NO176749B - Method of Destruction of Halogenated Aryl Products - Google Patents

Abstract

A process for the destruction of halogenated products and more particularly of chlorinated aromatic products or of oils containing these products, for example unchlorinated dielectric fluids contaminated with PCBs. The process is characterised in that these products are subjected to the action of an alcoholate and preferably sodium methylate at a temperature of between 250 and 290 DEG C.

Description

The present invention relates to a method for destroying halogenated aryl products and more particularly aromatic chlorinated products of, for example, the PCB type (polychlorinated biphenyls), optionally mixed with non-chlorinated organic products.

It has already been proposed in the prior art to remove PCBs contained in dielectric transformer oils or lubricating oils by extraction with methanol, see US-PS 4,387,018. Methanol is then separated from PCBs by distillation and then recycled. This method allows the amount of PCB to be reduced by 7056. EP-PS 0 099 951 suggests treating corresponding products with sodium in dispersion where the particle size is over 10 pm. EP application 0 107 404 describes the treatment of a transformer oil containing 652 ppm PCB with sodium salts of a polyethylene glycol. These processes have the disadvantage of necessitating separation and recycling or manipulating sodium. EP application 0 021 294 describes the destruction of dioxins and especially chlorinated anisoles containing 39.7 ppm 2,3,7,8-tetrachlorodibenzo-p-dioxin by reacting these products under pressure with sodium methylate in methanol at 160°C. Furthermore, an article by Gyula Pfeifer and Terez Flora in the Hungarian journal "Magy. Kem. Folyoirat", 71 (8), 343-6 (1965) describes that sodium methylate can begin a decomposition between 120 and 140"C. It has now been found a very simple and very effective method.

The present invention relates to a method for destroying halogenated aryl products contained in a non-halogenated organic product such as a polyarylalkane or a mineral oil and this method is characterized by: a) the products are brought into contact with at least one anhydrous alkali metal alcoholate in powder form for a period of time sufficient to convert the organic halides to

inorganic halides,

b) the amount of alcoholate is used in excess calculated on the stoichiometric amount of halogen compound, c) the alcoholate is chosen from methylate, ethylate, propylate or isopropylate of sodium, lithium or potassium,

d) the temperature is kept above 220"C, and that

e) the non-halogenated is recovered by distillation

product.

The invention finds particular interest in all halogenated products, but more particularly in the case of products containing aryl carbon compounds which are substituted with chlorine and/or bromine. In this family one finds, for example, chlorinated or brominated dioxins, chlorinated or brominated dibenzofurans, (polychloro)biphenyls, (polybromo)biphenyls, (polybromo)diphenyl ethers, (polychloro)diphenyl ethers. These products can be pure or mixed with each other or present in a mixture with non-halogenated organic compounds such as polyaryl alkanes or mineral oils.

Although the invention allows the destruction of every halogenated product, it is advantageously used on products containing less than 1% by weight halogen and preferably less than 1000 ppm halogen.

Although any alcoholate derived from a monoalcohol, a diol or a triol, as well as an alkali metal and among these methylates and glycol or polyglycol alcoholates can be used, sodium, lithium or potassium methylate, -ethylate, -propylate or -isopropylate are preferably used or a mixture of these products and preferably sodium methylate.

Preferably, alcoholates are added to the halogenated products or the mixture containing the halogenated products. Sodium methylate is preferably used in powder form. The stoichiometry is a function of alcohol per halogen atom to be removed, but an alcoholate quantity beyond this stoichiometry is used. A very good dehalogenation is achieved by using an excess of 5 to 10 times the stoichiometric. If, for example, a mixture contains PCB in an amount of 100 ppm expressed as chlorine, a sodium methylate amount of 0.145É is used.

One does not go outside the scope of the invention if, together with the alcoholate, another product is added which can convert organic chlorine into inorganic chloride, for example sodium carbonate or another alkaline agent.

Preferably, the contact between the organic halogenated product and the alcoholate takes place during stirring, for example in a stirred reactor or in a column, or another device that allows sufficient agitation so that the alcoholate is dispersed well and is in contact with the halogenated products during that time which is necessary for their destruction. The reaction can be carried out continuously or discontinuously. The reaction kinetics increases with temperature. You can use a temperature between 220 and 300°C, but you prefer to work between 250 and 290°C. According to the physical properties of the products (vapor pressure), you work at atmospheric pressure or a slightly higher pressure. The reaction duration is a function of the amount of organic halogenated compounds, temperature, amount of alcohol, stirring conditions, all to provide a good contact between the reactants, the time period is usually between 30 minutes and 10 hours.

The invention is particularly useful for destroying aryl halogen compounds contained in a mixture, for example a non-halogenated dielectric mixture or in a mineral oil mixture, containing PCBs. On such PCB-containing products or other chlorinated products, the method of the invention is used, after which, for example, inorganic halogenated products are separated from the other products by distillation. In this way, a mineral oil or a dielectric is obtained which is free organic chlorine.

To be sure of being able to carry out the most complete dehalogenation possible, an alcoholate excess is used. When treating a dielectric fluid containing a few tens of ppm of aromatic chlorinated products at the end of the reaction, you reach a dielectric, NaCl, transformation products of the aromatic chlorinated products and unreacted alcohol residue. It is usual to distill this mixture in order to recover the present dielectric in pure form without the content of aromatic chlorine. Furthermore, when the alcoholate used is sodium methylate, it is common not to exceed a distillation period of 12 hours at 295°C in order to avoid decomposition of the methylate.

The method according to the invention uses as a supplement a sodium carbonate process. Sodium carbonate is very easy to process, but does not allow to remove anything other than halogenated aliphatics and the most labile halogenated aryl compounds.

Method according to the invention allows to obtain a product with an aryl halide amount of less than 10 ppm. The advantage of the method is that, although it is used on products with little reactive halogen atoms, it does not require the use of solvents. That is to say, it is sufficient to add an alcoholate, for example, to the oil containing PCB without, in addition to the alcoholate, having to add the corresponding alcohol as in EP-PS 0 021 294. This method does not allow, by the end of the treatment, before the recovery of aryl halogen-poor products, preceding the separation of excess alcoholate and especially sodium methylate.

Another advantage of the present method is that all products that are formed, for example NaCl, halogenated aryl products that have been transformed with alcoholate and the rest of unreacted alcoholate, can be easily destroyed by combustion without giving toxic products.

The following examples are intended to illustrate the invention without limiting it.

Example 1

1000 g of dibenzyltoluene, DBT, containing 300 ppm aromatic chlorine in the form of monochlorobenzyltoluene is used. This mixture is placed in a reactor equipped with agitator, cooler and a nitrogen injector. After flushing for 15 minutes with a stream of nitrogen at 100°C, 1 wt.#, i.e. 10 g, of sodium methylate is added. The medium is refluxed at 285°C with stirring and purging with nitrogen for 3 hours. The product is then distilled after progressive application of negative pressure to 2 mm Hg so as not to exceed 300° C at the bottom. The distillate obtained has a total amount of aromatic chlorine compounds of 3 ppm.

For the sake of comparison, the treatment of the same product containing the same chlorinated compounds is carried out with sodium carbonate and a product is then obtained with a total aromatic chlorine amount of the order of 100 ppm.

Example 2

DBT is treated as in example 1, but with NaC^Hs, KOCH3, KOC2H5, NaOCH(CH3)2> under the conditions of example 1. The results are given in the table.

Example 3

a) DBT containing 1000 ppm PCB was treated for 3 hours at 280°C with 1% sodium methylate. A product is obtained

containing at least 15 ppm chlorine.

b) Identical to A except that DBT contains 1000 ppm tetrachlorobenzyltoluene.

The examples are given in the table.

Example 4

a) A mineral oil containing 1000 ppm PCB is treated for 3 hours at 280° C with 1$ CI^ONa. A product is obtained

containing at least 15 ppm halogen.

b) Identical to a) except that the oil contains 1000 ppm octabromobiphenyl.

The results are shown in the table.

Example 5

1600 g of DBT and 32 g of sodium methylate are added to a reactor equipped with agitator, cooler and nitrogen injector. The whole is brought to reflux at 290°C while flushing with nitrogen and stirring. The nitrogen flow is then stopped and the cooling outlet is connected to a water trap. After treatment for 70 hours at 290°C, no gas evolution is observed. After cooling and filtering, the reaction medium shows: that there are no light products in the filtrate,

this after chromatographic analysis; and

that the IR spectrum of the solid after washing with monochlorobenzene, hexane and drying in air (recovered weight = 95$ of added methylate) is exactly that of sodium methylate.

Claims (6)

1. Process for destroying halogenated aryl products contained in a non-halogenated organic product such as a polyarylalkane or a mineral oil, characterized in that a) the products are brought into contact with at least one anhydrous alkali metal alcoholate in powder form for a period of time sufficient to convert the organic halides into inorganic halides . distillation recovers the non-halogenated product. 2. Process according to claim 1, characterized in that the halogenated aryl products are products containing aryl carbons substituted with chlorine and/or bromine. 3. Method according to claim 2, characterized in that the products containing aryl carbons are benzyltoluenes or triphenylmethanes or their higher homologues. 4. Method according to claim 2, characterized in that the products containing aryl carbons are PCBs or dioxins or dibenzofurans. 5 . Method according to one of claims 1 to 4, characterized in that the temperature is kept between 220 and 300°C and preferably between 250 and 290°C. 6. Method according to one of claims 1 to 5, characterized in that sodium methylate is preferably used as the alcoholate.