Chemical reaction equilibrium for the solvent-free ethyl oleate synthesis

BRIOZZO, MARÍA; FORESTI, LAURA; TRUBIANO, GUSTAVO; FERREIRA, MARÍA LUJÁN; BORIO, DANIEL; BUCALÁ, VERÓNICA

Zacatecas, Méjico

Congreso; Chemical Reaction Engineering X; 2005

Engineering Conferences International

  Enzyme-catalyzed reactions are superior to conventional chemical methods owing to the mild reaction conditions, high catalytic efficiency and the inherent selectivity of natural catalysts which leads to much purer products. In this work, immobilized lipase from Candida antarctica was used for direct esterification of oleic acid and ethanol. The reaction was performed in a solvent free system, according to the amount of water in the reaction medium (either initially added or produced by the chemical reaction) one or two liquid phases were detected. Several experiments showed that the highest conversion of the fatty acid takes place when two liquid phases coexist. Therefore, the optimal operating conditions indicate the need of studying the liquid-liquid equilibrium together with the chemical equilibrium.            The reaction equilibrium constant for the formation of ethyloleate by a lipase-catalyzed reaction should be just dependent on temperature, if the standard states are properly selected. However, as it was found by many authors the biphasic equilibrium constant calculated as function of total equilibrium concentrations strongly depends on the initial reactants molar ratio. Although the biphasic equilibrium constant allows adjusting kinetic parameters that well fit experimental data, its use is far from the classic approach to handle reversible chemical reactions. In this work a novel approach is proposed to calculate the equilibrium concentrations. The biphasic nature of the reaction medium is taken into account, allowing the reactants and products to be transported through both phases. Since the liquid-liquid equilibrium calculations by UNIFAC indicate that the oleic acid has a very poor affinity for the aqueous phase, the reaction equilibrium constant is defined just in the oily phase. The reactants and products mols in the organic phase depend on the reaction conversion and on the mols transferred to/from the aqueous phase. Using an equilibrium constant defined by the classic thermodynamic (i.e., just one value for a given reaction temperature), the proposed combination of chemical reaction and liquid-liquid equilibrium allows to well predicting the equilibrium concentrations found experimentally.