Title: Development of Membrane Technology for the Separation of Azeotropic Refrigerant Mixtures

Although access to air-conditioning and refrigeration is imperative for the survival of people in Earth’s hottest regions, the use of refrigerants has an environmental impact. The same compounds that provide relief from increasing global temperatures are some of the most potent contributors to global warming. Today’s generation of refrigerants, hydrofluorocarbons, can have global warming potentials up to 4000 times higher than CO₂. The negative environmental impact of refrigerants has led to recent legislation such as the American Innovation and Manufacturing Act that requires a scheduled phasedown in refrigerant production over the next two decades. A process for separating multi-component, azeotropic refrigerant mixtures is urgently needed to account for the anticipated supply shortages in the refrigerant market and provide a stream of recycled refrigerant.  This work investigated membrane technology for the energy-efficient separation of R-410A, a widely used refrigerant mixture for residential and light commercial cooling and heat pump applications. R-410A is an azeotropic, 50-50 wt% mixture of difluoromethane and pentafluoroethane. This work has identified fluorinated, amorphous polymers to be promising materials for the separation of refrigerant gases due to high permeability, selectivity, resistance to plasticization, and stable separation performance over time. Investigation methods for polymeric materials included pure-gas permeability and mixed-gas permeability measurements with the pressure-rise method, solubility with the gravimetric method, and diffusivity analysis with Fickian models. The scale-up of promising materials was accomplished through the fabrication of composite hollow fiber membranes with a custom, reel-to-reel coating apparatus capable of producing submicron selective layers on hollow fiber supports. An amorphous copolymer of 30 mol% perfluoro(butenyl vinyl ether) and 70 mol% perfluoro(2,2-dimethyl-1, 3-dioxole) was used to create composite hollow fiber membrane modules that separate R-410A to a difluoromethane purity greater than 95 mol% in a single pass. ASPEN modelling of industrial scale separations with hollow fiber membranes showed that membrane technology can be utilized to achieve >99.5 wt% refrigerant purity with compact designs and minimal energy usage.