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Title: Adsorption and Transport Properties of Zeolite SAPO-34 for Krypton/Xenon Separations

Abstract

Nuclear power is an economical means of providing carbon-free energy, but requires effective ways to deal with the radioactive waste products. As part of the overall process for recycling used nuclear fuel (UNF), it is necessary to develop technologies to separate the off-gases formed during the fission of uranium and plutonium in nuclear power reactors. The off-gas contains {sup 129}I (radioisotope), NO, NO{sub 2}, CO{sub 2} containing {sup 14}C (radioisotope), {sup 3}H{sub 2}O (radioactive tritium oxide), {sup 85}Kr (radioisotope), and {sup 136}Xe. Separating and capturing each gas is essential to reduce the volume of radioactive waste for storage. Currently there exist economical technologies to separate {sup 129}I and {sup 14}CO{sub 2}. However, Kr and Xe separation is challenging because they are chemically inert and physically very similar. The Kr/Xe mixture is approximately 10/90 by volume and hence the separation of Kr would reduce the volume of radioactive {sup 85}Kr waste by a factor of 10. One way of separating them is by cryogenic distillation wherein they are condensed out as pure streams at very low temperature (Kr boiling point: -153 deg. C, Xe: -108 deg. C). Cryogenic distillation has intensive power requirements and a large system volume, resulting in highmore » capital, operating, and disposal costs. Membrane-based separation using radiation-stable materials such as nanoporous zeolites is an attractive alternative, if membranes with sufficient Kr flux and selectivity can be fabricated. An ideal membrane process would permeate a stream of pure Kr for storage and also produce a retentate of pure Xe which has commercial value (> $8/g at 99+% purity from Airgas{sup R}). Zeolites are nanoporous crystalline aluminosilicate materials with pores that are capable of separating molecules by shape and size. SAPO-34 is a silicoaluminophosphate zeolite with pore size of 0.38 nm. The SAPO-34 is a molecular sieve composed of 3D networks with CHA frame structure containing uniform micropores. Since this pore size is intermediate between the kinetic diameters of krypton (0.36 nm) and xenon (0.396 nm), it was hypothesized that SAPO-34 membranes can separate krypton and xenon by diffusivity differences. Previously we fabricated SAPO-34 membranes and showed that they are capable of separating Kr from Xe. Here we describe a more detailed study of the fundamental adsorption and transport properties of SAPO34. In particular, the permeabilities of Kr and Xe in SAPO-34 are dependent on both their adsorption and diffusion characteristics in the nanoporous zeolite. Typically, nanoporous materials show stronger adsorption of Xe than Kr (due to stronger van der Waals forces) but faster diffusion of Kr (due to smaller kinetic diameter). Therefore the overall membrane selectivity towards Kr will be determined by competition between these two effects. A main objective of this study is to quantify and understand adsorption, diffusion, and permeation in detail and thereby obtain: (1) fundamental parameters useful for design calculations of a Kr/Xe separation membrane process, and (2) an experimental and modeling framework that can provide guidance on the expected limits of performance of SAPO-34 and other zeolite materials. (authors)« less

Authors:
; ; ; ;  [1];  [2]
  1. Georgia Institute of Technology, Atlanta, GA, 30332-0100 (United States)
  2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831 (United States)
Publication Date:
OSTI Identifier:
22991870
Resource Type:
Journal Article
Journal Name:
Transactions of the American Nuclear Society
Additional Journal Information:
Journal Volume: 114; Journal Issue: 1; Conference: Annual Meeting of the American Nuclear Society, New Orleans, LA (United States), 12-16 Jun 2016; Other Information: Country of input: France; 14 refs.; Available from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 United States; Journal ID: ISSN 0003-018X
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ADSORPTION; BOILING POINTS; CARBON 14; DISTILLATION; IODINE 129; KRYPTON; KRYPTON 85; MEMBRANES; MOLECULAR SIEVES; NUCLEAR FUELS; NUCLEAR POWER; NUCLEAR POWER PLANTS; PLUTONIUM; RADIOACTIVE WASTES; TRITIUM OXIDES; URANIUM; VAN DER WAALS FORCES; XENON 136; ZEOLITES

Citation Formats

Kwon, Yeon Hye, Benjamin, Emily, Pisharodi, Vivek, Hwang, Junyoung, Nair, Sankar, and Bhave, Ramesh. Adsorption and Transport Properties of Zeolite SAPO-34 for Krypton/Xenon Separations. United States: N. p., 2016. Web.
Kwon, Yeon Hye, Benjamin, Emily, Pisharodi, Vivek, Hwang, Junyoung, Nair, Sankar, & Bhave, Ramesh. Adsorption and Transport Properties of Zeolite SAPO-34 for Krypton/Xenon Separations. United States.
Kwon, Yeon Hye, Benjamin, Emily, Pisharodi, Vivek, Hwang, Junyoung, Nair, Sankar, and Bhave, Ramesh. Wed . "Adsorption and Transport Properties of Zeolite SAPO-34 for Krypton/Xenon Separations". United States.
@article{osti_22991870,
title = {Adsorption and Transport Properties of Zeolite SAPO-34 for Krypton/Xenon Separations},
author = {Kwon, Yeon Hye and Benjamin, Emily and Pisharodi, Vivek and Hwang, Junyoung and Nair, Sankar and Bhave, Ramesh},
abstractNote = {Nuclear power is an economical means of providing carbon-free energy, but requires effective ways to deal with the radioactive waste products. As part of the overall process for recycling used nuclear fuel (UNF), it is necessary to develop technologies to separate the off-gases formed during the fission of uranium and plutonium in nuclear power reactors. The off-gas contains {sup 129}I (radioisotope), NO, NO{sub 2}, CO{sub 2} containing {sup 14}C (radioisotope), {sup 3}H{sub 2}O (radioactive tritium oxide), {sup 85}Kr (radioisotope), and {sup 136}Xe. Separating and capturing each gas is essential to reduce the volume of radioactive waste for storage. Currently there exist economical technologies to separate {sup 129}I and {sup 14}CO{sub 2}. However, Kr and Xe separation is challenging because they are chemically inert and physically very similar. The Kr/Xe mixture is approximately 10/90 by volume and hence the separation of Kr would reduce the volume of radioactive {sup 85}Kr waste by a factor of 10. One way of separating them is by cryogenic distillation wherein they are condensed out as pure streams at very low temperature (Kr boiling point: -153 deg. C, Xe: -108 deg. C). Cryogenic distillation has intensive power requirements and a large system volume, resulting in high capital, operating, and disposal costs. Membrane-based separation using radiation-stable materials such as nanoporous zeolites is an attractive alternative, if membranes with sufficient Kr flux and selectivity can be fabricated. An ideal membrane process would permeate a stream of pure Kr for storage and also produce a retentate of pure Xe which has commercial value (> $8/g at 99+% purity from Airgas{sup R}). Zeolites are nanoporous crystalline aluminosilicate materials with pores that are capable of separating molecules by shape and size. SAPO-34 is a silicoaluminophosphate zeolite with pore size of 0.38 nm. The SAPO-34 is a molecular sieve composed of 3D networks with CHA frame structure containing uniform micropores. Since this pore size is intermediate between the kinetic diameters of krypton (0.36 nm) and xenon (0.396 nm), it was hypothesized that SAPO-34 membranes can separate krypton and xenon by diffusivity differences. Previously we fabricated SAPO-34 membranes and showed that they are capable of separating Kr from Xe. Here we describe a more detailed study of the fundamental adsorption and transport properties of SAPO34. In particular, the permeabilities of Kr and Xe in SAPO-34 are dependent on both their adsorption and diffusion characteristics in the nanoporous zeolite. Typically, nanoporous materials show stronger adsorption of Xe than Kr (due to stronger van der Waals forces) but faster diffusion of Kr (due to smaller kinetic diameter). Therefore the overall membrane selectivity towards Kr will be determined by competition between these two effects. A main objective of this study is to quantify and understand adsorption, diffusion, and permeation in detail and thereby obtain: (1) fundamental parameters useful for design calculations of a Kr/Xe separation membrane process, and (2) an experimental and modeling framework that can provide guidance on the expected limits of performance of SAPO-34 and other zeolite materials. (authors)},
doi = {},
url = {https://www.osti.gov/biblio/22991870}, journal = {Transactions of the American Nuclear Society},
issn = {0003-018X},
number = 1,
volume = 114,
place = {United States},
year = {2016},
month = {6}
}