Figure 5. Temperature contour plots in the combined parallel plate heat
exchanger-reactor for hydrogen production by steam-methanol reforming.
The hydrogen molar fraction contour plots in the combined parallel plate
heat exchanger-reactor are illustrated in Figure 6 for hydrogen
production by steam-methanol reforming. The autothermal parallel plate
heat exchanger-reactor contains the layered catalyst member. The stream
is contacted with the layered catalyst member at a temperature
sufficient to initiate and sustain both catalytic partial oxidation and
steam reforming. The amounts of the hydrocarbon feed, water and air in
the inlet stream introduced into the autothermal reactor are typically
controlled to maintain a water to carbon ratio of at least about 0.3:1.0
and an oxygen to carbon ratio of from about 0.2 to 0.7:1.0. In general,
adiabatic conditions will prevail in the autothermal reactor due to the
fact that the partial oxidation reaction is exothermic in nature and the
heat generated in the course of such a reaction is usually sufficient to
initiate and sustain the steam reforming reaction which is endothermic
in nature. Accordingly, by proper selection of the preheat temperature,
reactor design, and volumetric hourly rate, both reactions may be
carried out within the reactor while the reactor temperature is kept
within the range of about 200 to about 280 °C without the need to supply
external heat or cooling to the reactor. However, it is necessary to
supply heat or cooling to the reactor as desired in order to
continuously maintain both reactions at high reaction rates. In the
second step of the process, the hydrocarbon feed is catalytically
partially oxidized by contact with the catalytic partial oxidation
catalyst layers. The resultant effluent will comprise hydrogen and
carbon oxides. In the third step of the process, hydrocarbons remaining
in the feed which are not catalytically partially oxidized are steam
reformed by contact with the steam reforming catalyst layers, thereby
producing a hydrogen-rich effluent. Preferably, the hydrogen-rich gas
effluent from the third step of the process is subjected to a further
water-gas shift reaction. In the course of the steam reforming reaction,
the hydrocarbon reacts with water to yield a product gas containing
primarily hydrogen and carbon monoxide, plus any unreacted hydrocarbons.
In order to reduce the carbon monoxide level and increase the hydrogen
gas level, the effluent may be passed into a converter in which the
effluent is contacted with a catalyst such that the carbon monoxide will
at with water to yield carbon dioxide and firer amounts of hydrogen.