Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 25

produces acids. Antioxidants prevent reactions that form acids. Acid acceptors act to neutralize
acids once they form in the solvent or are introduced into the operation from the work. Metal inhibi-
tors prevent reactions between the solvent and alkali metals and their salts.
Solvents stored in drums may eventually deteriorate and form enough acid to corrode the drums.
This happens when drums were not stored with airtight bungs or seals. Water vapor entering a drum
will condense and form liquid water, which l oats atop the solvent. Hydrolysis of impurities in the
solvent carried over from production will form acids that then progressively deteriorate the solvent.
A ring of pinholes at the solvent-water line near the top of the drum is a telltale sign of solvent
deterioration. Various stabilizing formulations were developed to mitigate acid formation during
solvent storage. Early solutions that stabilized TCE, perchloroethylene, and dichloromethane against
acid formation during storage included addition of gasoline; however, large quantities were required,
and the benei t of using a relatively nonl ammable cleaning agent was negated (Pitman, 1933).
Amylene, also known as 1-pentene, was added to TCE as an acid inhibitor more than 75 years ago
(Harris, 1933). A 1959 patent notes that metal tanks corroded and failed within months because of
the formation of acid that corroded tanks (Beckers, 1959). Such corrosion leads to leaks and con-
tamination of underlying soil and groundwater.
Perchloroethylene is susceptible to auto-oxidation when exposed to ultraviolet light in the pres-
ence of moisture. And in the absence of a metal stabilizer, methyl chloroform exposed to aluminum
salts will undergo a violent reaction that quickly reduces the solvent to a tarry mass and evolves
phosgene gas with potentially harmful or even fatal consequences to the equipment operator.
Carbon tetrachloride corrodes metals and brass in particular. Early i re extinguishers used
carbon tetrachloride in brass containers. Valves on these carbon tetrachloride i re extinguishers
corroded after lengthy storage and prevented them from discharging in the moment of need
(Snelling, 1914). Solvent stabilizers were proposed to remedy the problem in a 1913 patent applica-
tion i led in Pittsburgh, Pennsylvania.
To understand the challenges of solvent stabilization, some familiarity with the mechanics of
industrial applications using chlorinated solvents is necessary. Section 1.1.1 provides an overview of
the major industrial applications employing chlorinated solvents, with an emphasis on how these
industrial processes may have contributed to the composition of waste solvents and the contamina-
tion patterns found in the investigation of contaminated sites.
1.2.2 C ONSEQUENCES OF S OLVENT B REAKDOWN
Degreasing operations require periodic shutdowns for the cleaning of degreasing equipment to
remove accumulated metal i nes, to recycle solvent through distillation, and to maintain pumps,
seals, valves, nozzles, and other parts. When solvents become unstable, the degreasing equipment
itself may be damaged or require intensive cleaning, which results in additional labor, production
downtime, and loss of solvent. In early open-top vapor degreasers, operators faced potential hazards
from exposure to solvents during routine operations, even when the solvent was performing as
intended. The hazards increase considerably when solvents break down owing to runaway acid for-
mation. Degreaser maintenance practices have a bearing on the nature and composition of the waste
solvent that was stored in tanks, leaked, spilled, sent to landi lls, or sent off to facilities for solvent
recycling. Accordingly, the degreaser operating practices prescribed in guidance from degreasing
equipment manufacturers such as Baron-Blakeslee and from solvent providers such as Dow Chemical
may provide clues to the expected composition of waste solvent.
1.2.2.1 OperatorSafety
Reactions of acids and alkali metals with chlorinated solvents can produce several hazardous by-
products. Foremost among these is phosgene gas, also known as carbonyl chloride, or COCl 2 .
Phosgene forms during thermal decomposition of chlorinated solvents when they are overheated in