Hydrothermal Carbonization Techniques for Biomass Energy Production

Hydrothermal carbonisation (HTC) is a thermochemical conversion method that employs subcritical water at temperatures typically between 180 °C and 260 °C and autogenous pressures to transform wet biomass into a carbon-rich solid (hydrochar) and an aqueous phase rich in organics. The process proceeds through hydrolysis, dehydration, decarboxylation and polymerisation, ultimately yielding a material with increased fixed carbon content, higher heating value and enhanced energy density. Reaction parameters—temperature, residence time and biomass-to-water ratio—govern char yield, porosity and surface functionality, while the aqueous stream contains valuable organic acids and phenolics that can be valorised or further upgraded. HTC offers advantages over conventional drying and pyrolysis by treating high-moisture feedstocks directly, reducing energy input and enabling integration with biogas production, soil amendment and pollutant adsorption. Its global significance lies in converting agricultural residues, manures and industrial wastes into sustainable solid fuels, adsorbents and precursors for carbon sequestration.

Research from Nature Portfolio

Comparative studies of hydrothermal carbonisation and low-temperature pyrolysis of Eucommia ulmoides waste wood demonstrate that HTC achieves similar char yields at lower reactor temperatures, producing hydrochar with superior grindability, hydrophobicity and reduced inorganic content. The hydrochar exhibits H/C and O/C atomic ratios akin to sub-bituminous coals and outperforms pyrolytic biochar in combustion characteristic indices above 300 °C. This work establishes HTC as a viable pretreatment for solid biofuel production, emphasising its potential to deliver high-quality carbonised products with lower thermal input than conventional pyrolysis.

Hydrothermal Carbonization Techniques for Biomass Energy Production publication trend

The graph below shows the total number of articles in hydrothermal carbonization techniques for biomass energy production across all publications each year (not limited to Nature Index journals).

Technical terms

Hydrothermal carbonisation (HTC): Thermochemical conversion of wet biomass in subcritical water to produce carbon-rich hydrochar and an organic-rich liquid phase.

Hydrochar: The solid, carbon-dense material obtained from HTC, characterised by increased fixed carbon and energy density.

Subcritical water: Water heated above its boiling point (100 °C) and below its critical point (374 °C) under pressure, acting as a reactive medium.

Hydrothermal humification (HTH): A variant of HTC employing alkaline conditions to enhance formation of humic-like substances alongside hydrochar.

High heating value (HHV): The total energy released upon complete combustion of a fuel, including latent heat of vapourisation of water.

Energy densification ratio: The ratio of energy content per unit mass of hydrochar to that of the original biomass feedstock.

References

1. Maximizing the value of liquid products and minimizing carbon loss in hydrothermal processing of biomass: an evolution from carbonization to humification. Biochar (2024).
2. Hydrochar: A Review on Its Production Technologies and Applications. Catalysts (2021).
3. Comparative Evaluation of Hydrothermal Carbonization and Low Temperature Pyrolysis of Eucommia ulmoides Oliver for the Production of Solid Biofuel. Scientific Reports (2019).
4. Techno-Economic Assessment of Co-Hydrothermal Carbonization of a Coal-Miscanthus Blend. Energies (2019).