CA1231725A - Destruction of polychlorinated biphenyls and other hazardous halogenated hydrocarbons - Google Patents

Abstract

DESTRUCTION OF POLYCHLORINATED BIPHENYLS
AND OTHER HAZARDOUS HALOGENATED HYDROCARBONS

ABSTRACT OF THE DISCLOSURE

This invention relates to the destruction of polychlor-inated biphenyls (PCBs) and other hazardous halogenated hydro-carbons by forcing them through a molten bath containing molten metallic aluminum.

Description

~3~7~,~ t , 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.

L 7~ 5 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 . .
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 .

3 1'7 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 ,'- ,.
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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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the removal of chlorine from the molecules of polychlorinated biphenyls (PCBs) which comprises: brining the PCBs into contact with an active metal.

2. A process as in Claim 1 where the metal consists of aluminum, calcium, iron, rare earth metals, or other metal having an electronegativity lower than carbon.

3. A process as in Claim 1 in which the PCB is passed through the molten metal or mixture of metals.

4. A process as in any one of Claims 1, 2 or 3, in which the PCB is passed over a bed of heated metal or alloy at such temperature as will promote the reaction to remove the chlorine from the PCB molecule.

5. A process as in any one of Claims 1, 2 or 3, in which any hazardous or waste material comprising any halogenated organic compound is destroyed by reaction with an active metal at an elevated temperature.

6. A process as in any one of Claims 1, 2 or 3, in which the hazardous or waste halogenated organic compound is present in the pure state, or in solution in a transformer oil, solvent, or extract.

7. A process as in any one of Claims 1, 2 or 3, in which the hazardous or waste halogenated organic compound is present in the pure state, or in solution in a transformer oil, solvent, or extract, the material in the solvent or extract having been obtained by extracting the organic compound from a soil, or sludge, or from washing contaminated containers or equipment, or from any other source.

8. A process as in any one of Claims 1, 2 or 3 in which the products of the reaction are volatile, or unreactive solids which will not interfere in the main reaction, i.e. they will be removed from the reaction mixture in such way that the equilibrium is continuously shifted in favor of formation of the reaction products.

9. A process in which any metal which has a greater electronegativity than carbon will abstract halogen atoms (Cl, Br, or I) from organic molecules by disrupting the bond between the halogen and its associated carbon atom, and forming the corresponding metal halide.

10. A process in which PCB or other halogenated compound is brought into intimate contact with aluminum or other metal at an elevated temperature and allowed to react to form non-toxic non-hazardous products.