New insights into the base catalyzed depolymerization of technical lignins: a systematic comparison

Area of Science:

• Biomass Conversion and Biorefining
• Polymer Chemistry
• Organic Chemistry

Background:

• Technical lignins from various botanical sources and pulping methods present diverse structures.
• Efficient depolymerization methods are crucial for lignin valorization into value-added chemicals.
• Base catalyzed depolymerization (BCD) is a promising route for lignin breakdown.

Purpose of the Study:

• To systematically investigate the base catalyzed depolymerization (BCD) of diverse technical lignins.
• To quantify and structurally characterize the resulting lignin oil and residue fractions.
• To elucidate the influence of BCD process conditions and feedstock on product yields and structures.

Main Methods:

• BCD of five technical lignins (herbaceous, hardwood, softwood from soda, kraft, organosolv pulping).
• Characterization of lignin oil and residue using SEC, GC-MS, GC-FID, GC×GC-FID, ¹³C-NMR, HSQC NMR, DEPT-135, ³¹P NMR, and elemental analysis.
• Evaluation of depolymerization efficiency via lignin conversion, oil yield, monomer selectivity, and residue/char production.

Main Results:

• Lignin oil yields ranged from 20-31% (w/w) with 48-57% (w/w) total monomer content.
• Lignin oils contained dimers/oligomers with non-native interunit linkages, indicating deconstruction-recombination.
• Residues (43-70% w/w) were identified as condensed aromatic materials, not unreacted lignin, with lower molecular weights and higher phenolic content.

Conclusions:

• BCD effectively deconstructs diverse technical lignins into monomeric phenols and condensed aromatic residues.
• The study provides a comprehensive understanding of BCD, highlighting feedstock-dependent outcomes.
• Characterization of both fractions is key for the complete valorization of BCD-derived lignin streams.