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.