PERCHLOROETHYLENE

Perchloroethylene (PCE) is a colorless, nonflammable liquid with an ethereal odor. The chemical name for perchloroethylene is tetrachloroethylene; it is also known as tetrachloroethene and perc.



















Perchloroethylene is practically insoluble in water, but is miscible with the chlorinated organic solvents and most other common solvents such as ethanol, diethyl ether, and oils. It is a solvent for many substances, including fats, oils and tars. At 20EC, PCE has a vapor pressure of 1.87 kPa (14 mmHg). Table 2 summarizes the physical and chemical properties of PCE.























In the presence of light and air, perchloroethylene slowly autooxidizes to trichloroacetyl chloride. Stabilizers, such as amines or phenols, inhibit the decomposition process to extend solvent life and protect equipment and materials. Compared to other chlorinated ethanes and ethylenes, PCE is relatively stable, and generally requires only small amounts of stabilizers.












Perchloroethylene is produced domestically by three processes. These are :

(1) the direct chlorination of ethylene dichloride, 

(2) the oxychlorination of ethylene dichloride, and 

(3) hydrocarbon chlorinolysis. 







In the first two processes, PCE can be produced separately or as a coproduct of TCE with the raw material ratios determining the proportions of PCE and TCE. In the third process, PCE is manufactured as a coproduct with carbon tetrachloride.












Perchloroethylene may also be formed as a by-product during ethylene dichloride/vinyl chloride monomer manufactures Perchloroethylene is produced in purified, technical, USP, and spectrometric grades. The various grades are produced for dry cleaning, technical, industrial, and vapor-degreasing uses, respectively.










Perchloroethylene is commercially important primarily as a chlorinated hydrocarbon solvent and as a chemical intermediate. The major end use of PCE is as a dry cleaning solvent. 



Perchloroethylene largely replaced carbon tetrachloride (which is no longer used) in commercial, coin-operated, industrial and garment-rental dry cleaning operations. Some PCE is also used in textile processing as a scouring solvent and as a carrier solvent. 



Together these uses account for about 50 percent of total domestic demand for PCE. Approximately 25 percent of the PCE supply is used as a chemical intermediate in chlorofluorocarbon production (mostly for chlorofluorocarbon 113). Another 15 percent is consumed in organic solvent cleaning operations such as vapor degreasing and metal cleaning. The remaining 10 percent of the PCE supply is primarily consumed in other solvent applications. 







These applications include use :



(1) as a solvent in paints, coatings, and adhesives, 

(2) as a solvent in aerosol formulations, and 

(3) in miscellaneous solvent applications.




















Trichloroethylene and PCE are used in miscellaneous chemical synthesis and solvent applications. For example, TCE is used as a reactant to produce pesticide intermediates. An estimated 3,670 Mg of TCE were consumed for this purpose by the pesticide industry in 1984. 





Trichloroethylene may also be used in the chemical synthesis of flame- retardant chemicals; as a solvent in pharmaceutical manufacture; as a solvent in waterless preparation, dying, and finishing operations in the textile industry; and as a carrier solvent in formulated consumer products such as insecticides, fungicides, typewriter correction fluids, paint removers, and paint strippers. 










The known miscellaneous uses of PCE primarily include solvent applications. 



The pharmaceutical industry consumed about 7 Mg of PCE solvent in 1985. In textile processing, PCE functions as a scouring solvent, removing oils from fabrics after knitting and weaving operations, and as a carrier solvent for fabric finishes and water repellents, and for sizing and desizing. Perchloroethylene is miscible with other common solvents and is an ingredient in blended solvents.








Perchloroethylene is used as a carrier solvent in as printing inks, cleaners, polishes, lubricants, is also used as a recyclable dielectric fluid for heat transfer medium, and pesticide intermediate. many products such and silicones. It power transformers, heat transfer medium, and pesticide intermediate.



















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Michael Thang

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