Figure 4. Effect of temperature on the methanol mole fraction on the catalyst surface along the length of the process microchannel of the microchannel methanol steam reformer reactor.
The effect of temperature on the ratio of the methanol mole fraction along the fluid centerline to that on the catalyst surface is illustrated in Figure 5 along the length of the process microchannel of the microchannel reactor. As discussed above, steam reformers produce a reformate stream from water and a carbon-containing feedstock. Examples of suitable carbon-containing feedstocks include alcohols and hydrocarbons. Nonexclusive examples of suitable alcohols include methanol, ethanol, and polyols, such as ethylene glycol and propylene glycol. Methanol is a particularly well-suited carbon-containing feedstock for steam reforming reactions. Methanol steam reforming typically takes place at a lower temperature than when other carbon-containing feedstocks are reformed. For example, methanol steam reformers typically have reforming regions that are heated to temperatures of approximately 200-300 °C. Methanol steam reformers typically receive a feed stream having approximately a 1:1 molar ratio of methanol to water or approximately 64 percent methanol by weight, but this feed ratio may be varied and still produce sufficient amounts of hydrogen gas. In the present study, the methanol steam reformer receives a feed stream having approximately a 1:1.14 molar ratio of methanol to water. The feed stream may be delivered to the steam reformer via any suitable mechanism, such as by a suitable feed stream delivery system. The delivery system includes any suitable mechanism, device, or combination thereof that delivers the feed stream to the steam reformer. In the case of a methanol steam reformer, where the feed stream contains water and methanol, these components may be mixed together and delivered as a single stream. Alternatively, these components may be separately delivered to the reforming region. Traditionally, low temperature shift catalysts are used as methanol steam reforming catalysts. These catalysts were designed to catalytically facilitate the conversion of water and carbon monoxide to hydrogen and carbon dioxide at temperatures less than 280 °C, such as in the range of 200-280 °C. These catalysts typically are copper-based compositions, such as stabilized compositions of copper and zinc. More particularly, low temperature shift catalysts typically include copper oxide and zinc oxide supported on alumina.