PCBs AND ASSOCIATED AROMATICS 941
balance as conducting and/or absorptive particles. A series
of beds was constructed in the effluent flow path and 29
volts/12 amps passed into each of the less conducting beds
while 10 volts/15 amps was passed into each of the more
conductive beds. The electrodes were cooled so that the pro-
cess temperature could be minimized. The PCB concentra-
tion was reduced from 120 ppb to 1.5 ppb.DECHLORINATION REACTIONS OF ALKALI
METALS AND ORGANOMETALLIC REAGENTSThe chemical decontamination systems which have been
developed all share a common factor based upon the transfer
of electrons to the PCB molecule from an alkali metal such
as sodium or potassium, or an organometallic reagent, such
as an alkali metal-aromatic compound. The processes differ
in details such as the air and moisture sensitivity of the
reagent, side reactions to give partially dechlorinated toxic
products, inhibition by radical scavengers such as oxidation
inhibitors and the degree of processing required to produce a
useful, decontaminated product. Public scrutiny has required
that processes be researched very carefully to elucidate the
details of reactions so that the PCB “problem” is removed
rather than substituted.
The first large scale process for the PCB decontamina-
tion of fluids was developed (Parker^144 ) by Goodyear Tire
and Rubber Company in 1980 using the known chemistry
of sodium naphthalenide (NaNp) as a dechlorinating agent
for strongly bonded organic halogen compounds such as
chlorobenzenes. The process was applied to the decon-
tamination of heat transfer fluids containing about 120 ppm
of PCBs. Earlier, in 1978, Oku et al.^145 reported the use of
NaNp for the dechlorination of PCBs. Smith and Bubbar at
the University of Waterloo, Ontario performed a research
contract for the Canadian Electrical Association on the
application of NaNp to PCB contaminated transformer oils
in 1982. A patent issued on their process in 1982 (Smith
and Bubbar^107 ).
Sodium naphthalenide is prepared by reaction of an
excess of dispersed sodium metal with naphthalene in a
dry ether solvent, such as tetrahydrofuran, under a nitro-
gen atmosphere. The air unstable compound forms as dark
green crystals and reacts with PCBs to form chloride ions,
biphenyl and polyphenyls with a yield, based on chloride
ion concentration, of 99.5%. Analysis of some of the non-
chlorinated polymeric, aromatic residue by NMR spectros-
copy indicated that one solvent tetrahydrofuran molecule
was associated with each aromatic ring.
The reaction of NaNp with PCBs was found to be more
efficient when the recovery of naphthalene was increased.
This was interpreted as being due to the presence of an
impurity produced from a side reaction which acts as an
inhibitor to the dechlorination reaction. A similar inhibi-
tion of the dechlorination reaction was studied by Webber
and Wilson^62 in the reaction between dispersed sodium and
PCBs in oxidation inhibited transformer oils. The chemistry
of this method is discussed later in this section.Acurex Waste Technologies Inc. in Mountain View,
California, have adapted the Goodyear/University of
Waterloo process for use in the field to decontaminate
transformer oils because naphthalene is a priority pol-
lutant. The Acurex process utilizes a chemically similar,
proprietary alternative. The large scale process developed
by Goodyear was intended to yield a decontaminated fuel.
The Acurex process yields a decontaminated oil which is
filtered and returned to the customer for reuse or disposal
although the extent of required further treatment is uncer-
tain. Acurex does not recommend reuse of the oil. Smith
and Bubbar are proposing a continuous, cyclic system
which, it is claimed, can be built into a portable unit that
could be carried on a trailer for on-site processing to yield
a dielectrically acceptable oil.
Brown and Lynch at General Electric Company,
Schenectady, New York, have obtained a patent (#4,377,
471) in March 1983, on a method for the dechlorination of
PCBs in insulating oils by addition of a mixture of dispersed
metallic sodium, an aprotic ion-complexing solvent such as
tetrahydrofuran, and an oil-soluble electron carrier such as
naphthalene. It was noted in Smith and Bubbar’s patent on
the action of NaNp that the presence of free sodium metal
in the reaction medium, resulting from the use of an excess
of sodium metal in the formation of sodium naphthalenide,
appeared to enhance the effectiveness of the dechlorination
reaction. The use of sodium dispersions for the removal of
halogenated compounds from hydrocarbon oils is a well
known reaction in the refining of oils. The application of the
method to PCBs was described as early as 1973 by Japanese
workers who used it to decontaminate kerosene used as a
solvent for the extraction of PCBs from sewage sludge.
The B.C. Hydro process (Webber et al.^146 ) for the decon-
tamination of electrical insulating oils utilizes an alkali
metal such as sodium dispersed directly into the contami-
nated oil. Rate studies of the reaction performed by Pilgrim
and Webber^61 showed a trend which is characteristic of chem-
ical treatments, namely that the more highly chlorinated
PCBs react in a stepwise fashion to produce less chlori-
nated species which are ultimately completely dechlori-
nated. Samples withdrawn from the reacting dispersion
were analyzed at periodic intervals by gas chromatogra-
phy according to a method similar to the now standard-
ized ASTM D4509. The later peaks in the chromatogram
showed an initial decrease, declining sharply as the reac-
tion proceeded. The intermediate peaks showed an initial
increase, followed by a short plateau phase and a sharp
decline. The least retained, least chlorinated congeners
retain an almost constant peak height until the reaction
is almost complete, at which time they quickly disappear
from the chromatogram.
The suggested reaction scheme involves the formation
of anion radical intermediates followed by a dechlorination
step. Polyphenyls are produced from the reaction between
biphenyl free radical species and a chlorobiphenyl free radi-
cal, followed by further dechlorination and ultimate precipi-
tation as sludge. The reaction appears to be similar to the
ENSR (SunOhio) PCBX process.C016_003_r03.indd 941C016_003_r03.indd 941 11/18/2005 1:12:45 PM11/18/2005 1:12:45 PM