• Kontogeorgis, Georgios M.
• Hemptinne, Jean-Charles De
• Liang, Xiaodong
• Von Solms, Nicolas
• Olsen, Martin Due

Abstract

Many different models have been published with the aim of describingelectrolyte thermodynamics. In this study two successful Equations ofState (EoS) are compared. The models investigated in this work are theelectrolyte Cubic Plus Association (e-CPA) EoS and the electrolyte PolarPertubed Chain Statistical Associating Fluid Theory (e-PPC-SAFT). Themodel terms are not changed from previous works, but they arereparameterized with various models for the relative staticpermittivity. The models are parameterized as similarly and fairly aspossible by identifying key parameters in the models that are intendedto describe the same physics. Several different sets of comparableparameters are investigated to test the models with the inclusion ofvarious physics, and to avoid favoring one model due to the choice ofadjustable parameters. The parameters of the models are optimized withan objective function containing the properties mean ionic activitycoefficients (MIAC), osmotic coefficients and density in a widetemperature range of 273.15–473.15 K and they are tested for theirability to quantitatively describe these properties. The differencebetween e-CPA and e-PPC-SAFT is generally found to be relatively minorand the permittivity model and considered adjustable parameters aregenerally more important for the overall model performance. It is foundthat the permittivity models that only predict part of experimentaldecrease tend to perform the best for the properties MIAC, osmoticcoefficients and density. It is also found that including bothassociation parameters and dispersion/attractive parameters for ions isbetter than neglecting one type of parameters, even when the same numberof adjustable parameters is included. To be able to capture thetemperature trend of MIAC it is found to be important to include anadditional temperature dependency, which in this work is a temperaturedependent interaction parameter for the physical term. It is also foundthat it is important to include sufficiently strong ion association tobe able to obtain the correct qualitative trend for individual ionactivity coefficients.

Topics

• density
• impedance spectroscopy
• dispersion
• inclusion
• theory
• constant potential amperometry