Sono-Fenton-Assisted Depolymerization of Lignin to Valuable Phenolic Compounds

Area of Science:

• Biomass Valorization
• Green Chemistry
• Polymer Chemistry

Background:

• Lignin, a major component of lignocellulosic biomass, is an underutilized aromatic polymer in the paper, pulp, and bioethanol industries.
• Developing efficient and environmentally benign methods for lignin depolymerization is crucial for unlocking its potential value.

Purpose of the Study:

• To investigate the sonication-assisted Fenton treatment for alkali lignin depolymerization.
• To optimize reaction conditions for maximizing lignin oil yield and total phenolic content.
• To study the depolymerization kinetics and identify phenolic monomers produced.

Main Methods:

• Alkali lignin was depolymerized using a sonication-assisted Fenton process.
• Reaction parameters including time, lignin concentration, ultrasound power, hydrogen peroxide dosage, and ferrous sulfate amount were optimized.
• Lignin molecular weight reduction was monitored to study depolymerization kinetics.

Main Results:

• Optimal conditions yielded 37% lignin oil with a rate constant of 4.7 × 10^-5 min^-1.
• Total phenolic content in the liquid phase reached 0.75 mmol g^-1.
• Key phenolic monomers identified include vanillin, acetovanillone, vanillic acid, phenol, and guaiacol, with high vanillin selectivity (36%).

Conclusions:

• Sonication-assisted Fenton treatment is an effective and benign method for lignin depolymerization.
• Optimized conditions significantly enhance the yield of valuable phenolic compounds from lignin.
• This approach offers a promising route for the valorization of lignin into high-value chemicals.