High-pressure solubility of carbon dioxide in imidazolium-based ionic liquids with anions [PF6] and [BF4]

The solubility of carbon dioxide in three ionic liquids (ILs) under supercritical fluid condition was measured at pressures up to 32 MPa and at temperatures of 313.15, 323.15, and 333.15 K in a high-pressure view cell. The imidazolium-derivative ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), and 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]) were employed in this research. The effects of pressure, temperature, nature of anion and cation as well as the water content on the solubility of CO2 in the ILs were investigated experimentally. The solubility of CO2 in the IL was higher for the ILs with longer cationic alkyl group and for the ILs with lower anion polarity. The lower the water content or the lower the temperature as well as the higher the pressure, the higher was the solubility of CO2.