Enzyme-catalyzed synthesis and kinetics of ultrasonic assisted methanolysis of waste lard for biodiesel production

Abstract

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 biodiesel generation from waste lard bio-catalyzed by immobilized lipase [Candida antarctica Lipase B (CALB)] were investigated. A Ping Pong Bi Bi kinetic model approach was employed to study the effect of ultrasonic amplitude on the enzymatic transesterification. Kinetic constants of transesterification reaction were determined at different ultrasonic amplitudes (30%, 35%, 40%, 45%, and 50%) and enzyme concentrations (4, 6, and 8wt.% of fat) at constant molar ratio (fat:methanol); 1:6, and ultrasonic cycle; 5kHz. Parametric effects on the yield were studied using three sets of experiments namely A, B, and C. In experiment set A, two factors (ultrasonic amplitude and cycle) were investigated at three levels; in experiment set B, two factors (molar ratio and enzyme concentration) were examined at three levels; and in experiment set C, two factors (ultrasonic amplitude and reaction time) were investigated at five levels. A yield of 96.8% was attained in 20min at an ultrasonic amplitude (40%) at 5kHz, fat:methanol molar ratio (1:4) and catalyst level 6% (w/w of fat). The fitted curves of the kinetic mechanism showed a sigmoidal curve due to 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: at ultrasonic amplitude 40%, the reaction activities within the system seemed to be steady after 20min which means the reaction could proceed with or without ultrasonic mixing. The kinetic model approach employed describes the whole methanolysis process accurately.