Improving the production of hydrogen from the gasification of carbonaceous solids using supercritical water until 1000 bar

- Supercritical water (SCW) generates greater H2 volumes than steam.
- Purification of streams produced under supercritical conditions is easier.
- Gasification with steam releases lower amounts of CO2 than gasification with SCW.
- Optimal production of H2 depends on the gasifying conditions and the solid.

In this work, the advantages provided by supercritical water (SCW) to one of the most extended methods to produce H2, the gasification of carbonaceous materials, are investigated. The broad range of experimental conditions assayed (1-1000 bar) allows not only the comparison of the use of steam and SCW but also the investigation of how H2 production varies within the supercritical region. The results obtained reveal important advantages when the supercritical fluid is used. In the gasification with SCW, H2 production is greater, and in general, the consumption of the raw material is optimized since more H2 is obtained when the same amount of solid is consumed. Furthermore, the gaseous streams are very rich in H2 and CO2 and poor in CO and CH4. On the other hand, the use of two carbonized materials of different natures (a phenolic textile fiber and holm oak wood) allows us to highlight that H2 production depends strongly on the surface irregularities and surface chemistry of the solid. The material of vegetal origin is more suitable because more H2 is produced and mixtures of gases that are more easily purified are obtained from it. However, higher amounts of CO2 than those registered for the solid of synthetic origin are released during its gasification.

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