Lignin-first biorefinery of corn stalk via ZrCl4/NaOH-catalyzed aerobic oxidation for phenolic carbonyls production was reported. Under the co-catalysis of ZrCl4 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, ZrCl4 dosage, NaOH dosage, MeCN/H2O ratio, and initial O2 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, ZrCl4/NaOH-catalyzed lignin-first oxidation provided a novel approach for lignin valorization, and achieved the highest reported phenolic carbonyls selectivity.
Keywords: Catalytic aerobic oxidation; Corn stalk; Lignin-first biorefinery; Phenolic carbonyls; Zirconium.
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