Implementation of CP-PC-SAFT for Predicting Thermodynamic Properties and Gas Solubility in 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids without Fitting Binary Parameters

In this study, simple molecular-weight-based correlations for the CP-PC-SAFT parameters for [C_nmim][NTf₂] ionic liquids have been developed. These correlations allow a nearly precise modeling of densities, including at elevated pressures and at temperatures up to ∼400 K, as well as accurate predictions of the isobaric heat capacities, velocities of sound, and compressibilities. The accuracy of these predictions is superior to that of ePC-SAFT. The available data reveal that solubilities of gases are directly related to their critical temperatures. As the critical temperatures increase, the gas-IL systems become more symmetric, and the solubilities increase. The intrinsic robustness of the CP-PC-SAFT model, along with its agreement with the pure-compound critical temperatures, give this model the capability to accurately predict VLE in [C_nmim][NTf₂] systems of various gases, such as CO, O₂, CH₄, Kr, N₂O, H₂S, SO₂, R134a, R1234ze(E), and CO₂, without prior consideration of any mixture data or adjustment of binary parameters. At the same time, the entirely predictive implementation of the model poses unavoidable compromises in its accuracy. In particular, it overestimates LLE in the system R134a-[C₆mim][NTf₂] and substantially underestimates the extent of phase splits in CO₂ solutions above ∼50 bar. The latter flaw can be corrected by implementing a universal set of binary adjustable parameters. Similar accuracy of modeling can also be achieved with this set of binary parameters and with their zero values in the cases of additional CO₂-[NTf₂^-] IL systems.