Experimental determination of liquid-liquid equilibrium and interaction insights for ternary mixtures 2,2,2-trifluoroethanol + water + pyridinium-based ionic liquids

2,2,2-Trifluoroethanol (TFE) as an important fluorinated alcohol has been widely applied in industry. An aqueous solution containing TFE can be obtained during its production and applications. Because TFE and water can form an azeotrope, it is difficult to recover TFE by conventional distillation. To separate TFE and water by liquid-liquid extraction, three pyridyl ionic liquids (ILs), n-ethylpyridinium bis(trifluoromethyl sulfonyl)imide ([Epy][NTf2]), n-butylpyridinium bis(trifluoromethyl sulfonyl)imide ([Bpy][NTf2]) and n-hexylpyridinium bis(trifluoromethyl sulfonyl)imide ([Hpy][NTf2]) were adopted as the extraction reagents. The liquid-liquid equilibrium data for (ILs + TFE + water) were measured at 101.3 kPa and 298.15 K. The separation ability of the three extractants was assessed by distribution coefficient and selectivity. The experimental data were regressed using the NRTL model. The results showed that IL [Epy][NTf2] had a better ability to recover TFE from its aqueous solution compared to the other two ILs. The correlated results by the NRTL model agreed with the experimental data. Besides, the calculated values of bond length, interaction energy, electrostatic potential and reduced density gradient between the molecules of the ILs and TFE revealed the relation between the IL structures and their extraction performance, which can provide a route for designing a rational IL for separating the mixture of water and TFE.