Estimation of extraction properties of new imidazolide anion based ionic liquids on the basis of activity coefficient at infinite dilution measurements

Abstract

New ionic liquids, based on the 4,5-dicyano-2-(trifluoromethyl)imidazolide [TDI] anion proposed as a new electrolyte in Li-ion batteries, 1-butyl-3-methylimidazolium 4,5-dicyano-2-(trifluoromethyl)imidazolide, [BMIM][TDI] and the 1-butyl-3-methylpyridinium 4,5-dicyano-2-(trifluoromethyl)imidazolide, [BM3PY][TDI], were synthesized and purified. The basic thermal properties of the pure [BMIM][TDI] and [BM3PY][TDI] ionic liquids i.e. glass-transition temperatures, and the heat capacity change at glass transition have been measured using a differential scanning microcalorimetry (DSC). The densities, viscosities and surface tensions of [BMIM][TDI] and [BM3PY][TDI] in temperature range from 283.15K to 363.15K were measured. The density and viscosity correlation for these systems was tested by an empirical second-order polynomial and by the Vogel–Fucher–Tammann equation. The surface tensions of pure ionic liquid were measured at atmospheric pressure at five temperatures (298.15, 308.15, 318.15, 328.15 and 338.15)K. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values. The critical temperature, parachor and speed of sound for pure ionic liquids were described and compared with other ILs with the same cation. The activity coefficients at infinite dilution, γ13∞ were determined at the temperature range from 318.15K to 368.15K by gas–liquid chromatography in the ionic liquid [BMIM][TDI] and [BM3PY][TDI] for 67 solutes: alkanes, cycloalkanes, alkenes, alkynes, aromatic hydrocarbons, alcohols, water, thiophene, ethers, ketones and pyridine. The interaction of these 66 organic compounds and water with the ILs were described with the partial excess molar Gibbs energies, ΔG1E,∞, enthalpies ΔH1E,∞, and entropies TrefΔS1E,∞ at infinite dilution, calculated from the experimental γ13∞ values, obtained over the temperature range. The gas–liquid partition coefficients, KL were calculated for all solutes. The selectivities for different separation problems were calculated from γ13∞ and compared to literature values for N-methyl-2-pyrrolidinone (NMP), sulfolane, and other 1-butyl-3-methylimidazolium, or 1-butyl-3-methylpyridinium-based ionic liquids. Obtained values were compared to the literature values for the other ionic liquids, NMP and sulfolane. The selectivities in proposed extraction processes were not attractive in comparison with previously measured ILs, with exception of water/1-butanol system. However, in contrast with the former measured ILs, [BMIM][TDI] and [BM3PY][TDI] posses higher capacity for benzene and thiophene. The gas–liquid partition coefficients, KL were calculated for all solutes and the Abraham solvation parameter model was discussed.