Microstructured reformers

Figure 2 shows the microstructure of a sample of C-0.5Mo steel damaged by internal decarburization and Assuring. The service conditions were 790°F (421°C) at a hydrogen partial pressure of 425 pounds per square inch absolute (2.9 megapascals) for approximately 65,000 hours in a catalytic reformer. 

Pfeifer, P., Fichtner, M., Schubert, K., Liauw, M. A., Emig, G., Microstructured catalysts for methanol-steam reforming, in Ehrfeld, W. (Ed.), Microreaction Technology 3rd International Conference on Microreaction Technology, Proc. ofIMRET 3, Springer-Verlag, Berlin, 2000, 372-382. 

Hessel, V., Microstructured Reformer for fuel-cell applications, in Proceedings of the 3rd International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion, PowerMEMS (4—5 Dec. 2003), Global Emerging Technology Institute, New York, Makuhari, Japan, 2003. 

Kurr P, et al. Microstructural characterization of Cu/Zn0/Al203 catalysts for methanol steam reforming - a comparative study. Appl Catal A Gen. 2008 348(2) 153-64. 

Zhang XR, et al. A unique microwave effect on the microstructural modification of Cu/ZnO/Al2C>3 catalysts for steam reforming of methanol. Chem Commun. 2005(32) 4104-6. 

Gunter et al. (2001) XAS, TGA Cu/ZnO Microstructure of activated copper nanoparticles, detection of strain + n.a Methanol synthesis/ steam reforming... 

Cao, C., Wang, Y., and Rozmiarek, R.T. Heterogeneous reactor model for steam reforming of methane in a microchannel reactor with microstructured catalysts. Catalysis Today, 2005,110 (1—2), 92. 

The introduction of the catalyst presents one of the main problems in using MSRs for heterogeneously catalyzed reactions. There are some examples of reactors that are constructed directly from the catalytically active material. Kestenbaum et al. [145] used silver foils for the construction of a microchannel reactor for the partial oxidation of ethene to oxirane. A similar concept was proposed by Fichtner et al. [91,146], These authors used a microstructured rhodium catalyst for the partial oxidation of methane to syngas. This reaction can be considered as a coupling of the exothermic oxidation and the endothermic reforming of methane, which occur at different reaction rates. In such a case, the formation of a pronounced axial temperature profile can be avoided through the use of a material with high thermal conductivity. The reactor... 

P. Reuse, Production dTiydrogene dans un reacteur microstructure. Couplage themi-que entre le steam reforming et l oxydation totale du methanol, Ecole polytechnique federate de Lausanne, Lausanne, 2003. 

Fig. 6.13 Example of a heavy-pilot microstructured heat exchanger integrated 5 kW i reactor-heat exchanger system for selective oxidation to achieve gas purification of H2-rich reformer gas for fuel cells. (Source IMM.)...

Emphasize endothermic steam reformation to best take advantage of unique heat and mass transfer advantages available in engineered microstructures. 

Chemical stability of the membrane material is another key point. In order to run the reforming reaction at a low temperature without significant coke formation, the amount of steam in the reforming mixture must be reasonably high. Hence the membrane material must be stable against the water vapor corrosion. However, water vapor is not the only corrosive medium inside the reformer. Gases such as CO, CO2 as well as H2 can also react with membrane materials and destroy their microstructure. Reactions between catalyst/catalyst-additives and membrane materials are possible as well. All these possibilities demand membrane materials with... 

A large variety of catalysts for the steam reforming of methanol which include copper in their composition have been reported. " Commercial Cu/ZnO water-gas shift and methanol synthesis catalysts - have also been found to be active for the steam reforming reaction. Microstructural characteristics of the copper phase in Cu/ZnO catalysts depended on the aging time of the precipitate, resulting in changes in reducibility and crystallite size which produced an increase in the catalytic activity. Moreover,... 

Yu et al. [36] used metal foams as catalyst supports for a microstructured methanol reformer and investigated the infiuence of the foam material on the catalyst s selectivity and activity. Some electrically conducting materials such as silicon carbide (SiC) [37] are used as a foam as well as internal heating element, and the reactor can be heated very rapidly to temperatures in the range 800-1000 °C. Moreover, as a result of the high thermal conductivity of metal or SiC foams, axial and radial temperature profiles are minimized and nearly isothermal reactor operation is facihtated. 

Foams were proved to be highly suitable as catalytic carrier when low pressure drop is mandatory. In comparison to monoliths, they allow radial mixing of the fluid combined with enhanced heat transfer properties because of the solid continuous phase of the foam structure. Catalytic foams are successfully used for partial oxidation of hydrocarbons, catalytic combustion, and removal of soot from diesel engines [14]. The integration of foam catalysts in combination with microstructured devices was reported by Yu et al. [15]. The authors used metal foams as catalyst support for a microstructured methanol reformer and studied the influence of the foam material on the catalytic selectivity and activity. Moritz et al. [16] constructed a ceramic MSR with an inserted SiC-foam. The electric conductive material can be used as internal heating elements and allows a very rapid heating up to temperatures of 800-1000°C. In addition, heat conductivity of metal or SiC foams avoids axial and radial temperature profiles facilitating isothermal reactor operation. 

Figure 23.3 Methane steam reformer (built at the Forschungszentrum Karlsruhe) made of high-temperature steel and SEM of microstructure [38].

A rapidly increasing number of publications deal with steam reforming of fossil and renewable fuels in microstructured reactors. In most cases, the appUcation standing behind this work is the generation of hydrogen for portable, mobile and small-scale stationary fuel cell systems as future distributed source of electrical energy. 

Reuse et al. [16] applied a self-developed reactor carrying microstructured plates for the determination of methanol steam reforming kinetics over a commercial copper-based low-temperature water gas shift catalyst from Siid-Cliemie. Kinetic expressions were determined for both a tubular fixed-bed reactor containing 30 mg of catalyst particles and the microreactor coated with the catalyst particles. A power law... 

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