Silver-exchanged zeolites for collecting and separating xenon directly from atmospheric air

Abstract

More efficient adsorbents for Xe collection and separation from air could provide new alternatives for costefficient production of stable Xe as well as for trace measurements of atmospheric radioxenon. Silver-exchanged Zeolites (AgZs) have been reported to be more efficient than Activated Carbon (AC) in collecting Xe at low pressures and room temperature but never for Xe collection from air. Metal-Organic Frameworks (MOFs) have been reported for high Xe/Kr selectivities in Xe and Kr enriched gas streams but never for Xe collection from air either. Two AgZs (Ag-ETS-10 and Ag-ZSM-5), two MOFs (HKUST-1 and Ni-DOBDC) and one AC (Nusorb & REG; GXK) are compared to determine their potential for collecting and separating Xe from air. The acquired adsorbent samples were characterized (by SEM, PXRD, TGA, N2 adsorption at 77 K and CO2 adsorption at 273 K) and the results are in agreement with observations made previously in the literature. Both AgZs show an unprecedented Xe adsorption capacity in N2 at 13.5 mPa (approximately the Xe partial pressure in air) and room temperature with 0.15 and 0.13 mmol/kg for Ag-ETS-10 and Ag-ZSM-5, respectively. This high Xe adsorption capacity at low Xe concentration holds in dry air. Both AgZs have a high Xe selectivity over the major gas components in air at room temperature and they also show an unprecedented Xe selectivity over Kr of 1300 and 470 for Ag-ETS-10 and Ag-ZSM-5, respectively. Finally, it is possible to separate Xe from O2, Ar, CO2, Kr and Rn efficiently in both AgZs but it requires temperatures up to 521 K. The results clearly demonstrate that both AgZs investigated in this work are globally outperforming all other adsorbents for collecting and separating Xe from air. The only limitation found for the moment on these AgZs is the strong co-adsorption of moisture that significantly reduces the Xe collection at 50% R.H.