Prediction of conversion at equilibrium for lipase esterification in two-phase systems
Résumé
In this work, a calculation procedure to predict reactant conversion at equilibrium in the case of lipase esterification in two-phase water-organic solvent system has been developed. The method is based on conventional thermodynamics using the UNIFAC predictive model to calculate the value of activity coefficients of compounds. Our approach was validated by comparison with experimental results in the case of the enzymatic esterification of oleic acid by 1-butanol in a two-phase water/n-heptanesystem. In this configuration only 1-butanol partitions significantly between the two phases. With this procedure, it was shown that oleic acid conversion at equilibrium was influenced by the initial mole fraction ratio of reactants, the volume ratio of the organic phase to aqueous phase, as well as the temperature and the nature of the organic solvent. The value of the equilibrium constant of the reaction, which is required for the calculations, was estimated from experiments at 298.15 K and found equal to 78 ± 3. The results emphasize the prominent role of the thermodynamic activity of 1-butanol in the reactional mixture. In the case of different investigated solvents, it was shown that the thermodynamic activity of this compound has to be maximized to favor conversion of oleic acid at equilibrium.
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