Permittivity Modeling in Electrolyte PC-SAFT

Accurately modeling the thermodynamic properties of electrolyte systems is key to designing decarbonized energy and chemical processes. For this purpose, a promising model class are electrolyte equations of state. These electrolyte equations of state require the relative static permittivity as an important input. The permittivity in solution deviates from the solvent permittivity, particularly at high ion concentrations. This deviation necessitates an approach to account for this dielectric decrement. This work presents a model for the dielectric decrement in the electrolyte equation of state ePC-SAFT. For this purpose, we extend ePC-SAFT by integrating our previous model for the relative static permittivity, based on perturbation theory. To account for the dielectric decrement, we obtain ion-specific permittivity parameters by adjusting to experimental mean ionic activity coefficients of water–salt mixtures. With a relative deviation of 4.1% averaged over all studied mixtures, the proposed approach accurately models mean ionic activity coefficients for lithium salts, sodium salts, potassium salts, and hydrogen halides. Moreover, the approach outperforms the common linear mixing approach based on the mole fraction. In this work, ePC-SAFT is implemented in the open-source software framework for equations of state FeO_s and can be used as an easy-to-install Python package.