Expanded and updated results for supercritical water gasification of cellulose and lignin in metal-free reactors

We report updated and expanded results from a systematic study of the effects of process variables on the gasification of cellulose and lignin in supercritical water in quartz reactors. Quartz reactors eliminate potential catalytic effects from metallic walls. The gases produced were far from their equilibrium composition. High temperatures, high water densities, and long reaction times provide the highest H₂ yields. The total gas yields and energy content of the gas were largely insensitive to the water density and biomass loading, with lignin gasification at 1.0 wt % loading being the exception. The yields of CO₂, CH₄, and H₂ displayed an Arrhenius-like dependence on temperature. The apparent activation energies for CO₂ and H₂ production were about 15 and about 60 kJ/mol, respectively, and this difference suggests that these products did not primarily form together in a common reaction pathway. The activation energies for each of the product gases, however, were about the same for both cellulose and lignin. Comparing new results for gasification in quartz with literature data for gasification at identical conditions in stainless steel indicates that the significance ofcatalysis by metal reactor walls depends upon the experimental conditions used.