How to detect possible pitfalls in ePC-SAFT modelling: Extension to ionic liquids

Modeling Interfacial Properties with Spot-DGT-ePC-SAFT for Binary Mixtures Including Ionic Liquid-Based Systems

“…For example, in ePC-SAFT, the ionic term was used to describe the long-range electrostatic force between the cation and anion with a significant contribution, even at a very low density, leading to that the equilibrium vapor phase of ILs cannot be found at the packing fraction higher than 10 −12 and the mole fraction of IL greater than 10 −10 . 46,47 This is reasonable considering the negligible vapor pressure of ILs, and numerically, for a pure IL, this is not a serious problem in solving DGT. 40,41 While for ILbased mixtures, if the equilibrium composition cannot be solved, a serious numerical problem will be generated when calculating the density profile of vapor−liquid interphase because the local chemical potential does not equal the bulk chemical potential when approaching to the vapor phase.…”

“…Principally, DGT (i.e., full DGT) can be extended to the mixtures for common substances. − ,− However, for the IL-based systems, the extension can be a challenge due to the characterization of ILs with negligible vapor pressures. For example, in ePC-SAFT, the ionic term was used to describe the long-range electrostatic force between the cation and anion with a significant contribution, even at a very low density, leading to that the equilibrium vapor phase of ILs cannot be found at the packing fraction higher than 10 –12 and the mole fraction of IL greater than 10 –10 . , This is reasonable considering the negligible vapor pressure of ILs, and numerically, for a pure IL, this is not a serious problem in solving DGT. , While for IL-based mixtures, if the equilibrium composition cannot be solved, a serious numerical problem will be generated when calculating the density profile of vapor–liquid interphase because the local chemical potential does not equal the bulk chemical potential when approaching to the vapor phase. Besides, when modeling IL–CO 2 with the full DGT-ePC-SAFT model combined with the geometric-mean mixing rule, sharp changes in the density profile of CO 2 could lead to a large density gradient, breaking the assumption of low density gradient compared with the reciprocal of the intermolecular distance when developing DGT. , All of these indicated that combining DGT with ePC-SAFT is unsuitable for modeling the interfacial properties of IL-based mixtures.…”

How to Detect Possible Pitfalls in ePC-SAFT Modeling. 2. Extension to Binary Mixtures of 96 Ionic Liquids with CO2, H2S, CO, O2, CH4, N2, and H2

“…The pitfall occurrence of all studied pure ILs 36−43 has been investigated previously. 44 The results show that the pitfall only occurs in one single IL ([C 8 mpy][BF 4 ]) among all the 96 ILs in the temperature and pressure range of interest (>273.15 K and 1−200 bar for CO 2 separation).…”

“…have been described previously, 35,44 while for systems with associating term (e.g., H 2 S), the terms ( )…”

Comparison of CP-PC-SAFT and SAFT-VR-Mie in Predicting Phase Equilibria of Binary Systems Comprising Gases and 1-Alkyl-3-methylimidazolium Ionic Liquids

“…Several SAFT approaches, among them the initial version of PC-SAFT [45], exhibit certain undesired numerical pitfalls, such as predicting negative heat capacities [46] at high pressures and the additional unrealistic pure compound phase splits [47,48]. The latter phenomenon may seriously affect their accuracies in predicting properties of heavy compounds such as ILs and their mixtures [49][50][51]. In addition, SAFT models typically cannot represent critical pressures, temperatures, and saturated liquid densities in a simultaneously accurate manner [52,53].…”