Molecular Mechanism and Liquid–Liquid Equilibrium of Ionic Liquids for the Extraction Process of the Cyclohexane-Tert-Butanol Azeotropic System

Abstract

Cyclohexane (CYH) is commonly used for tert-butanol (TBA) dehydration, forming a difficult to separate at room temperature minimum-boiling azeotrope with TBA, which cannot be separated by simple distillation. Liquid–liquid extraction is particularly notable for its energy efficiency and environmental friendliness. Ionic liquids (ILs) can replace conventional extractants due to their low volatility and low toxicity. In this study, three trifluoroacetate-based ILs ([C₂MIM][TFA], [C₄MIM][TFA], [C₆MIM][TFA]) were identified through COSMO-RS screening and experimentally evaluated for CYH-TBA separation. Liquid–liquid equilibrium data for the CYH-TBA-ILs system were measured at 303.15 K and atmospheric pressure. Extraction performance was evaluated through computational distribution coefficients and selectivity. Experimental data were well-correlated using the NRTL model, with parameters validated through the “GMcal_TieLinesLL” tool analysis. Comprehensive quantum chemical analyses, including interaction energies, electrostatic potential mapping, IGMH, and QTAIM topological assessments, revealed the molecular-level separation mechanism. Results demonstrate significantly stronger IL-TBA interactions compared to IL-CYH, primarily mediated through hydrogen bonding rather than van der Waals forces. This work contributes significant understanding to the IL-mediated separation of azeotropic mixtures, revealing the fundamental principles governing this process.