Fractionation of pyrolysis oil via supercritical carbon dioxide extraction: Optimization study using response surface methodology (RSM)

Highlights: • Extraction of pyrolysis oil from palm kernel shell was performed using sc-CO₂. • Effect of temperature, pressure and CO₂ flowrate on extract yield was studied. • The maximum bio-oil extract yield obtained was 27.63%. • Acids and esters were significantly enriched in the extract. - Abstract: The extraction of bio-oil produced from pyrolysis of palm kernel shell (PKS) using supercritical carbon dioxide (sc-CO₂) was systematically studied using Response Surface Methodology (RSM) and optimized. Three parameters which included temperature (40-60 °C), pressure (20-35 MPa) and CO₂ flowrate (3-8 cm³ min⁻¹) were optimized for maximum extraction yield. The predicted optimum extraction condition at 48.0 °C, 28.2 MPa, 8.0 cm³ min⁻¹ CO₂ flowrate for maximum predicted extract yield of 30.03 (±2.65)% was validated with experimental extract yield of 27.63 (±1.00)%. The regression model developed provided accurate predictions of the extract yield, with coefficient of determination R² of 0.9501. The bio-oil extract obtained was then characterized by GC/MS, proximate, and ultimate analyses and compared with the raw bio-oil. Acids and esters were found to be enriched in the supercritical extract, while other classes of chemical compounds such as phenolics, aromatics, ketones and nitrogen compounds were also detected in the bio-oil extract. The interactive effects of process parameters on the extraction efficiency of sc-CO₂ and the quality of bio-oil extract obtained were presented and discussed.