Modeling the kinetics of biolubricant production from castor oil using Novozym 435 in a fluidized-bed reactor

Abstract

Biolubricant production by Novozym 435-catalyzed methanolysis of castor oil was studied in a fluidized-bed reactor operating in the batch recirculation mode. With 1g of enzyme and a methanol-to-oil molar ratio of 6:1, the highest yield of methyl ester was obtained (99.6%) after 24h at 40°C and a 30mL/min flow rate. The ping-pong bi-bi mechanistic model was used to treat the experimental data. Using non-linear regression analysis, a model with substrate inhibition by both methanol and castor oil gave the best fit, with kinetics constants Vmax=7.97mmol/Lmin, Km,oil=90.07mM, Km,methanol=733.27mM, Ki,oil=923.23mM, and Ki,methanol=317.11mM. The Km,oil value was indicative of the higher affinity of the lipase toward the oily substrate, and the castor oil was less inhibitory than methanol (Ki,methanol<Ki,oil). The reusability of Novozym 435 was also evaluated using repeated batch experiments, and no significant decreases in the methanolysis yields were observed after ten cycles.