Note: Descriptions are shown in the official language in which they were submitted.
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, BACKGROUND OF TIIE INVE~TION
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The ~estructlon of Polychlori.na~ecl ~i.phenyl.s
(P~Bs) ha~.been the sub~ect o~ la ~,reat (Ieal o~ speculation,
controversy, and research. The presen~ly acceptable metho(l
i5 high temperature incineration, followed by scrubbin~ the
off-gas to remove hydrogen chloride. l'his is reported to
be 99.99~/O efficient. This means that if one hundred tons
- are "destroyed" annually, that only twenty pounds will. be'
allowe~d to escape to the atmosphere in the vicinity of the
incinerator--a considerable quantity! Part of the material
which thus escapes can be ~resumed to be dioxins, which
a're extremely toxic, and thus a greater ha~ard than an
equLvalent quant.ity of PCB.
'Recent publications Chemlcal Week, Sept. 17, 1980,
i and Chemlcal and En~ineerin~_News, Sept. 22, 1980) have
publicized a liquid method which is portable, and reclaims
the transformer oils which are contaminated by the PCBs.
In addition to PCBs, there are many halogenated
pesticides, .chemical intermediates, and si.cle products which
are Eilling both legal and illegal dump sites and present
serious hazar~s to the public health. There are also mi].lions
oE tons of equipment, soils an~ slu~,es which are contamln-
ated with these materials. This invention is applicahle to
destruction of-these materials in a safe, inexpensive rnanner.
RRIEI;' DESCRIPTION OF T~IE; DRAWING
~ igure 1 is a schema~ic re~)re~eIlt.ation of an
embodiment o~ ~he invention.
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DESCRIPTION OF Tl-IF, IN FNl'ION
It has now been found tha~ l-alogella~ed orKanLc
compounds will react with hot alumlnum, and that the
chlorlne will be abstracted ~rom the organic material.
This reaction produces aluminum chloride, a volatile salt;
whlch may then distill Erom the reaction mixture. This
will leave a slag qf aluminum compounds, or a volatile or
liquid aluminum alkyl or aryl compound. Other metals
which have desirable chemical properties include the alkali
!O metals, alkaline earth metals, iron, zinc, and the "rare
earth" metals. The use of aluminum is preferred because
of its low meltin~ point, ready availability, stability at
ordinary temperatures, and the volatility of its anhydrous
chloride salt. Sodium-based methods require 23 pounds of
L5 sodium to remove 35.5'pounds of chloride, while only 9 pounds
of aluminum is required. Aluminum is also much easier and
safer to handle and ship.
The process of the invention includes 1) the
direct reaction of the liquid PCBs; 2) the passage o~ P~B-
cont~mlnated oils or solvents ~hrough the reactor, so the
P'CBs react, and the oils distill from the reactor; or 3~
the extraction of the PGBs Erom soil or other contaminated
material with a suitable high-boiling hydrocarbon solvent
and subsequent passage through the reactor. Reaction with
eithçr heated metal or molten metal is possible; however,
molten metal ,is preferred since ~c provide.s ~ bet~er con-
tact with the reactant PCB, and also provides a continuously
renewed reacLing surface to them.
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A present}y-preferred emboditn~nt of the invention
is shown in Figure 1. Thl~ emboclimen~ involves the extrac-
tion of th~ PCB, p'esticide, or ~her hazarclous halogenated
orgallic material. The extractant can be a hydrocarbon
solvent such as fuel oil or other inexpensive hydrocarbon
solven.t; In the event the waste materiaL is a contaminated
oil, it can be fed directly.to the reactor.
The contaminated solid ~air-dried or free~e-dried
to minimize moisture) is placed in hopper (1) from which it
is conveyed upward by a screw conveyor(2). The convey.or:
has an inlet for the solvent, and remains nearly full of
solvent.~ ~As thelcontaminated solids rise in the conveyor,
they are bathed in the solvent supplied by pump (3) from
the~oil~storage tank(4). As the solids rise, the concen-
tration of PCB in the extracting oil becomes less. The wet
solid~:.are~discharged onto a vacuum drum filter (5) where
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they are given a final spray rinse, with clear solvent
supplied by pamp(6.~, the solvent drawn ou~ by-vacuum, and
drained to:the.oil storage tank (4). The solids are dis~ .
charged from the face of the filter by means of a screw
conveyor (73 into a hopper or truck (8) for removal.
The extracting solvent grows progressively more
concentrate.d with contaminant as it passes downward through
the conveyor.trough (2) and finally passes over a weir (5)
which holds back most of the solids. The overflow passes .
in~o a laminar ~ow separator (10) which al.].ows the solids
to settle. .They are drawn nff along with enough solvent
to make a pumpable slurry, and pumped by pump (11) back to
the solids inlet. The PCB-containing solvent flows to a
storage tank (12) ready for destruction of the PCB. It is
pumped by pump (13) into a heat exchanger (14) which
flash-hea~s" the solvents'and PCB~s to vaporize them. The
vapor then passes throug~l apertures in the i.nlet pipe (15)
into the molten aluminum contained in the furnace/reactor
(16). .The PCBs react to form aluminum ch].oride; the solvcnt
passes through the reactor. Both are condens.ed in the
condensor (17). Since the aiuminum chloride is a solid,.
it'will be separated in the second laminar fl~w separator (18).
The solid AlC13 can~be removed under anhydrous conditions.,
puriiied and used in other processes. The~solvent will flow
into r'eservoir (19) and be transferred by pump (20) into the
ciean,solvent storage tank(24).. ~he slag formed in the
reactor will be skimmed as necessary through a lock system
(21), and placed in hopper (22) for disposal.
PCB-contaminated transformer oils will be stored
in storag~'tank (23). From here it can be pumped by pump
(13~'directly,into the flash heater (14~.
~ The embodiment uses a laminar-flow separator as
a means of separating fine solids from the PCB-containing
oils and the aluminum.chloride fro~ the distilled oils or
solvent only as a means of illustra~ing the principle.
Other me~ns of separation, including screening, filtering
or centrifugation, would serve the same purpose.
The embotliment uses a molten reaction mixture
consisting, o~ .~lyminum, only a.5 a mealls o~ ill.ustrati.ng
the principk? of reaction with a molten meLal. A low-boiling
eutec~ic of aluminum and zitlC, or of alumlrlum, zlnc and
magnesium; eutectic mixtures containing iron, calcium, or
.
other metals heated would be expected to give equivalent
results with the exception of the composition ~f th~ 2n~
products. Aluminum is preferred due ~o i~s low ~lting
point, reactiYity, ready avallability, ancl ].ow cost.
The embodiment describes the use ~f a separate
heat exchanger to convert ~he solvent and the PCB to the
vapor state at a pressure sufficient to drive it through
thé apertures into the rea¢tion melt. Including it as a
part of the reactor, or as a separate compartment of the
.0 r.eactor would perform the same function.
The embodiment also includes allowing the alu-
minum chloride to separate from the condensed solvent.
A lower temperature would ailow the soli~ salt to separate
from the solvent.
.5 The embodiment describes a treatment of PCB-con-
taminated oil or solids. It could also include reaction
~of pure PCBs, in which case, there would be no recovered
oi 1.
The embodiment also describes the use of pure
'O molten metals as a single-metal melt or as a eutectic
mixture of pure metals. Recovered "scrap" -netals could be
used as well, either alone or as eutectic melts.
The temperature of the reaction is not unduly
critical within practical limits. The process operates
well at any temperature at which the metal remains molten,
It must remain at a high enou~,h temperature to allow the
vapors to pas~hrough the metal.
The reactlQn wi]l also take place at temperatures
below the melEing point of aluminum, but the reaction
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prod~ct wlll coat the me~al, and the meta]. will not present
a continuously self-rerlewing surface.
~ The process of the i~vention can be optimized by
eleva~ing the temperature, thereby reducing the viscosity
j of the melt, but stopping short of the temperature at
whi~h the ~ransformer oil (non-PCB) or carrier solvent
becomes thermally unstable.
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. PROCESS
,
Thé process of the inventiorl involves bringing
O about the reaction of the PCBs with malten aluminum metal.
The reaction which would be expected to ensue include the
followi~g:
\( ~ Cl + Al --- Cl ~ ~ ~ ~ AlCl
Cl Cl Cl Cl Cl Cl Cl
Reaction of only one aluminum atom to abstract
three chlorine atoms from one of the rings will de-stabilize
the molecule, forming a free radical, and bringing about
further reaction:
Cl ~ ~ J ~ ~ ~ + AlC13
Further reaction would involve stripping all the
chlorine atoms off the molecule, leaving carbon or aluminum
çarbide and aluminum chloride. Since each molecule of PCB
O wlll be surrounded by aluminum atoms, and their associated
electrons, it is not expected ~hat ~lliS r~action would t:al<e
place in sucl~ a simplified sequence. l~ would more probably
result in the formation of AlCl3, Al4C3, and some carbon,
according to the over-all reaction:
3 Cl2Cllo + 58 Al --- 12 Al4C3 + 10 AlC13
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The aluminum chloride formed wouk~ be volatile at the
' temperature of the melt, and would disti.ll from the mixturc,
and could be co~densed to be lused as a catalyst for com~
merei,al Friedel, Crafts,reactions, or as a flocculaent for
waste water treatment. The carbide.could generate methane
gas upon hydrolysis.
Al4C3 + 6 H20 --- 2 A123 + 3 C~l4
........ .There follows several examples related to the invention.
.It is to.be. understood that these examples are illustrative,
-rather t.han llmiting.
. Exam~_e 1
A transformer oil containin~, PCB and having a .
boiling point of 280C was heated with strips of aluminum
foil. Partial decomposition was evidenced by the appear.ance '
of a green color, indîcating the probable formation of
aluminum carbide. The residue was found to contain 8.72%
chloride ion. This corresponds to a PCB concentration of
12.25% in the oil.
. Example 2
The.same transformer oil as was used in Example l
was distille~ in the prèsence of aluminum in a distillation
flask. This résulted in the formation of only 5.67% of
chl,oride. This indieates that the reaction was incomplete
in the time reguired for Ihe li~ui.d ~ di.stlll, hut COIl-
sti~u~es ~lrm/evidence tha~ this reaction does take place.
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Example 3 1 1,¦
The same oil was heated for 30 minutes in a
sealed tube~ with aluminum foil at 500C. This resulted in
recovery of 21.5% chloride. This indicates that, in the
absence of intimate contact with the metal, there is an
appreciable time requirement. This should be obviated by
the use of molten metal.
- Example 4
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The melting point of aluminum is 660C.
Addition of zinc metal lowers the melting point to a
minimum at 3~2C. At this point, the zinc must be 95%
of the melt, and might become a major reactant, resulting .,~
in the formation of ZnC12, which wouLd separate in the
molten state. The use of an intermediate concentratio~
of ~inc could lower the temperature.to obtain the optimal
conversion reaction. If the sluminum reacts preferentially, ~i
it would be possible to feed in fresh aluminum as it is
removed by the reaction. .I~ the zinc reacts preférentially,
it may be found to be more econo~ical than aluminum, when
energy requirements are taken into consideration.
Example 5
.
Aluminum forms a eutectic mixture with 79%
aluminum, 13~/o magnesium and 8~/o zinc. This has a minimum
meltin~ point at about 500~C. It is a~visahle to operate
at the lowest possible temperature at which the desired
reaction takes place efficiently. This allows the solvent
or transformer oil to pass through the system without thermal
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decomposition. The preponderance of aluminum in this '''
s.ystem,makes i.t economically desirable compared to the
high zinc eutectic.
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~t is to be understood that the invention can
be practised with any of the procedures on any halogena~ed
wastes, whe~her-hazardous or not; using any metals or
, ' mixtures of metals, under vario:us conditions of tempera-
~,.'' ture and pressure; includin~ those set forth hereinabove
.~' ' but not limited thereto. The selection of the metals,
~,i 10 eutectic mr,ixtures, temrperatures and apparatus can be
t,.l' varied. Those skilled in the a~t can readily vary and
'" adapt.,the teachings of.the invention to a set of circum-
stances found in a certain situation.
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