• Energy Research

Abstract The heavy palm oil industry in Malaysia has generated various oil palm biomass residues. These residues can be converted into liquids (bio-oil) for replacing fossil-based fuels and chemicals. Studies on the conversion of these residues to bio-oil via pyrolysis technology are widely available in the literature. However, thermochemical liquefaction of oil palm biomass for bio-oil production is rarely studied and reported. In this study, palm kernel shell (PKS) was hydrothermally liquefied under subcritical and supercritical conditions to produce bio-oil. Effects of reaction temperature, pressure and biomass-to-water ratio on the characteristics of bio-oil were investigated. The bio-oils were analyzed for their chemical compositions (by GC–MS and FT-IR) and higher heating values (HHV). It was found that phenolic compounds were the main constituents of bio-oils derived from PKS for all reaction conditions investigated. Based on the chemical composition of the bio-oil, a general reaction pathway of hydrothermal liquefaction of PKS was postulated. The HHV of the bio-oils ranged from 10.5 to 16.1 MJ/kg, which were comparable to the findings reported in the literature.

Abstract This paper presents the studies on the liquefaction of three types of oil palm biomass; empty fruit bunch (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) using water at subcritical and supercritical conditions. The effect of temperature (330, 360, 390 °C) and pressure (25, 30, 35 MPa) on bio-oil yields were investigated in the liquefaction process using a Inconel batch reactor. The optimum liquefaction condition of the three types of biomass was found to be at supercritical condition of water i.e. at 390 °C and 25 MPa, with PKS yielding the maximum bio-oil yield of 38.53 wt%, followed by EFB and PMF, with optimum yields of 37.39 wt% and 34.32 wt%, respectively. The chemical compositions of the bio-oils produced at optimum condition were analyzed using GC–MS and phenolic compounds constituted the major portion of the bio-oils, with other minor compounds present such as alcohols, ketones, aromatic hydrocarbons and esters.

Abstract The production of bio-oil from palm kernel shell (PKS) via subcritical and supercritical hydrothermal liquefaction was investigated. In order to maximize the bio-oil yield, design of experiment and optimization was performed using Response Surface Methodology (RSM) with central composite rotatable design (CCRD). Four factors which included temperature (330–390 °C), pressure (25–35 MPa), reaction time (60–120 min) and biomass-to-water ratio (0.20-0.50 wt/wt) were investigated. The regression model developed gave accurate predictions and fitted well with the experimental results, with coefficient of determination R 2 of 0.9109. Based on the model, the optimum liquefaction condition was predicted to be at temperature of 390 °C, pressure of 25 MPa, reaction time of 60 min and biomass-to-water ratio of 0.20 with a prediction yield of 15.48 wt%. This condition was validated by experimental runs which produced an average of 14.44 wt% bio-oil yield. Then, the mediation effect of supercritical CO 2 on bio-oil yield was studied. Hydrothermal liquefaction of PKS was performed at the optimum condition in the presence of supercritical CO 2 . The effect of supercritical CO 2 was found to be insignificant at higher liquefaction temperature of 390 °C but it was significant at lower liquefaction temperature of 300 °C, producing bio-oil yield of 11.35 wt%. GC/MS analysis showed that phenolic compounds constituted the major portion of the bio-oils, while ketones, aromatic compounds and carboxylic acid were also detected.

Abstract This paper presents the studies on the effect of three process parameters; temperature, pressure and reaction time on the subcritical and supercritical hydrothermal liquefaction of oil palm empty fruit bunch, palm mesocarp fiber and palm kernel shell. The effect of temperature (330–390 °C), pressure (25–35 MPa) and reaction time (30–240 min) on bio-oil yields were investigated using a Inconel batch reactor. The optimum liquefaction condition for empty fruit bunch, palm mesocarp fiber and palm kernel shell was at supercritical condition of water; 390 °C and 25 MPa. For the effect of reaction time, bio-oil from empty fruit bunch and palm mesocarp fiber attained maximum yields at 120 min, whereas bio-oil yield from palm kernel shell continued to increase at reaction time of 240 min. Lastly, a life cycle assessment based on a conceptual biomass hydrothermal liquefaction process for bio-oil production was constructed and presented.

Abstract Biomass, which its conversion into greener bio-based products, is able to achieve a more balanced carbon cycle through circular utilisation. The development of biomass industry, therefore, appears to be one priority area and is an important step to motivate the global circular economy and sustainability. However, due to the existence of commercialisation barriers, the biomass industry in developing country, such as Malaysia, is not on par with the increment of the country's gross domestic product. This paper overviews the barriers of development and challenges encountered by the biomass industry in Malaysia. Challenges are classified into four barrier categories, i.e., (i) technical barrier, (ii) financial barrier, (iii) social awareness barrier and (iv) misunderstanding and gaps between stakeholders. Based on the barriers identified, recommendations which embrace the areas of technology innovation, logistics management, interaction between academia and industry, policy and enforcement, social impact and international benchmarking, are proposed. These recommendations can act as good references for the development of biomass industry in Malaysia and reflection for other developing countries with biomass resources in the promotion of sustainability and commercialisation of biomass products. The role of the five key stakeholders in commercialising the biomass technologies are highlighted in this review.

Carbon monoxide (CO) is a highly valuable component of syngas which could be used to synthesize various chemicals and fuels. Conventionally, syngas is derived from fossil-based natural gas and coal which are non-renewable. To curb the problem, CO2 gasification offers a win-win solution in which CO2 is converted with wastes to CO, achieving carbon emission mitigation and addressing waste disposal issue simultaneously. In this review, gasification of various wastes by CO2 with particular focus given to generation of CO-rich syngas is presented and critically discussed. This includes the effects of operating parameters (temperature, pressure and physicochemical properties of feedstocks) and advanced CO2 gasification techniques (catalytic CO2 gasification, CO2 co-gasification and microwave-driven CO2 gasification). Furthermore, associated technological challenges are highlighted and way forward in this field are proposed.

Abstract Bio-oil is a highly valuable product derived from biomass pyrolysis which could be used in various downstream applications upon appropriate upgrading and refining. Extraction and fractionation are two promising methods to upgrade bio-oil by separating the complex mixture of bio-oil compounds into distinct fine chemicals and fractions enriched in certain classes of chemical compounds. In this review, various extraction techniques for bio-oil (organic solvent extraction, water extraction, supercritical fluid extraction, distillation, adsorption, chromatography, membrane, electrosorption and ionic liquid extraction), their associated features (extraction mechanisms involved, advantages and disadvantages), the characteristics of bio-oil extracts and their applications are presented and critically discussed. It was revealed that the most promising technique is via organic solvent extraction. Furthermore, the technological gaps and bottlenecks for each separation techniques are disclosed, as well as the overall challenges and future prospects of oil palm biomass-based bio-oil value chain. This review aims to provide key insights on bio-oil upgrading via extraction and fractionation, and a proposed way forward via technology integration in establishing a sustainable palm oil mill-based biorefinery.

The valorization of biochar as a green and low-cost adsorbent provides a sustainable alternative to commercial wastewater treatment technologies that are usually chemical intensive and expensive. This review presents an in-depth analysis focusing on the rice straw-derived biochar (RSB) for removal of various types of contaminants in wastewater remediation. Pyrolysis is to date the most established technology to produce biochar. Subsequently, biochar is upgraded via physical, chemical or hybrid activation/modification techniques to enhance its adsorption capacity and robustness. Thus far, acid-modified RSB is able to remove metal ions and organic compounds, while magnetic biochar and electrochemical deposition have emerged as potential biochar modification techniques. Besides, temperature and pH are the two main parameters that affect the efficiency of contaminants removal by RSB. Lastly, the limitations of RSB in wastewater remediation are elucidated based on the current advancements of the field, and future research directions are proposed.

Abstract The extraction and recovery of value-added chemical compounds, such as phenolic compounds present in bio-oil has been a vital subject of study recently. In this work, the extraction of bio-oil using supercritical carbon dioxide (sc-CO2) with particular interest in apparent solubility of phenol (a major chemical compound in pyrolysis oil) was evaluated at various temperatures (50, 60 and 70 °C) and pressures (30, 35 and 40 MPa). Highest extraction yield of bio-oil was obtained at 70 °C and 40 MPa. The phenol content in the extracted bio-oils were also studied and reported. As a preliminary study, the apparent solubility data of phenol in sc-CO2 was successfully modeled using the values from the correlation of Chrastil, Adachi & Lu and Bartle models. The model parameters for these equations were determined and reported in this work. It was found that Chrastil, Adachi & Lu and Bartle models produced satisfactory correlations on the solubility of phenol in sc-CO2, with AARD values of 1.51%, 6.52% and 1.85%, respectively.