Extension of eSAFT-VR Mie EoS to non-aqueous electrolyte solutions: a sensitivity analysis
One of the most challenging tasks for electrolyte models is their extension to non-aqueous solvents, either pure or mixed with water. At the same time, such a task is necessary to facilitate the incorporation of electrolyte models in routine engineering calculations for industrial purposes.
Currently most electrolyte models target aqueous solutions. One such model is the electrolyte Statistical Associating Fluid Theory with the Mie potential of Variable Range (eSAFT-VR Mie) equation of state (EoS). It is a relatively new electrolyte EoS combining the SAFT-VR Mie EoS [1] with a Debye-Hückel [2] and a Born term [3] that utilizes ionic parameters and has been developed for aqueous electrolyte solutions using a relative permittivity that is independent of the salt concentration [4].
An extensive analysis of the effect of the relative permittivity and characteristic diameter on the Born and Debye-Hückel term in the mean ionic activity coefficient of both aqueous and non-aqueous solutions has been performed. It has been found that the influence of these two modelling components in both terms is quite important.
Both terms show a great sensitivity to the characteristic diameters especially if low values are used. This is more pronounced as the relative permittivity of the solvent decreases, and as the molality of the salt increases. Furthermore, the Born term is more sensitive to both these parameters compared to the Debye-Hückel term.
Due to these observations, the relative permittivity of the model was switched to a composition dependent one and various relations have been tested. The model has been reparametrized based on Mean Ionic Activity Coefficient and density data of single solvent systems, both aqueous and non-aqueous.