PDD-VA Copolymers for the Separation of Azeotropic Refrigerant Mixtures

From central air conditioning in homes to safely storing perishable vaccines, refrigeration technology is vital to the modern human lifestyle. However, the use of refrigerants has a significant environmental impact on our world today. After chlorofluorocarbons (CFCs) were phased out due to their impact on the ozone depletion, hydrofluorocarbons (HFCs) were implemented across the world to replace them. However, it was found that some HFCs have high global warming potential (GWP). Recent legislation has been enacted to regulate the phase-down of these compounds. The 2020 American Innovation and Manufacturing (AIM) act has committed the United States to reducing 85% of HFC usage by 2035. Many of these HFCs are used in azeotropic mixtures, so finding innovative technology able to separate the mixtures is crucial to be able to reclaim and reuse the individual components. This study focuses on the separation of refrigerants using a copolymer of 75 mol% perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) and 25 mol% vinyl acetate (VA). Common refrigerants such as HFCs, hydrochlorofluorocarbons (HCFCs), and hydrofluoroolefins (HFOs) were studied. The permeability, solubility, and diffusivity of HFC-32 (CH2F2), HFC-125 (CHF2CF3), HFC-134a (CF3CH2F), HFO-1234yf (CH2═CFCF3), and HCFC-22 (CHClF2) were measured in polymer films at varying temperatures of 308.15, 323.15, 348.15, and 373.15 K. Arrhenius relationships were used to obtain the activation energy of permeation for each refrigerant. Arrhenius solubility and diffusivity relationships were then applied to HFC-32 and HFC-125 to obtain the activation energy of diffusion and heat of sorption. The overall results indicate that selectivity of the gases decreases as the temperature of the membrane increases. This is explained due to the higher activation energy of diffusion for larger molecules. A high selectivity of 35 can be obtained for HFC-32/HFC-125 while maintaining a high permeability at 308.15 K. Other high selectivities were achieved with refrigerant mixtures of HFC-32/HFC-125, HFC-32/HFO-1234yf, HFC-32/HFC-134a, and HCFC-22/HFC-125. These promising results show the potential of this copolymer having future commercial use in the separation of refrigerant mixtures.