Ester ammoniolysis in an enzymatic membrane reactor

Abstract

• A gas–liquid enzymatic membrane reactor was implemented for direct ammoniolysis. • Ethyl octanoate was converted to octanamide by immobilized C. antarctica lipase B. • High enzyme stability and selectivity toward the amide (95% at 40 °C) was achieved. A form of generating amides is by reaction of esters with ammonia (ammoniolysis) or with amines (aminolysis). This reaction can be catalyzed by free or immobilized lipases. The aim of this work is to develop a gas–liquid enzymatic membrane reactor in which the ammoniolysis of ethyl octanoate, catalyzed by Candida antarctica lipase B (EC 3.1.1.3), is improved through immobilization of the biocatalyst onto a membrane surface which also serves as gas–liquid interphase. After the selection of a suitable membrane for the process, data show that the higher the initial substrate concentration, the lower the reaction rate. A Michaelis–Menten type model with competitive product inhibition correlated well with the kinetic data. In addition, the temperature dependence of the reaction rate goes through a maximum. The yield of the amide was always above 92% in the range 25–55 °C, with a maximum of 95% at 40 °C. At 40 °C, and after 24 h of reaction, values comparable to those reported in the literature on the free enzyme-catalyzed ammoniolysis were achieved, but with much lower enzyme/substrate ratio. Moreover, the immobilized enzyme kept its activity for a long period of time (three weeks).