Experimental Analysis of Bio-Oil and Biochar Produced from the Pyrolysis of Palm Kernel Shell

494 Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 p ISSN: 2635-3342; e ISSN: 2635-3350 Original Research Article Experimental Analysis of Bio-Oil and Biochar Produced from the Pyrolysis of Palm Kernel Shell *1Akinsade, A., 2Akinola, A.O. and 2Yaru, S.S. *1Department of Mechanical Engineering, Olusegun Agaga University of Science and Technology (OAUSTECH), Okitipupa, Ondo State, Nigeria. 2Department of Mechanical Engineering, Federal University of Technology, Akure, Nigeria. *oredyn[email protected]m, [email protected] http://doi.org/10.5281/zenodo.18061685 ARTICLE INFORMATION ABSTRACT Article history: Received 14 Oct. 2025 Revised 05 Nov. 2025 Accepted 09 Nov. 2025 Available online 30 Dec. 2025 This study investigates the pyrolytic conversion of palm kernel shell (PKS) into bio-oil and biochar and the evaluation of their fuel and chemical potential. A 0.01489 m³ fixed-bed, batch-fed pyrolysis reactor was used to thermally decompose 1.0 kg of PKS at varying temperatures (300, 350, 400, and 450 °C). Product yields were measured, and the resulting bio-oil and char were characterised through proximate, ultimate, and physicochemical analyses. The biochar exhibited high carbon content (up to 74.89%) and low ash and moisture content, resulting in enhanced combustion efficiency and reduced emissions. The bio-oil obtained at 450 °C demonstrated favourable fuel properties, including low moisture (0.98%), high carbon content (86.84%), high flash point (96.28 °C), and a cetane number of 51.4. The Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography-Mass Spectroscopy (GC-MS) analyses confirmed the dominance of phenolic compounds, indicating potential for value-added chemical production. The study concludes that PKS is a viable biomass feedstock for sustainable biofuel and bioproduct applications, contributing to energy diversification and waste valorisation. © 2025 RJEES. All rights reserved. Keywords: Palm kernel shell Pyrolysis Bio-oil Biochar Fuel properties Phenolic compounds 1. INTRODUCTION The increasing global emphasis on sustainable energy solutions and environmental concerns about the emission of greenhouse gas (GHG) from burning fossil fuels has brought renewable energy sources to the forefront of discussion about energy security and environmental preservation (Efetobor et al., 2024). According to Onokwai et al., (2022a), proposed that, renewable energy sources are significant energy supply options that would address the world energy demand, climate change, and energy security. Amongst the renewable energy sources are solar, hydro, wind, biomass, etc., among these, biomass energy stands out as a promising alternative, particularly in developing countries where traditional 495 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 energy sources are often expensive or inaccessible since waste and virgin biomass have the advantage of their non-zero carbon footprint and abundant availability (Okokpujie et al., 2023). Biomass is an organic material that is derived from plants or animal waste. It is formed by the interaction of carbon dioxide (CO2), water (H2O), and sunlight (Ugwu et al., 2020). When a living thing dies, microorganisms break down the constituents into elementary components, water (H2O), carbon dioxide (CO2), and Adenosine Triphosphate (ATP) energy. The plant uses up the same carbon dioxide during photosynthesis, the amount of carbon dioxide (CO2) does not increase in the atmosphere, and thus, greenhouse gas (GHG) neutrality is achieved. It is recognised as an alternative, eco-friendly, renewable source for bioenergy production and is readily available globally (Onokwai et al., 2022c). Biomass utilisation is receiving great attention in mainstream energy as a result of the increased global demand for energy and environmental considerations. Biomass contains a small percentage of ash, nitrogen, and sulphur, which indicates that biofuel combustion yields less harmful gas emissions like soot, SO2, and NOX, and it is carbon neutral since CO2 emissions produced could be recycled for plant use during photosynthesis (Onokwai et al., 2022a). Generally, biomass is an indirect form of solar energy and a renewable source of carbon as plants convert sunlight and CO2 into stored chemical energy by photosynthesis (Muralidharan et al., 2024). Some important products like liquid biofuels for transportation, chemicals, bioenergy (heat and electricity), and other bio-based products are derived from the conversion of stored chemical energy into biomass (Razzaque, 2016). Therefore, there is a net reduction in greenhouse gas emissions, which may impact global climate change, and provide other benefits, such as reducing energy consumption from fossil sources can be actualised through the utilization of biomass (Okokpujie et al., 2023). In general, the main advantages of using lignocellulosic biomass as a fuel source are carbon neutrality, abundance, and highly economic in processing (Puri et al., 2024). According to Adeniyi et al., (2018), algae that belong to the third generation of biofuels offer benefits of high biomass productivity, high lipid yield, fast growth rate, an ability to be cultivated in wastewater or brine water, and the presence of valuable biochemicals such as β-carotene, astaxanthin, and lutein. Biomass is widely spread in different countries in large quantities that could be used as an energy resource. They are commonly and readily available from municipal solid wastes (MSW), sludge, industrial wastes, food wastes, forestry wastes such as sawdust, wood chips, etc., and agricultural wastes like rice husk, wheat straw, palm kernel shell, cocoa pod, etc., and they have reasonably high energy content (Guo et al., 2011). According to the report of Demirbas et al., (2006), palm kernel shell, among the categories of agricultural residues, represents an important potential for developing the bioenergy industry. According to Okokpujie et al., (2023), Nigeria produces enormous quantities of palm kernel shells from palm oil industries across the country, besides Malaysia. Palm kernel shells are being produced in large quantities as residue from the processed facility with no significant market value; some amounts are burnt without recovering their energy. These wastes have the potential to generate energy for motive power and valuable chemicals through thermochemical conversion to bio-oil, which affords more potency and benefits to replace fossil fuels (Onokwai et al. 2022b). Hence, its potency for energy generation has been explored by many researchers with encouraging results (Okokpujie et al., 2023). Biomass can be converted to thermal energy, liquid, solid or gaseous fuels, and other chemical products through a variety of conversion processes that have been proposed by many researchers (Sanchez, 2009). The thermochemical conversion process is the thermal decomposition of the organic components of biomass into biofuel, in which energy is produced by applying heat and chemical processes to biomass (Hassan et al., 2017). The major processes are combustion, torrefaction, liquefaction, gasification, and pyrolysis (Chowdhury et al., 2017). Among the thermochemical processes, pyrolysis stands out to be a more effective approach for biomass processing because of its ability to use a variety of feedstocks, being cheaper, minimizing environmental effects, and products are easy to transport and versatile in applications (Osman et al., 2023). 496 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 Pyrolysis is the thermal degradation of biomass in an inert condition at an elevated temperature with or without the presence of a catalyst to produce solid char, liquid pyrolysis oil (bio-oil), and noncondensable gas (Gahane et al., 2022). In biomass pyrolysis, the feedstock is first pre-treated before being charged into the reactor for thermal degradation to enhance the pyrolysis reaction. During the reaction, pyrolysis vapour is released from the volatile fraction of biomass upon thermal degradation, followed by condensation to separate bio-oil and gaseous products. The production of high-energydensity bio-oil can be used as a cleaner fuel source in boilers to replace petroleum crude oil and can also be further upgraded to hydrocarbon fuels to reduce the consumption of petroleum crude oil, and can be used to produce a wide spectrum of chemicals like phenolics, alcohols, and acids (Hu and Gholizadeh, 2020). On the other hand, char can be used for the manufacture of activated carbon for purification processes and soil amendments (Onokwai et al. 2022d). Nowadays, researchers in the field of renewable energy have shifted their attention to pyrolysis as a result of its contributions to safeguarding the environment and energy sustainability. Sukurmar et al., (2015), investigated the effect of particle size, temperature, and nitrogen gas flow rate on the product yield from fast pyrolysis of sweet lime empty fruit bunch in an electric furnace fixed-bed reactor. The results showed that the bio-oil yield of 28.3% was obtained at an optimum temperature of 5500C, 4mm of particle size, and 300cm3min-1 of gas flow rate. Mogaji et al., (2019) pyrolyzed sugarcane bagasse in a 35.5 litres fixed bed reactor, yielding 56.5 wt.% of bio-oil with a heating value of 17.33 MJ kg-1. Aziz et al., (2018), used a fixed-bed batch-type pilot-scale pyrolysis reactor to pyrolyze waste tyres. The results showed that with an operation running time of 185 minutes, 49 wt.% of oil, 38.3 wt.% of char, and 12.7 wt.% of pyrolytic gas were obtained. Kim et al., (2010), studied the influence of pyrolysis parameters on the bio-oil yield for the fast pyrolysis process of Palm Kernel Shells (PKS) using an electric-heater fluidized bed reactor to pyrolyze the sample. From this study, the highest yield of biooil (40.3%) is gained at temperature of 490 °C. In a laboratory free-fall reactor with three distinct hot zones, Punsuwan and Tangsathitkulchai, (2014), pyrolyzed palm shell, palm kernel, and cassava pulp residues to determine the effects of pyrolysis temperatures and particle sizes (0.18 - 1.55 mm) on the distribution and properties of pyrolysis products. They discovered that a higher pyrolysis temperature and smaller particle size promote gas production and reduce char yields. Keles et al., (2017), in their study, investigated the fast pyrolysis of hazelnut cupula in a laboratory-scale fixed-bed reactor by varying pyrolysis temperatures from 400 to 700 oC, sweeping gas flow rate, and particle size. They obtained a maximum oil yield at a temperature of 600 °C and a carrier gas flow rate of 200 mL/mm; they also noted uniform heating of particles of sizes ranging from 0.150 mm to 0.425 mm. In this study, the research focused on experimental analysis of the products (bio-oil and biochar) obtained from pyrolysis of PKS to determine their properties that can justify their use in bioenergy production as a means of maximizing the potential of the residue in oil palm processing. 2. MATERIALS AND METHODS 2.1. Source of the Materials The palm kernel shells (PKS) used in this study were sourced from the Oil Palm Industry located at Okitipupa in Ondo State, Nigeria. PKS was selected based on availability and its high content of lignocellulose compositions. The PKS was pre-treated by washing and sieved to remove sand and dirt, then sundried for ten days to reduce the moisture content to 5 %. The pre-treated samples were stored in a sealed polythene bag to prevent them from excessive humidity (Oyebanji et al., 2023). 2.2. Experimental Procedure of the Pyrolysis The pyrolysis of the PKS was done in a batch-fed, fixed-bed pyrolysis reactor system. The reactor chamber is made of stainless steel with dimensions ϕ270mm x260mm as shown in Figure 1. The dried samples were weighed using a weighing machine, and 1.0 kg of the samples was loaded, in succession, per batch, into the reactor chamber and pyrolyzed at varying temperatures of 300, 350, 400, and 450 °C. The volatiles from the reactor were condensed in a water-cooled condenser, and the non-condensable gases were flared into the atmosphere. The condensed oil (condensate) was collected in a liquid collector and weighed using a digital 497 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 weighing machine (Model: SF-400). The products of the experimentation are shown in Plate 1. The remaining solid residue (char) was allowed to cool gradually within the reactor, afterwards offloaded and weighed to determine its mass. The weight of non-condensable gases was determined by applying the mass difference. The liquid fuel and char yields at the specified temperatures were kept in well-sealed plastic containers and polythene bags, respectively, under room temperature. (a) Bio-oil (b) biochar Plate 1: The Products of Experimentation Figure 1: Photograph of the pyrolysis test rig 2.3. Characterization of the Products The proximate and ultimate analyses of the condensates obtained from each of the pyrolytic temperatures (300, 350, 400, and 450oC) were conducted at the Department of Chemical and Petroleum Engineering Research Laboratory of Afe Babalola University, Ado-Ekiti (ABUAD), Ekiti State, to determine the fuel properties of the condensates by ASTM standards. The Fourier Transform Infrared Spectroscopy (FTIR) and the Gas chromatography-Mass spectroscopy (GC-MS) analysis of the bio-oil obtained at the maximum 498 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 temperature of 450 °C were conducted to determine the functional groups and chemical composition of the bio-oil 3. RESULTS AND DISCUSSION 3.1. Proximate Analysis of the Biochar The result of the proximate analysis of the biochar is presented in Figure 2. The proximate analysis of biochar revealed that the moisture content of the biochar increases from 1.73% at 300°C to 4.11% at 450°C. This observation is consistent with the findings of Quan et al. (2016), who reported that higher moisture content reduces the effective calorific value due to latent heat losses during evaporation. Thus, the lower moisture level observed at a temperature 300°C in this study implies an improved calorific value of the biochar at a lower temperature. The ash content decreased significantly from 6.53% at 300 °C to 0.99% at 450 °C. This aligns with Chatterjee et al. (2020), who noted that reduced ash levels improve combustion efficiency and result in fewer emissions. The increase in fixed carbon content from 57.49% to 83.99% with rising temperature also agrees with the work of Mohabeer et al. (2017), who linked higher fixed carbon to enhanced energy density and cleaner combustion. These results therefore confirm that biochar produced at elevated temperatures is more energy-dense, stable, and environmentally sustainable. Figure 2: Proximate analysis of the biochar 3.2. Proximate Analysis of the Bio-oil Figure 3 presents the result of the proximate analysis of the bio-oil. The bio-oil exhibited a decrease in moisture content from 2.69% at 300 °C to 0.98% at 450 °C, a trend similar to that reported by Kasim et al. (2018), who associated lower moisture levels with improved combustion efficiency and fuel stability. The high total carbon content (86.84%) observed in this study corroborates the findings of Mohabeer et al. (2017), who emphasized that carbon-rich bio-oil enhances calorific value and overall combustion performance. Thus, the bio-oil obtained from this study demonstrates desirable fuel properties that are comparable to those reported in the literature. 499 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 Figure 3: Proximate analysis of the bio-oil 3.3. Ultimate Analysis of the Biochar Figure 4 presents the result of the ultimate analysis of the biochar. At 400°C, the biochar contained 74.89% carbon, which is consistent with the results of Zhang and Cheng (2018), who highlighted that carbon-rich biochar supports higher calorific values and stable combustion. The low nitrogen (0.4%) and sulphur (1.77%) contents recorded in this study agree with Ben-Iwo et al. (2016), who noted that biochar with low heteroatom concentrations contributes to cleaner energy production and reduced environmental hazards. The reduction in oxygen content from 28.32% at 300 °C to 16.1% at 450°C mirrors the observations of Zhang and Cheng (2018), where lower oxygen levels were associated with enhanced combustion efficiency and higher heating value. These comparisons confirm that the biochar produced in this study aligns with internationally reported standards for clean bioenergy applications. Figure 4: Ultimate analysis of the biochar 3.4. Ultimate Analysis of the Bio-oil Figure 5 presents the result of the ultimate analysis of the bio-oil. The ultimate analysis of the bio-oil revealed a high carbon content (68.63%), consistent with the findings of Kumar and Mohan (2020), who attributed high energy density in bio-oil to carbon-rich compounds such as phenols and aromatics. The low nitrogen (0.01%) and sulphur (2.15%) contents are in line with other reports (e.g., Ben-Iwo et al., 2016), reinforcing the environmental benefits of bio-oil as a cleaner alternative to fossil-derived fuels. 500 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 Figure 5: Ultimate analysis of the bio-oil 3.5. Physicochemical Properties of the Bio-oil Table 2 presents the results of the physicochemical properties of the bio-oil at a pyrolysis temperature of 450oC. The result revealed that the bio-oil has a pH of 3.03, which corresponded well with the published data (Sukiran et al., 2016; Czernik and Bridgwater, 2004), indicating that the bio-oil contained a substantial number of organic acids (acetic and formic acids) that lower the pH. This accounts for its corrosiveness to materials during the storage and application process and thus makes it extremely unstable (Sukiran et al., 2016). The bio-oil has a lower density of 0.99 g/cm3 at 40 oC because of the lighter end composition of the bio-oil (Adegoke et al., 2021; Oasmaa et al.,2010). This agrees with the density specification of fuel oil of 0.90 g/cm3, heavy fuel oil of 0.99 g/cm3, and furnace oil of 0.92 g/cm3 reported by Oyebanji et al., (2023), and Okokpujie et al., (2023). The bio-oil has a higher flash point of 96.28 oC, which falls within the conventional diesel (55 - 96oC), indicating that the bio-oil is safe in handling and transporting, unlike gasoline with a lower flash point that is highly volatile and can ignite more easily (Eze et al., 2021). The biooil also has a low pour point and viscosity of -7.3 oC and 4.23 cP, respectively. This makes the bio-oil suitable for low-temperature conditions and atomises better, creating a more homogeneous mixture that supports more complete combustion (Lau and Tan, 2019). The bio-oil shows a high Cetane number of 51.4, which falls within the range of diesel engines (40-55) (Tian and Zhao, 2020). This makes the bio-oil ignite more quickly after injection, leading to smoother combustion, better cold starting, lower emissions and less knocking (Gómez-Barea and Leppänen, 2014; Tian and Zhao, 2020). The higher heating value (21.78 MJ/kg) obtained in this study agrees with 21.23 MJ/kg reported by Okokpujie et al., (2023); and lower than those of light petroleum and heavy fuel oils, which are 42.9 MJ/kg and 40.7 MJ/kg (Duku, 2014. Oyebanji et al., 2023), but higher than cocoa pod (17.93MJ/kg), sugarcane bagasse (16.88MJ/kg), corn stalk (16.24MJ/kg), and corn cob (16.99MJ/kg) as reported by Duku, (2014). Table 2: Physicochemical Properties of the Bio-oil Physicochemical parameters Value pH 3.03 Specific gravity@ 40oC 0.99 Density @ 40oC (g/cm3) 0.99 Flash point (oC) 96.28 Pour point (oC) -7.3 Viscosity at 40 0C (cP) 4.23 Heating value (MJ/kg) 21.78 Cetane Number 51.45 0 10 20 30 40 50 60 70 80 300 350 400 450 Composition (%) Temperature (oC) Carbon Content (%) Hydrogen Content (%) Sulphur Content (%) Nitrogen Content (%) Oxygen Content (%) 501 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 3.6. FTIR Analysis of Bio-oil Figure 6 depicts the spectra of Fourier Transform Infrared Spectroscopy (FTIR) of the bio-oil yields from pyrolysis of PKS at the optimum operating temperature of 450 oC over a wavenumber range between 500 and 4000 cm-1 in the spectrum analysis. The peak wavelength (3104.25 cm-1) is ascribed to the O-H stretching vibration of Alcohol. The peak (2998.36 cm-1) is assigned to C-H stretching due to the presence of Alkanes, and the peak (1448.65 cm-1) is attributed to C=O stretching vibration of Ketones, aldehydes, and carboxylic acids. The peak wavelength of 1198.25 cm-1 indicates C═C stretching vibrations in aromatic rings containing Alkenes. The peak (1185.02 cm-1) represents the stretching vibration of -NO2indicates the presence of nitrogenous compounds. The C-H stretching vibration of the methoxy group occurring at the peaks of 1100.75 cm-1 comprises methoxy groups. Primary, secondary and tertiary alcohols are found in the C-H stretching vibration of the absorbance peak (1000.02 cm-1). The O-H stretching vibration with absorbance peak of 932.71 cm-1 indicated the presence of Phenol, esters, ethers, and aromatic compounds. The functional groups is similar to Ogunkanmia et al., (2018) and Okokpujiel et al., (2023). The functional group makes the bio-oil useful as fuel in furnaces, automobile vehicles, and marine equipment and can also be utilized as a catalyst for the production of plastic and drugs (Okokpujiel et al., 2023) Figure 6: FTIR spectrum of bio-oil yield from pyrolysis of PKS 3.7. GC-MS Analysis of the Bio-oil Figure 7 presents the bio-oil chemical composition achieved using gas chromatography-mass spectroscopy (GC-MS) analysis, which agrees with that presented by Okokpujie et al., (2023) and Laouge et al., (2020). The bio-oil is made up of Hexadecane, Phenol,2,4-dimethyl, 5,6-Dimethyl-1H-benzotriazole, β-DGlucopyranose,1,6-anhydro, and Phenol, with the highest values of peak area of 23.59%, 17.38%, 13.66%, 10.55% and 10.18% respectively. Phenol presence in the bio-oil was also found to be visible with the FTIR analysis. The concentrations of phenol and its derivatives were very high, indicating the suitability of the oil to be considered for value-added chemicals. In addition, it is possible to upgrade the bio-oil to obtain highergrade fuel through deoxygenation processes as suggested by Nasrul et al., (2014). 502 A. Akinsade et al. / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 494-504 Figure 7: GC-MS Analysis of the Bio-oil 4. CONCLUSION This study explores the pyrolysis of Palm Kernel Shells (PKS) in a fixed-bed batch-fed reactor at varying temperatures (300–450 °C), yielding significant insights into the potential of PKS as a sustainable bioenergy resource. The experimental results revealed that temperature has a profound influence on the yield and quality of pyrolysis products (biochar, bio-oil, and non-condensable gases). The biochar produced exhibited excellent fuel characteristics, particularly at higher temperatures. The biochar has a high fixed carbon content (83.99%), a low ash content (0.99%), and minimal moisture, indicating high energy density, improved combustion efficiency, and reduced emissions of harmful gases. The ultimate analysis further confirmed high carbon content (74.89%) and low concentrations of sulphur, nitrogen, and hydrogen, enhancing its environmental sustainability. The bio-oil demonstrated promising qualities for industrial fuel applications. With reduced moisture content (0.98%) and a high total carbon content (86.84%) at 450 °C, leading to improved energy density and combustion stability. Additionally, its physicochemical properties, such as a flash point of 96.28 °C, a cetane number of 51.4, a calorific value of 21.78 MJ/kg, and viscosity of 4.23 cp, fall within acceptable ranges for safe handling, efficient atomization, and clean combustion. Advanced characterization via FTIR and GC-MS confirmed the presence of valuable functional groups and high concentrations of phenol and its derivatives, indicating the feasibility of upgrading bio-oil for high-value chemicals and potential use in industrial applications beyond combustion. 5. CONFLICT OF INTEREST There is no conflict of interest associated with this work. REFERENCES Adegoke, S. O., Adeleke, A. A., Ikubanni, P. P., Falode, A. O., Alawode, A. J., Agboola, O. O., Adediran, A. A. (2021). Design and Fabrication of an Ablative Pyrolyzer for Production of Bio-lubricants and chemicals in Oil Well Drilling Application. International Conference on Energy and Sustainable Environment IOP Conf. Series: Earth and Environmental Science, pp. 665 Adeniyi, O. M., Azimoh, U., and Burluka, A. (2018): Algae Biofuel: Current status and future applications. Renewable and Sustainable Energy Reviews. 90: pp. 316-335. Aziz, M. A., Rahma, M. A., Molla, H. (2018). 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