Figure 1. Methanol mole fraction contour maps in the integrated combustion-reforming reactor in which combustion chambers are in direct thermal contact to reaction chambers for an endothermic steam-methanol reforming reaction.

The hydrogen mole fraction contour maps are illustrated in Figure 2 for the integrated combustion-reforming reactor in which combustion chambers are in direct thermal contact to reaction chambers for an endothermic steam reforming reaction. Control of the relative proportion of homogenous and heterogeneous combustion can be achieved by manipulation of the jet design [33, 34]. Either homogeneous or heterogeneous combustion can be increased as needed depending upon the application. As an example, a microchannel combustor that does not include an endothermic reaction may be enhanced via jet design by promoting homogenous combustion to reduce methanol or carbon monoxide emissions or to provide a hot gas stream for subsequent use in a unit operation. The distribution of jet orifices may depend on the intended use of the device. Hydrogen burns immediately, thus, to avoid hot spots, the jets should be spaced more evenly over the combustion chamber. Methane, which burns more slowly, preferably has jets loaded near the front of the combustion chamber. When the fuel is syngas, the distribution of jets is intermediate. The endothermic and exothermic reaction chambers preferably contain catalysts [35, 36]. Catalysts suitable for catalyzing a selected exothermic or endothermic reaction are well known to chemists and chemical engineers. Catalysts, especially an endothermic catalyst, can be a porous catalyst. Pore sizes in the range of about 0.6 to 600 microns enable molecules to diffuse molecularly through the materials under most gas phase catalysis conditions. The porous material can itself be a catalyst, but more preferably the porous material comprises a metal, ceramic or composite support having a layer or layers of a catalyst material or materials deposited thereon. The porosity can be geometrically regular as in a honeycomb or parallel pore structure, or porosity may be geometrically tortuous or random. The support of the porous material is a foam metal, foam ceramic, metal felt, or metal screen. The porous structures could be oriented in either a flow-by or flow-through orientation. The catalyst could also take the form of a metal gauze that is parallel to the direction of flow in a flow-by configuration. Alternatively, the catalyst support could also be formed from a dense metal shim or foil. A porous catalyst layer could be coated on the dense metal to provide sufficient active surface sites for reaction. An active catalyst metal or metal oxide could then be wash-coated either sequentially or concurrently to form the active catalyst structure. The dense metal foil or shim would form an insert structure that would be placed inside the reactor after bonding or forming the microchannel structure. Preferably, the catalyst inserts contact the wall or walls that are adjacent both the endothermic and exothermic reaction chambers. The porous catalyst could alternatively be affixed to the reactor wall through a coating process. The coating may contain a first porous layer to increase the number of active sites. Preferably, the pore diameter ranges from tens of nanometers to tens of microns. An active metal or metal oxide catalyst can then be sequentially or concurrently wash-coated on the first porous coating. The average pore size of the catalyst layers is preferably smaller than the average pore size of the support. Diffusion within these small pores in the catalyst layers is typically Knudsen in nature for gas phase systems, whereby the molecules collide with the walls of the pores more frequently than with other gas phase molecules. The catalyst, which is not necessarily porous, could also be applied by other methods such as wash coating. On metal surfaces, it is preferred to first apply a buffer layer by chemical vapor deposition and thermal oxidation, which improves adhesion of subsequent wash coats. The methanation catalyst can be a single material or a mixture of materials such as a methanation catalyst powder between methanation catalyst felts. A small reforming chamber, such as having a diameter of 0.8 mm or less provides superior results by enhancing uniformity of conditions such as reducing hot and cold spots and reducing channeling through a powdered catalyst. In this case, the reforming chamber is defined at one edge by the methanation catalyst. Where the catalysts are powders, there will not be a sharp delineation between reforming and methanation zones and some methanation catalyst powder will intermix with the reforming catalyst powder so that some methanation catalyst is present within the reforming chamber. The reforming chamber volume is defined by the volume where there is a significant amount of reforming catalyst such that a reforming reaction could take place under normal operating conditions. Methanol and water can be injected at room temperature into an inlet tube where they will be vaporized by heat conducted through the tube from the methanation and reforming catalysts. In practice, fuel processing systems may be significantly more complex. For example, heat from a combustor can also be used to supply heat for other processes such as steam generation that can be utilized for a steam reformer, autothermal reactor and water gas shift reactor. Heat loss is a function of surface area, lowering surface area for the same amount of heat reduces heat loss and puts thermal energy exactly where it is needed. Therefore, in some preferred designs, surface area is minimized. For example, in some environments, cylindrical reforming and combustion channels can perform better than planar geometries. Heat from the combustion chamber transfers through the thermally conductive wall into the endothermic reaction chamber and along the length of the endothermic reaction chamber where less than 8 percent of total heat flux into the endothermic reaction chamber is perpendicular to length.