GB2143521A - Process for producing decabromodiphenylether - Google Patents

Abstract

The flame retarder decabromodiphenylether is prepared by brominating diphenylether in a halogenated hydrocarbon solvent, followed by separation from the reaction medium and purification of the decabromodiphenylether, in which process: (A) the reaction liquid slurry containing decabromodiphenylether is introduced into hot water and then mixture is stream distilled to remove the halogenated hydrocarbon solvent; and (B) the decabromodiphenylether is pulverized to a powder of mean particle diameter not larger than 10 mu . r

Description

SPECIFICATION Process for producing decabromodiphenylether This invention relates to a process for producing decabromodiphenylether (hereinafter designated DBDE).

DBDE is a compound well known as a flame retarder to be added to synthetic resins or others.

The DBDE is usually produced by the bromination of diphenylether, and bromine is used generally as the bromination reagent while metal halides, such as halides of aluminium or iron, are employed as catalysts to accelerate the reaction.

Two methods are known for the bromination reaction. In one method, an inert solvent is used, while in the other method, bromine itself is used as solvent without employing any other solvent. In the latter method, the DBDE obtained is usually coloured yellow and less pure than that obtained in the former method. Consequently, the former method is usually followed for producing DBDE. In the former method, chloroform and carbon tetrachloride are used as solvents generally, and when the bromination reaction has been completed, excess bromine is removed and the reaction solution is neutralized with an alkaline solution, and then DBDE crystals are separated by filtration.However, the resultant crystal particles have a diameter as Irge as from 40 to 1501u, so that the crystals, if they are dried as they are, may contain several thousands to several ten thousands parts per million (ppm) of the solvent. If a flame retarder which has been prepared using a halogenated hydrocarbon as solvent and only incompletely purified is kneaded with a resin at a high temperature, the remaining halogenated hydrocarbon may thermally decompose to evolve hydrogen halide, leading to corrosion of processing and shaping machines, deterioration of the properties of the resin (for example, a remarkable decrease in the melt viscosity of polyester resins, such as polybutylene-terephthalate) and also pollution of the working environment.

For these reasons, an additional operation is required to wash the crude crystals of DBDE with a fresh organic solvent so as to remove the remaining residue of solvent.

Thus, the conventional process for producing DBDE requires complicated steps of operation; that is, bromination reaction neutralization )filtrationowashing with an organic solventefiltra- tiondrying, where the filtration of crystals and the treatment with organic solvent are repeated twice and organic solvent recovery steps are required correspondingly. Moreover, the crystals of DBDE produced by the conventional process are as large as several 1 Ou in diameter, and contain a large content of the solvent, showing inferior dispersion in synthetic resins and inferior flame retardation. Meanwhile, a process for lowering the solvent content and improving purity has been disclosed as a process for producing high purity DBDE (Japanese Pre-Grant Patent Publication No. Sho 53-116332).

In recent years, the toxicity of organic solvents has been of general concern and official regulations have been made more severe on the solvent conentration in working environments, requiring that the use of organic solvents such as in filtration should be minimized.

The object of the present invention is to provide a process for producing DBDE which can produce colourless DBDE, characterized in that the DBDE: 1) has a lower content of solvent, and 2) has better dispersion and flame retardant properties.

A further object of the invention is to provide a process which is much simpler and which can provide a working environment where workers are less exposed to toxic organic solvents.

Accordingly, the invention provides a process for producing decabromodiphenylether by brominating diphenylether in a halogenated hydrocarbon solvent, followed by separation form the reaction medium and purification of the decabromodiphenylether, in which process: (A) the reaction liquid slurry containing decabromodiphenylether is introduced into hot water and the mixture is steam distilled to remove the halogenated hydrocarbon solvent; and (B) the decabromodiphenylether is pulverized to a powder of mean particle diameter not larger than 10cm.

The invention provides also a method of rendering a material flame retardant by incorporating DBDE therein, wherein the DBDE has been prepared by the process of the invention.

In the present process, the reaction liquid slurry is generally neutralized before introduction into the hot water. The DBDE is generally pulverized after the steam distillation. Thus, generally, the reaction liquid slurry is neutralized, reaction liquid slurry is introduced into hot water, the mixture is steam distilled to remove the halogenated hydrocarbon solvent, and the decabromodiphenylether crystals obtained are pulverized to a powder of mean particle diameter not larger than lOit.

The powder is generally washed with water.

Preferably, the halogenated hydrocarbon solvent is chosen so that in the steam distillation it forms an azeotropic mixture with water and is azeotropically distilled at a temperature not higher than 100 C.

In a preferred embodiment, the present process comprises brominating diphenylether in a halogenated hydrocarbon solvent which forms an azeotropic mixture with water which azeotropically distills at a temperature not igher than 100'C, neutralizing the reaction solution, followed by steam distillation of the solution to remove the halogenated hydrocarbon solvent therefrom, pulverizing DBDE crystals obtained into a powder of less than 1 0it in mean particle diameter and washing the powder with water.

Thus, preferably, according to the invention, diphenylether is brominated in a halogenated hydrocarbon solvent which is capable of forming an azeotropic mixture with water and azeotropically distills at a temperature not higher than 1 00 C, and when the reaction is complete, DBDE is separated and purified from the neutralized reaction solution containing the halogenated hydrocarbon solvent. The separation and purification process is carried out in the invention by the following two steps of operation: in the first step, the reaction liquid slurry is introduced into hot water and the halogenated hydrocarbon is separated by steam distillation, and in the second step, preferably the DBDE crystals thus obtained are pulverized into powders of less than 1 OIL in particle diameter, followed by washing with water.

Preferred ways of carrying out individual steps of operation in the present process will now be described.

Reaction and Steam Distillation Steps: Diphenylether is brominated in a halogenated hydrocarbon solvent at a temperature from about 20 to 60on. The reaction liquid slurry containing neutralized DBDE is then introduced into hot water to effect steam distillation which removes the halogenated hydrocarbon solvent. As the halogenated hydrocarbon solvents used in the present invention, those which form an azeotropic mixture with water and are azeotropically distilled at a temperature not higher than 100 C, such as ethylenedichloride (hereinafter designated EDC), ethylenebromochloride (hereinafter designated EBC), ethylenedibromide (hereinafter designated EDB) and mixtures of them, are preferred.

There is no specific limitation on the concentration of the slurry containing DBDE, because it depends on the amount of the solvent during the bromination reaction and the amount of water added during neutralization after the reaction, but the concentration is preferably such that the slurry is not so thick as to impair the delivery of the slurry. Usually, about 50 to 1,000 ml of solvent is used per 100 g of DBDE. Preferably, the steam distillation is carried out while stirring.

The steam distillation is carried in a distillation vessel preferably with thorough agitation so as to avoid adherence of DBDE to the wall of the vessel. It is preferred that the slurry be introduced into the hot water while the solvent is being distilled from it, the slurry being introduced into the hot water at a rate lower than the rate of distillation of the organic solvent. This avoids solidification of DBDE. The steam distillation is usually carried out under atmospheric pressure, but may also be done under reduced pressure, either in hot water or by blowing steam into hot water. The temperature may be selected in a range from about 70 to 1 00 C under atmosphere pressure.

Pulverizing Step: DBDE crystals obtained through the steam distillation step are pulverized into powders of less than 10IL in mean particle diameter, and then washed with water. The crystals of DBDE obtained by the steam distillation usually have a particle diameter ranging from about 40 to 1 SOIL and contain halogenated hydrocarbons, such as EDB and EDC and other side products, each in amounts of several hundreds to several thousands ppm, and the crystals are tinged with yellow.

Pulverizing the crystals into powders of less than 1 O,u in particle diameter is effective for reducing the EDB and EDC contents each to less than 100 ppm. This treatment is also effective to remarkably decolour the DBDE crystals.

A conventional wet or dry process may be employed in the pulverization, but the wet process can be more advantageously applied to the present invention. When the wet process is used, about 0.05 to 21 of water is preferred per 100 g of DBDE depending on the capacity of the wet pulverizing machine.

For pulverization, conventional wet type pulverizing machines, such as a ball mill, a colloid mill or a homogeneous mixer, may be employed; these machines can divide DBDE crystals into powders of less than 1 OIL in particle diameter.

The pulverized DBDE slurry, after being filtered, is washed with water. For the washing, enough water should be used to removed ionic substances and drganic solvents from the surface of the powder. Thus 0.1 to 21 of water is preferred per 100 g of DBDE.

When the present process is carried out as described above, the resultant DBDE crystals are of small particle diameter, colourless, relatively free from impurities and excellent in dispersion and flame retardant properties.

In the steam distillation step, if steam is simply introduced into the slurry containing crude DBDE to remove the solvent by azeotropic distillation, the crystals are solidified into a cake in the later stage of the distillation, leading to difficulties in subsequent handling of the crystals and an insufficient recovery of the solvent. If, on the other hand, the slurry is introduced into hot water to conduct steam distillation according to the present invention, a uniformly dispered slurry of water and DBDE is obtained, and hence thorough recovery of the solvent is possible.

The DBDE thus obtained has an orangic solvent content ranging from several hundreds to several thoussands ppm, which represents a remarkable lowering of the organic solvent content compared with that of DBDE which has been produced by the conventional process of filtrationoorganic solvent washingefiltrationedrying.

So far as its thermal stability as observed by the weight decrease on heating and the melting point is concerned, the present DBDE is approximately the same as the DBDE produced by the conventional process.

If the steam distillation is performed in the present process without the subsequent pulverization, the resultant DBDE crystals are tinted yellow and it is desired that the organic solvent content be further decreased. This problem can be solved by combining the steam distillation with the pulverization.

Desirable lowering of the organic solvent content in the DBDE produced in the conventional methods could only be achieved by pulverizing the crystals down to 3,u or less in mean particle diameter in the pulverizing step. This would involve tremendous difficulty in commercial practice. According to the present invention, it is enough only to divide the crystals down to 10CL or less in mean particle diameter to achieve the desired lowering of the organic solvent content.

In a particular embodiment of the invention, the DBDE is pulverized to a mean particle diameter which lies from 3,u to 101l.

The present invention not only provides a simpler process which can advantageously produce, separate and purify DBDE, but also improves the working environment by reducing the danger of being exposed to organic solvent vapours.

The invention is illustrated by the following Examples.

Example 1 In the presence of 4.0 g of aluminium chloride, 78 g of diphenylether was brominated with 770 g of bromine in 320 ml of EDC. When the reaction was complete, excess bromine was removed by blowing ethylene into the reaction mixture. The reaction mixture, when neutralized with aqueous sodium hydroxide solution, contained 380 g of DBDE, 1 70 g of EDC, 1 70 g of EBC, 192 g of EDB and 200 ml of water.

This slurry mixture was introduced with stirring into hot water, maintained at 100 C by blowing steam, at a rate not exceeding the distillation rate of the organic solvent. After the introduction was complete, an additional 200 ml of water was distilled. A slurry containing 380 g of DBDE and 760 ml of water was pulverized at room temperature with a 0.6 continuous type Dyno (trade name) mill. The agitator was operated at 2,000 rpm and the stay period of the slurry was 70 sec. Then pulverized slurry was filtered by centrifuging, and crystals obtained were washed with 31 of water and dried at 80"C for a period of 10 hours. Analysis of the DBDE obtained is shown in the Table.

Example 2 The same procedure was followed as in Example 1, except that 320 ml of EDB was used as the solvent for the bromination reaction. Results are shown in the Table.

Comparative Example 1 A slurry mixture obtained after the bromination reaction as in Example 1 was filtered by centrifuging. The DBDE crystals obtained were washed with water and dried for 10 hours at 80"C. Results are shown in the Table.

Comparative Example 2 100 g of the DBDE crystals obtained in Comparative Example 1 were mixed with 100 ml of toluene, and the mixture was refluxed for 2 hours, and, after being cooled, filtered by centrifuging, followed by drying for 10 hours at 80"C. Results are shown in the Table.

Comparative Example 3 A slurry mixture obtained after the bromination reaction as in Example 1 was steam distilled and filtered by centrifuging. Crystals obtained were washed with 31 of water and dried for 10 hours at 80 C. Results are shown in the Table.

TABLE

Example Example Example comparative Comparative Comparativ Item L 2 Example Example Example 1 2 3 Mean Particle 3.3 5.8 20 - 70 50 - 101 30 - 70 Size (u) Purity (%) * 89.8 90.8 88.7 90.0 89.2 Solvent EDC below the detection limit Content (ppm) EBC 30 - 3450 120 3290 EDB 1 50 50 5160 430 3120 Melting Point( C) 302 303 300 302 300 Hunter's Degree 94.7 95.2 88.6 92.6 89.4 of Whiteness Tempera ture of 1 % 313 315 301 310 306 Weight Loss on 371 345 361 10 % 365 371 345 352 ( C) 50 % 416 417 402 412 405 Purity(%)* : Analysis by Gas Chromatography Conditions for Analysis by Gas Chromatography: Instrument : Shimazu GC7A Filler : Silicone OV-101 2% Chromosorb W 5 AW DMCS Column : 3 mmf x 1 m Conditions of Experiment: Inlet Temperature 3100C Column Temperature 3000C Carrier Gas N2 30 m/min.

Claims (11)

1. A process for producing decabromodiphenylether by brominating diphenylether in a halogenated hydrocarbon solvent, followed by separation from the reaction medium and purification of the decabromodiphenylether, in which process: (A) the reaction liquid slurry containing decabromodiphenylether is introduced into hot water and the mixture is steam distilled to remove the halogenated hydrocarbon solvent; and (B) the decabromodiphenylether is pulverized to a powder of mean particle diameter not larger than 10,u.

2. A process according to claim 1 wherein the reaction liquid slurry is neutralized, the neutralized reaction liquid slurry is introduced into hot water, the mixture is steam distilled to remove the halogenated hydrocarbon solvent, and the decabromodiphenylether crystals obtained are pulverized to a powder of mean particle diameter not larger than 101l.

3. A process according to claim 1 or 2 wherein the halogenated hydrocarbon solvent in the steam distillation forms an azeotropic mixture with water and is azeotropically distilled at a temperature not higher than 100"C.

4. A process according to any one of claims 1-3 wherein the halogenated hydrocarbon solvent is at least one of ethylenedichloride, ethylenebromochloride and ethylenedibromide.

5. A process according to any one of the preceding claims wherein the steam distillation is carried out while stirring.

6. A process according to any one of the preceding claims wherein the slurry is introduced into the hot water while the solvent is being distilled from it, the slurry being introduced into the hot water at a rate not exceeding the distillation rate of the solvent.

7. A process according to any one of the preceding claims wherein the slurry is introduced into the hot water which is maintained at 70 to 100"C.

8. A process according to any one of the preceding claims wherein the decabromodiphenylether is pulverized to a powder of mean particle diameter which lies from 3,u to 10y.

9. A process according to claim 1 performed substantially as described herein.

10. A process according to claim 1 performed substantially as described herein in Example 1 or Example 2.

11. A method of rendering a material flame retardant by incorporating decabromodiphenylether therein, wherein the decabromodiphenylether has been prepared by a process claimed in any one of the preceding claims.