Modelling and experimental studies on lipase-catalyzed isoamyl acetate synthesis in a microreactor

Abstract

A lipase-catalyzed synthesis of isoamyl acetate was studied in a continuously operated pressure-driven microreactor. The esterification of isoamyl alcohol and acetic acid occurred at the interface between n-hexane and an aqueous phase with dissolved lipase B from Candida antarctica. By adjusting flow rates of both phases, a parallel laminar flow with liquid–liquid boundary in the middle of the microchannel could be reestablished and a separation of phases was achieved at the y-shaped exit of the microreactor. Since product remained in the organic phase, this also enabled its continuous separation from the aqueous phase with the enzyme. A three-dimensional mathematical model was developed, considering the velocity profile developed for steady-state conditions between two immiscible fluids. The model contained convection, diffusion, and enzyme reaction terms, where esterification rate was described with a Ping-Pong Bi-Bi mechanism and inhibition by both substrates. Experimental data, which were in good agreement with model simulations, have demonstrated 35% conversion at residence time 36.5 s at 45 °C and at 0.5 M acetic acid and isoamyl alcohol inlet concentrations, which is much faster as in any literature reported so far. According to model simulations, obtained by non-equidistant finite differences numerical solutions of complex non-linear equations system, further microreactor design and process optimization are feasible.