Environmental Engineering Reference
In-Depth Information
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Historical Use of Chlorinated
Solvents and Their Stabilizing
Compounds
Thomas K.G. Mohr
This topic deals with four the major chlorinated solvents: methyl chloroform, trichloroethylene,
perchloroethylene, and dichloromethane. Carbon tetrachloride is also an important chlorinated solvent,
but it was more commonly used between 1900 and 1960. Its primary use since then has been as an
intermediate in the production of chlorol uorocarbons and other chemicals (Doherty, 2000a; Shepherd,
1962). The more common names for these four major solvents include 1,1,1-trichloroethane or TCA
(for methyl chloroform), trichloroethene or TCE (for trichloroethylene), tetrachloroethene or PCE (for
perchloroethylene), and methylene chloride (for dichloromethane).
Tables 1.1
and
1.2
present identi-
fying information and chemical structures for the four major chlorinated solvents, as well as lists of
synonyms and trade names.
Solvent stabilizers have been added to a wide variety of solvents, including chlorinated and other
halogenated solvents, petroleum solvents, ketone solvents, ether solvents, alcohol solvents, and
others. This topic focuses on the stabilizers for the chlorinated solvents, which were by far the most
frequently used solvents for degreasing, dry cleaning, cold cleaning, and dozens of other industrial
applications. This topic also provides brief discussion of stabilizers for the following additional
solvents: carbon tetrachloride, Freon 11, Freon 12, and Freon 113 (dichlorodil uoromethane, trichlo-
rol uoromethane, and 1,1,2-trichloro-1,2,2-tril uoroethane, respectively; Freon is a trademark name
for chlorol uorocarbons registered by E. I. Du Pont de Nemours and Company Corporation
of Delaware) and new replacement solvents limonene, 1-bromopropane, siloxanes, terpenes.
1.1 HISTORY OF CHLORINATED SOLVENTS
Chlorinated solvents have played an integral role in the world's industrial societies for more than
70 years. The majority of manufactured consumer products made of metals or incorporating elec-
tronic components have undergone some form of cleaning process using solvents to remove residu-
als from fabrication. Chlorinated solvents are nonl ammable, easy to recover from the vapor phase,
and easy to recycle when laden with oils and other debris by degreasing and dry-cleaning processes.
The relatively low boiling points of these chemicals make them economical for use in vapor degreas-
ing and dry cleaning, and their high solvency makes them extremely effective in a wide variety of
challenging cleaning applications, for example, cold cleaning and ultrasonic cleaning.
From the 1940s until recently, chlorinated solvents played a part in the production of most manu-
factured products. Today, many manufacturing processes continue to leverage the cleaning power
and effectiveness of halogenated solvents. However, in compliance with regulations that prevent
uncontrolled releases to the environment, these processes use equipment that has been engineered
to eliminate or minimize emissions. Chlorinated solvents provided an enormous benei t to the
industry and consumers alike; however, they pose a threat to water quality where they were released
to soil and groundwater. The unintended adverse consequences of past uncontrolled or undercon-
trolled solvent uses have taught us valuable lessons, which have guided major improvements in
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