Solubilities of the Gaseous and Liquid Solutes and Their Thermodynamics of Solubilization in the Novel Room-Temperature Ionic Liquids at Infinite Dilution by Gas Chromatography

Abstract

The solubilities of C2H4 and CO2 and the interactions of polar and nonpolar solutes with the novel ionic liquids (ILs) 1-butyronitrile-3-methylimidazolium bis(trifluoromethylsulfonyl) imidate (CpMIm[NTf2]), 1-butyronitrile-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imidate (CpMMIm[NTf2]), 1-butyronitrile-3-methylimidazolium dicyanamide (CpMIm[N(CN)2]), 1-butyronitrile-2,3-dimethylimidazolium dicyanamide (CpMMIm[N(CN)2]), 1-butyl-3-methylimidazolium palmitate (BMIm[n-C16H33COO]), and 1-butyl-3-methylimidazolium stearate (BMIm[n-C18H35COO]) were studied by gas chromatography at infinite dilution at T = (303.15, 313.15, 323.15, and 333.15) K. Henry's law constant kH of C2H4 and CO2 gas, infinite dilution activity coefficient γ∞, molar enthalpies of solution ΔsolH∞, and partial molar excess enthalpies of solution ΔHE∞ and of Gibbs energies ΔGE∞ were determined for polar and nonpolar solutes in these novel ILs. Compared with the 1,3-dialkylimidazolium ILs, cyano functional group substitution on the alkyl chain results in a remarkable decrease of the interactions of hydrocarbons. BMIm[n-C16H31OO] and BMIm[n-C18H35OO] demonstrate strong solubilization for both polar and nonpolar solutes. Straight lines of ln Vg versus 1/T and ln γ∞ versus 1/T were obtained for the majority of solutes in the temperature range. BMIm[NTf2] and 1-octyl-3-methylimidazolium tetrafluoroborate (OMIm[BF4]) show much better solubility for thiophene and are better solvents for the separations of thiophene from hydrocarbons.