Kinetic and mechanistic insights into hydrogenolysis of lignin to monomers in a continuous flow reactor

Industrial biorefineries remain limited due to inefficient valorization of their lignin streams. Rarely can a lignin depolymerization method be combined with a current polysaccharide-centric biorefinery process. Hydrogenolysis is among the more promising methods for depolymerizing lignin on an industrial scale. We performed reaction kinetics and mechanistic studies on lignin model compounds to understand lignin hydrogenolysis pathways, demonstrating that lignin end-units and internal units react significantly differently. Understanding the reaction mechanism and its sensitivity to variables helped us establish a continuous lignin upgrading process from various fractionated lignins. Near-theoretical yields of lignin platform monomers with >80% overall product selectivity were obtained in a continuous hydrogenolysis process using a Pd/C catalyst.