Transesterification of soybean oil using a novel heterogeneous base catalyst: Synthesis and characterization of Na-pumice catalyst, optimization of transesterification conditions, studies on reaction kinetics and catalyst reusability

The transesterification of soybean oil using sodium-loaded pumice (Na-pumice) catalyst synthesized through wet impregnation was investigated in this study. X-ray diffraction (XRD) spectroscopy, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) spectroscopy, and Brunauer-Emmett-Teller (BET) surface analysis were used to characterize the prepared Na-pumice catalysts. Response surface methodology (RSM) based on the three-factor, three-level Box-Behnken Design was employed to optimize the transesterification reaction at constant temperature of 60 degrees C. The process variables were reaction time, methanol-to-oil molar ratio, and catalyst dosage while the fatty acid methyl ester (FAME) yield was the main response variable. The optimum reaction conditions were X-1 (reaction time, h) = 2.75, X-2 (amount of catalyst, wt%) = 12.86, and X-3 (methanol/oil molar ratio) = 24: 1, with an actual FAME yield of> 99%. The kinetics of the transesterification process and the reusability of the catalyst were also investigated. Results showed that reaction kinetics at optimum conditions conformed to the pseudo-first order model with coefficient of determination and k values of 0.9862 and 0.0277 min(-1), respectively. More importantly, the washed catalyst maintained> 99% methyl ester yield even after three successive usage.