(374n) Separation of Refrigerant R-410A Using Porous Materials: Thermodynamic Modeling and Breakthrough Experiments

According to a report published by the United Nations in Summer 2021, the presence of atmospheric greenhouse gases (GHGs) has perpetuated anthropogenic global climate change. Global temperatures have risen 1.0-2.0 K throughout the 20^th century, and if GHG emissions are not reduced, this could result in an additional increase of 1.5-2.0 K throughout the 21^st century, further perpetuating sporadic and destructive weather patterns. Hydrofluorocarbons (HFCs) are among the GHGs cited as contributing to global climate change. The high global warming potentials (GWPs) of HFCs was noticed in the early 21^st century, which has led to worldwide legislation restricting production and use. The most recent is the U.S American Innovation and Manufacturing Act in December 2020.

There is currently an estimated 2,800 ktons of HFCs in global circulation. As HFCs are phased out and replaced with next-generation fluorocarbons, hydrofluoroolefins (HFOs), responsible action will be required to sustainably deal with the unused HFCs. Rather than venting or incinerating the HFCs, these unused refrigerants should ideally be reclaimed, recycled, and reused; however, such goals are difficult since many refrigerants currently in use are azeotropic or near-azeotropic HFC refrigerant blends. Before the refrigerant mixtures can be recycled, the HFCs must first be separated so that each species can be handled separately and efficiently. Traditional distillation techniques cannot effectively separate azeotropic mixtures; therefore, other separation methods must be developed so that HFC refrigerants can effectively be reclaimed and recycled. Adsorption-based separation has been proven to work for zeotropic, azeotropic, and isomeric fluorocarbon separations.

The following presentation will focus on using zeolites and carbons for the separation of refrigerant R-410A (50/50 wt% HFC-32/HFC-125), which is commonly used in commercial and domestic refrigerators and air conditioning units. Pure gas isotherm data was measured using a Hiden Isochema XEMIS gravimetric microbalance for basic and acidic zeolites, as well as activated carbons, and fit to isotherm models. Binary sorption of HFC-125 and HFC-32 on the same sorbents was additionally measured using a separate Hiden Isochema gravimetric microbalance that uses the integral mass balance (IMB) method. Sorbed phase activity coefficients were calculated from experimental data and fit to vapor-adsorption equilibrium (VAE) activity coefficient models. Both pure gas models and activity coefficient models were used in Real Adsorbed Solution Theory (RAST) to develop accurate thermodynamic models for binary sorption of HFC-125 and HFC-32. Breakthrough experiments have additionally been performed for various sorbents. Both thermodynamic modeling and breakthrough experiment results will be presented and discussed to assess the potential of the sorbents for separating R-410A.