Ag-X Zeolite Research Articles

A novel strategy for iodine removal from nuclear reactor accidental gases: efficient adsorption of CH3I on the moderately hydrophobic modified silver-loaded zeolite under high temperature and humidity conditions

ABSTRACT Ensuring nuclear energy safety through effective gas emission filtration from nuclear reactor containment in accident scenarios is paramount. The efficacy of hydrophobic modified Ag-loaded zeolites for methyl iodide (CH3I) removal under challenging conditions of high temperature, humidity, and irradiation is studied in this work. Through hydrophobic modification of AgX zeolite with three different silane coupling agents, a series of modified zeolites with varied hydrophobicity levels is produced. The adsorption capabilities of these modified materials are assessed using a self-designed gas adsorption setup, focusing on CH3I removal from a gas mixture emblematic of nuclear accident environments. Results indicate that all hydrophobically modified zeolites exhibited superior CH3I removal rates compared to their unmodified counterparts, with the variant modified with 10% phenyltriethoxysilane achieving the highest removal rate of 99%. Additionally, zeolites modified with octyltrimethoxysilane demonstrate commendable irradiation resistance at a radiation dose of 4.2 × 105 Gy. The results suggest that optimally hydrophobically modified AgX zeolites hold significant promise for filtering gases containing radioactive iodine, offering novel insights for the advancement of adsorbent materials in nuclear reactor containment discharge systems.

Enhanced adsorption performance for aromatic sulfur compounds over a hierarchical structured AgX zeolite

Schematic illustration of the design for the synthesis of hierarchical-AgX. (a) Sequential acid–alkali treatments of NaX; (b) silver supported on original NaX; (c) silver supported on hierarchical NaX after sequential acid–alkali treatments.

Ion-exchange modified zeolites X for selective adsorption desulfurization from Claus tail gas: Experimental and computational investigations

Zn, Co and Ag modified NaX zeolites were prepared by ion-exchange method and the post-synthesized samples were characterized using EDS, XRD, FT-IR, SEM and N2 adsorption. The selective adsorption performances for H2S and COS from Claus tail gas were evaluated in a fixed bed adsorption column. In addition, the underlying mechanism for H2S and COS adsorption on zeolites X was revealed by DFT computation. Among all the samples, AgX shows the most excellent adsorption performance, which shows the highest H2S and COS breakthrough adsorption capacities up to 1.53 mmol/g and 10.5 μmol/g, respectively. The used AgX zeolite can also be regenerated by thermal treatment at 350 °C under air atmosphere. The DFT study indicates that the S-M bond between H2S or COS and metal ion can be formed during the adsorption process. Furthermore, the Ag-sulfide complex shows the strongest S-M interaction, hence, benefits the adsorption of H2S and COS on Ag-exchanged zeolite X.

Investigation of the sorption of mercury vapour from exhaust gas by an Ag-X zeolite

AbstractThe removal of gaseous mercury from flue gases from coal-fired power plants is currently an environmental challenge under investigation. Therefore, the main aim of this paper was to evaluate the suitability of faujasite group zeolites (Na-X) to adsorb mercury compounds. Previous, initial tests showed negligible Hg0 uptake by Na-X zeolite, but silver impregnation improved adsorption markedly. Therefore, the testing of mercury adsorption from flue gases into Ag+- impregnated Na-X synthetic zeolite (Ag-X zeolite) derived from coal fly ash was carried out. This material was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, X-ray fluorescence and nitrogen adsorption/desorption before being evaluated for mercury removal from exhaust gas. After preliminary mercury adsorption tests (fixed bed) under a nitrogen atmosphere, the adsorbent was examined with a simulated flue gas composition under various conditions, i.e. weight of zeolite, temperature of experiment and zeolite in powder and granulated forms. The removal of mercury was shown to depend on the sorbent texture (powder or granulate), exhaust gas flow rate and contact time, as well as the temperature of the experiment. The Ag-X zeolite tested reduced the level of mercury in the flue gas and, depending on the experimental conditions, long-time mercury breakthrough ranges from 15 to 40% were obtained. The best results for mercury capture were obtained for granulated material.

Adsorption of ethyl, iso-propyl, n-butyl and iso-butyl mercaptans on AgX zeolite: Equilibrium and kinetic study

It has been shown that AgX zeolite has a distinctly higher adsorption capacity compared to NaX, NiX and NiAgX zeolites for ethyl mercaptan. Chosen as the best adsorbent, the adsorption isotherms of ethyl, iso-propyl, n-butyl and iso butyl mercaptans on AgX zeolite at three different temperatures of 26, 40 and 60°C had been studied. The AgX zeolite showed the highest adsorption capacity for the ethyl mercaptan adsorbate molecule. On the other hand, this mercaptan molecule was the easiest to be removed by thermal treatment in the range of 150–300°C. Except ethyl mercaptan, all the other mercaptan molecules showed increased adsorption on AgX zeolite with increasing the temperature in the range of 26–60°C. The kinetic analysis of the adsorption process showed that there exists a rational correlation between the size and configuration (linear or branched) of the molecules and the effective diffusion coefficient.

Zeolites Containing Mixed Cations for Air Separation by Weak Chemisorption-Assisted Adsorption

NaX zeolite was ion-exchanged to obtain LiX and AgX zeolites. The LiX form was further exchanged to replace 20% of the Li+ cations by Ag+, to obtain a LiAgX zeolite. Equilibrium adsorption isotherms of pure-component N2 and O2 were measured at 25 and 50 °C on these four zeolites. AgX was stable since the N2 isotherm was not affected after prolonged exposure of the zeolite to air at 350 °C. Bonding of N2 was substantially stronger on AgX than on the other zeolites. The high isosteric heat of adsorption (8.4 kcal/mol) and the relatively slow desorption of N2 on AgX indicated some degree of weak π-complexation, which was substantiated by molecular orbital calculation results using model systems. Binary N2/O2 selectivity (or separation factor, α) was calculated by using the ideal adsorbed solution theory. The high N2/O2 selectivities at low total pressures for AgX will result in difficult N2 desorption; therefore, AgX is not suitable for air separation. LiX is presently employed in industry as the sorbent for air separation by pressure-swing adsorption. Comparing LiX with LiAgX, the N2/O2 selectivities were higher for LiAgX at high total pressures and lower for LiAgX at lower pressures, due to a (relative) selectivity reversal. This result, combined with the higher N2 capacity for LiAgX, led to the conclusion that LiAgX can be superior to LiX for air separation.

129Xe NMR of AgX, CuX, ZnX and CdX zeolites. Comparative study of nd 10 element-xenon interactions

129Xe NMR spectroscopy of Xe adsorbed on silver-, copper-, zinc- and cadmium-exchanged sodium X zeolites is used for determining the location of these cations (inside or outside the supercages) and the nature of Xe—cation interactions.

129Xe NMR for the study of oxidized and reduced AgX zeolites

Xenon NMR spectroscopy was used to characterize xenon in silver-exchanged sodium X zeolites and the materials formed by treatment with oxygen and hydrogen. The unusual low-frequency chemical shift for the Ag +X form is attributed to a d π—d π donation from Ag + to Xe. After reduction, the high-frequency chemical shift is due to the silver metal—xenon interactions.

ChemInform Abstract: ESR STUDIES OF THE SILVER(2+) ION PRODUCED IN AG‐X ZEOLITE BY Γ‐IRRADIATION

Chemischer InformationsdienstVolume 10, Issue 4 Physical Inorganic Chemistry ChemInform Abstract: ESR STUDIES OF THE SILVER(2+) ION PRODUCED IN AG-X ZEOLITE BY Γ-IRRADIATION N. KANZAKI, N. KANZAKISearch for more papers by this authorI. YASUMORI, I. YASUMORISearch for more papers by this author N. KANZAKI, N. KANZAKISearch for more papers by this authorI. YASUMORI, I. YASUMORISearch for more papers by this author First published: January 23, 1979 https://doi.org/10.1002/chin.197904004AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue4January 23, 1979 RelatedInformation

ESR studies of the silver(2+) ion produced in Ag-X zeolite by .gamma.-irradiation

The silver-X zeolite was prepared and ..gamma..-irradiated by /sup 60/Co at room temperature. ESR measurements were made at -196/sup 0/C. A figure shows the ESR spectrum observed for silver-X ..gamma..-irradiated after evacuation at 350/sup 0/C. The anisotropic g factors, and the anisotropic hyperfine splittings obtained agree well with those of the divalent silver ion. The Ag/sup 2 +/ spectrum was broadened by exposing the sample to 150 Torr of oxygen, suggesting that the Ag/sup 2 +/ ions are located at the sites in the supercage. Upon the introduction of water vapor, the Ag/sup 2 +/ disappeared, suggesting that the polarization of water may result in the transfer of negative charge from anion center irradiation, and reduce the ion to Ag/sup +/. The effect of pretreatment temperature on the intensity of the Ag/sup 2 +/ spectrum increases up to 350/sup 0/, then it gradually decreases as the temperature increases, indicating that the zeolite structure can no longer stabilize the Ag/sup 2 +/ ion. The exposure of ..gamma..-irradiated Ag-X to pyridine changed the ESR spectrum showing 8 superhyperfine lines due to nitrogen nuclei, indicating 2 or 3 pyridine molecules adsorbed on one silver ion. The ESR spectrum of Ag/sup 2 +/ disappearedmore » upon heating the ..gamma..-irradiated sample to 150/sup 0/C, while the spectrum with nitrogen superhyperfine lines disappeared at 100/sup 0/C.« less

Dielectric studies of zeolite systems. Part 2.—Ag-X zeolite with dipolar and non-dipolar absorbates

Studies have been made over the range 6 Hz to 130 kHz and 170 to 450 K of dielectric absorptions in Ag-X zeolite evacuated at 10–5 Torr and 520 K and also with controlled contents of H2O, NH3, CH3CN or C6H6: adsorption isotherms were measured simultaneously. Introduction of a Teflon film with the compacted dielectric disc gave blocking-electrode conditions when the d.c. conductance was disturbingly large. In addition to this d.c. ionic conductance a separate dielectric absorption (I) was measured in the zeolite itself and further distinct processes, absorption II and III were characterized both in frequency and intensity (via Fuoss–Kirkwood parameters) and in activation enthalpy and entropy terms (via Eyring parameters). Processes I and II arise from ion-jumping within the lattice and are discussed in relation to their most probable mechanisms. Absorption III in Ag-X/H2O is due to H2O reorientation: it appears (sharply) at H2O contents above 160 molecules per unit cell and has an effective strength (µeff≈ 1.8 D) equivalent to that of the free H2O molecule.

Adsorption in AgX and AgY zeolites by carbon monoxide and other simple molecules

Carbon monoxide was strongly adsorbed in AgX and AgY zeolites to the extent of four molecules per supercage at 25 °C. An intense infrared absorption band was observed at 2195 cm −1, which was only slightly affected by preadsorbed ammonia. The isosteric heats of adsorption were 19.2 kcal/mole for AgX and 15.1 kcal/mole for AgY at very low coverages. More nitrogen was adsorbed in AgX than in AgY with heat of adsorption as high as 8.2 kcal/mole at a coverage of 0.1 mmole/g. In the AgY sample, the heat was only 4.6 kcal/mole. The specific adsorption was due to higher silver content in the AgX zeolite, which also had higher heats for the adsorption of carbon monoxide and carbon dioxide. The adsorption of oxygen at 25 °C in both zeolites was negligibly small. In addition to the initial reversible adsorption, a small amount of nitric oxide was slowly adsorbed in AgY. No migration of silver ions, when ammonia was adsorbed, could be inferred from adsorption measurement. No specific adsorption of carbon monoxide in AgX and AgY and of nitrogen in AgX was observed when the samples had been treated with carbon monoxide at 350 °C. Silver ions were probably reduced after this treatment.

ADSORPTIVE AND GAS CHROMATOGRAPHIC PROPERTIES OF VARIOUS CATIONIC FORMS OF ZEOLITE X

Gas chromatographic retention volumes for O2, N2, CH4, C2H6, C3H8, C4H10, C2H4, and C3H6 have been measured over a range of temperatures between 25 and 400 °C, on columns of the following ion-exchanged forms of zeolite X: Li+, Na+, K+, Mg++, Ca++, Ba++, and Ag+. In addition, for AgX zeolite, full isotherms have been determined for O2, N2, C2H6, and C2H4; and for NaX zeolite, isotherms for C2H6 and C2H4. The gas chromatographic retention volumes agree well with the isotherms in the case of NaX but are significantly low for AgX, presumably as the result of at least a portion of the adsorption process being slow. The heats of adsorption on NaX agree well with literature values for O2, N2, CH4, and C2H6 but are low for C3H8 and C4H10; further indication of slow processes and hence of a limitation of the g.c. technique. The observations can be correlated qualitatively in terms of the interplay of the following effects: (a) cationic field increases with decreasing ionic radius; (b) shielding of smaller cations is greater—at least in the six-membered oxygen-ring sites; (c) divalent cations, while having greater fields, are only half the number of monovalent cations and tend to be found in less exposed sites; and (d) the polarizing power of silver ion, which also occupies all types of exposed sites, is very strong. The most intense interactions were found with AgX; with ethylene a much stronger complex is formed than has been reported for any other silver compound. The significance of molecular quadrupole interactions on these heteroionic surfaces is shown by the much weaker cationic effects observed with O2 (which has negligible quadrupole moment) than with nitrogen.