Thermodynamics and Activity Coefficients at Infinite Dilution for Organic Compounds in the Ionic Liquid 1-Butyl-2,3-dimethylimidazolium Bis(trifluoromethylsulfonyl)imide

Abstract

The activity coefficients at infinite dilution (γ^∞_i) of 30 organic solutes (including alkanes, aromatics, acetonitrile, acetone, tetrahydrofuran, ethyl acetate, and chloromethanes) in the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([BMMIM][NTf₂]) were measured over the temperature range 313.15–353.15 K using gas–liquid chromatography. The temperature dependence of the IL density was determined at p = 101.33 kPa, and the gas–liquid partition coefficients (K_L) were calculated accordingly. From the temperature dependence of γ^∞_i, the partial molar excess enthalpies at infinite dilution (H̅^E,∞_i) were derived, and the entropies (T_refS̅^E,∞_i) and partial molar excess Gibbs free energies (G̅^E,∞_i) at the reference temperature T_ref = 298.15 K were obtained. The solubility parameter (δ) of [BMMIM][NTf₂] was determined using regular solution theory combined with the Flory combinatorial term, and solute–IL interactions were quantitatively assessed using a linear free energy relationship model. In addition, the selectivity (S^∞_ij) for n-hexane/solute systems at 313.15 K was calculated and compared with values reported in the literature for other [NTf₂]-based ILs.