Separation of binary mixtures based on gamma infinity data using [OMMIM][BF4] ionic liquid and modelling of thermodynamic functions

Abstract

The activity coefficients at infinite dilution (γi∞), gas-liquid partition coefficients (KL) of organic solutes (n-alkanes, alkenes, alkyl benzenes, acetonitrile, acetone, tetrahydrofuran, ethyl acetate, 1,4-dioxane, chloromethanes, alcohols and cycloalkene) in the ionic liquid 1-octyl-2,3-dimethylimidazolium tetrafluoroborate ([OMMIM][BF4]) have been measured using the gas-liquid chromatographic method (GLC) at five temperatures (313.15 K–353.15 K). The density of [OMMIM][BF4], as a function of temperature, was determined in atmosphere pressure p = 101.3 kPa. The values of the partial molar excess enthalpies at infinite dilution (H-iE,∞) were derived from the temperature dependence of the lnγi∞ values at a reference temperatureTref = 298.15 K. The entropies (TrefS-iE,∞) and Gibbs free energies (G-iE,∞) of organic solutes in [OMMIM][BF4] at a reference temperatureTref = 298.15 K were calculated from the γi∞ values. The Hildebrand’s solubility parameters of [OMMIM][BF4] were determined by the regular solution theory (RST) combined with Flory ‘‘combinatorial’’ equation. The interaction between the IL and the individual solutes can be disclosed and the nature of force for IL was explored by the linear free energy relationship (LFER) analysis. Selectivity (Sij∞) and capacity (kj∞) at infinite dilution at 323.15 K have been determined for n-hexane (i)/benzene (j), cyclohexane (i)/benzene (j). The results were analysed in comparison to literature data for alkylimidazolium ionic liquids (ILs) with [BF4]-.