Detoxification of Hazardous Waste Streams Using Microwave-Assisted Fluid-Bed Oxidation
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DETOXIFICATION OF HAZARDOUS WASTE STREAMS USING MICROWAVE-ASSISTED FLUIDBED OXIDATION R. VARMA, S. P. NANDI*, AND J. D. KATZ Los Alamos National Laboratory Los Alamos, New Mexico 87545 ABSTRACT
Microwave-assisted oxidation of trichloroethane (TCE) performed at 500-580°C has been found to be significantly more efficient than conventional oxidation methods. Experiments were conducted using a 6 kW, 2.45 GHz power supply and a 6 inch bed of silicon carbide granules in a 1 inch diameter quartz reactor tube which in turn was placed in a microwave cavity. After heating the reactor to a given temperature a TCE-air stream was passed through the silicon carbide bed. TCE was almost completely detoxified (98-99%) in a single pass through the silicon carbide bed at 500-580'C. The oxidation products are HCI, C02 and CO. By comparison the corresponding single-pass detoxification using conventional thermal methods results in only partial conversion. The principal products being dichloroethylene (C2H2C12) and HCl. INTRODUCTION State-of-the-art detoxification of halohydrocarbons is conducted by high temperature (>1200 0 C) incineration in air or oxygen stream. However, corrosion problems are severe, and control of the time-temperature parameter in the combustion zone to avoid PICs (products of incomplete combustion, including dioxines) may be difficult to achieve in practice. Microwave heating for combustion at 1000'C of radioactivity contaminated ion-exchange resins in low-level mixed wastes has been reported by Nahomi et al.1 We report here novel microwave-assisted surface effects that may be responsible for enhanced reactions observed in the case of oxidation of TCE by air at silicon carbide surfaces, in a packed or fluid bed of the same material. EXPERIMENTS AND RESULTS A one-inch diameter quartz tube with a fritted quartz disk on which the bed material (60 by 80 mesch technical grade silicon carbide) rested was used for both microwave and thermal runs. The settled bed height of 6 inches and two flow rates of air were used in the oxidation experiments. In the case of microwave runs, the bed temperature was maintained by dielectric heating by 2.45 Ghz microwaves. The bed was viewed through an opening in the cavity by using an infrared pyrometer (IRCON 6000 Series) for temperature measurement. In thermal runs, the same bed was electrically heated using a long (18-inch) tube furnace. Both the infrared pyrometer and the thermocouple sensors used in monitoring the bed-temperature in the thermal furnace were calibrated with a standard test furnace. Air-TCE gas mixtures were passed through the packed or fluid bed of silicon carbide, energized to the same temperature by dielectric-loss and thermal heating. Before we began a detoxification run, the TCE in the carrier gas was adsorbed by a preweighed active carbon bed at 00C, bypassing the reactor itself. The increase in weight of the carbon bed gave a reliable measure of the feed rate in an actual experiment. *
Argonne
National Laboratory,
Argonne, Illinois 60439
Mat. Res. Soc. Symp
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