Computer-Aided Design of Ionic Liquids as Absorbent for Gas Separation Exemplified by CO2 Capture Cases

In order to design ionic liquids as absorbents for gas separation, a systematic computer-aided ionic liquid design (CAILD) methodology is applied and demonstrated by three cases of CO2 capture. Mixed-integer nonlinear programming problems are formulated, where a mass-based Absorption-Selectivity-Desorption index (ASDI) integrating the most important thermodynamic properties of ILs (i.e., gas solubility, selectivity, and desorption capacity) is proposed as the objective function and calculated by the COSMO-GC-IL inputted COSMO-SAC model. The physical properties of ionic liquids are implemented as optimization constraints, which are estimated by semiempirical models. The reliability of the thermodynamic method for IL-gas systems is validated first by comparing a large number of experimental and calculated data of Henry’s law constant of different gases in ILs. Then, comparative CAILD studies are performed for CO2 separation from flue gas (CO2/N2) to demonstrate the importance of ASDI for identifying practically attractive ILs. Afterward, the developed method is applied to design IL solvents for the separation of CO2 from syngas (CO2/H2) and sour gas (CO2/H2S). The correspondingly designed ILs for each case ([OAc]− and COOH-functionalized pyridinium for CO2/H2 and CO2/N2; [AlCl4]− and long branched alkyl substituted pyridinium for CO2/H2S) are analyzed from the σ-profile point of view.