Study on kinetics-thermodynamics and environmental parameter of biodiesel production from waste cooking oil and castor oil using potassium modified ceria oxide catalyst

Abstract

Abstract Research on biodiesel production from waste material and lignocellulosic biomass using heterogeneous catalyst has been studied throughout the world to achieve a sustainable source of fuel. Heterogeneous base-catalyzed transesterification attracts more attention as it overcomes the flaws regarding homogeneous catalysis. In this study, potassium (K) modified ceria oxide (CeO2) was synthesized via auto combustion method and introduced as the heterogeneous base catalyst for transesterification of waste cooking oil and castor oil. It was found that catalyst having K/Ce atomic ratio 2, activated at 800°C showed highest efficiency of 99.09% and 98.49% FAME (fatty acid methyl ester or biodiesel) conversion in methyl esterification of waste cooking oil (WCO) and castor oil (CO) under moderate reaction condition. A robust base-catalyzed transesterification reaction mechanism was proposed based on FTIR result. The rate constants (kC) of the reaction at five different temperatures 45 to 65°C with 5°C interval were evaluated by mean of respective kinetic plots for methyl esterification of WCO and CO. Activation energy Ea for WCO and CO transesterification were calculated to be 50.1 kJ mol−1 & 48.55 kJ mol−1 with corresponding frequency factor 35.4 × 105 min−1 & 11.9 × 105 min−1. Enthalpy of activation (ΔH#) was obtained to be 47.35 kJ mol−1 and 45.989 kJ.mol−1with corresponding entropy of activation (ΔS#) −128.69 J.K−1. mol−1 and -137.21 J.K−1. mol−1 of methyl ester formation of WCO and CO. The Gibb’s free energy of activation (ΔG#) for both reactions was evaluated to be 90.85 kJ mol−1 and 92.66 kJ mol−1. The positive values of both ΔG# and ΔH# indicates that the reaction followed an endothermic non-spontaneous pathway while the negative ΔS# value informs the reduction in randomness during transesterification. The catalyst showed high turnover frequency and meager value of Environmental-factor which implies the catalyst is well efficient for fast production of biodiesel with minute waste generation.