Association‐based activity coefficient model for electrolyte solutions

Abstract

This work presents an association-based activity coefficient model that explicitly considers the solution nonideality due to associations among ions and solvent species. Built upon the electrolyte nonrandom two-liquid (eNRTL) model, the model greatly improves the accuracy of eNRTL model for strongly associating electrolyte solutions due to presence of ionic species with high surface charge density. The model successfully correlates mean ionic activity coefficients of 46 aqueous singlesalt systems from 10 cations and 5 anions at 298.15 K up to their solubility limits.With the ion-specific association parameters identified, the model accurately predicts activity and osmotic coefficients for aqueous mixed-salt systems at 298.15 K. The temperature dependence of the model results has also been examined at 273-373 K.With superior accuracy over a wide range of concentration and temperature, the model represents a major advancement over eNRTL model and has a great potential to be a next-generation model for electrolyte solutions.

Estimating CO2 Solubility in Aqueous Na+–K+–Mg2+–Ca2+–Cl––SO42– Solutions with Electrolyte NRTL–PC-SAFT Model

“…It implies that, for example, the CO 2 solubility in KCl solution would be higher than that in NaCl solution at the same ionic concentration, because Na + given its higher charge density (smaller radius) compared to K + would bind more strongly with water and permit less free water molecules to dissolve CO 2 molecules. This is corroborated by the recent work of Lin et al 93 in which they developed an association eNRTL model to capture system nonideality caused by associations between ions and solvent species. They studied the association strengths of 10 cations and 5 anions, and they reported that the association strength of an ion has a direct correlation to ionic radius and charge density.…”

Wertheim’s Association Theory for Phase Equilibrium Modeling in Chemical Engineering Practice

“…Molality-based mean ionic activity coefficients of acids and lithium salts in aqueous solution at 298.15 K. Points, experimental data (Hamer and Wu and Vega and Vera); solid lines, association electrolyte model of Lin et al; dotted line, eNRTL model of Song and Chen (2009) . Figure from ref reproduced with permission. Copyright 2022 American Institute of Chemical Engineers.…”

Electrolyte Thermodynamic Models in Aspen Process Simulators and Their Applications

“…Experimental data and the eNRTL model results for the solubilities of various salt forms in the aqueous Na + + Mg 2+ + SO 4 2– system …”

“…Without explicitly addressing such hydration and ion-pairing behavior, eNRTL is incapable of accurately representing the thermodynamic properties of these electrolyte systems with high charge density ions. This deficiency in eNRTL model formulation may have been addressed with the recent advent of the association eNRTL model . Incorporating an association term based on the Wertheim association theory − as formulated by Fu et al for activity coefficient models, this association eNRTL model is capable of accurately describing thermodynamic properties of electrolyte systems involving high charge density ions.…”

“…Incorporating an association term based on the Wertheim association theory − as formulated by Fu et al for activity coefficient models, this association eNRTL model is capable of accurately describing thermodynamic properties of electrolyte systems involving high charge density ions. A distinct feature of the association model is the adoption of species-specific association site numbers and dimensionless association strengths with the water self-association strength as the reference. ,, Given the association sites and the association strengths identified for true species, the association model is capable of reliably predicting association behavior of electrolyte solutions such as ion hydration and ion-pairing without the additional burden to quantify binary association parameters . As many mixed-solvent electrolyte systems involve solvents that self-associate and/or cross-associate, i.e., water and alcohols, the association model should also facilitate more accurate thermodynamic representations of mixed-solvent and nonaqueous electrolyte systems.…”