Liquid–Liquid Extraction of Benzene Using Low Transition Temperature Mixtures: COSMO-SAC Predictions and Experiments

To screen suitable low transition temperature mixtures (LTTMs) as solvents for the extraction process of a benzene and cyclohexane mixture, the extraction performance of the LTTMs (25 hydrogen-bond donors (HBDs) and 13 hydrogen-bond acceptors (HBAs)) was assessed based on COSMO-SAC predictions of infinite dilution activity coefficients of benzene and cyclohexane in different LTTMs. The effects of the molar ratio of HBD to HBA on extraction efficiency were also observed in the meantime. It is found that the LTTM sulfolane-tetrabutylammonium bromide 5:1 (ST 5:1), which has excellent extraction performance, is the most promising solvent. To explain the difference of extraction efficiency of various LTTMs, σ-profiles were adopted to study the molecular interactions between LTTMs and benzene or cyclohexane. The analysis for geometry, interaction energy, independent gradient model (IGM) and atoms in molecules (AIM) was performed to explain interaction mechanisms between benzene/cyclohexane and HBD/HBA. Moreover, the liquid–liquid equilibrium (LLE) data of benzene–cyclohexane-ST 5:1 were experimentally measured, and the consistency tests were conducted using the Othmer–Tobias equation. In addition, the LLE data were employed to fit the binary interaction parameters of the NRTL activity coefficient model. In conclusion, the LTTM ST 5:1 shows good extraction performance, which provides a reference for the extractive separation of the benzene–cyclohexane mixture in industry.