CO2 absorption with ionic liquids at elevated temperatures

Abstract

CO2 capture with ionic liquids (ILs) has attracted many attentions, and most works focused on absorption ability at ambient temperatures, while seldom research was concerned at elevated temperatures. This not only limits the CO2 absorption application at elevated temperature, but also the determination of the operation condition of the CO2 desorption generally occurring at higher temperature. This work mainly reported CO2 solubilities in ILs at elevated temperatures and related properties were also provided. 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnMIm][Tf2N]) ILs were selected as physical absorbents for CO2 capture in this work due to their relative higher CO2 absorption capacities and good thermal stabilities. The long-term stability tests showed that [CnMIm][Tf2N] is thermally stable at 393.15 K for long time. CO2 solubilities in [CnMIm][Tf2N] were systematically determined at temperatures from 353.15 K to 393.15 K. It demonstrated that CO2 solubility obviously increases with the increase of pressure while slightly decreases with increase of temperature. As the length of alkyl chain on the cation increases, CO2 solubility in ILs increases. Additionally, the thermodynamic properties including the Gibbs free energy, enthalpy, and entropy of CO2 were also calculated.