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Depolymerization of Lignin via Co-pyrolysis with 1,4-Butanediol in a Microwave Reactor

Tarves Paul C., Mullen Charles A., Strahan Gary D., Boateng Akwasi A.
ACS sustainable chemistry 2017 v.5 no.1 pp. 988-994
activated carbon, cresols, depolymerization, feedstocks, hydrocarbons, lignin, molecular weight, phenol, pyrolysis
The production of valuable compounds from low cost but abundant residual lignin has proven to be challenging. The lack of effective biochemical lignin depolymerization processes has led many to focus on thermochemical conversion methods. Bench scale microwave pyrolysis of lignin has been performed at 1200 W over the course of 15 min in the presence of a microwave absorber (activated charcoal). The liquid products obtained are composed of smaller polymeric components and moderate yields of monomeric phenols. However, upon the addition of 1,4-butanediol, repolymerization reactions that limit the yield of monomeric and other reduced molecular weight products are inhibited. A great reduction in the average molecular weight (∼85–90% decrease) of the liquid products was observed as well as an overall increase in liquid yield. At the optimized ratio of 2:1 lignin to 1,4-butanediol (w/w), the yield of selected monomeric phenols increased 3-fold to ∼3.4 wt % (based on feedstock), while the yield of monoaromatic hydrocarbons decreased by approximately 90%. The addition of the diol coreactant also led to a significant shift in selectivity toward the production of methoxy-phenols (guaiacols, syringols) over nonmethoxylated alkyl-phenols (phenol, cresols, etc.). The results obtained may lead to the development of novel lignin coprocessing methods.