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Effect of CO and O2 on hydrogen permeation through a palladium membrane
Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi.
Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad Fysik.
2000 (engelsk)Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 153, nr 4, s. 259-267Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Hydrogen permeation through a 25-µm thick palladium membrane during continuous exposures of hydrogen together with different combinations of oxygen and carbon monoxide has been studied at membrane temperatures of 100 °C-250 °C (total pressures of 40-150 Torr). Both CO and O2, individually, inhibit hydrogen permeation through the membrane. The cause of the inhibition is, however, somewhat different. CO blocks available hydrogen dissociation sites, while oxygen both blocks dissociation sites and also consumes adsorbed hydrogen through the production of water. When a combination of CO and O2 is supplied together with hydrogen, new reaction pathways will emerge. The carbon dioxide formation will dominate the water forming reaction, and consequently, the blocking effect caused by the formation of water will be suppressed. In a mixture of CO+O2+H2, the hydrogen permeation can become either larger or smaller than that due to only O2+H2 or CO+H2 depending on the CO/O2 ratio. It is thus possible to find a situation where carbon monoxide and oxygen react to form CO2 leaving adsorbed hydrogen free to permeate the membrane.

sted, utgiver, år, opplag, sider
2000. Vol. 153, nr 4, s. 259-267
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-47729DOI: 10.1016/S0169-4332(99)00357-8OAI: oai:DiVA.org:liu-47729DiVA, id: diva2:268625
Tilgjengelig fra: 2009-10-11 Laget: 2009-10-11 Sist oppdatert: 2021-12-01
Inngår i avhandling
1. Hydrogen Extraction with Palladium Based Membranes
Åpne denne publikasjonen i ny fane eller vindu >>Hydrogen Extraction with Palladium Based Membranes
2000 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Palladium membranes are commercially used to purify hydrogen gas and in dehydrogenation reactions. The combination of the catalytic ability of the membrane surface and the selectivity of hydrogen permeation offers a tool to extract pure hydrogen and to shift a dehydrogenation reaction towards the product side. In this thesis, hydrogen extraction over palladium and palladium-silver based membranes both from different gas mixtures and from dehydrogenated organic molecules is investigated. The aim has been to find the optimal conditions for hydrogen extraction in different environments.

The hydrogen permeation rate has been shown to depend on both silver concentration on the surface and in the bulk of a palladium based membrane. The diffusion through the membrane is the rate limiting step in the permeation process of most studied membranes. For a palladium membrane with 20 Å silver deposited on the upstream surface, the surface reactions, however, become rate limiting.

Co-adsorbed oxygen will inhibit hydrogen permeation by blocking hydrogen adsorption sites and by consuming already adsorbed hydrogen in the water forming reaction on Pd membrane surfaces. On Pd70Ag30 membranes, however, oxygen has no effect on the hydrogen permeation rate, mainly due to an effective hydrogen dissolution into silver and a strongly reduced water formation rate. CO blocks hydrogen adsorption sites on both Pd and PdAg membranes effectively below 150°C, but above 300°C, CO has almost no effect on hydrogen permeation.

Hydrogen can also be extracted through the dehydrogenation of organic molecules. A steady and continuous dehydrogenation of methanol and ethanol, and a subsequent hydrogen permeation, can be maintained in the presence of oxygen through both Pd and PdAg membranes. Without oxygen, a blocking contaminating layer is formed from the decomposition products, which prevents alcohol adsorption and thus also the hydrogen permeation. The hydrogen yield is larger over PdAg membranes than over Pd membranes mainly due to a smaller hydrogen consumption in the water forming reaction, but also due to a larger conversion of the alcohol on PdAg.

The long time objective of this research has been to develop a method to extract hydrogen from anaerobic bacteria degradation of organic waste material in a co-operation project with microbiologists at the Department of Water and Environmental Studies at Linköping University. The selectivity towards hydrogen permeation in palladium membranes offers a tool to obtain clean hydrogen, which can be used as an energy carrier. By draining the bacteria culture of hydrogen, and thereby reducing the partial pressure of hydrogen, the fermentation process is directed towards a higher production of hydrogen.

sted, utgiver, år, opplag, sider
Linköping: Linköping University, 2000. s. 55
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 651
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-181555 (URN)917219832X (ISBN)
Disputas
2000-10-20, Planck, Fysikhuset, Linköpings universitet, Linköping, 10:20
Opponent
Tilgjengelig fra: 2021-12-01 Laget: 2021-12-01 Sist oppdatert: 2023-03-13bibliografisk kontrollert

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