Bio-Oil Production and Fractionation Techniques
Summary
Bio-oil, a complex mixture of oxygenated organic compounds, is produced by thermochemical conversion of biomass feedstocks via processes such as fast pyrolysis, slow pyrolysis and hydrothermal liquefaction. Fast pyrolysis, carried out at moderate temperatures (450–550 °C) and short vapour residence times, yields high bio-oil quantities suitable for transport fuel precursors. Slow pyrolysis, with longer residence times and lower heating rates, favours the generation of phenolic-rich fractions. Hydrothermal liquefaction employs subcritical water conditions (200–350 °C, high pressure) to solubilise biomass, yielding a crude bio-oil often richer in heavier compounds. The raw bio-oils generally exhibit high water content, acidity, viscosity and chemical complexity, presenting challenges for storage, transport and direct application. Fractionation and upgrading techniques are therefore essential to tailor bio-oil properties for targeted applications. Physical separation methods—including liquid–liquid extraction, freeze concentration and distillation—partition bio-oil into light, mid-weight and heavy fractions enriched in acids, phenolics, ketones or hydrocarbons. Chemical upgrading, such as catalytic hydrogenation, hydrodeoxygenation or mild pyrolytic cracking, reduces oxygen content, acidity and viscosity, improving energy density and stability. Emerging techniques, notably supercritical carbon dioxide extraction, offer tunable solvent power for selective recovery of phenolic monomers and removal of unwanted acids. Integrated approaches that combine fractionation with catalytic upgrading are increasingly explored to produce fuel-grade bio-oils and value-added chemicals, highlighting the global significance of biomass valorisation in decarbonising energy and chemicals sectors.
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Bio-Oil Production and Fractionation Techniques publication trend
The graph below shows the total number of articles in bio-oil production and fractionation techniques across all publications each year (not limited to Nature Index journals).
Technical terms
Bio-oil: A dark, viscous liquid derived from thermochemical conversion of biomass, rich in oxygenated compounds.
Pyrolysis: The thermal decomposition of organic material in an inert atmosphere, producing bio-oil, gas and char.
Hydrothermal Liquefaction: Biomass conversion in hot, pressurised water to form a liquid bio-crude with reduced polymerisation.
Fractionation: The separation of a complex mixture into fractions based on differences in volatility, polarity or solubility.
Supercritical CO₂ Extraction: A separation technique using CO₂ above its critical point to selectively dissolve and recover target compounds.
Deoxygenation: A catalytic process that removes oxygen from bio-oil molecules, improving fuel properties and stability.
References
- Review on Biomass Pyrolysis with a Focus on Bio-Oil Upgrading Techniques. Analytica—A Journal of Analytical Chemistry and Chemical Analysis (2023).
- Production of phenolic-rich slow pyrolysis liquid extracts by supercritical carbon dioxide fractionation. Holzforschung (2024).
- Fractional Composition Analysis for Upgrading of Fast Pyrolysis Bio-Oil Produced from Sawdust. Energies (2022).
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