Separation of Cyclohexane and Isopropanol Azeotropic System by Liquid–Liquid Extraction Using Imidazolium-Based Ionic Liquids with Different Anions and Mechanism Analysis

Cyclohexane (CYH) and isopropyl alcohol (IPA) are both excellent solvents and raw materials for industrial production. Mixtures of IPA and CYH are generated during the production of rapeseed oil. Since the two form an azeotrope at atmospheric pressure, they cannot be separated by simple distillation. Liquid–liquid extraction is an energy-saving and environmentally friendly azeotrope separation method. Ionic liquids (ILs) are ideal extractants to replace conventional extractants due to their designability and negligible vapor pressure. Three ILs, 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM]­[TFA]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM]­[DEP]), and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM]­[DCA]), were selected as the extractants to separate the mixture of IPA and CYH. The liquid–liquid equilibrium (LLE) data of the IPA + CYH + ILs systems were determined at 303.15 K and atmospheric pressure. The partition coefficient (β) and selectivity coefficient (S) were calculated to evaluate the extraction effect of the ILs. Othmer–Tobias, Bachman, and Hand equations were used to check the consistency of the experimental data. The experimental LLE data were correlated by the NRTL model in Aspen Plus V11 software. Finally, the separation mechanism of the three ILs was investigated by interaction energy analysis, σ-profile analysis, and RDG analysis.