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

Biolubricant production by Novozym 435-catalyzed methanolysis of castor oil was studied in a fluidized-bed reactor operating in the batch recirculation mode. With 1 g of enzyme and a methanol-to-oil molar ratio of 6:1, the highest yield of methyl ester was obtained (99.6%) after 24 h at 40 degrees C and a 30 mL/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 V-max = 7.97 mmol/L min, K-m,K-oil = 90.07 mM, K-m,K-methanol = 733.27 mM, K-i,K-oil = 923.23 mM, and K-i,K-methanol = 317.11 mM. The K-m,K-oil value was indicative of the higher affinity of the lipase toward the oily substrate, and the castor oil was less inhibitory than methanol (K-i,K-methanol < K-i,K-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. (C) 2014 Elsevier B.V. All rights reserved.