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.