Thermochemical Conversion of Biomass in Molten Salts

Thermochemical conversion of biomass in molten salts harnesses the unique properties of high-temperature ionic media to promote efficient depolymerisation, gasification and catalytic upgrading of lignocellulosic feedstocks. Molten salts act as dual-function heat-transfer fluids and reactive solvents, offering uniform thermal profiles and stabilising reaction intermediates, which reduces undesirable char and tar formation. Chloride-based eutectic mixtures, particularly those of ZnCl2–KCl–NaCl, have been shown to lower activation energies for cellulose and lignin breakdown, yielding bio-oils enriched in phenolic monomers. Carbonate systems, such as eutectic blends of Li2CO3, Na2CO3 and K2CO3, combine biomass gasification with in situ carbon dioxide capture through reversible carbonate reactions, facilitating clean syngas production. Hydroxide–carbonate formulations extend this concept to syngas conditioning, absorbing CO2 while steering the H2/CO ratio. These approaches are poised to deliver decentralised renewable fuels, green hydrogen and biobased chemicals, with concomitant CO2 sequestration. Key challenges include salt corrosion, hydrolysis management and salt recovery optimisation, yet recent progress underscores the method’s potential for integrated biorefineries and carbon-neutral energy systems.

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Thermochemical Conversion of Biomass in Molten Salts publication trend

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Technical terms

Molten salt: An ionic compound or mixture melted above its fusion temperature, used as a high-temperature solvent with favourable thermal and catalytic properties.

Eutectic mixture: A blend of salts that melts at a lower temperature than any of its individual components, offering reduced operating temperatures.

Reverse Boudouard reaction: A gas-solid reaction in which carbon dioxide reacts with solid carbon to form carbon monoxide, enhancing gasification.

Bio-oil: A complex liquid product obtained from the thermal depolymerisation of biomass, rich in oxygenated organic compounds.

Syngas: A combustible gas mixture primarily composed of hydrogen and carbon monoxide, produced by gasification processes.

References

1. Pyrolysis of LignoBoost lignin in ZnCl2-KCl-NaCl molten salt media: Insights into process-pyrolysis oil yield and composition relations. Journal of Analytical and Applied Pyrolysis (2023).
2. Thermochemical Conversion of Biomass in the Presence of Molten Alkali-Metal Carbonates under Reducing Environments of N2 and CO2. Energies (2020).
3. Experimental and Model Study on Raw Biomass Gasification Syngas Conditioning in a Molten NaOH-Na2CO3 Mixture. Energies (2020).