Hydrolysis and regioselective transesterification catalyzed by immobilized lipases in membrane bioreactors

Abstract

An experimental study of two types of immobilized lipase membrane reactors for the bioconversion of lipophilic substrates is reported. In one part of the work, the performance of biphasic membrane reactors has been investigated as a function of selected operating conditions for the hydrolysis of olive oil. In this type of reactor, aqueous and organic phases flow tangentially past the two surfaces of an enzyme containing membrane; intramembrane mass transfer is diffusive. Another part of the study refers to the regioselective transesterification of 5,7-diacetoxyflavone in a monophasic non-aqueous membrane reactor wherein an organic phase solution of substrate is crossflow filtered through the wall of a tubular enzyme-loaded membrane; in this case, intramembrane mass transfer is convective. Immobilization of the enzyme both within the interior of the membranes and at their surfaces is considered. The influence of fluid dynamics parameters and immobilization site on the biphasic reactors performance has been studied using lipase from Candida rugosa. The effect of immobilization, of the amount of immobilized enzyme on the catalytic activity and regioselectivity efficiency in non aqueous system have been investigated using lipase from Pseudomonas cepacea. The observed specific activity of the enzyme in the biphasic membrane system was higher at relatively high transmembrane pressure, high aqueous flow rate and low organic phase flow rate. Immobilization of the enzyme in the sponge layer of the asymmetric membrane allowed higher catalytic activity and stability with respect to the enzyme immobilized on the dense layer. The stability and specific activity of the lipase Immobilized in the monophasic non-aqueous membrane reactor was higher compared to the suspended free lipase and was improved with decreasing the enzyme concentration in the membrane. An high regioselectivity for the immobilized lipase was obtained producing an intermediate natural flavone not yet available.