Thermodynamic Modeling of Ionic Liquids with PC-SAFT: Quantifying the Impact of Association and Dipolar Terms

The thermophysical properties of ionic liquids (ILs) are essential for CO₂ capture, yet their optimal modeling approach remains unclear due to complex intermolecular interactions. This work investigates the thermodynamic behavior of imidazolium-based ILs using the PC-SAFT equation in which ILs are modeled as electroneutral ion pairs with electrostatic interactions approximated by association or dipolar terms. Density, heat capacity, vapor pressure, and phase equilibria of IL-CO₂ and IL-water/ethanol are calculated to evaluate model performance. Three parametrization strategies based on different experimental data sets and four modeling schemes with 2 (011), 4 (022), and 10 (055) binding sites, as well as a polar nonassociating model, are examined. The results show that good performance requires simultaneously incorporating density, isobaric heat capacity, and vapor pressure in parameter fitting, and that increasing associating sites does not necessarily improve the accuracy. Analysis of association and dipolar contributions identified the 011 scheme as the most appropriate.