Studies of isotopic exchange between gaseous hydrogen and palladium hydride powder

Foltz, G. W.; Melius, Carl F.

doi:10.1016/0021-9517(87)90189-8

Cited by 33 publications

(31 citation statements)

References 15 publications

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“…This refers to the experimental observation that D→H exchanges are faster than H→D exchanges. In other words, the evolution of hydrogen from a bed loaded with hydrogen and dosed with deuterium is faster than the evolution of deuterium from a bed dosed by hydrogen [5]. The purpose of this study was to determine whether the simulated exchange process in a single spherical Pd particle could produce the observed effect.…”

Section: Calculations For Analysismentioning

confidence: 99%

“…where the dimensionless activity is: (6) and substituting the preceding equation into (3) specifies that…”

Section: Interdiffusion Of Two Species On a Latticementioning

confidence: 99%

“…There have been a number of models created for hydrogen exchange in a bed, but none of them treat the exchange process in the metal particles with the fidelity of this model [1][2][3][4][5][6][7][8][9]. In the SPEM model, the interaction between the two isotopes in the interstitial sites of the metal hydride is described with a fundamental physical model rather than with phenomenological parameters.…”

Section: Introductionmentioning

confidence: 99%

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Diffusional exchange of isotopes in a metal hydride sphere.

Wolfer¹,

Hamilton²,

James³

2011

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This report describes the Spherical Particle Exchange Model (SPEM), which simulates exchange of one hydrogen isotope by another hydrogen isotope in a spherical metal hydride particle. This is one of the fundamental physical processes during isotope exchange in a bed of spherical metal particles and is thus one of the key components in any comprehensive physics-based model of exchange. There are two important physical processes in the model. One is the entropy of mixing between the two isotopes; the entropy of mixing is increased by having both isotopes randomly placed at interstitial sites on the lattice and thus impedes the exchange process. The other physical process is the elastic interaction between isotope atoms on the lattice. The elastic interaction is the cause for -phase formation and is independent of the isotope species.In this report the coupled diffusion equations for two isotopes in the -phase hydride are solved. A key concept is that the diffusion of one isotope depends not only on its concentration gradient, but also on the concentration gradient of the other isotope. Diffusion rate constants and the chemical potentials for deuterium and hydrogen in the -phase hydride are reviewed because these quantities are essential for an accurate model of the diffusion process. Finally, a summary of some of the predictions from the SPEM model are provided.5

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Section: Calculations For Analysismentioning

confidence: 99%

“…where the dimensionless activity is: (6) and substituting the preceding equation into (3) specifies that…”

Section: Interdiffusion Of Two Species On a Latticementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diffusional exchange of isotopes in a metal hydride sphere.

Wolfer¹,

Hamilton²,

James³

2011

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“…In this section we summarize an attempt to fit the data from the slow and nearly isothermal exchange experiments of Foltz and Melius [30] with the TPLUG model, using the reaction mechanism consisting of (R1)-(R6) (neglecting (R4) initially, but including it later). The modeling work carried out by F&M is not a primary concern here, but some aspects of it are discussed below and in Appendix D.…”

Section: Application To the Foltz And Melius Experimentsmentioning

confidence: 99%

“…Obviously, this procedure is most likely to give reasonable results if the experimental conditions do not seriously violate the assumptions underlying the reactor model. We have therefore chosen to focus on the slow and nearly isothermal exchanges carried out by Foltz and Melius (F&M) [30][31][32]. They studied both D→H (slightly exothermic replacement of dissolved D with H) and H→D (slightly endothermic replacement of dissolved H with D), and both processes are simulated here with the same reaction mechanism (all steps being reversible).…”

Section: Introductionmentioning

confidence: 99%

Isotope exchange kinetics in metal hydrides I : TPLUG model.

Larson¹,

James²,

Nilson³

2011

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A one-dimensional isobaric reactor model is used to simulate hydrogen isotope exchange processes taking place during flow through a powdered palladium bed. This simple model is designed to serve primarily as a platform for the initial development of detailed chemical mechanisms that can then be refined with the aid of more complex reactor descriptions. The onedimensional model is based on the Sandia in-house code TPLUG, which solves a transient set of governing equations including an overall mass balance for the gas phase, material balances for all of the gas-phase and surface species, and an ideal gas equation of state. An energy equation can also be solved if thermodynamic properties for all of the species involved are known. The code is coupled with the Chemkin package to facilitate the incorporation of arbitrary multistep reaction mechanisms into the simulations. This capability is used here to test and optimize a basic mechanism describing the surface chemistry at or near the interface between the gas phase and a palladium particle. The mechanism includes reversible dissociative adsorptions of the three gas-phase species on the particle surface as well as atomic migrations between the surface and the bulk. The migration steps are more general than those used previously in that they do not require simultaneous movement of two atoms in opposite directions; this makes possible the creation and destruction of bulk vacancies and thus allows the model to account for variations in the bulk stoichiometry with isotopic composition. The optimization code APPSPACK is used to adjust the mass-action rate constants so as to achieve the best possible fit to a given set of experimental data, subject to a set of rigorous thermodynamic constraints. When data for nearly isothermal and isobaric deuterium-to-hydrogen (D→H) and hydrogen-to-deuterium (H→D) exchanges are fitted simultaneously, results for the former are excellent, while those for the latter show pronounced deviations at long times. These discrepancies can be overcome by postulating the presence of a surface poison such as carbon monoxide, but this explanation is highly speculative. When the method is applied to D→H exchanges intentionally poisoned by known amounts of CO, the fitting results are noticeably degraded from those for the nominally CO-free system but are still tolerable. When TPLUG is used to simulate a blowdown-type experiment, which is characterized by large and rapid changes in both pressure and temperature, discrepancies are even more apparent. Thus, it can be concluded that the best use of TPLUG is not in simulating realistic exchange scenarios, but in extracting preliminary estimates for the kinetic parameters from experiments in which variations in temperature and pressure are intentionally minimized.5

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A Numerical model of exchange chromatography through 3‐D lattice structures

Salloum

Robinson

2018

AIChE Journal

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in Wiley Online Library (wileyonlinelibrary.com) Rapid progress in the development of additive manufacturing technologies is opening new opportunities to fabricate structures that control mass transport in three dimensions across a broad range of length scales. We describe a structure that can be fabricated by newly available commercial 3-D printers. It contains an array of regular threedimensional flow paths that are in intimate contact with a solid phase, and thoroughly shuffle material among the paths. We implement a chemically reacting flow model to study its behavior as an exchange chromatography column, and compare it to an array of 1-D flow paths that resemble more traditional honeycomb monoliths. A reaction front moves through the columns and then elutes. The front is sharper at all flow rates for the structure with three-dimensional flow paths, and this structure is more robust to channel width defects than the 1-D array.

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Studies of isotopic exchange between gaseous hydrogen and palladium hydride powder

Cited by 33 publications

References 15 publications

Diffusional exchange of isotopes in a metal hydride sphere.

Diffusional exchange of isotopes in a metal hydride sphere.

Isotope exchange kinetics in metal hydrides I : TPLUG model.

A Numerical model of exchange chromatography through 3‐D lattice structures

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