SAFT-VRE:  Phase Behavior of Electrolyte Solutions with the Statistical Associating Fluid Theory for Potentials of Variable Range

Abstract

A modification of the statistical associating fluid theory has recently been developed to model non-conformal fluids with attractive potentials of variable range (SAFT-VR) Mills, S. J.; Burgess, A. N. J. Chem. Phys. 1997, 106, 4168] which gives a very good description of the phase behaviour of water and its mixtures with nonelectrolytes. In the present paper we extend the SAFT-VR approach to deal with strong-electrolyte solutions (SAFT-VRE). The water molecules are modeled as hard spheres with four attractive short-range sites to describe the hydrogen-bonding association. The electrolyte molecules are modeled with two hard spheres of different size which describe the anion and cation respectively. The mean-spherical approximation (MSA) is used for the restricted primitive model (RPM) to account for the long-range Coulombic ion-ion interactions, while the long-range water-water and ionwater attractive interactions are modeled as square-well dispersive interactions treated via a second-order high-temperature expansion in the spirit of the SAFT-VR approach. We have studied nine single-salt aqueous solutions and one mixed-salt system of characteristic strong electrolytes (alkali halides) in the temperature range between 273 and 373 K. Using only one transferable fitted parameter per ion, the experimental vapor pressures and densities are very well described by the SAFT-VRE theory. As a limit of the MSA, the DebyeHückel (DH) expression is used to describe the ion-ion interactions in one of the solutions. Due to the excellent description of the solvent in the SAFT-VR approach, the experimental vapor pressure for an aqueous solution of sodium chloride is also very well described with this simple approach.

Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state

“…A formulation of the MSA allowing for an explicit representation of the solvent was then developed by Wei and Blum [7], among others. In the late 1990s, molecular-based equations of state (EOSs), specifically the statistical associating fluid theory (SAFT) [8,9] and the cubic plus association (CPA) EOS [10], were combined with the classical approaches for charged species [1,5,6] and shown to provide an accurate description of the properties of strong electrolyte solutions [11][12][13], extending the range of applicability to more-concentrated solutions. The increasing accuracy in the description of the properties of the solvent and fidelity of the representation of the solvention interactions has been exploited in subsequent work [14][15][16][17][18][19][20][21][22].…”

“…The SAFT-VRE [13] approach has recently been revised [21] to acknowledge the specific importance of incorporating the Born [25] contribution to the free energy of the system, thus accounting for the charging process of the ionic species in the solvent medium. A robust set of models for strong electrolytes was presented, providing an accurate description of a broad range of properties, including the Gibbs free energy of solvation, with the aid of the Born treatment.…”

An accurate density functional theory for the vapor-liquid interface of associating chain molecules based on the statistical associating fluid theory for potentials of variable range

“…In this paper we follow a standard perturbative DFT approach 13 to develop a free energy functional for inhomogeneous associating chainlike fluids based on the SAFT-VR free energy for chains formed from spherical segments with attractive interactions of variable range. 47,48 We opt for the SAFT-VR description of the reference bulk fluid as it has already been shown to provide an excellent quantitative description of the vapor-liquid and liquid-liquid fluid phase equilibria of a wide variety of systems including alkanes and perfluoroalkanes, 47,49-52 replacement refrigerants, 53 water, 54 hydrogen chloride, 55 hydrogen fluoride, 56,57 carbon dioxide, 58,59 xenon, [60][61][62][63][64] boron trifluoride, 65 aqueous electrolytes, 54,66 and polyethylene polymers. [67][68][69] An adequate treatment of the correlations in the attractive term is crucial for an accurate description of both the bulk fluid phase equilibria and the interfacial properties ͑cf.…”

Enhanced Selectivity of the Separation of CO2from N2during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions

“…In this work, a modification of the model approach of Paricaud (2011) is used in which in contrast to the use of the SAFT-VRE equation of state (Galindo et al, 1999) the electrolyte NRTL model (eNRTL-model) (Chen et al, 1982;Chen and Evans, 1986;Bollas et al, 2008) is incorporated into the model to describe the liquid phase non-idealities in presence of TBAB In Equation (14), T…”