Isobaric Vapor–Liquid Equilibrium Experiment and Thermodynamic Model Correlation of Methyl Butyrate + <i>n</i> -Propanol with Different Ionic Liquids at 101.3 kPa

The separation of methyl butyrate (MB) and n-propanol (NPA) is of significant industrial importance for resource recovery in transesterification processes, biofuel formulation, and solvent recycling. However, the formation of a minimum-boiling azeotrope at atmospheric pressure poses a challenge for conventional distillation. In this study, 1-ethyl-3-methylimidazolium acetate ([EMIM][OAC]) and 1,3-dimethylimidazolium dimethyl phosphate ([MMIM][DMP]) were selected as entrainers to facilitate the separation process. The vapor–liquid equilibrium (VLE) of the binary system MB (1) + NPA (2), as well as ternary systems MB (1) + NPA (2) + [EMIM][OAC] (3) and MB (1) + NPA (2) + [MMIM][DMP] (3), was investigated at atmospheric pressure. The experimental data were correlated by using the NRTL, Wilson, and UNIQUAC thermodynamic models. Among them, the NRTL model was found to be more suitable for the studied systems. The results show that both ionic liquids effectively eliminate the azeotropic point, with [EMIM][OAC] demonstrating a slightly superior separation performance compared to that of [MMIM][DMP]. The average relative deviations (ARDs) calculated by the NRTL model were 1.87% for the binary system, while those for the ternary systems were 3.16% and 3.65%, respectively, demonstrating that this model can satisfactorily describe the phase equilibrium behavior of the system.