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Title: An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study

Here, this study demonstrated that lignin could be efficiently depolymerized in the solid state with minimal condensation and separated from biomass with high purity by dissolving and hydrolyzing cellulose and hemicelluloses, using an acidic lithium bromide trihydrate (ALBTH) system under mild conditions (with 40 mM HCl at 110 °C). The ALBTH lignins isolated from biomass sources representing the three plant classes (hardwoods, softwoods, and grasses) contained abundant uncondensed moieties (i.e., Hibbert's ketones and benzodioxanes). The benzodioxane structure was identified and confirmed for the first time in an acid-depolymerized lignin. Reactions using lignin model compounds (LMCs, guaiacylglycerol-β-guaiacyl ether and various aromatic monomers) confirmed the formation of the uncondensed moieties and revealed the synergy between LiBr and acid in inducing the crucial intermediate benzyl carbocations, which then led to cleavage of the β- O-4-aryl ether bonds to produce Hibbert's ketones, demethylation to produce benzodioxanes, and condensation reactions. Unlike in the LMC reactions, the condensation of the real lignin in biomass under ALBTH conditions was greatly diminished, possibly due to lignin remaining in the solid state, limiting its mobility and accessibility of the benzyl carbocation to the electron-rich aromatic sites for condensation. Preliminary results indicated that, because of its uncondensed nature, the ALBTHmore » lignin was a good lignin feedstock for hydrogenolysis. In conclusion, this study provided a new approach to effectively isolate depolymerized lignin from lignocellulose in a less condensed form for boosting its downstream valorization.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [4] ;  [5] ; ORCiD logo [2] ; ORCiD logo [1]
  1. University of Wisconsin-Madison, Madison, WI (United States). Department of Biological Systems Engineering
  2. University of Wisconsin-Madison, Madison, WI (United States). Department of Biological Systems Engineering and Department of Biochemistry
  3. University of Wisconsin-Madison, Madison, WI (United States). Department of Biological Systems Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center and Bioscience Division
  4. University of Wisconsin-Madison, Madison, WI (United States). Department of Biological Systems Engineering ; Chinese Academy of Forestry, Nanjing (China). Institute of Chemical Industry of Forestry Products
  5. University of Wisconsin-Madison, Madison, WI (United States). Department of Biological Systems Engineering; Guangdong University of Technology, Guangzhou (China). School of Chemical Engineering and Light Industry
Publication Date:
Grant/Contract Number:
SC0018409; FC02-07ER64494
Type:
Published Article
Journal Name:
Green Chemistry
Additional Journal Information:
Journal Name: Green Chemistry; Journal ID: ISSN 1463-9262
Publisher:
Royal Society of Chemistry
Research Org:
Great Lakes Bioenergy Research Center (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Contributing Orgs:
Magnetic Resonance Facility in the Chemistry Department at the University of Wisconsin–Madison
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; β–O–4-aryl ether bond; benzodioxane; Hibbert’s ketone; acidic lithium bromide trihydrate; lignin model compound
OSTI Identifier:
1467543
Alternate Identifier(s):
OSTI ID: 1455086; OSTI ID: 1459512

Li, Ning, Li, Yanding, Yoo, Chang Geun, Yang, Xiaohui, Lin, Xuliang, Ralph, John, and Pan, Xuejun. An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study. United States: N. p., Web. doi:10.1039/C8GC00953H.
Li, Ning, Li, Yanding, Yoo, Chang Geun, Yang, Xiaohui, Lin, Xuliang, Ralph, John, & Pan, Xuejun. An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study. United States. doi:10.1039/C8GC00953H.
Li, Ning, Li, Yanding, Yoo, Chang Geun, Yang, Xiaohui, Lin, Xuliang, Ralph, John, and Pan, Xuejun. 2018. "An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study". United States. doi:10.1039/C8GC00953H.
@article{osti_1467543,
title = {An uncondensed lignin depolymerized in the solid state and isolated from lignocellulosic biomass: a mechanistic study},
author = {Li, Ning and Li, Yanding and Yoo, Chang Geun and Yang, Xiaohui and Lin, Xuliang and Ralph, John and Pan, Xuejun},
abstractNote = {Here, this study demonstrated that lignin could be efficiently depolymerized in the solid state with minimal condensation and separated from biomass with high purity by dissolving and hydrolyzing cellulose and hemicelluloses, using an acidic lithium bromide trihydrate (ALBTH) system under mild conditions (with 40 mM HCl at 110 °C). The ALBTH lignins isolated from biomass sources representing the three plant classes (hardwoods, softwoods, and grasses) contained abundant uncondensed moieties (i.e., Hibbert's ketones and benzodioxanes). The benzodioxane structure was identified and confirmed for the first time in an acid-depolymerized lignin. Reactions using lignin model compounds (LMCs, guaiacylglycerol-β-guaiacyl ether and various aromatic monomers) confirmed the formation of the uncondensed moieties and revealed the synergy between LiBr and acid in inducing the crucial intermediate benzyl carbocations, which then led to cleavage of the β-O-4-aryl ether bonds to produce Hibbert's ketones, demethylation to produce benzodioxanes, and condensation reactions. Unlike in the LMC reactions, the condensation of the real lignin in biomass under ALBTH conditions was greatly diminished, possibly due to lignin remaining in the solid state, limiting its mobility and accessibility of the benzyl carbocation to the electron-rich aromatic sites for condensation. Preliminary results indicated that, because of its uncondensed nature, the ALBTH lignin was a good lignin feedstock for hydrogenolysis. In conclusion, this study provided a new approach to effectively isolate depolymerized lignin from lignocellulose in a less condensed form for boosting its downstream valorization.},
doi = {10.1039/C8GC00953H},
journal = {Green Chemistry},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {6}
}