Modeling of Strong Electrolytes with ePPC-SAFT up to High Temperatures

Abstract

An extension of the PPC-SAFT equation of state to treat strong electrolyte aqueous solutions is presented. It is capable of describing the behavior of such systems up to 473 K with a good precision and without requiring temperature-dependent model parameters. Long-range Coulombic interactions are taken into account using the mean spherical approximation (MSA) for a primitive model of the electrolyte solution, and the effect of solvation is described using short-range ion–water interactions mediated through association sites. Pairing between anions and cations is also treated through site–site interactions. A Born term is added to describe the change of dielectric constant resulting from solvation. A single ion-specific, temperature-independent model parameters are used, for 20 alkali-halide aqueous solutions. The Pauling ionic diameters are used for all terms (hard sphere, MSA, and Born). The dispersion energy of the ions is considered negligible. In the resulting ePPC-SAFT model, only the water–ion association energy is considered as an adjustable parameter. The results show coherent energy density behavior with respect to ionic size. The approach allows the calculation of the mean ionic activity coefficient, density, or vapor pressure of the aqueous solutions over a wide range of temperatures and molalities (298–573 K and 0–6 m). Moreover, salting out of carbon dioxide and methane in saline water can also be predicted accurately. A discussion of the changes in ion hydration at different salinity is also presented taking advantage of the model proposed that explicitly includes ion–water site–site interactions.

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

“…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].…”

“…A simple treatment to account for the introduction of a charged species in a dielectric medium was provided by Born [25]. The Born contribution has now been incorporated within cubic and CPA EOSs [26,27], and, more recently, within the ePPC-SAFT [20] and SAFT-VRE [21] approaches. A non-primitive treatment that incorporates a polar solvent within a SAFT formalism has also been presented [17,[28][29][30].…”

Prediction of thermodynamic properties of aqueous electrolyte solutions using equation of state

“…Among presented EOSs in the field of electrolyte solutions, just a few ones have focused on calculation of standard state and second order derivative properties. In most cases, prediction of phase equilibrium conditions was the primary goal of previous works . The statistical associating fluid theory (SAFT) EOSs have been also developed to electrolyte solutions.…”

“…The ion‐specific parameters and ion‐specific coefficients were fitted to experimental activity coefficients and solution densities data up to 473.15 K. Among all available SAFT models, the PC‐SAFT EOS has been widely applied to multitude of the systems including electrolyte solutions. The electrolyte PC‐SAFT versions have been developed by the combination of PC‐SAFT and Debye Hückel (DH) or MSA long range term . Recently, the electrolyte polar PC‐SAFT (ePPC‐SAFT) has been utilized to treat aqueous solution of single salts up to high temperature without requiring temperature‐dependent model parameters .…”

Modeling of CO2 solubility in single and mixed electrolyte solutions using statistical associating fluid theory

“…Diamantonis and Economou (2012) used both the PC-SAFT and the truncated PC-Polar SAFT (tPC-PSAFT) equations of state to study the vapor-liquid equilibria properties of CO 2 -H 2 O mixture. Rozmus et al (2013) developed the ePPC-SAFT EoS for 20 alkali halides salt solutions and studied the activity coefficient, density, vapor pressure and gas (CO 2 and CH 4 ) solubility of salt solutions.…”