Characterization and Catalytic Transfer Hydrogenolysis of Deep Eutectic Solvent Extracted Sorghum Lignin to Phenolic Compounds

Lalitendu Das, Mi Li, Joseph Stevens, Wenqi Li, Yunqiao Pu, Arthur J. Ragauskas, Jian Shi

Research output: Contribution to journalArticlepeer-review

68 Scopus citations

Abstract

Deep eutectic solvent (DES) is intrinsically cheaper than many ionic liquids (ILs) due to low precursor cost, simple synthesis, and improved recyclability. Meanwhile, DES can be as effective as ILs toward dissolving lignin from plant materials. However, the lignin depolymerization mechanism in DES, the structural and chemical properties of DES-extracted lignin (DES-EL), and the possible valorization pathways of DES-EL toward value-added products were not well understood. This study aims to characterize the lignin streams from DES (1:2 choline chloride:lactic acid) treated sorghum and further upgrade the extracted lignin to phenolic compounds. As revealed by HSQC, 13C, and 31P NMR analysis, DES cleaved nearly all ether linkages in native lignin, resulting in significant size reduction. We further catalytically upgraded DES-EL to phenolic compounds via catalytic transfer hydrogenolysis in the presence of isopropyl alcohol. Among the three tested catalysts (Ru/C, Pd/C, and Pt/C), Ru/C proved the most effective in deconstructing DES-EL, with oil, char, and gas yields of 36.3, 46.4, 17.3 wt %, respectively. Major lignin monomeric products in the oil were phenol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-propylphenol, and 4-hydroxy-benzenepropanoic acid. This study provides a mechanistic understanding of lignin depolymerization in DES and demonstrates a possible way to catalytic upgrading of DES-EL to low molecular weight phenolic compounds.

Original languageEnglish
Pages (from-to)10408-10420
Number of pages13
JournalACS Sustainable Chemistry and Engineering
Volume6
Issue number8
DOIs
StatePublished - Aug 6 2018

Bibliographical note

Publisher Copyright:
Copyright © 2018 American Chemical Society.

Keywords

  • Catalysis
  • Deep eutectic solvents
  • Hydrogenolysis
  • Lignin
  • Sorghum

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry
  • General Chemical Engineering
  • Renewable Energy, Sustainability and the Environment

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