Solubility of Isobutane in Ionic Liquids [BMIm][PF6], [BMIm][BF4], and [BMIm][Tf2N]

The solubility of isobutane in three ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([BMIm][Tf2N]) at temperatures ranging from 288.2 K to 313.2 K and pressures up to near atmospheric pressure were determined by a saturation technique. The solubility values were correlated using the PengRobinson equation of state with van der Waals 2-parameter mixing rules. In general, the model and the experimental data were in good agreement. Henrys constants were calculated on the basis of the solubility data at different temperatures and fitted to the BensonKrause (BK) equation well. The results showed that the solubilities of isobutane in these three ionic liquids increased with increasing pressure and decreased with increasing temperature and were in the sequence: [BMIm][Tf2N] > [BMIm][PF6] > [BMIm][BF4]. The solubility parameters (d) of these three ILs were calculated and were used to qualitatively explain the difference of the solubility of isobutane in different ILs. Partial molar thermodynamic functions of solvation such as standard Gibbs free energy, enthalpy, and entropy were calculated from the solubility results.