Physical Properties of 1-Butyl-3-methylimidazolium Tetrafluoroborate/ N -Methyl-2-pyrrolidone Mixtures and the Solubility of CO 2 in the System at Elevated Pressures

Densities and viscosities of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]) (1) + N -methyl-2-pyrrolidone (NMP) (2) with w 1 = 0.0000, 0.5000, 0.6999, 0.8981, and 1.0000 at T = (298.15 to 318.15) K were measured and fitted to standard equations. The results show that densities and viscosities of the hybrid solvents decrease with the increase of temperature and mass fraction of NMP. A high-pressure variable-volume view cell technique was used to determine the solubility of CO 2 in pure solvents and mixtures under elevated pressures up to 6 MPa at temperatures from (298.15 to 318.15) K. The results indicate that the solubility of CO 2 in the pure solvents and mixtures increases with the increase of pressure and with the decrease of temperature. The solubility of CO 2 in the mixtures increases with the increase of the mass fraction of NMP, but it is very close to that in pure [bmim][BF 4 ] as the mass fraction of NMP is around 0.1019.