Pervaporation-assisted enzymatic esterification of oleic acid and ethanol

Abstract

The batch and continuous processes of enzymatic esterification of oleic acid and ethanol coupled pervaporation (PV) unit were successfully developed in this study. Bacterial cellulose (BC) impacted with alginate film was used as selectively-permeable membrane to remove water from the reaction mixture. The effects of PV operating modes, amount of enzyme (Novozym 435) loading, flow pattern in the reactor were investigated. The enzymatic esterification of oleic acid and ethanol were carried out under the operating conditions as follows: molar ratio of oleic acid to ethanol of 1:2, temperature of 45oC, turbine rate at 250 rpm, enzyme loading at 5% (w/w oleic acid) and pressure permeate side at 10 mmHg. The result shows that the BCA membrane was high selectivity to water, in which the permeate containing about 95 %(w/w) water could be removed from the reaction mixture with the water flux of 140 – 270 gm-2h-1. Considering less energy consumption, the start operation of pervaporation at the end of the reaction (late pervaporation) to move equilibrium toward biodiesel product is suggested, in which the FFA conversion was increased from 84.37 % to 88.50 % by using the system coupled with the PV unit. On the study of the flow pattern in the reactor, it was shown that the higher initial rate and FFA conversion were obtained by using the expanded bed, as compared to the fixed bed at the same reactor volume. The evaluation of the continuous esterification process in the expanded bed reactor with the retention time of 50 min shows the improved of the FFA conversions from 65.88% to 69.73% by using the system coupled with the PV unit. From the observation of surface morphology of Novozym 435 being used in the esterification by SEM, it was demonstrated that the degrees of swelling of Novozym 435 in the batch and continuous processed coupled with pervaporation were less compared to those from the systems without the PV unit, which could be benefit for long term use of the biocatalyst.