(717e) Non-Catalytic Oxidative Depolymerization of Lignin with Molecular Oxygen to Produce Valuable Phenolic Monomers

Lignin as the only component of lignocellulosic biomass containing aromatics has gained increasing attention over the past decades. Lignin valorization could improve the efficiency and profitability of lignocellulosic biorefineries significantly. Recently, oxidative depolymerization of lignin into aromatic compounds have received considerable attention. Unlike hydrogenolysis, oxidative conversion does not require expensive hydrogen and can produce valuable phenolic monomers like vanillin and syringaldehyde. Our hypothesis was that at sufficiently high temperatures, lignin decomposition generates radicals that can activate molecular oxygen without any catalyst. Moreover, activated molecular oxygen can break C-O and C-C bonds, enhancing lignin decomposition and generating additional radicals. In order to test our hypothesis, technical and native lignin sources were depolymerized in presence of oxygen in various polar aprotic and polar protic solvents including acetonitrile, tetrahydrufuran, ethanol and a nonflammable solvent with high oxygen solubility. The reaction products were analyzed through GC/MS, GPC and 2D HSQC NMR techniques. Gas chromatogram of silylated bio-oil showed production of vanillin, syringaldehyde, acetosyringone, syringic acid and vanillic acid as the major monophenolic compounds. GPC results of the obtained bio-oil under oxygen atmosphere also showed lower molecular weight of the bio-oil compared to the obtained bio-oil under inert atmosphere which proves the need for oxygen to depolymerize lignin.