Modeling of Electrolyte Systems using the Non-Primitive Approach

Modeling electrolyte systems is a necessity both for the industry and the academy. Several modern electrolyte models are electrolyte equations of state (e-EoS in brief). Most practical engineering models, either based on e-EoS or activity coefficients, follow the so-called primitive approach, where the solvent (e.g., water) is considered a dielectric continuum characterized by its dielectric constant (relative static permittivity).

Very few models in the literature are based on the non-primitive approach, where the solvent is treated as a (dipolar) molecule interacting directly with ions, despite that such “non-primitive” approaches may be considered theoretically to be more accurate as all intermolecular interactions can be accounted for. Developing non-primitive approaches is, in principle, desirable from an academic point of view, even further if the aim is to model systems where mixed solvents are used, a situation with more scarce data and where primitive approaches start to depend more heavily on parametric models for the dielectric constant, a quantity naturally calculated by the non-primitive model. Although this might be a strength, it is also a difficulty.


Some non-primitive models rely on the solution of non-linear numerical models, which is not desirable for an engineering approach, where analytical models are preferred. Therefore, the fundamental understanding of interactions, research on the limitations of already established models, and the derivation of newer models from long-established, successful theories (e. g., the Poisson-Boltzmann equation) is of paramount necessity.


The purpose of this project is to develop a non-primitive electrolyte equation of state based on an association theory (CPA or PC-SAFT) as a basis for the “physical” interactions, coupled with suitable dipolar and electrostatic terms. The accurate representation of the solvents and interactions with ions is of crucial importance, as well as an enhanced study of dielectric effects. The project will follow a pragmatic approach where first, the limitations of some primitive models are verified. Further, the next target is to uncover the capabilities and limitations of the non-primitive approach over a wide range of conditions, properties, and systems and compare them with the results obtained in other projects using the primitive approach.

Main supervisor:

Prof., Georgios Kontogeorgis, Department of Chemical and Biochemical Engineering


Co- supervisor:

Assoc. Prof.,  Xiaodong Liang, Department of Chemical and Biochemical Engineering


Gabriel Moraes Silva
PhD student
DTU Chemical Engineering


Xiaodong Liang
Associate Professor
DTU Chemical Engineering
+45 45 25 28 77


Georgios Kontogeorgis
DTU Chemical Engineering
+45 45 25 28 59