Effect of ion pair formation on phase equilibria of electrolyte containing mixtures

Circular economy involves the re-use of waste material as renewable resource. This requires sometimes high technology processes, because high product purities may be required and the waste is generally a complex mixture. The optimization of such a process therefore necessitates a good understanding of the physico-chemical phenomena occurring during the separation steps. These steps are often based on phase separations between an aqueous stream and either a solvent, a vapour or a solid. Such phase equilibrium modelling is performed using thermodynamic models.
Thermodynamic modelling of aqueous electrolyte systems is particularly challenging because of several difficulties. The first is the complexity of the fluids, possibly containing organic or inorganic molecular species, acids, bases and dissolved metal ions. The presence of ionic species implies taking into account long-range electrostatic interactions between ions in addition to short range ones. The second complexity is related to the physical and/or chemical equilibria occurring within the fluid. These equilibria are very sensitive to the dielectric constant of the medium, that in turn depends on the fluid composition, temperature and pressure. It is therefore needed to couple reactive and physical equilibrium.
IFPEN has been working on this subject for a number of years, and has developed an equation of state that allows predictive phase equilibrium computations for molecular species. It has been found that the phase equilibrium behaviour of a mixture of water, alcohol together with an acid and a base, is extremely sensitive to ion pairing. This phenomenon can be modelled using a chemical equilibrium approach, but this implies (1) that these new species must be characterized and (2) that a combined chemical and physical equilibrium must be computed. The proposed research theme will focus on the modelling of such systems by investigating the effect of the formation of ion pairs. Multi-component mixtures (acid, base, co-solvent and water) will be used as test examples. New experimental data may need to be acquired.

Keywords: Thermodynamics, electrolytes, modeling, equation of state, aqueous phase

• Academic supervisor    Dr. SIMONIN Jean-Pierre, Phenix Laboratory (UMR 8234) https://orcid.org/0000-0002-8246-8154
• Doctoral School    Chimie Physique et Analytique de Paris Centre (ED388)
• IFPEN supervisor    Dr de HEMPTINNE Jean-Charles (Prof. IFP-School), Département Thermodynamique et Modélisation Moléculaire, https://orcid.org/0000-0003-1607-3960 (j-charles.de-hemptinne@ifpen.fr)
• PhD location    IFP Energies nouvelles, Rueil-Malmaison, France and Sorbonne Université (Campus P.M. Curie)
• Duration and start date    3 years, starting in fourth quarter 2021
• Employer    IFP Energies nouvelles, Rueil-Malmaison, France
• Academic requirements    University Master degree Chemical Engineering or Physical Chemistry
• Language requirements    Fluency in French or English, willingness to learn French
• Other requirements    Good knowledge of a programming language, ....