[Pyrolytic depolymerization mechanism of a lignin model compound with α-O-4 linkage]

Area of Science:

• Biomass Conversion
• Computational Chemistry
• Chemical Engineering

Background:

• Lignin, a complex biopolymer, presents challenges for efficient biomass conversion.
• Understanding lignin's pyrolysis mechanism is crucial for developing sustainable fuels and chemicals.
• The α-O-4 linkage is a primary bond in lignin, making its decomposition pathways a key research area.

Purpose of the Study:

• To elucidate the pyrolysis mechanism of the α-O-4 linkage in lignin using a model compound.
• To identify the primary decomposition pathways and resulting products.
• To assess the potential of lignin pyrolysis for biomass-based fuel production.

Main Methods:

• Utilized density functional theory (DFT) with the M06-2X method and 6-31+G(d,p) basis set.
• Performed full optimization of equilibrium geometries for reactants, intermediates, transition states, and products.
• Calculated activation energies for various pyrolysis pathways.

Main Results:

• Identified homolytic cleavage and concerted decomposition of the C(α)-O linkage as dominant pathways.
• Observed formation of phenolic compounds (phenol, 4-methylphenol, 4-vinylphenol, p-coumaryl alcohol).
• Detected light compounds including ethanol, methanol, and formaldehyde.

Conclusions:

• The pyrolysis of the α-O-4 lignin linkage proceeds through specific bond cleavage mechanisms.
• The identified products suggest lignin's potential as a source for biofuels and valuable chemicals.
• Computational modeling provides critical insights into lignin depolymerization for biorefinery applications.