A Practical Way to Separate Uncondensed Lignin during Biomass Pretreatment and Quantitatively Depolymerize It at a Low Temperature of 120°C with a Cheap Ni/Al2O3-SiO2 Catalyst

High-yield lignin monomer production from separated lignin in practical ways could greatly increase biorefinery productivity and profitability. However, lignin condensation caused by the formation of inter-unit carbon-carbon linkages during biomass pretreatment dramatically reduces lignin monomer yields; besides, high temperatures and noble-metal catalysts used in lignin hydrogenolysis depolymerization further increase the impracticality.

Recently, we have two significant findings which can largely drive the valorization of lignin. First, adding formaldehyde during biomass pretreatment produces a soluble lignin liquor that can be converted to guaiacyl and syringyl monomers at near-theoretical yields during subsequent hydrogenolysis; second, separated lignin can be readily depolymerized at a low temperature of 120°C with a cheap Ni/Al₂O₃-SiO₂ catalyst.  We achieved a yield of 45% for beech wood, and a yield of 78% for transgenic poplar wood with low levels of carbon-carbon linkages in native lignin (yields were on the basis of native lignin). These yields were 3-7 times those obtained without formaldehyde. Formaldehyde reacted with lignin side-chain alpha- and gamma- hydroxyl groups to form stable 1,3-dioxane structures and with lignin aromatic rings to block the active positions, which completely quenched the condensation of lignin and facilitate its depolymerization under mild catalytic conditions.

Research Interests: Catalytic conversion of biomass into fuels, chemicals and materials.

Teaching Interests:  Biomass conversion