Understanding Lignin Fractionation and Characterization from Engineered Switchgrass Treated by an Aqueous Ionic Liquid

Enshi Liu, Mi Li, Lalitendu Das, Yunqiao Pu, Taylor Frazier, Bingyu Zhao, Mark Crocker, Arthur J. Ragauskas, Jian Shi

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

Aqueous ionic liquids (ILs) have received increasing interest because of their high efficacy in fractionating and pretreating lignocellulosic biomass while at the same time mitigating several challenges associated with IL pretreatment such as IL viscosity, gel formation during pretreatment, and the energy consumption and costs associated with IL recycling. This study investigated the fate of lignin, its structural and compositional changes, and the impact of lignin modification on the deconstruction of cell wall compounds during aqueous IL (10% w/w cholinium lysinate) pretreatment of wild-type and engineered switchgrass. The 4CL genotype resulting from silencing of 4-coumarate:coenzyme A ligase gene (Pv4CL1) had a lower lignin content, relatively higher amount of hydroxycinnamates, and higher S/G ratio and appeared to be less recalcitrant to IL pretreatment likely due to the lower degree of lignin branching and more readily lignin solubilization. The results further demonstrated over 80% of lignin dissolution from switchgrass into the liquid fraction under mild conditions while the remaining solids were highly digestible by cellulases. The soluble lignin underwent partial depolymerization to a molecular weight around 500-1000 Da. 1H-13C HSQC NMR results demonstrated that the variations in lignin compositions led to different modes of lignin dissolution and depolymerization during pretreatment of engineered switchgrass. These results provide insights into the impact of lignin manipulation on biomass fractionation and lignin depolymerization and lead to possible ways toward developing a more selective and efficient lignin valorization process based on aqueous IL pretreatment technology.

Original languageEnglish
Pages (from-to)6612-6623
Number of pages12
JournalACS Sustainable Chemistry and Engineering
Volume6
Issue number5
DOIs
StatePublished - May 7 2018

Bibliographical note

Publisher Copyright:
© 2018 American Chemical Society.

Keywords

  • Engineered switchgrass
  • Ionic liquid
  • Lignin
  • Pretreatment

ASJC Scopus subject areas

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

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