Alkali-thermal gasification and hydrogen generation potential of biomass

Generating hydrogen gas from biomass is one approach to lowering dependencies on fossil fuels for energy and chemical feedstock, as well as reducing greenhouse gas emissions. Using both equilibrium simulations and batch experiments with NaOH as a model alkaline, this study established the technical feasibility of converting various biomasses (e.g., glucose, cellulose, xylan and lignin) into H2-rich gas via catalyst-free, alkalithermal gasification at moderate temperatures (as low as 300 °C). This process could produce more H2 with less carbon-containing gases in the product than other comparable methods. It was shown that alkali-thermal gasification follows C x H y O z + 2xNaOH + (x–z)H2O = (2x + y/2–z)H2 + xNa2CO3, with carbonate being the solid product which is different from the one suggested in the literature. Moreover, the concept of hydrogen generation potential (H2-GP)—the maximum amount of H2 that a biomass can yield, was introduced. For a given biomass C x H y O z , the H2-GP would be (2x + y/2–z) moles of H2. It was demonstrated experimentally that the H2-GP was achievable by adjusting the amounts of H2O and NaOH, temperature and pressure.