Peiming Wang

A speciation-based model for mixed-solvent electrolyte systems

A comprehensive model has been developed for the calculation of speciation, phase equilibria, enthalpies, heat capacities and densities in mixed-solvent electrolyte systems. The model incorporates chemical equilibria to account for chemical speciation in multiphase, multicomponent systems. For this purpose, the model combines standard-state thermochemical properties of solution species with an expression for the excess Gibbs energy. The excess Gibbs energy model incorporates a long-range electrostatic interaction term expressed by a Pitzer–Debye–Huckel equation, a short-range interaction term expressed by the UNIQUAC model and a middle-range, second virial coefficient-type term for the remaining ionic interactions. The standard-state properties are calculated by using the Helgeson– Kirkham–Flowers equation of state for species at infinite dilution in water and by constraining the model to reproduce the Gibbs energy of transfer between various solvents. The model is capable of accurately reproducing various types of experimental data for systems including aqueous electrolyte solutions ranging from infinite dilution to fused salts, electrolytes in organic or mixed, water + organic, solvents up to the solubility limit and acid–water mixtures in the full concentration range.

Computation of dielectric constants of solvent mixtures and electrolyte solutions

A general model has been developed for calculating the static dielectric constant of mixed-solvent electrolyte solutions. For mixtures of solvents without electrolyte components, the model is based on an empirical modification of the Kirkwood theory for multicomponent systems. For systems containing electrolytes, the model takes into account the effects of ions and ion pairs and, therefore, it is capable of reproducing the dependence of the dielectric constant on electrolyte concentration. For most solvent mixtures, dielectric constants can be reasonably predicted using only pure solvent properties. In the case of strongly nonideal solvent mixtures, the results can be significantly improved by adjusting a single binary parameter. The model has also been verified for a number of electrolyte solutions in various solvents over wide composition and temperature ranges. In particular, the increase in the dielectric constant due to ion pairing and its decrease due to the presence of ions and their solvation can be accurately represented.

Electrolyte solutions: from thermodynamic and transport property models to the simulation of industrial processes

Recent advances in modeling thermodynamic and transport properties of electrolyte solutions are reviewed. In particular, attention is focused on mixed-solvent electrolyte models, equations of state for high-temperature and supercritical electrolyte systems and transport property models for multicomponent, concentrated solutions. The models are analyzed with respect to their capability of computing thermodynamic and transport properties in wide ranges of conditions and composition (i.e. for aqueous or mixed-solvent, dilute or concentrated solutions). Various frameworks for the development of electrolyte models are discussed, i.e. models that treat electrolytes on a completely dissociated or undissociated basis and those that take into account the speciation of solutions. A new mixed-solvent electrolyte model is developed for the simultaneous calculation of speciation and phase equilibria. The role of speciation is discussed with respect to the representation of the thermodynamic properties of mixed-solvent electrolyte solutions and diffusion coefficients in aqueous systems.