Supercritical Water Gasification for Hydrogen Production

Supercritical water gasification (SCWG) is a thermochemical conversion process in which water above its critical point (374 °C, 22.1 MPa) acts as both solvent and reactant to transform wet biomass or organic residues into a hydrogen-rich synthesis gas. In this environment the distinct dielectric properties of supercritical water enhance solubility of organics and promote rapid reaction kinetics, eliminating the need for feedstock drying and reducing tar formation. Catalytic SCWG employs homogeneous or heterogeneous catalysts—such as alkali salts or metal-supported carbon—to lower reaction temperatures and steer selectivity towards hydrogen. Typical reaction pathways encompass hydrolysis, reforming and water–gas shift steps, achieving near-complete carbon conversion in residence times of minutes. Key technical challenges include material corrosion under hydrothermal conditions, deposition of char leading to reactor plugging and catalyst deactivation by sintering or coking. Advances in reactor design, process control and catalyst development are driving scale-up efforts for integrated biorefineries, with potential to valorise wet wastes, reduce greenhouse gas emissions and support a circular hydrogen economy.

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Supercritical Water Gasification for Hydrogen Production publication trend

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Technical terms

Supercritical water: Water above its critical temperature and pressure exhibiting both gas-like diffusivity and liquid-like density, used as an efficient reaction medium.

Gasification: Conversion of solid or liquid carbonaceous feedstocks into gaseous products (principally H₂, CO and CO₂) through thermochemical reactions.

Catalyst sintering: Irreversible growth of active metal particles under high temperature, leading to loss of surface area and diminished catalytic activity.

Plugging: Obstruction of reactor flow by deposition of solid residues or char, resulting in operational instability in continuous processes.

Water–gas shift reaction: Reaction between carbon monoxide and water vapour to form carbon dioxide and additional hydrogen, used to adjust syngas composition.

References

1. Particle size effects in Ru/CNF catalysts during supercritical water gasification of glycerol. Applied Catalysis B Environment and Energy (2023).
2. Supercritical Water Gasification of Biomass: A Literature and Technology Overview. Energies (2015).
3. Hydrogen Production by Supercritical Water Gasification of Biomass with Homogeneous and Heterogeneous Catalyst. Advances in Condensed Matter Physics (2014).
4. Analysis of operational issues in hydrothermal liquefaction and supercritical water gasification processes: a review. Biomass Conversion and Biorefinery (2021).