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Title: Quenching of reactive intermediates during mechanochemical depolymerization of lignin

Abstract

Mechanochemical reactions are performed to depolymerize organosolv lignin with sodium hydroxide in a mixer ball mill. GPC analysis reveals that rapid depolymerization into small oligomers occurs within minutes of milling time, followed by a slower reduction in average relative molecular mass over the next 8 h of milling. Monomeric products are identified by GC–MS and quantified by GC-FID. The extent of depolymerization appears to be limited by repolymerization reactions that form bonds between products. Suppression of these repolymerization reactions can be achieved through the addition of methanol as a scavenger or adjustment of the moisture content of the feedstock. These modifications result in lower average relative molecular masses and higher yields of monomers. These results are an important step towards designing an efficient pathway for lignin valorization.

Authors:
 [1];  [1];  [1];  [1];  [2];  [2];  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1364389
Report Number(s):
PNNL-SA-120623
Journal ID: ISSN 0920-5861; PII: S0920586117302997
Grant/Contract Number:
AC05-76RL01830
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Catalysis Today
Additional Journal Information:
Journal Volume: 302; Journal ID: ISSN 0920-5861
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; mechanocatalysis; biomass; ball mill; Organosolv lignin; scavenger; hydrolysis

Citation Formats

Brittain, Alex D., Chrisandina, Natasha J., Cooper, Rachel E., Buchanan, Michael, Cort, John R., Olarte, Mariefel V., and Sievers, Carsten. Quenching of reactive intermediates during mechanochemical depolymerization of lignin. United States: N. p., 2017. Web. doi:10.1016/j.cattod.2017.04.066.
Brittain, Alex D., Chrisandina, Natasha J., Cooper, Rachel E., Buchanan, Michael, Cort, John R., Olarte, Mariefel V., & Sievers, Carsten. Quenching of reactive intermediates during mechanochemical depolymerization of lignin. United States. doi:10.1016/j.cattod.2017.04.066.
Brittain, Alex D., Chrisandina, Natasha J., Cooper, Rachel E., Buchanan, Michael, Cort, John R., Olarte, Mariefel V., and Sievers, Carsten. Wed . "Quenching of reactive intermediates during mechanochemical depolymerization of lignin". United States. doi:10.1016/j.cattod.2017.04.066. https://www.osti.gov/servlets/purl/1364389.
@article{osti_1364389,
title = {Quenching of reactive intermediates during mechanochemical depolymerization of lignin},
author = {Brittain, Alex D. and Chrisandina, Natasha J. and Cooper, Rachel E. and Buchanan, Michael and Cort, John R. and Olarte, Mariefel V. and Sievers, Carsten},
abstractNote = {Mechanochemical reactions are performed to depolymerize organosolv lignin with sodium hydroxide in a mixer ball mill. GPC analysis reveals that rapid depolymerization into small oligomers occurs within minutes of milling time, followed by a slower reduction in average relative molecular mass over the next 8 h of milling. Monomeric products are identified by GC–MS and quantified by GC-FID. The extent of depolymerization appears to be limited by repolymerization reactions that form bonds between products. Suppression of these repolymerization reactions can be achieved through the addition of methanol as a scavenger or adjustment of the moisture content of the feedstock. These modifications result in lower average relative molecular masses and higher yields of monomers. These results are an important step towards designing an efficient pathway for lignin valorization.},
doi = {10.1016/j.cattod.2017.04.066},
journal = {Catalysis Today},
number = ,
volume = 302,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2017},
month = {Wed May 10 00:00:00 EDT 2017}
}

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  • Chemoselective blocking of the phenolic hydroxyl (Ar-OH) group by methylation was found to suppress secondary repolymerization and charring during lignin depolymerization. Methylation of Ar-OH prevents formation of reactive quinone methide intermediates, which are partly responsible for undesirable secondary repolymerization reactions. Instead, this structurally modified lignin produces more relatively low molecular weight products from lignin depolymerization compared to unmodified lignin. This result demonstrates that structural modification of lignin is desirable for production of low molecular weight phenolic products. This approach could be directed toward alteration of natural lignification processes to produce biomass more amenable to chemical depolymerization.
  • A detailed study of chemical changes in lignin structure during the ionic liquid (IL) pretreatment process is not only pivotal for understanding and overcoming biomass recalcitrance during IL pretreatment, but also is necessary for designing new routes for lignin valorization. Chemical changes in lignin were systematically studied as a function of pretreatment temperature, time and type of IL used. Kraft lignin was used as the lignin source and common pretreatment conditions were employed using three different ILs of varying chemical structure in terms of acidic or basic character. The chemical changes in the lignin structure due to IL pretreatment processesmore » were monitored using 1H-13C HSQC NMR, 31P NMR, elemental analysis, GPC, FT-IR, and the depolymerized products were analyzed using GC-MS. Although pretreatment in acidic IL, triethylammonium hydrogensulfate ([TEA][HSO4]) results in maximum decrease in β-aryl ether bond, maximum dehydration and recondensation pathways were also evident, with the net process showing a minimum decrease in the molecular weight of regenerated lignin. However, 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) pretreatment yields a smaller decrease in the β-aryl ether content along with minimum evidence of recondensation, resulting in the maximum decrease in the molecular weight. Cholinium lysinate ([Ch][Lys]) pretreatment shows an intermediate result, with moderate depolymerization, dehydration and recondensation observed. The depolymerization products after IL pretreatment are found to be a function of the pretreatment temperature and the specific chemical nature of the IL used. At higher pretreatment temperature, [Ch][Lys] pretreatment yields guaiacol, [TEA][HSO4] yields guaiacylacetone, and [C2C1Im][OAc] yields both guaiacol and guaiacylacetone as major products. These results clearly indicate that the changes in lignin structure as well as the depolymerized product profile depend on the pretreatment conditions and the nature of the ILs. The insight gained on lignin structure changes and possible depolymerized products during IL pretreatment process would help future lignin valorization efforts in a potential IL-based lignocellulosic biorefinery.« less
  • Chemoselective blocking of the phenolic hydroxyl (Ar–OH) group by methylation was found to suppress secondary repolymerization and charring during lignin depolymerization. Methylation of Ar–OH prevents formation of reactive quinone methide intermediates, which are partly responsible for undesirable secondary repolymerization reactions. Instead, this structurally modified lignin produces more relatively low molecular weight products from lignin depolymerization compared to unmodified lignin. This result demonstrates that structural modification of lignin is desirable for production of low molecular weight phenolic products. Finally, this approach could be directed toward alteration of natural lignification processes to produce biomass that is more amenable to chemical depolymerization.
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