Perchloroethylene,

There are three processes used in the making of perchloroethylene (tetra-chloroethylene melting point -19°C, boiling point 121°C, density 1.6227), but the majority is made from ethylene dichloride. 

Perchloroethylene and trichloroethylene are produced in a single-stage oxychlorination process from ethylene dichloride and chlorine. 

Chlorination of hydrocarbons, such as propane, and acetylene with chlorine also produces perchloroethylene via trichloroethylene. 

1 -trichloroethylene is usually made in the same apparatus or as a coproduct. Both chlorination and oxychlorination are used to supply the reagents needed. The reactions follow the same pattern as those for ethane and methane chlorination. Temperatures, pressures, and reagent ratios are somewhat different, however. 

The main use of perchloroethylene is in dry cleaning and textile processing other uses are as a chemical intermediate, in industrial metal cleaning (vapor and cold degreasing), in adhesives, in aerosols, and in electronics. 

The percutaneous LDso values for 2 4-hour occluded contact on the skin of rabbits were 1.41ml/kg for males and 0.81 for females. Times of death ranged from 45 minutes to 1 day. Signs of toxicity were dilated pupils within 15-30min, convulsions in one animal, and excess, blood-stained saliva. Local signs of inflammation were erythema, edema, and necrosis. In survivors, inflammation persisted for up to 7 days with scab formation by 2 weeks. Instilled in the eye of rabbits, the liquid produced mild conjunctivitis without corneal injury. 

Although irritant effects do not appear until high concentrations are reached, it is expected that the low odor threshold (0.01 ppm) could provide adequate warning of exposure to 2,4-pentanedione.  

4-Pentanedione caused sister chromatid exchange increases in Chinese hamster ovary (CHO) cells and an increase in the incidence of micronuclei in peripheral blood eiythroqU es of mice. It was not mutagenic in a Salmonella typhimurium assay. 

A threshold limit value (TLV) has not been established for 2,4-pentanedione. 

Krasavage WJ, O Donoghue JL, Divincenzo GD 2,4-Pentanedione. In Clayton GD, Clayton FE (eds) Patty s Industrial Hygiene and Toxicology, Vol 2C, Toxicology, pp 4773-4776. New York, Wiley, 1982 

Perchloreihylenc ii a clear, water-while liquid at ordinary icmpctaturcs. It is completely miscible with most organic liquids. The stabilized product. Pcrchlor, can be used with any of the common construction metals. 

Flash Point (Tag open cup) Fire Point (Tag open cup) None None (8-hour TW A) ppm 100 

Specific Gravity, 20 C/20 C Nonvolatile Residue, wt % Free Chlorine Moisture 

Specification Clear, free of suspended matter 15 maximum Characteristic no residual No spot or slain 1.623 to 1.628 0.0025 maximum None 

Typical Analysis Clear, free of suspended matter 8 

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Chloroacetic acid forms a2eotropes with a number of organic compounds. It can be recrystaUized from chlorinated hydrocarbons such as trichloroethylene, perchloroethylene, and carbon tetrachloride. The freezing poiat of aqueous chloroacetic acid is shown ia Figure 1. 

Chlorinated Solvents. Originally, successive chlorination and dehydro-chlorination of acetylene was the route to trichloroethylene [79-01-6], C2HCI3, and perchloroethylene [127-18-4], C2C1. ... 

Ethylene dichloride, vinyl chloride monomer, trichloroethylene, perchloroethylene. 

Acetate and triacetate are essentially unaffected by dilute solutions of weak acids, but strong mineral acids cause serious degradation. The results of exposure of heat-treated and untreated triacetate taffeta fabrics to various chemical reagents have been reported (9). Acetate and triacetate fibers are not affected by the perchloroethylene dry-cleaning solutions normally used in the United States and Canada. Trichloroethylene, employed to a limited extent in the UK and Europe, softens triacetate. 

Halogenation and Hydrohalogenation. Halogens add to the triple bond of acetylene. FeCl catalyzes the addition of CI2 to acetylene to form 1,1,2,2-tetrachloroethane which is an intermediate in the production of the industrial solvents 1,2-dichloroethylene, trichloroethylene, and perchloroethylene (see Chlorocarbons and chlorohydrocarbons). Acetylene can be chlorinated to 1,2-dichloroethylene directiy using FeCl as a catalyst... 

Minor amounts of acetylene are used to produce chlorinated ethylenes. Trichloroethylene (trichloroethene) and perchloroethylene (tetrachloroethene) are prepared by successive chlorinations and dehydrochlorinations (see Chlorocarsons and chlorohydrocarsons). The chlorinations take place in the Hquid phase using uv radiation and the dehydrochlorinations use calcium hydroxide in an aqueous medium at 70—100°C. Dehydrochlorination can also be carried out thermally (330—700°C) or catalyticaHy (300—500°C). 

Chlorinated C2> Perchloroethylene (PCE) and trichloroethylene (TCE) can be produced either separately or as a mixture in varying proportions by reaction of C2-chlorinated hydrocarbons, eg, C2-chlorinated waste streams or ethylene dichloride, with a mixture of oxygen and chlorine or HCl. 

Partial oxidation of natural gas or a fuel oil using oxygen may be used to form acetylene, ethylene (qv) and propylene (qv). The ethylene in turn may be partially oxidi2ed to form ethylene oxide (qv) via advantages (/) and (5). A few of the other chemicals produced using oxygen because of advantages (/) and (5) are vinyl acetate, vinyl chloride, perchloroethylene, acetaldehyde (qv), formaldehyde (qv), phthaHc anhydride, phenol (qv), alcohols, nitric acid (qv), and acryhc acid. 

In the CSIRO process, a reactive polyurethane prepolymer is appHed to a garment from perchloroethylene. The garment is then pressed and subsequendy steamed in an oven. A second polymer may sometimes be used in conjunction with the prepolymer. When this is employed, the process is termed the Serolan BAP Process (178). A number of alternative treatments are being investigated to achieve finishes that are more environmentally friendly (179). 

Chlorination of various hydrocarbon feedstocks produces many usehil chlorinated solvents, intermediates, and chemical products. The chlorinated derivatives provide a primary method of upgrading the value of industrial chlorine. The principal chlorinated hydrocarbons produced industrially include chloromethane (methyl chloride), dichloromethane (methylene chloride), trichloromethane (chloroform), tetrachloromethane (carbon tetrachloride), chloroethene (vinyl chloride monomer, VCM), 1,1-dichloroethene (vinylidene chloride), 1,1,2-trichloroethene (trichloroethylene), 1,1,2,2-tetrachloroethene (perchloroethylene), mono- and dichloroben2enes, 1,1,1-trichloroethane (methyl chloroform), 1,1,2-trichloroethane, and 1,2-dichloroethane (ethylene dichloride [540-59-0], EDC). 

Trichloroethylene use has declined as a result of environmental concerns. However, trichloroethylene may replace some 1,1,1-trichloroethane appHcations. Perchloroethylene used in small businesses for dry cleaning will be regulated for emissions under the same guidelines as those that govern the large chemical producers. This will cause replacement of perchloroethylene for those appHcations where recovery is uneconomical. Methylene chloride has been classified as a suspected carcinogen and its use will decline in aerosol and paint stripping appHcations because of health concerns. 

Typical reactions using either 1,2-dichloroethane or 1,2-dichloropropane to produce carbon tetrachloride and tetrachloroethylene by the chlorinolysis reaction are shown in equations 21—23. Continued removal of tetrachloroethylene and recycling of carbon tetrachloride can result in a net zero production of carbon tetrachloride. Most chemical producers using chlorinolysis for the production of perchloroethylene in the future will take advantage of the per/tet equiUbrium to maximize perchloroethylene to avoid carbon tetrachloride ipiod.uction.From 1,2-dichloroethane ... 

As chlorination proceeds from methyl chloride to carbon tetrachloride, the length of the C—Cl bond is decreased from 0.1786 nm in the former to 0.1755 nm in the latter (3). At ca 400°C, thermal decomposition of carbon tetrachloride occurs very slowly, whereas at 900—1300°C dissociation is extensive, forming perchloroethylene and hexachloroethane and Hberating some chlorine. Subjecting the vapor to an electric arc also forms perchloroethylene and hexachloroethane, as well as hexachlorobenzene, elementary carbon, and chlorine. 

Chlorination of Hydrocarbons or Chlorinated Hydrocarbons. Chlorination at pyrolytic temperatures is often referred to as chlorinolysis because it involves a simultaneous breakdown of the organics and chlorination of the molecular fragments. A number of processes have been described for the production of carbon tetrachloride by the chlorinolysis of various hydrocarbon or chlorinated hydrocarbon waste streams (22—24), but most hterature reports the use of methane as the primary feed. The quantity of carbon tetrachloride produced depends somewhat on the nature of the hydrocarbon starting material but more on the conditions of chlorination. The principal by-product is perchloroethylene with small amounts of hexachloroethane, hexachlorobutadiene, and hexachloroben2ene. In the Hbls process, a 5 1 mixture by volume of chlorine and methane reacts at 650°C the temperature is maintained by control of the gas flow rate. A heat exchanger cools the exit gas to 450°C, and more methane is added to the gas stream in a second reactor. The use of a fluidi2ed-bed-type reactor is known (25,26). Carbon can be chlorinated to carbon tetrachloride in a fluidi2ed bed (27). 

Miscellaneous Reactions. Chlorinolysis of mixtures containing 1,1,2-trichloroethane at 550°C was found to give primarily perchloroethylene and hexachloroethane (97). 

A Japanese process developed by Taogosei Chemical Co. chlorinates ethylene directly in the absence of oxygen at 811 kPa (8 atm) and 100—130°C (32). The products ate tetrachlorethanes and pentachloroethane [76-01-7J, which ate then thermally cracked at 912 kPa (9 atm) and 429—451°C to produce a mixture of trichloroethylene, perchloroethylene [127-18-4] and hydrochloric acid. 

Tetrachloroethylene [127-18-4] perchloroethylene, CCl2=CCl2, is commonly referred to as "perc" and sold under a variety of trade names. It is the most stable of the chloriaated ethylenes and ethanes, having no flash poiat and requiring only minor amounts of stabilizers. These two properties combiaed with its excellent solvent properties account for its dominant use ia the dry-cleaning iadustry as well as its appHcation ia metal cleaning and vapor degreasiag. 

Elastomeric Fibers. Elastomeric fibers are polyurethanes combiaed with other nonelastic fibers to produce fabrics with controlled elasticity (see Fibers, elastomeric). Processing chemicals must be carefully selected to protect all fibers present ia the blend. Prior to scouriag, the fabrics are normally steamed to relax uneven tensions placed on the fibers duriag weaving. Scouriag, which is used to remove lubricants and siting, is normally conducted with aqueous solutions of synthetic detergents and tetrasodium pyrophosphate, with aqueous emulsions of perchloroethylene or with mineral spidts and sodium pyrophosphate. 

Dry Cleaning. In colorfastness to dry cleaning, ISO 105-D01 a specimen of the textile is placed in a cotton fabric bag together with stainless steel disks and agitated in perchloroethylene (30 min, 20°C) and the effect of the shade and the color of the solvent assessed using the grey scale. 

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