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 FeOs and can be used as an easy-to-install Python
package.