Combining soft-SAFT and COSMO-RS modeling tools to assess the CO2–SO2 separation using phosphonium-based ionic liquids

The development of efficient CO2 separation techniques from post-combustion flue gases is a key area of research to green-house gas control. However, CO2 capture is typically affected by the presence of other acid impurities, such as traces of SO2. In that sense, this work assesses CO2 separation from a CO2/SO2 mixture with a set of phosphonium-based ILs. Two different modeling tools, soft-SAFT and COSMO-RS, have been used cooperatively to study the CO2 gas separation on ILs. From one side, the soft-SAFT equation of state, which has been employed for the first time in this family of ILs, has been used to effectively reproduce the absorption properties of these promising CO2 absorbents in a wide range of pressures/temperatures. Additionally, COSMO-RS, employed to evaluate the charge distribution so as to develop representative models for soft-SAFT, has been capable of reproducing the low-pressure absorption region in a purely predictive way. In both cases, the enthalpy and entropy of dissolution and the selectivity of the mixtures are predicted. Also, several ternary diagrams have been built to analyze different acid gas compositions. [Display omitted] •Phosphonium-based ILs density, surface tension and derivative properties are characterized using theoretical modeling.•COSMO-RS is helpful in building representative molecular models for ILs to use in soft-SAFT EoS.•Soft-SAFT EoS captures the overall shape of gas absorption isotherms in these ILs with a single binary interaction parameter.•COSMO-RS reproduces adequately the low-pressure gas absorption properties of ILs without fitting any parameters.•The highest absorption of SO2 suggests that it is more efficient to separate CO2 via SO2 capture.