Spectroscopic investigation of reactions in subcritical and supercritical water

Supercritical water along with subcritical water has been attracting much attention as a reaction medium. The motivation for using SCW as a reaction medium is because of the continuous effort by people looking for environmentally benign chemistry, or in another modern words, “Green Chemistry ”. Among all research with applications in SCW, supercritical water oxidation (SCWO) has received the most attention because SCWO has shown extremely promising potential as a waste treatment technology. Understanding the kinetics of the oxidation process becomes prominently important to model and design SCWO reactors and processes. In this work, laser flash photolysis and pulse radiolysis have been used to study two types of model reactions in subcritical and supercritical water: ionic reactions and free radical reactions.; There are several major findings in this work.; Firstly, the ability of sub-critical water to support ionic chemistry is evident from the successful generation of 9-R-xanthenium carbocations at temperatures up to 330°C using laser flash photolysis. In addition, we determined the bimolecular rate constants for the reactions of xanthenium cation and 9-phenylxanthenium cation with amylamine, a neutral nucleophile.; Secondly, the bimolecular rate constants of the addition reaction between hydroxyl radical (·OH) and nitrobenzene (C₆H ₅NO₂) were measured in water at temperatures between ambient and 390°C. The measured bimolecular rate constants showed non-Arrhenius behavior from ambient to 350°C, but increased in the subcritical and supercritical region between 350 and 390°C. To our knowledge, this is the first report of the bimolecular rate constant for a reaction involving the addition of ·OH in SCW.; Finally, the experimentally measured bimolecular rate constants of the conditions to the supercritical region were presented. The bimolecular rate constants showed Arrhenius temperature dependence over the studied temperature steps in SCWO elementary reaction models. To our knowledge, this is the first report of the bimolecular rate constant for a reaction involving the hydrogen...