Finely Designing Dicarboxylic Acid-Based Protic Ionic Liquids System for Tailoring Lignin Structure via Demethylation...

Area of Science:

• Green Chemistry
• Polymer Science
• Biomass Conversion

Background:

• Lignin, a renewable aromatic polymer, is underutilized due to its recalcitrance.
• Current lignin demethylation methods often involve hazardous reagents, hindering industrial application.
• Developing sustainable and efficient lignin modification strategies is crucial for biomass valorization.

Purpose of the Study:

• To design and implement novel dicarboxylic acid-based protic ionic liquids (DAPILs) for the efficient demethylation of industrial lignin.
• To investigate the impact of DAPILs on lignin structure and functional groups.
• To establish a halogen-free and environmentally friendly approach for lignin valorization.

Main Methods:

• Synthesis of DAPIL systems using ethanolamine and dibasic organic acids (aspartic acid, glutamic acid, succinic acid, glutaric acid) at specific stoichiometric ratios.
• Treatment of industrial lignin with designed DAPILs, particularly [EOA][GA].
• Characterization of modified lignin using 2D HSQC and 1H NMR spectroscopy to analyze structural changes.

Main Results:

• The [EOA][GA] treatment increased polyphenol content in lignin by over 1.58 times.
• Demethylation led to the cleavage of the β-O-4' bond and a decrease in S and G lignin units and the S/G ratio.
• High recovery rates (over 95%) were achieved for both the ionic liquid and the modified lignin.

Conclusions:

• DAPILs provide a novel, halogen-free, and environmentally friendly strategy for lignin demethylation.
• This approach enhances the high-value utilization of lignin and expands the applications of protic ionic liquids.
• The developed method offers a sustainable alternative for activating lignin's functional groups for industrial use.