Palladium membrane, catalytic

Effect of a Model Hydrogenation on a Catalytic Palladium Membrane... 

M. Arai, K. Yamada, and Y. Nishiyama, Evolution and separation of hydrogen in the photolysis of water using titania-coated catalytic palladium membrane reactor, 7. Chem, Eng, Jap, 25 761 (1992). 

M. Arai, Y. Wada, and Y. Nishiyama, Thiophene hydrodesulfurization by catalytic palladium membrane systems, Sekiyu Cakkaishi 36 44 (1993). 

Lin, Y.M. and M.H. Rei, Separation of hydrogen from the gas mixture out of a catalytic reformer by using supported palladium membrane, Sep. Purif. Technol., 25,87-95,2001a. 

Nazarkina, E. B. and N. A. Kirichenko 1979. Improvement in the steam catalytic conversion of methane by hydrogen liberation via palladium membranes Khim. Tekhnol. Topi. Masel. 3 5-10. 

Kurungot et al. [48] developed a novel membrane material and a catalytic membrane reactor for the partial oxidation of methane. The driver of the development was the fact that rates of reforming reactions are much higher compared with the low permeability of conventional palladium membranes [49], Silica was previously recognized as a low-cost alternative to palladium [50], Additionally, the conventional... 

In addition to packed and wall-coated systems, numerous researchers have investigated the fabrication of membranes, within microchannels, in which catalytic material can be incorporated. Employing a protocol developed by Kenis et al. (1999), Uozumi et al. (2006) deposited a poly(acryla-mide)-triarylphosphane palladium membrane (PA-TAP-Pd) (1.3 pm (wide), 0.37 mmol g-1 Pd) within a glass microchannel [100 pm (wide) x40pm (deep) x 1.4 cm (long)]. Once formed, the membrane was used to catalyze a series of Suzuki-Miyaura C-C bond-forming reactions, the results of which are summarized in Table 21. 

In spite of the advances made by these researchers, it remains unclear how membrane surfaces undergo restructuring and how these changes influence the catalytic and transport properties of the material. Furthermore, there is a need to link surface structure and composition with long-term performance of palladium membranes under continuous reaction conditions. One... 

Lin Y.-M., Rei M.-H. An integrated purification and production of hydrogen with a palladium membrane-catalytic reactor. Catalysis Today 1998 44 343-349. 

Liu, Y. Dixon, A. Ma, Y. Moser, W. Permeation of Ethylbenzene and Hydrogen Through Untreated and Catalytically Treated Alumina Membranes Separation Science and Technology 25 (1990) 1511- 1521. Mardilovich, P. She, Y. Ma, Y. Rei, M. Defect-Free Palladium Membranes on Porous Stainless Steel Support AIChEJ 44(2) (1998) 310-322. 

A catalytically active membrane was obtained by mixing palladium on carbon, [C4Ciim][PF6] and a poly(vinylidene fluoride) co-polymer.[81] The presence of the ionic liquid increases the flexibility of the system and thus... 

In the case of catalytic dense membranes such as palladium alloy sheets or tubes, a smooth membrane surface suffers from a small active surface area per unit volume of catalyst. This drawback can be remedied to some extent by adopting some conventional catalyst preparation methods to roughen the membrane suiface(s) to ensure that only the region near the surface is affected unlike the Raney metal catalysts where the entire matrix is leached. For example, Gryaznov [1992] suggested the use of thermal diffusion of a chemically active metal into a Pd alloy sheet followed by acid treatment to remove this metal. 

Not only the permeability, permselectivity and mechanical properties, but also the catalytic properties are affected by the two hydride forms that can exist in palladium. The a phase corresponds to solid solutions with a H/Pd ratio of about 0.1 and the P phase with a H/Pd ratio of about 0.6. The phase change is associated with a large change in lattice constant that often leads to microcracks and distortion in the palladium membrane. As a result, the mechanical properties are reduced. The transformation depends on the operating conditions such as temperature and hydrogen partial pressure. Repeated thermal cycles, for example, between 100 and 250 C under 1 atm of hydrogen pressure can make a 0.1 mm thick Pd foil expand to become 30 times thicker [Armor, 1992]. 

The alloying of palladium with some other metals permits one to overcome the disadvantages of pure palladium and to prepare the materials with a hydrogen permeability above that of palladium. The insertion of a second and a third component into the palladium membrane may increase its mechanical strength, the hydrogen solubility, and catalytic activity of the membrane toward hydrogen dissociation. This was discussed in many original papers and reviews [26-36]. 

Takeuchi et al. 7 reported a membrane reactor as a reaction system that provides higher productivity and lower separation cost in chemical reaction processes. In this paper, packed bed catalytic membrane reactor with palladium membrane for SMR reaction has been discussed. The numerical model consists of a full set of partial differential equations derived from conservation of mass, momentum, heat, and chemical species, respectively, with chemical kinetics and appropriate boundary conditions for the problem. The solution of this system was obtained by computational fluid dynamics (CFD). To perform CFD calculations, a commercial solver FLUENT has been used, and the selective permeation through the membrane has been modeled by user-defined functions. The CFD simulation results exhibited the flow distribution in the reactor by inserting a membrane protection tube, in addition to the temperature and concentration distribution in the axial and radial directions in the reactor, as reported in the membrane reactor numerical simulation. On the basis of the simulation results, effects of the flow distribution, concentration polarization, and mass transfer in the packed bed have been evaluated to design a membrane reactor system. 

---