Solid fuel production from oil palm shell by hydrothermal ...

1. 　Introduction

Oil palm is tropical vegetation which grows

well in the Southeast Asia region such as Indonesia,

Malaysia, and Thailand. Due to its high economical

value, oil palm becomes an important agricultural

commodity for these countries. In 2008, the total

mature area of oil palm plantation in the three

countries amounted approximately to 9.33 million

ha1). After oil palm is harvested in the plantation,

the fruit is processed in palm oil mills to produce

crude palm oil (CPO) as a main product. However,

a considerable amount of solid residues comes

from the process. Oil palm shell is a typical solid

residue abundantly generated in the palm oil mill.

Indonesia, the world's largest CPO producer, wasted

approximately 4.83 million ton of shell in 20052).

The amount will steadily increase as the rising trend

of Indonesia's CPO production. Regarding its annual

growth, it is estimated that around 7.56 million ton

of shell has been produced in 2009. Such a huge

amount of this residue is an obviously potential

source of environmental pollution when it is not

properly treated.

Although most palm oil mills utilize oil palm shell

as an additional fuel for their boiler, the generated

energy is relatively low due to considerably high

moisture and a large amount of oxygen-containing

functional groups. Extensive works for more effective

utilization of oil palm shell by adopting common

biomass conversion methods, like pyrolysis and

gasification, have already been studied. Yang et al.3)

investigated pyrolysis of oil palm shell using a bench-

scale packed bed reactor with countercurrent

flow, toyield gas with a moderate heating value of

about 14-16 MJ/m3. Mae et al4) reported that the

gasification of oil palm shell could be promoted

through modification of the lignin structure. Li

et al5) conducted catalytic steam gasification of

various oil palm wastes, including oil palm shell, in

a fixed bed reactor using a tri-metallic catalyst to

produce hydrogen-rich gas. Nevertheless, a need of

more energy for operating these processes at high

* Graduate School of Engineering, Kyushu University Present address: Faculty of Engineering, Gadjah Mada University** Faculty of Engineering, Kyushu University, Japan*** Research and Education Center of Carbon Resources, Kyushu University, Japan**** Corresponding author : 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan e-mail: [email protected]

【Original article】

Solid fuel production from oil palm shell by hydrothermal carbonizationAhmad T. Yuliansyah*, Tsuyoshi Hirajima** ****, Satoshi Kumagai***, Keiko Sasaki**

Abstract: In this study, the production of solid fuel from oil palm shell which is a solid residue from oil milling process operating in tropical countries was investigated by hydrothermal carbonization. The experiments were conducted in a 500 mL batch-autoclave in a temperature range of 200-380℃ with the initial pressure of 2.0 MPa, and the residence time of 30 min. About 35-60 wt% of original materials was recovered as a solid product and the fuel characteristics became more favorable with the yield lower. That is, the solids exhibited gross calorific value ranging from 23.2 to 33.0 MJ/kg (dry ash-free basis) and the equilibrium moisture content was between 6.7 and 3.1 wt%. The carbon content varied from 57.1 to 80.9 wt%, while the oxygen content was from 36.8 to 13.5 wt% (dry ash-free basis) after the treatments. Changes in carbon-functional groups measured by FT-IR and 13C-NMR during the carbonization process were also examined and discussed.

Keywords: oil palm shell, hydrothermal carbonization, solid fuel

木質炭化学会誌 7 ( 1 ), 19-26 (2010)ｃ The Wood carbonization Rescarch Society○

–19–

–20–

temperature (>500℃) makes the interest lessen.

In this study, modification of oil palm shell into a

solid fuel with high calorific value by hydrothermal-

carbonization was investigated. There are two

reasons for employing this means : one is much lower

operating temperature (　380℃) compared to those of

pyrolysis and gasification, and another is unnecessary

drying of raw material because the carbonization

process is conducted in a wet environment. This

paper focused on characterization of solid products

obtained at various temperatures and thus discussed

on the decomposition behavior of oil palm shell.

2.　Experimental

2.1　Material

Oil palm shell as the raw material was collected

from an oil palm plantation in southern Sumatra,

Indonesia. Prior to use, it was air-dried and pulverized

to form powder with a maximum particle size of 1

mm. The chemical composition of raw material is

listed in Table 1.

2.2　Apparatus and experimental procedure

All of experiments were carried out in a 500

mL batch-type autoclave (Taiatsu Techno MA 22)

which was equipped with a stirrer and an automatic

temperature controller. Slurry made of 300 mL water

and 30 g oil palm shell was loaded into the autoclave.

N2 was used to purge the autoclave and to establish

the initial pressure of 2.0 MPa. While stirring at

200 rpm, the autoclave was gradually heated up to a

designed temperature at an average heating rate of

6.6℃/min. The designed temperature ranging from

200 to 380℃was automatically controlled. After

holding the temperature for 30 min as the residence

time, the autoclave was cooled down to room

temperature by air blow using an electric blower.

Afterward, the remaining slurry was withdrawn and

filtered with No. 5C filter (ADVANTEC) to separate

the solid fraction from the liquid fraction. The

recovered solid was then dried to constant weight at

105℃ for obtaining the final solid product.

2.3　Analysis of solid product

The solid product was composed of unconverted

sample and precipitated solid resulting from

polymerization of water soluble compounds and

condensed tar. All of the solid products were

characterized in several aspects. The elemental

composition was determined by using Yanaco CHN

Corder MT-5 and MT-6 elemental analyzer. The

content of cellulose, hemicellulose, and lignin were

Table 1　Chemical composition of raw shell　

Fig.1　Schematic representation of experimental apparatus

2. The amount of products decreased at elevated

temperature suggesting that degradation reactions

accomplished more completely. Around 59.5 wt% of

original sample was obtained as product at 200℃,

while only 35 wt% recovered at 380℃. As can be

seen in this table, raw shell contained carbon as high

as 50.6 wt%, signaling its potential of energy source.

However, a very high oxygen content (43.0 wt%)

reduced its attractiveness, as reflected from its low

calorific value of 21.4 MJ/kg.

Progressive decomposition occurred at higher

temperature, leading to an increase in carbon

content and a decrease in oxygen content. Treatment

at 380℃ increased carbon content to 80.9 wt%

and, on the contrary, decreased oxygen content to

13.5 wt%. This led to increase in C/O atomic ratio

from 1.6 (raw) to 8.0 (380℃) and gross calorific

value from 21.4 (raw) to 33.0 MJ/kg (380℃). A

dramatic increase in carbon content suggests that a

carbonization process occurred during the treatment.

Furthermore, a remarked decrease in oxygen

content during the treatment denotes that most of

oxygen-rich compounds were degraded to remove

from the material. However, a small difference in

the solid yield was observed at higher temperature

range. For example, within 330-380℃ the solid

yield decreased slightly from 37.3 to 35.0 wt%. It

–21–

measured by applying a procedure recommended by

the US National Renewable Energy Laboratory6) that

is substantially to the same as that of ASTM E1758-

01. Proximate, total sulfur and calorific analyses were

carried out according to JIS M 8812, JIS M 8819, and

JIS M 8814, respectively. For equilibrium moisture

content (EMC) determined according to JIS M 8811,

an aliquot of the sample was placed in a desiccator

with a saturated salt solution. After equilibrium was

reached, the moisture was quickly measured by a

moisture analyzer (Sartorius MA 150). Identification

of the chemical structure and functional groups

was performed on a Fourier-transform infrared

(FT-IR) spectrometer (JASCO 670 Plus) with a KBr

disk. Cross polarization/magic angle spinning (CP/

MAS) 13C-NMR spectra were taken on a solid-

state spectrophotometer (JEOL CMX-300) with the

following conditions: scanning time,10,000; contact

time, 2 ms; spinning speed, >12 kHz; pulse repetition

time, 7 s. The obtained spectrum was calibrated with

hexamethyl benzene. Curve fitting analysis was made

using Grams/AI 32 ver. 8.0 software.

3　Results and Discussion

3.1　Proximate and ultimate analyses results

Properties of solid products obtained at

various temperatures are summarized in Table

Table2　 Proximate and ultimate analyses of raw material and solid products

indicates that water-soluble compounds produced

during the hydrothermal condition polymerize to

build higher molecular compounds that subsequently

precipitated7,8).

The data of fixed carbon and volatile matter at

different temperatures show that the dramatically

changes of properties occurred mainly within the

200-300℃ range. Approximately 66.3 % of the

increase of total fixed carbon and decrease in volatile

matter, by changing from the basic condition to

380℃, took place in this temperature range. A

similar trend was observed for other solid properties.

3.2　van Krevelen Diagram

Figure 2 shows the percentage of biomass

components in the 200-300℃ products in

comparison with the composition of original

feed. The treatment significantly degraded both

hemicellulose and cellulose to produce a lignin-

concentrated solid. The solid produced at 200℃still

contained a small amount of hemicellulose, which

completely vanished on 240℃ treatment. Meanwhile,

a considerable amount of cellulose remained at

240℃, although it was eliminated at 270℃. As

a result, the portion of non-sugar compounds,

lignin and its derivatives, steadily increased along

temperature range and it became the predominant

component in the　　270℃ products. These data

suggest that cellulose and hemicellulose were

relatively easier to decompose completely than

lignin. This behavior was in agreement with other

earlier reports9-11)

During the hydrothermal process, oil palm

shell underwent a coalification-like process, as

illustrated in Figure 3. That is raw shell has high

atomic H/C and O/C ratios, and both ratios gradually

decreased during the treatment. The slope of the

trajectories suggests that the content of O decreased

in proportion to that of H, probably due to the

dehydration reaction. It is clear that both decreases

of O and H occurred mainly in the range of 200-

270℃. Less significant changes were observed at

higher temperature.

Figure 3 also compares the relative composition

for shell's product and other solid fuels. It seems

that shell's solid produced at 270 and 380℃ had

H/C ratios similar to those sub-bituminuos and

bituminous coal. However, the sub-bituminuos and

bituminous coals had lower O/C ratios.

3.3　FT-IR and 13C-NMR Spectra

FT-IR spectra analysis was performed to

understand the change of functional groups in solids.

Peaks assignment was made based on literature

data12-14). Figure 4 describes spectra of raw shell and

–22–

Fig.2　Percentage components for the productsobtained 　　　in the region of 200-300℃ in comparison with raw 　　　material

Fig.3　van Krevelen diagram for products obtained at different temperatures and other solid fuel (1, raw material; 2, 3, 4, 5, 6, 7, and 8; products obtained at 20 0 , 2 4 0 , 270 , 30 0 , 330 , 350 , and 38 0℃)

groups in lignin (56 ppm), C-6 carbon atoms

in cellulose (62-65 ppm), C-2/C-3/C-5 atoms in

cellulose (72-75 ppm), C-4 atoms in cellulose (84-

89 ppm), C-1 atoms in hemicellulose (102 ppm),

C-1 atoms in cellulose (105 ppm), unsubstituted

olefinic or aromatic carbon atoms (110-127 ppm),

quaternary olefinic or aromatic carbon atoms (127-

143 ppm), olefinic or aromatic carbon atoms with

OH or OR substituents (143-167 ppm), esters and

carboxylic acids (169-195 ppm) including acetyl

groups in hemicellulose (173 ppm), and carbonyl

groups in lignin (195-225 ppm). For all of these

various resonance, for the purpose of making semi-

quantitative analysis the spectra could be simply

classified into aliphatic (0-59 ppm), carbohydrate (59-

110 ppm), aromatic (110-160 ppm), carboxyl (160-

188 ppm), and carbonyl regions (188-225 ppm)18,19).

Figure 5 shows that the solids obtained at

200 and 240℃ exhibited spectra identical with

that of raw material; accompanying progressively

diminished peaks of hemicelullose and cellulose.

Furthermore, the spectra were found to become more

aromatic at 270℃. The relative amount of aromatics,

associated with the lignin or its derivatives, increased

within 200-270℃, while the carbohydrate content

–23–

Fig.5　13C-NMR spectra with curve fitting for raw shell and 　　 products obtained at different temperaturesthe corresponding solid products. As can be seen

in the figure, the peak assigned to aliphatic CHn

groups appearing at 2900 cm-1 weakened, indicating

that several long aliphatic chains of molecule

in the solid were broken down. For the peak of -OH groups appeared at 3500 cm-1, its intensity

decreased at elevated temperature. This indicated

that dehydration reaction occurred. More distinctive

peaks were observed in region below 2000 cm-1. The

peak at 1700-1740 cm-1 corresponded to carbonyl

(C=O) stretching vibration and glycosidic bond peak

derived from the cellulose was detected at 1050

cm-1. However, the latter peak steadily weakened

to completely disappear at temperature >270℃.

It can thus be pointed out that most of cellulose

fraction was degraded at this temperature. Also

decomposition of lignin was suggested from decrease

of intensity of aromatic skeletal vibrations mode

at 1515 and 1595 cm-1 and C-O-C aryl-alkyl ether

linkage at 1230 cm-1.

In order to complement the above-mentioned

result of FT-IR, 13C-NMR measurements have been

conducted. Its typical spectra for raw biomass

with peak assignment are found in numerous

publications15-19). According to these information,

resonance peaks in spectra for raw shell can be

assigned to CH3 in acetyl groups (21 ppm), methoxyl

Fig.4　FT-IR spectra for raw shell and the products

decreased. It is in good agreement with the

component analysis result suggesting that lignin and

derivatives are the most dominant component found

at products at 270℃ (Fig. 2).

3.4　EMC

The result of EMC listed in Table 2 demonstrated

that hydrothermal treatment effectively reduced the

relevant value. That is, treatment at 200℃ reduced

the original value of 9.9 wt% to 6.7 wt%. Further

treatment at 380℃ led to EMC as low as 3.1 wt%.

However, it was likely that the decrease in EMC

mainly occurred in the range of 200-270℃. These

situations were in agreement with the change of

solid components given in Figure 2.

In the ability of water adsorption, hemicellulose

is superior to cellulose and lignin. Since hemicellulose

could be preferentially removed from solid at low

temperatures, it is reasonable to consider that the

equilibrium moisture rapidly diminished in the

relevant period. In contrast, solid with high content

of lignin could adsorb only a small amount of

moisture20). Furthermore, such EMC results were

consistent with the above 13C-NMR results exhibiting

an increased proportion of aromatic compounds in

solid. In a word, hydrophobic aromatic compounds

are resistant to humidity and water adsorption from

air. Therefore, the higher aromatic content can lead

to the lower equilibrium moisture. The correlation of

aromatic carbon in the products with the EMC was

illustrated in Figure 6.

EMC and calorific value are two important

properties of solid fuel. When the fuel is combusted,

a part of energy is consumed for water vaporization.

In brief, a solid organic material with higher EMC

will consume more energy to evaporate the moisture.

Thus, a good solid fuel should have a high calorific

value, and a low EMC. Our experiments show that

both properties could be adequately improved by the

hydrothermal carbonization process.

4.　Conclusion

Oil palm shell was successfully converted into

good solid fuel via hydrothermal carbonization in a

batch reactor at 200-380℃. The produced solids had

higher carbon content, lower oxygen content, higher

calorific value, and lower EMC when the treatments

were conducted at higher temperatures. The van

Krevelen diagram showed that oil palm shell was

subjected to a coalification-like process whereby

the composition of solids was comparable to those

of sub-bituminuos and bituminous coals. The FT-IR

analysis confirmed that the progressive elimination

of oxygen due to dehydration was in conjunction

with decomposition of hemicellulose and cellulose

occurred at 200-270℃ . Meanwhile, the structure of

solid was markedly changed and was dominated by

lignin and its derivatives at 270℃, as ascertained

by the 13C-NMR spectra. Based on these results, it

is proposed that hydrothermal carbonization could

become an advantageous technology for producing

solid fuel from biomass.

Acknowledgment

The authors are grateful for support of this

research by a Grant-in-Aid for Scientific Research No.

21246135 from the Japan Society for the Promotion

of Science (JSPS) and the Global COE program (Novel

Carbon Resources Sciences, Kyushu University).

–24–

Fig.6　Relationship between EMC and the proportion of　　　 aromatic carbon

References

1) Oil World : in Investor Bulletin of PT Astra Agro

　 Lestari, 2nd edition, March 2009

2) Yuliansyah A.T., Hirajima T., Rochmadi (2009) J.

　 MMIJ, 125, 583-589

3) Yang H., Yan R., Chen H., Lee D.H., Liang D.T.,

Zheng C. (2006) Fuel Process. Technol. 87, 935-

942

4) Mae K., Hasegawa I., Kawashita H., Miura K.(2001)

J. Jpn. Inst. Energy, 80, 436-443

5) Li J., Yin Y., Zhang X., Liu J., Yan R. (2009) Int. J.

Hydrogen Energy, 34, 9108-9115

6) Sluiter A., Hames B., Ruiz R., Scarlata C., Sluiter J.,

Templeton D., Crocker D. (2005) Determination of

structural carbohydrates and lignin in biomass,

The US NREL Technical Report, 2005

7) Knezevic D., van Swaaij W.P.M., Kersten S.R.A.

(2009) Ind. Eng. Chem. Res., 48, 4731-4743

8) Kumar S., Gupta R.B. (2009) Energy Fuels, 23,

5151-5159

9) Ando H., Sakaki T., Kokusho T., Shibata M., Uemura

Y., Hatate Y. (2000) Ind. Eng. Chem. Res., 39,

　 3688- 3693

10) Inoue S., Uno S., Minowa T. (2008) J. Chem. Eng.

Jpn., 41, 210-215

11) Minowa T., Fang Z., Ogi T., Varhegyi G. (1998) J.

Chem. Eng. Jpn., 31, 131-134

12) Kobayashi N., Okada N., Hirakawa A., Sato T.,

Kobayashi J., Hatano S., Itaya, Y., Mori, S. (2009)

Ind. Eng. Chem. Res., 48, 373-379

13) Ozcimen D., Ersoy-Mericboyu A. (2010)

Renewable Energy, 35, 1319-1324

14) Yang H., Yan R., Chen H., Lee D.H., Zheng C. (2007)

Fuel, 86, 1781-1788

15) Atalla R.H., VanderHart D.L. (1999) Solid State

Nucl. Magn. Reson., 15, 1-19

16) Capanema E.A., Balakshin M.Y., Kadla J.F. (2005) J.

　 Agric. Food Chem., 53, 9639-9649

17) Liitia T., Maunu S.L., Sipila J., Hortling B. (2002)

Solid State Nucl. Magn. Reson., 21,171-186

18) Wikberg H., Maunu S.L. (2004) Carbohydr.

Polym., 58, 461-466

19) Wooten J.B., Kalengamaliro N.E., Axelson D.E.

(2009) Phytochemistry, 70, 940-951

20) Morohoshi N. (1991) Mokushitsu Biomass no

Riyou Gijyutsu, Buneido Shuppan (Tokyo, Japan),

p.84

(Received 9 Mar. 2010; Accepted 5 July 2010)

–25–

【研究報告】 水熱炭化法によるオイルパームシェルからの固体燃料生産

アハマド T ユリアンシャー，平島　剛，熊谷　聡，笹木圭子

概要：パームオイル生産工程で固形残渣として副生されるオイルパームシェルは，インドネシア， マレーシ

アおよびタイといった熱帯諸国において，エネルギー資源として潜在的に多く存在している。本研究では，

水熱炭化法を用いたオイルパームシェルからの固体燃料生産法について検討した。実験は，内容積 500 mL

のオートクレーブを用いて，反応温度 200-380℃，反応時間 30 min の条件にておこなった。その結果，原

料基準で約 35-60 wt％の収率で，固体燃料として好ましい特徴を有する固体生成物が得られた。すなわち，

固体の発熱量は 23.3-33.0 MJ/Kg へ増加し，平衡含水率は 6.7 から 3.1 wt％の範囲内であった。さらに，炭

素含有割合は 57.1 から 80.9 wt％に増加し，酸素含有割合は 36.8 から 13.5 wt％に減少した。また，処理過

程における固体残渣の化学組成変化は，FT-IR および 13C-NMR 分析によって決定された炭素官能基の変化と

同様であった。

キーワード： オイルパームシェル，水熱炭化法，固体燃料

–26–