Thermodynamics and selectivity of separation based on activity coefficients at infinite dilution of various solutes in ionic liquid [HMMIM][BF4

Abstract

Abstract The activity coefficients at infinite dilution ( γ i ∞ ), gas–liquid partition coefficients ( K L ) of organic solutes (n-alkanes, alkenes, alkyl benzenes, acetonitrile, acetone, tetrahydrofuran, ethyl acetate, chloromethanes, alcohols and 1,4-dioxane) in the ionic liquid 1-Hexyl-2,3-dimethylimidazolium tetrafluoroborate ([HMMIM][BF4]) have been measured using the gas–liquid chromatographic method (GLC) at five temperatures: 313.15 K, 323.15 K, 333.15 K, 343.15 K, 353.15 K. The density of [HMMIM][BF4], as a function of temperature, was determined in atmosphere. The values of the partial molar excess enthalpies at infinite dilution ( H ‾ i E , ∞ ) were derived from the temperature dependence of the In γ i ∞ values. The entropies ( T ref S ‾ i E , ∞ ) and Gibbs energies ( G ‾ i E , ∞ ) of organic solutes in [HMMIM][BF4] at a reference temperature T r ef = 298.15 K were calculated from the γ i ∞ values. The Hildebrand’s solubility parameters of the IL [HMMIM][BF4] were determined by the regular solution theory (RST) combined with Flory ‘‘combinatorial’’ equation. Selectivity ( S ij ∞ ) and capacity ( k j ∞ ) at infinite dilution at 323.15 K have been determined for n-hexane ( i )/benzene (j), cyclohexane ( i )/benzene (j). The results were analyzed in comparison to literature data for alkylimidazolium ionic liquids (ILs) with [ BF 4 ] - . The interaction between the IL and the individual solutes can be disclosed by the linear free energy relationship (LFER) analysis.