The phase behavior of the carbon dioxide+1-methylimidazole binary system has been investigated in a high-pressure variable-volume view cell using an analytical method. Phase equilibrium data for the system carbon dioxide+1-methylimidazole was measured at 293.15, 309.75 and 323.15 K. The pressure under investigation was between 2.83 and 14.16MPa. There coexisted three phases (LLV) of the binary system, which were found in a temperature range of 297.85-313.95 K. The densities of the binary mixture at phase transition points were also measured. The experimental data were correlated well by the Peng-Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the binary systemmight be classified to Type-IV or Type-Vaccording to the classification of six principal types of binary phase diagrams.

High-pressure phase behavior of CO2/acetone/1-n-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6]) system was studied by the analytical method at 313.15K and at pressures up to 15MPa. The ternary system forms two phases at most conditions. At pressures from 4.9 to 8.1MPa, a three-phase region appeared in the system. Pressure influenced the slopes of the tie lines in the two-phase region greatly. On the basis of phase equilibrium data, the distribution coefficients of the components between different phases were calculated. CO2 distribution coefficient decreased with increasing pressure while acetone distribution coefficient increased with pressure.

Many room temperature ionic liquids (ILs) are nonvolatile solvents which have huge potential applications in various chemical processes. However, the synthesis of ILs usually uses different kinds of volatile organic solvents in the reaction and subsequent separation process. In this work, supercritical (sc) CO2, an environmentally benign solvent, has been utilized as the medium to synthesize ILs, 1-butyl-3-methylimidazolium bromide ([bmim]Br) and 1,3-dimethylimidazolium trifluoromethanesulfonate ([Me2Im]TfO). The results show that ILs can be synthesized in scCO2 with 100% yield and the excess reactants added can be extracted in situ by scCO2 without any cross-contamination. The whole process is green and very effective.