Kinetic Study of Hydrolysis of Methylene Chloride from 100 to 500 °C

Abstract

Methylene chloride (CH2Cl2) is a representative model compound commonly found in aqueous wastes, process effluents, and contaminated soils and sediments. Oxidation in supercritical water provides a viable treatment and remediation pathway to convert CH2Cl2 to CO2, H2O, and HCl. However, in earlier work, partial hydrolysis was observed at subcritical temperatures (<374 °C). This low-temperature reactivity complicates the measurement of kinetic data. In this study, the kinetics of CH2Cl2 hydrolysis in sub- and supercritical water were experimentally measured and modeled. Catalytic effects from a high nickel content alloy used for the reactor were studied by comparing kinetic data obtained in quartz ampules with and without metal present. No heterogeneous catalysis effects were observed. Reaction rates from 100 to 500 °C were measured to check the reproducibility of existing published data (up to 150 °C) and to extend the database for hydrolysis to the supercritical region in order to develop a robust empirical global rate expression. The data show a local maximum in the rate constant below the critical point of water, consistent with a possible change in the reaction mechanism induced by changes in the solvent's physical properties (dielectric constant, density, etc.). Variations in the global rate constant agree quantitatively with predictions obtained by applying the Kirkwood model, which accounts for changes in the dielectric constant and density of the solvent.