期刊
ACS SUSTAINABLE CHEMISTRY & ENGINEERING
卷 6, 期 4, 页码 5504-5512出版社
AMER CHEMICAL SOC
DOI: 10.1021/acssuschemeng.8b00369
关键词
Phenolation; Softwood kraft lignin; Hardwood biorefinery lignin; beta-elimination
资金
- USDA grant through Domtar
- Biomass to Biochemicals and Biomaterials Research Consortium
Phenolation can be used to improve the reactivity and decrease the molecular weight of lignin, thereby making it more useful for various applications. We report an effective phenolation process with only a catalytic amount of sulfuric acid and using phenol as solvent. The optimum phenolation conditions for pine kraft lignin and sweetgum biorefinery lignin were determined to be lignin/phenol (LIP, wt/wt) of 3/5, 5% acid charge at 90 degrees C for 2 h and L/P of 2/5, 5% acid charge at 110 degrees C for 2 h, respectively. Phenolation resulted in introducing 30 wt % of phenol onto pine kraft lignin and 60 wt % of phenol onto sweetgum biorefinery lignin and significantly decreasing in the molecular weight of lignin. Phenol was incorporated onto both the side chains and aromatic nuclei of lignin. All lignin substructures of beta-O-4', beta-5'/alpha-O-4', beta-beta, alpha-carbonyl, etc. were reacted, resulting in a significant decrease in aliphatic hydroxyl groups and increase in the phenolic hydroxyl groups. The comprehensive characterization revealed that most of the ethers linkages were cleaved during phenolation. The beta-elimination of the gamma-hydroxymethyl group as formaldehyde was the main reaction of side chains. The released formaldehyde reacted with phenol and lignin to form diphenylmethanes. Plausible mechanisms for lignin phenolation are also discussed.
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