(355k) Porous Media for the Separation of Fluorocarbon Refrigerant Mixtures

The most popular fluorocarbon refrigerants in circulation today are hydrofluorocarbon (HFC) refrigerants. However, HFCs have significantly higher global warming potentials (GWPs) compared with carbon dioxide. As a result, the production and use of HFCs is currently being phased down according to the Kyoto Protocol (2005), F-gas regulations in the European Union (2014), the Kigali Amendment to the Montreal Protocol (2016), and most recently the coronavirus relief bill passed by the U.S. Congress and signed by the president (2020). Therefore, there is a pressing need to replace existing HFC refrigerants with more environmentally sustainable options. The next generation of fluorocarbon refrigerants are based on hydrofluoroolefins (HFOs). While many HFCs have a GWP of over 1000, HFOs have a GWP of 1-10. To replace the existing HFCs with HFOs, this will require the removal of an estimated 846 million kilograms of refrigerant currently in use worldwide. Rather than venting or incinerating the HFCs, a more environmentally sustainable option is required. However, several HFC refrigerants exist as mixtures which form azeotropic compositions; the separation of these refrigerants is more challenging and new technologies will be required to efficiently recycle these gases.

Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) is working toward developing needed technologies for fluorocarbon refrigerant mixture separation. The project is currently investigating the use of the following to achieve this goal: ionic liquids, membranes, and porous materials. This poster presentation first introduces Project EARTH, its main goals, and its progress. Attention is then directed toward porous materials. Porous materials such as zeolites, activated carbons, and metal organic frameworks (MOFs) have been proven in the literature to successfully separate zeotropic, azeotropic, and isomeric fluorocarbon mixtures. Work has been conducted using a Hiden Isochema XEMIS gravimetric microbalance to measure the pure gas sorption isotherms of HFC-125 (pentafluoroethane) and HFC-32 (difluoromethane) with zeolites 3A, 4A, and 5A. These sorption measurements have revealed the potential for the use of zeolites in separating the commercial refrigerant R-410A (50/50 wt% HFC-125/HFC-32). Results from these experiments will be presented along with a discussion of how they can be used to direct future work. A close examination of sorption isotherm results, along with heats of adsorption measurements performed using a Setaram calorimeter, can be used to obtain insight into the possible chemical and physical properties of absorbents needed for such separations.