Liquid–liquid equilibria studies on ammonium and phosphonium based ionic liquid–aromatic–aliphatic component at T = 298.15 K and p = 1 bar: Correlations and a-priori predictions

The commercial ionic liquids (IL), namely tris (2-hydroxyethyl) methylammonium methylsulfate and tributyl methyl phosphonium methyl sulphate were used for the separation of three systems namely benzene–hexane, toluene–heptane and thiophene–cyclohexene at ambient conditions. Liquid–liquid equilibrium (LLE) data were measured for the ternary systems namely, [TEMA][MeSO4] (1)–benzene (2)–hexane (3); [TEMA][MeSO4] (1)–toluene (2)–heptane (3) and [P4441][MeSO4] (1)–thiophene (2)–cyclohexene (3) at T = 298.15 K and p = 1 bar. The selectivity and distribution coefficient were further calculated from the tie line data. It was observed that the IL required for the extraction will be less and the cross contamination is nearly zero in both the phases. A comparison was made with the available LLE data of imidazolium and pyridinium cations where the distribution ratios for the present work were the lowest irrespective of cation. Similarly, the experimental selectivity values for benzene–hexane separation were higher than the reported selectivities of different cations. Further the experimental tie line data for ternary systems were correlated with NRTL and UNIQUAC models. For all three ternary systems, the RMSD value ranges from 0.22% to 0.88% and 0.31% to 1.05% for NRTL and UNIQUAC model, respectively. Finally, the quantum chemical based COSMO-RS predictions gave RMSD values of 2.9%, 5.78% and 10.3% for IL–benzene–hexane, IL–thiophene–cyclohexene and IL–toluene–heptane systems, respectively.