Lignin-first biorefinery of corn stalk via zirconium(IV) chloride/sodium hydroxide-catalyzed aerobic oxidation to produce phenolic carbonyls

Lignin-first biorefinery of corn stalk via ZrCl 4 /NaOH-catalyzed aerobic oxidation for phenolic carbonyls production was reported. Under the co-catalysis of ZrCl 4 and NaOH, lignin in corn stalk was oxidized into phenolic aldehydes ( p -hydroxybenzaldehyde, vanillin, and syringaldehyde), ketones ( p -hydroxyacetophenone, acetovanillone, and acetosyringone), acids ( p -hydroxybenzoic acid and vanillic acid), and other derivatives. Reaction conditions, including time, temperature, ZrCl 4 dosage, NaOH dosage, MeCN/H 2 O ratio, and initial O 2 pressure were comprehensively screened, and the optimal lignin-derived monomer yields of 13.2 wt% was obtained. Among these aromatic compounds, phenolic aldehydes were the main products, and the overall selectivity of phenolic carbonyls was as high as 93%. Cellulose-rich residues after lignin-first oxidation were further characterized by thermogravimetry and analytical pyrolysis with corn stalk as the control, proving the good fragmentation and dissolution of lignin streams. In general, ZrCl 4 /NaOH-catalyzed lignin-first oxidation provided a novel approach for lignin valorization, and achieved the highest reported phenolic carbonyls selectivity.