Thermodynamic model for CO₂ absorption in imidazolium-based ionic liquids using cubic plus association equation of state

In order to achieve efficient capture of carbon dioxide (CO₂) by ionic liquids (ILs), IL with good performance of high CO₂ absorption capacity and low energy consumption need to be explored. Density, heat capacity, CO₂ solubility and absorption enthalpy are key properties for the performance evaluation of IL solvents. In this work, the cubic plus association equation of state (CPA EoS) was applied for the integrated modelling of above properties in CO₂ physical and chemical absorption by 22 imidazolium-based ILs. The results show that the density, heat capacity of pure ILs and CO₂ solubility in a broad range of temperature (281–403 K) and pressure (0.1–23 MPa) were accurately calculated with deviations less than 1.27%, 0.54% and 3.73%, respectively. CO₂ chemisorption was satisfactorily described by CPA EoS with an error of 0.12% considering interactions for the reactive sites between CO₂ and amino groups in IL. Furthermore, the prediction capabilities of CPA EoS were verified with results showing good quantitative agreement with density and solubility data in literature. The effects of structures of ILs studied in this work on the CO₂ solubility and absorption enthalpy were analyzed. [NH₂emim][BF₄], [Omim][Tf₂N] and [Emim][eFAP] were found to have better performance of CO₂ absorption. This model provides a feasible approach to determine synthetically the key properties of CO₂-IL systems for the selection of proper ILs, design and simulation of the CO₂ capture process.