Ionic liquid-assisted extractive distillation for separating the isoamyl formate–isoamyl alcohol azeotrope: experimental VLE, molecular insight and process simulation

The separation of isoamyl formate (IAF) and isoamyl alcohol (IA) is challenging due to the formation of an industrial azeotrope, making extractive distillation a promising alternative. In this work, 1-hexyl-2,3-dimethylimidazolium acetate ([HMMIM][OAc]) was selected as an entrainer via COSMO-RS screening. Isobaric vapor–liquid equilibrium (VLE) data for the IAF + IA binary system and the IAF + IA + [HMMIM][OAc] ternary system were measured at 101.3 kPa. The data passed the thermodynamic consistency test and were well correlated with the non-random two-liquid (NRTL) model. The minimum IL mole fraction required to break the azeotrope is 0.030. σ-Profile analysis and MD simulations revealed that [HMMIM][OAc] significantly enhances the relative volatility of IAF to IA, with improved efficiency at higher ionic liquid loadings. An extractive distillation process employing the ionic liquid for separating the IAF + IA azeotrope was simulated in Aspen Plus, and its performance was economically evaluated using the total annual cost (TAC). The optimized process achieved a minimum TAC of about 907 k$/year. These findings demonstrate that [HMMIM][OAc] is an efficient entrainer for IAF/IA separation and provide both experimental and theoretical foundations for designing processes for C5 alcohol–ester azeotropic systems.