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Title: Adsorption Equilibrium and Modeling of Water Vapor on Reduced and Unreduced Silver-Exchanged Mordenite

Abstract

This work is related to the removal of tritiated water and radioactive iodine from off-gases released during spent nuclear fuel reprocessing. Specifically, it is focused on the adsorption equilibrium of water on reduced silver mordenite (Ag 0Z), which is the state-of-art solid adsorbent for iodine retention in the off-gas treatment. As the off-gases contain different gas species, including iodine and water, Ag 0Z would take up iodine and water simultaneously during the adsorption process. Therefore, understanding the adsorption of water on Ag 0Z is important and necessary for studying the performance of Ag 0Z in off-gas treatment processes. The isotherms of water (nonradioactive water) on Ag 0Z were obtained at temperatures of 25, 40, 60, 100, 150, and 200 °C with a continuous-flow adsorption system. The data were analyzed using the Heterogeneous Langmuir and generalized statistical thermodynamic adsorption (GSTA) models, and thermodynamic parameters of the isotherms were obtained from both models. Both models were found capable of describing the isotherms. Isotherms of water on the unreduced silver mordenite (AgZ) were also obtained at 25, 40, and 60 °C and parametrized by the GSTA model. Through the comparison of the isotherms of Ag 0Z and AgZ, it was found that Agmore » 0Z had a higher water adsorption capacity than AgZ. The comparison of their thermodynamic parameters suggested that the interaction of water molecules with the H + in Ag 0Z was stronger than that with the Ag + in AgZ.« less

Authors:
ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [2];  [2];  [3]; ORCiD logo [1]
  1. Syracuse Univ., NY (United States)
  2. Georgia Inst. of Technology, Atlanta, GA (United States)
  3. Georgia Inst. of Technology, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1399935
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Industrial and Engineering Chemistry Research
Additional Journal Information:
Journal Volume: 56; Journal Issue: 28; Journal ID: ISSN 0888-5885
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Nan, Yue, Lin, Ronghong, Liu, Jiuxu, Crowl, Tyler B., Ladshaw, Austin, Yiacoumi, Sotira, Tsouris, Costas, and Tavlarides, Lawrence L. Adsorption Equilibrium and Modeling of Water Vapor on Reduced and Unreduced Silver-Exchanged Mordenite. United States: N. p., 2017. Web. doi:10.1021/acs.iecr.7b01180.
Nan, Yue, Lin, Ronghong, Liu, Jiuxu, Crowl, Tyler B., Ladshaw, Austin, Yiacoumi, Sotira, Tsouris, Costas, & Tavlarides, Lawrence L. Adsorption Equilibrium and Modeling of Water Vapor on Reduced and Unreduced Silver-Exchanged Mordenite. United States. doi:10.1021/acs.iecr.7b01180.
Nan, Yue, Lin, Ronghong, Liu, Jiuxu, Crowl, Tyler B., Ladshaw, Austin, Yiacoumi, Sotira, Tsouris, Costas, and Tavlarides, Lawrence L. Mon . "Adsorption Equilibrium and Modeling of Water Vapor on Reduced and Unreduced Silver-Exchanged Mordenite". United States. doi:10.1021/acs.iecr.7b01180.
@article{osti_1399935,
title = {Adsorption Equilibrium and Modeling of Water Vapor on Reduced and Unreduced Silver-Exchanged Mordenite},
author = {Nan, Yue and Lin, Ronghong and Liu, Jiuxu and Crowl, Tyler B. and Ladshaw, Austin and Yiacoumi, Sotira and Tsouris, Costas and Tavlarides, Lawrence L.},
abstractNote = {This work is related to the removal of tritiated water and radioactive iodine from off-gases released during spent nuclear fuel reprocessing. Specifically, it is focused on the adsorption equilibrium of water on reduced silver mordenite (Ag0Z), which is the state-of-art solid adsorbent for iodine retention in the off-gas treatment. As the off-gases contain different gas species, including iodine and water, Ag0Z would take up iodine and water simultaneously during the adsorption process. Therefore, understanding the adsorption of water on Ag0Z is important and necessary for studying the performance of Ag0Z in off-gas treatment processes. The isotherms of water (nonradioactive water) on Ag0Z were obtained at temperatures of 25, 40, 60, 100, 150, and 200 °C with a continuous-flow adsorption system. The data were analyzed using the Heterogeneous Langmuir and generalized statistical thermodynamic adsorption (GSTA) models, and thermodynamic parameters of the isotherms were obtained from both models. Both models were found capable of describing the isotherms. Isotherms of water on the unreduced silver mordenite (AgZ) were also obtained at 25, 40, and 60 °C and parametrized by the GSTA model. Through the comparison of the isotherms of Ag0Z and AgZ, it was found that Ag0Z had a higher water adsorption capacity than AgZ. The comparison of their thermodynamic parameters suggested that the interaction of water molecules with the H+ in Ag0Z was stronger than that with the Ag+ in AgZ.},
doi = {10.1021/acs.iecr.7b01180},
journal = {Industrial and Engineering Chemistry Research},
number = 28,
volume = 56,
place = {United States},
year = {Mon Jun 26 00:00:00 EDT 2017},
month = {Mon Jun 26 00:00:00 EDT 2017}
}

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  • The adsorption process of iodine, a major volatile radionuclide in the off-gas streams of spent nuclear fuel reprocessing, on hydrogen-reduced silver-exchanged mordenite (Ag 0Z) was studied at the micro-scale. The gas-solid mass transfer and reaction involved in the adsorption process were investigated and evaluated with appropriate models. Optimal conditions for reducing the silver-exchanged mordenite (AgZ) in a hydrogen stream were determined. Kinetic and equilibrium data of iodine adsorption on Ag 0Z were obtained by performing single-layer adsorption experiments with experimental systems of high precision at 373–473 K over various iodine concentrations. Results indicate approximately 91% to 97% of the iodinemore » adsorption was through the silver-iodine reaction. The effect of temperature on the iodine loading capacity of Ag 0Z was discussed. In conclusion, the Shrinking Core model describes the data well, and the primary rate controlling mechanisms were macro-pore diffusion and silver-iodine reaction. © 2016 American Institute of Chemical Engineers AIChE J, 2016« less
  • Capture of radioactive iodine is a significant consideration during reprocessing of spent nuclear fuel and disposal of legacy wastes. While silver-exchanged mordenite (AgZ) is widely regarded as a benchmark material for assessing iodine adsorption performance, previous research efforts have largely focused on bulk material properties rather than the underpinning molecular interactions that achieve effective iodine capture. As a result, the fundamental understanding necessary to identify and mitigate deactivation pathways for the recycle of AgZ is not available. In this paper, we applied X-ray Absorption Fine Structure (XAFS) spectroscopy to investigate AgZ following activation, adsorption of iodine, regeneration, and recycle, observingmore » no appreciable degradation in performance due to the highly controlled conditions under which the AgZ was maintained. Fits of the extended XAFS (EXAFS) data reveal complete formation of Ag 0 nanoparticles upon treatment with H 2, and confirm the formation of α-AgI within the mordenite channels in addition to surface γ/β-AgI nanoparticles following iodine exposure. Analysis of the nanoparticle size and fractional composition of α-AgI to γ/β-AgI supports ripening of surface nanoparticles as a function of recycle. Finally, this work provides a foundation for future investigation of AgZ deactivation under conditions relevant to spent nuclear fuel reprocessing.« less
  • To remove lead from petrol and thereby promote a cleaner environment, other means must be found to keep the octane number or anti-knock qualities of the petrol high. It is found that this can be accomplished by increasing the proportion of highly branched chain hydrocarbon isomers in the fuel. This in turn promotes processes for the separation of the hydrocarbon isomers and in the case of hexane, it is an easy matter to separate out n-hexane from the more substituted isomers but it is difficult to separate out the mono- from the di-branched isomers. This work addresses itself to suchmore » challenging separations using modified zeolites as the separating agent, and by studying the heats of sorption of these isomers on zeolites using gas chromatographic techniques to find a trend in the potential abilities of these modified zeolites to effect a good separation. In this work mordenite zeolite was modified by a range of double cation exchanges and the resulting modified zeolites were investigated for their ability to sorb the hexane isomers 3-methylpentane and 2,3-dimethylbutane. These two isomers are closely related in size as they both have the same kinetic diameter of 0.56 nm. In this work only heats of sorption have been investigated and measurement of the diffusion coefficients, which also affect the ability of the modified zeolites to act as good separating agents, is currently under investigation.« less
  • The adsorption of ammonia and other simple molecules on an activated Eu(III) ion exchanged mordenite (Eu-M) has been studied by the measurement of the luminescence of the Eu/sup 2 +/ ion, which was produced by dehydration at 500/sup 0/C. The emission peak of the Eu/sup 2 +/ ion shifted to a shorter wavelength on exposure to ammonia and other simple molecules. The magnitude of the shift was correlated to the specific dielectric constant of the adsorbate. The quantum yield for the Eu/sup 2 +/ emission bands decreased after the adsorption of NH/sub 3/ and CH/sub 3/CN. Also, the lifetime inmore » the Eu/sup 2 +/-adsorbate system was shorter than that in an activated Eu-M sample. The rate constant for the radiationless transitions was more sensitive to the nature of the adsorbate, and the order of the quenching power was CH/sub 3/CN > NH/sub 3/ > (CH/sub 2/NH/sub 2/)/sub 2/. 30 references, 6 figures, 4 tables.« less
  • The adsorption of oxygen in an activated europium ion-exchanged mordenite (Eu-M) was studied over the temperature range 25-600/sup 0/C by the measurement of fluorescence of Eu/sup 2 +/ ion and a temperature programmed desorption(TPD) spectra of oxygen. When oxygen was exposed to a activated Eu-M, the intensity of emission band for Eu/sup 2 +/ ion extremely decreased. After the adsorption of oxygen at room temperature, the emission intensity was increased with a rise of degassing temperature and restored to the original emission intensity above 300/sup 0/C. While, in Eu-M, at least four different states of adsorbed oxygen were indicated bymore » the appearance of four TPD peaks with peak maxima located at about 70/sup 0/C(..cap alpha..), 220/sup 0/C(..beta..), 300/sup 0/C(..gamma..) and >500/sup 0/C(delta). The intensity of TPD peaks was dependent on the adsorption temperature. In the case of adsorption at 300/sup 0/C or 600/sup 0/C, the total amount of desorbed oxygen corresponded to one oxygen molecule adsorbing per Eu/sup 2 +/ ion.« less