(717a) Computation of Melting Points, Crystalline Free Energies, and Transport Properties of Molten Salts

Ionic liquids, salts that are liquid near ambient temperatures, are finding application in separations, catalysis, and lubrication fields. More traditional salts such as alkali halide eutectic mixtures are being used as industrial heat transfer fluids in solar power generation systems, where it is required to store and utilize heat for producing electrical energy in periods of low or no sun.

Properties such as viscosity, thermal conductivity, density and melting point are all critical for the use of these salts in a given application. Experimental determination of these properties is difficult, particularly for the high temperature systems, and so there is a great desire to develop computational approaches for predicting properties of molten salts.

Melting points have been one of the most difficult properties to estimate from simulations. A new method developed in our group recently [1-2] allows accurate computation of melting points. In our recent study [3], we computed the melting points of the two known crystal polymorphs of the ionic liquid 1-n-butyl-3-methylimidazolium chloride, which are an orthorhombic and a monoclinic structure. We also computed the free energy difference between the two structures, and hence this leads to a new application where we can determine relative stabilities of crystal polymorphs by computing their relative free energy differences.

In the area of heat transfer fluids, we use simulations to predict how properties depend on the ratio of different cations in nitrate-based salts used in solar energy applications.

[1] D. M. Eike, J. F. Brennecke, and E. J. Maginn, J.Chem. Phys. 122, 014115 (2005).

[2] D. M. Eike and E. J. Maginn, J. Chem. Phys. 124,164503 (2006).

[3] S. Jayaraman and E. J. Maginn, J. Chem. Phys. 127, 214504 (2007).