CA1179381A - Process for dehalogenating a polyhalogenated organic material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Polychlorinated biphenyls in oils such as transformer oil are dechlorinated to yield environmentally safe products by reacting the compounds with at least one of sodium naphthalenide and biphenyl sodium under reduced pressure in tetrahydrfuran solvent, excess sodium compound is removed by reaction with carbon dioxide in the presence of air or oxygen, and the solvent is removed by distillation. The resulting liquid is passed through heated Fuller's earth to yield clean oil.

Description

This lnyen-tion rela-tes to a rnethod of dehalogena-ting a polyhalogenated organic material, ancl in particular to a method of dehalogenating polychlorinated biphenyls.
Polychlorinated biphenyls (hereinaf-ter referred to as PCB's) are commonly used in heat trans~er fluids for transformers.
I~oweve~, the disposal of such PCB's presen-ts a considerable problem.
One solution to the disposal problem has been to incinerate the PCB's~ thus convertlng them into nontoxic compounds. Combustion of the Pcsls is usually carried out in specially designed, high temperature furnaces. Combustion results in the formation of gases, which must be vented to atmosphere. If combustion is incomplete or interrupted, harmful PCB's escape into the atmosphere. Another, more practical solution to the problem is dcscribed in an earlier patent application by -the same inventor. The method c~escribed in such patent application includes -the step of treat1.ng the l'CB's w:ith the sodiurn naphthalenide in an inert a-tmosphere -to convert the PCB's to dechlorinated, environmentally acceptable compounds. The chlorine of the PCB's reacts with the sodium to form sodium chloride.
The object of the present invention is to improve upon the method described in the inventor's earller patent application, and in particular to provide a new process for deha].ogenating a polyhalogenated organic material.
Accordingly the invention relates to a method of dehalo-genating a polyhalogenated hydrocarbon comprising the step of reacting said hydrocarbon with a reagent selected from the group consisting of sodium naphthalenide, biphenyl sodium and mixtures thereof under reduced pressure in an ether-type solvent.
The use of reduced pressure, i.e. an at least partial vacuum provides a distinct advantage over applicant's earlier ^ process. Sodium is used in the process for producing the sodium containing carbon reagent. If wa-ter is present in the reaction mixture, a violent reaction between the water and the sodium occurs.
Explosive hydrogen produced is merely dispersed in-to the partial vacuum.
In accordance with an impor-tant aspect of the invention, following the reaction with the reac~ent, the resu]-tin~ mixture is treated with carbon dioxide in the presence of oxygen -to remove any organic sodium compounds, and then the remaining mixture is subjected to distillation to recover the solvent.

. ..
~ It will be noted that not only does the new method provide additional reagents for reaction wi-th polyhalogenated hydrocarbons, but it also results in subs-tan-tially complete recovery oE the solvellt for reuse. Any excess sodium compounds are des-troyed. The eal~l. ier method provides no means for removing excess sodium-con-tainillg reagent from the reaction mixture.
The residue from -the carbon dioxide/oxygen trea-tment whlch -consists of a liquid substantially free of halogenated hydrocarbon, inorganic and organic sediments is separated to yield a holoyenated hydrocarbon-free liquid. The separation is effected by a variety of methods. Inorganic sediments may be removed Erom the bottom of the liquid, and the liquid distilled. Alternatively, the organic liquid phase may be passed through heated Fuller's earth to deposit inorganic and organic impurities. Before passing through the Fuller's earth, the liquid can be subjected -to cyclone separation to remove inorganic salts.
The invention will now be described in greater detail with re-Eerence to the accompanying drawing, -the only figure of which is a schematic flow diagram of an apparatus for carrying out the method of the present invention.

il'7~
With reference to the drawiny, the apparatus for carry-ing out the method of the present invention includes a reactionvessel 1 equipped with an agitator 2. Biphenyl and/or naph-thalene is introduced into the vessel 1 via an inlet duct 3 and a valve 4. The vessel 1 is evacuated. While reduced pressure or a vacuum is preferred~ the vessel 1 may be filled with an inert gas such as nitrogen or argon. Solvent such as tetra-hydrofuran from a solvent reservoir 5 is fed to the vessel 1 through duct 6 and valve 7. Freshly cut sodium is added to the vessel 1 through an inlet duct 8 and a valve 9. Upon completion of the reaction between the biphenyl and/or naphthalene and the sodium to form biphenyl sodium and/or sodium naphthalenide, oil contaminated with a chlorine-containing compound is added to the vessel 1 via inlet duct 10 and valve 11.
Upon completion of the reaction, the resulting mixture is transferred via line 12 and valve 13 to a sodium reaction vessel 14. Additional solvent washings of the reaction vessel 1 are also transferred to the sodium reaction vessel 14. Solid or gaseous carbon dioxide and air or oxygen are fed into the vessel 14 through an inlet duct 15. In the presence of air or oxygen and at atmospheric pressure, the carbon dioxide produces sodium carbonate in small quantities. Excess sodium naphthalenide or biphenyl sodium reacts with carbon dioxide to form acid salts which precipitate. Any water in the mixture as an impurity in the solvent or as the oil reacts with sodium to produce sodium hydroxide, and the addition of carbon dioxide yields sodium bicarbonate, which separates from the mixture as a precipitate.
The mixture from the vessel 14 is fed through line 16 and valve 17 to a degasser and solvent recovery vessel 18. The vessel 18 is a heated vessel into which liquid is sprayed. Any C02 gas in the oil is removed, and t~le solvent is distilled under reduced ~'7~3~81 pressure. Some o~ the naphtllalene may be sublimed and rernoved with -the solvent. The solvent is distilled in the recovery vessel 18 by heating in the presence of an inert gas, or under reduced pressure and is transferred through lines 19 and 20, and valves 21 and 22, respectively in such lines to the solvent reservoir 5. The solvent may also be re-turned to -the reaction vessel 1 :Eor reuse v.ia li.nes 19 and 23, and valves 21 and 24, respectively. Alternatively, the solvent can be distilled before the mixture from -the vessel 1 is transferred to the sodium reaction vessel 14.
From the residue, which consists of oil freed of or ~ith a reduced chlorinated compound content, any organic or inorganic sediments are separated by any of various means. [noryanic sed:in~ent may be transferred directly to a neutrali~ation tank 25 v.ia ].ine 26 and valve 27. The cleaned oil is recovered by distill.atioll via outle-t lines 28 and 29, and valve 30. Alternatively, -the organic phase is transferred via valve 31, line 32 and valve 33 to a heated tow~r 34 containing Fuller's earth. By passing the organic phase through the Fuller's earth in the tower 34, inorganic salts and dechlorinated organic compound are removed from the oil, yielding an efEluent free of such organic compound. The e:Efluent :is discharged from the tower 34 via line 35 and valve 36.
Alternatively, the organic phase is fed via line 37 and valve 38 to a cyclone separator 39. In the separator 39, inorganic salts are spun down from the residue, and the resul-ting oil/organic compound mixture is discharged through line 40 and valve 41 to the tower 34. Inorganic salts in the vessel 18 and -the separator 39 may be transferred to the neutralization tank 25 via lines 26 and 42, and valve 43. Dilute acid or water is added to the tank 25 through inlet duct 44, and the tank is drained through line 45. The 30- addition of water or dilute acid to the tank 25 produces a water ~ g38i soluble inorganic salt and sets ~xec an oil layer, which is dis-charged via line 46 and valve 47 -to line 40 and tower 34.
The apparatus is completed by a line 48 and valve 49 for withdrawing samples from the reaction vessel 1 for analysis.

EXAMPI.ES

The inventor previously showed that sodlum naphthalenide can be used to substantially quantitatively dechlorinate PCB's coverting them to chlorine-free, low mclecular weight organic polymer. The impor-tance of this method lies in using sodium na-phthalenide as a means of chemically destroying PCB's or other environmentally hazardous halogenated organic compounds present as contaminents in transformer oil, so that the oil is recovered for reuse. This example describes the use of sodium naphthalenide eor ~t the dechlorination of PCB's using the method o the present invention.

Naphthalene is placed in the reaction vessel 1, and the ~
vessel is evacuated and ~illed with an inert gas (nitrogen or argon).
,~ ~
Alternatively, the reaction vessel is evacuated, and the reaction is carried out under reduced pressure. A solvent, in this case ~ 2~ tetrahydrofuran is added to the reaction vessel 1, and freshly - ~ cut excess sodium metal in the form of small pieces or wires is added. The reaction mixture is agitated using the stirrer 2 for the required reaction time (lS minutes - 2 hours) at room temp-:j : : :
; erature. Then, a measured amount of contaminated oil containing PCB's containing less than 50 ppm water or recycled oil is added and the reaction mixture is agitated for a time sufficient to complete the reaction (15 minutes - 2 hours). A sample of the reaction mixture is withdrawn via line 48 and valve 49, and tested ; using gas chromatography to determine whether any PCB's are present.
3~; Upon completion of the reaction, the oil mixture is , . .

transferred to the sodium reaction vessel 14 where solid carbon dioxide is added in the presence of air. Excess sodium in the oil reacts with -the carbon dioxide and oxygen from the air, and is converted into sodium carbonate. The oil mixture is -transferred to the solvent recovery vessel 18. The tetrahydrofuran solvent is distilled, and returned to the solvent reservoir 5 via valve 21, line 19, valve 22 and line 20.
Oil containing inorganic salts is passed from the vessel 18 through lines 28 and 32 to the heated tower 34, which contains ~uller's earth, the salts and inert organic polymer are retained in the tower and clean oil is recovered from the bot-tom of the tower through line 35. Alternatively, the oil mix-ture passes through lines 28 and 37 to the separa-tor 39 Eor cyclone separation.
In the separator, inorganic sal-t settles to the bottom and oil is decanted and discharged via line 40 -to the heated -tower 34. Oil is recovered from the inorganic sediment by adding water and then neutralizing wi-th dilu-te acid in the tank 25. The bottom water soluble layer is drained from the neu-tralization tank through the line 45, and the oil layer is passed through lines 46 and 40 to the tower 34 for cleaning in the manner described above. Clean oil is also recovered by distillation from the inorganic salts and organic polymer removed from the bottom of the tank 25.
Yet another alternative is to add water to the oil contain-ing polymer and inorganic salts. The aqueous bottom layer is drained, and the oil is recovered and further purified as described here-inbefore. The aqueous salt and oil mixture is neutralized using dilute acid and the organic layer is separated and washed with water. The organic layer containing oil and organic polymer is either distilled to recover the oil or passed -through the tower 34.
3C- In the second cycle, naphthalene dissolved in tetrahydro-furan is added to the reaction vessel 1, tetrahydLofuran frorn the reservoir 5 is pumped into the vessel 1. ~ollowing formation of sodium naphthalenide, the oll contalnln~ Pcs~s is added to -the reaction vessel as described hereinbefore. The remalnder of the second cycle is ldentical to the flrst cycle and subsequent cycles are repeats of the second cycle.

DETAILED DESCRIPTIO~ OF AN EXPERIMENT USING SODIUM NAPI-ITHAI,~NIDE

AND TRANSFORMER OIL CONTAII~ING 100 PPM AROC~LOR 1254 (PCB's) 1.0 g of naph-thalene was placed in a three neck flask equipped with a dropping funnel and inert gas and vacuum inlets.
9`0 ml of tetrahydrofuran was added via the dropping funnel. A
piece of freshly-cut sodium metal was added quickly through one of the inlets and low vacuum was applied until there was an effervesence. The reaction mix-ture was agitàted at room -temp-era-ture. 250 ml of -transformer oil containing :lO0 ppm of PCB's was added -through the funnel, and 10 ml of tetrahydrofuran was used to transfer -the oil. The reaction mixture was agitated Eor an addi-tional 30 minutes - 2 hours a-t room -temperature.
The reaction mixture was transferred to a separatory funnel, leaving excess sodium me-tal in the flask. A small piece of dry ice was added to des-troy excess sodium naphthalenide. The test for PCB's was performed on a gas chromatograph. No detectable PCB's were left in the oil.
In a second test of the same type, sodium naphthalenide prepared from 1.0 g of naphthalene was treated with 100 g of transformer oil contaminated with 1000 ppm of PCB's. The oil mixture was then treated as follows:
(1) 100 ml of water was added to the oil mixture and dilute nitric acid was then added to adjust the pH to 3-5.
The organic layer was separated and washed twice with 100 ml .~ 3;~1 Ol distilled water. The organic layer was dried over magnesium sulphate, filtered, and the solven-t was removed on a rotary eva-porator. The oil was cleaned by passing the mix-ture through a column of Fuller's earth.

(2) The tetrahydrofuran solvent was distilled and recovered for reuse. The remaining oil was distilled to recover the oil or passed over the Fuller's earth.
When the resulting oil was tested using gas chromatography, no PCB's were detected.
EXA~~LE 2 The method described in Example 1 was used start:ing with 1.0 g biphenyl. The biphenyl was reacted with sodiurn to produce biphenyl sodium, and -the biphenyl sodium was used in the same manner as the sodium naph-thalenide to decon-taminate a 100 ml sample of transformer oil con-taining 100 ppm PCB's. The resul-ts were -the same as those described in Example 1, i.e. no detectable PCB's were left in the oil following the treatment with biphenyl sodium.

The method descrihed in Example 1 was duplicated using a mixture of equal parts of naphthalene and biphenyl. The naphthalene and biphenyl were reacted with sodium to produce sodium naphthalenide and biphenyl sodium, and the latter were used to treat transformer oil containing PCB's. The results were the same as those described in Examples 1 and 2. Similar results were obtained using different proportions of naphthalene and biphenyl.
Sodium naphthalenide and/or biphenyl sodium can be used to decontaminate transformers containing PCB's. A transformer is immersed in paraffin oil or transformer oil in a container under reduced pressure or under an inert gas. Tihe above-mentioned reagent 3J is added, and the mixture is agitated and neutralized with CO2.

ne PCB's are dechlorin~ted, ancl the transformer can be xe-used.
It is wor-th noting -that the sodium metal can be replaced with a mixture of sodium and potassium or with ~aK alloy and the results obtained will be essentially those clescribed in the foregoing examples.
S ~MARY
The foregoin~ method leads -to the safe disposal of environ-mentally harmful po]ychlorinated organic compounds, and specifically polychlorinated biphenyls present as contaminents in oils such 1~ as transformer oil. As mentioned hereinbefore, the combustion ~f the PCB's is not a satisfactory solution to the problem. The dëstruction of PCB's in a sealed system eliminates con-tamination of the atmosphere. Monitoring oE the process conEirms that chemical destruction of the hazardous material has been comple-ted. IE the destruction is incomplete, the process can be xepeated beEore expos-ing the reaction products to the environment. The process or method can be batch or continusous in that sequential batch reac-tions can be run using recovered tetrahydrofuran -to prepare the sodium-containing reagent. Because the process avoids the use of water for destxoying excess sodium/ violent reaction and the formation of highly explosive hydrogen gas are prevented.

_3 _ g _

Claims (8)

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

1. A method of dehalogenating a polyhalogenated hydro-carbon comprising the steps of reacting sodium with at least one of naphthalene and biphenyl to form a reagent; reacting said hydrocarbon with said reagent under a partial vacuum and in ether-type solvent; treating the mixture resulting from the hydrocarbon/
reagent reaction with carbon dioxide in the presence of oxygen, the amount of carbon dioxide being sufficient to remove any organic sodium compounds from the mixture; and subjecting the remaining mixture to distillation to recover said solvent.

2. A method according to claim 1 wherein said hydrocarbon is polychlorinated biphenyl.

3. A method of dehalogenating a polyhalogenated hydrocarbon in an oil comprising the steps of reacting sodium with at least one of naphthalene and biphenyl to produce a reagent;
treating said oil with said reagent under partial vacuum and in tetrahydrofuran solvent; treating the oil mixture resulting from the reagent treatment with carbon dioxide in the presence of oxygen, the amount of carbon dioxide being sufficient to remove any organic sodium compounds remaining in said oil mixture; and subjecting the remaining oil mixture to distillation to recover the tetrahydrofuran.

4. A method according to claim 3, wherein said hydrocarbon is a polychlorinated biphenyl.

5. A method according to claim 4 including the steps of separating inorganic sediment from said remaining oil mixture following said distillation to recover tetrahydrofuran and distilling the resulting oil mixture to yield clean oil.

6. A method according to claim 4, including the steps of separating an organic phase from said remaining oil mixture following said distillation to recover tetrahydrofuran; and passing said organic phase through an adsorbent to yield clean oil.

7. A method according to claim 6, wherein said adsorbent is Fuller 15 earth.

8. A method according to claim 4, wherein said organic phase is subjected to cyclone separation prior to passage through said adsorbent.