Pyrolysis Mechanisms and Product Analysis of Lignin

Lignin pyrolysis encompasses the thermal decomposition of the complex aromatic heteropolymer under oxygen-starved conditions, yielding gases, vapours and solid char. The process initiates through homolytic cleavage of ether and C–C bonds, most notably the β-O-4 linkage, generating phenolic monomers, radicals and reactive intermediates. Primary pathways include demethoxylation, demethylation, decarboxylation and decarbonylation, which liberate light gases (CO, CO₂, CH₄), while repolymerisation of intermediate radicals leads to char formation. Catalytic pyrolysis over zeolites or acid-base catalysts introduces additional routes via quinone methides and ketenes, enhancing selectivity towards targeted phenolics or small aromatics. Product distributions are strongly influenced by lignin origin and isolation process, reactor design (fluidised bed, fixed bed), heating rate, residence time and atmosphere. Fast pyrolysis tends to favour volatile phenolic compounds, whereas slower heating and higher pressures promote secondary aromatics and polycyclic aromatic hydrocarbons. Comprehensive analytical techniques—thermogravimetric analysis, Py-GC/MS, PEPICO spectroscopy and advanced mass spectrometry—have been instrumental in resolving transient intermediates and quantifying end products. Progress in catalyst design, co-processing with hydrogen-rich feedstocks and reactor engineering continues to refine yield, selectivity and the valorisation potential of lignin streams in biorefineries.

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Pyrolysis Mechanisms and Product Analysis of Lignin publication trend

The graph below shows the total number of articles in pyrolysis mechanisms and product analysis of lignin across all publications each year (not limited to Nature Index journals).

Technical terms

Pyrolysis: Thermal decomposition of organic matter in the absence of oxygen.

Lignin: A complex, irregular polymer of phenylpropanoid units in plant cell walls.

β-O-4 bond: The most abundant ether linkage between lignin monomers.

Quinone methide: A reactive intermediate formed by dehydroxylation and ring rearrangement.

Ketene: A highly reactive species (R2C=C=O) involved in catalytic pathways.

Phenolic compounds: Aromatic products bearing hydroxyl functionalities.

Char: Solid, carbon-rich residue formed through radical recombination and condensation.

References

1. Catalytic pyrolysis mechanism of lignin moieties driven by aldehyde, hydroxyl, methoxy, and allyl functionalization: the role of reactive quinone methide and ketene intermediates. Green Chemistry (2024).
2. A review on lignin pyrolysis: pyrolytic behavior, mechanism, and relevant upgrading for improving process efficiency. Biotechnology for Biofuels and Bioproducts (2022).
3. Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol, resorcinol and hydroquinone. Chemical Science (2021).