Lignocellulosic biomass is a renewable, CO₂ neutral feedstock for the production of liquid and gaseous fuels. Lignocellulosic biomass consists of cellulose, hemicellulose and lignin. Cellulose is a polymer of the six-carbon sugar glucose, hemicellulose is a polymer of five-carbon sugar xylose, and lignin is a polymer of phenylpropane units. In general, monomeric carbohydrate compounds such as glucose and xylose can be non-catalytically gasified in supercritical water at a temperature greater than 600°C and pressure of 240 bar to yield a gas stream primarily composed of H₂, CO₂, and CH₄. However, due to the endothermic nature of the gasification reaction, and relatively low rates of heat transfer in conventional tubular reactors, the residence time for complete gasification of carbohydrates is at least 20 seconds. Microchannel reactor technology offers significant promise to intensify the gasification of biomass constituents by increasing the rate of heat transfer to the reaction. In this study, we considered gasification of soluble biomass constituents by supercritical water in a microchannel reactor. The novel stainless-steel microchannel reactor consisted of serpentine parallel array of 75 µm by 500 µm rectangular channels. This reactor greatly intensified the gasification reaction in supercritical water. For example, at 750°C and 250 bar, a 0.1 molar solution of glucose was gasified to 53% H₂, 35% CO₂, 10% CH₄, and 0.5% CO in less than 2.5 seconds. The liquid effluent was clean and contained only trace amounts of acetic acid. Ongoing work using other biomass constituents, including xylose, monomeric lignin precursors, and an alkali-soluble hemicellulose/lignin stream isolated by NaOH pretreatment of grass straw, is also described.

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