4.7 Article

Comparison of the Degradation Performance of Seven Different Choline Chloride-Based DES Systems on Alkaline Lignin

Journal

POLYMERS
Volume 14, Issue 23, Pages -

Publisher

MDPI
DOI: 10.3390/polym14235100

Keywords

alkaline lignin; choline chloride; deep eutectic solvent (DES); degradation

Funding

  1. National Natural Science Foundation of China
  2. [32271797]

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In this study, lignin was degraded using deep eutectic solvent (DES), and it was found that acidic DES was more effective in depolymerizing alkaline lignin. The degradation process was characterized using NMR hydrogen spectroscopy, FT-IR spectroscopy, and GPC.
Lignin is a natural polymer second only to cellulose in natural reserves, whose structure is an aromatic macromolecule composed of benzene propane monomers connected by chemical bonds such as carbon-carbon bonds and ether bonds. Degradation is one of the ways to achieve the high-value conversion of lignin, among which the heating degradation of lignin by deep eutectic solvent (DES) can be an excellent green degradation method. In this study, choline chloride (CC) was used as the hydrogen bond acceptor, and urea (UR), ethylene glycol (GC), glycerol (GE), acetic acid (AA), formic and acetic mixed acid (MA), oxalic acid (OX), and p-toluenesulfonic acid (TA) were used as hydrogen bond donors to degrade lignin. NMR hydrogen spectroscopy was used for the simple and rapid determination of phenolic hydroxyl groups in lignin. FT-IR spectroscopy was used to characterize the changes of functional groups of lignin during DES treatment. GPC observed the molecular weight of lignin after degradation and found a significant increase in the homogeneity (1.6-2.0) and a significant decrease in the molecular weight M-w (2478-4330) of the regenerated lignin. It was found that acidic DES was more effective in depolymerizing alkaline lignin, especially for the toluene-choline chloride. Seven DES solutions were recovered, and it was found that the recovery of DES still reached more than 80% at the first recovery.

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