Response Surface Modeling and Optimization of Immobilized Candida antarctica Lipase-Catalyzed Production of Dicarboxylic Acid Ester

Dicarboxylic acid esters are one of the important classes of synthetic lubricants which exhibit good oxidation and thermal stability, low volatility, shear stability, high viscosity index and low toxicity. In this work, enzymatic synthesis of dioleyl adipate ester was performed in batch mode with a stirred tank reactor (STR). Immobilized Candida antarctica lipase B was used as the biocatalyst for the esterification reaction. Response surface methodology (RSM) based on a four-factor-five-level central composite rotatable design (CCRD) was employed to model and analyze the reaction. The effects of all investigated parameters including amount of enzyme (1-10%w/w), temperature (35-75oC), time (30-480 min) and impeller speed (1-500 rpm) were significant (P<0.0001). All factors positively affected the yield with reaction time having the most significant effect. The highest obtained conversion yield was 96.2% under experimental conditions of 60.0oC, 323.7 min, amount of enzyme 6.0%w/w of the substrates and 500 rpm impeller speed. Verification experiments exhibited good correspondence between actual yields and the values predicted by the statistical model. The predictive model was successfully applied for optimization of upscale synthesis of adipate ester.