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

- Novel Na-pumice catalyst was synthesized and characterized.
- Higher amounts of Na in the catalyst improved FAME yield.
- Optimum transesterification reaction conditions gave >99% FAME yield.
- Transesterification reaction kinetics followed pseudo-first order model.
- Washed Na-pumice gave >99% FAME yield per cycle.

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 0.0277 min−1, respectively. More importantly, the washed catalyst maintained >99% methyl ester yield even after three successive usage.

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