Computer Aided Design of Ionic Liquids for Thermal Energy Storage Applications

Ionic liquids (ILs) and salts have properties that make them attractive for thermal energy storage (TES). In particular, ILs have high heat capacity, density, and thermal decomposition temperatures which are key properties for TES. Further, ILs and salts can be tuned to optimize these properties. Since very large numbers of IL structural variations are possible we utilize a computer-aided ionic liquid design (CAILD) method to select optimal IL structures for this application. The design problem is posed as an MINLP model where the objective is to maximize energy density and constraints relate to structural feasibility, and bounds on viscosity, melting point (M.Pt.) and thermal decomposition temperature. This MINLP model is solved to design optimal IL structures. Three specific problems related to design of ionic salts (M.Pt. < 140 C), ionic liquids (M.Pt. < 100 C), and room temperature ionic liquids (M.Pt. < 25 C) are presented. In depth analysis on structural features and functional groups that contribute to optimized properties are discussed. Comparison between designed ionic liquids and current industrial thermal storage fluids is also presented.