Vapor–Liquid Equilibrium of Methyl Acetate + Ethanol with 1-Butyl-3-methylimidazolium Dibutyl Phosphate and 1-Ethyl-3-methylimidazolium Diethyl Phosphate at 101.3 kPa

This study explores the separation of the ethanol–methyl acetate azeotrope using ionic liquids as entrainers. Vapor–liquid equilibrium (VLE) data for the binary system and ternary systems containing 1-butyl-3-methylimidazolium dibutyl phosphate ([BMIM][DBP]) and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]) were measured at 101.3 kPa. Both ionic liquids effectively eliminated azeotropic behavior, with [EMIM][DEP] showing superior performance across the full composition range, attributed to stronger hydrogen bond basicity and reduced unfavorable interactions. Comparison with literature data for [EMIM][OAc], [BMIM][OAc], [EMIM][MeSO3], and DMSO confirmed that ionic liquids generally outperform DMSO. For [BMIM]+-based systems, separation efficiency is as follows: [EMIM][OAc] ≈ [BMIM][OAc] > [BMIM][DBP] > [EMIM][MeSO3] > DMSO. For [EMIM]+-based systems, [EMIM][DEP] provides higher relative volatility in ethanol-rich regions, highlighting the selective capability of the [DEP]− anion. The VLE data were well correlated by the NRTL model, with overall average relative deviations below 5%, and thermodynamic consistency tests confirmed data reliability. These findings indicate that [DEP]−-based ionic liquids are promising entrainers for high-purity methyl acetate production via extractive distillation.