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

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 k 1 ( TG + CH 3 OH → DG + FAME ) , k - 1 ( DG + FAME → TG + CH 3 OH ) , k 2 ( MG + CH 3 OH → MG + FAME ) , k - 2 ( MG + FAME → DG + CH 3 OH ) , k 3 ( MG + CH 3 OH → GL + FAME ) and k - 3 ( GL + FAME → MG + CH 3 OH ) 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.