Department of Civil and Environmental Engineering
College of Engineering and Technology
Norfolk, Virginia 23529-0241
Phone: (757) 683-3898, Fax: (757) 683-5354
Dec 25, 2015
Biomass Conversion & Biorefinery
Dear Prof. Kaltschmitt:
We have revised our manuscript ef-2015-00308d.R1 “Preparation of activated carbon
from un-hydrolyzed biomass residue” in accordance with the reviewer’s comments and would like
to resubmit it for publication in your esteemed journal. We want to thank the reviewer for taking
his time and the valuable comments that helped us improve our manuscript.
We addressed all the comments and provided the required information in the respective
sections. For your convenience, Our responses to the reviewer’s comments are provided below.
Thank you for your time. We look forward to hearing from you.
Yours sincerely,
Sandeep Kumar, Ph.D.
Assistant Professor
Director, Energy Cluster
Response to Reviewer’s comments: Manuscript number: BCAB-D-1500055R1
Authors highly appreciate the valuable comments from the reviewers. All suggestions have been
incorporated in the revised manuscript as follows:
Reviewer #1:
Point 1: Page 3 line 56: a short basic description of AFEX is worth to be added here for the reader,
linked to a reference for a more detailed insight. The exact chemical composition of UHS should be
given (see also another comment on this later on), as it could be also partially, rather than "un-",
hydrolyzed. This issue should be better discussed in the first part of the article.
Response to Point 1:
Table 2 is added to provide additional chemical composition. In the revised paper, table 4 already
includes the elemental composition. The following paragraph and references are being added to
briefly describe the process:
Ammonia Fiber Explosion (AFEX) which is a physiochemical process was used for the
pretreatment of corn stover under moderate temperatures (60-100 ℃) and high pressure (250-300
psi) for 5 min with liquid anhydrous ammonia, followed by the released pressure, during which
procedure the conversion of cellulose and hemicellulose to fermentable sugars is completed.
AFEX treatment offers unique advantages than other biomass treatments, such as almost all the
ammonia could be restored and recycled through the procedure, there is no liquid stream produced
and cellulose and hemicellulose are well preserved without much degradation during the
process(Mosier, Wyman et al. 2005; Teymouri, Laureano-Perez et al. 2005; Li, Balan et al. 2010).
Three new references is added here.
Li, B.-Z., V. Balan, et al. (2010). "Process optimization to convert forage and sweet sorghum bagasse to
ethanol based on ammonia fiber expansion (AFEX) pretreatment." Bioresource Technology
101(4): 1285-1292.
Mosier, N., C. Wyman, et al. (2005). "Features of promising technologies for pretreatment of
lignocellulosic biomass." Bioresource Technology 96(6): 673-686.
Teymouri, F., L. Laureano-Perez, et al. (2005). "Optimization of the ammonia fiber explosion (AFEX)
treatment parameters for enzymatic hydrolysis of corn stover." Bioresource Technology 96(18):
2014-2018.
Table 2 Chemical composition of UHS.
Sample
Glucan,wt%
Xylan,wt%
UHS
RSD
13.90
<1.5
5.79
<1.2
Arabinan
wt%
1.05
<1.0
Lignin, wt%
Ash,wt%
52.49
<2.0
12.32
<2.0
Point 2:Table 1: is O calculated by difference? Please specify this in the legend.
Response to Point 2:
The component percentages of C, H and N were measured by combustion analyzer and the amount
of oxygen and other elements were measured by energy-dispersive spectrometry (EDS).
Point 3:Page 4 line 17: did you observed any sintering/melting of the feedstock at the end of the
procedure of sample preparation (i.e. at the end of drying)? Did you observe the sample at SEM or
measured the porosity through BET? Please add these info to the article, if possible. As a general
comment, authors in the paper do not discuss about the lowsintering/melting characteristics of the
feedstock, and the related considerations towards physical vs chemical activation to AC.
Response to Point 3:
The UHS sample was dried at 65°C for 48 h, since the temperature is low, no sintering/melting
phenomenon was observed. The UHS sample was observed by SEM and the pictures is shown in
of figure 3a of the revised paper. The BET area of UHS is 1.34 m2/g; Pore volume is 4.36×103cc/g, all results are averaged based on triplicated measurement.
After mixing with activation chemicals, UHS sample stick together with activation chemicals and
the color turned dark. The mixture was grinded several minutes before charging to the reactor.
Point 4:Page 4 line 21: we do not understand what authors mean with "The suspension which was
dried after filtration was labeled as filtration ZnCl2 and UHS feedstock.". You did not mention
"filtration" before, please explain and describe the procedure in an accurate way.
Response to Point 4:
Two different pretreatments were taken, one is activation chemical water solution mix with UHS
and then dry out(co-precipitation), another is drying the UHS suspension after filtration(mix and
filtration). The accurate description is showed in figure 2 in the revised manuscript.
Point 5:Figure 2: please explain what "Flite" means. Also the grinding method must be described in
details in the text. As regards the experiments, a table summarizing the combinations of experiments
(and setting the combined conditions for each test), and the overall number of experiments is
necessary, and should be added to the article.
Response to Point 5:
“Flite” is a spelling mistake, it should be “filter”.
Following table 3 is added to the paper which give all overall number of experiments.
Table 3 Experiment list
Exp.
No
Temp.(oC)
Heating
ratio
Reaction
Impregnation
Activation
Time(min)
Ratio
Chemical
Preparation
method
(oC/Min)
1
500
40
60
0.175
ZnCl2
2
500
47
60
0.175
ZnCl2
3
500
11.8
75
0.175
ZnCl2
4
500
9.5
90
0.175
ZnCl2
5
500
7.75
90
0.09
ZnCl2
4
500
7.1
90
2
ZnCl2
5
500
125
90
2
ZnCl2
6
500
52.6
90
2
ZnCl2
7
500
66.6
60
2
ZnCl2
8
500
62.5
60
1
ZnCl2
9
500
62.5
60
1.5
ZnCl2
10
600
56.1
60
2
ZnCl2
11
500
62.5
60
2.5
ZnCl2
12
550
55
60
2
ZnCl2
13
450
60
60
2
ZnCl2
14
400
61.5
60
2
ZnCl2
15
500
58.8
60
3
ZnCl2
16
500
62.5
60
2
ZnCl2
17
500
7.1
90
2
ZnCl2
18
500
125
90
2
ZnCl2
19
500
55.5
60
1.5
ZnCl2
20
500
55.5
60
2.5
ZnCl2
20
500
31
60
1.7
H3PO4
21
500
52.8
60
1.7
H3PO4
22
600
52.1
90
8
H3PO4
Mix and
Filtration
Coprecipitation
Coprecipitation
Point 6: Page 9 line 22.Please specify, referring to fig 2, at which point the UHS sample has been
taken for the SEM analysis. Before pretreatment/drying or afterwards, for instance? Grinding? How?
Response to Point 6: After drying The UHS was grinded about ten minutes then was taken for
SEM analysis.
Did you carry out a BET analysis of the UHS before the activation step? If not, why?
Response to Point 6: The BET analysis of UHS was carried out before the activation step. The
BET area of UHS is 1.34 m2/g; Pore volume is 4.36×10-3cc/g, all results are averaged based on
triplicated measurements.
After UHS with ZnCl2, impregnation ratio 1:2, The BET area of UHS is 1.26×10-4 m2/g; Pore
volume is 2.4×10-6cc/g. After UHS co-precipitation with H3PO4, impregnation ratio 1:1.7, The
BET area of UHS is 8.84×10-4 m2/g; Pore volume is 3.04×10-3cc/g. Since they are too small and
beyond the accurate range, I did not list them on the paper.
Point 7:Table 1. It is very important to know also the amount of remaining sugars and lignin,
respectively, present in the UHS. Can you add this information? In the 400-600 °C you assign the
devolatilization of UHS to the release of lignin volatiles. But, what about any sugar remained in the
feedstock? They also devolatilize in this region, and the amount contained in the feedstock could be
relevant...
Response to Point 7:
A new table about carbohydrates composition is introduced in paper
Table 1 Carbohydrates composition of UHS.
Sample
Glucan,wt%
Xylan,wt%
UHS
RSD
13.90
<1.5
5.79
<1.2
Arabinan
wt%
1.05
<1.0
Lignin, wt%
Ash,wt%
52.49
<2.0
12.32
<2.0
The most component in feedstock is lignin. The percentage is more than 50%. The discussion is
focused on lignin. After activation, almost no sugar carbon left in the residue.
Point 8:Figure 5. It would be important to have, maybe noted in the same figures, also the result from
the BET analysis at each point in the graphs. In fact, yield is a very important result, but together with
the porosity (which, at first instance, can be represented by the result of the BET analysis). The
combined investigation of these two aspects, yield & porosity, can provide indications for optimal
conditions.
Response to Point 8:
A new indicator total surface area is introduced in the revised manuscript page, the calculation
formulate is as follow.
Yeild Surface area = yeild percentage × surface area
The graph yield Surface area VS activation temperature is show in figures 7 of the revised
manuscript.
600
yeild Surface Area(m2/g)
550
500
450
400
350
300
250
200
150
350
400
450
500
Temperature(ºC)
550
600
650
Figure 7 Yield surface area as a function of activation temperature: activation time is 60 mins, heating rate is
around 60 mins/℃ and impregnation ratio is 2
When the temperature reaches 450ºC, the yield surface area has the maximum value of 459m2/g,
then decrease slowly.
Point 9:BET analysis and Figure 6. Please provide detailed information on how the BET experiment
was carried out: how many replicates were done? How replicable was the analysis with the material
under study? Can you provide the dispersion range of results for each measure? This is very
important for the type of experiment you are discussing here.
Response to Point 9:
Surface Area Analyzer with 5% accuracy, only if the R2 >0.99, the value of surface area will be
adopted. Duplicate samples were taken for BET measurement, using the averaged value drawing
graph and raw data was also shown in the graph. Duplicate experiment was also completed in the
optimized condition.
1200
0.3
1000
0.25
800
0.2
600
0.15
400
0.1
200
0.05
0
0
350
400
1400
450
500
550
Temperature (ºC)
Surface Area
600
650
0.6
Pore Volume
1200
Surface Area (m2/g)
Pore Volume(cc/g)
Pore Volume
0.5
1000
0.4
800
0.3
600
0.2
400
0.1
200
0
0
0
0.5
1
1.5
2
Impregnation Ratio
2.5
3
Pore Volume(cc/g)
Surface Area (m2/g)
Surface Area
Surface Area
0.3
Pore Volume
0.2
800
0.15
600
0.1
400
0.05
200
0
0
40
60
80
100 120
Heating Rate (Mins/ºC)
Surface Area
800
Surface Area (m2/g)
20
Pore Volume
140
0.03
0.025
600
0.02
0.015
400
0.01
0.005
200
0
50
70
Reaction time (mins)
90
Pore Volume(cc/g)
0.25
1000
Pore Volume(cc/g)
Surface Area (m2/g)
1200
Reviewer #2:
Reviewer #2: The research presented in this manuscript is interesting and should be considered for
publication. The following concerns should be addressed prior to publication.
Point 1:. The authors have met the goals of the research objectives to a great extent but some
details on the experimental design and analysis are missing. It was mentioned that a fractional
design was used but details on this design method are not discussed in the manuscript.
Response to Point 1:
Fractional design is not mentioned in the paper. A single factorial design (instead of fractional
design) was used to optimize the activation process and five different parameters (pretreatment
methods, impregnation ratio, activation time, activation temperature, and temperature increasing
rate) were analyzed with respect to their influence on BET surface area and pore volume.
Point 2:. Reliability and validation of the results with statistical significance should be discussed in
detail.
Response to Point 2:
Reliability description are added to the paper and figures are modified to show the validation of
the results.
Triplicated measurement were taken to measure Bulk density, moisture content, ash content and
Iodine number, the results show the averaged value. Surface Area Analyzer with 5% accuracy.
Duplicated experiment was taken for BET measurement, using the averaged value drawing graph
and raw data was also shown in the graph. Every ultraviolet-visible (UV-vis) spectro-photometry
measurement were duplicated, using the averaged value drawing graph and raw data was also
shown in the graph. Duplicated experiment was done in the optimized condition, the yield
percentage graph shows the result.
All the figures are changed.
1200
0.3
Pore Volume
1000
0.25
800
0.2
600
0.15
400
0.1
200
0.05
0
0
350
400
450
500
550
Temperature (ºC)
600
650
Pore Volume(cc/g)
Surface Area (m2/g)
Surface Area
1400
Surface Area
0.6
Pore Volume
0.5
1000
0.4
800
0.3
600
0.2
400
Pore Volume(cc/g)
Surface Area (m2/g)
1200
0.1
200
0
0
0
0.5
1
1.5
2
2.5
3
Impregnation Ratio
Surface Area
0.3
Pore Volume
0.25
1000
0.2
800
0.15
600
0.1
400
0.05
200
0
0
20
40
60
80
100 120
Heating Rate (Mins/ºC)
140
Pore Volume(cc/g)
Surface Area (m2/g)
1200
Surface Area (m2/g)
Pore Volume
0.03
0.025
600
0.02
0.015
400
Pore Volume(cc/g)
Surface Area
800
0.01
0.005
200
0
50
70
Reaction time (mins)
250
UHS-ZnCL2 AC
90
Freundlich Model
Qe(mg/g)
200
150
100
50
0
0
100
200
300
Ce(mg/L)
400
500
200
180
160
Ct(mg/g)
140
120
100
80
60
40
20
0
0
200
400
600
800
1000
1200
1400
1600
Time(mins)
300
Qe(mg/g)
250
200
150
100
3
5
7
9
11
pH
Point 3:. There are numerous studies related to preparation of ACs from various sources. Authors
are encouraged to provide a clear description on how this research and methods are novel in nature
with a tabular form of presentation and comparison of benefits and results if possible.
Response to Point 3:
There are some discussions about production of ACs from biomass waste in page 2. A new Table
is added. Additional 7 references are added here to introduce the chemical activation AC
production method. Chemical activation is a commonly used AC production and easily getting
high surface AC, so the method is introduced, a new description is add in page 2.
Chemical activation is a commonly used method for AC production, the summary of biomass
feedstock chemical activation for ACs production is show in table 1. High surface area (700~2000
m2/g) activated carbon is expected, when the biomass waste is used as feedstock and chemical
activation is production method.
Table 1 Summary of biomass feedstock chemical activation for ACs production
Feed stock
Reaction
Time(min)
Activation
chemicals
Surface
area(m2/g)
Temp.(oC)
Ref.
Wood
850
60
H3PO4
1708
(Macías-Pérez,
Bueno-López et al.
2007)
(Nowicki,
Wachowska et al.
2010)
Plum stones
500
60
KOH
2174~3228
Coconut shell
800
-
Strong base
931
(Elsayed, Seredych
et al. 2009)
Corn cob
500
30~240
ZnCl2
400~1410
(Tsai, Chang et al.
1997)
Olive-seed
800
60
KOH
1339
(Stavropoulos and
Zabaniotou 2005)
Pecan shell
--
-
H3PO4
682
(Ahmedna, Marshall
et al. 2004)
Cassava peel
750
180
KOH
1378
(Sudaryanto,
Hartono et al. 2006)
Bean pods
700
60
K2CO3
1580
(Cabal, Budinova et
al. 2009)
Apricot stone
shells
800
120
ZnCl2
783
(Aygün, YenisoyKarakaş et al. 2003)
Almond shell
800
120
ZnCl2
736
Hazelnut shell
800
120
ZnCl2
793
Walnut shell
800
120
ZnCl2
774
olive stones
850
120
-
677
(El-Sheikh,
Newman et al.
2004)
olive stones
650
120
ZnCl2
790
(Kula, Uğurlu et al.
2008)
Pecan Shell
450
60
-
>800
(Ahmedna, Marshall
et al. 2000)
Jackfruit peel
500
30
H3PO4
907~1260
(Prahas, Kartika et
al. 2008)
Rice husk
700
30
ZnCl2
750
Bagsse
700
30
ZnCl2
674
(Kalderis, Bethanis
et al. 2008)
Palm shell
800
120
K2CO3
1170
(Adinata, Daud et
al. 2007)
1. M.C. Maci´as-Pe´ rez, A. Bueno-Lo´ pez, M.A. Lillo-Ro´ denas, C. Salinas-Marti´nez de
Lecea, A. Linares-Solano, SO2 retention on CaO/activated carbon sorbents. Part I:
importance of calcium loading and dispersion, Fuel 86 (2007) 677–683.
2. P. Nowicki, H. Wachowska, R. Pietrzak, Active carbons prepared by chemical activation of plum
stones and their application in removal of NO2, Journal of Hazardous Materials 181 (2010)
1088–1094.
3. Y. Elsayed, M. Seredych, A. Dallas, T.J. Bandosz, Desulfurization of air at high and low H2S
concentrations, Chemical Engineering Journal 155 (2009) 594–602.
4. Tsai WT, Chang CY, Lee SL. Preparation and characterization of activated carbons from corn cob.
Carbon 1997;35:1198–200.
5. Stavropoulos GG, Zabaniotou AA. Production and characterization of activated carbons from
olive-seed waste residue. Micropor Mesopor Mater 2005;82:79–85
6. Ahmedna M, Marshall WE, Husseiny AA, Rao RM, Goktepe I. The use of nutshell carbons in
drinking water filters for removal of trace metals. Water Res 2004;38:1062–8.
7. Sudaryanto Y, Hartono SB, Irawaty W, Hindarso H, Ismadji S. High surface area activated carbon
prepared from cassava peel by chemical activation. Bioresource Technol 2006;97:734–9.