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Catalytic Depolymerization of Native and Technical Lignin into Phenolic Compounds Using Nickel Catalyst


Increasing greenhouse gas emissions as well as a series of environmental issues caused by fossil fuels combustion have motivated the development of renewable energy sources. Nonfood lignocellulosic biomass is a promising renewable source for making liquid fuels and valuable chemicals, due to its high energy content stored by the biosphere. However, the efficient utilization of biomass has been significantly hindered by its recalcitrant nature. Herein, we have investigated the use of Ni/C for the catalytic depolymerization of native lignin in Miscanthus, a grassy biomass. Under optimized conditions, over 69% yield of select aromatic products were obtained from lignin. Carbohydrates remaining after lignin removal were recovered as a solid residue, which upon treatment with iron chloride produced useful platform chemicals (furfurals and levulinic acid). Understanding bond connectivity in biomass (between lignin and carbohydrates) advances the development and commercialization of more efficient catalytic methods for biomass utilization. To achieve this goal, Dynamic Nuclear Polarization (DNP) Enhance Solid State NMR (ssNMR) was used to probe the atomic level structure of biomass pre- and post- lignin treatment. Our results revealed an increase in the relative ratio of crystalline cellulose upon the catalytic depolymerization of lignin (CDL) using Ni/C catalyst. In parallel with direct catalysis of native lignin in raw biomass, organosolv pretreatment was used to produce sulfur-free technical lignin in high purity. Our study investigated the effect of biomass substrate and organosolv pretreatment methods on the isolated lignin towards further upgrading over a Ni/C catalyst. By comparing different solvents (acetic acid/formic acid, acetone and methanol) applied for lignin extraction, methanol was revealed to minimize the undesirable re-condensation of organosolv lignin.

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