Absorption of CO2 by ionic liquid/polyethylene glycol mixture and the thermodynamic parameters

Absorption/desorption of CO2 by ionic liquid (IL) where both cation and anion are from renewable materials, (2-hydroxyethyl)-trimethyl-ammonium (S)-2-pyrrolidine-carboxylic acid salt [Choline][Pro], and [Choline][Pro]/polyethylene glycol 200 (PEG200) mixture, were studied in the 308.15 K to 353.15 K range at ambient pressure. It was demonstrated that both the neat ionic liquid (IL) and the IL/PEG200 mixture could capture CO2 effectively and could be easily regenerated under vacuum or by bubbling nitrogen through the solution, and the molar ratio of CO2 to the IL could exceed 0.5 slightly, which is the theoretical maximum for absorption of CO2 chemically, indicating that both chemical and physical absorption existed. Addition of PEG200 in the IL could enhance the rates of absorption and desorption of CO2 significantly. The solubility of CO2 in [Choline][Pro]/PEG200 at different pressures from 0 to 1.1 bar was also measured, and the enthalpy and entropy of solution of CO2 were calculated from the solubility data. At all the conditions, the enthalpy and entropy of solution were large negative values, indicating that the absorption process is exothermic.