Ultrasound assisted production of fatty acid methyl esters from transesterification of triglycerides with methanol in the presence of KOH catalyst: Optimization, mechanism and kinetics

• Analysis of changes in the concentrations of reactants and products.
• Analysis of kinetics and rate-determining step of transesterification during ultrasound irradiation.
• Rate determining step was found to be the reaction of MG with methanol into GL and FAME.

Ultrasound assisted transesterification of triglycerides (TG) with methanol in the presence of KOH catalyst was investigated, where the changes in the reactants and products (diglycerides (DG), monoglycerides (MG), fatty acid methyl esters (FAME) and glycerin (GL)) concentrations were discussed to understand the reaction mechanism and kinetics under ultrasound irradiation. The optimum reaction condition for the FAME production was the concentration of KOH 1.0 wt.%, molar ratio of TG to methanol of 1:6, and irradiation time of 25 min. The rate constants during the TG transesterification with methanol into GL and FAME were estimated by a curve fitting method with simulated curves to the obtained experimental results. The rate constants of k1(TG+CH3OH→DG+FAME),k-1(DG+FAME→TG+CH3OH),k2(MG+CH3OH→MG+FAME),k-2(MG+FAME→DG+CH3OH),k3(MG+CH3OH→GL+FAME)andk-3(GL+FAME→MG+CH3OH) were estimated to be 0.21, 0.008, 0.23, 0.005, 0.14 and 0.001 L mol−1 min−1, respectively. The rate determining step for the TG transesterification with methanol into GL and FAME was the reaction of MG with methanol into GL and FAME.