Activity Coefficients of Organic Solutes at Infinite Dilution in Ionic Liquids. 1. 1-Hexyl-3-Methylimidazolium Hexafluorophosphate and 1-Octyl-3-Methylimidazolium Hexafluorophosphate and Their Application to Alkane/Aromatic and Aromatic/Aromatic Hydrocarbon Separation

Activity coefficients at infinite dilution, γi,3, for organic solutes (alkanes, alkenes, alkyl benzenes, alcohols, chloromethanes, acetonitrile, ethyl acetate, dioxane, tetrahydrofuran, and acetone) in 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF6] and 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM][PF6] have been determined using gas–liquid chromatography at temperatures from 303.15 to 363.15 K with the ionic liquids as the stationary phase. The partial molar excess enthalpies at infinite dilution of the ionic liquids were calculated for the solutes from the temperature dependence of the experimental activity coefficients at infinite dilution. The solubility parameters of ionic liquids were also determined by the regular solution theory. The selectivities of various ionic liquids for the alkane/aromatic hydrocarbon and aromatic/aromatic were summarized from literature and calculated from γi,3.