Solubilities of CO2, H2, N2 and O2 in ionic liquid 1-n-butyl-3-methylimidazolium heptafluorobutyrate

Ionic liquids (ILs) are promising in the capture and separation of CO2. In this work, IL 1-n-butyl-3-methylimidazolium heptafluorobutyrate, [C4mim][CF3CF2CF2COO], has been synthesized and characterized by 1H, 13C and 19F NMR spectra. Solubilities of CO2, H2, N2 and O2 in this IL have been determined at the temperature range from (303.15 to 333.15) K and the pressure up to 8.9 MPa. From these data, the Henry’s constant, the standard state solution Gibbs energy, standard state solution enthalpy and standard state solution entropy of these gases in [C4mim][CF3CF2CF2COO] were derived and analyzed from molecular interactions. It was shown that the solubility of CO2 is obviously higher than that in [C4mim][CF3COO] and [C4mim][CF3SO3] reported in literature, which makes this IL an attractive solvent for gas separation processes. Furthermore, these solubility data were well correlated by Pitzer model.

► Ionic liquid [C4mim][CF3CF2CF2COO] was synthesized and characterized.
► Solubilities of CO2, H2, N2 and O2 in the IL were determined from 303.15 to 333.15 K and up to 8.9 MPa.
► CO2 solubility is 6–10 times that of the other three gases in this IL.
► The dissolution of CO2, O2, N2 and H2 in [C4mim][CF3CF2CF2COO] was controlled by entropy term.
► These solubility data were correlated with high accuracy by the Pitzer model.