Chlorinated solvents priority pollutants

Benzene and its derivatives are used widely throughout the chemical industry as solvents and raw materials. Mono-, di-, and trichlorobenzenes are used directly as pesticides for their insecticidal and fungicidal properties. Benzene, toluene, and chlorobenzene are used as raw materials in the synthesis of at least 15 pesticides, although their main use is as a carrier solvent in 76 processes. Additional priority pollutant aromatics and chlorinated aromatics exist as impurities or as reaction byproducts because of the reactions of the basic raw materials and solvent compounds. 

The chlorinated ethanes and ethylenes are used as solvents, cleaning agents, and intermediates. Vinyl chloride (chloroethylene) is used in the production of plastic polyvinyl chloride (PVC). In the pesticide industry, approximately 23 products are suspected to contain a member of this group of priority pollutants. The main pollutants include 1,2-dichloroethane, which is used as a solvent in seven pesticides and tetrachloroethylene, which is used as a solvent in two pesticides. 

Residence time for supercritical water oxidation systems may be as short as several minutes at temperatures of 600 to 650°C. More than 99.9 percent conversion of EPA priority pollutants such as chlorinated solvents has been achieved in a pilot-scale plant with retention time less than 5 minutes. The system is limited to treatment of liquid wastes or solids less than 200 microns in diameter. Char formation during reaction may impact the oxidation time of the organics, while separation of inorganic salts during the process may be a problem. Typical materials for the reactor are Hastelloy C-276 and Iconel 625 (high nickel alloys), which can withstand high temperatures and pressmes and the corrosive conditions. 

---