Torrefaction Processes in Biomass Conversion

Torrefaction is a thermal pretreatment that upgrades diverse biomass feedstocks by heating them in an inert or low‐oxygen atmosphere at temperatures typically between 200 °C and 300 °C. This mild pyrolytic process drives off moisture and light volatiles, leading to a solid product with enhanced energy density, hydrophobicity and grindability. The resulting torrefied biomass exhibits altered chemical composition, characterised by reduced oxygen‐to‐carbon ratios and an increased fixed‐carbon fraction, making it an attractive substitute for fossil coal in co‐firing applications or as feedstock for downstream thermochemical conversion routes such as fast pyrolysis or gasification. Contemporary research spans mechanistic studies of devolatilisation kinetics, reactor design for steam and wet torrefaction, catalytic approaches to tailor liquid coproducts, and process modelling to optimise scale‐up. These efforts underpin the integration of torrefaction into circular bioeconomies, enabling sustainable management of agricultural residues, municipal wastes and forestry by‐products, while contributing to greenhouse‐gas mitigation and energy security on a global scale.

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Torrefaction Processes in Biomass Conversion publication trend

The graph below shows the total number of articles in torrefaction processes in biomass conversion across all publications each year (not limited to Nature Index journals).

Technical terms

Torrefaction: A mild thermal treatment of biomass under inert conditions, typically at 200–300 °C, to improve fuel properties by removing moisture and light volatiles.

Biochar (Hydrochar): The carbon-rich solid residue produced by thermal treatments such as torrefaction or hydrothermal carbonisation of biomass.

Syngas: A mixture of hydrogen, carbon monoxide and light hydrocarbons generated by gasification of torrefied or untreated biomass.

Levulinic acid: A platform chemical derived from carbohydrate decomposition during wet torrefaction, used as a precursor for biofuels and value-added chemicals.

Fixed-carbon content: The proportion of solid carbon remaining in biomass after devolatilisation, indicative of its energy density and combustion characteristics.

References

1. Assessment of biochar developed via torrefaction of food waste as feedstock for steam gasification to produce hydrogen rich gas. Carbon Research (2023).
2. Catalytic wet torrefaction of biomass waste into bio-ethanol, levulinic acid, and high quality solid fuel. Chemical Engineering Journal (2024).
3. Numerical modeling of the co-firing process of an in situ steam-torrefied biomass with coal in a 230 MW industrial-scale boiler. Energy (2023).