(512e) Computational Studies of Mixtures of Refrigerants, Ionic Liquids and Deep Eutectic Solvents for Absorption Refrigeration Systems

Heating and cooling buildings in the U.S. consumes an enormous amount of energy (>10 quadrillion BTU), and is responsible for adding ~1 billion metric tons of CO₂ in the earth’s atmosphere every year. Much of this energy is used as electricity in vapor-compression systems; however, this technology is mature and only evolutionary improvements are expected in the near future. Several recent studies^[1],[2],[3]have shown that several common ionic liquids (ILs) can be combined with standard fluorocarbon refrigerants for use in absorption refrigeration systems that use waste heat at relatively low temperatures (~100 °C). Nevertheless, there is limited understanding (and data) on the VLE behavior of these systems, and only one working example of an absorption system using this type of mixture. Furthermore, deep eutectic solvents (DESs), a relatively new class of solvents, share many of the properties of ILs while being considerable cheaper and mostly nontoxic. A fundamental understanding of how the chemical structure of the different species affects the solubility of fluorocarbons in a DES is crucial to design mixtures suitable for use in absorption refrigeration systems that use solar energy or waste heat. In this work, we performed molecular dynamics simulations of mixtures of a conventional fluorocarbon refrigerant, 1,1,1,2-tetrafluoroethane (R134a) with three common deep eutectic solvents (1:2 choline chloride/urea, 1:2 choline chloride/glycerol and 1:2 choline chloride/ethylene glycol). We report and discuss a number of properties for these systems, including Henry’s law constants of R134a in the three DESs as a function of temperature, radial distribution functions, and diffusion coefficients. We will also describe our recent efforts aimed at computationally screening a large number of mixtures of standard fluorocarbon refrigerants with ILs and DESs. Here we used the quantum chemistry-based conductor-like screening model for real solvents (COSMO-RS) and other theoretical tools, to quickly predict values of several key properties (e.g., solubility, viscosity, phase equilibrium and thermochemical data), and perform thermodynamic evaluations of absorption refrigeration cycles using these working fluid mixtures.