Molecular Dynamics Simulations of Mixtures of Refrigerants and Deep Eutectic Solvents

Molecular dynamics simulations of mixtures of refrigerants and deep eutectic solvents

 

Rubaiyet Abedin, John C. Flake and Francisco R. Hung

 

Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803

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. Remarkably, a few studies 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 study, we used molecular dynamics (MD) simulations to study mixtures of a conventional fluorocarbon refrigerant, 1,1,1,2-tetrafluoroethane (R134a) with two conventional DESs (1:2 choline chloride/urea and 1:2 choline chloride/glycerol). Results for the Henry's law constant of R134a in the two DESs as a function of temperature are reported and analyzed in terms of molecular level properties (radial distribution functions, relevant interaction energies).