The solubility data of carbon dioxide (CO2) in a series
of ionic liquids (ILs): 1-ethyl-3-methylimidazolium tetrafluoroborate
([EMIM]+[BF4]−), 1-butyl-3-methylimidazolium
tetrafluoroborate ([BMIM]+[BF4]−), 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([OMIM]+[Tf2N]−), and their
binary mixtures (i.e., [EMIM]+[BF4]− + [OMIM]+[Tf2N]− and [BMIM]+[BF4]− + [OMIM]+[Tf2N]−) 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]+[BF4]− (or [BMIM]+[BF4]−) in [OMIM]+[Tf2N]−. The solubility data of CO2 in pure ILs were correlated with the Peng–Robinson
equation of state (PR EOS), whereas the solubility data of CO2 in mixed ILs can be well predicted based on the mole fraction
average of [EMIM]+[BF4]− (or
[BMIM]+[BF4]−) and [OMIM]+[Tf2N]− over the solubility of
CO2 in pure ILs. It was found that the solubility of CO2 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]+[BF4]− + [OMIM]+[Tf2N]− > [EMIM]+[BF4]− + [OMIM]+[Tf2N]− at the same content of
[OMIM]+[Tf2N]−. The use of
mixed ILs provides the opportunity to tune the solubility and selectivity
for capturing CO2 at high pressures. It is the first work
for us to present the solubility data of CO2 in binary
mixtures of ILs at high pressures for physical absorption.
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