Effect of the anion in phosphonium-based ionic liquids to recovery efficiently 2-propanol from an azeotropic mixture with water

The use of ionic liquids (ILs) as solvent in the separation of azeotropic mixtures have an environmental and economy benefit. The amount of different ILs is large, due to the ILs can be composed by a wide variety of cations and anions. Therefore, to understand the effect of the IL's anion characteristics in the separation of azeotropic mixtures has a great interest. In this work, the anions bis(2,4,4-trimethylpentyl)phosphinate (Phosph-), chloride (Cl-) and bromide (Br- ) in trihexyl(tetradecyl)phosphonium-based ILs (TDTHP+) have been studied in the separation of the azeotropic mixture water + 2-propanol. The liquid-liquid equilibria data for the three ternary mixtures, water + 2-propanol + [TDTHP][Phosph], [TDTHP][Cl] or [TDTHP][Br], were measured at different work temperatures and atmospheric pressure. The capability as solvents of the different ILs to separate and recover 2-propanol from water was studied and compared through the distribution coefficient and selectivity, taking into account their molecular structure. In addition, two different activity coefficients models, non-random two-liquid (NRTL) and universal quasichemical (UNIQUAC), were studied to know which one allows a closer approach to the reality according to the IL's anion present in the mixture. Thus, the preferable activity co-efficients model for each case was established, verified its consistency and, with it, the thermodynamic pa-rameters for the three ternary mixtures at different temperatures were calculated. Finally, the capability to extract 2-propanol from water of the three ILs were compared with the capability of other ILs from the literature that look suitable for this aim.