(381y) Thermodynamic and Dynamic Breakthrough Measurements of Pentafluoroethane (HFC-125) and Difluoromethane (HFC-32) for R-410A Separation

Mitigating global climate change is currently among the most pressing challenges facing the scientific community. According to the United Nations International Panel on Climate Change (IPCC) report in 2021, anthropogenic greenhouse gas (GHG) emissions are directly perpetuating global warming. Projections showed that a 1.5-2.0 °C increase in global temperature must be avoided in the 21^st century to maintain a sustainable environment. Although a substantial effort toward environmental research is currently underway, recent reports from the National Oceanic and Atmospheric Administration (NOAA) still show a global temperature increase in recent years. Compared to the 20^th century average of 13.9 °C, a 0.84, 0.86, and 1.18 °C global temperature increase was reported in 2021, 2022, and 2023, respectively. Since CO₂ accounts for the majority of atmospheric GHGs, a large emphasis is being placed on technologies such as carbon capture; however, other problematic species must also be addressed including CH₄, NO₂, and fluorocarbons.

Fluorocarbons are among the most potent contributors to environmental destruction, with global warming potentials (GWPs) up to 10,000 times that of CO₂ on a per mass basis. As of 2020, 83% of Heating, Ventilation, Air-Conditioning, and Refrigeration (HVACR) working fluids consisted of fluorocarbons, with over 2,800 ktonnes in global circulation. Due to high global warming potential (GWP)s, recent legislative efforts are currently phasing down the use and production of hydrofluorocarbons (HFCs), the most widely used fluorocarbons today. In 2020, the U.S. American Innovation and Manufacturing (AIM) Act imposed an 85% reduction of high‑GWP HFCs by 2035, whereas in 2014 EU protocol 517/2014 imposed a 66% reduction of fluorinated GHGs by 2030. As HFCs are phased out with increasing regulatory efforts, technology will be needed for recycling common refrigerants such as R-410A (50/50 wt% CH₂F₂ (HFC-32)/CH₂FCF₃ (HFC-125)) and R-407C (23/25/52 wt% HFC-32/HFC-125/HFC-134a (CH₂FCF₃)), which must first be separated before being reused; however, separating HFC refrigerant mixtures is nearly impossible due to azeotropic or near-azeotropic properties.

Many technologies are currently being investigated for separating HFC refrigerants such as extractive distillation using ionic liquids, and both membrane- and adsorbent-based processes. Thousands of adsorbents exist, each having unique physical and chemical properties to be exploited for challenging gas separations. Furthermore, the separating capabilities of adsorbents such as activated carbons, zeolites, and metal-organic frameworks (MOFs) have been proven in industrial applications and, in recent years, through extensive studies on carbon capture. In an effort to develop industrially viable HFC separation processes, our group previously showed that many adsorbents, including zeolites 5A, 13X, and H-ZSM-5 can effectively separate refrigerant R-410A. Since HFC-32 has a lower GWP than that for HFC-125 (i.e., 675 compared to 3,500), adsorbents with HFC-125 selectivity are desired so that purified HFC-32 is produced during a continuous separation process. The following presentation will discuss our recent progress in using both zeolites and activated carbons for HFC-125 selective separation of refrigerant R-410A. Dynamic breakthrough experiments have been performed for various basic, acidic, and siliceous zeolites, as well as activated carbons. For select adsorbents, thermodynamic data have been gathered. Pure adsorption experiments were performed using a Hiden Isochema XEMIS gravimetric microbalance, whereas additional measurements were made with a separate XEMIS that uses the Integral Mass Balance (IMB) method to calculate binary adsorption. Dynamic and thermodynamic behavior will be presented and discussed to investigate the possible fundamental properties that influence HFC-125 selectivity.