Ultrasound–assisted enzymatic biodiesel production using blended feedstock of non–edible oils: Kinetic analysis

Abstract

The present study reports ultrasound–assisted biodiesel synthesis using blended feedstock of non–edible oils and commercial immobilized lipase from Thermomyces lanuginosus. Optimum process parameters obtained using Box–Behnken statistical design were as follows: alcohol/oil molar ratio = 7.64:1, enzyme loading = 3.55% (w/w) and temperature = 36 °C, conversion = 90%. Sonication of reaction mixture resulted in lowering of activation energy to 100.4 kJ/mol (from 124.4 kJ/mol under mechanical agitation). Addition of water to reaction mixture (10% v/v) not only boosted biodiesel yield from 90% to 94% but also lowered activation energy to 78.7 kJ/mol. Analysis of reaction kinetics using ordered Bi–Bi model revealed drastic rise (∼1.6×) in reaction velocity with concurrent changes in Michaelis–Menten and dissociation constant of both substrate and products. Finally, the recycled enzyme showed good retention of activity up to 6 cycles in presence of ultrasound, which further enhanced with water addition to reaction mixture.