Solubility and selectivity of CO2 in ether-functionalized imidazolium ionic liquids

• Solubilities of CO2, N2 and O2 in [EOMmim][PF6] and [EOMmim][Tf2N] were determined.
• Introduction of ether group results in increase of CO2/N2 and CO2/O2 selectivity.
• The solution of CO2 in the ionic liquids is an exothermic and orderly process.
• Experimental solubility data have been well correlated by Pitzer model.

Ionic liquids are widely recognized new materials in carbon dioxide capture and separation technology. In this work, we synthesized and characterized two kinds of ether-functionalized imidazolium ionic liquids, 1-methoxyethyl-3-methylimidazolium hexafluoroborate ([EOMmim][PF6]) and 1-methoxyethyl-3-methylimidazolium bis(trifluoro-methylsulfony)imide ([EOMmim][Tf2N]). Solubility values of CO2 in these ionic liquids were determined by isometric weight method at the temperatures from 298.15 K to 343.15 K and the pressure up to 5.185 MPa. Furthermore, solubilities of other flue gases, N2 and O2, in these two ionic liquids were also measured at 303.15 K. It was shown that little influence had been exerted on CO2 solubility by the introduction of ether groups on the cation, but it decreased N2 and O2 solubility, resulting in the remarkable increase of CO2/N2 and CO2/O2 selectivity. In addition, the solubility data were well correlated by Pitzer model, and the standard state solution Gibbs energy, solution enthalpy and solution entropy of CO2 in the two ionic liquids were reported. Regeneration characteristics of the investigated ionic liquids was also studied by vacuum desorption and atmospheric desorption, respectively.