(218e) Optimization of Hydrothermal Liquefaction of Palm Kernel Shell to Bio-Oil By Response Surface Methodology and Synergistic Effect of Supercritical CO2

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 R² 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 synergistic effect of supercritical CO₂ on bio-oil yield was studied. Hydrothermal liquefaction of PKS was performed at the optimum condition in the presence of supercritical CO₂. The effect of supercritical CO₂ was found to be insignificant at liquefaction temperature of 390 °C but it was significant at 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.