been cleaned by circulation cleaning that all the
Table 2. The most commonly used cold solvent
cleaners (from Poliakoff 1973).
solvent be purged from the system.
If mechanical force, such as high-pressure
spraying, hand wiping or brushing, or ultrasonic
1,2-dichloroethane
methylchloroform
energy is applied, inorganic contaminants can be
acetone
methylene chloride
benzene
mineral spirits
scrubbed from the surface by the applied energy
carbon tetrachloride
perchloroethylene
(Poliakoff 1973). In the absence of these mechani-
chloroform
toluene
cal aids, solvent cleaners are not effective in re-
ethanol
trichloroethylene
isopropanol
trichlorotrifluoroethane
moving inorganic and most water-soluble contam-
methanol
turpentine
inants (Poliakoff 1973). Solvent soaking can be
methyl ethyl ketone
used to remove contaminants that have penetrat-
ed a permeable material but this can be a time-
needed, or 4) an ultra-clean product is needed for
consuming process, and the solvent may carry
manufacturing purposes (adapted from Poliakoff
contaminants deeper into the matrix before out-
1973). Organic solvents work primarily by dis-
ward movement occurs (Esposito et al. 1985).
solving the contaminants. Generally like dissolves
One problem associated with using cold clean-
like. That is, nonpolar solvents dissolve nonpolar
ing is that workers will be exposed to vapors of
organic contaminants, and polar solvents dissolve
the organic solvents, and many of these solvents
polar organic contaminants. Table 2 lists the most
are toxic. In addition, the solvents may be flam-
mable. A person working with these chemicals
commonly used solvent cleaners (a large majority
should wear the recommended protective equip-
of these solvents would not be suitable for clean-
ment and should be aware that some organic
ing sampling devices because they are target ana-
solvents can penetrate some types of protective
lytes). Thus, solvent cleaners will soften, dissolve,
clothing. Another problem with using organic sol-
and remove contaminants composed of oils, tars,
vents is that many can degrade the surfaces being
asphaltics, and other substances that are not readi-
cleaned. Many polymers (thermoplastics, thermo-
ly soluble in water. Materials like salt, soil, and
sets, elastomers, and rubbers) are degraded by
sugars are not readily dissolved by solvent clean-
organic solvents, especially the chlorinated hydro-
ers (Poliakoff 1973).
Solvent cleaning is typically classified as cold
carbons. Alcohols are generally gentler on most
cleaning or vapor cleaning. Cold cleaning is done
polymeric surfaces, and most organic solvents do
by applying the unheated organic solvent in sev-
not react chemically with metal surfaces. Dispos-
eral ways: 1) wiping the surfaces with a cloth or
ing of organic solvents is an additional problem
scrubbing with a brush, 2) immersing the object
unless the solvents can be sent for recycling.
in some type of tank, 3) spraying the surface with
Vapor cleaning is carried out in a chamber
atomized droplets of solvent or flushing it with a
where the solvent is boiled and the vapor is re-
solid stream of solvent, and 4) cleaning equip-
condensed by means of cooling coils. The cold
ment in place by circulation cleaning (Poliakoff
article is placed in the vapor, solvent condenses
1973). The first method utilizes agitation and the
on it and dissolves soluble contaminants that drain
action of the solvent. For immersion cleaning to
from the surface into the heated solvent where
be effective, either the piece being cleaned or the
solvent is again vaporized, leaving the involatile
solvent should be agitated to ensure rapid clean-
contaminants in the heated solvent sump. The
ing (Poliakoff 1973). However, this process typi-
process continues until the article has attained the
cally leaves some residual contaminated film on
vapor temperature (Wadsworth 1975). Providing
the surface because the solvent becomes contami-
the volume of solvent condensed is sufficient, there
nated in the cleaning process. Using a series of
is no possibility of a residual film (Wadsworth
tanks containing cleaner and cleaner solvent can
1975). This is why this method is preferred for
reduce this problem. For spray cleaning, selecting
items that need to be critically cleaned or ultra-
the correct pattern of spray is essential for effi-
clean.
cient cleaning (Poliakoff 1973). The first three
A number of other novel solvent cleaning con-
methods are typically used for smaller items, and
cepts exist (e.g., using Freon 113 and supercritical
the last method is typically used for larger equip-
fluids), but these methods would be expensive
ment that cannot be easily moved. Poliakoff (1973)
and do not appear to be either practical or neces-
also cautions that before using a system that has
sary for most groundwater sampling devices.
6
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