Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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_THOD FOR REMOVING POLYCHLORINATED
BIPHENYLS FROM TRANSFORMER OIL
Background of the Invention
Polychlorinated biphenyls, or "PCB' S" were
long used as dielectric fluids in electrical equipment
because these materials have excellent heat stability,
are non-flammable in nature, have low volatility and a
good viscosity characteristic at operating temperatures.
Because of their environmental persistence, however,
continued manufacture, import, or use in the United
States was banned under the Toxic Substances Control
Act of 1976, and the U.S. Environmental Protection
Agency was directed to promulgate rules and regulations
for their removal from the economy.
As of July 1, 1979, EPA regulations define as
"PCB-contaminated" any material containing more than 50
ppm of mono-, di-, or polychlorinated biphenyl. The
regulations permit disposal of PCB-contaminated
materials by either incineration in an approved manner
or in an approved landfill, but such procedures have
rarely proven acceptable to community neighbors. Since
considerable fractions of the transformer oils, e.g.,
refined asphaltic-base mineral oil, or heat exchange
oils, e.g., hydrogenated terphenyls, now in service
are PCB-contaminated, the problem of disposing of
PCB-contaminated hydrocarbon oils in an effective
manner presents a serious challenge. As used herein-
after" the term "transformer oil" signifies a mineral
insulating oil of petroleum origin for use as an
insulating and cooling madia in electrical apparatus,
for example, transformers, capacitors, underground
cables, etc.
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Various techni~ues for meeting this challenge
have been proposed. One method is shown by D.K. Parker
et al, Plant Engineering, August 21, 1980, Pages 133-134.
The method of Parker et al is based on the formation of a
solution of an organo-sodium reagent, such as sodium
naphthalenide, in a carrier solvent, for example,
tetrahydrofuran, which is then added to the contaminated
oil. The Parker et al process requires a multistep
procedure involving first the formation of organo-
sodium reagent, next the incorporation of such organo-
sodium compound into the PCB-contaminated oil followed
by at least 2 more hours for the reaction to be complete,
followed by a water quench and distillation and
purification steps to recycle the tetrahydrofuran.
Another procedure, somewhat similar to the Parker et al
process, is described by Smith et al, University of
Waterloo, based on the graduate thesis of James G.
Smith and G.L. Bubbar, "The Chemical Destruction of
Polychlorinated Biphenyls by Sodium Naphthalenide".
Again, a lengthy, multistep procedure is necessary
before effective destruction of the PCB is achie~ed.
A further procedure is shown by Hiraoka et al, Japan
Kokai 74 822,570, Chem. Abstracts 8988831K, Vol.
82, 1975, which describes the destruction of poly-
chlorinated biphenyls utilizing a sodium dispersion
in kerosene, but requires a 6 hour heating period at
120C
The present invention is based on the
discovery that destruction of PCB's can be achieved
directly without the necessity of preforming an organo-
sodium reagent, by adding finely divided sodium metal
directly into PCB-contaminated transformer oil along
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with a suitable organic electron carrier, such as
benzophenone, biphenyl, naphthalene, etc., and an
aprotic ion-solvating solvent, such as diglyme, or
tetrahydrofuran, etc., while agitating the mixture
under an inert atmosphere. The direct addition of
finely divided sodium metal to the PCB-contaminated
mixture eliminates the several hours of processing
required in making the preformed qodium complex.
Further, the direct addition of the organic electron
carrier and aprotic ion-solvating solvent along with
the sodium metal has been found to significantly
reduce total reaction time, limit the requirements
for ion-complexing solvent to the point where the
solvent recovery and recycling steps are unnecessary,
and to permit the reaction to be carried out at
ambient temperatures.
Statement of the Invention
There is provided by the present invention,
a method which comprises, agitating under an inert
atmosphere, a mixture comprising by weight
(a) contaminated transformer oil having up
to 1% by weight of polychlorinated
biphenyl and less than 60 ppm of water,
(b) 0.1 to 2% of finely divided sodium metal,
(c) 1 to 10% of an aprotlc ion-complexing
solvent, and
(d) 0.1 to 1% of an oil-soluble electron
carrier,
where agitation of the mixture is continued until the
polychlorinated biphenyl content of the mixture is
reduced to less than 5Q ppm, and the weight of (b),
(c) and (d), respectively is based on the weight of (a).
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There is included within the definition of
aprotic ion-complexing solvent, materials such as
tetrahydrofuran, ethylene glycol dimethyl ether
("glyme"), diethylene glycol dimethyl ether ("diglyme"),
other oligomeric ethylene glycol dialkyl ethers
("triglyme", "tetraglyme", etc.), dimethyl formamide,
hexamethyl phosphoramide, etc.
Among the oil-soluble electron carriers which
can be utilized in the practice of the present invention,
there are included for example, benzophenone, alkylated
benzophenones, naphthalene, alkyl naphthalenes, biphenyl,
alkyl biphenyls, etc.
In the practice of the present invention, a
dispersion of finely divided sodium metal is incorporated
into the PCB-contaminated oil while it is agitated under
an inert atmosphere at ambient temperatures. Preferably,
the oil-soluble electron carrier is then added as a
solution in the aprotic ion-complexing solvent. However,
it has been found that the order of addition of the
aforementioned ingredients is not critical. Finely
divided sodium metal can be obtained by heating fresh
sodium metal in an inert mineral oil having low volatil-
ity at 150-170C for S-10 minutes with vigorous stirring
under an inert atmosphere, such as nitrogen, or
purchased from commercial sources (e.g., Coronet
Chemical Company, Newark, N.J.).
In order to avoid possible reaction of the
sodium metal with the water which might be present in
the contaminated transformer oil, the transformer
oil should be carefully dried within the above-
described limits prior to the addition of metallic
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sodium. One method, for example, is to pass the oil
through a molecular sieve. Preferably, total water
content should not exceed 60 ppm of the oil. At the
termination of the reaction the mixture can be
filtered to effect the removal of salts if desired
to make the decontaminated oil commercially reusable.
The level of PCB-contamination before and
after treatment can be readily determined by use of
gas chromatography in accordance with the procedure
of O. Hutzinger et al, the Chemistry of PCB, Chemical
Rubber Company Press Inc., 1974, pp. 197-218.
In order that those skilled in the art will
be better able to practice the invention, the following
examples are given by way of illustration and not by
way of limitation. All parts are by weight.
Example 1
There was added 0.2 parts of sodium metal
in the form of a 40% dispersion in a light mineral
oil (matheson, Coleman and Bell), along with 0.23%
by weight of benzophenone and 3% by weight of
diethylene glycol dimethylether as a solution to 100
parts of transformer oil having about 800 ppm of
Aroclor 1260 and less than 60 ppm of water. The
additions were carried out under a nitrogen atmosphere
at about ~4C. The mixture was stirred for 3 hours
and analysis by gas chromatography showed that the
PCB level was reduced to about 0.7 ppm.
Example 2
There was added 0.28 parts of sodium metal
as a 20% dispersion in mlneral oil (Coronet Chemical)
and a solution of 0.35 parts of naphthalene in 5 parts
- of diethylene glycol dimethylether to 100 parts of
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1171~Q9
transformer oil contaminated with 832 ppm of Aroclor
1260. The contaminated oil had been passed through a
column of Linde 4A Molecular Sieve #87956 to effect
the removal of excess water. The mixture was stirred
at ambient temperatures and gas chromatographic
analysis showed the presence of only about 17 ppm of
PCB after 15 minutes stirring and 1 ppm after 1 hour.
Example 3
There are added at ambient temperatures
uner a nitrogen atmosphere, 0.15 part of finely
divided sodium metal in mineral oil, and 0.35 part
of naphthaiene in 15 parts of diethylene glycol to
100 parts of transformer oil contaminated with 100
ppm of Aroclor 1260. The contaminated oil has less
than 60 ppm of water. After the mixture is stirred
for two hours, gas chromatographic analysis shows the
; mixture contains less than 1 ppm of PCB.
Although the above examples are directed
to only a few of the very many variables in the
method of the present invention, it should be under-
~tood that the present invention is directed to the
use of a much broader variety of aprotic ion-
complexing solvents and oil-soluble electron
- carriers which are shown in the description preceding
these examples.
