Understanding the behavior of chitin in Subcritical and Supercritical Water in a continuous reaction system

Abstract

After cellulose, chitin is the second most widespread biopolymer worldwide. Its best-known applications, thanks to its antibacterial, toxicological and biocompatibility properties, are oriented to the medical and pharmaceutical industry, cosmetics, agriculture, and water treatment, among others. Being a biopolymer, chitin is formed by [ -1,4-poly(n-acetyl-D-glucosamine)] units, which can be treated to obtain oligomers and monomers, N-acetylglucosamine (depolymerization) and glucosamine (deacetylation). These monomers constitute nitrogen containing building blocks that open the way to sea-waste biorefinery for obtaining molecules of interest, such as furan-based monomers or amines1. Studies have shown that chitin, like cellulose, can be dissolved and hydrolyzed in sub- and supercritical water; however, due to its high crystallinity, this process occurs less easily2. Processes studied have used sub- and supercritical technology in batch-type systems as pre-treatments in enzymatic processes, managing to dissolve and even obtain monomers in times of up to 1 minute2. However, degradation compounds have been obtained or even the prevalence of side reactions competing with hydrolysis has been observed (depending on the reaction conditions). The present work shows the behavior of chitin in subcritical and supercritical media, seeking to understand the effect of water properties (density, viscosity, ionic product) at conditions surrounding the critical point; specifically, to investigate the reaction mechanism of chitin in SubCW and SCW media using ultrafast continuous reactors.