Application of pervaporation system to lipase-catalyzed esterification in organic solvent

Abstract

Esterification of oleic acid with n-butanol in the presence of $Lipozyme^®$ was carried out at 25℃ in isooctane with various initial water activities. Initial reaction rate as well as equilibrium conversion decreased at high initial water activity. Therefore, removal of water present in the reaction mixtures was essential. A pervaporation process was applied to the lipase-catalyzed synthesis of n-butyl oleate to remove water. Pervaporation selectively separated water from the reaction mixture using a non-porous polymeric membrane, cellulose acetate. Therefore, pervaporation is potentially applicable to remove the water produced from various enzymatic processes, such as synthesis of various esters, peptides, and glycosides in solvent system as well as in solvent-free system. Lipase-catalyzed esterification of n-butyl oleate was carried out in n-hexane as a model reaction. The optimal activity of Candida rugosa lipase was shown in the water activity ($a_w$) range of 0.52 to 0.65 at 30℃. The water produced from the esterification was removed by the tubular type pervaporation system. The rate of ester formed from enzymatic esterification was allowed to be the same rate of water removal by maintaining optimal aw of the reaction system using the on-off dewatering control device. The reaction rate and yield with aw control was increased two folds in comparison with those of the uncontrolled reaction. The enantioselective esterification of racemic ibuprofen was carried out in n-hexane using lipase. Candida rugosa lipase was most suitable in the resolutio of racemic ibuprofen. The optimal water activity ($a^w$) of Candida rugosa lipase was 0.52 at 30℃. Dodecanol among various primary alcohols was suitable in the resolution of racemic ibuprofen. The water produced from the esterification was removed by tubular type pervaporation system. The on-off dewatering control using a computer was developed for a continuous control of the desired water activity ($a^w$). The rate o...