Catalytic Conversion of Lignin in Woody Biomass into Phenolic Monomers in Methanol/Water Mixtures without External Hydrogen

Abstract

The valorization of lignin in renewable lignocellulosic biomass is an important target in the transition to a more sustainable production of fuels and chemicals. We present here a modification of the “lignin-first” approach that does not hinge on the use of external hydrogen. Instead, we use methanol/water mixtures as a suitable solvent that can be partly reformed into hydrogen. We propose a one-step process in which in planta lignin (wood sawdust) is converted to phenolic monomers over a Pt-based catalyst in an inert atmosphere. The role of the methanol/water mixture is not only to supply hydrogen but also to extract lignin fragments from the biomass matrix. Pt catalyzes methanol reforming to obtain hydrogen and the stabilization of reactive lignin intermediates by hydrogenation of reactive bonds. The latter aspect is crucial to avoid unfavorable condensation of fragments. Under optimized conditions, a yield of phenolic monomers of nearly 50% can be obtained from birch wood at a temperature of 230 °C in 3 h.