,
Univerzitet u Beogradu,
Karnegijeva 4, 11000 Beograd,
Srbija
4
Institut za nuklearne nauke
„Vinča”, Univerzitet u Beogradu,
11001 Beograd, Srbija
Chem. Ind. Chem. Eng. Q. 22 (1) 65−73 (2016)
UTICAJ NEKIH PARAMETARA SOL-GEL SINTEZE
MEZOPOROZNOG TIO2 NA FOTOKATALITIČKU
DEGRADACIJU ZAGAĐIVAČA
Nanoprahovi titan-dioksida (TiO2) su proizvedeni sol-gel tehnikom iz tetrabutil-titanata kao
prekursora, varirajući neke parametre sol-gel sinteze kao što su temperatura kalcinacije
(500 i 550 °C) i dužina kalcinacije (1,5; 2 i 2,5 h). XRPD rezultati su pokazali da su svi
sintetizovani nanoprahovi dominantno u anataz fazi sa prisustvom malih količina rutilne
faze u uzorcima kalcinisanim na 550 °C. Saglasno rezultatima dobijenim Williamson-Hall
metodom, kristaliti anataza rastu sa vremenom kalcinacije (od 24 do 29 nm u uzorcima
kalcinisanim na nižoj temperaturi, i od 30 do 35 nm u uzorcima kalcinisanim na višoj temperaturi). Analize pomeraja i poluširine najintenzivnijeg Eg Ramanskog moda anataza su
potvrdile XRPD rezultate. Parametri veličine pora dobijeni pomoću eksperimentalnih podataka sorpcije azota su ukazali na to da su svi uzorci mezoporozni, sa srednjom veličinom
pora u opsegu 5-8 nm. Fotokatalitička aktivnost dobijenih nanoprahova je testirana na degradaciji tekstilne boje (C.I. Reactive Orange 16), karbofurana i fenola.
Ključne reči: nanostrukture, anataz, difrakcija X-zraka na prahu, rasipanje.
NAUČNI RAD
73
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
MEHDI ASADOLLAHZADEH1,2
SHAHROKH SHAHHOSSEINI1
MEISAM TORAB-MOSTAEDI2
AHAD GHAEMI1
1
Department of Chemical
Engineering, Iran University of
Science and Technology (IUST),
Tehran, Iran
2
Nuclear Fuel Cycle Research
School, Nuclear Science and
Technology Research Institute,
Tehran, Iran
SCIENTIFIC PAPER
UDC 54:66.063
DOI 10.2298/CICEQ150426022A
CI&CEQ
THE EFFECTS OF OPERATING PARAMETERS
ON STAGE EFFICIENCY IN AN
OLDSHUE-RUSHTON COLUMN
Article Highlights
• Stage efficiency of the investigated column is high in comparison with other extractors
• Stage efficiency is strongly dependent on the agitation rate and interfacial tension
• Stage efficiency is better when the mass transfer direction is from continuous to
dispersed phase
• Empirical correlation is derived for prediction of stage efficiency
Abstract
In this research, stage efficiency was measured in a 113 mm Oldshue-Rushton
column for two systems including toluene-acetone-water and n-butyl acetate-acetone-water. The experiments were performed in two directions of mass
transfer. The effects of different parameters such as rotor speed, dispersed
and continuous phase velocities and direction of mass transfer on the stage
efficiency were investigated. The experimental data show that the stage efficiency is strongly dependent on the agitation rate and interfacial tension, but
only slightly dependent on phase velocities. It was observed that the stage
efficiency is better when the mass transfer direction of acetone is from the continuous to the dispersed phase in comparison to opposite direction due to the
presence of oscillations created by surface tension gradient. The investigated
column is one of the extraction columns with high stage efficiency. An empirical correlation is proposed to describe the stage efficiency in terms of Reynolds and Froude numbers. The predictions of the equation had good agreement with the experimental data.
Keywords: Oldshue-Rushton column, stage efficiency, axial mixing,
throughput.
Solvent extraction is one of the key unit operations in the processes including the petrochemical,
pharmaceutical, hydrometallurgical, and environmental industries. Among various types of solvent extraction units, the extraction column is emerging as
one of the best choices because of a high throughput
and stage efficiency [1].
The droplet size and the degree of turbulence
are dependent on the mechanical agitation in the
extraction column. Mixing can intensify the stage efficiency due to the large interfacial area with small dispersed drops [2,3]. As drop size decreases with agitCorrespondence: S. Shahhosseini, Department of Chemical
Engineering, Iran University of Science and Technology (IUST),
P.O. Box 16765-163, Tehran, Iran.
E-mail: shahrokh@iust.ac.ir
Paper received: 26 April, 2015
Paper revised: 24 June, 2015
Paper accepted: 2 July, 2015
ation speed, the relative velocity between the dispersed phase and continuous phase decreases likewise, which lowers the throughput. In addition, the
agitation can increase the axial mixing and reduce the
extraction efficiency by decreasing solute concentration gradients and as a consequence the mass
transfer rate. Neglecting the effect of axial mixing
when designing an extraction column can lead to
overestimation of mass transfer efficiency of about
30% or more [4]. Thus, the mechanical agitation can
be used to control the droplet size, dispersed phase
holdup, stage efficiency and, consequently, the performance of the extraction columns [5].
In several studies, a number of authors have
reported different methods to decrease axial mixing
by coalescing small drops in the section between
stages. Internal column geometry reduces axial mixing, increases droplet coalescence and breakage
75
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
rates resulting in increased mass transfer rates, and
affects the mean residence time of the dispersed
phase, which allows the handling of large loads with
small differences of interfacial tension and density,
improving the hydrodynamic performance of the column and, subsequently, the extraction efficiency [6,7].
The experimental set up with the mixing part
and the packing part alternately to promote drop
coalescence in the packing part has been reported by
Scheibel [8]. For the same objective, a three-dimensional lattice as a partition of the mixing stages was
investigated by Steiner et al. [9].
The coalescence-dispersion pulsed-sieve-plate
extraction column (CDPSEC) is a modified pulsedsieve-plate extraction column (PSEC). It was reported
that the CDPSEC with 50 mm in the plate spacing
was of 120% overall mass transfer efficiency over the
standard PSEC [10]. However, when the plate
spacing of the CDPSEC was reduced to 25 mm, it
was reported that the mass transfer efficiency of the
CDPSEC was only about 50% that of the standard
PSEC, although the interface renewal frequency was
doubled [11].
Horvath and Hartland achieved the high stage
efficiency with a mixer-settler extraction column in
which the inter-stage mixing was extremely small,
similar to the throughput of the column [12]. Schweitzer reported a rectangular mixer-settler tower with
horizontal arrangement of the mixer and settler in
each stage. The arrangement between stages can
reduce the axial mixing and result in the enhancement of separation efficiency [13]. The comparison of
performance of various columns is shown in Table 1.
The Oldshue-Rushton column manufactured by
the mixing equipment company and commonly known
as the Mixco column was developed in 1940 thanks to
the best endeavors of Rushton and Oldshue. The unit
consists of an outer shell in which horizontal stage
separators are constructed to form the desired number of processing stages, each equivalent to a sepa-
rate mixing operation [14]. Experimental work in Oldshue-Rushton columns is limited and the studies
about stage efficiencies in the column have rarely
been referred to in the literature.
The objective of the present work is to investigate the influence of operating parameters such as
rotor speed and velocity of dispersed and continuous
phase on the stage efficiency for mass transfer directions as well as the two systems. An empirical
correlation for prediction of stage efficiency is recommended in terms of physical properties of liquid systems and operating conditions.
EXPERIMENTAL
A pilot plant Oldshue-Rushton extraction column
is used in these experiments. The column built in a
cylindrical glass section was equipped with impellers
with accurate speed control and the internal parts
were constructed from stainless steel; a schematic
diagram of the Oldshue-Rushton column used in this
study is presented in Figure 1. The specifications of
this column and range of operating variables are
listed in Table 2.
In normal operation, two types of immiscible
liquids with different densities flow counter-currently
through the apparatus. One of them is in large quantity (continuous phase), while the other, being in
minute quantity (few percent), is dispersed as drops.
Two flow meters are employed to supply and monitor
the fixed flow rates of continuous and dispersed
phases. The inlet and outlet of the column are connected to four tanks, each of 85 L capacity. The interface is maintained at the required level by using an
optical sensor as previously described.
Two chemical systems for instance tolueneacetone-water (high interfacial tension), and n-butyl
acetate-acetone-water (medium interfacial tension)
are examined on the extraction column for both mass
transfer directions. The European Federation of
Table 1. Comparison of performance of various columns [12]
Diameter
m
Stage height
m
NTS/m
1/m
Throughput
3
–2 –1
m m h
Mass transfer
direction
Enhanced coalescing column
0.072
0.060
Kühni column
0.060
0.350
45
3-7.5
10-60
d→c
100/130
2.9-3.7
4-10
Packed column
0.070
-
d→c
-
1.8-2.5
15-30
d→c
Pulsed packed column
0.070
Pulsed sieve plate column
0.050
-
-
3.8-5.8
18-20
d→c
0.100
60
3.5-6.0
20-30
Karr reciprocating column
0.050
d→c
0.025
15
3.5-6.0
30-40
d→c
Rotating disc column
0.070
-
-
2.8-3.5
15-35
d→c
Mixer settler extraction column
0.152
0.150
97
6.5
2-6
c→d
Mixer settler extraction column
0.152
0.150
170
11.3
2-4
d→c
Column
76
Stage efficiency
%
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
Figure 1. Schematic flow diagram of Oldshue-Rushton column.
Chemical Engineering (EFCE) has adopted these
systems as recommended systems.
Table 2. Technical description of the Oldshue-Rushton column
Parameter
Table 3 [15]. In the present work, the values of physical properties have been assumed to correspond to
the arithmetic-mean concentrations of the continuous
and dispersed phases at the inlet and outlet of the
column.
Value
Unit
Column height (H)
700
mm
Column internal diameter (Dc)
113
mm
Diameter of the rotor
50
mm
Settler diameter
169
mm
Physical
property
9
-
ρc / kg m
No. number of stages
Table 3. Physical properties of liquid systems at 20 °C [15]
Toluene/acetone/water
n-Butyl acetate/
/acetone/water
–3
994.4-995.7
994.3-995.8
864.4-865.2
879.6-881.4
Height of the stages
67
mm
ρd / kg m–3
Fractional free cross section area
25
%
μc / mPa s
1.059-1.075
1.075-1.088
0.574-0.584
0.723-0.738
Continuous phase flow rate
18-36
l/h
μd / mPa s
Dispersed phase flow rate
18-36
l/h
σ / mN m
Rotor speed
100-240
rpm
Dc / m2 s–1
2
Dd / m s
All experiments are carried out far from flooding
conditions. Conditions became steady, as evidenced
by a constant interface level, after three or four column volume of operation depending on the phase
flow rates and rotor speed. At the end of each experiment, the average hold-up of the column was measured by using the shutdown procedure (interface
position changes).
In all experiments, dilute solutions were investigated with approximately 3.5 wt.% acetone in the
organic phase. The acetone content of the aqueous
and organic stream was measured by UV-Vis
spectroscopy. The physical properties of the liquid–
liquid systems used in these experiments are listed in
–1
–1
27.5-30.1
12.4-13.2
1.09-1.14×10
2.7-2.8×10
-9
-9
1.01-1.06×10
-9
2.16-2.18×10
-9
The drops were photographed by a very high-resolution Nikon D5000 camera. Next, droplet dimensions were compared with the thickness of stators as
a reference. It is found that the curved surface of the
glass extraction column and significant differences
between air and the glass refractive indices leads to a
parallax deformation of the objects photographed in
the extraction column. In order to omit this phenomenon, a container filled with water was attached to
the extraction column and the photographic approach
was used to calculate the size of stator thickness
served as the reference for drop size measurements.
Consequently, digital image analysis software was
77
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
applied in order to investigate the taken high quality
photograph. A minimum of 1000 drops was analyzed
for each experimental condition in order to guarantee
the statistical significance of the determined size
distributions.
In the case of non-spherical droplets, the major
and minor axes, d1 and d2, were measured and the
equivalent diameter, de, was calculated from Eq. (1):
stage efficiency. The stage efficiency, Eoy, based on
the concentration of organic phase is illustrated as
follows:
(
d e = d 12d 2
)
1/3
(1)
The Sauter mean diameter was then calculated
according to the following equation:
N
d 32 =
 ni d i3
i =1
N
(2)
 n i d i2
i =1
E oy =
( y n − y n −1)
(y
*
n
− y n −1
)
where y n* = mxn is the organic phase concentration in
equilibrium with the aqueous phase of nth stage, the
value of m is 0.68 and 0.91 for toluene-water and
n-butyl acetate-water, respectively. Figure 2 illustrates the typical concentration profile for the organic
and continues phase for two systems and two directions of mass transfer. The experimental results
obtained in these experiments are given in Tables A.1
and A.2 in Appendix and the pictures of drop sizes for
two systems is shown in Figure 3.
Effect of agitation speed
where ni is the number of droplets of the mean
diameter di within a narrow size range i.
RESULTS AND DISCUSSION
The performance of an extraction column with
well-defined stages can be expressed in terms of
Figure 4a shows the effect of changing the agitation speed on the stage efficiency for both systems
from dispersed to continuous phase mass transfer. It
was observed that the stage efficiency in both systems is heavily dependent on the agitation speed. At
low speeds, the stage efficiency is low due to inadequate mixing, resulting in low holdup and large drops
Figure 2. Typical concentration profile along the column (N=140 rpm, Vd= Vc=0.66 mm/s).
78
(3)
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
Figure 3. Variation of drop sizes with rotor speed and interfacial tension for toluene-acetone-water: a) 140, b) 160, c) 180 rpm, and for
n-butyl acetate-acetone-water: d) 140, e) 160, f) 180 rpm.
(low interfacial area) that is also observed in Figure 3.
The stage efficiency increases with an increase in the
agitation speed and reaches a maximum of 58% for
toluene-acetone-water system at a speed of 220 rpm
and a maximum of 59% for n-butyl acetate-acetone-water system at a speed of 180 rpm.
Having reached its maximum, the stage efficiency falls to further increasing at agitation speed. A
decrease in the stage efficiency could contribute to
the a significant decrease in mass transfer rates due
to small droplets behaving as rigid spheres, in which
case molecular diffusion would govern mass transfer
in the system.
The effect of rotor speed on the values of the
stage efficiencies in the water-acetone-n-butyl acetate
test system (medium interfacial tension) is greater
than that of the water-acetone-toluene test system
(high interfacial tension). The size of the droplets in
higher interfacial tension test systems is larger than
the droplet size in the lower interfacial tension test
systems (Figure 3), which results in a decrease in
their residence time in the column. Finally, the slip
velocities increase and, consequently, the value of
the dispersed phase holdup and stage efficiency will
decrease; consequently, the column will operate in a
more-stable manner.
Effect of mass transfer direction
Figure 4. Effect of rotor speed on the stage efficiency: a) surface
tension and b) direction of mass transfer (Vc= Vd= 0.66 mm/s).
The effect of the mass transfer direction on the
stage efficiency is shown in Figure 4b. It is found from
this figure that the mass transfer direction has a
considerable effect on the stage efficiency. The stage
efficiency in the continuous to dispersed phase transfer is lower than that in the opposite direction. This is
due to the interfacial tension gradients that leads to
the smaller drop sizes in continuous to dispersed
phase transfer and larger drop sizes in the opposite
direction. Therefore, the higher values of the stage
efficiency in the case of the dispersed to continuous
phase transfer are resulted from the increased mass
transfer rates in drops of bigger sizes due to the presence of oscillations created by coalescence between
the droplets enhanced by the Marangoni effect [16].
79
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Effect of dispersed phase velocity
As shown in Figure 5a, the stage efficiencies
increase with an increase in dispersed phase velocity
for mass transfer direction from the dispersed to the
continuous phase. This observation could be attributed to an increase in mean drop sizes because of
an increase in drop formation and higher coalescence
frequency. The increment of the number of dispersed
droplets leads to an increase in the dispersed phase
holdup. It is observed that the effect of the holdup on
the interfacial area is larger than that of mean drop
size, i.e., the interfacial area increases with an increase in the dispersed phase velocity; albeit an increase in the dispersed phase velocity leads to the
reduction of mass transfer coefficient, a decrease is
more predominant when the increase in the interfacial
area is considered. Therefore, the stage efficiency
decreases along the column.
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
leads to an increment in the holdup due to the reduction of the relative velocity between the drops and
continuous phase, but it is not appreciable on the
drop sizes. Therefore, the interfacial area increases
with the positive effect of the holdup. An increase in
drag forces arising from the relative velocity between
the continuous and dispersed phases leads to the
circulation in a drop and consequently, overall mass
transfer coefficient increases with an increase in Vc.
The stage efficiency increases with both increase in
overall mass transfer coefficient and interfacial area.
As mentioned earlier, it is observed from Figures 5b
and 6b that the stage efficiency in the dispersed to
continuous phase transfer is higher than that in the
opposite direction.
Figure 6. Effect of continuous phase velocity on the stage
efficiency: a) surface tension and b) direction of mass transfer
(Vd= 0.66 mm/s).
Figure 5. Effect of dispersed phase velocity on the stage
efficiency: a) surface tension and b) direction of mass transfer
(Vc= 0.66 mm/s).
Effect of continuous phase velocity
The effect of the continuous phase velocity on
the stage efficiency is shown in Figure 6a. This effect
80
Comparison of other type of extractors with present
column
A comparison of the separation performance of
the Oldshue-Rushton column with some other type of
extraction extractors is described in Figure 7. The pattern is, as proposed by Pratt and Stevens, the number
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
of theoretical stages per unit of length against total
volumetric throughput of both phases [5]. This plot is
of value in facilitating the comparison of the relative
areas of application of various extractor types, despite
being based on the data for a single system, viz.
toluene-acetone-water in a phase ratio of 1.5. The
present Oldshue-Rushton column reached values of
between 5.14 and 6.55 NTS/m at low total throughputs. Therefore, it can be concluded that the present
column has high stage efficiency while its throughput
is low.
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
ation can predict the stage efficiency of the column
accurately.
Figure 8. Comparison between experimental data and the
proposed correlation.
CONCLUSION
Figure 7. Comparison of extractor performance; toluene–acetone-water system, Vd/ Vc = 1.5.
Proposed correlation for stage efficiencies
There is no correlation for prediction of stage
efficiency in the Oldshue-Rushton column. The experimental data on the stage efficiency are correlated in
terms of dimensionless numbers Re and Fr for both
mass transfer directions as well as the two systems
by using the least square method, as follows:
E oy = 1.399Re −0.203Fr −0.169
(4)
where:
g
Fr =
d RN 2
Re =
ρcd 32V s
μc
Stage efficiency was measured in a 113 mm
Oldshue-Rushton column for two systems. It is shown
in this work that the performance of the column
depends largely on the rotor speed. The stage efficiency increased with agitation speed and reached a
maximum, but after having reached its maximum, it
fell to further increase in agitation speed. The comparison between the stage efficiencies for the two
drops under the the same conditions of the two systems shows that the drop in n-butyl acetate-acetonewater system with a lower value of interfacial tension
has a higher value of Eoy. It was observed that the
stage efficiency is higher when the mass transfer
direction is from the continuous to the dispersed
phase. The comparison of Oldshue-Rushton column
with some other types of extractors revealed that the
stage efficiency is high in this column.
Nomenclature
(5)
(6)
The experimental data are compared with the
calculated results from the above equation in Figure
8. The stage efficiency calculated according to this
correlation reproduces the experimental data with an
average error of 4.64%. Thus, the proposed correl-
d32
D
Dc
dR
Eoy
g
N
NTS
Re
Fr
m
Sauter mean drop diameter (m)
molecular diffusivity (m2/s)
column diameter (m)
rotor diameter (m)
stage efficiency
acceleration due to gravity (m/s2)
rotor speed (1/s)
number of stage efficiency
Reynolds number
Froude number
distribution ratio
81
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
t
V
Vs
yn
x
time (s)
superficial velocity (m/s)
slip velocity (m/s)
mass fraction of acetone in dispersed phase
mass fraction of acetone in continuous phase
Greek letters
density (kg/m3)
interfacial tension (N/m)
viscosity (Pa s)
dispersed phase holdup
ρ
σ
μ
φ
Subscripts
c
d
o
continuous phase
dispersed phase
overall value
Superscripts
*
equilibrium value
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
[4]
M.S.A. Nabli, P. Guiraud, C. Gourdon, Chem. Eng. Res.
Des. 76 (1998) 951-960
[5]
H.R.C. Pratt, G.W. Stevens, in Science and Practice in
Liquid–Liquid Extraction, Oxford University Press, Oxford,
1992, pp. 491-502
[6]
W. Batey, J.D. Thornton, Ind. Eng. Chem. Res. 76 (1989)
1096-1101
[7]
M. Jaradat, M. Attarakih, H. J. Bart, Ind. Eng. Chem. Res.
50 (2011) 14121-14135
[8]
E.G. Scheibel, Chem. Eng. Prog. 44 (1948) 681-690
[9]
L. Steiner, E.V. Fisher, S. Hartland, AIChE Symp. Ser. 80
(1984) 130-138
[10]
H.B. Li, G.S. Luo, W.Y. Fei, J.D. Wang, Chem. Eng. J. 78
(2000) 225-229
[11]
X.J. Tang, G.S. Luo, H.B. Li, J.D. Wang, Pet. Technol. 32
(2003) 1046-1050
[12]
M. Horvoth, S. Hartland, Ind. Eng. Chem. Process Des.
Dev. 24 (1985) 1220-1225
[13]
P.A. Schweitzer, Hanson Mixer-Settler Handbook of
rd
Separation Techniques for Chemical Engineering, 3 ed.,
McGraw-Hill, New York, 1997, p. 230
REFERENCES
J. Rydberg, C. Musikas, G.R. Choppin, Solvent extraction
principles and practice, CRC Press, New York, 2004, p.
15
[14]
J.H. Rushton, S. Nagata, T.B. Rooney, AIChE J. 10
(1964) 298-302
[15]
[2]
J.C. Godfrey, M.J. Slater, Liquid-Liquid Extraction Equipment, Wiley, New York, 1995, p. 40
T. Míšek, R. Berger, J. Schroter, EFCE Publ. Ser. 46
(1985)
[16]
[3]
G.M. Ritcey, A.W. Ashbrook, Solvent extraction: principles and applications to process metallurgy, Vol. 1,
Elsevier, New York, 1984, p.100
M. Wegener, J. Grünig, J. Stüber, A.R. Paschedag, M.
Kraume, Chem. Eng. Sci. 62 (2007) 2967-2978.
[1]
APPENDIX
Table A.1. Experimental data obtained in the experiments for toluene-acetone-water system
Qd / l h–1
82
Qc / l h–1
d to c transfer
rpm
c to d transfer
φ
d32 / mm
φ
d32 / mm
2.44
24
24
140
0.0687
2.48
0.072
24
24
160
0.0755
2.22
0.0792
2.09
24
24
180
0.089
1.9
0.0945
1.805
24
24
200
0.111
1.48
0.116
1.41
24
24
220
0.115
1.35
0.125
1.282
24
24
240
0.128
1.12
0.134
1.02
24
18
160
0.0703
2.23
0.0751
2.1
24
30
160
0.0768
2.19
0.08391
2.06
24
36
160
0.0805
2.17
0.0876
2.01
24
18
200
0.108
1.5
0.111
1.45
24
30
200
0.116
1.47
0.1205
1.37
24
36
200
0.119
1.46
0.1264
1.34
18
24
160
0.0671
2.16
0.0716
2.04
30
24
160
0.0818
2.28
0.0879
2.14
36
24
160
0.0893
2.39
0.0966
2.17
18
24
200
0.1045
1.42
0.1073
1.38
30
24
200
0.1212
1.53
0.1248
1.45
36
24
200
0.1331
1.63
0.1373
1.52
M. ASADOLLAHZADEH et al.: THE EFFECTS OF OPERATING…
Chem. Ind. Chem. Eng. Q. 22 (1) 75−83 (2016)
Table A.2. Experimental data obtained in the experiments for n-butyl acetate-acetone-water system
–1
–1
Qd / l h
Qc / l h
rpm
φ
24
24
100
0.0748
2.02
24
24
120
0.0893
1.7092
24
24
140
0.0978
1.4191
24
24
160
0.119
1.25
24
24
180
0.129
1.08
24
24
200
0.14
0.95
24
18
120
0.0848
1.7186
24
30
120
0.0943
1.6882
24
36
120
0.098
1.66
24
18
160
0.1145
1.263
24
30
160
0.1231
1.242
24
36
160
0.1262
1.22
18
24
120
0.0828
1.6512
30
24
120
0.0998
1.7412
36
24
120
0.1086
1.8092
18
24
160
0.1125
1.224
30
24
160
0.1256
1.309
36
24
160
0.1337
1.367
MEHDI ASADOLLAHZADEH1,2
SHAHROKH SHAHHOSSEINI1
MEISAM TORAB-MOSTAEDI2
AHAD GHAEMI1
1
Department of Chemical
Engineering, Iran University of
Science and Technology (IUST),
Tehran, Iran
2
Nuclear Fuel Cycle Research
School, Nuclear Science and
Technology Research Institute,
Tehran, Iran
NAUČNI RAD
d32 / mm
EFEKTI RADNIH PARAMETARA NA EFIKASNOST
STUPNJA OLDŠUE-RUŠTONOVE KOLONE
U ovom istraživanju, efikasnost stupnja je ispitivana u Oldšue-Ruštonovoj koloni, prečnika
113 mm, za dva sistema: toluen-aceton-voda i n-butil acetat-aceton- voda. Eksperimenti
su uključili oba pravca prenosa mase. Ispitivan je uticaj različitih parametara, kao što su:
brzina mešanja, brzine strujanja dispergovane i kontinualne faze i pravac prenosa mase,
na efikasnost stupnja. Eksperimentalni podaci pokazuju da efikasnost stupnja jako zavisi
od brzine mešanja i međufaznog napona, a malo od brzine strujanja faza. Primećeno je da
je efikasnost stupnja bolja kada je smer prenosa mase acetona od kontinualne prema dispergovanoj fazi u odnosu na suprotan smer zbog prisustva oscilacija stvorenih gradijentom
površinskog napona. Ispitivana kolona je jedna od ekstrakcionih kolona sa visokom efikasnošću stupnja. Predložena je empirijska korelacija koja povezuje efikasnost stupnja sa
Rejnoldsovim i Frudovim brojem. Predviđanja jednačine se dobro slažu sa eksperimentalnim podacima.
Ključne reči: Oldšue-Ruštonova kolona, efikasnost stupnja, aksijalna mešanje,
kapacitet.
83
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
XIAOLEI LI
CHUNYING ZHU
School of Chemical Engineering
and Technology, State Key
Laboratory of Chemical
Engineering, Tianjin University,
Tianjin, China
SCIENTIFIC PAPER
UDC 66.06/.07:66.021.3:54
DOI 10.2298/CICEQ141001021L
CI&CEQ
GAS–LIQUID MASS TRANSFER WITH
INSTANTANEOUS CHEMICAL REACTION IN A
SLURRY BUBBLE COLUMN CONTAINING
FINE REACTANT PARTICLES
Article Highlights
• A mass transfer model based on penetration theory was developed
• The effect of particle dissolution near the gas-liquid interface was considered in the
model
• The absorption of SO2 into Mg(OH)2/water slurry was experimentally investigated in a
bubble column
Abstract
In this study, the mass transfer accompanied by an instantaneous irreversible
chemical reaction in a slurry bubble column containing sparingly soluble fine
reactant particles has been analyzed theoretically. Based on penetration
theory combined with the cell model, a one-dimensional mass transfer model
was developed. In the model, the effects of particle size and particle dissolution near the gas-liquid interface on mass transfer were taken into account.
The mass transfer model was solved and an analytical expression of the time-mean mass transfer coefficient was attained. Reactive absorption of SO2 from
gas mixtures into Mg(OH)2/water slurry was investigated experimentally in a
bubble column reactor to validate the mass transfer model. The results indicate
that the present model has good predicting performance and could be used to
predict mass transfer coefficient for the complicated gas-liquid-solid threephase system with an instantaneous irreversible chemical reaction.
Keywords: mass transfer, desulfurization, bubble column, instantaneous
reaction, slurry.
Gas absorption accompanied by chemical reactions in slurries is widely employed in the chemical
industry. Many chemical reactions involved in the
process could be regarded as instantaneous when
their rates are much greater than the rates of the
molecular diffusion. Some typical examples are the
removal of SO2 by means of the aqueous Mg(OH)2 or
Ca(OH)2 solution, the absorption of CO2 or H2S in the
aqueous Mg(OH)2 or Ca(OH)2 solution, etc. Ramachandran et al. [1] theoretically analyzed gas absorption into slurries by reactant particles using film theory
for the first time, and proposed and solved analytically
Correspondence: C. Zhu, School of Chemical Engineering and
Technology, State Key Laboratory of Chemical Engineering,
Tianjin University, Tianjin 300072, China.
E-mail: zhchy971@tju.edu.cn
Paper received: 1 October, 2014
Paper revised: 27 April, 2015
Paper accepted: 1 July, 2015
a steady-state homogeneous phase model. Subsequently, many studies on the gas absorption
accompanied by instantaneous chemical reactions
into slurries containing sparingly soluble reactant particles have been reported, and many theoretical
models were developed. Ramachandran [2] has summarized the gas absorption in slurries containing fine
reactant particles till 2007. The models of gas-liquid
mass transfer accompanied by instantaneous chemical reactions could be mainly classified into two
categories: steady-state models and unsteady-state
models. Uchida et al. [3], Dagaonkar et al. [4,5], Scala
[6] and Juvekar [7] developed and solved analytically
the steady-state models in terms of film theory. The
steady-state models based on film theory of mass
transfer are well adapted for actual situations when
the processes are steady-state and homogeneous
phase, but they are unreasonable and could bring
great errors for the unsteady-state processes. By
85
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
comparison, penetration theory and surface renewal
theory are more reasonable for describing the
unsteady-state processes. Mehra [8] studied the
effect of particle size distribution on the gas absorption, established and solved numerically an unsteadystate model based on the penetration model using a
population balance approach to track the evolving
particle size distributions. Kakaraniya et al. [9,10] extended the model of Mehra [8] to the SO2-Mg(OH)2–MgSO3 system and CO2-Ca(OH)2-CaCO3 system.
Akbar et al. [11] studied the three-phase mass transfer in a spray scrubber with dissolving reactive particles, proposed and solved numerically an unsteadystate model based on the penetration model. The
studies on the gas-side mass-transfer coefficient of
bubbles have been conducted. Patoczka [12], Mehta
[13], Filla [14], Cho [15], Rocha [16], Guedes [17],
Ricardo [18] and Sada [19] have reported the gasside mass-transfer coefficient for the bubble columns.
The experimental conditions in this work are similar to
that of Sada [19], thus the estimation of mass transfer
proposed by Sada would be employed directly. Up to
now, the effect of particle size on the mass transfer of
a gas-liquid-solid system with an instantaneous irreversible chemical reaction has not been theoretically
analyzed and discussed in detail, and the particle size
and the particle dissolution near the gas-liquid interface have a great influence on the mass transfer in
the actual process. Therefore, in this paper, a theoretical analysis of gas absorption accompanied by an
instantaneous chemical reaction in slurries containing
sparingly soluble fine reactant particles is presented,
and a mathematical model of mass transfer is
developed and solved analytically based on penet-
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
ration theory by taking into account the effect of particle size and particle dissolution near the gas-liquid
interface on the mass transfer. Mg(OH)2 has drawn
widespread attention as an absorbent for SO2 removal in recent years because of the advantages of
high removal efficiency, recycling, no secondary pollutants, etc. Thus, the mass transfer process of the
fast reactive absorption of SO2 into aqueous Mg(OH)2
slurry in a bubble column was experimentally investigated to validate the proposed mass transfer model.
EXPERIMENTAL
The schematic diagram of the experimental
setup is shown in Figure 1, which consisted of the
mixing gas generation unit, exhaust detection devices
and a bubble column. The bubble column was made
of stainless steel with 20 cm in diameter and 45 cm in
height.
Firstly, the column was filled with Mg(OH)2/water
slurry, the air was fed into the bubble column until the
system reached steady-state. Then, SO2 with volume
fraction 0.98 (Tianjin Kermel Chemical Reagent Co.,
Ltd.) supplied from a cylinder was mixed in the gas
mixer with the air from the air compressor (Shanghai
Jiebao Compressor Manufacture Co., Ltd.), and the
air-SO2 mixture was continuously fed at the bottom of
the column. After SO2 reacted with Mg(OH)2 (particle
size: 1-10 μm, Tianjin Kermel Chemical Reagent Co.,
Ltd.) in the liquid phase, the concentration of SO2 in
the exhaust was detected by a flue gas analyzer
(Qingdao Minhope electronic instrument Co., Ltd) with
the accuracy of 0.1 mg m-3. The gas flow rates were
controlled by a rotameter (LZB-type, Tianjin flow Ins-
Figure 1. Schematic diagram of the experimental setup: 1) sulfur dioxide cylinder; 2) air compressor; 3) valve; 4) pressure reducing
valve; 5) manometer; 6) rotor flow meter; 7) gas mixer; 8) bubble column; 9) feed tank; 10) flue gas detector; 11) manometer.
86
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
trument Co., Ltd.) with a measuring range of 0-100 ml
min-1 for SO2 and 0-100 L min-1 for air; the accuracy of
rotameters was ±1.5%. For each experimental condition, at least triplicate independent experiments
were conducted to obtain the average value of the
volume mass transfer coefficient. The experiments
were carried out at 298.15 K and atmospheric pressure.
A number of methods have been developed to
measure the volumetric mass transfer coefficient,
they could be divided into two main categories: 1)
based on the measure of the concentration of the
solute gas in the liquid phase; 2) based on the
measure of the gas concentration in the gas phase.
The gas balance method is more adequate for the
three-phase system, because it is very difficult to
measure the concentration of the solute gas in the
liquid phase [20]. When the reaction is rapid and
instantaneous, the concentration of the solute gas A
in the bulk liquid phase can be regarded as zero. In
this experiment, low superficial gas velocities were
adopted to form a bubble flow regime, thus the mass
balance of SO2 is:
QinC in − Q outC out = K tolaV L (C avg − CL )
(1)
where Cin and Cout are inlet and outlet bulk gas-phase
concentrations respectively; Cavg is the logarithmic
mean liquid phase equilibrium concentration of SO2
and CL bulk liquid-phase concentration.
In our experiment, the inlet volume fraction of
SO2 in the gas mixture is very low, thus the variation
of the gas phase volume is negligible. For an instantaneous reaction, the concentration of the gas reactant
in liquid could be regarded as zero. Therefore, the
volume mass transfer coefficient could be calculated
by:
K tola =
Q (C in − C out )
C avg
(3)
The logarithmic mean liquid phase concentration of SO2 in liquid, Cavg could be calculated:
C avg
(P / H − Pout / H )
= in
 P /H 
ln  in

 Pout / H 
The Henry coefficient of SO2 was obtained by
[21]:
H = exp ( −55788 T − 8.7615lnT + 68.48 )
(5)
Theory
The mass transfer accompanied by an instantaneous irreversible chemical reaction in a slurry bubble column reactor containing sparingly soluble fine
reactant particles is schematized in Figure 2. The
solute diffuses from the gas phase into the liquid
phase and reacts immediately and completely with
the reactant present in the slurry, and then a sharp
reaction plane parallel to the gas-liquid interface is
formed. In the zone between the interface and the
reaction plane (0 < x < Λ) only the reactant A exists.
Beyond the reaction plane (x > Λ) only the reactant B
exists. The following simplifying assumptions are
made for the modeling of gas absorption enhanced by
sparingly soluble fine reactant particles: 1) the solid
particles are spherical and uniform in size, smaller
than the scale of the diffusion length; 2) there is no
surface kinetic resistance to particle dissolution, and
the solid reactant has a low solubility in the liquid
phase and dissolves slowly, thus that particles shrinkage can be neglected [2-6].
(2)
The equilibrium concentration of SO2 in liquid
phase could be calculated by Henry’s law:
C SO2 = PSO2 / H
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
(4)
where Pin is the inlet partial pressure of SO2 and Pout
is the outlet partial pressure of SO2.
Figure 2. Schematic of mass transfer with instantaneous
reaction in the slurry.
It is supposed that the particle and the surrounding liquid establish a micro-cell. If rp is the solid
particle radius and εp is the solid hold-up of the
particle, the radius of each micro-cell is [7]:
rC = rp
3
εp
(6)
In the zone between the interface and the
reaction plane (0 < x < Λ), the mass transfer inside
each micro-cell could be considered as a steady-state
process due to the very small particle size. In the
zone between the interface and the reaction plane
87
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
(0 < x < Λ), each micro-cell is divided into two parts by
the micro-spherical reaction plane rλ. The mass
transfer process inside each micro-cell may be stated
as follows:
d
dr
 2 dC B
r dr


=0

(7)
B.C.: r = rp, CB = Bs; r = rλ, CB = 0.
d
dr
 2 dC A 
r
=0
dr 

(8)
B.C.: r = rλ, CA = 0; r = rC, CA = CAL.
The solutions of Eqs. (7) and (8) are respectively:
CB = B s ( rλ r − 1) (rλ rp − 1)
(9)
C A = C AL (1 − rλ r ) (1 − rλ rC )
(10)
In position of the micro-spherical reaction plane
rλ, the following equation can be gotten:
dC B
DB
dr
dC A
rλ = − D A
dr
(11)
rλ
Substitution of Eqs. (9) and (10) into Eq. (11)
yields:
rλ = rp (1 + DBB s D AC AL ) (1 + rpDBB S rCD AC AL )
(12)
Combining the Eqs. (10) and (12), the rate of
mass transfer in the interface of the micro-cell is:
−D A
dC A
dr
rC
(
)
= (D AC AL + DBB s ) [rC rC rp − 1 ]
(13)
The consumption rate of reactant A per unit
volume of slurry can be obtained:

R A = 4π rC2  −D A

dC A
dr
rC
(



( 4π r 3 ) =
3
C
)
(14)
In the zone beyond the reaction plane (x > xΛ),
the mass transfer process inside each micro-cell may
be represented as:

RB = 4π rC2  −DB

dCB
dr
= −3 DB (B s − CBL ) [r
(15)
2
C



(r
C
( 4π r 3 ) =
3
C
(17)
rp − 1)]
According to Figure 2, the mass transfer process accompanied by an instantaneous irreversible
chemical reaction in a slurry containing sparingly
soluble fine reactant particles is divided into two parts
by the reaction plane (x = rλ): A-only region from the
interface to the reaction plane (0 < x < Λ) and B-only
region beyond the reaction plane (x > Λ). The reactant A and the reactant B react in the reaction plane,
and the concentrations of the reactant A and the
reactant B can be regarded as zero. The material
balance in the liquid phase before and after the reaction plane is given:
∂C AL
∂ 2C AL
= 1− εp DA
−
∂t
∂x 2
(
)
(
)
−3 (D AC AL + DBB s ) [rC2 rC rp − 1 ] (0 < x < x Λ )
∂CBL
∂ 2CBL
= 1 − ε p DB
+
∂t
∂x 2
(
)
(
(18)
(19)
)
+3 DB (B s − CBL ) [rC2 rC rp − 1 ] ( x Λ < x )
I.C.: t = 0, x > 0, CAL = 0, CBL = Bs
B.C.: x = 0, CAL = C A∗
∂C AL
∂CBL
x = xΛ, CAL = CBL = 0, D A
= −DB
∂x
∂x
x = ∞, CBL = Bs
To solve Eqs. (18) and (19), the equal diffusivities condition and the concept of negative concentration of the solute are introduced [22]. And it is
assumed that:
The
defined:
following
(20)
dimensionless
variables
are
A = CAL/ C A∗ , B = CBL/ C A∗ , D = (1−εp)DA = (1−εp)DB,
k = 3 D A [rC2 ( rC rp − 1)]
(21)
x > Λ to B = −A and A' = A+qB = 1+Bs/ C A∗ , Eqs. (18)
and (19) become identical:
B.C.: r = rp, CB = Bs; r = rC, CB = CBL.
The solution of Eq. (15) is:
CB = B s ( rC r − 1) ( rC rp − 1) +
) (1− r
p
rC )
∂A '
∂2A'
=D
− kA '
∂t
∂x 2
(16)
I.C.: t = 0, x > 0, A ' =0
B.C.: x = 0, A ' =1+qB = 1+Bs / C A∗
x = ∞, A ' =0
88
rC
By putting the concentration of B in the range of
d  2 dC B 
=0
r
d r 
d r 
(
The consumption rate of reactant B per unit volume of slurry can be obtained:
DA = DB; CBL = –CAL
= 3 (D AC AL + DBB s ) [rC2 rC rp − 1 ]
+CBL 1 − rp r
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
(22)
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
The gas-liquid specific interfacial area [23]:
Solving Eq. (22) yields:
A ' (1 + q B ) = 0.5(exp( − x k D )erfc (
x
+ exp( x k D )erfc (
4tD + kt
x
4tD − kt
a = 6ε g d
)+
(23)
))
∂C AL
∂x
x =0
= (1 + q B )C A∗ D Ak
( ( kt ) + e
× erf
− kt
π kt
)
(
)
1− ε p ×
(24)
(25)
NA
(−D A
∂C AL
∂x
(26)
θ0
k θ0
)
πθ0 k + e −k θ0 ) D A (πθ0 )C A∗
(27)
From Eq. (27) the mass transfer coefficient can
be calculated by:
K L = (1 + q B ) 1 (1 − ε p )(( k + 0.5 θ0 ) ×
×erf
(
k θ0
)
πθ0 k + e −k θ0 ) D A (πθ0 )
(
(28)
)
where k = 3 D A [rC2 rC rp − 1 ] (Eq. (21), unit: s-1), θ0
is the average exposure time (unit: s). Then the terms
in square brackets is dimensionless. Thus the unit of
KL is the same as D A / (πθ0 ) .
For the gas absorption accompanied by instantaneous chemical reactions in slurry bubble columns containing sparingly soluble fine reactant particles, as the partial pressure of the gas reactant is
low, the gas-side mass transfer resistance could not
be ignored. The total mass transfer coefficient can be
expressed as:
1
K tol
=
1
(
1
Kg
+
H
)
KL
(29)
The gas-side volume mass transfer coefficient is
[19]:
K ga = 170u b0.73
0.25
(32)
2
(1− ε )
53
g
(33)
u single = ( 2.14σ L ρLd + 0.505gd )
0.25
(34)
The bubble diameter [24]:
0.3333
(35)
The bubble volume:
x = 0 )dt
N A = (1 + q B ) 1 (1 − ε p )(( k + 0.5 θ0 ) ×
(
u b = u single (1 − ε g )
d = 2 ( 3V 4π )
Substitution of Eq. (24) into Eq. (26) using the
relationship between D and DA yields:
×erf
)
The average bubble rising velocity [24]:
Eq, (24) can be integrated:
0
(
The single bubble rising velocity:
θ0 = d u b

=
The gas hold-up [24]:

The exposure time can be estimated by the
bubble diameter and bubble rising velocity:
θ0
(31)
3
ε g (1 − ε g ) = 0.086 u single
ρL2 η ( ρL − ρg ) g 
The mass transfer rate of A can be obtained:
−D A
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
(30)
V = 0.976 (Q N )
1.2
g 0.6
(36)
At 298.15 K, the diffusion coefficient of SO2 in
the liquid phase, DA, is 1.49×10-9 m2·s-1; the solubility
of Mg(OH)2 in water [4], Bs, is 0.46 mol·m-3.
RESULTS AND DISCUSSION
The experimental data are the average values of
the volume mass transfer coefficient from the beginning to the SO2 concentration detected by the flue gas
analyzer reaching 40 mg·m-3.
The calculated values according to the Eqs.
(28)-(30) by MATLAB are shown in Figures 3–6.
Effect of the solid hold-up
The effect of the solid hold-up in the Mg(OH)2
slurry on the volume mass transfer coefficient of SO2
is presented in Figure 3, indicating that with increasing the solid hold-up in the Mg(OH)2 slurry, the
volume mass transfer coefficient of SO2 increases. In
the previous work, four mechanisms of mass transfer
enhancement were introduced, including the shuttling
mechanism, the boundary layer mixing mechanism,
the coalescence inhibition mechanism and boundary
layer reaction mechanism [25]. In this work, for gas
absorbed chemically into a slurry, the fine particles
could provide reactants into the liquid film to enhance
the mass transfer process, the enhance of mass
transfer could be explained through the boundary
layer reaction mechanism. Alper [26-28] introduced
the concept of effective film thickness to explain the
effect of the catalyst concentration on the mass
transfer enhancement for the gas absorption in cat-
89
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
alytic slurry reactors. Alper believed that the effective
film thickness would decrease with the increase of the
solid concentration. Increasing the solid hold-up would
lead to an increase of the number of particles per unit
volume of slurry in the liquid film, making the reaction
plane shift closer to the interface, which leads to decrease of the effective film thickness and intensify the
mass transfer process. The higher the solid hold-up
is, the closer the reaction plane shifts to the interface,
which provides a higher value of the liquid-side mass
transfer coefficient, KL. Thus the total volume mass
transfer coefficient of SO2 increases with Mg(OH)2
solid hold-up in the slurry.
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
fies that the mass transfer model proposed in this
paper is reasonable and acceptable in accuracy.
Figure 4. Effect of the gas flow rate on the volume mass transfer
coefficient, Mg(OH)2 solid hold-up: 0.6356×10-3; inlet partial
pressure of SO2: 0.2 kPa.
Effect of the particle size and the particle dissolution
near the gas-liquid interface
Figure 3. Effect of the Mg(OH)2 solid hold-up on the volume
mass transfer coefficient, gas flow rate: 20 L·min-1; inlet partial
pressure of SO2: 0.2 kPa.
Effect of the gas flow rate
Figure 4 presents the effect of the gas flow rate
on the volume mass transfer coefficient of SO2. It
could be found from Figure 4 that, when the gas flow
rate increases, the volume mass transfer coefficient
of SO2 increases. An increase in the gas flow rate
could increase the gas hold-up and provide more gasliquid interfacial area. And increasing the gas flow
rate also speeds up the bubble rising velocity, which
promotes the turbulence in the liquid, and then leads
to the increase of the liquid-side mass transfer coefficient. As a result, the volume mass transfer coefficient of SO2 increases with the increase of the gas
flow rate.
Figures 3 and 4 show the comparison of experimental mass transfer coefficients with the predicted
values; the average deviation of present model is 1%.
It can also be seen clearly that the calculated results
agree well with the experimental values, which veri-
90
When the solid hold-up is constant, the effect of
the particle size near the gas-liquid interface on the
volume mass transfer coefficient of SO2 is shown in
Figure 5. For a given solid hold-up, when the radius of
particle is smaller than 5 μm, the change of the particle size is found to have notable effect on the volume mass transfer coefficient. With the decrease of
particle size, the particle number near the gas-liquid
interface, especially in the zone between the interface
and the reaction plane (0 < x < Λ), increases more
and more greatly because the volume of the particle
is proportional to the cube of the particle radius. Decreasing the particle size would lead to an increase of
the solid-liquid interface area, which would result in a
marked increase of the particle dissolution rate
(according to Eqs. (9) and (10)). Alper [28] believed
that only the size of particle is smaller than the
effective thickness could increase the absorption rate
for the gas absorption in catalytic slurry reactors. As
the particle size increases, it becomes increasingly
closer to the effective film thickness, and then the
intensification of mass transfer is weakened. In addition, with the increase of particle size (e.g., the particle radius is larger than 7 μm), the influences of the
particle size variation on the particle number become
small, and the solid-liquid interface area decreases
obviously, leading to the decrease of the particle dissolution rate and the reaction rate. Thus, the intensification of mass transfer is weakened and the vol-
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
ume mass transfer coefficient is remarkably decreased. Therefore, the influence of the variation of the
particle size on the volume mass transfer coefficient
becomes more and more significant with the decrease of the particle size.
Figure 5. Effect of the radius of particles on the volume mass
transfer coefficient, Mg(OH)2 solid hold-up: 0.4237×10-3;
inlet partial pressure of SO2: 0.2 kPa.
Figure 6 demonstrates the effect of the solubility
of the particle reactant in the liquid phase on the
volume mass transfer coefficient of SO2. The increase
of solubility of the particle reactant in the liquid phase
enhances the rate of the particles dissolution rate and
the driving force of reactant B transferring from the
bulk liquid to the reaction region. Therefore, the concentration of reactant B in reaction region increases,
and as a result, the reaction rate is accelerated, the
reaction plane moves close to the gas-liquid interface,
and the effective thickness of mass transfer is reduced, thus the mass transfer between two phases is
obviously intensified [29].
CONCLUSION
Mass transfer accompanied by an instantaneous
chemical reaction in a slurry bubble columns containing sparingly soluble fine reactant particles has
been studied theoretically and experimentally. A
model has been developed and analytically solved
based on the penetration model. The analytical expression of the time-average mass transfer coefficient
has been derived. The fast reactive absorption of SO2
into aqueous Mg(OH)2 slurry in a bubble column was
experimentally investigated. The volume mass transfer coefficient of SO2 increases with the increase of
the solid hold-up in Mg(OH)2 slurry, the gas flow rate
and the solubility of the particle reactant in the liquid
phase. For constant solid hold-up of Mg(OH)2, when
the particle is large (> 7 μm), the variation of the
particle size has little influence on the volume mass
transfer coefficient; when the particle is small (< 5
μm), the particle size has notable effect on the volume mass transfer coefficient. The calculated value
by the present model agrees well with the experimental data, which validates the proposed mass transfer
model.
Acknowledgement
The authors gratefully acknowledge the financial
support of the National Natural Science Foundation of
China (No. 21306127).
Nomenclature
a
A
A'
B
C A*
Bs
CA-B
CAL-BL
Cavg
Cin
CL
Cout
C SO2
Figure 6. Effect of the solubility of B on the total volumetric
mass transfer, Mg(OH)2 solid hold-up: 0.8475×10-3; inlet partial
pressure of SO2: 0.2 kPa; radius of particles:10 μm.
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
D
DA-B
d
gas-liquid specific interfacial area (m2 m-3)
dimensionless concentration of A, defined by
Eq. (21)
defined by A+qB
dimensionless concentration of B, defined by
Eq. (21)
interfacial concentration of A (mol·L-1)
solubility of B (mol·L-1)
concentration of reactant A or B in the micro
cell (mol·L-1)
liquid concentration of reactant A or B (mol·L-1)
average equilibrium concentration of SO2 in
the liquid phase (mol·L-1)
inlet concentration of SO2 in the gas phase
(mol m-3)
concentration of SO2 in liquid phase
outlet concentration of SO2 in the gas phase
(mol m-3)
equilibrium concentration of SO2 in the liquid
phase (mol·L-1)
defined by Eq.(21)
molecular diffusivity of A or B (m2 s-1)
bubble diameter (m)
91
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
g
H
k
Kg
KL
gravitational acceleration (m·s-2)
Henry coefficient (kmol·m-3·atm-1)
defined by Eq.(21)
gas-side mass transfer coefficient (m·s-1)
liquid-side physical mass transfer coefficient
(m·s-1)
total mass transfer coefficient (m·s-1)
number of holes on the gas distributor plate
average flux of A relative to a phase boundary (mol·m-2·s-1)
partial pressure of SO2, Pa
inlet partial pressure of SO2, Pa
outlet partial pressure of SO2, Pa
defined by Bs/ C A∗
flow rate of gas (m3·s-1)
radial coordinate from the particle (m)
radius of the micro cell (m)
radius of the particle (m)
radius coordinate of the reaction plane in
micro-cell (m)
consumption rate of A or B per unite volume
of slurry (mol·m-3·s-1)
average total flux of A in the bubble column
(mol·s-1)
time (s)
temperature (K)
superficial gas velocity (m·s-1)
rise velocity of a single bubble (m·s-1)
average volume of the bubble (m3)
volume of the liquid in the bubble column
(m3)
distance from the surface (m)
reaction plane distance from the interface (m)
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
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Ktol
N
NA
PSO2
Pin
Pout
qB
Q
r
rc
rp
rλ
RA-B
RSO2
t
T
ub
usingle
V
VL
x
xΛ
Greek symbols
εg
εp
θ0
η
λ
Λ
ρL
ρg
σL
92
gas hold-up
the solid hold-up of the particles
exposure time (s)
effective slurry viscosity (kg·m-1·s-1)
radius distance of the reaction plane from the
particle (m)
reaction plane distance from the interface (m)
liquid density (kg·m-3)
gas density (kg·m-3)
surface tension of liquid (N·m-1)
X. LI, C. ZHU: GAS–LIQUID MASS TRANSFER WITH INSTANTANEOUS…
XIAOLEI LI
CHUNYING ZHU
School of Chemical Engineering
and Technology, State Key
Laboratory of Chemical
Engineering, Tianjin University,
Tianjin, China
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 85−93 (2016)
PRENOS MASE GAS–TEČNOST PRAĆEN
TRENUTNOM HEMIJSKOM REAKCIJOM U
BARBOTAŽNOJ KOLONI U PRISUSTVU FINIH
ČESTICA REAKTANTA
U ovom radu analiziran je teorijski prenos mase praćen trenutnom nepovratnom hemijskom reakcijom u barbotažnoj koloni u prisustvu slabo rastvornih finih čestica reaktanta.
Na osnovu teorije penetracije, u kombinaciji sa modelom ćelija, razvijen je jedno-dimenzionalni model prenosa mase. Ovaj model uzima u obzir uticaj veličine čestica i brzine
rastvaranja blizu kontaktne površine gas-tečnost na prenos mase. Model prenosa mase je
rešen, tako da je dobijen analitički izraz za koeficijent prenosa mase u funkciji vremena.
Reaktivna apsorpcija SO2 iz gasne smeše u suspenziji Mg(OH)2 u vodi je eksperimentalno
ispitana u reaktoru tipa barbotažne kolone radi validacije modela prenosa mase. Rezultati
pokazuju da razvijeni model dobro predviđa koeficijent prenosa mase u komplikovanom
trofaznom sistemu gasno-tečno-čvrsto sa trenutnom ireverzibilnom hemijskom reakcijom.
Ključne reči: prenos mase, desumporizacija, barbotažna kolona, trenutna reakcija, suspenzija.
93
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
JELENA POPOVIĆ1
GORAN RADENKOVIĆ2
JOVANKA GAŠIĆ1
SLAVOLJUB ŽIVKOVIĆ3
ALEKSANDAR MITIĆ1
MARIJA NIKOLIĆ1
RADOMIR BARAC1
1
Department of Restorative
Dentistry and Endodontics, Clinic
of Dentistry, Medical Faculty,
University of Niš, Niš, Serbia
2
Department of Production
Engineering, Faculty of Mechanical
Engineering, University of Niš, Niš,
Serbia
3
Department of Restorative
Dentistry and Endodontics, Faculty
of Dentistry, University of Belgrade,
Belgrade, Serbia
SCIENTIFIC PAPER
UDC 669.245:669.14.018.8:616.314-08
DOI 10.2298/CICEQ150103023P
CI&CEQ
THE EXAMINATION OF SENSITIVITY TO
CORROSION OF NICKEL-TITANIUM AND
STAINLESS STEEL ENDODONTIC
INSTRUMENTS IN TOOTH ROOT CANAL
IRRIGATING SOLUTIONS•
Article Highlights
• Corrosion of Ni-Ti and stainless steel endodontic files in irrigating solutions was examined
• Testing of sensitivity to corrosion was performed by dynamic potentiometric method
• Measurements were performed in 5.25% NaOCl, 0.2% CHX and 17% EDTA
Abstract
The application of irrigating solutions is essential in chemomechanical treatment of tooth root canal. However, chemical and electrochemical aggressiveness of the solutions, which directly act on the instruments, may damage their
surface. The aim of this study was to investigate the sensitivity of the nickeltitanium (Ni-Ti) and stainless steel endodontic files to corrosive action of the
sodium hypochlorite (NaOCl), chlorhexidine gluconate (CHX) and ethylenediamine tetraacetic acid (EDTA). Testing of sensitivity to corrosion of the
instruments was performed by dynamic potentiometric method. Measurements
were made in 5.25% NaOCl, 0.2% CHX and 17% EDTA. Ni-Ti instruments
immersed in 5.25% NaOCl showed the most intensive corrosive changes and
the lowest value of pitting potential of 1.1 V. Stainless steel instruments
immersed in 5.25% NaOCl showed higher value of pitting potential of 1.5 V.
Stainless steel instruments immersed in 0.2% CHX showed lower corrosive
surface changes and higher value of pitting potential of 1.6 V, whereas Ni-Ti
instruments immersed in 0.2% CHX showed the pitting potential of 1.9 V. The
corrosion was not observed in both types of instruments after immersion in
17% EDTA. The use of 5.25% NaOCl and 0.2% CHX may cause severe surface corrosion of Ni-Ti and stainless steel endodontic files.
Keywords: corrosion, irrigating solutions, nickel-titanium, stainless steel,
endodontic instruments.
Chemomechanical root canal preparation is
essential during endodontic treatment and involves
procedures of cleaning and shaping with endodontic
instruments and irrigating solutions. The purpose of
mechanical instrumentation is to obtain a continuous
Correspondence: J. Popović, Department of Restorative Dentistry and Endodontics, Clinic of Dentistry, Medical Faculty, University of Niš, Blv. Dr Zorana Djindjica 52, 18000 Niš, Serbia.
E-mail: jelenadp@gmail.com
Paper received: 3 January, 2015
Paper revised: 11 June, 2015
Paper accepted: 5 July, 2015
•
The paper was given as poster presentation at the Rosov pin
2014, the second regional roundtable: Refractory, process industry and nanotechnology.
tapering funnel shape, flowing with the original canal
from the coronal access to the apex. The functions of
the irrigants are to act as media for removing debris,
as lubricants, to dissolve smear layer from dentinal
walls and to promote root canal sterility [1]. Many solutions, such as sodium hypochlorite (NaOCl), hydrogen peroxide (H2O2), citric acid (C6H8O7), ethylenediamine tetraacetic acid (EDTA), chlorhexidine gluconate (CHX) and physiological saline, have been
used for root canal irrigation [2]. Even though the
benefits of irrigating solutions are essential for chemomechanical preparation, chemical and electrochemical aggressiveness of these solutions may
damage the surface of the instruments [3].
95
J. POPOVIĆ et al.: THE EXAMINATION OF SENSITIVITY TO CORROSION…
There are many literature data about susceptibility to corrosion of endodontic instruments in irrigating solutions [2,4]. The corrosion process could be
activated during chemomechanical treatment, chemical disinfection of the instruments and sterilization
[5]. Corrosion adversely affects the metallic surfaces
by causing pitting and porosity, and decreases the
cutting efficiency of endodontic files [6]. Several studies [7,8] have shown that corrosion of the endodontic files can degrade the mechanical properties
and suddenly cause undesirable cracks that occur
during root canal preparations.
The purpose of this study was to evaluate sensitivity to corrosion of nickel-titanium and stainlesssteel endodontic files in most commonly used root
canal irrigating solutions, NaOCl, CHX and EDTA.
EXPERIMENTAL
The study included 36 hand endodontic files
divided according their type; 18 nickel-titanium (I-FLEX, IMD, USA) and 18 stainless-steel (NTI-Kahla
GmbH, Germany). To remove all debris received from
the manufacturers, the files were cleaned in an ultrasonic bath (JUS-S01, JEOL) with distilled water for 15
min at the frequency of 28 kHz immediately after
taking them from the original packages. Each type of
the instrument was divided into three groups according to the irrigant solutions examined in the study, so
each group consisted of six files.
Measurements were performed in 5.25% NaOCl
(prepared in the laboratory), 0.2% CHX (R4, Septodont, France, diluted to 0.2%) and 17% EDTA (prepared in the laboratory). All solutions used in this
study were freshly prepared, and stored in adequate
conditions. The corrosion behaviour was assessed
using potentiodynamic method. The experiments
were carried out in an ordinary, three-compartment
cylindrical glass cell. The counter electrode was a Pt
foil and the reference electrode was a saturated calomel electrode (SCE). All potentials were referred to
SCE. The working electrode – endodontic instrument –
was placed into the cell in such a way that only the
working part of the instrument was immersed in the
solution, whereas the base and the hand were above
the solution. The instruments were immersed 15 s
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
before the start of the potential rise and this time was
set by the program. Anodic E–I polarization curves
were recorded by using software Par Stat by means
of the linear sweep technique (sweep rate 0.2 mV/s)
in an air atmosphere at room temperature of 23±3 °C.
Potential value that showed sharp rise of the current
was assigned as pitting potential. The sharp increase
of the current was a result of local dissolution of the
metal and forming of the pits. The measurements
were repeated six times for each solution and the
each type of the file, and the results were given as
mean values. Statistical analysis was carried out
using Student’s t-test and Mann-Whitney U test
(SigmaStat statistical software). Electrochemical testings were performed at Department of Production
Engineering, Faculty of Mechanical Engineering, University of Niš, and Department of Physical Chemistry
and Electrochemistry, Faculty of Technology and
Metallurgy, University of Belgrade.
RESULTS AND DISCUSSION
The results of the study are shown in Table 1.
The corrosion resistance was the lowest in the group
of Ni-Ti instruments immersed in 5.25% NaOCl. The
pitting potential was recorded at 1.1 V (Figure 1).
Higher resistance to corrosion was observed in Ni-Ti
instruments tested in 0.2% CHX. The measurements
showed that the pitting potential was 1.9 V (Figure 2).
Based on the obtained results it can be stated that Ni-Ti instruments immersed in 5.25% NaOCl and 0.2%
CHX showed current increases and hence the tendency to pitting corrosion (Figures 1 and 2). Comparing
the behavior of Ni-Ti instruments in 5.25% NaOCl and
0.2% CHX we can notice that NaOCl caused higher
current increase that means less corrosion resistance. Statistical analysis showed that this difference
was statistically significant (P < 0.001). On the contrary, Ni-Ti instruments immersed in 17% EDTA showed
the highest resistance to corrosion. The rise of the
current was not observed in the whole range of examined potentials and the value remained approximately
constant (Figure 3).
Similar behavior was observed in the group of
stainless steel instruments. The increase of current
density was also high in 5.25% NaOCl (1.5 V) and
Table 1. Pitting potential values of the Ni-Ti and stainless steel instruments in tested irrigant solutions
Instrument
Ni-Ti
Stainless steel
96
Irrigants
Mean±SD
Std. Error
C.I. of Mean
Max-Min
5.25% NaOCl
1.1±0.089
0.037
±0.094
1.2-1.0
Median
1.1
0.2% CHX
1.9±0.141
0.058
±0.148
2.1-1.7
1.9
5.25% NaOCl
1.5±0.141
0.058
±0.148
1.7-1.3
1.5
0.2% CHX
1.6±0.063
0.026
±0.066
1.7-1.5
1.6
J. POPOVIĆ et al.: THE EXAMINATION OF SENSITIVITY TO CORROSION…
0.2% CHX (1.6 V), but the difference was not statistically significant (Figures 4 and 5). No significant increase of current in wide range of examined potentials
was observed after immersion of stainless steel instruments in 17% EDTA (Figure 6).
-2
Ni-Ti
NaOCl
1,0x10
-2
5,0x10
-3
1,0
Ep
1,2
1,4
1,6
Potential, V (SCE)
Figure 1. Potentiodynamic polarisation curve of the Ni-Ti file in
5.25% NaOCl.
0,0
-1,0x10
-3
-3
-2
1,2
0,0
Ep
1,2
1,6
1,8
2,0
-2
-4
1,0
1,4
Figure 3. Potentiodynamic polarisation curve of the Ni-Ti file in
17% EDTA.
8,0x10
5,0x10
1,0
Potential, V (SCE)
Ni-Ti
CHX
1,4
1,6
1,8
2,0
Potential, V (SCE)
Figure 2. Potentiodynamic polarisation curve of the Ni-Ti file in
0.2% CHX.
Current density, A/cm2
2
Current density, A/cm
1,0x10
Ni-Ti
EDTA
-2
2
1,0x10
0,0
1,5x10
rosion and deterioration of the endodontic instruments
[9-11]. Corrosion is a deterioration of a metal by chemical or an electrochemical reaction with its environment, and a technique that evaluates the electrochemical properties of the instrument-irrigating solutions
system would seem most appropriate in studying corrosion [12]. Electrochemical techniques that are
based on the electrode potential-current characteristics define the susceptibility of a metal to react with
its environment [13].
Current density, A/cm
2
Current density, A/cm
1,5x10
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
6,0x10
4,0x10
2,0x10
-2
-2
-2
Ep
0,0
0,6
According to the examined potentials in both
types of the instruments, after immersion in 5.25%
NaOCl Ni-Ti instruments showed less corrosion
resistance compared to the stainless steel instruments and this difference was statistically significant
(P < 0.001). After immersion in 0.2% CHX, Ni-Ti instruments showed higher resistance to corrosion compared to the stainless steel instruments, and the difference was statistically significant (P < 0.01).
The chemical mechanisms that occur either
during instrumentation and irrigation of the root canal
system, or after instrumentation (in procedures of instrument disinfection and sterilization), may cause cor-
SS
NaOCl
0,8
1,0
1,2
1,4
1,6
1,8
Potential, V (SCE)
Figure 4. Potentiodynamic polarisation curve of the stainless
steel file in 5.25% NaOCl.
During endodontic therapy, the most frequently
used irrigant is sodium hypochlorite (NaOCl) in a concentration range of 0.5–6% [14]. It is an agent with
wide spectrum of antimicrobial action and tissue dissolution capacity [15], which is also used as a presoaking solution in cleaning procedures of endodontic
instruments after clinical use [9]. However, it is highly
corrosive to metals and could cause corrosion of the
endodontic files. Corrosion pattern involves pitting
97
J. POPOVIĆ et al.: THE EXAMINATION OF SENSITIVITY TO CORROSION…
-3
Current density, A/cm2
1,5x10
SS
CHX
-3
1,0x10
-4
5,0x10
0,0
Ep
-4
-5,0x10
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Potential, V (SCE)
Figure 5. Potentiodynamic polarisation curve of the stainless
steel file in 0.2% CHX.
Chlorhexidine gluconat (CHX) at concentrations
0.1-2% is a broad spectrum antimicrobial agent that is
used during root canal irrigation. Its cationic structure
provides a unique property, named substantivity. This
prolonged antimicrobial activity in the root canal may
last up to 12 weeks [22]. However, the literature data
revealed that CHX can cause severe corrosion of
98
endodontic instruments [2]. The results of this study
confirmed that intensive surface corrosion can occur
after immersion of the files in 0.2% CHX. According to
the Matamala [23], this high rate of corrosive changes
may depend on its acidic pH (5.72), as the acidic
environment increases the corrosion rate.
Current density, A/cm2
and potentially weakening of the structure of the instruments [16]. NaOCl contains active Cl-, and it is
well-known that Cl- is an aggressive ion that generally
increases corrosion rates [17]. This study showed that
the corrosion rate of the endodontic files was high in
5.25% NaOCl. These results are in accordance with
the results of earlier studies and confirm that the
corrosion of endodontic files in NaOCl is possible.
NaOCl is corrosive to many metals and selectively
removes nickel from the Ni-Ti alloy [18]. Busslinger et
al. [19] found measurable release of titanium when
Lightspeed Ni-Ti files were immersed in NaOCl solution for 30 and 60 min. In the study of Stokes et al.
[6] corrosion was visually observed on endodontic
files after immersion in 5.25% NaOCl, there was significant difference in corrosion frequency between
brands, but there was no difference between stainless
steel and Ni-Ti instruments. Oztan et al. [2] revealed
severe corrosion on the surface of the stainless steel
endodontic instruments after immersion in 5.25%
NaOCl, in accordance to O’Hoy et al. [9] who have
shown evident signs of corrosion after overnight
immersion of endodontic instruments in NaOCl. The
fact that chloride and fluoride ions have negative
effects on the corrosion resistance of stainless steel
and Ni-Ti alloys is used in few investigations to promote electrochemical dissolution and removing endodontic instruments in cases where they are fractured
in the root canal system [20,21].
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
1,5x10
-3
1,0x10
-3
5,0x10
-4
SS
EDTA
0,0
-4
-5,0x10
Ep
-3
-1,0x10
0,8
1,0
1,2
1,4
1,6
1,8
Potential, V(SCE)
Figure 6. Potentiodynamic polarisation curve of the stainless
steel file in 17% EDTA.
Ethylenediamine tetraacetic acid (EDTA) is the
chelating irrigant with inorganic tissue dissolution capacity, and is used due to ability to lubricate and facilitate root canal instrumentation especially in preparation of narrow and curved root canals. In endodontics it is used as 15-17% solution [24]. The results
of potentiodynamic test in this study did not reveal
corrosion of endodontic files after immersion in 17%
EDTA, and it was in accordance with literature data
[2,4,25]. Öztan et al. [2] have reported the lowest
corrosion rate of stainless steel endodontic files in
17% EDTA. They have stated that EDTA forms complexes with metal ions (Fe, Ni, Cr, Co, etc.) at pH
values < 4. EDTA’s ability to protect and passivate
instruments is due to its ability to complex with iron to
form an inhibiting barrier to oxidation and corrosion
[26]. According to Darabara et al. [4], large molecules
of R-EDTA have greater difficulty in concentrating and
orienting the pit so as to increase the acidity to adequate values for trigger corrosion. Atomic force microscopic evaluation of Fayyad and Mahran [25] showed
that immersion in 17% EDTA did not affect the surface roughness of the Ni-Ti endodontic instruments.
Endodontic files and reamers are generally
accepted as reusable instruments. In purpose to eliminate the risk of infection transmission, these instruments need to be cleaned and sterilized thoroughly
after clinical use [27]. However, these procedures
could potentiate surface corrosion in irrigating sol-
J. POPOVIĆ et al.: THE EXAMINATION OF SENSITIVITY TO CORROSION…
utions [28]. Casella and Rosalbino [29] confirmed that
sterilization process had negative influence on the
corrosion behavior of endodontic instruments, and the
effect appears to be more dramatic for longer sterilization treatment periods. The presence of protein debris in form of ground tooth structure or collagen, with
NaOCl solutions, could increase the severity of the
surface attack on the instrument [13]. Stokes et al. [6]
evaluated the corrosive effect of 5.25% NaOCl on
stainless steel and Ni-TI files using five commercial
brands. They reported that both the corroding and
non-corroding files were present in the same packages. Those results showed that the severity of corrosive changes could also depend on manufacturing
process and quality control.
CONCLUSION
The results of this study indicated that 5.25%
NaOCl and 0.2% CHX, used as root canal irrigants,
cause severe corrosion on the surface of the Ni-Ti
and stainless steel endodontic files. The use of EDTA
did not cause corrosion of the surface of both types of
instruments. Due to the possibility of corrosion acting
to deteriorate endodontic instruments, irrigants should
be rinsed from files immediately after use and files
should be replaced frequently.
Acknowledgement
This work has been supported by the grant No.
175102 of the Serbian Ministry Education, Science
and Technological Development.
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
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[8]
Y. Shen, G.S. Cheung, B. Peng, M. Haapasalo, J. Endod.
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[9]
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[10]
A.A. Yahya, K.W. Majida, AL-Hashimi, J. Bagh. College.
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[11]
G. Spagnuolo, G. Ametrano, D. D’Antò, C. Rengo, M.
Simeone, M. Riccitiello, M. Amato, Int. Endod. J. 45
(2012) 1148–1155
[12]
G. Radenković, S.K. Zečević, Z. Cvijović, D.M. Dražić, J.
Serb. Chem. Soc. 60 (1995) 51-59
[13]
H.J. Mueller, J. Endod. 8 (1982) 246-252
[14]
I. Heling, I. Rotstein, T. Dinur, Y. Szwec-Levine, D. Steinberg, J. Endod. 27 (2001) 278-280
[15]
S. Stojicic, S. Zivkovic, W. Qian, H. Zhang, M. Haapasalo, J. Endod. 36 (2010) 1558-1562
[16]
E. Berutti, E. Angelini, M. Rigolone, G. Migliaretti, D.
Pasqualini, Int. Endod. J. 39 (2006) 693-699
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H. Katayama, M. Yamamoto, T. Kodama, Corros. Eng. 49
(2000) 41-44
[18]
N.K. Sarkar, W. Redmond, B. Schwaninger, A.J. Goldberg, J. Oral. Rehabil. 10 (1983) 121-128
[19]
A. Busslinger, B. Sener, F. Barbakow, Int. Endod. J. 31
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[20]
L.R.L. Aboud, F. Ormiga, J.A.C.P. Gomes, Int. Endod. J.
47 (2014) 155-162
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48 (2015) 137-144
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J. Gasic, J. Popovic, S. Zivkovic, A. Petrovic, R. Barac,
M. Nikolic, Microsc. Res. Tech. 75 (2012) 1099-1103
[23]
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[24]
M. Hülsmann, M. Heckendorff, A. Lennon, Int. Endod. J.
36 (2003) 810-830
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D.M. Fayyad, A.H. Mahran, Int. Endod. J. 47 (2014) 567–573
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[2]
D.M. Öztan, A.A. Akman, L. Zaimoglu, S. Bilgiç, Int.
Endod. J. 35 (2002) 655-659
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G. Reinhard, M. Radtke, U. Rammelt, Corros. Sci. 33
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M. Darabara, L. Bourithis, S. Zinelis, G.D. Papadimitriou,
Int. Endod. J. 37 (2004) 705–710
M.A. Saghiri, F. Garcia-Godoy, M. Lotfi, P. Mehrvazfar,
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(2012) 309-315
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K. Sood, B. Mohan, L. Lakshminarayanan, Endodontology 18 (2006) 34-41
X.R. Nóvoa, B. Martin-Biedma, P. Varela-Patiño, A. Collazo, A. Macías-Luaces, G. Cantatore, M.C. Pérez, F.
Magán-Muñoz, Int. Endod. J. 40 (2007) 36–44
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W.O. Stokes, M.P. Di Fiore, T.J. Barss, A. Koerber, L.J.
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99
J. POPOVIĆ et al.: THE EXAMINATION OF SENSITIVITY TO CORROSION…
JELENA POPOVIĆ1
GORAN RADENKOVIĆ2
JOVANKA GAŠIĆ1
SLAVOLJUB ŽIVKOVIĆ3
ALEKSANDAR MITIĆ1
MARIJA NIKOLIĆ1
RADOMIR BARAC1
1
Odeljenje za bolesti zuba i
endodonciju, Klinika za
stomatologiju, Medicinski fakultet,
Univerzitet u Nišu, Niš, Srbija
2
Katedra za proizvodno-informacione tehnologije i
menadžment, Mašinski fakultet,
Univerzitet u Nišu, Niš, Srbija
3
Klinika za bolesti zuba i
endodonciju, Stomatološki fakultet,
Univerzitet u Beogradu, Beograd,
Srbija
NAUČNI RAD
Chem. Ind. Chem. Eng. Q. 22 (1) 95−100 (2016)
ISPITIVANJE OSETLJIVOSTI ENDODONTSKIH
INSTRUMENATA OD NIKL-TITANIJUMA I
NERĐAJUĆEG ČELIKA NA KOROZIJU U
RASTVORIMA ZA IRIGACIJU KANALA
KORENA ZUBA
Primena sredstava za irigaciju kanala korena zuba je od suštinskog značaja u endodontskoj terapiji. Međutim, hemijska i elektrohemijska agresivnost ovih rastvora, koji
direktno deluju na instrumente, može oštetiti njihovu površinu. Cilj istraživanja je bilo
ispitivanje osetljivosti endodontskih turpija od nerđajućeg čelika i nikl-titanijuma (Ni-Ti) na
koroziono delovanje natrijum-hipohlorita (NaOCl), hlorheksidin-glukonata (CHX) i etilendiamin tetrasirćetne kiseline (EDTA). Ispitivanje otpornosti instrumenata na koroziju je
izvedeno potenciodinamičkom metodom. Merenje je izvedeno u rastvorima 5,25% NaOCl,
0,2% CHX i 17% EDTA. Najintenzivnije korozione promene i najnižu vrednost piting
potencijala od 1.1 V su pokazali Ni-Ti instrumenti potapani u 5,25% NaOCl. Višu vrednost
piting potencijala od 1.5 V su pokazali instrumenti od nerđajućeg čelika posle potapanja u
5,25% NaOCl. Manji intenzitet korozionih promena i piting potencijal od 1.6 V pokazali su
instrumenti od nerđajućeg čelika potapani u 0,2% CHX, dok su Ni-Ti instrumenti potapani
u 0,2% CHX pokazali vrednost piting potencijala od 1.9 V. Korozija nije zapažena kod obe
vrste instrumenata nakon potapanja u 17% EDTA. Primena 5,25% NaOCl i 0,2% CHX
može izazvati ozbiljnu koroziju površina endodontskih turpija od nerđajućeg čelika i
nikl-titanijuma.
Ključne reči: korozija, irigacioni rastvori, nikl-titanijum, nerđajući čelik, endodontski instrumenti.
100
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
O.S. GLAVAŠKI1
S.D. PETROVIĆ2
V.N.
RAJAKOVIĆ-OGNJANOVIĆ3
T.M. ZEREMSKI1
A.M. DUGANDŽIĆ2
D.Ž. MIJIN2
1
Institute of Field and Vegetable
Crops, Novi Sad, Serbia
2
Faculty of Technology and
Metallurgy, University of Belgrade,
Belgrade, Serbia
3
Faculty of Civil Engineering,
University of Belgrade, Bulevar
Belgrade, Serbia
SCIENTIFIC PAPER
UDC 543.544:632.954:66
DOI 10.2298/CICEQ150608025G
CI&CEQ
PHOTODEGRADATION OF DIMETHENAMID-P
IN DEIONISED AND GROUND WATER
Article Highlights
• Photocatalytic degradation of dimethenamid-P herbicide is presented
• Degradation was studied in deionised and ground water under different conditions
• Photocatalytic degradation of dimethenamid-P is much faster in ground water
• HPLC showed almost complete removal of herbicide after 90 min in both water
• TOC showed herbicide was mineralized 64% in deionised and 50% in ground water
Abstract
The study of photodegradation of dimethenamid-P herbicide was performed in
deionised and ground water using TiO2 as a catalyst under UV light. The effect
of electron acceptor (H2O2), scavenger of •OH radicals (C2H5OH) and scavenger of holes (NaCl and Na2SO4) as well as solution pH was analyzed. The
photodegradation of dimethenamid-P was followed by HPLC. The formation of
transformation products was followed using high performance liquid chromatography-electrospray mass spectrometry. Ion chromatography and total organic
carbon measurements were used for the determination of the mineralization
level. HPLC analysis showed the almost complete removal of herbicide after
90 min in deionised and ground water, while total organic carbon analysis
showed that dimethenamid-P was mineralized 64 and 50% in deionised and
ground water, respectively. The ion chromatography results showed that the
mineralization process leads to the formation of chloride, sulphate and nitrate
anions during the process. Transformation products were identified and the
degradation mechanism was proposed.
Keywords: salt effect; ion chromatography; liquid chromatography-electrospray mass spectrometry; photocatalysis; titanium dioxide.
Modern agricultural production in the last decade involves the use of pesticides to a large extent.
Dimethenamid-P (2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl) acetamide, DMA-P)
belongs by its chemical properties and structure to
the group of chloroacetamides and plays an important
role in the crop protection of broadleaf weeds and
annual grasses in row crops [1], primarily in corn,
soybean and sorghum [2]. These components include
highly toxic and persistent substances and due to
exceptional reactivity threaten to jeopardize the aquatic environment through agricultural circle and washing [3-5]. The European Union has stipulated that the
Correspondence: D.Ž. Mijin, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade,
Serbia.
E-mail: kavur@tmf.bg.ac.rs
Paper received: 8 June, 2015
Paper revised: 6 July, 2015
Paper accepted: 8 July, 2015
levels of pesticides in drinking water should not
exceed 0.1 mg dm-3 for the individual components,
i.e., for some of their transformation products concentration should not exceed 0.5 mg dm-3 [6]. Within the
strategy of protection of environmental resources,
heterogeneous photocatalysis has proved to be one
of the most effective techniques for the degradation of
organic pollutants [7]. It involves fotoinduction reaction accelerated by a solid catalyst [8].
TiO2 as a photocatalytic semiconductor is the
most suitable chemical compound for removal of
harmful substances from the environment by photocatalytic process. Its chemical inertness, stability to
the photo and chemical corrosion, as well as low price
are its advantages as a catalyst [9]. Photocatalytic
degradation is based on the irradiation of UV light,
which results in the generation of oxidative species
that are characterized by high and non-selective reactivity, so they can easily attack and decompose the
101
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
molecules of organic pollutants. Photon has energy
which is greater or equal to the band gap energy of
semiconductor (TiO2). In that way electron (e–) from
the valence band (VB) excitates to the conduction
band (CB), leaving a positive hole (h+) behind. The
energy level at the bottom of the valence zone effectively reduces the potential of photoelectrons, while
the peak energy of the valence zone creates its ability
to oxidize. Electrons and cavities migrate to the surface of the catalyst and reduce species present on its
surface. Photogenerated cavities may oxidize organic
molecules or react with OH−, or H2O, oxidising them
to •OH. Photogenerated electrons can also react with
oxygen, translating it into superoxide anion O2−• radical. This reaction leads to additional formation of •OH.
These radicals as very strong oxidative agents having
the ability to oxidize organic pollutants adsorbed on
the surface of TiO2 to mineral products [10]. Redox
reactions including photons can be presented by Eqs.
(1)-(5):
TiO2 + hν(UV) → TiO2(e−CB + h+VB)
TiO2(h
+VB
TiO2(e
−CB
•−
+
•
) + H2O → TiO2 + H + OH
) + O2 → TiO2 + O2
+
O2 + H → HO2
•−
•
HO2• + H+ + TiO2(e−CB) → H2O2 + TiO2
(1)
(2)
(3)
(4)
(5)
Conclusively, photocatalytic degradation of pesticides can be presented in simplified form by Eqs.
(6)-(8):
Pesticide + h+VB → oxidation products
Pesticide + e
−CB
→ reduction products
Pesticide + •OH → transformation products
(6)
(7)
(8)
In order to get higher yield, agriculture relies on
the application of pesticides. The negative effects of
pesticides on the quality of ground and surface water
are well known [5]. The environmental issues concerning pesticides comprehend: inadequate control of
the usage (excessive concentrations of pesticides),
non-biodegradability, long decomposition time and
high mobility in different eco-systems. Dimethenamid-P belongs to the group of chloroacetamides which
are persistent organic pollutants. Its specific feature is
the migration from the soil to the ground and groundwater [2].
In this work, the study on the photocatalytic
behavior of DMA-P in aquatic environment is presented for the first time. the influence of various parameters on the photocatalytic process, such as the initial concentration of catalyst, initial DMA-P concentration, the concentration of added H2O2, C2H5OH,
102
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
NaCl, and Na2SO4 as well as pH value of water solution in two different types of water (deionised and
ground water) were studied. HPLC/MS (high performance liquid chromatography-electrospray mass spectrometry) were applied for qualitative identification of
transformation products.
EXPERIMENTAL
Materials
DMA-P (purity higher than 99%) was supplied
by Riedel de-Haen (Seelze-Hannover, Germany).
Titanium dioxide (TiO2) labeled as P25 supplied by
Evonik was used in experimental part of the work. All
other chemicals were p.a. or higher grade. Deionized
water (DW) was obtained from a Millipore water purification system. Ground water (GW) was obtained
from public-utility company Water supply and sewage
treatment in Novi Sad, as alluvium of Danube. The
ground water contains 269.6 mg dm-3 of HCO3−/CO32–,
57.5 mg dm-3 of SO42−, 20 mg dm-3 of Cl–, 1.496 mg
dm-3 of NO3–, 0.343 mg dm-3 of Mn2+, 0.600 mg dm-3
of NH3, 84 mg dm-3 of Ca2+, 17.5 mg dm-3 of Mg2+ and
2.810 mg dm-3 of Fe (total). Conductivity of deionized
and ground water was 0.55 and 58.5 µS cm–1 while
pH was 5.9 and 7.20, respectively.
Photocatalytic experiment
The photodegradation of DMA-P was investigated in two different types of water, in the deionised
and ground water, with pesticide concentration of
34.5 mg dm-3. All the reactions were performed in an
open reactor, thermostated at 25 °C [11]. For the
irradiation an Osram Ultra Vitalux® 300 W lamp was
used, with ratio of UV-A and UV-B lights 13.6:3. The
position of lamp was 40 cm from the surface of the
reaction mixture. The temperature of solution
changed for 2 °C after 90 min of irradiation. For every
experimental cycle 25 cm3 of the solution was placed
into the reactor and stirred for 30 min in the dark.
Continuous stirring was maintained during the reaction. The aliquots were taken at defined time intervals
(after 10, 20, 30, 60 and 90 min from the beginning of
the reaction). All the aliquots were filtrated by 0.45 μm
Cronus 13 mm Nylon Syringe filters, in order to remove the suspended TiO2 particles before the analysis.
All the experiments were done in triplicate.
Analytical procedures
During 90 min of irradiation time, the samples
were taken from the suspension. The concentration of
herbicide was determined by HPLC (high performance liquid chromatography) analysis. All analysis
were performed at room temperature.
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
The HPLC determinations were carried out with
HPLC instrument Agilent 1100 Series equipped with
Zorbax Eclipse XDB-C18 (Agilent). The analyses
were performed in isocratic mode using water/methanol/acetic acid (200:300:5 V/V/V), the mobile phase
had flow rate of 0.8 cm3 min-1 and the column temperature was 25 °C. The injection volume was 5 μL and
UV detection was carried out at 240.4 nm.
The pH value of the samples was adjusted by
the addition of 0.1 mol dm-3 NaOH or HCl and the
determination of pH value was performed on pH
metar Inolab pH 730 (Germany).
The chromatographic separations were followed
by an MS analyzer, Hypersil Gold Thermo Scientific
(Bremen, Germany) (50 mm×2.1 mm, 3 mm particle
size) termostated at 25 °C using a Thermo survey
(USA) HPLC instrument. Injection volume was 50 μL
and flow rate was 0.2 cm3 min-1. The mobile phases
were: A (0.10% acetic acid/99.9% water) and B
(0.10% acetic acid/99.9% acetonitrile). The analyses
were performed in isocratic mode. A LCQ Deca mass
spectrometer equipped with an atmospheric pressure
interface and an ESI ion source was used as a detector. The LC column effluent was delivered into the
ion source using nitrogen as sheath and auxiliary gas.
The tuning parameters adopted for ESI source were:
capillary voltage 45 V, capillary temperature 275 °C,
spray voltage 6 kV and gas flow was 20 arbitrary
units. The analysis was performed in positive ion
mode. Mass spectra were recorded across the range
100–400 m/z.
Ion chromatographic (IC) analysis was performed on a Dionex DX-300 ion chromatograph at
ambient temperature (25 °C) with a suppressed conductivity detector. Ion chromatograph was equipped
with a Dionex IonPac AS14 column.
Total organic carbon (TOC) was measured
using a Zellweger LabTOC 2100 instrument.
RESULTS AND DISCUSSION
Preliminary experiments
In the beginning of the photocatalytic study,
three different experiments have been carried out in
aqueous environmental matrices with the aim to
evaluate adsorption and photolysis of the studied
DMA-P. These experiments were conducted under
the following conditions:
a) investigation of DMA-P adsorption on the
TiO2 in the dark (Ckat: 2.0 g dm-3, C(DMA-P) 0: 34.5 mg
dm-3, V: 25 cm3, T: 25 °C),
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
b) investigation of DMA-P degradation under
UV light, in the absence of TiO2 (photolysis) (C(DMA-P) 0:
34.5 mg dm-3, V: 25 cm3, T: 25 °C),
c) heterogeneous photocatalysis of DMA-P solution under UV light and a catalyst (Ckat: 2.0 g dm-3,
C(DMA-P) 0: 34.5 mg dm-3, V: 25 cm3, T: 25 °C).
DMA-P concentrations have not changed significantly in the case of adsorption and photolysis.
The results of the adsorption experiment show slight
decrease in herbicide concentration (less than 5%)
during a period of 90 min, indicating only slight adsorption on the TiO2 surface. Photolysis results show
insignificant fall of the initial concentration of DMA-P.
On the other hand, photocatalysis shows almost complete destruction of this active substance (more than
99% determined by HPLC) both in deionised and
ground water. The comparison of photocatalysis and
adsorption processes implies that stirring of suspension for 30 min in the dark prior to the photocatalysis
process is an important step for reaching the adsorption equilibrium [9].
To determine the optimum concentration of TiO2
for the photodegradation of DMA-P, experiments
were conducted by varying the initial concentration of
TiO2 from 0.5 to 3.0 g dm–3, while keeping other parameters constant. It was found out that the maximum
removal efficiency of the chloroacetamide has been
achieved with the catalyst concentration of 2.0 g dm–3,
and, therefore, this concentration of TiO2 has been
selected as the optimum one. Further increase of the
catalyst concentration decreases the rate of photodegradation, and reduces the efficiency of degradation process. Theoretically, the increase of the catalyst concentration above an optimum value should
not have effect on the photodegradation rate since all
the light available is already utilized. However, higher
mass concentrations of TiO2 Evonik P25 led to the
aggregation of its particles and thus to a decrease of
contact surface between the substrate and the photocatalyst. This caused a decrease in the number of
active sites and a lower rate of photodegradation.
When the concentration of catalyst is exceeded, a
part of the UV light is not utilized because of the
increased turbidity of solution and increased light
scattering by the photocatalyst particles, and therefore the overall performance decreases [12].
Initial concentration of DMA-P affects the rate of
its photocatalytic degradation. The increase of the
initial substrate concentration on the catalyst surface
number of molecules/ions that react with •OH increases and the rate of degradation decreases. The
increase of the initial substrate concentration above
an optimum value leads to the decrease of the effi-
103
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
ciency of the photocatalytic process. the substrate
molecules may adsorb on the catalyst surface instead
of OH– and water molecules, which then result in the
generation of fewer •OH [7,9]. But since very small
adsorption was observed, the reduced photoactivity of
semiconductor may be due to the absorbtion of light
by organic molecules [13].
The effect of the pH value
The influence of pH value on the photocatalytic
degradation can be explained by electrostatic interactions between the surface of TiO2, solvent molecules, substrate and electrically charged radicals
formed during the process. At pH values above the
value of point of zero charge (PZC) of TiO2 (6.8), the
surface will remain negatively charged. For pH < PZC
the surface will remain positively charged [14]. For the
influence of pH value on the photocatalytic degradation five different pH values were analyzed. The
adjustments of acidic medium (pH 2.0 and 4.0) and
alkaline medium (pH 9.0 and 11.0) were made with
diluted HCl or NaOH. Before any adjustments the pH
value of pesticide solution in DW and GW was measured and the obtained values were 6.33 and 7.34 for
DW and GW, respectively. The photocatalytic degradation rate of DMA-P in DW and GW as a function of
pH value is shown in Figure 1. Lower degradation
rate for both aqueous media was at pH values near to
PZC. The possible explanation for this phenomenon
is the fact that the TiO2 particles tend to agglomerate
and thus decrease the yield of degradation. As reported, at pH values equal to the PZC, aggregate particles are larger, and number of active sites on the
catalyst surface is decreased and degradation rate
reduced [15,16].
Figure 1. The effect of pH value on the photocatalytic
degradation rate of DMA-P (34.5 mg dm-3) in deionised and
ground water (ccat 2.0 g dm-3).
104
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
The difference in DMA-P degradation rate
caused by the change of pH value was more significant in ground than in the deionised water. The
reaction rate in ground water is decreased in neutral
and in the alkaline medium and pH has an insignificant effect on the rate of degradation in deionised
water. The explanation for the effect of pH on the
photocatalytic reaction might be in the influence of
electrically charged surface of the TiO2 on the physical and chemical properties of the parent molecule.
Although DMA-P molecule is electrically neutral it can
be repulsed from the negatively charged surface of
the photocatalyst at pH value above 6.8 due to
unequal distribution of electron density in the substrate molecule when electronegative atom like Cl is
present [4].
The disappearance rate in the process of photocatalytic degradation can be described by a pseudofirst kinetic order, as shown by Eqs. (9) and (10):
C 
ln  0  = kt
C 
C = C 0e −kt
(9)
(10)
where C is the concentration of DMA-P at irradiation
time t, and C0 is the initial concentration of DMA–P.
The effect of the addition of electron acceptor
When TiO2 is used as a photocatalyst, one of
the problems that arise is the recombination of the e–h+
pair. This problem is particularly apparent in the absence of appropriate electron acceptors which also
reduces the efficiency of photocatalytic reaction [17].
In order to enhance the formation of •OH and inhibit
e–h+ pair recombination, the effect of addition of H2O2
as an electron acceptor on the efficiency of photodegradation has been investigated in a number of experiments conducted in both deionised and ground
water [17,18]. In this study, a series of experiments
has been carried out in both media. The obtained
results have shown that for H2O2 concentration of up
to 0.005 mol dm-3 the reaction time is increased by 2
times in deionised water and by 1.6 times in ground
water (as shown in Figure 2). This may be due to the
increased concentration of •OH. Faster degradation
rate in the presence of H2O2 may be attributed to the
generation of •OH and OH– in the presence of UV
radiation, and not to the formation of less powerful
O2•- oxidant by the reduction of O2 [19]. At higher
concentrations (above 0.005 mol dm-3), H2O2 acts as
a “scavenger” of •OH and holes on the catalyst
surface, leading to the formation of HO2• that react
with •OH to generate oxygen and water as illustrated
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
by Eqs. (11) and (12). As the result, the efficiency of
photocatalytic degradation is reduced.
H2O2 + •OH → HO2• + H2O
+
•
+
H2O2 + h → HO2 + H
(11)
(12)
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
the inhibition of catalytic degradation is more pronounced in ground water where gradual addition of
ethanol (up to 0.8 mol dm-3) decreases the reaction
rate 15 times, while in deionised water the reaction
rate decreases 3 times under the same conditions.
According to some researchers, if reaction products, such as oxygen and H2O2 are not present near
the surface of TiO2, electron-hole pairs recombine
and adsorbed energy is dissipated as heat. H2O2
added in smaller concentrations is able to prevent this
reaction [4].
Figure 3. The effect of the added of C2H5OH on the
photocatalytic degradation rate of DMA-P (34.5 mg dm-3) in
deionised and ground water (ccat 2.0 g dm-3).
The effect of the inorganic ions
Figure 2. The effect of the added H2O2 on the photocatalytic
degradation rate of DPA-P (34.5 mg dm-3) in deionised and
ground water (ccat 2.0 g dm-3).
The effect of the •OH scavenger
To confirm and to prove if heterogeneous photocatalysis is taking place through •OH, the effect of
ethanol added in the reaction mixture containing
DMA-P and TiO2 Evonik P25 on the reaction rate has
been investigated in both deionised and ground water
(Figure 3). It was determined that as the ethanol concentration increases, the degradation rate decreases,
compared with the same reaction without addition of
this solvent. The obtained result is in agreement with
previous research from this field [20]. In the same
research the effect of various solvents on the photocatalytic degradation of benzidene yellow was studied. The results showed that the degradation efficiency decreases with the addition of solvents in the
following order: hexane < acetonitrile < 2-propanol <
< 1-butanol < 2-methyl-2-propanol. The obtained
results confirm that alcohols are good •OH scavengers and the products of reaction are weaker oxidants
(alkoxy-radicals) that react with the substrate. The
results obtained in the present study also show that
When comparing the results of the rate of photocatalytic degradation of DMA-P in two types of water,
the great difference can be noticed. The rate of
decomposition of DMA-P in ground water is two times
faster than in deionised water. This could be ascribed
to the presence of nitrate ions. Reaction of nitrate
ions with photons ends with hydroxyl radicals according to the Eqs (13)-(15) [21]:
NO3– + hν → NO2– + O
(13)
NO3– + hν → NO2• + O•–
(14)
•–
•
•
O + H2O → OH + OH
(15)
Taking into account the fact that groundwater
from the Danube alluvium is slightly alkaline it can be
expected that hydroxyl radicals formed together with
photogenerated oxidative species generated with the
irradiated TiO2, have higher degradation rates of
DMA-P. Chen et al. [21] reported that NO3– as
constituents found in natural waters absorb solar
radiation in UV range less than 350 nm with maximum at 302 nm. Photolysis of these anions leads to
formation of •OH under influence of UV radiation, as
shown by Eqs (13)-(15).
Ground water also contains dissolved metal
ions, such as Fe3+, Mn2+, Ca2+ and Mg2+. Wei et al.
indicated another possible explanation for the differ-
105
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
ences observed in the kinetics of the process taking
place in these two aqueous media [22]. The effect of
Fe3+ on the photodegradation efficiency of metamidophos was studied by varying amount of Fe3+ from
0.001 to 0.8 mmol dm-3. The results showed that
when higher Fe3+ concentrations were added (up to
0.5 mmol dm-3) its photodegradation efficiency increased rapidly (from 37.3 to 55.0%). When the concentration of this cation exceeds this value, photodegradation efficiency is greatly reduced. It has been
concluded that positively charged Fe3+ absorbed on
surface of the TiO2 are more easily reduced (Fe3+ + e–
→ Fe2+) thus decreasing electron-hole pair recombination. This favours the formation of •OH and O22– on
the surface of the TiO2. The following reactions occur
at the same time:
Fe2+ + H2O2 + H+ → Fe3++ •OH + H2O
2+
•
+
3+
Fe + HO2 + H → Fe + H2O2
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
Cl– + h+ → Cl•
–
(18)
•
Cl + OH → ClOH
•–
•–
(19)
•
+
ClOH + H → Cl + H2O
•
–
Cl + Cl → Cl2
(20)
•–
(21)
SO42– + h+ → SO4•2–
2–
•
•–
(22)
-
SO4 + OH → SO4 + OH
•–
–
SO4 + eCB → SO4
2–
(23)
(24)
(16)
(17)
It has also been shown that the presence of Na+,
K+, Ca2+ and Mg2+ has no effect on the photodegradation rate. This is explained by the fact that these
ions are in their most stable oxidation state and as
such they do not show affinity for bonding photogenerated electrons and holes [23].
Physicochemical composition of groundwater
indicates the presence of HCO3–. When investigating
the previous studies the effects of HCO3– on the rate
of photocatalytic degradation, showed that concentrations above 0.1 mol dm-3 lead to reduced photodegradation efficiency due to the formation of greater
number of CO3•- radical-ions which are less reactive
than •OH [24]. However, in ground water where pH is
slightly alkaline, HCO3- are present to a greater extent
than CO32- and their concentration in this medium is
below 0.05 mol dm-3, being, according to the findings
of Lair et al., the most probable explanation for increased efficiency of herbicide degradation [25].
The effect of the added salts
In addition, the salt effect on the reaction rate
(Figure 4) was studied, using NaCl and Na2SO4. The
salts were used at concentrations of 20 and 200 mmol
dm-3, for each of the added salts. As can be seen from
Figure 4, the photodegradation reaction is slower in the
presence of salts in deionized water. Sodium chloride
proved to be the stronger inhibitor than sodium sulfate. While chloride ions have hole scavenging properties, sulfate anions react with positive holes and
hydroxyl radicals [26,27]. There is also a competitive
adsorption between DMA-P and chlorides and/or sulfates [24]. These influences can be described by the
Eqs. (18)-(24) [7,26–29]:
106
Figure 4. Effect of salt on the photocatalytic degradation of
DMA-P (34.5 mg dm-3) in the presence of TiO2 (ccat 2.0 g dm-3)
in deionized water (A) and ground water (B).
Chloride ions inhibit photocatalytic degradation
in both of analyzed waters, deionized and ground
water. The inhibitor effect of these anions can be explained through electrostatic interactions between surface of photocatalyst and anions. In acidic solution
surface of photocatalyst is positively charged and
attracts anions, which has influence on the reduced
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
adsorption of molecules of DMA-P and intermediates
and therefore reduced rate of degradation process
and mineralization. In alkaline solutions such adsorption would be unlikely because of repulsive electrostatic forces [24]. Sulfate ions inhibit photocatalytic
degradation in deionized water (at mildly acidic solution, for pH 6.33), which can be explained by the
same inhibitor effect as for chloride ions. In ground
water (in mild alkaline solution, for pH 7.34) these
anions increase rate of the degradation process
which can be explained by oxidative ability of sulfate
anions radicals. Although the sulfate anion radical is
less reactive than •OH, it may oxidize the DMA-P molecule. At mild alkaline pH, both SO4•− and •OH are
responsible for the degradation of DMA-P [24].
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
The results lead to the conclusion that the formation rates of Cl–, SO42– and NO3– are slower compared
to the degradation rate of DMA-P, and indicate the
formation of intermediates that contain chlorine, sulphur and nitrogen.
The mineralization of DMA-P was studied by the
total organic carbon analysis. For the period of 90
min, the TOC elimination was 64% in deionised water
and 50% in ground water (Figure 6). This indicates
that the TOC removal rate was not proportional to the
rate of DMA–P photodegradation and also confirms
the formation of the organic intermediates.
Results of total organic carbon elimination and ion
chromatography
The results of ion chromatography (shown in
Figure 5) and TOC analysis have been used for the
determination of the mineralisation level of DMA-P.
Considering that the molecule of DMA-P contains one
atom of chlorine, nitrogen and sulphur, Cl-, SO42– and
NO3– may be separated after their complete mineralization. The degradation results in deionised water
show that after 90 min of degradation 95% of chlorine
is converted into chloride, while during the same
period of irradiation 23% of total nitrogen is converted
into NO3– and 8% of sulphur is converted into SO42–
ions. However, mineralisation of the DMA-P in ground
water is almost unnoticeable.
Figure 6. Time dependence of TOC concentration during the
photocatalytic degradation of DMA-P (34.5 mg dm-3) in
deionised and ground water (ccat 2.0 g dm-3).
Figure 5. Time dependence of inorganic ions (nitrates, sulphates and chlorides) concentration during the photocatalytic degradation of
DMA-P (34.5 mg dm-3) in deionised and ground water (ccat 2.0 g dm-3).
107
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
Results of HPLC/MS analysis
In order to identify intermediates formed during
the photocatalytic process, a qualitative analysis of
aliquot samples taken at various periods of degradation process was carried out. From the analysis of
the obtained peaks identified by the value of m/z
ratios, based on the molecular weight and the nature
of the chemical bond in the molecule of DMA-P, the
occurrence of transformation products can be confirmed, which is illustrated in Figure 7. The efficiency
of LC-MS hyphenated techniques for the characterization of various photodegradation [30,31] products
has been recently reported for chloracetamide herbicide acetochlor, which has similar structure as the
investigated dimethenamide-P.
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
At the end of the photodegradation reaction (90
min) only traces of DMA-P were detected. When
DMA-P was electrochemically degradated the major
degradation product was formed by C-N bond cleavage, while Cl elimination produced minor degradation
product [1].
CONCLUSION
The elimination of DMA-P from water with the
mediation of TiO2 has been studied for the first time in
this study. Under optimal conditions almost complete
disappearance of 34.5 mg dm-3 of herbicide (determined by HPLC) and 50% TOC removal, occurred
within 90 min in deionised and ground water, while
Figure 7. The degradation mechanism proposed for DMA-P photocatalytic degradation.
HPLC/MS analysis of the reaction mixture after
10 minutes of the photocatalytic degradation, revealed the presence of one degradation product with
m/z of 110.5. From the structural analysis of DMA-P it
can be assumed that the cleavage of C-N bond occurred (path I) and that the dimethylthiophenyl cation has
been formed, as shown in Figure 7.
The existence of ion fragment with m/z 262.1
may be explained by ordinary loss of CH3 group in
side chain of a parent molecule (II).
Another abundant degradation product was detected after 30 min of the photocatalytic degradation
with m/z 148.5 (III). the formation of this structure can
be explained by the following subsequent processes:
elimination of chlorine and then loss of ketene, followed by rearrangement and cyclization to obtain a
bicyclic product (Figure 7).
108
TOC analysis showed that DMA-P was mineralized
64 and 50% in deionised and ground water, respectively. The ion chromatography results showed that
the mineralization process leads to the formation of
chloride, sulphate and nitrate anions during the process. DMA-P degradation products were identified by
HPLC/MS analysis. They were formed by: C-N bond
cleavage (m/z 110.5), loss of CH3 group (m/z 262.1),
elimination of chlorine and ketene, followed by rearrangement and cyclization (m/z 148.5).
Acknowledgement
This work has been financially supported by
Ministry of Education, Science and Technological
Development, Republic of Serbia, under Grant No.
172013.
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
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Directive 2000/60/EC, EU Official Journal, 2000. L327,
Council Directive 2000/60/EC establishing a framework
for Community action in the field of water policy (Water
Framework Directive), pp. 1–73.
[7]
S. Ahmed, M.G. Rasul, R. Brown, M.A. Hashib, J.
Environ. Manage. 92 (2011) 311–330
[8]
N.A. Laoufi, F. Bentahar, Desalin. Water Treat. 52 (2014)
1947-1955
[9]
D.A. Lambropoulou, I.K. Konstantinou, T.A. Albanis, A.R.
Fernández-Alba, Chemosphere 83 (2011) 367-378
[10]
A. Verma, M. Sheoran, A.P. Toor, Indian J. Chem.
Technol. 20 (2013) 46-51
[11]
D. Mijin, M. Savić, S. Perović, A. Smiljanić, O. Glavaški,
M. Jovanović, S.D. Petrović, Desalination 249 (2009)
286-292
[12]
B. Abramović, S. Kler, D. Šojić, M. Laušević, T. Radović,
D.Vione, J. Hazard. Mater. 198 (2011) 123-132
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W.Y. Wang, Y. Ku, Colloids Surfaces, A 302 (2007) 261–
–268
109
O.S. GLAVAŠKI et al.: PHOTODEGRADATION OF DIMETHENAMID-P…
O.S. GLAVAŠKI1
S.D. PETROVIĆ2
V.N. RAJAKOVIĆ-OGNJANOVIĆ3
T.M. ZEREMSKI1
A.M. DUGANDŽIĆ2
D.Ž. MIJIN2
1
Institut za ratarstvo i povrtarstvo,
Maksima Gorkog 30, 21000 Novi
Sad, Srbija
2
Tehnološko-metalurški fakultet
Univerziteta u Beogradu,
Karnegijeva 4, 11120 Beograd,
Srbija
3
Građevinski fakultet Univerziteta u
Beogradu, Bulevar Kralja
Aleksandra 73, 11 000 Beograd,
Srbija
NAUČNI RAD
110
Chem. Ind. Chem. Eng. Q. 22 (1) 101−110 (2016)
FOTODEGRADACIJA DIMETANAMIDA-P U
DEJONIZOVANOJ I PODZEMNOJ VODI
Proučavanje reakcije fotodegradacije herbicida dimetanamida-P, izvršeno je u prisustvu
TiO2 kao katalizatora i pod dejstvom UV zračenja, u dejonizovanoj i podzemnoj vodi. Ispitan je uticaj koncentracije elektron-akceptora (H2O2), ″hvatača″ •OH radikala (C2H5OH) i
šupljina (NaCl and Na2SO4), kao i uticaj pH sredine na brzinu reakcije fotodegradacije.
Promena koncentracije dimetanamida-P praćena je pomoću HPLC. Nastajanje degradacionih proizvoda analizirano je pomoću HPLC/MS. Jonska hromatografija kao i metoda
određivanja ukupnog organskog ugljenika primenjene su u cilju određivanja nivoa mineralizacije herbicida. HPLC analiza je pokazala da se u toku 90 min herbicid skoro potpuno
uklanja u dejonizovanoj i podzemnoj vodi. Metodom određivanja ukupnog organskog
ugljenika utvrđeno je da se dimetanamid-P mineralizije 64% u dejonizovanoj, a 50% u
podzemnoj vodi. Jonska hromatografija je pokazala da pri degradaciji ispitivanog molekula
nastaju hloridni, sulfatni i nitratni anjoni. HPLC/MS analiza ukazala je da pri degradaciji
dolazi do raskidanja C-N veze (m/z 110,5), gubitka CH3 grupe (m/z 262,1), kao i do eliminacije hlora i ketena, praćene premeštanjem i ciklizacijom (m/z 148,5).
Ključne reči: uticaj soli; jonska hromatografija; tečna hromatografija-elektronsprej masena spektrometrija; fotokataliza; titan-dioksid.
Available on line at
Association of the Chemical Engineers of Serbia AChE
www.ache.org.rs/CICEQ
Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 111−115 (2016)
SONJA V. SMILJANIĆ1
SNEŽANA R. GRUJIĆ1
MIHAJLO B. TOŠIĆ2
VLADIMIR D. ŽIVANOVIĆ2
SRĐAN D. MATIJAŠEVIĆ2
JELENA D. NIKOLIĆ2
VLADIMIR S. TOPALOVIĆ2
1
University of Belgrade, Faculty of
Technology and Metallurgy,
Belgrade, Serbia
2
Institute for the Technology of
Nuclear and Other Raw Mineral
Materials, Belgrade, Serbia
SCIENTIFIC PAPER
UDC 666.1.031:66
DOI 10.2298/CICEQ150213031S
CI&CEQ
EFFECT OF La2O3 ON THE STRUCTURE AND
THE PROPERTIES OF STRONTIUM BORATE
GLASSES
Article Highlights
• Selected lanthanum-strontium-borate glasses were prepared by conventional melt-quenching technique
• The density and the molar volume were increasing with increasing La2O3 content
• Oxygen molar volume values were increasing opposite to oxygen packing density
values
• The HSM results were employed for obtaining the viscosity curves using VFT equation and GS
Abstract
The selected lanthanum-strontium borate glasses were prepared by a conventional melt-quenching technique. The compositions of the investigated glasses
were chosen to be: 5.7, 9.5, 14.3, 19.1 mol% for La2O3, 22.9, 19.1, 14.3, 9.5
mol% for SrO and 71.4 mol% for B2O3. The density, molar volume, oxygen molar
volume, oxygen packing density, oxygen/boron ratios and structural transformations in the glass network were investigated according to the substitution of SrO
by La2O3. The density and the molar volume increased in parallel with La2O3
content increase. Simultaneously, oxygen molar volume values increased while
the oxygen packing density values decreased. A hot stage microscope (HSM)
and a differential thermal analysis (DTA) were used to determine the characteristic temperatures. By increasing the content of lanthanum, the glass transition
temperatures, changed with the same trend as the molar volume. Glass stability
parameters were calculated from the temperatures obtained by DTA and HSM.
The HSM results were used to obtain the viscosity curves by applying the Vogel–Fulcher-Tamman (VFT) equation.
Keywords: glass, DTA, HSM, glass viscosity.
A growing interest recently has been focused on
alkaline earth-borate glasses due to their applications
as laser hosts, nonlinear optical and other photonic
devices [1]. The structure of vitreous B2O3 consists of
a random network of [BO3] triangles connected by
bridging oxygen at all three corners to form
completely linked network. The addition of a network
modifier in B2O3 glass could induce the conversion of
[BO3] triangles to [BO4] tetrahedra. This conversion of
boron from 3- to 4-fold coordination occurs only until
the network reaches some critical concentration of
tetrahedral coordinated boron, and is then followed by
Correspondence: S.V. Smiljanić, University of Belgrade, Faculty
of Technology and Metallurgy, Karnegijeva 4, Belgrade, Serbia.
E-mail: szdrale@tmf.bg.ac.rs
Paper received: 13 February, 2015
Paper revised: 27 June, 2015
Paper accepted: 8 July, 2015
a formation of non-bridging oxygen (NBO) caused by
additional network modifier [2]. Therefore in borate
glasses, the main structural units are both [BO3] triangles and [BO4] tetrahedra forming boroxol rings and
chains with different number of NBO [2].
The present study aims to characterize the
physical and structural properties of the selected lanthanum-strontium borate glasses. Glass compositions
for the synthesis were selected within the glass forming range of increasing content of La2O3, decreasing
content of SrO and constant content of B2O3. Also,
the goal of this work was to determine glass stability
and viscosity behavior of the selected glasses. The
physical and structural properties of the glasses were
investigated by measuring the densities of the glass
samples, and calculating the molar volume, oxygen
molar volume, oxygen packing density values and
111
S.V. SMILJANIĆ et al.: EFFECT OF La2O3 ON THE STRUCTURE…
ratios of oxygen to boron atoms [2,3]. Differential
thermal analysis (DTA) was applied to determine the
glass transition temperature, Tg, the crystallization
onset, Tx, and the crystallization peak temperature,
Tp. Hot stage microscope (HSM) was acquired for
estimation the temperatures of: the first shrinkage
(TFS), the maximum shrinkage (TMS), the deformation
(TD), the sphere TS, the half-ball temperature (THB)
and the flow temperature (TF). The glass stability (GS)
parameters were calculated on the basis of these
characteristic temperatures. Viscosity curves of the
glasses were set based on the results from the HSM
using the Vogel-Fulcher-Tamman (VFT) relation [4].
EXPERIMENTAL
The glasses with nominal composition yLa2O3–xSrO-(100-x-y)B2O3, where y = 5.7, 9.5, 14.3 and
19.1 and x = 22.9, 19.1, 14.3 and 9.5 (Table 1), were
melted in a covered platinum crucible in an electric
furnace and melted at 1200 °C for 30 min. The
reagent grade of H3BO3, SrCO3 and La2(CO3)3 were
used as raw materials, mixed and homogenized in an
agate mortar. Covered crucible and relatively short
melting time at relatively low temperature were
applied in order to minimize boron evaporation. The
melt was cast and cooled on a stainless steel plate in
air at room temperature. The measurements of the
weight loss due to the melting indicated that the glasses were within 1–2 wt.% of the desired compositions.
The obtained glasses were transparent without visible
bubbles.
Table 1. The glass compositions, density, molar volume, oxygen
molar volume and oxygen packing density
Glass sample
Parameter
1
2
3
4
La2O3, mol%
5.7
9.5
14.3
19.1
SrO, mol%
22.9
19.1
14.3
9.5
B2O3, mol%
71.4
71.4
71.4
71.4
ρ, g cm-3
3.21
3.25
3.56
3.66
28.65
30.90
31.21
33.26
Vo, cm mol
11.28
11.81
11.50
11.84
OPD, mol dm-3
88.68
84.70
86.95
84.45
O/B
1.78
1.83
1.90
1.97
Vm, cm3 mol-1
3
-1
The densities of the glasses were determined by
using the pycnometer method, with uncertainty ±0.01.
A hot-stage microscope (E. Leitz Wetzlar) equipped with a Cannon camera, and differential thermal
analysis (DTA) were used to determine the characteristic temperatures during the heating of the glass
powder. The samples were prepared by crushing and
112
Chem. Ind. Chem. Eng. Q. 22 (1) 111−115 (2016)
grinding the bulk glass in an agate mortar and sieving
to grain size < 0.048 mm. The DTA curves were
recorded by a Netzch STA 409 EP instrument at the
heating rate 10 °C min-1, using Al2O3 as a reference
material.
HSM analysis was performed on the previously
prepared glass powder pressed into cylinders, which
were placed on a platinum plate, on an alumina support, contacted with a (Pt/Rh/Pt) thermocouple. The
heating rate was 10 °C min–1. With temperature increase, the geometric shape of the samples changed.
Micrographs obtained were used to determine the
temperatures corresponding to the typical glass viscosity points [5-7]. Combination of the DTA and HSM
methods enabled determination of the GS parameters. The HSM results were applied to obtain viscosity
curves using the VFT relation [4,5].
RESULTS AND DISCUSSION
The densities (ρ) of the glass samples determined in the present study are shown in Table 1. The
molar volume (Vm) of the glass samples was calculated using the relative molecular mass (M) and density (ρ) by the following relation [8]:
Vm =
M
ρ
(1)
These values are included in Table 1 together
with the values of oxygen molar volume (Vo) and
oxygen packing density (OPD), calculated using the
following relations:
V 0 =V m
1
(2)
n
OPD = 1000
ρ
n
M
(3)
where n is the number of oxygen atoms per formula
unit.
The following equation, based on the glass stoichiometry, was used for the calculated number of
oxygen:
Number of oxygen = x + 3 y + 71.4
(4)
where x is mol% of the SrO, y is mol% of the La2O3
and 71.4 is constant content of the B2O3 in the
glasses.
The density and the molar volume of the glasses
increased in parallel with La2O3 content increase in
the glasses. The increase of the density could be
explained considering the higher relative molecular
mass of lanthanum oxide as compared to the relative
molecular mass of strontium oxide. With the increase
S.V. SMILJANIĆ et al.: EFFECT OF La2O3 ON THE STRUCTURE…
of La2O3 content in the glasses, the oxygen content
rises as well, increasing the molar volume of the
glass. The oxygen molar volume increases opposite
to the oxygen packing density with the increasing
La2O3 content in glasses, indicating a less tight packing of the glass network and more open glass network
[9]. The O/B ratios increased together with La2O3
content increase. The ratios of the O/B indicated the
presence of the metaborate structures, so the both
[BO3] triangles and [BO4] tetrahedra units are present
in the glass systems.
The characteristic temperatures obtained by HSM
and DTA measurements are summarized in Table 2.
Тhe Tg exhibits the same trend of the changes as of
Vo. The increase in the Tg could be attributed to the
greater bond strength of the La-O (244 kJ mol-1) bond
in comparison with the Sr-O bond (134 kJ mol-1). The
addition of the La2O3 increased the Tg, which can be
explained by higher field strength of La3+ (0.52 Å-2)
with respect to Sr 2+ (0.32 Å-2) [10]. The decline in the
Tg for the sample 3 could be explained by stoichiometry composition of this glass [11].
Chem. Ind. Chem. Eng. Q. 22 (1) 111−115 (2016)
maximum shrinkage (TMS) is the temperature where
the sample shrinks to the maximum possible level,
but still has sharp edges, before softening, at
viscosity log η = 7.8±0.1. The TD is the point of log η =
= 6.3±0.1 when the first signs of softening could be
observed and the edges of the samples are rounded.
The TS is the temperature at which the sample
becomes spherical, at log η = 5.4±0.1, whereas the
half-ball temperature (THB), at log η = 4.1±0.1, is the
temperature at which the observed section of the
sample forms a semicircle. The flow temperature (TF)
is the temperature at which the height of the drop of
molten glass corresponds to a unit on the microscopic
scale, at log η = 3.4±0.1 [5].
Table 2. Characteristic temperatures (°C) obtained by HSM and
DTA
Temperature
Glass sample
1
2
3
4
TFS
600
600
600
680
TMS
680
719
739
740
TD
700
720
760
760
TS
740
760
800
800
THB
840
900
1000
1050
TF
890
950
1020
1060
Tg
622
640
638
644
Tx
735
763
723
765
Tp
809
792
749
792
The photomicrographs for the glass sample 3,
obtained by HSM, with the graphs of the shrinkage
are shown in Figure 1 [11]. The shrinkage of the
samples is determined by the ratios of A/A0 and H/H0,
where A0 is the initial area of the sample whereas A is
the area at the temperature T, H0 is the initial height
and H is the height at the temperature T.
The temperatures corresponding to the typical
viscosity points were determined from the photomicrographs, by observing the geometric shape of the
specimens, obtained by HSM (Figure 1). The temperature of the first shrinkage (TFS) is the temperature at
the typical viscosity, log η = 9.1±0.1, where η is in
dPa·s. At this temperature the sample shrinks to
about 3-5% of its initial height. The temperature of the
Figure 1. The photomicrographs obtained by HSM with the
graphs of the shrinkage.
These temperatures obtained by DTA and HSM
were used to determine the GS parameters, the
Hruby parameter, KH, the Weinberg, KW, and the
parameter KLL proposed by Lu and Liu [12]. Within
this work, the used TF was determined by HSM.
The glass stability parameters are defined by
the equations:
T x −Tg
TF −T x
(5)
KW =
Tp −Tg
TF
(6)
K LL =
Tp
Tg +TF
(7)
KH =
The calculated parameters for the glasses are
shown in Table 3. The resistance of a given glass
against crystallization upon reheating defines GS.
High values of the parameters indicate high glass
stability, higher stability of the glass with respect to
113
S.V. SMILJANIĆ et al.: EFFECT OF La2O3 ON THE STRUCTURE…
Chem. Ind. Chem. Eng. Q. 22 (1) 111−115 (2016)
devitrification. The lowest values of the parameters
are related to the sample 3. This glass shows the
smallest GS and the highest tendency toward crystallization [11]. Increase of lanthanum content in the
glasses was followed with decrease of the GS.
for the glasses, log η = f(T) as shown in Figure 2 in
the upper left corner. The activation energy of the
viscous flow is obtained from the Arrhenius equitation,
from the slope of the log η = f (1/T) curves (Figure 2,
Table 4).
Table 3. Glass stability parameters
Table 4. VFT parameters and the activation energies of the viscous flow
Glass sample
1
KH
KW
KLL
0.73
0.21
0.53
Glass sample
Parameter
1
2
3
4
-3.30
-6.12
1.22
5103
11603
808
684
462
135
1142
365
340
297
543
2
0.66
0.16
0.50
3
0.29
0.11
0.45
A
-0.315
4
0.41
0.14
0.46
B
1780
T0 / K
Ea / kJ mol-1
The viscosity values of the glasses and VFT
parameters were determined based on the photomicrographs and the typical temperatures, obtained by
HSM:
logη = A +
B
T −T0
(8)
where η is viscosity in dPa·s, A, B and T0 (K) are
constants. These constants were obtained from Eq.
(8) by resolving a couple equations, using temperatures and viscosity values obtained by HSM (Table 4).
These equations are used to calculate the viscosity
CONCLUSION
The investigation of the physical properties of
the glasses showed that the substitution of SrO by
La2O3 increased the density, molar volume, oxygen
molar volume and decreased oxygen packing density.
The density increase was attributed to the higher relative molecular mass of the glass containing more
La2O3. The decrease of the oxygen packing density
indicated a less tightly packed the glass network. The
increase in the Tg could be attributed to the greater
Figure 2. Log η versus reciprocal temperature curves for the glass samples: a) 1, b) 2, c) 3 and d) 4.
114
S.V. SMILJANIĆ et al.: EFFECT OF La2O3 ON THE STRUCTURE…
Chem. Ind. Chem. Eng. Q. 22 (1) 111−115 (2016)
bond strength of the La-O (244 kJ mol-1) bond in
comparison to the Sr-O bond (134 kJ mol-1). Parallel
with lanthanum content increase, the GS decreased.
[4]
S. Samal, S. Kim, H. Kim, J. Am. Ceram. Soc. 95 (2012)
1595-1603
[5]
Acknowledgement
M.J. Pascual, A. Duran, M.O. Prado, Physis. Chem.
Glasses 46 (2004) 512-520
[6]
C. Lara, M.J. Pascual, M.O. Prado, A. Duran, Solid State
Ionics 170 (2004) 201-208
[7]
C. Lara, M.J. Pascual, A. Duran, J. of Non-Crys. Solids
348 (2004) 149-155
[8]
S. Bale, S. Rahman, A.M. Awasthi, V. Sathe, J Alloy
Compd. 460 (2008) 699-703
[9]
A. Goel, D.U. Tulyaganov, V.V. Kharton, A.A. Yaremchenko, J.M.F. Ferreira, Acta Mater. 56 (2008) 3065–3076
The authors are grateful to the Ministry of Education, Science and Technological Development of
the Republic of Serbia for the financial support (Projects 172004 and 34001).
REFERENCES
[1]
M. Kaur, O. P. Pandey, S. P. Singh, J. Non-Crys. Solids
358 (2012) 2589-2596
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J.E. Shelby, Introduction to Glass Science and Technology, The Royal Society of Chemistry, Cambridge, 2005
N. Sasmal, M. Garai, A.R. Molla, A. trafder, S.P. Singh,
B. Karmakar, J. Non-Crys. Solids 387 (2014) 62-70
[11]
[3]
S.V. Smiljanić, S.R. Grujić, M.B. Tošić, V.D. Živanović,
S.D. Matijašević, J.D. Nikolić, V. Topalović, Effect of
La2O3/SrO ratio on properties of La2O3–SrO–B2O3 glasses,
th
in Proceedings of 12 International Conference on Fundamental and Applied Aspects of Physical Chemistry,
Belgrade, Serbia (2014), Vol. II, pp. 667-670
S. Smiljanić, S. Grujić, M. Tošić, V. Živanović, J. Stojanović, S. Matijašević, J. Nikolić, Ceram Int. 40 (2014)
297-305
[12]
A. Kozmidis-Petrovic, J. Sestak, J. Therm. Anal. Calorim.
110 (2012) 997–1004.
SONJA V. SMILJANIĆ1
SNEŽANA R. GRUJIĆ1
MIHAJLO B. TOŠIĆ2
VLADIMIR D. ŽIVANOVIĆ2
2
SRĐAN D. MATIJAŠEVIĆ
JELENA D. NIKOLIĆ2
VLADIMIR S. TOPALOVIĆ2
1
Univerzitet u Beogradu,
Tehnološko-metalurški fakultet,
Karnegijeva 4, 11000 Beograd,
Srbija
2
Institut za tehnologiju nuklearnih i
drugih mineralnih sirovina, Bulevar
Franša d’Eparea 86, 11000
Beograd, Srbija
NAUČNI RAD
UTICAJ La2O3 NA STRUKTURU I SVOJSTVA
STRONCIJUM-BORATNIH STAKALA
Izabrana lantan-stroncijum-boratna stakla su dobijena uobičajenom tehnikom topljenja i
naglog hlađenja rastopa stakla. Sastavi ispitivanih stakala su: 5,7; 9,5; 14,3; 19,1 mol%
La2O3; 22,9; 19,1; 14,3; 9,5 mol% SrO i 71,4 mol% B2O3. Ispitivan je uticaj izmene SrO sa
La2O3 na: gustinu, molarnu zapreminu, molarnu zapreminu kiseonika, gustinu pakovanja
kiseonika, odnose kiseonik/bor kao i strukturalne transformacije u mreži stakla. Gustina i
molarna zapremina se povećavaju sa porastom sadržaja lantan-oksida. Primećen je trend
rasta molarne zapremine kiseonika dok gustina pakovanja kiseonika opada. Za određivanje karakterističnih temperatura korišćene su diferencijalna termijska analiza (DTA) i
termomikroskop (TM). Sa porastom sadržaja lantan-oksida temperature transformacije
stakla su se menjale na isti način kao i molarna zapremina. Parametri stabilnosti stakla
izračunati su na osnovu temperatura određenih TM i DTA. Na osnovu rezultata dobijenih
termomikroskopom postavljene se krive viskoznosti upotrebom Vogel-Fulcher-Tamman
(VFT) jednačine.
Ključne reči: staklo, DTA, TM, viskoznost stakla.
115
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Chemical Industry & Chemical Engineering Quarterly
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
MARIJA ŠLJIVIĆ-IVANOVIĆ
ALEKSANDRA MILENKOVIĆ
MIHAJLO JOVIĆ
SLAVKO DIMOVIĆ
ANA MRAKOVIĆ
IVANA SMIČIKLAS
University of Belgrade, Vinča
Institute of Nuclear Sciences,
Belgrade, Serbia
SCIENTIFIC PAPER
UDC 637.5’62:621:66.081
DOI 10.2298/CICEQ150323024S
CI&CEQ
Ni(II) IMMOBILIZATION BY BIO-APATITE
MATERIALS: APPRAISAL OF CHEMICAL,
THERMAL AND COMBINED TREATMENTS•
Article Highlights
• Apatite materials derived from bovine bones were studied as Ni(II) ions sorbents
• Raw bones were compared with chemically, thermally and chemically/thermally
treated samples
• Different sorption mechanisms were identified by sorption data and FT-IR spectra
analysis
• Combined chemical/thermal treatment produced material with the highest sorption
capacity
• Sorbed Ni(II) was very stable at low sorbent loads, while largely mobile at high
loadings
Abstract
Animal bones are a natural and rich source of calcium hydroxyapatite (HAP),
which has been found to be a good sorbent material for heavy metals and radionuclides. Various treatments can reduce the content of bone organic phase and
improve sorption properties. In this study, sorption capacities of raw bovine bones
(B) and samples obtained by chemical treatment with NaOH (BNaOH), by heating
at 400 °C (B400) and by combined chemical and thermal treatment (BNaOH+400),
were compared, using Ni(II) ions as sorbates. Maximum sorption capacities increased in the order B < BNaOH < B400 < BNaOH+400. Based on different sorption data
and FT-IR analyses, the mechanism of Ni(II) sorption was found to be complex,
with participation of both HAP and organic phase (when present). Sequential extraction analysis was applied for testing the stability of Ni(II) ions sorbed by
BNaOH+400. Majority of Ni(II) was found in residual phase (65%) at lower level of
sorbent loading, while with the increase of sorbent saturation carbonate fraction
became dominant (39%). According to the results, BNaOH+400 can be utilized in
water purification systems. As an apatite based material with low organic content
and high efficiency for Ni(II) sorption, it is also a good candidate for in situ soil
remediation, particularly at lower contamination levels.
Keywords: bovine bones, treatments, apatite, Ni(II), sorption, sequential
extraction.
Nickel is naturally occurring heavy metal, which
is in trace amounts essential for living organisms [1].
On the other hand, exposure to high nickel concentrations may cause various health effects, even death.
Correspondence: M. Šljivić-Ivanović, University of Belgrade,
Vinča Institute of Nuclear Sciences, P.O.Box 522, 11000
Belgrade, Serbia.
E-mail: marijasljivic@vin.bg.ac.rs
Paper received: 23 March, 2015
Paper revised: 20 June, 2015
Paper accepted: 8 July, 2015
th
•
Part of this paper was presented at the 12 International Conference on Fundamental and Applied Aspects of Physical
Chemistry, September 22-26, 2014, Belgrade, Serbia.
Single-dose oral lethality studies indicate that soluble
nickel compounds are more toxic than less-soluble
nickel compounds. Oral LD50 values of 46 or 39 mg
Ni per kg as nickel sulfate in male and female rats [2]
and 116 and 136 mg Ni per kg as nickel acetate in
female rats and male mice, respectively [3] have been
reported for soluble nickel compounds. In contrast,
the oral LD50 values in rats for less-soluble nickel
oxide and subsulfide were >3,930 and >3,665 mg Ni
per kg, respectively [2]. The concentration of nickel
and nickel compounds in the environment increases
due to anthropogenic activity. For example, this metal
is frequently found in industrial products such as
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M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
stainless steel, metal alloys, catalysts, rechargeable
batteries, and various products of common use, even
jewelry [4]. Moreover, long lived radioactive isotopes
59
Ni and 63Ni are frequent constituents of liquid radioactive waste [5]. Thus, the decontamination of wastewater streams containing Ni(II) ions is essential and it
can be conducted using different separation processes, including sorption onto selective and high
capacity materials. In addition to conventional sorbents, different waste products were considered for
Ni(II) removal like red mud [6], fly ash [7], tea factory
waste [8], animal bones [9], etc. It was shown that
utilization of waste products as sorbent materials can
be particularly a cost-effective way of wastewater
purification.
Animal bones are a natural source of hydroxyapatite (HAP), which has been found to be a suitable
matrix for heavy metal immobilization [10]. The studies on Ni(II) immobilization using synthetic hydroxyapatite [11,12], fluoroapatite [13] and apatite derived
from fish and animal bones [9,14], have been
reported so far. Thus, beside the synthetic apatites
and phosphate rocks, usage of biogenic apatite forms
represents one of the alternatives.
Raw animal bones contain 30-40% of organic
constituents, mostly fats and proteins (collagen).
Since the nanoparticles of HAP are well “packed” in
the organic matrix, specific surface area of bones is
extremely low [15]. Consequently, crushed, raw bones
were found to be poorer sorbents, compared to synthetic apatite forms [16,17]. In order to reduce organic
content, extraction of HAP has been carried out by
different chemical or physical treatments. Heating in
air atmosphere is one of the methods for decomposition of organic compounds. The influence of heating
temperature on bone physicochemical and sorption
properties has been investigated, and the optimal
temperature was found to be 400 °C [15,18]. At lower
temperatures organic phase was removed incompletely, while higher temperatures resulted in sintering of HAP nanoparticles and deterioration of sorption capacities.
Beside thermal decomposition processes, organic solvents such as ethanol and hexane have been
applied for fat tissue removal, while collagen degradation was studied using NaOH or H2O2 solutions [19].
The comparison of chemical agents efficiency has
revealed that highest capacity sorbent was obtained
using hot (60 °C) 0.1 mol L-1 NaOH solution [19].
Recently, the effects of various treatment conditions on bioapatite properties were compared [20].
Using experimental design methodology, the influence of five process variables was investigated. Type
118
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
of the chemical reagent (H2O2 or NaOH), concentration of the reagent (0.1 or 2 mol L-1), reaction temperature (20 or 60 °C), contact time (1 or 3 h) and
sample annealing (without or at 400 °C), were considered. By simultaneous variation of process variables between lower and higher level, materials with
different properties were obtained. Impact of treatment factors was compared by statistical analysis,
and it was concluded that annealing had predominant
influence on surface properties, as well as sorption
capacity towards Cd2+ [20].
Considering the results achieved so far, this
study aims to compare performances of bone sorbents obtained under conditions of chemical and thermal treatments that were found to provide the highest
sorption capacities [15,18-20]. In addition, synergistic
effect of both treatments, applied one after the other,
was tested and the results were compared with the
efficiency of raw, powdered bones. To evaluate sorption kinetics and maximum capacities, experiments
were conducted in wide ranges of initial Ni(II) concentrations and contact times. Various sorption data,
spectroscopic and sequential extraction analyses
were considered in order to get insight into the Ni(II)
sorption mechanisms.
EXPERIMENTAL
Preparation and characterization of the sorbents
At first, bovine femur bones, collected from the
butchers shop, were cleaned from meat and cut using
a circular saw. Pieces of approximate size 2-3 cm
were boiled three times for about 3 h in distilled water,
for the removal of fats. After drying at 80 °C, one part
of the material was left for the preparation of referent
(untreated) sorbent, whereas the remaining quantity
was exposed to different treatments. Thermally treated
sample (B400) was obtained by heating the obtained
residues at 400 °C, in the electrical oven for 4 h.
Chemically treated sample (BNaOH) was prepared by
mixing 50 g of boiled bones with 1 L of 2 mol L-1
NaOH, for 3 h, at 60 °C. The obtained suspension
was filtered on the Buhner funnel. Solid residue was
thoroughly rinsed with 2 L of distilled water and then
dried at 80 °C. Finally, the sample denoted as
BNaOH+400 was produced by applying previously described thermal treatment on the sample BNaOH. The
referent sorbent (B) and treated sorbents were powdered in an electric mill, and after sieving, the fraction
with particle size 45-200 μm was used for further
experiments.
Ca/P mole ratio of apatite sorbents was determined as a measure of HAP stoichiometry. Sorbents
M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
were dissolved by the process of microwave-assisted
digestion in the mixture of HNO3 and H2O2, described
previously in detail [20]. Contents of Ca and P were
measured by ICP-OES (Thermo Scientific iCAP 6500
Duo ICP).
Specific surface areas (SSA) of samples B, B400
and BNaOH+400 have been previously reported [15,20].
Additionally, the SSA of BNaOH was determined via
sorption–desorption isotherm of N2, at –196 °C, by the
McBain gravimetric method, where the sample was
firstly degassed at 100 °C and vacuumed for 24 h.
Determination of BNaOH mineral composition was
performed using X-ray diffraction (XRD). The Philips
PW 1050 diffractometer with CuKα1,2 radiation was
used, employing step/time scan mode of 0.05 °/s, and
exposure time of 6 s, in the 2θ range 20–60°.
Obtained diffraction peaks were compared to Powder
Diffraction File database (PDF2). XRD patterns of
samples B, B400 and BNaOH+400 have already been
published [15,20].
Sorption experiments
For the evaluation of Ni(II) sorption, separate
batches were prepared in 50 mL polypropylene centrifuge tubes. Each one contained 0.1000 g of sorbent
and 20 mL of solution prepared from NiCl2 salt and
distilled water. Initial pH values of metal solutions
were fixed at 6.0±0.1 in all experiments. Adjustments
of initial pH were performed by adding small aliquots
of HCl or NaOH solutions. The suspensions were
mixed on the rotary overhead shaker at 10 rpm.
The kinetics of Ni(II) sorption was examined
using 6×10-3 mol L-1 Ni(II) solution, and varying contact time between 15 min and 24 h.
The effect of initial Ni(II) concentrations was investigated by varying concentrations in the range 10-4–
–6×10-3 mol L-1, while contact time was fixed at 24 h.
After a given reaction time, liquid phases were
separated from spent sorbents by centrifugation at
7000 rpm for 10 min. Equilibrium pH values were
measured in clear supernatants. Determinations of
residual Ni(II) concentrations, as well as the concentrations of Ca(II) ions released from bio-apatite phase,
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
were performed using a Perkin Elmer 3100 atomic
absorption spectrometer. The amounts of Ni(II) removed from the solution were calculated as the differences between the initial and the equilibrium concentrations.
FT-IR analysis of unloaded and Ni-loaded
bio-apatites
In order to determine interactions of bio-apatite
surfaces with Ni(II) ions, Fourier Transform Infrared
(FT-IR) Spectroscopy was performed. Unloaded sorbents, and the solid residues obtained after equilibration of sorbents with the most concentrated Ni-solution (6×10–3 mol L-1) were scanned. FTIR spectra of
the samples were recorded at ambient conditions in
the mid-IR region (400-4000 cm-1) with a Nicolet IS 50
FT-IR spectrometer operating in the ATR mode and
using resolution of 4 cm-1 with 32 scans.
Major functional groups were identified in the
FT-IR spectra, and the surfaces of starting materials
and fully loaded samples were compared.
Sequential extraction of the sorbed Ni(II)
Stability of Ni(II) ions, sorbed onto the material
with the highest sorption capacity (BNaOH+400), was
analyzed by a sequential extraction protocol. For this
purpose, the sorbent was firstly equilibrated with
either 1.5×10-4 mol L-1 or 6×10-3 mol L-1 Ni(II) solution,
in order to obtain samples with different degrees of
saturation. Batches containing 1.000 g of BNaOH+400
and 20 mL of each Ni(II) containing solution, were
equilibrated for 24 h. After centrifugation, Ni(II) loaded
bio-apatite samples were rinsed with 20 mL of distilled water, centrifuged again, and dried at room temperature. The sequential extraction analysis was performed according to a modified Tessier procedure
[21]. Sorbed Ni(II) ions were portioned into 5 operationally defined phases: exchangeable (F1), acid soluble (F2), reducible (F3), oxidizable (F4) and residual
(F5). The modification of the original Tessier protocol
refers to residual phase extraction, which was performed by digestion in 6 M HCl [22,23]. The summarized procedure is presented in Table 1.
Table 1. The modified sequential extraction procedure applied in this study (mass of dry sorbent sample 1.00 g)
Phase
Fraction
Experimental procedure
F1
Exchangeable
Loaded samples were treated with 8 mL of 1 M MgCl2 (pH 7.0), 20 °C, 1 h.
F2
Acid soluble
8 mL of 1 M CH3COONa (pH 5, adjusted with CH3COOH), 20 °C, 5 h
F3
Reducible
20 mL of 0.04 M NH2OH·HCl in 25 vol.% CH3COOH, 96±3 °C, 6 h
F4
Oxidizable
3 mL of 0.02 M HNO3 and 5 mL of 30% H2O2 (pH 2, adjusted with HNO3), 85±2 °C, 2 h
3 mL aliquot of 30% H2O2 (pH 2, adjusted with HNO3), 85±2 °C, 3 h
5 mL of 3.2 M CH3COONH4 in 20 vol.% HNO3 was added and the sample was diluted to 20 mL, 20 °C, 30 min
F5
Residual
50 ml of 6 M HCl, 85±2 °C, 9 h
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M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
RESULTS AND DISCUSSION
Sorbents characteristics
XRD analysis of the sample BNaOH is presented
in Figure 1. Peaks characteristic for HAP crystalline
phase (PDF2, card No. 09-0432) with the intensive
background were identified.
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
decreases; therefore, the rate of process is stabilized.
Equilibrium was attained after 3h using BNaOH+400,
whereas approximately 24 h was required for other
samples. Sorbed amounts of Ni(II) ions at equilibrium
increased in the order B (0.22 mmol g-1) < BNaOH (0.28
mmol g-1) < B400 (0.30 mmol g-1) < BNaOH+400 (0.35
mmol g-1).
Figure 1. XRD pattern of the sample BNaOH.
The reported XRD patterns of samples B, B400
[15] and BNaOH+400 [20] also showed the presence of
HAP as a major crystalline phase. HAP peaks were
generally of low intensities and fused, indicative of
small grain size, low crystallization degree and high
defectiveness of bone apatite crystals. Although the
apatite samples might contain some other calciumphosphate phases [24], their presence was not confirmed by XRD analysis. Furthermore, different intensities of the background in the XRD spectra can be
ascribed to the different amounts of organic matter.
Ca/P mole ratio of the sample BNaOH+400 was
found to be 1.23 [20], whereas molar ratios of 1.20,
1.17, and 1.16 were calculated for B, BNaOH and B400,
respectively. Compared to the stoichiometric HAP
Ca/P ratio = 1.67, considered bio-apatite samples
were Ca-deficient. Determined SSA of BNaOH was 35
m2 g-1, which is much higher than SSA of raw bones
(0.1 m2 g-1 [15]), but lower than SSA of thermally
treated bones (85 m2 g-1 for B400 [15] and 78 m2 g-1 for
BNaOH+400 [20]).
Sorption kinetics
Sorption kinetics curves (Figure 2a) were of
typical shape: a sharp increase at the beginning followed by slower metal uptake. With time, the active
sites on the sorbent surface become increasingly
occupied and Ni(II) concentration in the liquid phase
120
Figure 2. a) Time-dependent sorption of Ni(II) ions on different
bone sorbents. b) Data fitting using pseudo-second order kinetic
model. Solid/liquid ratio 1/200, initial Ni(II) concentration 6×10-3
mol L-1, initial pH 6.0. Symbols: (■) B, (●) BNaOH, (▲) B400 and
(▼) BNaOH+400.
The experimental results were analyzed using
pseudo-second order kinetic equation [25] which is
widely used for sorption data modeling. The linear
form of pseudo-second order model is given by the
following equation:
t
1
t
=
+
q t k 2q e2 q e
(1)
M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
where qt and qe (mmol g-1) are sorbed amounts at
time t and at equilibrium, respectively, k2 (g mmol-1
min-1) is the pseudo-second-order rate constant. The
denominator of the first member at right side is
denoted as the initial sorption rate h (mmol g-1 min-1).
Results of data fitting are presented in Figure 2b
and Table 2. Equilibrium sorbed amounts calculated
by the model were 0.21, 0.29, 0.32 and 0.36 mmol g-1
for B, BNaOH, B400 and BNaOH+400, respectively, closely
matching the values obtained experimentally. In addition, high R2 values indicated good agreement between
experimental results and mathematical model.
erally increased in the order B < BNaOH < B400 <
< BNaOH+400. Ni(II) removal from aqueous media using
samples BNaOH and BNaOH+400 was especially enhanced
in the low concentration range (10-4–5×10-4 mol L-1).
Equilibrium pH values (Figure 3c) decreased
along with the increase of initial metal concentration,
which may be related to the phenomenon known as
specific cation sorption [29]. Specifically sorbed cations are attached strongly to the surface functional
groups causing the release of H+ ions:
Table 2. Pseudo-second order model parameters for Ni(II) sorption by differently treated bones
where S−OH and S−OH2+ respectively denote neutral
or protonated surface functional groups of both HAP
(phosphate) and organic phase, if present.
Additionally, hydrolysis of Ni ions takes place
according to the reactions:
Sorbent
Parameter
B
-1
BNaOH
B400
BNaOH+400
qe / mmol g
0.21
0.29
0.32
0.36
k2 / g mmol-1 min-1
0.043
0.40
0.071
0.18
h / mmol g-1 min-1
0.0020
0.0035
0.0072
0.0230
R2
0.991
0.998
0.999
0.999
Calculated values of k2 and h where in the range
0.043-0.40 g mmol-1 min-1 and 0.0020–0.023 mmol g-1
min-1, respectively. Treatments have improved sorption of Ni(II) and led to an increase in the speed of
sorption. Rate constant k2 increased in the order
B < B400 < BNaOH+400 < BNaOH, while h increased as
follows: B < BNaOH < B400 < BNaOH+400.
Good correlation between pseudo-second-order
model and experimental data has already been reported for the sorption of divalent cations onto various
sorbents: Pb2+, Cd2+, Zn2+ and Sr2+ by synthetic HAP
[26], Cr3+ and Sr2+ by bone char [17,27], Co2+ by animal bones [15], Pb2+ and Cu2+ onto magnetic eggshell-Fe3O4 powder [28], Pb2+, Zn2+ and Cd2+ onto
Fe(III)-modified zeolite [29], etc. Theoretically, agreement between the sorption kinetic data and mathematical models such as pseudo-second order implies
that chemical reaction is the rate-controlling step [30].
However, sorption processes governed by different
mechanisms (surface-complexation, dissolution/precipitation, ion-exchange, etc.) were equally well described by this model [17,31,32]. This basically means
that the applicability of this model is not sufficient evidence for mechanistic interpretations, but it is suitable
for mathematical description of the process, prediction of qe values, and data comparison.
Sorption equilibrium
The sorption isotherms of Ni(II) ions onto raw
and differently treated bovine bones are presented in
Figure 3a and b. The sorbed amounts of Ni(II) gen-
S − OH + Ni2+ = S − ONi+ + H+
S − OH+2 + Ni2+ = S − ONi+ + 2H+
Ni2+ + H2O = Ni ( OH) + H+ , pK = 9.86 [33]
+
Ni ( OH) + H2O = Ni ( OH)2 + H+ , pK = 9.14 [33]
+
Calculation of Ni-species distribution in respect
to solution pH showed that Ni2+ are dominant up to pH
8 [6]. Hydrolysis starts at pH > 8, reaching the maximum amount of insoluble Ni(OH)2 at pH 10. Taking
this into account, large sorption of Ni(II) by BNaOH+400
observed in the low concentration range, can be
linked to the equilibrium pH values close to the
Ni(OH)2 precipitation threshold.
The sorption of Ni(II) from the solutions of different initial concentrations, was followed by almost linear
increase of aqueous Ca(II) concentrations (Figure
3d). Direct linear proportionality between the amounts
of sorbed and released ions points toward ion-exchange as one of the operating sorption mechanisms. The ion exchange mechanism was already
recognized as the sorption mechanism characteristic
for HAP phase in the case of divalent Cd and Zn
sorption onto synthesized HAP [34]. Also, Cheung et
al. [35] investigated sorption of Cu2+ and Zn2+ onto
bone char, the heterogenous sorbent produced from
the destructive distillation of dried, crushed cattle
bones. Knowing that the main sorbent components
are calcium hydroxyapatite, CaCO3 and carbon, the
authors concluded that the main sorption mechanisms are ion-exchange in HAP lattice and chemisorption onto carbon surface. Moreover, Al-Asheh et
al. [9] reported that the main sorption mechanism of
Ni(II) ions onto raw animal bones was ion-exchange.
Our study strongly supports the ion-exchange scenario. Mole ratios Ca(II):Ni(II) were less than 1:1, for
all investigated sorbents, which can be explained by
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M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
Figure 3. Ni(II) sorption isotherms: a) values predicted by Freundlich equation; b) values predicted by Langmuir model
(symbols - experimental points, lines - fitting by theoretical models, error bars - deviations between experimental and predicted values);
c) relationship between equilibrium pH values and initial Ni (II) concentrations; d) relationship between amounts of released Ca(II) and
sorbed Ni(II) ions. Symbols: (■) B, (●) BNaOH, (▲) B400, and (▼) BNaOH+400.
Ca-deficient bio-apatite crystal lattice [20] and the
participation of other sorption mechanisms.
Sorption isotherms were described using Langmuir and Freundlich theoretical models, in the following linear forms:
ce ce
1
=
+
q e q m q mK L
ln q e = ln K f +
1
n
ln c e
(2)
(3)
where ce (mmol L-1) denotes the equilibrium concentrations of Ni(II) ions in the liquid phase, qm (mmol
g-1) is the maximum sorption capacity, KL (L g-1) is the
Langmuir constant related to the energy of adsorption, while Kf (mmol1−(1/n)·L1/n·g−1) and n are the
Freundlich constants related to the capacity and
intensity of the sorption process.
122
Calculated parameters are summarized in Table
3. Based on the correlation coefficients (R), a good
agreement exists between the models and experimental data. Calculated maximum sorption capacities
increased in the order B < B400 < BNaOH < BNaOH+400,
which is somewhat different in respect to experimentally obtained order, probably as a consequence of
linearization and fitting errors. The determined KL and
Kf values increased in the same order as experimentally determined maximum sorption capacities:
B < BNaOH < B400 < BNaOH+400.
From the Langmuir constant KL, the dimensionless separation factors RL can be calculated:
RL =
1
1 + C 0K L
(4)
RL is related to the nature of sorbate/sorbent attraction and isotherm type and it gives the information on
whether the process is: unfavorable (RL > 1), linear
M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
Table 3. Ni(II) sorption parameters calculated using Langmuir and Freundlich isotherms
Sorbent
Langmuir model
Freundlich model
qm / mmol g-1
KL / L mmol-1
R2
Kf / mmol1−(1/n)·dm3/n·g−1
n
R2
B
0.274
1.06
0.974
0.118
1.78
0.993
BNaOH
0.332
1.20
0.952
0.162
1.65
0.865
B400
0.321
2.66
0.993
0.200
2.02
0.974
BNaOH+400
0.357
4.89
0.990
0.264
3.14
0.991
(RL = 1), favorable (0 < RL < 1), or irreversible (RL =
= 0). The calculated RL values increased in the order:
BNaOH+400 (RL = 0.033) < B400 (RL = 0.059) < B (RL =
= 0.14) ≈ BNaOH (RL = 0.12) and indicated that all
investigated processes were favorable.
The qm values for commercially available synthetic HAP and HAP synthetized in the laboratory
were found to be 0.184 and 0.274 mmol g-1 [12].
Furthermore, sorption capacities of 0.039 [36] and
0.617 mmol g-1 [37] for different nano HAP were also
reported. Consequently, it can be concluded that
treated bio-apatites applied in this study can be used
as an alternative sorbent for synthesized hydroxyapatite.
FT-IR analysis
Since peaks in the XRD spectra of bone
samples appeared to be wide and fused, and did not
provide information about the content and the composition of organic matter, FT-IR analysis was performed. The contribution of the bone organic and
mineral phases to the overall FT-IR spectrum can be
analyzed almost separately as their peaks occur in
different regions of the spectra. FT-IR analysis of all
unloaded samples showed peaks characteristic for
HAP phase, whereas the content and qualitative composition of organic matter was related to the applied
treatment (Figure 4).
Figure 4. FT-IR analysis of investigated sorbents before (black lines) and after (gray lines) Ni(II) sorption.
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M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
The HAP phase is characterized by the most
intense peaks in the spectra at about 1020, 960, 600
and 560 cm−1, which correspond to various modes of
PO43- vibrations. In addition, peaks at 1410, 1450 and
near 870 cm−1 can be attributed to the CO32− group,
demonstrating carbonate substitution in HAP crystal
lattice [15,38]. The occurrence of −OH vibrations from
different sources and Amide A and B vibrations was
evident from a broad peak at 3700-3000 cm−1 [38].
The largest number of bands characteristic for organic phase functional groups was observed in spectra
of untreated bones (Figure 4a). Peaks at approximately 1640, 1540 and 1240 cm−1 belong to amide I,
II and III bands, respectively, peak at 1740 cm−1 is
characteristic for carbonyl group, and doublet at near
2920 and 2850 cm−1 originates from −CH2 vibrations
[38].
Bone treatments caused the reduction of organic phase content (Figure 4b-d). The intensity of
−OH and amide A and B stretching vibrations at high
wave numbers (3700-3000 cm−1) was markedly reduced, and almost completely lost in the sample
BNaoH+400. After chemical treatment (Figure 4b) −CH2
vibrations were still visible, so as small intensity
bands of Amide I and II. In the Figure 4c, only traces
of amide I and II vibrations were visible, thus, the
thermal treatment appeared to be more efficient than
chemical, for the exclusion of bone organic phase.
Higher organic content of BNaoH in respect to B400 can
be associated with its lower SSA. The spectrum of
BNaOH+400 was organic phase free (Figure 4d), i.e., it
resembles the spectrum of synthetic carbonate containing HAP [38].
The greatest changes in the appearance of
FT-IR spectrum before and after Ni(II) sorption were
observed for sample B. Reduced intensities of absorption peaks coming from −OH, amide and carbonyl
groups implies their participation in Ni(II) complexation mechanism. Similarly, removal of Ni(II) by pigeon pea pod biosorbent was attributed to the presence of C=O, C–O, O–H bonds which were identified
as responsible for coordination with Ni(II) [39]. The
FT-IR spectra of treated bone samples were almost
unaffected by the presence of Ni(II) sorption. The
fundamental apatite structure was preserved after
sorption of Ni(II) ions, which is in agreement with ionexchange mechanism.
Sequential extraction analysis
Previous experiments have shown that BNaOH+400
was the most efficient sorbent, thus it was selected to
investigate the stability of sorbed Ni(II) ions (Figure
5). After metal sorption from 0.15 mmol L-1 solution,
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Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
the majority of sorbed metal was found in F5 and F2,
about 65 and 17%, respectively. In F1 and F3 phase,
Ni(II) ions were present with about 7.5% while almost
insignificant amounts were found in F4 phase. Ni(II)
distribution extremely changed with the increase of
sorbent loading. After equilibration with 6×10-3 mol L-1
Ni(II) solution, the percentages in F1, F2 and F3
increased up to 24, 39 and 26%, respectively,
whereas content in F5 was reduced to 7%.
Figure 5. Effect of initial metal concentration on the distribution
of Ni(II) ions sorbed by BNaOH+400.
As a result of strong bonds with Ni(II) ions,
BNaOH+400 can be recommended for utilization in water
purification systems. Based on the results of sequential extraction analysis, the regeneration of the sorbent loaded with Ni(II) ions could hardly be feasible.
Utilization of Ca2+ solutions might cause the removal
of a part of exchangeable Ni(II) ions (maximum 7–
–24%, depending on the previously sorbed amount).
On the other hand, removal of Ni(II) ions bound to
phases F3-F5 requires more aggressive conditions
(Table 1). Thus, the removal of at least 40-60%
(depending on the sorbed amount) of Ni(II) would
result in deterioration and dissolution of HAP phase.
Consequently, proper disposal of spent sorbent
needs to be considered. Furthermore, such high stability of Ni(II) in sorbed form is preferential for soil
remediation processes [40]. Knowing that the pollutants bonded to F1 phase are considered as mobile
and potentially bioavailable [40], it can be concluded
that stabilization of Ni(II) ions is more efficient when
lower amounts were sorbed. Thus, usage of BNaOH+400
as an amendment for in situ remediation of Ni(II)
contaminated soil can be recommended especially for
lower contamination levels.
M. ŠLJIVIĆ-IVANOVIĆ et al.: Ni(II) IMMOBILIZATION BY BIO-APATITE…
Ni(II) sorption mechanism
Experimental results indicate high complexity of
Ni(II) sorption mechanism by variously treated bone
sorbents. Relationships between sorbed metal quantities, equilibrium pH values, quantities of released
Ca(II) ions and organic phase composition, indicated
that several sorption mechanisms were operating:
specific cation sorption, ion-exchange with Ca2+ from
HAP surface, Ni(II) hydrolysis (with possible precipitation) and complexation with organic functional groups.
Also, coprecipitation of new crystal phase cannot be
excluded. However, the new Ni-containing HAP
phases would be hard for detection using XRD analysis due to the fact that the XRD patterns of investigated samples have intensive background and broad
peaks. Ion-exchange and specific surface sorption
were common mechanism for all sorbents as they
relate to HAP phase. On the other hand, chemical
bonding by organic functional groups was mainly
detected in case of untreated bones (sample B). The
presence of functional groups such as -OH, amide,
carbonyl, etc., can explain relative high sorption capacity of sample B considering very low specific surface area of powdered bovine bones (0.1 m2 g-1 [15]).
Due to various treatments, organic phase removal
caused the increase of specific surface area [15,20],
which resulted in improved Ni(II) sorption capacities.
In addition to above, Ni(II) removal from aqueous
media using sample BNaOH+400 was especially enhanced
in the low concentration range, due to Ni(II) hydrolysis
and probably its precipitation.
CONCLUSION
Efficiency of bovine bones towards Ni(II) sorption was compared to the performance of materials
produced following chemical, thermal and combined
treatments. Sorption equilibrium was satisfactorily
described by Langmuir and Freundlich isotherm
models, while kinetics obeyed pseudo-second order
kinetics. All tested treatments improved sorption capacity toward Ni(II) ions in respect to raw bones and
different synthetic HAP samples. For initial metal concentrations higher than 10-4 mol L-1, sorption capacities increased in the order B < BNaOH < B400 <
< BNaOH+400. The material with the highest sorption
capacity towards Ni(II) was obtained by synergetic
effect of chemical and thermal treatments indicating
great utilization possibilities in water purification systems. The mechanism of Ni(II) sorption was extremely
complex, and involved inorganic (HAP) and organic
phase, when present. Sequential extraction analysis
of BNaOH+400 loaded with lower amounts of Ni(II)
Chem. Ind. Chem. Eng. Q. 22 (1) 117−126 (2016)
showed that metal was preferentially found in residual
fraction. This implies that BNaOH+400 can be considered
as an additive for soil remediation, at lower levels of
contamination.
Acknowledgement
This work was supported by the Ministry of Education, Science and Technological Development of
the Republic of Serbia (Project III 43009).
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MARIJA ŠLJIVIĆ-IVANOVIĆ
ALEKSANDRA MILENKOVIĆ
MIHAJLO JOVIĆ
SLAVKO DIMOVIĆ
ANA MRAKOVIĆ
IVANA SMIČIKLAS
Univerzitet u Beogradu, Institut za
nuklearne nauke "Vinča", Beograd,
Srbija
NAUČNI RAD
IMOBILIZACIJA Ni(II) BIO-APATITNIM
MATERIJALIMA: PROCENA EFIKASNOSTI
HEMIJSKOG, TERMIČKOG I KOMBINOVANOG
TRETMANA
Životinjske kosti su prirodni i bogat izvor kalcijum-hidroksiapatita (HAP), koji predstavlja
pogodan materijal za sorpciju teških metala i radionuklida. Sadržaj organske faze kostiju
se može redukovati različitim tretmanima i na taj način se poboljšavaju sorpciona svojstva.
U ovoj studiji, upoređeni su sorpcioni kapaciteti sirovih goveđih kostiju (B) i uzoraka dobijenih hemijskim tretmanom pomoću NaOH (BNaOH), žarenjem na 400 °C (B400) i kombinovanim hemijskim i termičkim tretmanom (BNaOH + 400), korišćenjem Ni (II) jona kao sorbata.
Maksimalni kapacitet sorpcije povećavao se u nizu B <BNaOH <B400 <BNaOH + 400. Na osnovu
rezulata sorpcionih eksperimenata i FT-IR analize, utvrđeno je da je mehanizam sorpcije
Ni(II) složen i da u njemu učestvuju i HAP i organska faze (ako je prisutna). Stabilnosti Ni
(II) jona sorbovanih uzorkom BNaOH + 400 ispitana je primenom sekvencijalne ekstrakcije. Pri
nižem opterećenju sorbenta najveća količina Ni(II) je detektovana u rezidualnoj fazi (65%),
dok karbonata frakcija postaje dominantna (39%) sa porastom zasićenja sorbenta. Rezultati ukazuju na mogućnost primene BNaOH + 400 u prečišćavanju vode. Kao materijal na bazi
apatita, sa niskim sadržajem organske materije i visokom efikasnošću sorpcije Ni(II),
takođe je dobar kandidat za in situ remedijaciju zemljišta, posebno pri nižim koncentracijama metala u zemljištu.
Ključne reči: goveđe kosti, tretmani, apatit, Ni (II), sorpcija, sekvencijalna ekstrakcija.
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