Difluoromethane (HFC-32) and Pentafluoroethane (HFC-125) Sorption on Linde Type A (LTA) Zeolites for the Separation of Azeotropic Hydrofluorocarbon Refrigerant Mixtures

Abstract

Worldwide use of hydrofluorocarbons (HFCs) is currently being regulated and phased out because of high global warming potentials (GWPs). Separation techniques for recycling refrigerants are needed so that HFCs can be dealt with responsibly. Many HFCs currently in use are azeotropic or near-azeotropic refrigerant blends and must be separated so that the components can be recycled and repurposed effectively. One such refrigerant is R-410A, which is a near-azeotropic 50/50 wt % mixture of pentafluoroethane (HFC-125) and difluoromethane (HFC-32). This study examined the use of the LTA zeolites for separating HFC-32 from HFC-125. Pure gas isotherms were measured using a XEMIS gravimetric microbalance with zeolites 3A, 4A, and 5A. Reversible sorption was observed for HFC-32 with zeolites 4A and 5A, whereas irreversible sorption was observed for HFC-125 with zeolite 5A. Negligible sorption was observed for HFC-125 with zeolites 3A and 4A, and although sorption of HFC-32 with zeolite 3A was observed, the process was slow, making the sorbent not commercially viable. The enthalpy of adsorption was predicted using the vapor adsorption equilibrium (VAE) analogue of the Clausius−Clapeyron equation and measured using a calorimeter for HFC-125 and HFC-32 with zeolite 5A and for HFC-32 with zeolite 4A. Molecular-level interactions between the LTA zeolites and HFCs were discussed and used to interpret pure gas isotherms and enthalpy of adsorption results. Overall, zeolites 4A and 5A were found to be good candidates for kinetically and thermodynamically separating R-410A, respectively.

Separation of Azeotropic Hydrofluorocarbon Refrigerant Mixtures: Thermodynamic and Kinetic Modeling for Binary Adsorption of HFC-32 and HFC-125 on Zeolite 5A

“…These data were presented and discussed in our previous study . The XEMIS operates in static, as opposed to dynamic, mode and was previously described in detail …”

“…As molecules diffuse through a zeolite crystal, energetic barriers exist that the molecule must overcome to continue diffusing . The unit cell features of zeolite 5A were previously discussed in detail . Zeolite 5A consists of a three-dimensional channel network.…”

“…A separate Hiden Isochema XEMIS gravimetric microbalance was used to measure pure gas adsorption isotherms for HFC-125 and HFC-32 with zeolite 5A. These data were presented and discussed in our previous study . The XEMIS operates in static, as opposed to dynamic, mode and was previously described in detail …”

“…The same zeolite 5A sample used in our previous study was also used for binary adsorption experiments . The zeolite 5A powder (Lot No.…”

“…Presented is a continuation of a study on using Linde Type A (LTA) zeolites for the separation of R-410A. Our previous work presented pure gas isotherm measurements made for HFC-32 and HFC-125 with zeolites 3A, 4A, and 5A along with enthalpy of adsorption predictions and measurements . It was concluded that both zeolite 4A and 5A have the potential to separate R-410A, with the former providing a kinetic separation and the latter a thermodynamic separation.…”