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○
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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
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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
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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
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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).
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Fig.6 Relationship between EMC and the proportion of aromatic carbon
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(Received 9 Mar. 2010; Accepted 5 July 2010)
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【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
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