Extremely Low Vapor‐Pressure Data as Access to PC‐SAFT Parameter Estimation for Ionic Liquids and Modeling of Precursor Solubility in Ionic Liquids

Abstract

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed‐Chain Statistical Associating Fluid Theory (PC‐SAFT), vastly depends on the quality of the pure‐component parameters. The pure‐component parameters for low‐volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture‐independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure‐IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor‐pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor‐pressure data of a series of 1‐ethyl‐3‐methyl‐imidazolium‐based [C2mim]‐ILs with various IL‐anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC‐SAFT parameter estimation. The so‐determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid‐density data only for the molecular PC‐SAFT and the ion‐based electrolyte PC‐SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure‐component vapor‐pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion‐specific parametrization in the long term.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion

“…For the presently investigated ionic liquids, it varies from 136 ± 18 kJ/mol for m-C 6 H 4 (CH 2 ImMe)][NTf 2 ] 2 to 147 ± 12 and 147 ± 13 kJ/mol for [DABCO10][NTf 2 ] and [p-C 6 H 4 (CH 2 ImBu)][NTf 2 ] 2 , respectively, and finally to 180 ± 17 kJ/mol for [C 6 Py][NTf 2 ]. These values are consistent with those previously reported for the other ionic liquids [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

“…ILs containing the B(CN) 4 anion have p v comparable to that of NTf 2 samples [ 31 ]. Bulow et al reported a comparison of the vapor pressure of ILs containing the same 1-ethyl-3-methyl-imidazolium cation and a series of anions, such as PF 6 , B(CN) 4 , (C 2 H 5 O) 2 PO 2 , NTf 2 , SCN, CF 3 CO 2 , CF 3 SO 3 , BF 4 , C(CN) 3 , (C 2 F 5 ) 3 PF 3 , 4-CH 3 -Ph-SO 3 [ 32 ]. Finally, in the last couple of years some models were also proposed to derive the vapor pressure and vaporization enthalpy values from the knowledge of the structure of ILs [ 33 , 34 , 35 ].…”

Predicting Vapor–Liquid Equilibria for Sour-Gas Absorption in Aqueous Mixtures of Chemical and Physical Solvents or Ionic Liquids with ePC-SAFT

“…One which accounts for the ionic character and utilizes ion-specific parameters, and one that, similar to conventional solvents, is based on a molecular parameterization. In a recent publication, the molecular and ion-specific approaches have been compared with emphasis on the prediction of sour-gas absorption into the pure IL . Although utilizing the extremely low vapor pressure of the IL in the parameter estimation in the molecular approach, the ion-specific parameter set was superior at higher pressures.…”

“…In a recent publication, the molecular and ion-specific approaches have been compared with emphasis on the prediction of sour-gas absorption into the pure IL. 44 Although utilizing the extremely low vapor pressure of the IL in the parameter estimation in the molecular approach, the ion-specific parameter set was superior at higher pressures. Therefore, an ion-specific approach is also chosen here to model the IL.…”

Molecular Thermodynamic Modeling of Hybrid Ionic Liquids for Biogas Upgrading

“…47 The remaining molecular parameters (i.e., m, σ, ε) were obtained from fitting to available liquid density data, which is acceptable considering the low vapor pressure of ILs, and the reduced degree of freedom during parametrization from fixing the association parameters a priori. 56,57 The diluents were also modeled taking into account their governing intermolecular interactions. The dipolar diluents acetone and NMP were modeled with explicit consideration of their dipolar nature.…”