KINETICS AND THERMODYNAMICS STUDIES ON OIL EXTRACTION FROM SOUTHERN KADUNA PALM KERNEL SEEDS USING SUBCRITICAL WATER EXTRACTION TECHNOLOGY

Abstract

Subcritical water has the potential to be highly efficient, non-toxic and low-cost alternative extraction solvent due to its unique properties under certain conditions. In this current study, we used the process variables (extraction temperature, time and particle size) to investigate the kinetics of palm kernel oil (PKO) extraction using subcritical water as solvent by considering the power law and Elovich’s kinetic law models. The laws of thermodynamics were employed to determine the spontaneity and nature of the PKO extraction process by evaluating thermodynamic parameters such as the Gibbs free energy (ΔG), enthalpy change (ΔH) and entropy change (ΔS). The experimental result showed that the conditions for the optimum yield of PKO using subcritical water were established at 0.5 mm, 120 minutes and 493K (200 ◦C) where the highest oil yield was (49.02%). The experimental data was found to best fit the power law model compared to the Elovich’s model, as a result of its highest R² and lowest SD and RMS values. Thermodynamics analysis showed that PKO extraction has positive enthalpy and entropy values of 7.23×10^-4kJ/mol and 0.0304kJ/molK respectively, indicating an endothermic and irreversible process. The negative values of Gibbs free energy (– 12.56 to -14.99kJ/molK) indicated that the extraction process is spontaneous. Gas chromatography analysis showed that lauric acid (48.1%) appears as the predominant fatty acid in the extracted oil followed by myristic acid (16.0%) and linoleic acid (14.9%). The subcritical water technology was therefore, highly recommended for the extraction of PKO due to its high potentials as shown in the high oil yield obtained. The power law model was also recommended due to the overall comparative fitness to the experimental data while the thermodynamics specifications as verified in this work were also recommended to be used for process design of PKO extraction.