Acid-Catalyzed Chitin Liquefaction in Ethylene Glycol

This paper describes chitin liquefaction in ethylene glycol (EG) under the catalysis of sulfuric acid for the first time. Up to 75% of chitin was liquefied at 165 °C within 90 min by using 8 wt % of acid (refer to the mass of EG). The major products (30% yield) were identified to be hydroxyethyl-2-amino-2-deoxyhexopyranoside (HADP) and hydroxyethyl-2-acetamido-2-deoxyhexopyranoside (HAADP) by GC-MS and confirmed by NMR. Kinetic studies were conducted based on which a plausible mechanism for product formation was proposed. HADP was dominant during the reaction, whereas HAADP formed fast at an initial stage and then most of it was hydrolyzed to HADP. Unreacted chitin residues with different reaction times were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and solid state NMR. The FTIR results showed that negligible deacetylation reaction occurred, supporting the assumption that HADP was produced from the hydrolysis of HAADP rather than directly from chitin polymer chains. The XRD analysis revealed the gradual decrease in crystallinity with the increase in reaction time, indicating the damage of the crystalline domain by the liquefaction process. The simple, cheap, and efficient liquefaction of chitin opens up a new route to produce chemicals and materials from waste in the fishing industry