Degradation of chlorinated volatile organic compounds in waste gas by catalytic plasma system

Abstract

Dichloromethane (DCM), one of the main components of chlorinated volatile organic compounds (Cl-VOCs), is recognized as extremely hazardous and severely affects human health and the environment. In this study, a self-designed Dielectric Barrier Discharge (DBD) reactor combined with different catalysts to treat the exhaust DCM gas containing ppm concentration levels. A plasma system can generate high-energy electrons and free radicals (such as hydroxyl radical (OH·), and superoxide radical (O2·)) to degrade DCM in the industrial exhaust gas into most HCl and CO2. The removal efficiency can achieve 98.7% under the conditions, a flow rate of 1042 mLmin−1, the residence time of 76.72 ms, concentration of DCM of about 1650 ppm, and specific input energy of 591 JL−1. Although the plasma was highly reactive, the selectivity of the desired products was low, and there were unwanted toxic byproducts such as CHCl3 (1.7%) and CCl4 (13.8%). Thus catalysts were loaded in the plasma discharging zone to enhance removal efficiency and change product distribution. The catalysts were conducive to producing water-soluble products such as HCl. At the same time, the formation of some unwanted byproducts, CHCl3 and CCl4, were also inhibited. We found that using 11.5 kVpp plasma operating voltage combined with 200 mg Co3O4/HZSM-5 can lower the DCM concentration of the outlet stream from 1650 ppm to 53 ppm. Under this condition, the removal efficiency was about 96.7%, attaining permitted emissions.