Solubility of CO2 in Binary Mixtures of Room-Temperature Ionic Liquids at High Pressures

The solubility data of carbon dioxide (CO 2 ) in a series of ionic liquids (ILs): 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM] + [BF 4 ] − ), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] + [BF 4 ] − ), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIM] + [Tf 2 N] − ), and their binary mixtures (i.e., [EMIM] + [BF 4 ] − + [OMIM] + [Tf 2 N] − and [BMIM] + [BF 4 ] − + [OMIM] + [Tf 2 N] − ) at temperatures (313.2 and 333.2) K and pressures up to 6 MPa were measured by a high-pressure view-cell technique. The mixed ILs tested were (0, 20, 50, 80, and 100) wt % [EMIM] + [BF 4 ] − (or [BMIM] + [BF 4 ] − ) in [OMIM] + [Tf 2 N] − . The solubility data of CO 2 in pure ILs were correlated with the Peng–Robinson equation of state (PR EOS), whereas the solubility data of CO 2 in mixed ILs can be well predicted based on the mole fraction average of [EMIM] + [BF 4 ] − (or [BMIM] + [BF 4 ] − ) and [OMIM] + [Tf 2 N] − over the solubility of CO 2 in pure ILs. It was found that the solubility of CO 2 in pure or mixed ILs increases with increasing pressure at all temperatures but decreases with increasing temperature. The Henry’s constants follow the order of [BMIM] + [BF 4 ] − + [OMIM] + [Tf 2 N] − > [EMIM] + [BF 4 ] − + [OMIM] + [Tf 2 N] − at the same content of [OMIM] + [Tf 2 N] − . The use of mixed ILs provides the opportunity to tune the solubility and selectivity for capturing CO 2 at high pressures. It is the first work for us to present the solubility data of CO 2 in binary mixtures of ILs at high pressures for physical absorption.