(58d) Reductive Conversion of Lignin with Copper-Doped Catalysts

The lignin component of biomass has potential as a renewable source for industrially useful aromatic chemicals. While technologies for the selective conversion of the carbohydrate components have been successful, lignin is generally treated as waste and burned for low grade heat. We have developed a catalytic system, based on a copper-doped porous oxide, which can reductively disassemble lignin in supercritical methanol with little to no char formation. While the copper-doped porous oxide catalyzes C-O hydrogenolysis of aryl-ether bonds linking lignin monomers, it also catalyzed ring methylation and hydrogenation, leading to lignin disassembly product proliferation. We have found that adding dimethyl carbonate can significantly suppress the hydrogenation of the phenolic intermediates responsible for much of the undesirable product diversity by methylation of phenolic hydroxyl groups to form a more stable aryl ether species. Using the methanol and dimethyl carbonate solvent system with the copper-doped porous oxide catalyst, O-methylation of phenolic hydroxyl groups was effective at increasing aromatic yields from a number of lignin model polymer systems and poplar organosolv lignin. These results demonstrate the promise of our copper-doped porous oxide catalyst when used in the presence of methanol and dimethyl carbonate to facilitate aromatic compound production from lignin.