Determination of activity coefficients at infinite dilution of organic solutes in the ionic liquid, trihexyl(tetradecyl)-phosphonium tris(pentafluoroethyl) trifluorophosphate, by gas–liquid chromatography

Activity coefficients at infinite dilution, γ i ∞ , have been determined for polar and non-polar organic solutes in the high molecular weight ionic liquid, trihexyl(tetradecyl)-phosphonium tris(pentafluoroethyl) trifluorophosphate at T = 308.15, 318.15 and 328.15 K. The experimental activity coefficient data presented are the first to be reported for the phosphonium-based ionic liquid. For the measurement of γ i ∞ , the technique of steady-state gas–liquid chromatography has been employed. The organic solutes that were investigated were normal alkanes (pentane, hexane, heptane and octane), alkenes (1-hexene, 1-heptene and 1-octene), alkynes (1-hexyne, 1-heptyne and 1-octyne), cycloalkanes (cyclopentane, cyclohexane and cycloheptane), alcohols (methanol, ethanol and propanol) and benzene. The partial molar excess enthalpies at infinite dilution, H i E , ∞ , were also determined for the solutes from the temperature dependency of the γ i ∞ values. i ∞ data obtained for trihexyl(tetradecyl)-phosphonium tris(pentafluoroethyl) trifluorophosphate in this investigation have been compared to that obtained for other ionic liquids available in literature and the potential for the use of ionic liquids as solvents in industrial solvent-enhanced separation processes such as extractive distillation has been discussed.