Isobaric Vapor–Liquid Equilibrium and Intermolecular Interactions in Benzene + Ethanol + Ionic Liquid Ternary Systems

The separation of the benzene + ethanol azeotrope is of great significance for environmental protection and resource conservation. 650 ionic liquids composed of 26 cations and 25 anions were screened using the COnductor-like Screening MOdel for Realistic Solvents thermX (COSMOthermX) software (version C2.1, release 01.11) with BP_TZVPD_FINE_C30_1601 parametrization as the entrainer for the separation of benzene + ethanol azeotrope. Tetraoctylammonium acetate ([N8,8,8,8][OAC]), tetrabutylphosphonium acetate ([P4,4,4,4][OAC]), and tributylethylphosphonium acetate ([P4,4,4,2][OAc]) were chosen. To compare the separation capabilities of the three ionic liquids, the isobaric vapor–liquid equilibrium (VLE) data of the benzene + ethanol mixture containing ionic liquids were measured under atmospheric pressure (101.3 kPa). The experimental data were correlated using the nonrandom two-liquid (NRTL) model. The order of the separation capacity of the ionic liquids is [P4,4,4,2][OAc] > [P4,4,4,4][OAc] > [N8,8,8,8][OAC] on the basis of the NRTL equation. The mechanisms of separation were analyzed by means of Sigma profiles (σ profiles), interaction energies (ΔE), electrostatic potentials (ESP), and interaction region indicators (IRI). Fourier-transform infrared (FT-IR) spectroscopy was used to confirm the presence of molecular interactions between ionic liquids and ethanol.