Entrainers selection and vapour-liquid equilibrium measurements for separating azeotropic mixtures (ethanol + n-hexane/cyclohexane) by extractive distillation

Abstract

For synthesis of ethyl propionate with ethanol and propionic acid as raw materials, n-hexane and cyclohexane are usually used as water-carrying agents. However, ethanol can form the minimum boiling azeotropic mixtures with n-hexane and cyclohexane. For separating the binary azeotropic mixtures (ethanol + n-hexane) and (ethanol + cyclohexane) by extractive distillation, in this work, the suitable entrainers were explored by selectivity and relative volatility, and the influence of the selected entrainers on the azeotropic system phase behaviour was analyzed. Based on the selection results, butyl propanoate and butyl butanoate were adopted as the entainers. The vapour-liquid equilibrium (VLE) data for the four binary mixtures (n-hexane + butyl propanoate), (n-hexane + butyl butanoate), (cyclohexane + butyl propanoate) and (cyclohexane + butyl butanoate) were investigated. Furthermore, the VLE data was validated using the van Ness and Herington tests. Also, the experimental data was fitted by the Wilson, UNIQUAC and NRTL models. The binary interaction parameters were optimized for the separation process design and simulation.