Figure 4. Sensible enthalpy profiles along the length of 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 temperature contour maps are illustrated in Figure 5 for the integrated combustion-reforming reactor in which combustion chambers are in direct thermal contact to reaction chambers for an endothermic steam reforming reaction. In the steam reformation of methanol, methanol is reacted with water to give hydrogen and carbon dioxide and also carbon monoxide. In addition to industrial processes for synthesis gas production, in particular applications in mobile systems such as fuel cells are of importance. Fuel cells require hydrogen which can be produced by steam-reforming methanol. For vehicle drives or mobile fuel cells, for example, it is of importance here to be able to carry out the steam reformation in a small reactor of low weight. This is made possible, in particular, by catalysts which catalyze the reaction of methanol and water and have a high activity with low volume. In this case it is useful to make up the catalysts in tablet form, in which case the tablets are to have very small dimensions, in order to achieve a high bulk density and a high ratio of surface area to volume. Also, a copper-based catalyst is excellent in low temperature activity and selectivity, but has the problem of heat resistance. In particular, since the activity and the selectivity are extremely reduced under the high temperature in excess of 300 °C, it is difficult to use such catalyst for a long time under the high temperature. In addition to this, metallic copper as active species is oxidized and sintered under the atmosphere containing the oxygen to cause the reduction in the activity. In contrast, a palladium-based catalyst that has strong resistance against the high temperature oxidizing atmosphere has the problem that it promotes the decomposition reaction of the methanol and thus generates a large quantity of carbon monoxide that is injurious to the fuel cell. It is an object of the present design to provide a methanol reforming catalyst capable of maintaining a high activity with good stability even in a high temperature and oxygen atmosphere while suppressing carbon monoxide generation. Since a palladium component is alloyed with the zinc, generation of carbon monoxide due to the methanol decomposition reaction is suppressed. Also, since both the palladium-zinc alloy and the metal oxide as the support are stable in the high temperature oxidizing atmosphere, the partial oxidation reaction as the exothermic reaction using the oxygen gas is proceeded simultaneously with the steam reforming reaction as the endothermic reaction or prior to the steam reforming reaction. That is, auto thermal reaction that proceeds the steam reforming reaction by utilizing the heat generated by the partial oxidation reaction is proceeded stably. A fuel cell of the present design comprises the methanol reforming apparatus, a fuel cell, a pipe supplying a gas reformed by the reforming apparatus to the fuel cell, and a pipe supplying an oxygen-containing gas to the fuel cell. Since the reforming apparatus having the above methanol reforming catalyst is used, the size reduction of the overall fuel cell system can be achieved. Therefore, the fuel cell system is suitable for the fuel cell system which is installed in the mobile body such as a car and a ship whose apparatus size is limited. The steam reforming reaction is an endothermic reaction and is normally affected by passing a mixture of the desulphurized methanol feedstock and steam through tubes containing a steam reforming catalyst, normally nickel supported on a shaped support such as rings of alumina or a calcium aluminate cement, while strongly heating the tubes. The tubes are usually heated in a furnace fueled with a suitable methanol-containing stream; alternatively, the tubes may be located within a high temperature convective heat exchange reformer. In this type of heat exchange reformer, the catalyst is disposed in tubes extending between a pair of tube sheets through a heat exchange zone. Reactants are fed to a zone above the upper tube sheet and pass through the tubes and into a zone beneath the lower tube sheet. The heating medium, for example the hot product of combusting a fuel with air, is passed through the zone between the two tube sheets.