Solubility of carbon dioxide in ammonium-based ionic liquids: Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide

Abstract

Solubility results of carbon dioxide (CO2) in two ammonium-based ionic liquids, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N4,1,1,1][Tf2N]) and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N1,8,8,8][Tf2N]), are presented at pressures up to approximately 45 MPa and temperatures ranging from 303.15 K to 343.15 K. The solubility was determined by measuring bubble point pressures of mixtures of CO2 and ionic liquid using a high-pressure equilibrium apparatus equipped with a variable-volume view cell. Sharp increase of equilibrium pressure was observed at high CO2 compositions. The CO2 solubility in ionic liquids increased with the increase of the total length of alkyl chains attached to the ammonium cation of the ionic liquids. The experimental data for the CO2+ionic liquid systems were correlated using the Peng-Robinson equation of state.