Co-Evolution of Volatiles and Pyrolytic Residue during Lignin Pyrolysis

Area of Science:

• Biomass Conversion
• Pyrolysis Chemistry
• Organic Chemistry

Background:

• Lignin slow pyrolysis is a key thermochemical conversion process.
• Understanding volatile evolution during pyrolysis is crucial for optimizing bio-oil production.
• Existing methods lack the resolution to track stage-specific volatile changes.

Purpose of the Study:

• To develop and apply a modified Py-GCMS method for in situ analysis of lignin pyrolysis volatiles.
• To elucidate the coevolution mechanisms of volatiles and pyrolytic residues.
• To identify the key reactions and energy barriers governing lignin pyrolysis.

Main Methods:

• Modified Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GCMS) for in situ volatile capture.
• Thermogravimetric-Fourier Transform Infrared Spectroscopy (TG-FTIR).
• Cross-Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (CP/MAS NMR).
• Kinetic analysis and activation energy determination.

Main Results:

• Progressive reactions observed with increasing temperature (150-750 °C), including ether and side-chain C-C bond cleavage, and repolymerization.
• Lignin volatilization is primarily linked to side-chain cleavage, with side chains evolving from unsaturated to methyl groups or being removed.
• Predominant volatile components significantly varied across distinct pyrolysis stages.
• Activation energy analysis indicated that α- and β-ether bond homolysis are the most facile reaction pathways.

Conclusions:

• The modified Py-GCMS method successfully tracks stage-specific volatile evolution during lignin pyrolysis.
• Lignin pyrolysis involves complex, temperature-dependent reactions affecting both volatiles and solid residues.
• Understanding these mechanisms provides insights for controlling product distribution in biomass conversion.