Solubilities of the Gaseous and Liquid Solutes in the Ionic Liquids at Infinite Dilution by Gas Chromatography

Research of ionic liquids (ILs) is one of the most rapidly growing fields in the past years, much of which has the ultimate aim of large scale industrial application [1]. Due to their unique properties such as negligible vapor pressure at room temperature, stable liquid phase over a wide temperature range and stability at high temperatures, ionic liquids created interest to use them in the separations of gas mixtures and extraction processes. So, it is very important to know the solubility of the gases and liquid solutes in the IL phase. Gas chromatography has been considered to be a particularly convenient technique for the determination of the solubility of gases in nonvolatile liquids based on Henry’s law constants for a certain range of temperatures. Activity coefficients at infinite dilution of a solute i (γi∞) can be used to quantify the volatility of the solute as well as to provide information on the intermolecular energy between solvent and solute [2,3]. Values of γi∞ are also important for evaluating the potential uses of ILs in liquid-liquid extraction and extractive distillation. In our work, The activity coefficients at infinite dilution, γi∞, for both polar and non-polar liquid solutes in the ionic liquid 1-hydroxyethyl-3-methylimidazolium hexafluorophosphate ([HOEMIM][PF6]) and 1-hydroxyethyl-3-methylimidazolium perfluorobutanesulfonate ([HOEMIM][CF3(CF2)3SO3]) have been determined by gas-liquid chromatography at different temperatures (from 303 K to 353 K). And the solubilities of O2 and CO2 in the ionic liquids: [HOEMIM][PF6], [HOEMIM][CF3(CF2)3SO3], 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [EMIM][FAP], 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB], 1-butyl-3-methylimidazolium bis(oxalato)borate [BMIM][BOB], 1-hexyl-3-methyl-imidazolium bis(oxalato)borate [HMIM][BOB], N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([CnPY][NTf2], n = 2, 4, 5) and [N1123][RNHC3SO3] (R= H, Bu) were studied by gas chromatography at T = 303K, 313K and 323K. The partial molar excess enthalpies at infinite dilution HiE,∞ of the liquid solutes in the ionic liquids [HOEMIM][PF6] and [HOEMIM][CF3(CF2)3SO3] were also calculated from the temperature dependence of the γi∞ values. The selectivities for the hexane/benzene and cyclohexane/benzene separation problems were calculated from experimental infinite dilution activity coefficient values and compared to the other ionic liquids, taken from the recent literature