Carbon dioxide absorption in the ionic liquid 1-ethylpyridinium ethylsulfate and in its mixtures with another ionic liquid

• Carbon dioxide absorption in the ionic liquid [C2py][EtSO4] has been studied.
• The mixture [C2py][EtSO4] + [C2mim][NTf2] leads to synergies in absorption capacity.
• This synergy may be related to positive excess molar volumes for the mixture.
• The physical properties deviations of the mixture were correlated by Redlich–Kister polynomials.
• The absorption process is fully reversible.

Ionic liquids are a potential alternative of interest for the replacement of volatile organic compounds in the technologies currently used for the capture of carbon dioxide from gaseous streams. Most studies carried out to date on the absorption of CO2 by ionic liquids focus on imidazolium ionic liquids. Pyridinium ionic liquids can exhibit a similar CO2 absorption capacity, while optionally possessing some advantages over the imidazolium ones. In this work, we have investigated the ability of the ionic liquid 1-ethylpyridinium ethylsulfate ([C2py][EtSO4]) to absorb CO2 at 298.2 K, up to a pressure of ca. 1.6 MPa. In a strategy for optimisation of the solvent to be used in a CO2 absorption process, mixtures of [C2py][EtSO4] with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]), have been studied. For the mixtures [C2py][EtSO4] + [C2mim][NTf2], the variation of the CO2 solubility and of the thermal and physical properties have been analysed as a function of the composition of the mixture. Higher absorption capacity than that corresponding to the weighted average of the capacity of the pure ionic liquids is observed for these mixtures. This synergistic effect might be in connection, at least in part, with the positive excess molar volumes observed for the mixture.