Micro-Reactors for Fuel Processing

In contrast to ceramic and metallic monoHths developed for automotive exhaust treatment purposes, which nowadays carry chaimels on the microscale and are actually micro-reactors by definition, the micro-reactors discussed in this chapter rather cover plate heat-exchanger technology with chaimels on the microscale. An overview of the fundamentals, practical applications, and production issues of micro-reactors for fuel-processing purposes is provided. 

Micro-reactors by definition are chemical reactors that carry one or a multitude of channels at least one dimension of which does not exceed 1 mm. Micro-reactors have some specific features compared with conventional technology. The flow regime is usually laminar, diffusion paths for heat and mass transfer are very small, and they have a small surface-to-volume ratio, which leads to domination 

Fuel Cell Science and En neering Materials, Processes, Systems and Technology, 

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An analytical solution exists for the velocity profile under conditions of laminar, incompressible flow in a rectangular channel [1]. An approximate solution was derived by Purday [2] for a rectangular channel with a width 2a and a height 2b  

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Many authors mention the use of micro reactors for fuel processing as one of the most promising fields [1,104]. Wegeng et al. point at using this micro-fuel processing for transportation [Ij. The placement of reformers imder the hood of an automobile for converting liquid hydrocarbons to hydrogen is explicitly mentioned. 

Design Concepts of Micro Structured Reactors for Fuel Processing Applications... 

Micro Structured Test Reactors for Fuel Processing I 289... 

E. R., de Croon, M. H. J. M., Schouten, J. C., Fuel processing in micro-reactors for low power fuel cells, Chem. Eng. Commun. 2005, accepted for publication. 

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. 

Rapid progress in recent years in miniamrising chemical reactors has led some researchers to explore the fabrication of micro-scale fuel-processing reactors for fuel cells. Here we are considering systems that require a few watts or less of power, where the systems can be built on a chip and where, in principle, the mass manufacturing methods of the semiconductor industry could be applied. Figure 8.16 shows a conceptual system, devised by researchers at the University of Bethlehem, PA (Pattekar et al 2001). 

Accordingly, serious commercially oriented attempts are currently being made to develop special gas-phase micro and mini reactors for reformer technology [91, 247-259], This is a complex task since the reaction step itself, hydrogen formation, covers several individual processes. Additionally, heat exchangers are required to optimize the energy balance and the use of liquid reactants demands micro evaporators [254, 260, 261], Moreover, further systems are required to reduce the CO content to a level that is no longer poisonous for a fuel cell. Overall, three to six micro-reactor components are typically needed to construct a complete, ready-to-use micro-reformer system. 

Other studies on membrane micro-reactors were carried out for integrating different process steps in one micro-device for portable hydrogen production for fuel cell applications (see a.o. Ref. [60-62]). 

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