Ionic Liquid / CO₂ Co-Fluid Refrigeration: CO₂ Solubility Modeling and Life Cycle Analysis

Improving our current refrigeration systems is important from an energy standpoint as well as from an environmental standpoint. One method of improving our refrigeration systems is developing new working fluids that reduce the energy required for operation, and have less of an environmental impact. One of the possible types of working fluids that displays a great deal of potential is a mixture involving CO₂ (the refrigerant) and an ionic liquid (the co-fluid). The ionic liquid co-fluid greatly reduces the pressure that would be required if CO₂ alone was used. To identify appropriate ionic liquids, two important aspects are the properties of ionic liquid / CO₂ mixtures and the potential environmental impact of the ionic liquid / CO₂ co-fluid refrigeration system over its entire life cycle. In this work properties of various ionic liquids are modeled using the SAFT equation of state. This modeling has been done for both pure component and CO₂ solubility and it shows the effects of impact of the association term for these compounds in regards to the goodness of fit. Furthermore properties of untested ionic liquids are predicted using the same model. Synthesis routes are also predicted for the synthesis of both 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and trihexyl(tetradecyl)phosphonium 1,2,3-triazolide. From these synthesis routes, and from an estimation of the refrigeration systems theoretical efficiencies, environmental impacts can be determined and analyzed.