Journal of Power and Energy Engineering, 2015, 3, 185-193
Published Online April 2015 in SciRes. http://www.scirp.org/journal/jpee
http://dx.doi.org/10.4236/jpee.2015.34026
How to cite this paper: Yakub, M.I., et al. (2015) Pyrolysis of Oil Palm Residues in a Fixed Bed Tubular Reactor. Journal of
Power and Energy Engineering, 3, 185-193. http://dx.doi.org/10.4236/jpee.2015.34026
Pyrolysis of Oil Palm Residues in a Fixed
Bed Tubular Reactor
Mohammed Isah Yakub1, Abakr Yousif Abdalla1, Kabir Kazi Feroz2, Yusuf Suzana3,
Alshareef Ibraheem4, Soh Aik Chin4
1Energy, Fuel and Power Technology Research Division, School of Engineering, The University of Nottingham
Malaysia Campus, Selangor Darul Ehsan, Malaysia
2Department of Chemical Engineering and Applied Chemistry, Aston University, Birmingham, UK
3Depart ment of Chemical Engineering, Universiti Teknology Petronas (UTP), Tronoh, Malaysia
4Crops for the Future (CFF), The University of Nottingham Malaysia Campus,
Selangor Darul Ehsan, Malaysia
Received November 2014
Abstract
Searching for alternative energy sources continues to grow in recent times due to the fear of
energy insecurity in the near future and environmental and sociopolitical issues associated with
the use of fossil fuel. Among the renewable energy sources, biomass is the only source that has
carbon in its building blocks which can be processed to liquid fuel. In this study, pyrolysis of oil
palm residues (trunk, frond and empty fruit bunch) was carried out in a fixed bed tubular reactor
under nitrogen atmosphere at 30 mL/min, 30˚C/min heating rate and 600˚C rea cti on temperature.
Pyrolysis products (bio-oil, bio-char and non-condensable gas) were characterized. Water content,
acidity (pH), higher heating value (HHV) and oxygen content of the bio-oil varied between 39.28 -
43 wt%, 2.92 - 3.20, 19.29 - 21.92 MJ/kg and 58.47 - 59.85 wt% respectively. Low pH, highwater
and oxygen contents in the oil make it unsuitable for being used as fuel and therefore require up-
grading. Scanning electron microscopy and ultimate analysis of the bio-char suggests that it is a
porous material and consists mainly carbon between 82.22 - 84.96 wt% and has HHV in the range
of 25.98 - 27. 65 MJ/kg. This may be used as solid biofuel, adsorbent and source of carbon. High
percentage of hydrogen (H2) and carbon monoxide (CO) were observed in the non-condensable
gas which may be processed to transportation fuel via Fisher-Tropsch process. Oil palm residues
represent good source of renewable energy when all the pyrolysis products are efficiently uti-
lized.
Keywords
Oil Palm Residue, Pyr olysi s, Bio-Oil , Bio-Char, Non-Condensable Gas
1. Introduction
Energy demand continues to grow with increasing population and industrialization which has put heavy depen-
dence on the fossil fuel. Recently, the demand for fossil oil stands at about 94.4 million barrel per day [1] which

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may continue to rise. This will definitely put more pressure on the known reserves and may lead to energy crises
in future. Another consequence with the use of fossil fuel is emission of greenhouse gas that has impacted nega-
tively on our environment. Several measures have been suggested but the cost of treating the greenhouse gas is
high and may not be economical feasible [2] [3] particularly in the present time of declining crude oil price.
The dwindling crude oil price may not be far from a deliberate political move to discourage the develop-
ment of renewable energy. If we must keep our environment safe, viable for agricultural production and
avoid energy crises in future, the time to act is now and the development of alternative renewable energy is
inevitable.
The use of lignocellulosic biomass (non-food materials) such as forest residues, agro-wastes, energy grasses,
aquatic plants and algae etc for biofuel production continue to gain tremendous attention as they are evenly dis-
tributed across the globe and have also eliminated initial public perception of food insecurity associated with
first generation biofuels which were produced from food materials [4]-[6]. In addition, these materials have low
level of sulfur, nitrogen and ash content which make them relatively environmental friendly. Malaysia is one of
the countries in the world that is in to agricultural enterprises. This sector generates million tons biomass an-
nually which create disposal problem. In 2009, about 243.6 million tons of biomass was generated. This value is
projected to be 312 million tons in 2020 in which biomass from palm oil industry constitutes largest portion.
[7]-[11]. In order for this sector to remain attractive, efforts are geared towards utilization of the biomass for
sustainable energy production [9] [12] [13]. The objective of this paper was to carry out pyrolysis of oil palm re-
sidues to bio-oil, bio-char and syngas and characterization of the products.
2. Experiment
2.1. Materials
Oil palm residues such as trunk (OPT), fronds (OPF) and empty fruit bunch (OPEFB) chopped 6 to 8 cm were
collected from Crops for the Future (CFF) field Research Centre and transported in plastic bags to research
building of University of Nottingham Malaysia campus. Samples from the OPT were taken from first 10 ft from
bottom (OPT/10ft), between 10 ft and 20 ft (OPT/20ft) and between 20 and 30 ft (OPT/30ft) while fronds were
grouped to stem only (OPFS) and fronds total (OPFT) which consist of stem and leaves. The materials were
oven dried at 105˚C for moisture content determination according to BS EN 14774-1 standard [14]. The dried
materials were then shredded in a rotor beater mill RetschR to particle sizes between 0.2 - 2 mm and stored in air
tight plastic bags.
2.2. Feedstock Characterization
Volatile matter and ash content on dry basis were determined according BS EN 15,148 [15] and BS EN 14,775
[16] respectively. Fixed carbon was computed by subtracting the percentage compositions of ash and volatile
matter from the bone dry sample mass. Elemental composition of the ash was analyzed using energy dispersive
X-ray (EDX). Higher heating value (HHV) was determined using oxygen bomb calorimeter Parr 6100 following
BS EN 14,918 [17]. Elemental compositions of the biomass were determined using CHNS analyzer, LECO
Corporation USA. Thermo gravimetric study was carried out in thermo gravimetric analyzer (TGA) Perkin El-
mer Simultaneous thermal analyzer (STA) 6000 in nitrogen atmosphere, flow rate 20 mL/min at temperature be-
tween 300 - 1000 K and heating rate of 10 K/min. Structural composition of the biomass was determined ac-
cording to NREL/TP-510-42618 [18].
2.3. Pyrolysis and Pyrolysis Products Characterization
Pyrolysis was carried out in a fixed bed tubular reactor of length 102 cm and diameter 10.5 cm (Figure 1) under
nitrogen atmosphere of 30 mL/mi n and reaction temperature of 600˚C. This condition has been established in
our previous studies [19]. The reactor was heated electrically at heating rate of 30˚C/min. 30 g of biomass sam-
ple (2 - 4 mm particle size) was used in each experiment. The reaction time was kept at 15 min (±2 min) or until
no significant amount of non-condensable gas was observed. The pyrolysis vapor was condensed in a condenser
connected to chiller with cooling water at 4˚C and the oil was collected for further analysis. Non-condensable
gas was passed through a gas scrubber and the dried gas composition was analyzed. Bio-char was collected at
end of each experiment after the reactor temperature cool to room temperature and further analyzed.

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P
FH
G
E
A
B
C
J
K
L
M
I
N
2
D
N
N
Figure 1. Fixed bed Pyrolysis System. (A) Nitrogen cylinder, (B) pressure gauge, (C)
nitrogen flow meter, (D) digital thermometer, (E) thermocouple, (F) tubular furnace, (G)
packed bed, (H) alumina tube, (I) furnace control button, (J) condenser, (K) oil collector,
(L) gas scrubber, (M) gas analyzer, (N) non-condensable gas discharge.
After each production, characterization of bio-oil was carried out within 24 hours. The oil was first filtered
using PTFE syringe filter of 0.45 µm pore size and 13 mm diameter. Higher heating value was determined using
oxygen bomb calorimeter Parr 6100 according to ASTM D240-09 [20]. Walk LAB microcomputer pH meter
TI9000 was used to determine the pH. Density and viscosity were determined using Anton Paar density meter
DMA 4500 M and Brookfield DV-E viscometer respectively. Bio-oil water content was determined using Karl
Fischer V20 volumetric titrator Mettler Toledo for water content according to ASTM E 203-01 [21] [22]. Ele-
mental compositions of the oil were determined using the procedure outlined above under the feedstock charac-
terizatio n. Composition of non-condensable pyrolysis product was determined using Dräger X-am 5000 gas analy-
zer. Proximate and ultimate analyses of bio-char were carried out following the same procedures used for the
feedstock characterization. Scanning electron microscope (SEM) FEI Quanta 400 FE-SEM was used to evaluate
surface characteristics of the bio-char.
3. Results and Discussion
3.1. Feedstock Characteristics
Proximate, ultimate and structural analyses results are shown in Table 1. Moisture content in the samples varied
from 8.44 to 77.52 wt% with OPEFB having the least moisture content while the highest percentage was rec-
orded in the OPT/30ft. Moisture content is an important parameter as it affects biomass quality, storage and
handling especially if it is to be converted via thermo chemical process. During pyrolysis, the initial moisture in
the biomass takes up heat from the system and vaporizes and later condenses in the bio-oil which leads to lower
value of HHV. Volatile matter on dry basis were found to be 82, 82.05, 80.11, 80.88, 79.69 and 75.01 wt% for
OPT/10ft, OPT/20ft, OPT/30ft, OPFS, OPFT and OPEFB respectively. The ash content and heating values were
between 2.07 and 6.51 wt%, and 16.07 and 18.60 MJ/kg. The ash consist mainly potassium (K), chlorine (Cl),
silicon (Si) and calcium (Ca). Other elements identified include phosphorus (P), aluminum (Al), magnesium
(Mg) and traces of sodium (Na) and manganese (Mn) (Table 2). Ultimate analysis revealed that oil palm resi-
dues have 45.05 - 60.17 wt% carbon, 5.1 - 6.12 wt% hydrogen, 0.06 - 1.82 wt% nitrogen, 0.04 - 1.63 wt% sulfur
and 32.61 - 48.82 wt% oxygen. Similarly, the cellulose, hemicellulose and lignin content were between 28 -
38.77 wt%, 14.85 - 26.28 wt% and 21.42 - 31.07 wt% correspondingly. These characteristics are in agreement

M. I. Yakub et al.
188
Table 1. Characteristics of oil palm residues (average values 3 replicates). aAs received; bdry basis; cby difference.
Property Biomass
OPT/10ft OPT /20ft OPT/30ft OPFS OPFT OPEFB
Proximate analysis (wt%)
Moisture contenta 49.27 72.90 77.52 11.71 31.92 8.44
Volatile matterb 82.00 82.05 80.11 80.88 79.69 7 5.01
Fixed carbonc 15.03 15.88 14.36 15.51 13.80 20. 23
Ash contentb 2.97 2.07 5.53 3.61 6.51 4.76
HHV (MJ/kg) 17.73 17.91 17.33 17.55 18.60 16.07
Ultimate analysis (wt%)
Carbon 54.22 59. 77 60.17 45.05 50.68 4 5.26
Hydrogen 7.10 7.28 7.93 5.86 6.12 5.13
Nitrogen 0.06 0.06 0.06 0.23 0.90 1.82
Sulfur 0.26 0.28 0.28 0.04 1.63 0.50
Oxygenc 38.36 32.61 31.56 48.82 4 0.67 47.29
Structural composition (wt%)
Cellulose 38.73 33.96 31.08 38.77 32.23 29.56
Hemi cellu lose 18. 87 20.77 19.96 19.43 26.28 28.71
Li g n i n 29.20 30.76 31.07 21.42 24.54 1 4.85
Table 2. Ash elemental composition determined by EDX. Each value is an average of 3 repli cates.
Biomass
Elemental composition (wt%) dry ash basis
Na Mg Al Si P S Cl K Ca Mn Others
OBEFB - 3.25 1.16 14.21 1.20 2.58 16.73 58.51 2.30 - 0.06
OPFT - 2.20 1.60 36.33 2.25 1.13 6.49 23.86 24.40 1.51 0.23
OPFS - 1.51 0.64 2.72 2.15 3.24 19.75 50.22 19.68 - 0.09
OPT/30ft 0.24 2.43 3.99 3.92 1.08 4.03 14.85 41.12 27.75 - 0.59
OPT/20ft 0.38 4.86 0.86 3.83 2.74 5.64 6.86 47.45 24.96 - 2.42
OPT/10ft 0.56 6.99 1.12 9.08 2.00 7.53 4.52 55.74 11.09 - 1.37
with Thermo gravimetric analysis (TGA) result as shown in Figure 2.
DTG showed thermal decomposition of various components in the each oil palm residue. Peak (a) at 478 K
may be attributed to decomposition of extractives. While (c) and (d) correspond to decomposition of hemicellu-
lose at temperatures 543 K and cellulose at 600 K respectively. Beyond 600 K, Point (e), signifies decomposi-
tion of lignin [23]. No noticeable peak was observed in the lignin decomposition region. Consequently, it can be
deduced that lignin contents of oil palm residues have uniform thermal decomposition.
3.2. Pyrolysis Products Distribution and Characteristics
The pyrolysis products (bio-oil, bio-char and non-condensable) distribution are shown in Table 3. Bio-oil yield
recorded was 31.97, 34.26, 31.47, 29.56, 34.23 and 30.23 wt% from OPT/10ft, OPT/20ft, OPT/30ft, OPFT,
OPFS and OPEFB respectively with corresponding bio-char of 30.56, 29.67, 34.69, 35.50, 29.43 and 38.45 wt%.
The amount of non-condensable gas was computed by subtracting the percentage compositions of bio-oil and
bio-char from the bone dry sample mass. The high yield of oil recorded from OPT/20ft and OPFS may be attri-

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Figure 2. Thermo gravimetric analysis of oil palm residues (A) TGA, (B) DTG under nitrogen atmosphere (20 mL/min);
heating rate (10 K/min).
Table 3. Pyrolysis product distribution from oil palm residue at 600˚C, 30 mL/min N2 flow and 30˚C/min heating rate.
Biomass Pyrolysis products distribution (wt%)
Oil Gas Char
OPT/10ft 31.97 37. 47 30.56
OPT/20ft 34.26 36. 07 29.67
OPT/30ft 31.47 33. 84 34.69
OPEFB 29.56 34.94 35.50
OPFS 34.23 3 6.34 29.43
OPFT 30.23 31.32 38.45
buted to lower ash level in the respective biomass sample since high biomass ash normally favor char formation
[23].
From the physicochemical characteristics of bio-oil obtained (Table 4). Bio-oil collected in this study from
each feedstock was dark brown homogenous liquid. Acidity (pH) of the oil was between 2.92 and 3.20. This is
an indication that the oil may contain substantial amount of organic acids [24] [25]. Water content of the oil va-
ried from 39.28 - 43.0 wt% which was mainly due to product of dehydration during pyrolysis reaction [26].
Density was between 1.02 and 1.04 g/cm3 which are higher than that of gasoline (0.723 g/cm3) and diesel (0.838
g/cm3) fuels. Viscosity was found to be between 2.06 and 2.41cp. Ultimate analysis revealed that the bio-oil has
32.96 - 35.74 wt% carbon, 6.06 - 6.99 wt% hydrogen, 0.01 - 1.02 wt% nitrogen, 0.01 - 0.99 wt% sulfur and
58.47 - 59.85 wt% oxygen.
Low nitrogen and sulfur contents of the oil suggest that bio-oil from oil palm residues can be used as a source
of clean energy. Higher heating value of the oil ranged between 19.24 and 21.92 MJ/kg. These values are only

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about 41% - 47% of higher heating value of gasoline (47 MJ/kg) and 43% - 49% that of diesel (45 MJ/kg). This
can be attributed to the high water and oxygen contents in the oil and hence the need for upgrading.
The non-condensable gas measured using Dräger X-am 5000 gas analyzer were methane (CH4), hydrogen
(H2), carbon monoxide (CO), and traces of hydrogen sulfide (H2S) (Table 4). The presence of H2S may be at-
tributed to sulfur in the source biomass. The gas consist mainly CH4, H2 and CO which are due to reforming and
cracking and cracking hydrocarbons, and cracking of oxygenated organic compounds respectively in the vola-
tiles at high temperature [27] [28].
High composition of H2 and CO in the gas was observed which went beyond the measuring range (0.2 vol %)
of the gas analyzer. This signifies that the non-condensable gas can be used as a source of hydrogen for upgrad-
ing of bio-oil to meet the fuel standard. In addition, it can also be processed to transportation fuel via Fisher-
Tropsch synthesis due to high value H2/CO (vol/vol) [29] [30].
Table 4. Properties of bio-oil, bio-char and non-condensable gas from oil palm residues produced at 600˚C, 30˚C/min, 30
mL/min N2 f l ow.
Property Bio-Oil
OPT/10ft OPT /20ft OPT/30ft OPFS OPFT OPEFB
Appearance Dark brown
Physicochemical properties
pH 3.20 3.18 3.20 3.08 2.92 3.16
Water content (wt%) 43.00 41.00 42.00 3 9.28 39.78 40.22
HHV (MJ/kg) 19.24 21.76 20.15 21.92 21.22 21.61
Viscosity (cp) at 25˚C 2.06 2.22 2.11 2.41 2.36 2.29
Density (g/cm3) 1.02 1.03 1.03 1.04 1.04 1.03
Ultimate analysis (wt%)
Carbon 32.96 33. 80 33.10 3 4.11 34.08 33.96
Hydrogen 6.99 6.22 6.94 6.06 6.10 6.13
Nitrogen 0.01 0.01 0.02 0.11 0.36 1.02
Sulfur 0.19 0.16 0.18 0.01 0.99 0.21
Oxygen* 59.85 59.81 59.76 59.71 58.47 58.68
Proximate analysis (wt%) Bio-char (dry basis)
Ash content 11.65 11.53 11.99 12.10 12.59 13.02
Volatile matter 23.16 23.86 23.77 2 3.45 22.95 22.45
Fixed carbon (%)* 65.19 6 4.61 64.24 64.45 64.46 64.53
HHV (MJ/kg) 27.65 27.68 27.16 26.21 26.42 25.98
Ultimate analysis (wt%)
Carbon 84.90 84. 10 83.81 8 4.96 83.21 82.22
Hydrogen 2.96 2.80 2.90 2.77 2.97 2.88
Nitrogen 0.09 0.08 0.09 0.08 0.29 0.21
Sulfur 0.02 0.02 0.02 0.08 0.11 0.11
Oxygen* 12.03 13.00 13.18 12.11 13.42 14.58
Non-condensable gas (volume %) nitrogen free basis
H2S 0.0016 0.0014 0.0015 0.0 011 0.0018 0.0017
CH4 2.66 2.71 2.68 2.76 2.69 2.59
CO >0.2 >0.2 >0.2 >0.2 >0.2 >0 .2
H2 >0.2 >0.2 >0.2 >0.2 >0.2 >0.2

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Characteristics of the bio-char are also given in Table 4. From the proximate analysis, ash content, volatile
matter and HHV were between 11.53 - 13.02 wt%, 22.45 - 23.86 wt% and 25.96 - 27.68 MJ/kg while fixed car-
bon ranged between 64.24 and 65.19 wt%. The low volatile content recorded was as a result of removal of vola-
tiles during the pyrolysis. Ultimate analysis revealed that the bio-char is predominantly made up of carbon and
less hydrogen and oxygen content. Lower composition of nitrogen and sulfur were also observed in the bio-char
sample. Atomic ratio of hydrogen/carbon (H/C) and oxygen/carbon (O/C) of bio-char was evaluated and com-
pared with that of bio-oil and the source biomass as shown in Van Krevelen diagram in Figure 3. The plot
showed distinct regions for bio-char, bio-oil and the source biomass with bio-char appearing at the lower left
hand corner, biomass at the middle and bio-oil at top right hand corner. The lower values of H/C and O/C rec-
orded in the bio-char samples are indications of loss of hydrogen and oxygen due to hydration, decarboxylation
and decarbonylation [30] which lead to enrichment of the bio-char with carbon. SEM evaluation (Figure 4) re-
vealed that bio-char samples have porous structures and can be used as adsorbent and in soil amendment.
Figure 3. Van Krevelen diagram of oil palm residues and their corresponding bio-
oil and bio-char .
Figure 4. SEM images of bio-char from oil palm residue. Scanning conditions: HV
(20 kV), Mag (2400×), low vacuum and size (40 µm) .

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4. Conclusions
Pyrolysis of oil palm residues was carried out in a fixed bed tubular reactor under nitrogen atmosphere at 30
mL/min and reaction temperature of 600˚C. Bio-oil, bio-char and non-condensable gas yield were between
29.56 - 34.26 wt%, 29.43 - 38.45 wt% and 31.32 - 37.47 wt% respectively. The bio-oil was acidic (pH: 2.92 -
3.2), highly oxygenated (58.47 - 59.85 wt%) and had high moisture content between 39.28 - 43 wt%. The higher
heating value of the oil was between 19.24 - 21.92 MJ/kg.
These characteristics suggest that the bio-oil require further upgrading in order to meet fuel quality standard.
The bio-char recorded was highly carbonaceous (82.22 - 84.96 wt% carbon) and had higher heating value be-
tween 25.96 - 27.68 MJ/kg. Scanning electron microcopy revealed that bio-char is made of porous structure.
These properties indicate that bio-char can be used as asolid biofuel, asource of carbon and as an adsorbent. The
composition of non-condensable gas was mainly hydrogen and carbon monoxide which can be further processed
to transportation fuel. In addition, it can also serve as a source of hydrogen for upgrading of the bio-oil.
This study has shown that oil palm residues are good sources of renewable energy which can be sustained
when all the pyrolysis products are efficiently utilized.
Acknowledgements
This research was supported by the Crops for the Future (CFF) and the University of Nottingham under grant
BioP1 -005.
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