This study aims to investigate how the morphology of cellulose influences the hydrolysis and carbonization during hydrothermal treatment at temperatures between 180 and 240 °C. The morphology of cellulose, especially different crystallinities and degrees of polymerization, is represented by microcrystalline cellulose and α-cellulose. Kinetic analysis is considered a tool to allow the determination of the mechanisms of the two types of cellulose during the hydrothermal process. A kinetic model, in which cellulose is assumed to be hydrolyzed to a limited extent, is proposed. Five scenarios are used as models for pyrolysis of nonhydrolyzed cellulose that forms primary char, along with reaction pathways of hydrolyzable cellulose and its derivatives that latterly form secondary char. The morphologies of solid products are in good agreement with the results of the proposed model.

The purpose of this study was to elucidate the decomposition characteristics of 8 xylose, a model compound for hemicellulose, in subcritical and supercritical water. The 9 experiment was carried out at temperatures of 300-450 °C, a pressure of 25 MPa, and a 10 residence time of less than 7 s; xylose decomposed rapidly, but it was still detected at a 11 temperature of 300 °C. Furfural and retro-aldol condensation products were found to be the 12 major liquid intermediates. A reaction network was proposed and the kinetics parameters of 13 all reactions were calculated on the basis of data fitting, assuming that all reactions are first-14 order. Finally, the temperature effect was used to classify the reactions as radical reactions 15 (showing Arrhenius behavior in the supercritical region) or as ionic reactions (not showing 16 Arrhenius behavior in the supercritical region).

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 the temperature range of this study.

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