Journal
ACS CATALYSIS
Volume 8, Issue 7, Pages 6507-6512Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.8b00200
Keywords
technical lignin; kraft lignin; C-C cleavage; model lignin; biorefinery lignin; selective catalysis
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Funding
- Catalysis Center for Energy Innovation, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001004]
- National Science Foundation [CBET-1403873]
- Div Of Chem, Bioeng, Env, & Transp Sys [1403873] Funding Source: National Science Foundation
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Biorefinery and paper pulping lignins, referred hereto as technical lignins, contain condensed C-C interunit linkages. These robust C-C linkages with higher bond dissociation energies are difficult to disrupt under hydrogenolysis conditions, which are generally used for cleaving C-O bonds of native lignin in biomass or model C-O linked compounds. Thus, selective interunit C-C cleavage to release aromatic monomers for high-value applications is a challenge. We report an effective catalytic system to cleave such C-C bonds selectively under mild conditions. A representative methylene-linked C-C model dimer achieves 88% yield of mainly two aromatic monomers within 1.S h at a reasonably low temperature (250 degrees C) using a commercial CoS2 catalyst. Aromatic monomers convert to nonaromatic products upon the reaction for a prolonged time. The interunit C-C bond of the dimer become unreactive to cleavage upon dehydroxylation of aromatic rings, while the methoxyl group has little effect on the cleavage. beta-1 and 5-5 C-C linked model dimers formed demethoxylated hydroxyl dimers as the major products. Depolymerization of a purified kraft lignin fraction yields five aromatic monomers and lower-molecular-weight soluble products. This study opens up the possibility of valorization of technical lignins using inexpensive catalysts.
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