Hydrocarbons for Hydrogen Generation - Hydrogen Generation, Storage, and Utilization - page 13

the product gas (75%) [3]. In addition, since no gases need to be compressed
in the feed, the reaction can easily be carried out at higher pressure, thus
keeping membranes as an option for the successive gas clean-up step. The
endothermicity of the reaction, however, requires external heating of the
reactor, which makes it challenging to achieve short start-up times and fast
transient behavior desired for some applications, such as in automobiles.
Like in steam methane reforming, efficient conversion of methanol to hydro-
gen requires the use of catalysts. Common catalysts for this purpose include
Cu/ZnO/Al 2 O 3 , Cu-Mn-O, and Cu-based binary metals, such as Cu/Cr, Cu/
Zn, and Cu/Zr [4, 5]. The choice of catalyst has a great influence on the
methanol conversion and carbon dioxide selectivity of the reforming
reaction.
Besides large-scale reformers, there is interest in developing small reform-
ers for portable electronics applications. Toward this goal, a silicon-chip
based microreactor has been successfully fabricated and tested to carry out
the reaction of methanol reforming for microscale hydrogen production [6].
The developed microreactor, in conjunction with a micro fuel cell, is pro-
posed as an alternative to conventional portable sources of electricity, such
as batteries, due to its ability to provide an uninterrupted supply of electricity
as long as a supply of methanol and water can be provided. The microreformer-
fuel cell combination does not require recharging, as compared with conven-
tional rechargeable lithium-ion batteries, and affords a significantly higher
energy storage density. The microreactor consists of a network of catalyst-
packed parallel microchannels of depths ranging from 200 to 400 μm with
a catalyst particle filter near the outlet fabricated using photolithography and
deep-reactive ion etching (DRIE) on a silicon substrate. Experimental runs
have demonstrated a methanol to hydrogen molar conversion of at least
85-90% at flow rates enough to supply hydrogen to an 8- to 10-W fuel cell.
Similar to methane or methanol, ethanol can also be used for hydrogen
generation through steam reforming. Unlike methane and methanol, however,
ethanol can be prepared from agricultural products and residues, and thus
represents a renewable resource. One of the major mechanisms proposed for
ethanol steam reforming is given below [7]:

C H OH H O CH + → + CO + 2 H

(2.6)

2 5 2 4 2 2

CH + H O CO → + 3 H

(2.7)

4 2 2

CO H O CO + → + H

2 .

(2.8)

2 2

Similar to other steam reforming reactions, catalysts play a critical role in
ethanol steam reforming [7]. For example, an earlier study has found that