Xenon Capture on Silver-Loaded Zeolites: Characterization of Very Strong Adsorption Sites

Abstract

INGENIERIE+SAG:YSC:DFAThe number and strength of adsorption sites for Xe in silver-modified zeolites are estimated from isotherm measurements at various temperatures over a broad range of pressure (from 1 ppm to atmospheric pressure). Fully and partially exchanged silver zeolites were synthesized starting from Na-ZSM-5(25), Na-ZSM-5(40), Na-Beta, NaX, and NaY. We have discovered that silver-modified zeolites may present one or two distinct adsorption sites depending on the nature of the material and silver loadings. The strongest adsorption sites are characterized by isosteric heat of adsorption in the order of -40 to -50 kJ.mol(-1). For Pentasil-type zeolites, we observe a linear 2:1 correlation between the total amount of silver and the number of strong sites. The highest concentration of strong sites is found for fully silver exchanged ZSM-5 (5.7 X 10(-4) mol/g), which presents the largest silver content for Pentasil-type zeolite. The equilibrium constant of Ag-ZSM-5 at low pressure is about 50 times larger than that of AgX. Qualitative correlations were established between Xe adsorption isotherms and Xe NMR signals. We show that Xe NMR could be used as a quantitative method for the characterization of the strength and of the number of strong Xe adsorption sites on silver-exchanged zeolites. The numbers of strong adsorption sites responsible for the Xe adsorption at 10-1000 ppm can be determined by the length of the plateau observed at low Xe uptake. In practice, our findings give guidelines for the discovery and optimization of silver-loaded zeolites for the capture of Xe at ppm levels. It appears that the amount of silver is a key parameter. Silver-modified ZSM-5 shows adsorption capacities 2-3 orders of magnitude larger than currently applied adsorbents for atmospheric Xe capture

129Xenon NMR: Review of recent insights into porous materials

“…In order to develop more efficient detectors, the quantification of the number and strength of silver adsorption sites, for Xe atoms, in silver-exchanged zeolites, NaX, NaY, BEA and ZSM-5 have been investigated by Xe isotherms and 129 Xe NMR experiments [121].…”

Spalax™ new generation: A sensitive and selective noble gas system for nuclear explosion monitoring

“…The air processing unit includes also a major evolution within the concentration/purification process. Hence, a silver doped zeolite (MFI zeolite) has been tested (Daniel et al, 2013;Deliere et al, 2014) at the different stages of the process in place of the current carbon adsorbent materials, activated charcoal for the ovens dedicated to the first concentration and purification steps and carbon molecular sieve for those related to the ultimate concentration step. A major increase of xenon retention capacity, by at least a factor 10 compared to the current activated charcoal, has been achieved.…”

SPALAX new generation: New process design for a more efficient xenon production system for the CTBT noble gas network

“…The objective of the evolution is to reduce the overall size of the columns and the energy consumption needed to heat these columns. A silver doped zeolite Ag@ZSM-5 (also called Ag-PZ2-25) has been prepared by exchanging all of the Na þ cations from the native Na@ZSM-5 zeolite for Ag þ cations (Daniel et al, 2013). This new material exhibits a large xenon retention capacity, leading to a reduction of the column sizes by a factor of at least 10.…”

“…The purification step evolution consists of replacing the AC by a new adsorbent of much higher Xe retention capability. The silver-doped zeolite Ag@ZSM-5 is prepared in the laboratory according to a protocol described previously (Daniel et al, 2013). Ag@ZSM-5 is especially well-adapted to the adsorption of Xe at the concentration close to 1 ppm that is typically observed in the membrane exhaust gas.…”

“…The formation of silver nanoparticles enables the creation of strong adsorption sites at low xenon concentrations that do not exist in the native zeolite (Deliere et al, 2014). Ag@ZSM-5 exhibits a retention capability more than two order of magnitudes higher than AC at approximately 10 À1 Pa of pure xenon, corresponding to a partial pressure of approximately 1 ppm of Xe at atmospheric pressure (Daniel et al, 2013). Two sets of three columns with 12 g of Ag@ZSM-5 adsorbent per column (granulometry from 300 to 500 mm) have been installed in the SPALAX in place of the two sets of three columns with 150 g of AC adsorbent (granulometry from 300 to 500 mm).…”