PHASE-EQUILIBRIA AND MULTIPLE AZEOTROPY OF THE ACETIC-ACID ISOBUTYL-ACETATE SYSTEM

Azeotropy is a manifestation of vapor-liquid equilibrium and therefore is a function of the strength of intermolecular forces in both the vapor and liquid phases. The three non-electrolyte binary systems which have been shown to display multiple azeotropy do so because of intermolecular forces in the liquid phase which produce multiple extrema in the molar excess Gibbs free energy (g(E)) of the liquid mixtures. Multiple azeotropy should also be observed in binary systems which strongly associate in the vapor phase and exhibit a single maximum in the g(E) curve. Calculations of vapor-liquid equilibrium for the acetic acid-isobutyl acetate system at 117-degrees-C predict a system with a double azeotrope and a g(E) curve with a single maximum. Distillation of several mixtures at atmospheric pressure confirms the existence of two azeotropes for the acetic acid-isobutyl acetate system.