Contributions to ionic activity coefficients: A review and comparison of equations of state with molecular simulations

Abstract

Advanced Equations of State for electrolyte solutions (e-EoS) consist of many contributions stemming from different intermolecular forces, e.g. repulsion, dispersion, hydrogen bonding, as well as ionic interactions between ions, ion solvation and possibly others. It is difficult to establish a priori which is the correct balance of the various contributions, and different parameter estimation strategies may result in similar performance of models having entirely different trends with respect to the contribution of the various terms. The first part of this work is a literature review on the balance of forces exhibited by existing electrolyte models, both activity coefficient models and e-EoS. In the second part of this work, the activity coefficients and the contributions of the various terms calculated by molecular simulation (MS) based on the recent studies by Saravi and Panagiotopoulos are analyzed and compared to their e-EoS counterparts at 25 °C and 1 bar. We have considered three e-EoS from literature, namely the eSAFT-VR Mie, ePPC-SAFT and e-CPA. MS studies have been presented in literature both using the so-called implicit and explicit simulations, but only the latter are considered here where water is treated as a molecule, as these are in closer agreement to experimental data. Although correspondence between MS contributions and e-EoS terms is not fully established, some conclusions related to the performance of e-EoS are obtained.