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.