The Catalytic Valorization of Lignin for the Production of Renewable Chemicals

The catalytic valorization of lignin for the production of renewable chemicals has been discussed. The polymerization by random phenol radical-radical coupling reactions under chemical control leads to the formation of lignin vascular plants. The dominant linkage in both softwood and hardwood is the β-O-4 linkage, consisting of approximately 50% of spruce linkages and 60% of birch and eucalyptus linkages. The composition of softwood and hardwood lignin varies in the relative abundance of the p-coumaryl, coniferyl, and sinapyl alcohols. The additional methoxy groups on the aromatic rings prevent formation of 5-5 or dibenzodioxocin linkages, and thus cause the hardwood lignin polymer to form more linear structures relative to softwood. Several different lignin sources, derived from a specific form of biomass pretreatment, can be significantly used as feedstock for lignin valorization in a biorefinery.