Process optimization, kinetic and thermodynamic studies on biodiesel production by supercritical methanol transesterification with CH₃ONa catalyst

This study provided a novel supercritical methanol transesterification process with little amount of CH₃ONa catalyst to synthesize biodiesel from soybean oil by response surface technology. The maximum biodiesel yield was 97.42% under the optimal conditions of 250 °C, methanol to oil molar ratio of 23:1, 1.0 wt% CH₃ONa and 20 min. Temperature was proved to have the most significant effect on transesterification, followed by methanol to oil molar ratio and catalyst amount. The kinetic model suggested a 1.5th order reaction with the activation energy of 27.06 kJ·mol⁻¹ and the pre-exponential factor of 102.71. The values of thermodynamic parameters including enthalpy, entropy and Gibbs free energy for this process were calculated as 23.15 kJ·mol⁻¹, −0.22 kJ·mol⁻¹·K⁻¹ and 137.43 kJ·mol⁻¹ at 250 °C, respectively. Reduced reaction temperature, catalyst amount, and reaction time are among the advantages of the integrated process for biodiesel production over single supercritical process and conventional catalytic methods.