Competitive lipase-catalyzed ester hydrolysis and ammoniolysis in organic solvents; Equilibrium model of a solid-liquid-vapor system

Enzymatic ester hydrolysis and ammoniolysis were performed as competitive r eactions in methyl isobutyl ketone without a separate aqueous phase. The re action system contained solid ammonium bicarbonate, which dissolved as wate r, ammonia, and carbon dioxide. During the reaction an organic liquid phase , a vapor phase, and at least one solid phase are present. The overall equi librium composition of this multiphase system is a complex function of the reaction equilibria and several phase equilibria. To gain a quantitative un derstanding of this system a mathematical model was developed and evaluated . The model is based on the mass balances for a closed batch system and str aightforward relations for the reaction equilibria and the solubility equil ibria of ammonium bicarbonate, the fatty acid ammonium salt, water, ammonia , and carbon dioxide. For butyl butyrate as a model ester and Candida antar ctica lipase B as the biocatalyst this equilibrium model describes the expe riments satisfactorily. The model predicts that high equilibrium yields of butyric acid can be achieved only in the absence of ammoniolysis or in the presence of a separate water phase. However, high yields of butyramide shou ld be possible if the water concentration is fixed at a low level and a mor e suited source of ammonia is applied. (C) 1999 John Wiley & Sons, Inc.