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

Abstract

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°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 X1 (reaction time, h)=2.75, X2 (amount of catalyst, wt%)=12.86, and X3 (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 0.0277min−1, respectively. More importantly, the washed catalyst maintained >99% methyl ester yield even after three successive usage.