Temperature dependence and short-range electrolytic interactions within the e-PPC-SAFT framework

Understanding and modelling electrolyte systems is of interest both in an industrial context and from a fundamental point of view. Their importance is related to their key role played in traditional and emerging industries, and to the ubiquitous presence of saline solutions in biological, chemical, and geological environments. The development of electrolyte equations of state has advanced greatly in recent years, with the aim to describe the properties of electrolyte systems using a limited number of parameters, in a way that allows describing accurately the equilibrium properties of these solutions. Here, we explore the temperature and salt concentration dependence of various PPC-SAFT-based models, using simple alkali halide salts (primarily NaCl). The dispersion and association free-energy terms characteristic of SAFT-like equations are compared for the description of the ion-solvent non-Coulombic interactions. Several formulations of the dielectric constant are also investigated. In all models the MSA term is used to account for the electrostatic interactions between the ions and the Born term is added to model the ion-solvent electrostatic interactions. The molecular model parameters are determined by comparison to experimental enthalpy of solution, activity coefficient, osmotic coefficient and apparent molar volume data. We find that equivalent results can be obtained with or without incorporating a explicit salt concentration dependence in the treatment of the dielectric constant; the most accurate results (smallest average absolute relative deviation) when comparing to experimental the data chosen are found in the case that salt concentration is not explicitly considered. For each approach, the most sensitive parameters are identified, which makes it possible to reduce the number of adjustable parameters without significantly affecting the overall quality of the model. We find that both the approach incorporating a dispersion term and that using an association term in the treatment of short-range interactions yield similar results. Unfortunately, none of the models can describe accurately and with physically meaningful parameters the correct low-temperature trend of the mean ionic activity coefficient observed experimentally. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Understanding and modelling electrolyte systems is important in both industrial and fundamental research. The development of electrolyte equations of state has advanced greatly, aiming to accurately describe the equilibrium properties of solutions. This study explores the effects of temperature and salt concentration on various models and compares different parameters. The results show that equivalent results can be obtained regardless of whether the salt concentration dependence is considered in the treatment of the dielectric constant.