Analysis of solvent-free ethyl oleate enzymatic synthesis at equilibrium conditions

V. BUCALÁ; M.L. FORESTI; G.C. TRUBIANO; M.L. FERREIRA; M. BRIOZZO; S. BOTTINI

ENZYME AND MICROBIAL TECHNOLOGY

Elsevier

Lugar: Shannon, Ireland; Año: 2006 vol. 38 p. 914 - 920

0141-0229

This work reports experimental equilibrium data for the esterification of oleic acid and ethanol, using an immobilized Candida antarctica B lipase as catalyst. Reactions were performed in a solvent free system, containing a mixture of substrates and different amounts of distilled water. According to the initial amount of water and the extent of the reaction, one or two liquid phases are present. Therefore, equilibrium conditions imply simultaneous liquid-liquid and chemical reaction equilibria. Experimentally, it is found that the equilibrium constant for the synthesis of ethyl oleate varies not only with temperature, but also with the initial ratio of substrates and with the amount of water added to the reaction medium. In general, the problem of these partially miscible reactive systems has been handled in the literature by the definition of a biphasic apparent equilibrium constant that depends on partition coefficients and volume ratio of the two liquid phases. Although this method can be a valuable tool to explore equilibrium shifts in biphasic systems, its application is limited to ideal systems with constant partition coefficients. The aim of this work is to consider the biphasic nature of the reactive mixture through a computational procedure that takes into account simultaneously liquid-liquid and reaction equilibria. This approach enabled the determination of a classical temperature-dependent thermodynamic equilibrium constant, which accurately fitted experimental equilibrium conversions in all the range of concentrations studied.