Experimental Study on Liquid–Liquid Equilibrium for the Separation of Cyclohexane and Isobutyl Alcohol Using Imidazolium Ionic Liquids and Its Mechanism Analysis

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To address the limitations of conventional methods in separating the challenging cyclohexane (CYH) and isobutyl alcohol (IBA) binary azeotrope at atmospheric pressure, a highly efficient and green separation process was developed. Three ionic liquids ([EMIM][TFA], [BMIM][TFA], and [HMIM][TFA]) were identified as promising extractants through COSMO-RS screening. The liquid–liquid extraction (LLE) data for the respective ternary systems (CYH + IBA + IL) were experimentally measured at 298.15 and 303.15 K, with their reliability validated via the Othmer-Tobias and Hand equations. Subsequent data regression via the NRTL model accurately correlated the phase equilibria, with parameters verified using “Gmcal_TieLinesLL”. Thermodynamic evaluations demonstrated the exceptional extraction capacity of the ILs toward IBA. To elucidate the underlying microscopic mechanisms, comprehensive analyses combining σ-profiles, interaction energies, electrostatic potential (ESP), independent gradient model based on Hirshfeld partition (IGMH), quantum theory of atoms in molecules (QTAIM) topological analysis, and Fourier transform infrared spectroscopy (FTIR) were conducted. These theoretical investigations unequivocally revealed a preferential IL-IBA affinity predominantly driven by hydrogen bonding. Furthermore, Aspen Plus V14 process simulations confirmed the technical feasibility of the extraction scheme. Ultimately, this comprehensive study clarifies the fundamental mechanisms of IL-mediated azeotrope disruption, providing vital insights for the design of highly efficient separation systems.