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.

Experimental measurements of benzene oxidation in supercritical water

“…Ž . al., 1995, thiodiglycol Lachance et al, 1999 , and methylene Ž chloride Marrone et al, 1995Marrone et al, , 1998aSalvatierra et al, . 1999 .…”

Boundary conditions for developing a safety concept for an exothermal reaction

“…In view of indications contained in Refs. [13,14] K 95 = 1.25 was chosen for the rate constants and K 95 = 1.05 for the enthalpies of reaction. This means that 90% of the values are comprised within intervals of ±25% for rate constants and ±5% for reaction enthalpies, respectively.…”

Effect of Temperature on Anisotropic Crystal Growth of Boehmite under Hydrothermal Condition

“…It has been pointed out that the changes in properties of water by temperature and pressure can drastically affect some reaction rates in sub-and supercritical water. For example, the hydrolysis of CH 2 Cl 2 was diminished under supercritical conditions by the reduction of dielectric constant as CH 2 Cl 2 is less polar and more stable than the products in lower dielectric constant media [16]. In crystallization processes, analogically, if the polarities of precursors are higher than those of the products, the crystallization could be facilitated under lower dielectric constant conditions.…”