Holistic Lignin Valorization via Flow Photocatalysis towards vanillin and bioplasticizers

Lignin valorization has become an urgent priority due to its status as the most abundant natural biopolymer containing aromatic structures, yet industrially unexploited. In this study, we present a photocatalytic method using a simple anthraquinone catalyst to break down lignin's recalcitrant structure into valuable monomers. Notably, this process is described under flow conditions for the first time. The monomer yields achieved are the highest reported in literature, although lignin is not fully depolymerized. However, the remaining oligomers can be effectively repurposed as polylactic acid (PLA) plasticizers, significantly enhancing PLA's mechanical properties and imparting shape-memory behavior. Thus, by processing lignin through a photochemical flow reactor, it is fully converted either into industrially relevant monomers, such as vanillin and syringaldehyde, or fragmented sufficiently for use as PLA plasticizers. This approach ensures that no wasteful by-products are generated, offering a sustainable pathway for lignin valorization.