Depolymerization of Lignin into Monophenolics by Ferrous/Persulfate Reagent under Mild Conditions

Area of Science:

• Green Chemistry
• Biomass Conversion
• Catalysis

Background:

• Lignin depolymerization is crucial for valorizing biomass.
• Existing methods often require harsh conditions or are inefficient.
• Developing mild and effective depolymerization strategies is essential.

Purpose of the Study:

• To develop a novel reagent system for efficient lignin depolymerization.
• To optimize reaction conditions for maximizing monophenolic compound yield.
• To elucidate the depolymerization mechanism using computational and spectroscopic methods.

Main Methods:

• Utilized persulfate and transition metal ions as the depolymerization reagent.
• Employed Box-Behnken experimental design and response surface methodology for optimization.
• Applied density functional theory (DFT) calculations to investigate the reaction mechanism.
• Used gel permeation chromatography (GPC) and 2D-NMR spectroscopy for structural analysis.

Main Results:

• Achieved up to 99% depolymerization of lignin dimers to veratraldehyde under mild conditions (<100°C, ambient pressure).
• Successfully depolymerized industrial lignins, yielding significant amounts of phenolic oils and monophenolic compounds.
• DFT calculations revealed a persulfate radical mechanism with a lower activation barrier compared to hydroxyl radicals.
• GPC and 2D-NMR confirmed effective cleavage of lignin's β-O-4 bonds.

Conclusions:

• Persulfate-based reagents offer an efficient and mild pathway for lignin depolymerization.
• The identified mechanism provides valuable insights into lignin breakdown.
• This approach holds promise for the sustainable production of valuable phenolic compounds from lignin.