Catalytic oxidation of biorefinery corncob lignin via zirconium(IV) chloride and sodium hydroxide in acetonitrile/water: A functionality study

In order to realize the efficient utilization of biorefinery corncob lignin, the promising catalytic oxidation strategy was carried out by using ZrCl 4 and NaOH as the co-catalyst and dioxygen as the oxidant in MeCN/H 2 O. GC/MS, GC-FID, and MALDI-TOF/MS were employed to recognize the produced monomers and oligomers , and GPC was used to monitor the molecular weight changes of lignin fragments. In addition, specific structural evolution of corncob lignin during ZrCl 4 /NaOH-catalyzed oxidation were revealed by quantitative 13 C (Q 13 C) and 2D HSQC NMR techniques. Results showed that the total yields of produced oxidation monomers reached 6.8 wt%, and aromatic aldehydes were the major species, in which vanillin and 4-hydroxybenzaldehyde were the two dominant products. After ZrCl 4 /NaOH-catalyzed oxidation, the weight-average molecular weight of corncob lignin and its products decreased from 2000 Da to 300 Da after oxidation with 16 h. Moreover, Q 13 C NMR analysis showed the decrease percentage of C O aliphatic carbons (including methoxyl carbons), the increase percentage of C C aliphatic and carbonyl carbons, and the relative stable percentage of aromatic carbons with reaction prolonged. These results combined with the further confirmation from HSQC indicated the oxidative cleavage of C O aliphatic linkages and removal of methoxy groups within corncob lignin, as well as the formation of C C aliphatic bonds and carbonyl groups. The work presented a comprehensive insight into the catalytic oxidative depolymerization of biorefinery corncob lignin.