(462h) Binary Adsorption of Pentafluoroethane (HFC-125) and Difluoromethane (HFC-32) for R-410A Separation

Global climate change is among the most pressing issues in the 21^st century. According to a 2021 report published by the United Nations (UN), anthropogenic greenhouse gas (GHG) emissions are directly related to the changing climate. Although CO₂ emissions are the most prevalent, other problematic GHGs include CH₄, NO₂, and fluorocarbons. Continued release of GHGs at the current rate is projected to increase global temperatures by 1.5-2.0 K, further increasing the severity of global weather patterns including drought and flooding; therefore, society must act quickly to decrease the release of harmful GHGs. Hydrofluorocarbons (HFCs) are among the most harmful GHGs, with global warming potentials (GWPs) up to 10,000 times that of CO₂ on a per mass basis; therefore, global legislation is currently phasing out the use and production of HFC refrigerants including 1,1,1,2-tetrafluoroethane (HFC-134a, CH₂FCF₃, GWP 1,430), pentafluoroethane (HFC-125, CHF₂CF₃, GWP 3,500), and 1,1,1-trifluoroethane (HFC-143a, CH₃CF₃, GWP 4,470). The U.S American Innovation and Manufacturing (AIM) act in 2020 calls for the reduction of HFC production and use by 85% in the next 20 years. Other countries have already banned the use of certain HFCs altogether. It is expected that HFC refrigerants will be further restricted as the next-generation, low GWP hydrofluoroolefin (HFO) refrigerants are phased in.

There is currently an estimated 2,800 ktonnes of HFCs currently in global circulation; therefore, as HFOs replace the HFCs currently in use, action will be needed to responsibly handle the unused HFCs. Ideally, the HFCs can be recovered, recycled, and reused rather than vented or incinerated, which would further perpetuate global climate change; however, recycling HFC refrigerants is difficult since many are azeotropic or near-azeotropic HFC mixtures that must first be separated. Since traditional distillation cannot be used, alternative methods for separating HFC mixtures have been studied including extractive distillation and both membrane- and adsorbent-based separation technologies. Our group previously showed that zeolites 4A and 5A could effectively separate refrigerant R-410A (50/50 wt% HFC-125/HFC-32) through comparative gravimetric measurements. Other groups have produced similar results using other zeolites, carbons, and MOFs with HFCs commonly used in refrigerant mixtures (i.e., HFC-32, HFC-125, HFC-134a, and HFC-143a).

The following presentation will discuss further work on the use of zeolites and activated carbons for the separation of refrigerant R-410A. An emphasis will be placed on the selective adsorption of HFC-125 over HFC-32 so that recovery of pure HFC-32 (i.e., the lower GWP species) is attainable. Pure adsorption isotherms have been measured using a Hiden Isochema XEMIS gravimetric microbalance. Additional measurements have been made with a separate XEMIS gravimetric microbalance that uses the Integral Mass Balance (IMB) method to calculate binary adsorption. Both pure and binary adsorption measurements will be presented for various zeolites and activated carbons. The results will be compared and possible mechanisms will be discussed for attaining optimal HFC-125 selectivity. Thermodynamic modeling of binary adsorption data for process design using both Ideal Adsorbed Solution Theory (IAST) and Real Adsorbed Solution Theory (RAST) will further be presented and discussed.