(520h) The Use of Zeolites and Carbons for the Separation of Refrigerant R-410A: Thermodynamic Modeling of Pure Gas and Binary Sorption

Worldwide legislation is currently phasing out the use and production of hydrofluorocarbons (HFCs) due to large global warming potentials (GWPs). The most recent is the U.S. American Innovation and Manufacturing (AIM) act in December 2020, which calls for a 15% reduction of HFC production and use by 2035. The United Nations recently published a report in Summer 2021 that cited HFCs as a contributor toward anthropogenic global climate change. The report further states that if atmospheric HFCs, along with other potent greenhouse gases (GHGs), are not reduced during the 21^st century, this will result in a 1.5-2.0 K global temperature increase, further perpetuating extreme weather patterns. As HFCs are phased out of use, an estimated 2,800 ktons of global refrigerant supply will need to be effectively and responsibly disposed of. Instead of venting or incinerating the HFCs, which would perpetuate global climate change, the unused HFCs should be reclaimed, recycled, and repurposed.

Recycling HFC refrigerants is a challenging task since many are azeotropic or near-azeotropic HFC refrigerant blends. In order to effectively recycle these refrigerants, the HFC blends must first be separated so that the constituent species can be dealt with individually. Traditional distillation techniques cannot separate azeotropes. Adsorption-based separation is an alternative to traditional distillation that has proven to effectively separate zeotropic, azeotropic, and isomeric fluorocarbon mixtures. Furthermore, adsorption-based separations have the potential to require less energy and produce a higher purity of products than traditional distillation. The following presentation will focus on the use of basic zeolites, acidic zeolites, and activated carbons for the separation of refrigerant R-410A (50/50 wt% HFC-32/HFC-125).

In order to effectively design any separation process, reliable thermodynamic models are required. Thermodynamic measurements have been made using a Hiden Isochema XEMIS gravimetric microbalance for pure gas sorption of various basic and acidic zeolites, as well as activated carbons. Resulting isotherms were fit to pure gas isotherm models, which were used in Ideal Adsorbed Solution Theory (IAST) to predict binary sorption behavior and selectivity trends. Binary sorption measurements were made using a separate Hiden Isochema gravimetric microbalance that uses the integral mass balance (IMB) method to calculate sorption of HFC-125 and HFC-32 on each sorbent. Using experimental data, sorbed phase activity coefficients were calculated, fit to vapor-adsorption equilibrium (VAE) activity coefficient models, and integrated into Real Adsorbed Solution Theory (RAST) sorption models to improve IAST predictions. Thermodynamic modeling development, as well as molecular level interpretations of results will be discussed. Conclusions will be drawn regarding the potential of each adsorbent to separate refrigerant R-410A.