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Lignin depolymerization to aromatic monomers with high yields and selectivity is essential for the economic feasibility of many lignin-valorization strategies within integrated biorefining processes. Importantly, the quality and properties of the lignin source play an essential role in impacting the conversion chemistry, yet this relationship between lignin properties and lignin susceptibility to depolymerization is not well established. In this study, we quantitatively demonstrate how the detrimental effect of a pretreatment process on the properties of lignins, particularly β-O-4 content, limit high yields of aromatic monomers using three lignin depolymerization approaches: thioacidolysis, hydrogenolysis, and oxidation. Through pH-based fractionation of alkali-solubilized lignin from hybrid poplar, this study demonstrates that the properties of lignin, namely β-O-4 linkages, phenolic hydroxyl groups, molecular weight, and S/G ratios exhibit strong correlations with each other even after pretreatment. Furthermore, the differences in these properties lead to discernible trends in aromatic monomer yields using the three depolymerization techniques. Based on the interdependency of alkali lignin properties and its susceptibility to depolymerization, a model for the prediction of monomer yields was developed and validated for depolymerization by quantitative thioacidolysis. These results highlight the importance of the lignin properties for their suitability for an ether-cleaving depolymerization process, since the theoretical monomer yields grows as a second order function of the β-O-4 content. Therefore, this research encourages and provides a reference tool for future studies to identify new methods for lignin-first biomass pretreatment and lignin valorization that emphasize preservation of lignin qualities, apart from focusing on optimization of reaction conditions and catalyst selection.
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One-pot production of oxygenated monomers and selectively oxidized lignin from biomass based on plasma electrolysis
Herein, we report a novel method to obtain oxygenated chemicals and high-quality lignin from biomass in one-pot using a single step process. Plasma electrolysis of red oak was conducted by applying high-voltage alternating current electricity in γ-valerolactone using sulfuric acid as the electrolyte. Red oak was completely solubilized to produce levoglucosenone and furfural as the two major monomers with the respective yields of up to 44.9 mol% and 98.0 mol%. During the conversion, an oxidized lignin was also simultaneously produced in high purity. The valorization potential of the plasma electrolysis-derived lignin evaluated using the pyrolysis method showed that depolymerization of this lignin could produce significantly higher yields of phenolic monomers than the natural lignin or the lignin isolated during conventional solvolysis. Our investigation showed that benzylic carbon of the natural lignin was selectively modified during plasma electrolysis to limit the formation of interunit C–C bonds, significantly improving the subsequent lignin valorization to aromatic monomers. Overall, this study demonstrated a simple green approach to improve chemical production without using costly catalysts or tedious biomass fractionation. This study also presented a novel and highly efficient way to modify lignin for enhanced valorization.
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- PAR ID:
- 10311055
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 23
- Issue:
- 22
- ISSN:
- 1463-9262
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1gc03315h
