Hydrogen separation dehydrogenation

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

N.V. Orekhova and N.A. Makhota, The Effect of Hydrogen Separation Through the Mem-branesfrom Palladium Alloys on Dehydrogenation of Butane, Membrane Catalysts Permeable for Hydrogen or Oxygen (in Russian), Moscow, Nauka, 1985, p. 49. 

Franz AJ, Schmidt MA, Jensen KF, and Firebaugh S. Integrated palladium-based micromembranes for hydrogen separation and hydrogenation/dehydrogenation reactions. US Patent 6,541,676, Apr 2003. 

The influence of substrate structure is briefly as follows. The active entity (H in hydrogenation and dehydrogenation reactions) must be adsorbed, even in the surface layer, in sites which make crystallographic sense, as these proper sites will be those of lowest potential energy on the surface. For example, atoms chemisorbed on metals will be located in interstitial surface sites which fall on the lattice of interstitial sites for the crystal as a whole. Adsorption immediately above surface atoms is improbable, adsorption in surface interstices probable. Diffusion into the solid from the surface is then by a path similar to the subsequent stages in the bulk solid. The oxygen atoms adsorbed on oxides will occupy proper anion lattice sites and will either create or destroy defects. The defects created will be able to diffuse immediately beneath the surface and appear at the site where their properties are required. Molecular reactants of any size cannot usually penetrate the catalyst surface, but atoms or radicals may be separated from them. The molecule itself is chemisorbed with efficiency only if certain structural inter-relations are satisfied. Beeck and coworkers (62) have demonstrated this adequately for the adsorption of ethylene on various metals and on various crystal planes of the same metal. The adsorption of gases... 

In all three, hydrogen separation will take place the dehydrogenation of propane to propylene, the dehydrogenation of ethylbenzene to styrene, and the water-gas shift reaction. 

We have made significant advances in hydrogen separating ceramic membrane (H-membrane) technology [10]. The purpose of this work is to demonstrate its application to catalytic dehydrogenation of ethane and assess the feasibility of enhancement of olefin production in a membrane reactor. 

Metallic membranes are not considered as belonging to ceramic membranes so that its related applications will not be discussed in detail. Ordinarily, these membranes are mainly made up of Pd-based alloys and are used for hydrogen separation and hydrogenation or dehydrogenation reaction control [175-177]. Metallic membranes exhibit high hydrogen separation... 

The compounds to be hydrogenated or dehydrogenated are separated from the hydrogen gas to react or to be formed, respectively, by a solid electrolyte diaphragm. 

In the following section, methods for the fabrication and deposition of Pd-based and zeolite MMs are discussed, as well as applications in (de) hydrogenation, SR, WGS, partial oxidation (POx) reactions and fine chemical synthesis. The research on Pd-based MMRs for hydrogen separation, purification and production (by dehydrogenation, SR and WGS reactions) has been selected as a case study, as significant research and, therefore, much information can be found in the literature on this field. 

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