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Glucose was gasified in supercritical water within a microchannel reactor at 650°C
750°C, and 250 bar to yield H2 rich gas with a low concentration of CO. The feed
glucose concentration was 0.1 M. Two microchannel reactor configurations were
tested at fluid residence times ranging from 0.5 sec to 24 sec. The first was a single
tube microchannel reactor that consisted of a 2.0 m serpentine stainless steel tube
imbedded within a heating block. Inner diameters of the tubing were 254 µm and 508
µm. The second was a serpentine microchannel reactor configuration, which consisted
of a serpentine parallel array of 75 µm by 500 µm channels. It was fabricated in
stainless steel by a combination of micromachining, laser cutting, and hotpress
microlamination bonding techniques. Hydrogen yields averaged 5.7 ± 0.29 and peaked
at 6.3 moles of hydrogen gas produced per mole of glucose fed in the serpentine
microchannel reactor at 750°C and 250 bar. Typical gas compositions at 750°C and
250 bar were 52.5 % H2, 35.0 % CO2, 12.1 % CH4, and 0.4 % CO. Gas composition
and H2 yield were not dependent on residence time, indicating that the gas products
were moving toward equilibrium. Complete glucose conversions were obtained in less
than a 1.0 sec fluid residence time, and minimal organic acids were detected in the
liquid products. Glucose, which subsequently decomposed to H2, CO2, CH4, and CO,
first decomposed to organic acids, rather than reformed by water directly to H2, and
CO2. Acetic acid was the major intermediate. Measured hydrogen yield and gas
composition were similar to stoichiometric hydrogen yield and gas composition based
on the decomposition of glucose through an acetic acid intermediate. The presence of
acetic acid in the liquid product and CH4 present in the gas product confirms that
glucose was being decomposed to organic acids that were further gasified to H2, CO2,
CO, and CH4. |
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