Enzymatic production of alkyl esters through lipase-catalyzed transesterification reactions in organic solvents: Solvent effects and prediction capabilities of equilibrium conversions

The solvent effect on the equilibrium position of the transesterification r eaction of hexanol with ethyl acetate catalyzed by a lipase has been invest igated in a variety of non-polar and polar solvents - and binary mixtures. The results obtained indicate that the solvent effect on the equilibrium co nversion is very small as compared to that for the direct esterification re actions. Equilibrium conversions were then predicted using the equilibrium constant for the reaction obtained from Gibbs free energy of formation information f or reactants and products in combination with the UNIFAC activity coefficie nt model. A solvent independent equilibrium conversion was obtained, which was in good agreement with the observed average value for all solvents. Thi s indicates that UNIFAC provides satisfactory estimates of the activity coe fficients but its group contribution structure does not allow the predictio n of the small differences in conversion among the solvents examined. Finally plots of these conversions versus the solvent octanol/water partiti on coefficient or the solubility of water in the solvent, that provide the correct trend in direct esterification reactions, did not achieve the same for transesterification.