(381l) Investigating Adsorbent-Based Separation of Refrigerant R-410A through Dynamic Breakthrough Experiments and Thermodynamic Behavior

Addressing the existential threat of rising global temperatures is at the forefront of current research toward environmental sustainability. According to the United Nations International Panel on Climate Change (IPCC) report in 2021, a direct correlation exists between anthropogenic greenhouse gas (GHG) emissions and global warming. It was concluded that global temperatures cannot rise another 1.5-2.0 °C within the 21^st century in order to avoid further perpetuating extreme and life-threatening environmental conditions including extreme droughts, flooding, and tropical storms. Despite increased research efforts toward environmental sustainability in recent years, reports from the National Oceanic and Atmospheric Administration (NOAA) still show increasing global temperatures. Relative to the 20^th century average of 13.9 °C, the average global temperature in 2021 was 0.84 °C higher, whereas an increase in 0.86 and 1.18 °C was observed in 2022 and 2023, respectively. Carbon capture technology has been stressed as a pivotal technology required to address global warming; however, mitigating other high global warming potential (GWP) species including CH₄, NO₂, and fluorocarbons is also crucial and must be addressed.

Fluorocarbons, including hydrofluorocarbons (HFCs), have a determinantal effect on atmospheric sustainability. Some HFCs have GWPs that are up to 10,000 times that for CO₂ per mass of substance. Over 2,800 ktonnes of fluorocarbon refrigerants currently exist in global circulation, comprising 83% of the working fluids used in the Heating, Ventilation, Air-Conditioning, and Refrigeration (HVACR) as of 2020. To mitigate primary emissions of HFCs from HVACR appliances, countries have taken strong legislative action to phase down the use and production of high-GWP fluorocarbons including HFCs. Both the United States (U.S.) and the European Union (E.U.) have implemented strict phase-downs through the U.S. American Innovation and Manufacturing (AIM) Act and EU protocol 517/2014, respectively. By 2035, high-GWP HFCs will be banned by both the U.S. and E.U. As HFC refrigerants are replaced with next-generation refrigerant blends (e.g., low-GWP hydrofluoroolefins (HFOs) blended with HFCs), technology will be needed to recycle the unused fluorocarbon refrigerants; however, many are either azeotropic or near-azeotropic mixtures that must first be separated before being recycled.

Traditional separation methods such as distillation cannot separate many HFC refrigerant mixtures such as R-410A (near-azeotropic, 50/50 wt% HFC-32 (CH₂F₂)/HFC-125 (CHF₂CF₃)), and so other technologies are currently being investigated including extractive distillation using ionic liquids, and both membrane- and adsorbent-based processes. Adsorption-based separation via cyclic, continuous processes such as vacuum swing adsorption (VSA) are of particular interest. Thousands of adsorbents, each with different chemical and physical properties, exist that can be used to optimize a given separation. Furthermore, adsorption-based separations of highly complex mixtures are effective both in previous industrial applications, and more recently, newly emerging carbon capture technologies. The following presentation focuses on using adsorbents for separating refrigerant R-410A. Dynamic breakthrough experiments have been performed with many zeolites and activated carbons to investigate adsorbent properties that influence both HFC-32 and HFC-125 selectivity. Both pure and binary adsorption data have been collected using XEMIS gravimetric microbalances and the Integral Mass Balance (IMB) method. Both thermodynamic and breakthrough experiment results will be presented and discussed in the context of designing and scaling up a viable R-410A separation process.