Catalytic reactors for fuel processing

Decentralized and Mobile Energy Technology Department, Fraunhofer ICT-IMM, Mainz, Germany 

Steam reforming is the gas phase conversion of energy carriers such as hydrocarbons and alcohols described by the general formula CxHyOz with steam to a mixture of carbon monoxide and hydrogen according to the following reaction  

The product mixture of the reaction is named reformate. The reaction is endothermic and thus requires heat supply. Besides 

The WGS reaction increases the hydrogen concentration of the reformate. This reaction is usually fast enough at the elevated temperatures of hydrocarbon reforming to achieve thermodynamic equilibrium. Owing to its exothermic character, higher reaction temperatures favor the reverse reaction. 

Partial oxidation is the conversion of fuels under oxygen-deficient atmosphere  

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Fuel industry is of increasing importance because of the rapidly growing energy needs worldwide. Many processes in fuel industry, e.g. fluidized catalytic cracking (FCC) [1], pyrolysis and hydrogenation of heavy oils [2], Fischer-Tropsch (FT) synthesis [3,4], methanol and dimethyl ether (DME) synthesis [5,6], are all carried out in multiphase reactors. The reactors for these processes are very large in scale. Unfortunately, they are complicated in design and their scale-up is very difflcult. Therefore, more and more attention has been paid to this field. The above mentioned chemical reactors, in which we are especially involved like deep catalytic pyrolysis and one-step synthesis of dimethyl ether, are focused on in this paper. 

G. Kolb, V. Hessel, V. Cominos, et ol. Selective oxidations in micro-structured catalytic reactors—For gas-phase reactions and specifically for fuel processing for fuel cells. Catal. Today 2007, 120, 2-20. 

Membrane reactors (MRs) for fuel processing combine the unit operation of membrane separation with catalytic reactions such as reforming and WGS. The membrane separation process is usually performed by hydrogen removal from the reformate by application of membranes made of ceramics or palladium and palladium alloys, while polymeric membranes are less convenient for systems of smaller than industrial scale, because several separation steps are required owing to their relatively low selectivity of the separation process. In MRs the equilibrium... 

Gorgiin et al. presented the developments of observers for fuel processing reactors such as a partial oxidation reformer, tvater-gas shift and preferential oxidation cleanup reactors [454]. Simplified models tvere used for the observer design. The principle of an observer-based control strategy is to run a simplified reactor model in the controller sofiware. Model parameters are then permanently adopted by measurements during the control process. For each reaction, vhich vas considered in one of the reactors, one measurement vas used to adopt the models. With catalytic partial oxidation and preferential oxidation the reactor temperature and one species... 

SASOLII a.ndIII. Two additional plants weie built and aie in operation in South Africa near Secunda. The combined annual coal consumption for SASOL II, commissioned in 1980, and SASOL III, in 1983, is 25 x 10 t, and these plants together produce approximately 1.3 x lO" m (80,000 barrels) per day of transportation fuels. A block flow diagram for these processes is shown in Figure 15. The product distribution for SASOL II and III is much narrower in comparison to SASOL I. The later plants use only fluid-bed reactor technology, and extensive use of secondary catalytic processing of intermediates (alkylation, polymerisation, etc) is practiced to maximise the production of transportation fuels. 

NASA conducted studies on the development of the catalysts for methane decomposition process for space life-support systems [94], A special catalytic reactor with a rotating magnetic field to support Co catalyst at 850°C was designed. In the 1970s, a U.S. Army researcher M. Callahan [95] developed a fuel processor to catalytically convert different hydrocarbon fuels to hydrogen, which was used to feed a 1.5 kW FC. He screened a number of metals for the catalytic activity in the methane decomposition reaction including Ni, Co, Fe, Pt, and Cr. Alumina-supported Ni catalyst was selected as the most suitable for the process. The following rate equation for methane decomposition was reported ... 

In seeking new and improved ways for achieving the ultralow levels of sulfur in the fuels of the future, it is important to understand the nature of the sulfur compounds that are to be converted (especially PASCs), as described in Section III. It is equally important to understand how these transformations occur through interactions with catalytic surface species, the pathways involved during these transformations, and the associated kinetic and thermodynamic limitations. These considerations dictate the process conditions and reactor process configurations that must be used to promote such transformations. In this section, we describe the reactor configurations and process conditions being used today what is known about the catalyst compositions, structure, and chemistry and what is known about the chemistry and reaction pathways for conversion of PASCs in conventional HDS processes. 

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