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.