Modeling the thermodynamic and physical properties of ternary mixtures of ionic liquids (i.e. room temperature molten salts)
Modeling the thermodynamic properties (including phase equilibria) and physical properties of multicomponent systems is of great industrial importance nowadays. The metallurgical and chemical industries commonly use thermochemical packages to simulate chemical reactions and phase equilibria for process development. The thermodynamic and phase equilibrium modeling of multicomponent salt systems consists in expanding the Gibbs energy of a phase as a function of temperature, pressure and composition, and finding a global energy minimum. Model parameters of the Gibbs energy functions are obtained by optimizing their values in order to best reproduce simultaneously the experimental data found in the literature (enthalpy, liquidus, etc.). Parameters form a database and the models are used to predict phase equilibria and thermodynamic properties in the multicomponent system. Models for the density, viscosity and electrical conductivity of multicomponent inorganic molten salts, all linked to the thermodynamic model that gives an estimation of the structure of the melt, were previously developed and applied successfully to inorganic electrolytes such as NaCl-KCl-MgCl2-CaCl2 and NaF-AlF3-CaF2-Al2O3-LiF-MgF2.
“Room temperature molten salts” (or “ionic liquids”) are involved in numerous potential applications (solvents and catalysts, electrochemistry,
). They are usually composed of a large organic cation and an inorganic anion, and they melt at relatively low temperatures (often below room temperature). Since 2000 the research on ionic liquids has grown dramatically and it has focused on the design of single compounds with tailor-made properties. As suggested by Plechkova and Seddon, ionic liquid ternary mixtures may be considered, where the 1st component would control and define the chemistry of the system, the 2nd component would allow fine tuning of the physical properties (such as density and viscosity) of the system, and the 3rd component would be cheap and inert, thus lowering the global cost of the system. Ionic liquid mixtures have been studied relatively little, and most of the existing studies correspond to binary mixtures.
The proposed project consists in developing models and databases of parameters for the prediction of phase equilibria (in particular, the liquidus temperature) and physical properties (mainly density and viscosity) of ternary mixtures of the type CX-CY-CZ (where C is a large organic cation such as 1-alkyl-3-methyl-imidazolium, and X, Y and Z are three small anions such as Cl-, NO3- and CH3SO3-). The thermodynamic properties (mainly phase diagram) of the liquid solution will be modeled with the Modified Quasichemical Model in the Pair Approximation. The experimental data necessary for the calibration of the model will be provided by QUILL (Queens University Ionic Liquid Laboratories), located in Northern Ireland. Depending on the progress in this project, the density and viscosity of the ionic liquid ternary mixtures will also be modeled.
