Hardwood and softwood lignins from sulfite liquors: Structural characterization and valorization through...

Area of Science:

• Biomass valorization and chemical engineering.
• Sustainable chemistry and green processes.

Background:

• Lignin, a complex biopolymer from wood, is an underutilized resource.
• Sulfite liquors contain lignin suitable for chemical modification.
• Oxidative depolymerization offers a pathway to high-value aromatic compounds.

Purpose of the Study:

• To characterize hardwood and softwood lignins from sulfite liquors.
• To evaluate their potential for producing phenolic monomers via oxidative depolymerization.
• To optimize reaction conditions for maximizing monomer yield and minimizing degradation.

Main Methods:

• Lignin isolation via ultrafiltration and freeze-drying.
• Characterization using inorganic content analysis, nitrobenzene oxidation, 13C NMR, and molecular weight determination.
• Alkaline oxidative depolymerization using oxygen, with optimization of reaction time and oxygen supply.

Main Results:

• Hardwood lignin yielded primarily syringaldehyde, while softwood lignin produced mainly vanillin.
• Optimized conditions, including shorter reaction times, minimized product degradation.
• Hardwood lignin exhibited higher reactivity, necessitating careful control to prevent degradation.

Conclusions:

• Lignin from hardwood and softwood sulfite liquors is a viable feedstock for producing phenolic aldehydes.
• Oxidative depolymerization can be optimized to yield valuable products like vanillin and syringaldehyde.
• Process control is crucial for maximizing yields and preserving product integrity.