Reaction mechanism of hydrolysis in Supercritical water

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For understanding specific features of reactions in supercritical water, kinetic study was conducted for the hydrolysis of cellulose model compounds by using a flow-type micro-reactor. At supercritical conditions, hydrolysis rate increased with increasing water density. Comparison of the kinetics with water density or proton concentration suggests a reaction mechanism that hydrolysis reaction undergoes via the direct attack of water molecule to the substrate. Through this study, importance of understanding the local hydration structure around a solute has been suggested for evaluating the reaction kinetics and mechanisms in supercritical water. Thus, we evaluated hydration structure around a substrate by using in-situ UV spectroscopy. The shift of the absorption spectrum of nitrogen containing organic compounds has been analyzed to evaluate the hydrogen bonding and solvation structure around the solute. We found the followings; namely degree of hydrogen bonding decreases with increasing temperature (decreasing water density) in subcritical region, and the hydration structure changes greatly around the critical point, and became significant with increasing water density under the supercritical condition.