Preparation of activated carbons by utilizing solid wastesfrom palm oil processing mills

Jia Guo Æ Ben Gui Æ Shou-xin Xiang Æ Xiu-ting Bao ÆHu-ji Zhang Æ Aik Chong Lua

Received: 21 November 2006 / Published online: 30 May 2007

� Springer Science+Business Media, LLC 2007

Abstract Feasibility of producing activated carbons by

utilizing solid wastes (extracted flesh fibre and seed shell)

from palm oil processing mills was investigated. The

effects of activation conditions (CO2 flow rate, activation

temperature and retention time) on the characteristics of the

activated carbons, i.e. density, porosity, BET surface area,

pore size distribution and surface chemistry were studied.

In this study, the optimum conditions for activation were

an activation temperature of 800 �C and a retention time of

30 min for fiber or 50 min for shell, which gave the

maximum BET surface area. Pore size distribution revealed

that the shell-based activated carbons were predominantly

microporous whilst fiber activated carbon had predominant

mesopores and macropores, suggesting the application of

shell and fiber activated carbon as adsorbents for gas-phase

and liquid-phase adsorption, respectively. This was con-

firmed by further gas- and liquid-phase adsorption tests.

Keywords Oil palm solid waste � Activated carbon �CO2 activation � Pore structure � Surface chemistry �Adsorption

1 Introduction

Oil palm (Elaeis guineensis Jacq.) fruit is a major source of

vegetal oil, which is extracted from its flesh and kernel. In

1999, the world production of oil palm fruit was about

95 million tons leading to about 17 million tons oil. They

are produced mainly in South East Asia (Malaysia, Indo-

nesia, and Thailand), Africa (Nigeria and Cameroon), and

several southern provinces of China. During palm-oil

processing, there are two major solid wastes generated,

extracted flesh fiber (or called mesocarp) and seed shell (or

called endocarp) [1]. For example, in Malaysia, which is

the largest palm oil producer in the world, about 2 million

tones (dry weight) of oil-palm shell and 1 million tones of

extracted oil-palm flesh fiber are generated annually [2].

Normally, they are used as boiler fuels or building mate-

rials. To make better utilization of these cheap and abun-

dant wastes, it is proposed to convert them into value-

added products.

Since the price of commercial activated carbon has

dropped continually over the last decade or so, interests are

growing in the use of other low-cost and abundantly

available lignocellulosic materials as precursors for the

preparation of activated carbon [3]. Compared to coal as

the conventional precursor, the renewable oil-palm solid

wastes have another merit of high carbon but low ash

contents, which are associated with the feasibility of cre-

ating highly porous structures within the carbon matrix [4].

Preliminary study has shown it is feasible to prepare chars

with sufficient densities and high porosity from oil palm

fruit wastes [5, 6]. In fact, some oil palm solid wastes have

been successfully converted into activated carbons. Nor-

mah et al. [7] prepared activated carbon from oil palm shell

by steam gasification. The optimum duration of activation

was 45 min, which gave a specific surface area of 710 m2/g

J. Guo (&) � B. Gui � S.-x. Xiang � X.-t. Bao �H.-j. Zhang

Hubei Key Laboratory of Novel Reactor and Green Chemical

Technology, School of Chemical and Pharmaceutical

Engineering, Wuhan Institute of Technology, Wuhan 430073,

P.R. China

e-mail: guojia@mail.wit.edu.cn

A. C. Lua

Division of Thermal and Fluid Engineering,

Nanyang Technological University, Singapore 639798,

Republic of Singapore

123

J Porous Mater (2008) 15:535–540

DOI 10.1007/s10934-007-9129-z

and a yield of 21%. Hussein et al. [8] found that activated

carbon from palm shell by ZnCl2 activation is essentially

microporous with a fairly high surface area of 1,500 m2/g.

However, this method involved using some chemicals,

which may generate a secondary environmental pollution

during waste solution disposal. Therefore, it is not used as

commonly as the physical method using carbon dioxide

(CO2) gas as the activating agent.

The aim of this work was to prepare and characterize

activated carbons from oil palm flesh fiber and seed shell

for adsorption in gaseous and/or aqueous phases. The ef-

fects of CO2 activation conditions, i.e. CO2 flow rate,

activation temperature and retention time, on the textural

and chemical properties of the activated carbons were

investigated to optimize the process.

2 Experimental

2.1 Sample preparation

As-received oil palm flesh fiber and seed shell were first

dried at 110 �C for 24 h to reduce the moisture content.

The dried fiber and shell were then cut, ground and sieved.

Size fractions of 0.5–1.0 mm for fiber and 2.0–2.8 mm for

shell were used. Both pyrolysis and activation were carried

out in a stainless-steel reactor (550 mm length and 38 mm

internal diameter) placed in a vertical tube furnace (818P,

Lenton). About 15 g of the materials were placed on a

metal mesh in the reactor. During pyrolysis, purified

nitrogen at a flow rate of 150 cm3/min was used as purge

gas. The furnace temperature was increased from room

temperature to 600 �C and held at this temperature for 2 h.

The resulting chars were then activated at 500–900 �C for

10–60 min under a CO2 flush of various flow rates. In both

cases, a heating rate of 10 �C/min was used.

2.2 Textural characterization

A thermogravimetric analyzer (TA-50, Shimadzu) was

used for proximate analysis of volatile matter (VM),

fixed carbon (FC) and ash (AS). An ultra-pycnometer

(UPY-1001, Quantachrome) and a mercury intrusion po-

rosimeter (Poresize-9320, Micromeritics) were used to

measure the solid and apparent densities, respectively. For

a known solid density, qs, and apparent density, qa, the

porosity, e, can be calculated as e = [(qs–qa)/qs] · 100%.

Adsorption characteristics were determined by nitrogen

adsorption at –196 �C with an accelerated surface area and

porosimeter (ASAP-2000, Micromeritics). The BET sur-

face area (SBET) was calculated from the adsorption iso-

therms and the pore size distribution calculated using the

BJH model [9]. A scanning electron microscope (S360,

Cambridge Instruments) and a transmission electron

microscope (JEM2010, Leco) were used to verify the

presence of porosity on the sample surface and to study the

atomic structure of the sample, respectively. The charac-

teristics of the starting materials and chars are listed in

Table 1. Oil palm flesh fiber and seed shell appeared to be

suitable raw materials for making high-quality activated

carbons because of their inherent high densities and carbon

contents, especially after pyrolysis.

2.3 Chemical characterization

The surface organic functional groups were studied by

Fourier transformed infrared spectroscopy (FTIR-2000,

Perkin Elmer). The spectra were recorded from 4000 cm–1

to 400 cm–1.

2.4 Adsorption test

Adsorption of NO2 and SO2, two representative gaseous

pollutants, was also carried out in the TGA. NO2 or SO2

(2,000 ppm, balanced by N2) was introduced into the

analyzer chamber, where a platinum sample holder with an

about 20 mg sample was suspended. At room temperature

(30 �C), the subsequent sample weight gain due to the

amount of NO2 or SO2 adsorbed was recorded. In addition,

adsorption of iodine from solution was determined. 100 mg

samples were equilibrated with 25 cm3 of I2/KI solution for

1 h. The value taken for monolayer coverage was the

amount adsorbed at a concentration of 0.5 mmol/dm3.

Table 1 Characteristics of oil palm fruit solid wastes and derived chars

Sample Density and porosity Proximate analysis (wt.%) Surface area (m2/g)

qs (g/cm3) qa (g/cm3) e (%) VM FC AS SBET

Oil palm fiber 1.66 1.62 2.4 80.8 18.3 0.9 1.2

Fiber char 1.73 1.29 25.4 30.9 62.4 6.7 266

Oil palm shell 1.53 1.47 3.9 77.6 19.8 2.6 1.5

Shell char 1.62 1.31 19.1 34.5 59.4 6.1 147

536 J Porous Mater (2008) 15:535–540

123

3 Results and discussion

3.1 Density and porosity

The density of an activated carbon depends on not only the

nature of its raw material but also its preparation [10].

Table 2 shows the weight losses, densities and porosities of

the activated carbons prepared from oil palm fiber and shell

under different activation conditions. For the same reten-

tion time (30 min for fiber and 50 min for shell), increasing

the activation temperature up to 800 �C increased the solid

densities and decreased the apparent densities, resulting in

development of porosity. However, with activation tem-

perature of 900 �C, the apparent density increased and

porosity decreased. This was probably due to excessive

burn-off of the carbon, accompanied by a marked weight

loss, resulting in a reduction of porosity.

3.2 Surface area

The most important property of activated carbon is its

adsorptive capacity, which is related to its specific surface

area. Generally, the higher the surface area, the larger is its

adsorptive capacity [11]. The effects of CO2 flow rate on

the BET surface areas of the fiber and shell derived acti-

vated carbons prepared at 800 �C for 30 and 50 min,

respectively, are shown in Fig. 1. With a low CO2 flow

rate, the BET surface area was small due to an insufficient

amount of CO2 reacting with the carbon to produce pores.

However, with a flow rate too high, the carbon–CO2

reaction was so severe that carbon was burnt off, reducing

the quality of the activated carbon. From the results, a flow

rate of 100 cm3/min was used for subsequent experiments.

Figures 2 and 3 show the BET surface areas of the

activated carbons prepared from fiber and shell under

various activation temperatures. For shell at the low tem-

perature of 500 �C, increasing retention time resulted in a

proportionate increase in BET surface area. At 800 �C with

up to 50 min retention time, the surface area increased

progressively from development of new pores, then de-

creased because of carbon burn-off from excessive expo-

sure. At a higher temperature of 900 �C, the surface area

Table 2 Densities and

porosities of activated carbons

prepared

Sample Activation

temperature (�C)

Retention time

(min)

Weight loss

(%)

qs (g/cm3) qa (g/cm3) e (%)

Palm fiber 500 30 42.1 1.87 1.13 39.6

600 30 51.3 1.95 0.97 50.3

700 30 58.4 2.02 0.92 54.5

800 30 60.7 2.09 0.88 57.9

900 30 78.3 2.14 1.24 42.1

Palm shell 500 50 52.4 1.80 1.10 38.9

600 50 58.9 1.83 0.90 50.8

700 50 64.2 1.90 0.83 56.3

800 50 66.8 1.95 0.71 63.6

900 50 75.7 2.03 1.02 49.8

25 50 100 150 200

CO2 flow rate (cm3/min)

0

200

400

600

800

1000

1200

TE

Bcafrus

m(aera

e2

g/)

Fibre

Shell

Fig. 1 Effect of CO2 flow rate on BET surface area

20 30 40 50 60

Retention time (min)

600

700

800

900

1000

1100

1200

cafrusT

EB

em(

aera2

g/)

500oC

800oC

900oC

Fig. 2 BET surface areas of activated carbon prepared from oil palm

shell at various activation temperatures

J Porous Mater (2008) 15:535–540 537

123

deteriorated from an initial high value with retention time.

Oil palm fiber showed a similar trend. The optimum con-

ditions for CO2 activation for maximum BET surface area

were found to be an activation temperature of 800 �C and a

retention time of 50 min for oil palm shell and 30 min for

fiber.

3.3 Pore size distribution

In the classification by the International Union of Pure and

Applied Chemistry (IUPAC), pores are classified as mi-

cropores (<2 nm diameter), mesopores (2–50 nm diameter)

and macropores (>50 nm diameter) [12]. This classification

is important because most molecules of gaseous pollutants

vary from 0.4 nm to 0.9 nm in diameter. Gas-phase acti-

vated carbons usually consist predominantly of micropores

whilst liquid-phase activated carbons have significant

mesopores because of the larger sizes of liquid molecules.

Figure 4 shows the pore size distributions of activated

carbons from oil palm fibre and shell prepared under dif-

ferent activation conditions. For the shell carbon, there was

a predominance of micropores. The predominance was

more marked for the carbon prepared at 800 �C for 50 min,

and less so for the carbon prepared at 900 �C for 50 min

which had more mesopores and macropores because of the

severe reaction of carbon–CO2. The high microporosity in

shell activated carbon suggests potential applications in

gas-phase adsorption for air pollution control. However,

fiber activated carbon had predominantly mesopores and

macropores, which make them more suitable for liquid-

phase adsorption for example wastewater treatment or

drinking water purification. Low magnification SEM

micrographs (·1000) of the surface of the fiber and shell

activated carbons (Fig. 5a and b) clearly showed the dif-

ferences. The fiber carbon had a more porous structure with

abundant macropores, whereas the shell carbon had few

cavities. It could be seen from the TEM micrographs at

high magnification (·106) that the shell carbon (Fig. 6b)

was a typical amorphous carbon. The gaps between dif-

ferent carbon atom layers (parallel lines) can be considered

slit-shape micropores, of mostly less than 2 nm. However,

in the fiber carbon (Fig. 6a), there was no regular carbon

lattice, giving a lower microporosity.

10 20 30 40 50

Retention time (min)

300

400

500

600

700

BE

Tsu

frac

era

aem(

2)g/

500°C800°C900°C

Fig. 3 BET surface areas of activated carbons prepared from oil

palm fiber at various activation temperatures

100 2 3 4 55 101 2 3 4 55 102 2 3 4 55

Pore Diameter (nm)

0.0

0.1

0.2

0.3

0.4

oP

reo

Vul

em

(cm

3g/)

800oC-50min (shell)

900oC-50min (shell)

800oC-30min (fibre)

900oC-30min (fibre)

MESOPORE MACROPORE

Fig. 4 Pore size distributions of activated carbons from oil palm fiber

and shell

Fig. 5 SEM micrographs of activated carbon surfaces: (a) fiber;

(b) shell

538 J Porous Mater (2008) 15:535–540

123

3.4 Surface chemistry

The adsorptive capacity of the activated carbon is also

influenced by its surface chemical structure. The FTIR

spectra of the chars and activated carbons are shown in

Fig. 7. The spectrum of the char from shell displayed the

following bands: 3,528 cm–1: O–H stretching in alcohols;

2,972 cm–1: C–H stretching in alkanes, 1,747 cm–1: C=O

stretching in ketones; 1,648 cm–1: C=O stretching in qui-

nones; 1,507 cm–1: C=C stretching in aromatic rings;

1,262 cm–1: C–O stretching in ethers; 817 and 719 cm–1:

C–H out-of-plane bending in benzene derivatives. The

spectra of the fiber char displayed the following bands:

3,520 cm–1: O–H stretching in alcohols; 2,357 cm–1: C=O

stretching in ketones; 1,645 cm–1: C=O stretching in qui-

nones; 1,602 cm–1: C=C stretching in aromatic rings. The

main oxygen groups were suggested to be carbonyl groups

(such as ketones and quinones), ethers and phenols in the

shell char, and ketones, quinones and phenols in the fibre

char. These results agree with the surface chemistries of

other agricultural by-products, such as peach stones [13]

and rockroses [14]. After CO2 activation, the ether and

ketonic groups were not found due to their instabilities in

the slightly oxidative atmosphere, and only the quinones

and phenols remained. These groups are typical organic

functional groups on the activated carbon surface. Hence,

the difference between the shell activated and fiber acti-

vated carbons was insignificant. The surface structure of

the thermally activated carbon from oil palm shell or fiber

is given below:O

HO

3.5 Adsorptive capacity

Both gaseous and aqueous phases adsorption onto the

activated carbons prepared and some commercial activated

carbons were carried out (Table 3). The commercial acti-

vated carbons tested include Microcarb� (Grade: FY5,

surface area: 1,150 m2/g) and Carbochem� (Grade: LQ-

830, surface area: 950 m2/g). Table 3 shows that the shell

activated carbon adsorbed more gaseous pollutants but less

iodine from solution than the fiber carbon. Notwithstanding

the gaseous or liquid phase adsorption, the adsorptive

Fig. 6 TEM micrographs of activated carbons: (a) fiber; (b) shell

4000 3400 2800 2200 1600 1000 400

Wave Number (cm-1)

msnarT

iyrartibra(

ecnattstinu)

800oC-30min (fibre)

Fibre char

800oC-50min (shell)

Shell char 917

718

6212

1846

47 17

2792

8253

70511

20615463

025

3275

Fig. 7 FTIR spectra of the chars and activated carbons from oil palm

fiber and shell

Table 3 Adsorptive capacities of the activated carbons

Phase Adsorbate Adsorbent Amount adsorbed

(mg/g)

Gaseous SO2 Fiber activated carbon 38

Shell activated carbon 76

Microcarb� 71

NO2 Fiber activated carbon 136

Shell activated carbon 219

Microcarb� 194

Aqueous Iodine Fiber activated carbon 721

Shell activated carbon 692

Carbochem� 815

J Porous Mater (2008) 15:535–540 539

123

capacities or the qualities of the activated carbons from oil

palm fruit solid wastes were comparable to those of com-

mercial carbons.

The amounts of SO2 adsorbed onto the activated carbons

prepared from oil-palm-shell and apricot stone versus the

micropore volume are shown in Fig. 8. For both the oil-

palm-shell and apricot-stone activated carbon, when the

micropore volume increased, the amount of SO2 gas ad-

sorbed increased progressively. Actually, a linearly pro-

portional relationship between the adsorptive capacity and

the micropore volume was suggested. For the apricot-stone

activated carbon, a relatively larger adsorptive capacity

was possibly due to a wide range of micropores within the

adsorbents. However, some sub-micropores (less than

0.5 nm diameter) were accessible to SO2 at normal tem-

peratures, but not detectable during micropore measure-

ments by N2 adsorption at a low temperature of –196 �C

due to ‘‘activated diffusion’’ problems.

4 Conclusions

Experimental results have shown that it possible to prepare

activated carbons with a high density and well-developed

porosity from oil palm fruit solid wastes. The CO2 flow

rate, activation temperature and retention time had impor-

tant influences on the BET surface area. The optimum

conditions for CO2 activation for maximum BET surface

area were an activation temperature of 800 �C and a

retention time of 50 min for oil palm shell and 30 min for

fiber. The predominance of microporosity in shell activated

carbon suggested its possible application as granular

adsorbent in gas-phase adsorption for air pollution control;

the fiber activated carbon consisted predominantly of

mesopores and macropores, suggesting its application as

powder adsorbent in liquid-phase adsorption for wastewa-

ter treatment. This was confirmed by gas-phase adsorption

of SO2 and NO2 and liquid-phase adsorption of iodine onto

the activated carbons, as well as comparisons with com-

mercial activated carbons, including activated carbons

prepared from apricot stones.

In the future, research work can be carried out on the

relationship between surface chemistry of the activated

carbon and their adsorptive capacity, kinetic studies for

gaseous and aqueous adsorption processes, and the feasi-

bility of using combined CO2 and steam gases as the

activating agent in order to further improve the adsorptive

capacity of the activated carbons prepared.

Acknowledgments The author (Dr. J. Guo) appreciates the financial

supports from the Program for New Century Excellent Talents in

University (Contract No. NCET-05-0681) and the Scientific Research

Foundation for the Returned Overseas Chinese Scholars (Contract No.

2005-383), Ministry of Education, P.R. China.

References

1. W.M.A.W. Daud, W.S.W. Ali, Bioresour. Technol., 93(1), 63

(2004)

2. G. Singh, in Utilisation of Oil Palm Tree and Other Palms, ed. by

M.P. Koh, M.M. Yusoff, K.C. Khoo, N.M. Nasiv (Kepong, Forest

Research Institute Malaysia, 1994), pp. 19–25

3. F. Derbyshire, M. Jagtoyen, R. Andrews, in Proceedings of the2nd Asia Pacific Conference on Sustainable Energy and Envi-ronmental Technologies, ed. by G.Q. Lu, V. Rudolph, P.F.

Greenfield (Brisbane, The University of Queensland, 14–17 June,

1998) pp. 457–462

4. W.M.A.W. Daud, W.S.W. Ali, M.Z. Sulaiman, J. Chem. Technol.

Biotechnol., 78(1), 1 (2003)

5. A. C. Lua, J. Guo, Carbon, 36(11), 1663 (1998)

6. J. Guo, A.C. Lua, J. Anal. Appl. Pyrolysis, 46(2), 113 (1998)

7. M. Normah, K.C. Teo, A.P. Watkinson, in Bioproducts Pro-cessing: Technologies for the tropics, ed. by M.A. Hashim

(Institutes of Chemical Engineers, Rugby, United Kingdom,

1995), 93 pp

8. M.Z. Hussein , R.S.H. Tarmizi, Z. Zainal, R. Ibrahim, M. Badri,

Carbon, 34(11), 1447 (1996)

9. S.J. Gregg, K.S.W. Sing. Adsorption, Surface Area and Porosity.

(Academic Press, New York, 1982), 85 pp

10. A. Jumasiah, T.G. Chuah, J. Gimbon, T.S.Y. Choong, I. Azni,

Desalination 186(1–3), 57 (2005)

11. H. P. Yang, R. Yan, T. Chin, D.T. Liang, H. P. Chen, C.G. Zheng,

Energy Fuels, 18(6), 1814 (2004)

12. IUPAC, 1982. Manual of Symbols and Terminology of ColloidSurface. (Butterworths, London), p. 1

13. R. Arriagada, R. Garcia, M. Molina-Sabio, F. Rodriguez-Rein-

oso, Microporous Mater., 8, 123 (1997)

14. V. Gomez-Serrano, J. Pastor-Villegas, C.J. Duran-Valle, C.

Valenzeula-Calahorro, Carbon, 34, 533 (1996)

15. A. G. Pandolfo, M. Amini-Amoli, J.S. Killingley, Carbon, 32(5),

1015 (1994)

0.0 0.2 0.4 0.6 0.8 1.0Micropore Volume (cm3/g)

0

20

40

60

80

100

120A

mou

nt o

f SO

2 A

dsor

bed

(mg/

gC)

Oil-palm shell

Apricot stone

Fig. 8 Amounts of SO2 gas adsorbed versus micropore volume of the

activated carbons

540 J Porous Mater (2008) 15:535–540

123