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(501f) Stabilization with Aldehydes for the High Yield Production of Targeted Monomer Mixtures from Lignin during Integrated Biomass Depolymerization

Authors: 
Luterbacher, J. S., Ecole polytechnique fédérale de Lausanne
Lignin is the fraction of lignocellulosic biomass with the highest energy density and is one of the few natural large-scale sources of aromatic molecules. However, the lack of practical depolymerization processes that can produce a limited number of lignin monomers at high yields has limited the options for upgrading lignin. The development of these processes has been restricted by the presence of inter-unit carbon-carbon bonds within native lignin, and further by formation of such linkages during lignin extraction. We report that adding aldehydes and forming their associated protection group during biomass pretreatment produces a soluble lignin fraction that can be converted to guaiacyl and syringyl monomers at near-theoretical yields during subsequent hydrogenolysis. Up to a 48% yield can be achieved from wild type wood while yields as high as 78% can be achieved from high-syringyl transgenic poplar with low levels of carbon-carbon linked units. Furthermore, the nature of the aldehyde and upgrading conditions can be used to reduce the distribution of monomers. The resulting monomer yields were 3-7 times greater than those obtained without using aldehydes as protection groups, which prevented lignin condensation primarily by forming 1,3-dioxane structures with lignin side-chain hydroxyl groups. By depolymerizing cellulose, hemicelluloses, and lignin separately, overall monomer yields between 76 and 90% were achieved for these three major biomass fractions. Recovery of an isolated lignin fraction that is soluble in an organic solvent and can produce high yields of a limited number of monomers could facilitate continuous lignin processing and the development of heterogeneous catalysts for lignin conversion.