Screening of ionic liquids to capture CO₂ by COSMO-RS and experiments

A screening method is proposed for the molecular design of ionic liquids (ILs) to capture carbon dioxide (CO₂), which can reduce efficiently the necessary experimental efforts. The COSMO-RS method is implemented to predict the Henry's law constants of CO₂ in 408 ILs with various combinations of cations and anions. It is found by the screening that the ILs with the anion tris(pentafluoroethyl)trifluorophosphate ([FEP]) show improved capability to capture CO₂, compared with other ILs reported in literature. Then, three [FEP]-based ILs are chosen to perform the solubility measurements by the intelligent gravimetric analyzer (IGA 003, Hiden Analytical), with cations of 1-hexyl-3-methylimidazolium ([hmim]), 1-butyl-1-methylpyrrolidinium ([bmpyrr]), and S-ethyl-N,N,N',N'-tetramethylthiouronium ([ETT]) at 283.2, 298.2, and 323.2 K, up to the pressure of 1.8 MPa. The experimental data show that the solubility of CO₂ in [hmim][FEP] is about 15% higher than that in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf₂N]), which is in fair agreement with the screening results, indicating the method proposed in this work is reliable. © 2008 American Institute of Chemical Engineers AIChE J, 2008