The present invention relates to the chemical detoxification of polychlorinated biphenyls by converting them to non-hazardous substances. In particular, the invention relates to chemically destroying polychlorinated biphenyls on site for decontamination purposes without creating pollution or hazardous situations.
Polychlorinated biphenyls (PCBs) are chlorinated aromatics used as inert liquids for insulating power transformers, utility boxes, etc. PCBs are known to be carcinogenic and highly toxic in small quantities, when ingested, and for that reason, they are disposed of by burial in approved landfills. PCB spills from damaged utility boxes or during transfer and similar situations have created problems causing PCB contamination of the soil or areas where the spills occurred. This has necessitated the digging up and removal of soils and other materials, and transferring them to safe disposal sites for burial, but this does not detoxify the PCBs. Destruction of PCBs by combustion creates other hazards, since deadly airborne dioxins are produced if the combustion temperature is below 2500 degrees C.
Other methods for chemically reducing PCBs, such as by Raney nickel or cobalt catalysts, are unsatisfactory in that byproducts which may be hazardous to health and environment are produced. Reduction of PCBs by Raney nickel may leave nickel salts, which are known carcinogens, in the reaction medium. Other prior methods for chemically reducing PCBs do not dispose of biphenyl or polyphenylene, which is sticky, and non-biodegradable under ordinary conditions, and has sufficient toxicity to warrant still being a pollutant. Methods using sodium metal, sodium or potassium alloys, sodium hydride, and sodium amides are all impossible to use with water and aqueous systems, and, therefore, are hazardous for using to detoxify contaminated soils on site. Anhydrous conditions are rarely found at PCB spill sites.
Polychlorinated biphenyls (PCBs) are made by chlorinating biphenyl to obtain several isomers. The biphenyl, which has all positions occupied by hydrogen, is converted to polychlorinated biphenyl where 2 or more hydrogen atoms are replaced by chlorine, i.e. x=2 to 10 chlorines, depending upon the isomer, as shown below: ##STR1##
A two-step method has been sought which will convert PCBs directly into more easily handled, less toxic, more biodegradable, water or alkali soluble byproducts.
The present invention herein describes the reduction of the PCB isomers back to biphenyl, followed by oxidation to yield simpler, less toxic, more biodegradable organic carboxylic acids.
With the present invention a process is provided whereby PCBs can be chemically destroyed on site to detoxify contaminated soil and other areas. The process, as hereinafter described is useful in health, safety and pollution control since PCB contamination of water and soil is a major health and environment hazard.