Kinetic study of hydrolysis of methylene chloride from 100 to 500 degrees C

Methylene chloride (CH2Cl2) is a representative model compound commonly fou nd in aqueous wastes, process effluents, and contaminated soils and sedimen ts.' Oxidation in supercritical water provides a viable treatment and remed iation pathway to convert CH2Cl2 to CO2, H2O, and HCl. However, in earlier work, partial hydrolysis was observed at subcritical temperatures (<374 deg rees C). This low-temperature reactivity complicates the measurement of kin etic data. In this study, the kinetics of CH2Cl2 hydrolysis in sub- and sup ercritical water were experimentally measured and modeled. Catalytic effect s from a high nickel content alloy used for the reactor were studied by com paring kinetic data obtained in quartz ampules with and without metal prese nt. No heterogeneous catalysis effects were observed. Reaction rates from 1 00 to 500 degrees C were measured to check the reproducibility of existing published data (up to 150 degrees C) and to extend the database for hydroly sis to the supercritical region in order to develop a robust empirical glob al rate expression. The data show a local maximum in the rate constant belo w the critical point of water, consistent with a possible change in the rea ction mechanism induced by changes in the solvent's physical properties (di electric constant, density, etc.). Variations in the global rate constant a gree quantitatively with predictions obtained by applying the Kirkwood mode l, which accounts for changes in the dielectric constant and density of the solvent.