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Abstract
Comparison with other biomass thermochemical gasification, such as air gasification or steam gasification, the supercritical water gasification can directly deal with the wet biomass without drying, and has high gasification efficiency in lower temperatures. The cost of hydrogen production from supercritical water gasification of wet biomass was several times higher than the current price of hydrogen from steam methane reforming. Biomass is gasified in supercritical water at a series of temperatures and pressure during different resident times, and the product gas is composed of H2, CO2, CO, CH4, and a small amount of C2H4 and C2H6. Supercritical water is a promising reforming media for the direct production of hydrogen at 875–1,075 K temperature with a short reaction time (2–6 s). As the temperature is increased from 875 to 1,075 K the H2 yield increases from 53 to 73% by volume, respectively. In addition to being a high mass transfer effect, supercritical water also participates in reforming reaction. Pressure has a negligible effect on hydrogen yield above the critical pressure of water.