Enzyme-Catalyzed Synthesis and Kinetics of Ultrasonic-Assisted Methanolysis of Waste Choice White Grease for Fatty Acid Methyl Ester Production

In this study, the effects of ultrasonic parameters (amplitude, cycle, and pulse) and major reaction factors (molar ratio and enzyme concentration) on the reaction kinetics of fatty acid methyl ester (FAME) generation from waste choice white grease (CWG) biocatalyzed by immobilized lipase [Candida antarctica lipase B (CALB)] were investigated. A yield of 98.2% was attained in 20 min at an ultrasonic amplitude (40%) at 5 kHz, fat/methanol molar ratio (1:4), and catalyst level of 6% (wt/wt of fat). The effect of ultrasonic mixing on the reaction kinetic of enzymatic transesterification was investigated using a Ping Pong Bi Bi kinetic model approach. Kinetic constants of the transesterification reaction were determined at different ultrasonic amplitudes (30, 35, 40, 45, and 50%) and enzyme concentrations (4, 6, and 8 wt % of fat) at a constant molar ratio (fat/methanol) of 1:6 and ultrasonic cycle of 5 kHz. The fitted curves of the kinetic mechanism showed a sigmoidal curve as a result of mass-transfer limitations, which controlled the process at the beginning of the reaction. The kinetic model results also revealed interesting features of ultrasound-assisted enzyme-catalyzed transesterification. The kinetic model approach described the whole methanolysis process accurately. At the ultrasonic amplitude of 40%, the reaction activities within the system seemed to have steadied after 20 min, which means that the reaction could proceed with or without ultrasonic mixing