Influence of the enzyme concentration on the phase behaviour for developing a homogeneous enzymatic reaction in ionic liquid–CO2 media

Abstract

A homogeneous enzymatic reaction in an ionic liquid (IL)–CO2 medium integrated with the separation of the product is proposed. It takes advantage of the miscibility switch phenomenon using CO2, which is able to force two immiscible phases to form one homogeneous phase to perform the reaction. After completion of the reaction the homogeneous fluid phase is split in two or three phases upon pressure decrease in order to facilitate the product recovery. For this purpose the enzymeCandida antarctica lipase B (CaL B) and the IL 1-hydroxy-1-propyl-3-methyl imidazolium nitrate (HOPMImNO3) are used. In this study the solubility of CO2 in solutions of CaL B in HOPMImNO3 was experimentally determined using the Cailletet apparatus, which operates according to the synthetic method. Concentrations of the enzyme vary from 3 to 12% by weight, and concentrations of CO2 from 5 to 20 mol% were investigated in a temperature range from 30 to 75 °C and pressures up to 12 MPa were applied. No precipitation of the enzyme was observed when dissolving CO2 in the IL. At constant CO2/IL ratios the pressure of the bubble points remained almost unchanged with the enzyme concentration. Triacetin tests showed that the reduction of the activity of the enzyme after storage for three months in liquid HOPMImNO3 was only of the order of 20%. Recovery and purification of the IL was possible by precipitation of the enzyme using isopropanol (IPA) as an anti-solvent.