Measurement of infinite dilution activity coefficients of alcohols, ketones, and aromatic hydrocarbons in 4-methyl-N-butylpyridinium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate by gas-liquid chromatography

The infinite dilution activity coefficients of C₁ to C ₅ alcohols, acetone, 2-butanone, acetylacetone, toluene, and xylene isomers in 4-methyl-N-butylpyridinium tetrafluoroborate ([bmpy][BF₄]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) were measured by gas - liquid chromatography (GC) from (306.6 to 334.8) K and atmospheric pressure. In these measurements with GC, [bmpy][BF4] or [bmim][PF₆] was used as a stationary phase. The infinite dilution activity coefficients in this work were not affected by the gas flow rate. It was found that the values of 1-propanol, 1-butanol, and 1-pentanol for the infinite dilution activity coefficients in [bmim] [PF₆] were larger than those for their isomers. For xylene isomers, the activity coefficients of m-xylene are the largest. The effects of the cation and anion species composing ionic liquid on the activity coefficients were also investigated. The activity coefficients for alcohols, ketones, and aromatic hydrocarbons in the ionic liquids were affected by the anion species more strongly than the cation species of the ionic liquid. The partial molar excess enthalpies at infinite dilution for the solutes in ionic liquids were obtained from the temperature dependence of the infinite dilution activity coefficients. Moreover, the partial molar excess entropies were also calculated from the enthalpies. The excess enthalpy and entropy contributions to the activity coefficients in ionic liquid were investigated.