Historical Use of Chlorinated Solvents and Their Stabilizing Compounds - Environmental Investigation and Remediation - page 39

Additional measures of solvent stability and solvent oily waste content include viscosity (mea-
sured in a viscometer), electrical conductivity, and specii c gravity. A hydrometer is often used for
measuring differences in specii c gravity for nonaqueous materials whose density is markedly
higher or lower than water, such as fuels, or dense nonaqueous phase liquids including the major
chlorinated solvents. However, a hydrometer is not sensitive enough to detect the small variations in
specii c gravity that occur when a solvent becomes contaminated with oily waste. The mixtures of
lighter oils and heavy solvents approach the specii c gravity of water and may become lighter than
water as increasing amounts of oil are dissolved into the solvent. Perchloroethylene, TCE, and
dichloromethane have initial specii c gravities of 1.62, 1.46, and 1.36, respectively; as the oil content
approaches 10% by volume, the specii c gravities of all three solvents converge on 0.92 (Solvay SA,
2002b; see Chapter 3 for further discussion). To determine the specii c gravity of used solvents, a
pycnometer or an electronic specii c gravity meter is used. A pycnometer is a bottle that holds a
specii c volume of liquid and is weighed on a balance (Tarrer et al., 1989).
Solvent performance tests were generally run on samples obtained from the condensate tank on
a vapor degreaser, because the condensate solvent was expected to hold the lowest level of stabilizers
for dichloromethane, TCE, and perchloroethylene. Maintaining the stabilizers at recommended
levels in the condensate ensures proper stabilizer levels throughout the vapor degreaser environment
(Dow Chemical Company, 1999b).

1.2.5.1 Acid Acceptance Value
The total AAV test has been the most common method for determining whether acid in a solvent was
sufi ciently inhibited with acid-acceptor compounds. The standard for this test was ASTM D 2942,
“Test Method for Total Acid Acceptance of Halogenated Organic Solvents—Nonrel ux Method.”
The AAV test gauges solvent condition by monitoring the concentration of neutral acid acceptors
in the solvent. An aliquot of acid is added, and the solvent is titrated with sodium hydroxide to deter-
mine the amount of base required to neutralize the acid. Various degreasing equipment manuals
advise operators to maintain AAV above 0.03% sodium hydroxide. For methyl chloroform, solvent
with an AAV of less than 0.08% sodium hydroxide was considered to have a “borderline” condition,
and solvent having an AAV of less than 0.04% was considered to be “unacceptable.” Guidelines
such as those mentioned in Table 1.20 informed operators when to distill, remove for recycling, or
discard waste solvent.
Dow Chemical currently provides its own acid acceptance test kit to monitor stabilizer concen-
tration for Dow Methylene Chloride Vapor Degreasing Grade, TCE Neu-Tri solvent, and perchloro-
ethylene SVG (Dow Chemical Company, 1999b). Dow's test kits incorporate alkalinity testing as
well as acid acceptance monitoring. In some cases, where the acid acceptance was maintained at a
satisfactory level, corrosion could still be found in the degreaser equipment when there had been a
drop in the pH of the solvent before the loss of acid acceptor. Solvent pH is normally greater than
8.5, primarily because of the reserve alkalinity from the antioxidants in the stabilizer system.

TABLE 1.20
European Guidance for Acid Acceptance Values Requiring Solvent Management Action

Solvent Fresh Add Fresh Solvent Replace or Distill Solvent

Tovoxene (trichloroethylene) 0.05 0.02

>0.16

Soltene™ (perchloroethylene) 0.03 0.02

>0.10

Solvaclene™ (dichloromethane) 0.10 0.08

>0.30

Source: Solvay, S.A., 2002a, Chlorinated solvents stabilisation. GBR-2900-0002-W-EN Issue 1—19.06.2002, Rue du
Prince Albert, 33 1050 Brussels, Belgium. http://www.solvaychemicals.com (accessed November 9, 2003).
Note: AAVs are expressed in wt% NaOH.