Base-Free, Vanadium-Catalyzed Conversion of Chitin into Acetic Acid under Low Oxygen Pressure

The "shell biorefinery" has been proposed and developed rapidly in recent years, which valorizes the underestimated chitin biopolymer from oceanic waste to complement the lignocellulosic biomass for renewable chemicals. Herein, we exploited a simple and effective method to convert chitin biomass into acetic acid (AA) by using vanadium pentoxide (V2O5) and oxygen gas (O2) in base-free water, which makes the process more environmentally and economically favorable than previous methods. Under optimal conditions, the highest AA yield was obtained in 33.4% and 30.0% from the chitin monomer N-acetyl-d-glucosamine (NAG) and ball milled chitin (BM chitin) polymer. The V2O5 catalyst has multifunctionally facilitated the hydrolysis, deacetylation, and subsequent oxidation into AA. FTIR and XRD analyses were conducted for the solid residues after the reaction. The FTIR spectra of the solid residues highly resembled that of chitin, inferring that chitin hydrolysis into NAG probably happened prior to deacetylation. Besides, XRD data demonstrated that the reaction system could effectively destruct the crystalline regions during the reaction. The study demonstrated a new catalytic approach for chitin biorefinery to renovate the shell waste into valuable chemicals.