Vapor–Liquid Equilibria and Conceptual Design of Extractive Distillation for Separating Ethanol and Ethyl Propionate

Ethyl propionate is usually produced from esterification of propionic acid and ethanol in the industry. However, the purification of ethyl propionate remains a challenge because the unreacted ethanol forms an azeotrope with ethyl propionate. In this work, extractive distillation was adopted, and isobutyl acetate was chosen as the entrainer to separate the mixture of ethanol and ethyl propionate. The vapor–liquid equilibria for binary systems of ethanol/ethyl propionate + isobutyl acetate were measured at atmospheric pressure, and the experiment data were correlated with the nonrandom two-liquid model, universal quasi-chemical model, and Wilson model. Then, the thermodynamic analyses, using residue curves, isovolatility curves, and extractive composition profile of the ethanol + ethyl propionate + isobutyl acetate ternary system, were performed to confirm the feasibility of separating the azeotrope with isobutyl acetate as the entrainer. The extractive distillation process was designed and optimized by the sequential iterative procedure based on the total annual cost. Results of the extractive distillation simulation also verified the reliability of thermodynamic analysis.