Models for the thermodynamic properties of molten salt systems: Perspectives for ionic liquids

• Thermodynamic model for the LiN(FSO2)2–KN(FSO2)2–CsN(FSO2)2 system.
• Thermodynamic model for the [C2mim]Cl–AlCl3 system.
• The Modified Quasichemical Model was used for the molten salt phase.
• Volume-based Thermodynamics tested on methyl-imidazolium ionic liquid compounds.

Over the past several years, the Modified Quasichemical Model for short-range ordering has been used successfully to obtain a quantitative thermodynamic description of various multicomponent high temperature inorganic molten salt systems. In the present paper, it was applied to the (LiN(FSO2)2 + KN(FSO2)2 + CsN(FSO2)2) ternary system and the ([C2mim]Cl + AlCl3) binary system (where [C2mim]Cl refers to 1-ethyl-3-methyl-imidazolium chloride), which both involve some ionic liquid compounds. Those two systems were selected as prototypes since experimental data were available for them in the literature. The (LiN(FSO2)2 + KN(FSO2)2 + CsN(FSO2)2) liquid displays relatively little short-range ordering, and the experimental ternary eutectic at T = 309 K or 312 K was satisfactorily reproduced by using solely the optimized binary parameters along with a standard symmetric interpolation method. The ([C2mim]Cl + AlCl3) liquid displays strong negative deviations from ideality, and two different compositions of maximum short-range ordering (near the [C2mim]AlCl4 and [C2mim]Al2Cl7 compositions) were introduced. All available experimental data (phase diagram, emf measurements, partial enthalpies of mixing) were satisfactorily reproduced by the model. The Volume-based Thermodynamics (VBT) from Glasser and Jenkins was used to assess the missing thermodynamic data for [C2mim]Cl, and it was also tested on several ionic liquid compounds of the methyl-imidazolium type.