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.