Detailed Mechanism of Xylose Decomposition in Near-Critical and Supercritical Water

Abstract

The aim of this study was to determine the complete reaction network of xylose decomposition in sub- and supercritical water, including small-molecule intermediates, such as organic acids, which are thought to be the final intermediates in the formation of gaseous products. Solutions of xylose in water were heated under sub- and supercritical conditions in the temperature range of 350–450 °C in a continuous reactor at a controlled pressure of 25 MPa. The intermediates found in the liquid phase were xylulose, furfural, retro-aldol products (glyceraldehyde, glycolaldehyde, dihydroxyacetone, and formaldehyde), and organic acids (acetic and formic acids). The reaction types involved were classified according to Arrhenius behavior: the ionic reaction (not showing Arrhenius behavior in the supercritical region) and the free-radical reaction (showing Arrhenius behavior in the supercritical region). Formic acid was the final intermediate before gasification, while acetic acid and formaldehyde were not gasified in...