Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 6

1.1.1.1.3 Perchloroethylene
The primary use of perchloroethylene is dry cleaning; about 60% of the 1991 perchloroethylene
production was used for dry cleaning, whereas only 15% of that year's production was used for
vapor degreasing (USEPA, 1994b). A minor use of perchloroethylene was as a dielectric l uid.
Improvements in dry-cleaning machinery to minimize solvent losses, in response to increasing the
regulatory oversight of perchloroethylene use in dry-cleaning operations, have greatly curtailed
perchloroethylene consumption. Compared to other solvents, the solvent losses from perchloroeth-
ylene vapor degreasers were more easily controlled because of the higher vapor density of perchlo-
roethylene (Dow Chemical Company, 2006d). By 1998, the total annual U.S. production of
perchloroethylene had declined to 341 million pounds; the total consumption by dry cleaners had
fallen to 40% of the total perchloroethylene production, and only 10% was used for metal degreas-
ing. The rest was used as a feedstock for the production of l uorocarbons (chlorol uorocarbons and
hydrol uorocarbon) for refrigerant, blowing agent, and l uoropolymer applications.
Perchloroethylene was preferred for cleaning alkali metals such as magnesium and aluminum,
particularly before stabilized methyl chloroform became available, because perchloroethylene is
more stable against reactions with metals than the other chlorinated solvents (Dow Chemical
Company, 2001; Solvay SA, 2002a; Morrison et al., 2006). Perchloroethylene has seen uses similar
to those of TCE, including vapor degreasing of metals and electronics. Perchloroethylene was pre-
ferred for removing wax and resin residues with high melting points, such as those used in the plating
industry, because of its high boiling point. Its high boiling point results in a high-temperature vapor
that completely dries wet work * because it vaporizes the moisture trapped in porous metals, deeply
recessed parts, and blind holes (Dow Chemical Company, 2000). The high-temperature perchloro-
ethylene vapor, compared with solvents that boil at lower temperatures, also provides a longer contact
time because the room-temperature work—considered “cold” relative to the high-temperature sol-
vent vapor—takes longer to warm to perchloroethylene's high boiling point (Morrison et al., 2006;
Dow Chemical Company, 2006d). Perchloroethylene was also used in ultrasonic cleaning.
Perchloroethylene is used as an extractant in the production of pharmaceuticals and in veterinary
formulations for deworming pets (NEMA worm capsules). It has also reportedly been used in the
past as an anthelminthic † in the treatment of hookworm and some trematode ‡ infestations in humans
on the Indian subcontinent and other subtropical regions (USEPA, 2001).
In addition to dry cleaning, perchloroethylene was used for cleaning leather; as a scouring,
sizing, and desizing agent for processing textiles; as a carrier solvent for fabric dyes and i nishes;
and as a water repellant in textile manufacture. It was used in mixtures with grain protectants and
some liquid grain fumigants. Perchloroethylene with a surfactant additive is preferred for vapor
drying of glass products and some metal products requiring a high-quality surface i nish. Aerosol
formulations for the automotive aftermarket used perchloroethylene, particularly for brake cleaning
(HSIA, 1999). Other applications were as an insulating l uid and cooling gas in electrical transform-
ers; in paints, lacquers, and varnishes; in oil rei neries for the regeneration of catalysts; in paint
stripping; in cleaning printing equipment; in aerosol formulations; in polishes and lubricants; and as
a solvent in various consumer products for household use (Doherty, 2000a; European Chemicals
Bureau, 2004, 2005; Morrison et al., 2006).
1.1.1.1.4 MethylChloroform
Before being phased out in the mid-1990s owing to its listing as a stratospheric ODC, methyl
chloroform was most commonly used for metal cleaning by cold cleaning, vapor degreasing, and
* In this topic, the adjective “wet” is used in reference to water and not other liquids; the verb “wetting” takes on another
meaning, as described in Chapter 2.
† Drugs that expel parasitic worms (helminthes) from the body.
‡ Parasitic l atworms, also called l ukes. Some species chemically castrate their hosts: a capsule of perchloroethylene was
most likely seen as a benign and preferred alternative!