One-Pot Technical Lignin Catalytic Depolymerization and Demethylation towards Valuable OH-Enriched Oligomers

The catalytic upgrading of technical lignin into valuable functional materials represents a key challenge for sustainable chemistry. This work presents a one-pot hydrogenolysis and demethylation process to transform Kraft lignin into hydroxyl (OH)-enriched oligomers suitable for bio-based polymer applications. Hydrogenolysis reactions were conducted using isobutanol as solvent and heterogeneous catalysts: CoMo(Ox/S)/Al2O3, CoMo(Ox/S)/ZrO2, Mo2C/C, and Pd/C. Products mixtures were separated into isobutanol soluble/insoluble and light/heavy fractions, and characterized by 31P NMR, 13C NMR, HSQC, and SEC. Among the selected candidates, alumina-supported CoMoS and CoMoOx were the most efficient. CoMoS/Al2O3 enhanced demethylation, producing catechol-type OH groups while CoMoOx/Al2O3 favored depolymerization, generating more soluble oligomers but with lower demethylation. Light fractions were especially enriched in guaiacyl and catechol groups, while heavier ones retained more condensed C5 structures. These results confirm that demethylation and limited depolymerization (IUB ether bond cleavage) can be achieved, using a typical CoMoS/Al2O3 catalyst under hydrogenolysis conditions, primarily affecting smaller, soluble lignin-derivatives fragments. These fractions are promising intermediates for bio-based polyol for polymer synthesis, providing a sustainable route to valorize technical lignins using conventional hydrotreating catalysts.