Catalytic Hydrothermal Upgrading of Algal Biofuels

Catalytic hydrothermal upgrading represents an integrated route to convert wet algal biomass into high-quality biofuels. The process begins with hydrothermal liquefaction (HTL), whereby microalgae are treated in subcritical water (typically 300–375 °C, 10–25 MPa) to produce a water-insoluble biocrude alongside aqueous and solid coproduct streams. This crude biocrude is rich in oxygenated and nitrogenous compounds, which depress energy density and fuel stability. Catalytic upgrading employs heterogeneous catalysts under hydrothermal or hydrotreatment conditions—often with added hydrogen—to remove heteroatoms (O, N, S), crack high-molecular-weight species and enhance hydrocarbon yield. Transition-metal catalysts (for example Pd, Ni, Ru) supported on carbonaceous or oxide materials and metal-doped zeolites have shown promise in deoxygenation, denitrogenation and aromatics control. Key challenges include catalyst hydrothermal stability, resistance to fouling by solids and ash, and optimisation of reaction parameters to balance conversion, selectivity and energy efficiency. Advances in continuous-flow reactor design, catalyst recovery and the valorisation of aqueous-phase organics are driving the technology towards scalable routes for renewable diesel, jet and petrochemical precursors.

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Catalytic Hydrothermal Upgrading of Algal Biofuels publication trend

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Technical terms

Hydrothermal liquefaction (HTL): A thermochemical process using water at high temperature and pressure to convert wet biomass into a crude biocrude oil.

Biocrude: A complex, oxygen-rich oil resulting from HTL, requiring further upgrading to meet fuel specifications.

Catalytic upgrading: The use of solid catalysts under hydrothermal or hydrotreatment conditions to remove heteroatoms and increase hydrocarbon content.

Heteroatoms: Non-carbon atoms (commonly O, N, S) in biocrude that lower energy density and cause instability.

Hydrotreatment: A catalytic process conducted in the presence of hydrogen to hydrogenate, deoxygenate and desulfurise bio-oils.

References

1. Ni‐Ru/CeO2 Catalytic Hydrothermal Upgrading of Water‐Insoluble Biocrude from Algae Hydrothermal Liquefaction. BioMed Research International (2018).
2. Nanoparticles of Pd supported on bacterial biomass for hydroprocessing crude bio-oil. Fuel (2017).
3. Stability and Activity of Doped Transition Metal Zeolites in the Hydrothermal Processing. Frontiers in Energy Research (2015).