Case Studies in Thermal Engineering 12 (2018) 711–716
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Case Studies in Thermal Engineering
journal homepage: www.elsevier.com/locate/csite
Extraction of bio-oil during pyrolysis of locally sourced palm kernel
shells: Effect of process parameters T
J.O. Ogunkanmia, D.M. Kullaa, N.O. Omisanyaa,b, M. Sumailaa, D.O. Obadaa,⁎,
D. Dodoo-Arhinc,d,⁎
aDepartment of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria
bNational Automotive Design and Development Council, Zaria, Nigeria
cDepartment of Materials Science and Engineering, University of Ghana, Legon, Ghana
d Institute of Applied Science and Technology, University of Ghana, Legon, Ghana
A R T I C L E I N F O A B S T R A C T
Keywords: The aim of this study was to determine the effect of particle size, pyrolysis temperature and
Fixed bed reactor residence time on the pyrolysis of locally sourced palm kernel shells and to characterize the bio-
Pyrolysis oil products. Pyrolysis experiments were performed at pyrolysis temperatures between 350 °C
Biomass and 550 °C and particles sizes of 1.18mm, 2.36mm and 5mm for a residence time not greater
Palm kernel shell than 120min. The maximum bio-oil yield was 38.67 wt% at 450 °C for a feed particle size of
Bio-oil
1.18mm with a residence time of 95min. It was observed that the percentage of liquid collection
was 28% of the total biomass feed for particle size of 1.18mm. In terms of the effect of tem-
perature, the lowest bio-oil yield was 28% of the total biomass feed at temperature of 550 °C. For
the variation in residence time and the associated effects, the maximum liquid product was
38.67 wt% of biomass feed, at a particle size of 1.18mm for 95min. As observed, the optimum
residence time was 95min as times either side led to a decrease in the liquid yield. The bio-oil
products were analysed by Fourier Transform Infra-Red Spectroscopy (FTIR) and Gas
Chromatography-Mass Spectrometry (GC-MS). The FTIR analysis showed that the bio-oil was
dominated by phenol and its derivatives. The phenol (38.44%), 2-methoxy-phenol (17.34%) and
2, 6-dimethoxy phenol (8.65%) that were identified by GC-MS analyses are highly suitable for
extraction from bio-oil as value-added chemicals. The highly oxygenated oils can therefore be
upgraded in order to be used in other applications such as transportation fuels.
1. Introduction
Biomass has been recognized as a major renewable energy source to supplement declining fossil fuels. It is a popular form of
renewable energy and currently, biofuel production is becoming much promising. Transformation of energy into useful and sus-
tainable forms that can fulfil and suit the needs and requirements of the work force in the best possible way is the common concern of
scientists, engineers and technologists. From the view point of energy transformation, pyrolysis is more attractive among various
thermochemical conversion processes because of its simplicity and higher conversion capability of biomass into bio-oil [1]. Biomass
utilization gives the possibility of generating value-added products such as chemicals, activated carbon, sandpaper production etc.
which means an attractive economic and technological solution [2–4]. Among the palm oil wastes, palm kernel shell (PKS) has a great
⁎ Corresponding authors at: Department of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria.
E-mail addresses: doobada@abu.edu.ng, ddodoo-arhin@ug.edu.gh (D. Dodoo-Arhin).
https://doi.org/10.1016/j.csite.2018.09.003
Received 9 July 2018; Received in revised form 28 August 2018; Accepted 14 September 2018
Available online 14 September 2018
2214-157X/ © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license 
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
J.O. Ogunkanmi et al. Case Studies in Thermal Engineering 12 (2018) 711–716
potential as a source of biomass to develop renewable energy sources. Since the PKS produced from palm oil mills is abundant, cheap
and does not require significant effort to collect, it is currently used as a low energy efficiency fuel for industrial applications, for
instance, boilers [5].
Converting palm kernel shells to bio-oil under a thermal process provides a greater benefit to use as biomass energy to replace
fossil fuels, and it minimizes the disposal problems associated with the generation of agricultural by-products. Omoriyekomwan et al.
[6] studied the catalytic fixed bed and microwave pyrolysis of palm kernel shells using activated carbon and lignite char (LC) as
catalysts. It was observed that the addition of catalyst increased the bio-yield but decreased the selectivity of phenol in the fixed bed.
The highest concentration of phenol and total phenolics in the bio-oil were obtained at 500 °C. Kabir et al. [7] devolatilized oil palm
mesocarp fibre (OPMF) and palm frond (PF) by pyrolysis to oils, bio-oils and biochars. In particular, the OPMF-oil and PF-oil were
produced to a maximum yield of 48 wt% and 47wt% bio-oils at 550 °C and 600 °C, respectively.
Catalytic intervention in pyrolysis has received a lot of attention because of the significant increase in phenol rich bio-oils.
However, the methods involving the use of catalysts have associated cost effects and require high pressures for reaction. Thus it is
important to evaluate low cost approaches and indeed the effect of process parameters in bio-oil production especially in developing
economies. In this study, we investigate the effects of the particle sizes of PKS on the production of bio-oil, char and gas, and further
investigate the influence of pyrolysis temperature and residence time on the optimum bio-oil yield without catalytic intervention.
2. Materials and methods
2.1. Raw material collection and analysis
Samples of the palm kernel shell were collected from Oloje Oil Palm Industry in the South Western Region of Nigeria. The palm
kernel shells were sun dried for 7 days to reduce the moisture content below 10%, after which they were crushed and sieved using
U.K standard sieve sizes or openings of 1.18mm, 2.36mm and 5mm (standard mesh numbers (US):16, 8 and ISO respectively) to
produce the desired particle sizes. The proximate and ultimate analyses were done according to the ASTM (D-3175) standard test
method [12] and results presented in Table 1.
2.2. Experimental procedure
The obtained palm kernel shells were subjected to pyrolysis in an externally heated in-house built fixed bed reactor system which
was made of mild steel. The effective length of the reactor was 300mm with diameter of 90 mm. Dry sand with a thermal con-
ductivity of 0.27W/mK was used as insulation material considering the operating temperatures (350, 400, 450, 500 and 550 °C) of
the fixed bed pyrolysis plant and its availability. The connecting pipe was 900mm with diameter of 19.04mm, which was connected
on the cover plate of the reactor at both ends with the help of nipples. The schematic diagram of the fixed bed pyrolysis system is
shown in Fig. 1. The reactor was manually filled with 1.5 kg of the palm kernel shells. The reactor was then externally heated at
different temperatures (350, 400, 450, 500 and 550 °C) via a manual charcoal furnace equipped with a digital thermocouple (Kane-
May KM340, −50 °C≈ 1500 °C) and the pyrolysis residence time for each operation was recorded. Pyrolysis vapour was condensed
into liquid in the ice bath-cooled condenser while the non-condensable gases were flared to the atmosphere. The bio-oil products and
char were weighed to calculate the percentage of the yield. The effect of PKS particle size, pyrolysis temperature and residence time
on the yield of the pyrolysis products were investigated.
The functional groups present in the bio-oil obtained at optimum conditions were identified using Fourier transform-infrared
(FTIR) spectroscopy. A Magna-IR550 Nicolet Madison Spectrum series II FTIR device with a resolution of 1.0 cm−1 was used to
investigate the functional groups presents in the bio-oil within the range of 400 cm−1–4000 cm−1. The gas chromatography- mass
spectroscopy (GC-MS) analysis of the bio-oil product was performed in accordance with ASTM E2997 standard [14] using Agilent
Technologies GC 6890N with 5973N mass selective detector (MS). The oven temperature was started at 35 °C for 2min, increased to
250 °C at a rate of 20 °Cmin−1 and held at this temperature for 20min. The injector port temperature and the detector temperature
were set at 280 °C. The carrier gas, helium, was set at a flow rate of 47.5 l per min and the split ratio of the injector port was set at
50:1. An amount corresponding to 0.03 g of bio-oil was used and diluted with methanol HPLC grade to the volume of 0.5 ml using a
vial. After that, the mixture was shaken and filtered. Finally, 1.0 µl of mixture was injected with a 5.0 µl syringe into the GC-MS
apparatus.
Table 1
(Comparison of proximate and ultimate analysis of kernel shells obtained in current work with literature).
Proximate analysis Value (wt%) Ultimate analysis Value (wt%)
As-Used Ref.5 Ref. 6 Ref.11 Ref.13 As-Used Ref.5 Ref. 6 Ref.11 Ref.14
Moisture 5.69 11.00 14.90 6.33 9.4 Carbon 46.92 49.74 49.90 44.29 44.56
Volatile matters 69.10 67.20 74.68 62.82 82.5 Hydrogen 8.95 5.32 5.25 9.01 5.22
Fixed Carbon 23.49 19.70 23.68 19.10 1.4 Nitrogen 1.15 0.08 0.36 2.37 0.4
Ash 1.72 2.10 1.64 11.75 6.7 Sulphur 2.35 0.16 0.95 1.20 0.05
Oxygen 40.63 44.86 43.54 43.13 49.77
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Fig. 1. Schematic of experimental set-up.
3. Results and discussion
3.1. Effect of particle size on the pyrolysis yield
Fig. 2 shows the percentage weight of liquid, char and gas products for different particle sizes (1.18mm, 2.35mm and 5mm) of
PKS feedstock at a maximum temperature of 550 ° C and residence time of 120min. It was observed that the percentage of liquid
collection was a maximum of 28% of total biomass feed for particle size of 1.18mm while a reduced amount of liquid was obtained
from the feed with larger particle sizes. A possible explanation for this is that larger sized particles do not get sufficiently heated up
during the rapid pyrolysis process, thereby leading to an incomplete process which reduces the liquid product yield. As shown in
Fig. 2, the highest char yield of 70.67% was obtained using the particle size of 5mm, while the lowest char yield of 19.33% was
obtained using the particle size of 1.18mm. Similarly, the highest and lowest gas yields were obtained using the particle size of
1.18mm (52.67%) and 5mm (14.67%), respectively. An increase in particle size causes greater temperature gradients inside the
particle so that at a given time the core temperature is lower than that of the surface, which possibly gives rise to an increase in the
char yields and a decrease in liquids and gases. Particle size is known to influence the yield of pyrolysis products. If the particle size is
sufficiently small it can be heated uniformly, and this corroborates findings obtained elsewhere [8].
3.2. Effect of temperature on the pyrolysis products yield
Fig. 3 shows the variation of percentage weight of liquid, char and gaseous products at different bed temperatures (350, 400, 450,
500 and 550 °C) with the optimum biomass feedstock particle size of 1.18mm as obtained in this study. It this way, it is found that at
the lowest pyrolysis temperature (350 °C), the decomposition process was relatively slow and the char was the major product. As the
temperature increased from 350 to 450 °C, the amount of condensable liquid product increased to a maximum value in the range of
34.67–38.67%. At higher pyrolysis temperatures of 500 and 550 °C, the bio-oil decreased with quantity in the range of 30.67–28%
following the same trend with the results presented in literature [9,10]. The results obtained from these series of experiments show
Fig. 2. Effect of Particle Size on pyrolysis products yield.
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Fig. 3. Effect of temperature variation on pyrolysis products yield.
that at a pyrolysis temperature of 450 °C, the maximum bio-oil yield obtained was 38.67% of the total biomass feed while the lowest
bio-oil yield was 28% of the total biomass feed when the temperature was raised to 550 °C. The char yield decreased significantly as
the final pyrolysis temperature was raised from 350 to 550 °C. The highest char yield was 38.67% of the total biomass feed at the
temperature of 350 °C and the lowest char yield was 19.33% of the total biomass feed obtained at the temperature of 550 °C. The
decrease in char yield with an increase in temperature can be ascribed to the greater primary decomposition of the PKS at higher
temperatures or through secondary decomposition of the char residues.
The highest and lowest gas yields obtained were 52.67% and 29.33% at temperatures of 550 °C and 350 °C respectively. The gas
products increased with an increase in pyrolysis temperature. An increase in gas products is thought to occur predominantly due to
the secondary cracking of the pyrolysis vapour at higher temperatures.
3.3. Effect of residence time on the pyrolysis products yield
Fig. 4 shows the plot of product yield (wt.%) of liquid, char and gas against variation of residence time. The maximum liquid
product is 38.67 wt.% of biomass feed at 1.18mm particle size and 95min residence time. As observed, residence times higher or
lower than the pyrolysis time of 95min led to a decrease in the liquid yield. This is due to insufficient pyrolysis reaction time and
higher rate of gas discharge.
3.4. Identification of functional group using FTIR
The FTIR spectrum of the bio-oil obtained from pyrolysis of palm kernel shell at the pyrolysis temperature of 450 °C, particle size
of 1.18mm and residence time of 95min (optimum parameters) is shown in Fig. 5. The O-H stretching vibrations between 3200 cm–1
and 3355 cm−1 indicate the presence of phenol and alcohols. The C-H stretching vibrations between 2922 cm−1 and 2848 cm−1 and
Fig. 4. Effect of residence time on pyrolysis products yield.
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Fig. 5. FTIR Spectra of the bio-oil. (O-H:Phenol and alcohols, C-H:Alkanes, C˭O:Ketones, aldehydes and carboxylic acid C˭C:Alkenes and aromatic,
C-O:Esters and ether).
C-H deformation vibrations between 1384 cm−1 and 1222 cm−1 indicate the presence of alkanes. The C=O stretching vibrations
between 2140 cm−1 and 1703 cm−1 represent the presence of ketones, aldehydes, carboxylic acids and their derivatives. The ab-
sorbance peaks between 1595 cm −1 and 1502 cm −1 represent C=C stretching vibrations indicative of alkenes and aromatics.
Absorptions possibly due to C-O vibrations from carbonyl components (i.e., alcohols, esters, carboxylic acids or ether) occur between
1111 cm−1 and 887 cm−1 of the analyzedanalysed bio-oil. The absorbance peaks between 753 cm−1 and 693 cm−1 indicate the
possible presence of single, polycyclic and substituted aromatic groups.
3.5. Identification of chemical compounds and peak area using GC-MS
Gas chromatography-mass spectroscopy (GC-MS) analysis as shown in Fig. 6 was carried out on the bio-oil produced at optimum
conditions. The result indicates that the highest values of the peak areas of possible compounds were Phenol; Phenol, 2-methoxy and
Phenol, 2, 6-dimethoxy, with 38.44%, 17.34% and 8.65% respectively. The concentrations of Phenol and its derivative were high,
indicating the suitability of the oil to be considered for value-added chemicals. In addition, it is possible to deoxygenate the bio-oil to
obtain higher-grade fuel [11].
4. Conclusions
The effect of particle size on the bio-oil products yield shows that 1.18mm is the optimum particle size of PKS to produce bio-oil
and gas products, and 5mm is the optimum particle size to produce char at the same temperature (550 °C). Also, the effect of
temperature and residence time on products yield showed that a temperature of 450 °C at 95min residence time was the optimum
Fig. 6. Identification and peak areas of chemical compounds in the bio-oil.
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temperature to produce the bio-oil, 350 °C at a residence time of 60min was the best temperature to produce the char and 550 °C at a
residence time of 120min is the maximum temperature to produce the gas product under the same conditions of particle size. The
FTIR results showed that the bio-oil composition was dominated by oxygenated species. GC-MS analysis showed that the con-
centration of phenol and its derivative were very high, indicating the suitability of the oil to be considered for value-added chemicals.
Conflict of interest
Authors declare no conflict of interest in the research work and its publication.
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