Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers
journal homepage: www.elsevier.com/locate/jtice
Activated carbon from durian shell: Preparation and characterization
Thio Christine Chandra a, Magdalena Maria Mirna a, Jaka Sunarso b,
Yohanes Sudaryanto a, Suryadi Ismadji a,*
a
b
Department of Chemical Engineering, Widya Mandala Surabaya Catholic University Kalijudan 37, Surabaya 60114, Indonesia
Division of Chemical Engineering, The University of Queensland, St. Lucia, Qld 4072, Brisbane, Australia
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 11 August 2008
Received in revised form 13 October 2008
Accepted 13 October 2008
Activated carbons were prepared from durian shell by chemical activation with potassium hydroxide. In
order to find the optimum pore characteristics, different KOH to durian shell ratio (0.25–1.0) and
activation temperature (673–923 K) was employed. The adsorption isotherm of activated carbons
produced within these range of temperature and impregnation ratio is a mixture of type I and type IV
isotherms. While activated carbons obtained at low chemical impregnation ratio of 0.25 were essentially
microporous, with higher impregnation ratio, they become predominantly mesoporous. KOH to durian
shell ratio of 0.5 and activation temperature of 773 K can be pinpointed as the optimum condition to
obtain high surface area activated carbon.
ß 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords:
Activated carbon
Pore structure
Durian shell
Activation
1. Introduction
Activated carbons are still in wide-use for adsorption of
pollutants within gaseous and liquid phases. Numerous economic
and industrial sectors, such as food and beverage processing,
chemical, pharmaceutical, petroleum, mining, nuclear, automobile, and vacuum manufacturing employ this material within their
processing units. Some of these applications are very demanding
with regard to the surface chemistry and characteristics of these
carbon adsorbents (Stavropoulos and Zabaniotou, 2005). In
general, activated carbons with high surface area and pore
volumes can be prepared from a variety source of carbonaceous
materials such as coal (Chattopadhyaya et al., 2006; Jibril et al.,
2007; Li et al., 2007; Pietrzak et al., 2007), coconut shell (Achaw and
Afrane, 2008), sawdust (Ismadji et al., 2005), agricultural wastes
and plant materials (Asadullah et al., 2006; Cao et al., 2006; CuerdaCorrea et al., 2008; Deiana et al., 2008; Elizalde-Gonzalez and
Hernandez-Montoya, 2007; Gercel et al., 2007; Soleimani and
Kaghazchi, 2007) including agricultural industrial by-products
(Bouchelta et al., 2008; Li et al., 2008; Lua and Yang, 2005; Nabais
et al., 2008; Olivares-Marin et al., 2007; Stavropoulos and
Zabaniotou, 2005; Sudaryanto et al., 2006; Suzuki et al., 2007).
Among these precursors, coal and coconut shell are the two main
sources within industrial practice.
* Corresponding author. Tel.: +62 31 3891264; fax: +62 31 3891267.
E-mail addresses: suryadi@mail.wima.ac.id, suryadiismadji@yahoo.com
(S. Ismadji).
The pore structure and pore size distribution of activated
carbon commonly varies based on the nature of raw materials and
activation method. Activated carbons are generally obtained using
two main steps, e.g. carbonization of the raw materials below
1000 8C in an inert atmosphere followed by activation of the
resulting char in the presence of suitable oxidizing agents. In
carbonization, most of the non-carbon elements like hydrogen and
oxygen are being removed onto gaseous form by pyrolytic
decomposition resulting in a carbon with fixed mass and a
rudimentary pore structure. The following activation step is then
employed to enlarge the diameter of fine pores and also create new
pores so that the adsorptive power of the carbonization product is
enhanced (Hu et al., 2001).
Activation can be carried out by chemical or physical means.
Generally within chemical activation process, carbonization and
activation take place simultaneously as facilitated by chemical
activating agents, i.e. dehydrating agents and oxidants. On the
other hand for physical activation, carbonization of a precursor
occurs in priori followed by their activation at elevated temperature in the presence of suitable activating agents, i.e. carbon
dioxide or steam. It has been noticed that chemical activation
process normally takes place at a temperature lower the physical
activation process (Ahmadpour and Do, 1997). The impregnation
of precursor materials with chemical agents such as ZnCl2, H3PO4,
and KOH can inhibit tar formation while also reduce the volatile
matter evolution resulting in high precursor to carbon conversion.
Therefore, the development of a porous structure is improved with
chemical activation process (Ahmadpour and Do, 1997). Among
the chemical activating agents, zinc chloride (ZnCl2) in particular is
1876-1070/$ – see front matter ß 2008 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jtice.2008.10.002
458
T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462
the most frequently used chemical in activated carbon preparation.
Nowadays however, zinc chloride is less employed as it cause
environmental problem. In addition, activated carbons from zinc
chloride are not suitable in pharmaceutical and food industries due
to its possibility to contaminate products. Another more favorable
agent, KOH has been claimed to be the most effective alkali salt for
activated carbons production (Ahmadpour and Do, 1997).
Shell of durians is a major agricultural waste in Indonesia.
Production of durians in Indonesia reached 562,710 tones per year
at 1998, which is likely to be increased during the next few years as
durian can be harvested several times in a year. Furthermore,
increasing rate of durian (also called king of fruits) consumption is
evident as most people like it which more or less would guarantee
their availability as disposed products. While their waste disposal
or pilings has become a common observation, it can bring about
more problems such as respiratory diseases, apart from their
pungent smell. These durian shells can therefore be employed as
carbon precursor to derive more economic value while at the same
time overcome the problem.
To obtain very specific materials with a given pore size
distribution from low cost precursors at low temperature is
considered a challenge. In our previous work, we have utilized
activated carbon made from durian shell for methylene blue
removal however only a short description about the preparation
was given while its emphasis was on adsorption (Chandra et al.,
2007). Within this work, preparation details including the effect of
various parameters onto surface development and characteristics
are given.
2. Experimental
2.1. Materials
Durian shell (Montong variety) was collected from local durian
processing industry in Surabaya. The pristine durian shells have
high water content (40%), hard shell texture and also strong durian
flavor. As an initial step, the size of these materials was reduced to
1 1 cm. Prior to the process, durian shell was repeatedly washed
with distilled water in order to remove dust and other inorganic
impurities, then oven-dried for 24 h at 393 K to reduce its moisture
content until less than 6%. Subsequently, as-dried durian shell was
grounded in micro hammer mill until it became powder (40/60 mesh)
and then stored in desiccators for further use. Potassium hydroxide,
KOH (ACS reagent) with purity 85% (Sigma–Aldrich) was purchased
from Kurniajaya Pty Ltd.
The proximate analysis of durian shell was carried out
according to ASTM standard E 870-82, while the ultimate analysis
was conducted according to ASTM D3176-89 (2002). The
proximate and ultimate analysis of the durian shell is given in
Table 1. The C, H, N, O and S elements content in the ultimate
analysis were determined by an elemental analyzer (Heraeus,
CHN-O-RAPID). Table 1 reveals that durian shell has high carbon
and low ash content. In comparison with other materials (Table 2),
Table 1 shows that durian shell has a quite high carbon content
which justifies its suitability as activated carbon precursor.
Table 1
Proximate and ultimate analysis of durian shell.
Analysis
wt%
Variation (%)
Proximate
Moisture
Volatile matter
Fixed carbon
Ash
5.53
69.59
22.36
2.52
1.0
1.2
0.8
1.5
Ultimate
Carbon
Nitrogen
Hydrogen
Oxygen
Sulphur
60.31
3.06
8.47
28.06
0.10
1.4
1.4
1.4
1.4
1.4
The impregnation was conducted in 250 mL round bottle flask
equipped with stirrer. During the impregnation period, the
mixture was stirred at 200 rpm. The mass ratio of chemical
activating agent to durian shell was in the range of 1:4 to 1:1. The
resulting homogeneous slurry was then poured onto porcelain disc
and dried at 383 K for 24 h in a forced circulating oven. The dried
product was later placed on horizontal tubular furnace and
carbonized at desired temperatures (673, 723, 773, 823, 873 and
923 K). The activation was performed under nitrogen flow rate of
150 cm3/min. The activation process was initiated by heating the
sample at ramp rate of 10 K/min from room temperature (around
303 K) until the desired temperature was reached. Samples were
held at desired temperature for 1 h before cooling down under
nitrogen flow. Sudaryanto et al. (2006) and Diao et al. (2002) in
their studies found that the activation time does not cause
significant change on the activated carbon. Therefore, 1 h was
chosen as the activation time. The resulting carbons have particle
sizes between 60 and 120 meshes. These activated carbons were
washed sequentially with a 0.5 N HCl solution. Consecutively,
carbon powders were repeatedly washed with hot distilled water
until the pH of solution reach 6.5 and finally washed with cold
distilled water. After that, these powders were dried at 383 K for
24 h and stored in dessicator.
2.3. Characterization
The pore structure characteristics of activated carbons were
determined using N2 adsorption, X-ray diffraction (XRD), and
scanning electron microscope (SEM). Nitrogen adsorption was
conducted at 77 K using an automatic Micromeritics ASAP-2010
volumetric sorption analyzer. Prior to gas adsorption measurements, the carbon was degassed at 573 K in a vacuum condition for
24 h. Nitrogen adsorption isotherms were measured over a relative
pressure (P/Po) range from approximately 10 5 to 0.995. The BET
surface area, micropore volume and micropore surface area of the
activated carbons were determined by application of the
Brunauer–Emmett–Teller (BET) and Dubinin–Asthakov (DA) analysis software available with the instrument, respectively. The BET
surface area was measured by means of the standard BET equation
applied in the relative pressure range from 0.06 to 0.3. The pore
2.2. Activated carbon preparation
Chemical activation of durian shell was performed using KOH.
Different carbonization temperatures and impregnation ratios
were employed to find the optimal conditions resulting in high
surface area activated carbons from durian shell. The activation
was performed as follows namely 25 g of durian shell in the form of
powder was mixed with KOH solution (50%) with different
impregnation ratio for 5 h at room temperature (around 303 K).
Table 2
Fixed carbon content from several kinds of raw materials.
Raw material
Fixed carbon (% wt)
Cassava peel (Sudaryanto et al., 2006)
Durian shell (this work)
Palm shell (Daud and Ali, 2004)
Coconut shell (Daud and Ali, 2004)
Teak sawdust (Ismadji et al., 2005)
28.90
22.36
18.70
18.60
23.38
T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462
459
size distribution of the carbons was ascertained using the
Micromeritics density functional theory (DFT) software, with
medium regularization.
SEM images were recorded using JEOL JSM-6400F field emission
SEM. A thin layer of platinum was sputter-coated on the samples
for charge dissipation during FESEM imaging. The sputter coater
(Eiko IB-5 Sputter Coater) was operated in an argon atmosphere
using a current of 6 mA for 3 min. The coated samples were then
transferred to the SEM specimen chamber and observed at an
accelerating voltage of 5 kV, spot size of 8, aperture of 4 and 15 mm
working distance. TGA–DSC curve was obtained using TGA/DSC 1
star system (Mettler toledo) with ramping and cooling rate of
10 K/min from room temperature to 1173 K under 20 mL/min
nitrogen flow with gas controller GC200.
3. Results and discussion
A series of activated carbons were prepared from durian shell as
precursor with chemical activation using KOH as activating agent.
The effects of different preparation variables on the pore
characteristic of activated products were also studied. Details
are discussed as follows.
3.1. TGA–DSC of durian shell
Fig. 1 depicts the TGA–DSC curve for carbonization of durian
shell. The experiment was conducted at a ramping rate 10 K/min
from 298 to 1173 K, dwelling at 1173 K for 10 min and than cooling
down at the same ramping rate to 298 K. The weight lost at the
beginning of the process (373 8C) was due to evaporation of free
moisture content. With further temperature increase, bound water
in durian shell also evaporated. Sharp decrease of weight
evidenced at temperatures between 543 and 643 K was caused
by the release of volatile matter from durian shell while above
643 K, decomposition of some structure within durian shell still
takes place.
3.2. Yield of activated carbon
For the production of commercial activated carbons, relatively
high product yields are expected. Activation temperature plays an
important role on the yield of activated carbon. Fig. 2 depicts the
effect of activation temperature on the yield of activated carbon at
different activation time and impregnation ratio. As seen in Fig. 2,
activation temperature has quite significant effect on the yield of
carbon. With increasing activation temperature, the yield of
activated carbon decrease as the weight loss rate is higher
Fig. 1. TGA–DSC curve for durian shell.
Fig. 2. Effect of carbonization temperatures on the yield of activated carbon.
primarily due to the initial large amount of volatiles that can be
easily released with higher temperature as well as the loss of
moisture to a lesser extent. Lower yield that comes with higher
KOH to durian shell ratio might be attributed to the enhancement
of carbon burn-off by extra KOH widening (micropore into
mesopore).
3.3. Pore structure of activated carbons
Identifying the pore structure of activated carbons by nitrogen
adsorption at 77 K is an essential procedure before applying them
onto liquid phase experiments. The N2 adsorption isotherms of
activated carbons prepared at different impregnation ratios and
activation temperatures are shown in Fig. 3. The shape of
adsorption isotherm can provide preliminary qualitative information on the adsorption mechanism as well as on the porous
structure of carbon. These isotherms clearly show the predominantly microporous nature of the carbons, with some mesopores
leading to gradual increase in adsorption after the initial filling of
the micropores, followed by more rapid enhancement near
saturation. Adsorption isotherm of these activated carbons at
carbonization temperature 673–923 K and impregnation ratio
0.25–1.00 can be properly classified as a mixture of type I and type
IV isotherms (see Fig. 4). According to IUPAC classification, type I
isotherm can be associated with microporous structure while type
IV isotherm exhibited by mixture of microporous and mesoporous
material. The plateau of this isotherm commences at high relative
pressures (P/Po) and toward the end of isotherm, steep gradient
exist as a result of a limited uptake of nitrogen, indicating capillary
condensation in the mesopores. These features indicate the
development of micro and mesoporous structure on this char
during activation process, further confirmed by the DFT (density
functional theory) pore size distributions as shown in Fig. 4 (KOH
to durian shell ratio 0.25 and 0.5). The pore size distribution
delineates a model of solid internal structure, which assumes that
an equivalent set of non-interacting and regularly shaped model
pores can represent the complex void spaces within the real solid.
The pore size distribution is closely related to both kinetic and
equilibrium properties of porous material and perhaps is the most
important aspect for characterizing the structural heterogeneity of
porous materials employed in industrial application. It is apparent
from Fig. 4 that the pore size distribution was largely dependent on
the KOH to durian shell ratio. Activated carbons obtained at low
chemical ratio (0.25) were essentially microporous and as the
chemical ratio increases, the activated carbons become mostly
460
T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462
Fig. 3. Adsorption isotherms of nitrogen at 77 K on durian shell activated carbons. (For interpretation of the references to color in this figure legend, the reader is referred to
the web version of the article.)
mesoporous. A similar tendency was also observed by Timur et al.
(2006).
Table 3 shows the pore properties of all activated carbons
prepared from durian shell with KOH activation. The BET values
(519–992 m2/g) are comparable to the commercially available
activated carbon (Wu et al., 2005), e.g., 300–600 m2/g for ICI
Hydrodarco 3000, 1044 m2/g for Calgon Filtrasorb-400 and
Fig. 4. Pore size distributions of durian shell activated carbons. (a) KOH to durian
shell ratio 0.25 and (b) KOH to durian shell ratio 0.50.
1000 m2/g for Westvaco Nuchar WL. Increased temperature from
673 to 773 K results in higher BET surface area and micropore
volume as indicated in Table 3. This phenomenon was due to the
release of volatile matters; however the continual decreases in
these two properties with increasing temperature from 773 to
923 K were probably due to the sintering effect of the volatiles and
the shrinkage of the carbon structure, resulting in the narrowing
and closing up of some of the pores. Table 3 also showed that
activated carbons prepared at temperature of 773 K and impregnation ratio 0.5 yielded the largest BET surface area and micropore
volume.
The effect of KOH to durian shell ratio on BET surface area and
total pore volume can also be seen in Table 3. They suggested
that KOH is not only responsible for the development of new
micropores but also for the enlargement of as-existing micropores to mesopores (see Fig. 4 and Table 3). At the same
temperature, the BET surface area as well as the total pore
volume in general, enlarges with increase in KOH to durian shell
ratio. At KOH to durian shell ratio 0.25 and 0.5, a large amount of
micropore was created, resulting in the increase of BET surface
area and micropore volume. When KOH to durian shell ratio
reaches 1, the widening of existing micropores and development
of new micropores occurred simultaneously, leading to higher
BET surface area and total pore volume as indicated in Table 3. At
high ratio of KOH to durian shell, the microporosity development
is mostly attributed to the intercalation of potassium metal in
the carbon structure. Pore widening normally begins when a
number of opened pore exists in the structure which is the case
when the chemical ratio is reasonably high (Mohanty et al.,
2006).
The surface morphology of the activated carbons produced was
characterized using scanning electron microscope. Fig. 5 depicts
the SEM micrographs of pristine durian shell and activated carbon
obtained at activation temperature of 723 K and impregnation
ratio 0.5 (773/0.5). The SEM micrograph showed that some
macropores were created on the external surface of the carbon
during the activation process. This phenomenon is mainly
due to the release of volatile matter and reaction between
potassium hydroxide and the carbon atom in the precursor
(Ganan et al., 2004) in accordance to the reaction of
6KOH + 2C ? 2K + 3H2 + 2K2CO3. The presence of metallic potassium then intercalates the carbon matrix resulting in the
widening of spaces between carbon atomic layers (Ahmadpour
and Do, 1997).
T.C. Chandra et al. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 457–462
461
Table 3
Pore characteristic of durian shell activated carbon (DSAC).
Carbon code
BET surface area (m2/g)
Micropore surface area (m2/g)
Micropore volume (cm3/g)
Total pore volume (cm3/g)
673/0.25
723/0.25
773/0.25
823/0.25
873/0.25
923/0.25
673/0.50
723/0.50
773/0.50
823/0.50
873/0.50
923/0.50
673/1.00
723/1.00
773/1.00
823/1.00
873/1.00
923/1.00
560
579
900
717
541
520
674
872
992
927
866
467
663
890
979
934
780
674
199
283
681
334
319
278
521
551
849
765
779
291
480
533
805
731
592
450
0.160
0.308
0.367
0.285
0.130
0.284
0.342
0.326
0.368
0.324
0.297
0.137
0.211
0.337
0.349
0.309
0.241
0.218
0.198
0.347
0.402
0.413
0.341
0.345
0.381
0.374
0.411
0.378
0.331
0.172
0.328
0.389
0.423
0.392
0.329
0.304
4. Conclusion
Activated carbons were prepared from durian shell by KOH
activation method at different KOH to durian shell ratio and
activation temperatures. Pore properties of the carbons including
the BET surface area, pore volume and pore size distribution were
characterized using nitrogen adsorption. The KOH to durian shell
ratio of 0.5 and activation temperature of 773 K was found as the
optimum conditions to acquire high surface area activated carbon
from durian shell. In addition, by adjusting the activation
temperature and impregnation ratio, the pore structure of carbon
can be tailored.
Acknowledgements
This research was financially supported by Sub-Project Management Unit Technological and Professional Skills Development Sector
Project (ADB Loan No. 1792-INO) through Widya Mandala TPSDP
Student Grant 2006. Many thanks to Professor Joao C Diniz da Costa
from Division of Chemical Engineering, The University of Queensland Australia for providing TGA-DSC analysis.
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