Conversion of glucose to hydrogen gas by supercritical water in a microchannel reactor

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 um and 508 aem. The second was a serpentine microchannel reactor configuration, which consisted of a serpentine parallel array of 75 um by 500 um 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.