Monday, April 30, 2007

Rapid and selective conversion of glucose to hydrogen gas by supercritical water within a microchannel reactor

Gregory L. Rorrer and Aaron Goodwin. Department of Chemical Engineering, Oregon State University, Department of Chemical Engineering, Corvallis, OR 97331

Glucose, which is obtained from renewable resources such as cellulosic biomass and starch, is a potential feedstock for fuel-cell hydrogen production.   Glucose can be non-catalytically gasified to a mixture of hydrogen and carbon dioxide by supercritical water at 240 atm and temperatures exceeding 600 oC.  However, the highly endothermic nature of the reaction combined with relatively low rates of heat transfer in conventional tubular reactors results in residence times exceeding 20 seconds and the formation of recalcitrant byproducts such as coke, carbon monoxide, and acetic acid.  One way to reduce residence time and increase product selectivity of the glucose gasification reaction is to improve the rate of heat transfer to the reacting fluid by reducing the reactor conduit dimensions.  To address this need, a novel stainless steel microchannel reactor was fabricated which consisted of a parallel array of 75 micron channels.  At 240 bar and 750 oC, glucose conversion was complete within a residence time of less than 2.0 seconds and produced a gas containing at 52% H2, 38% CO2, 10% CH4 with less than 0.5% CO.  Liquid products were clean and contained only traces of acetic acid, and hydrogen yields exceeded 6.0 mole H2 / mole glucose.  This study shows that microchannel reactor technology offers significant promise for the gasification of biomass resources to useful fuels.