CN1012142B - Process for destroying chlorinated products at low temp. - Google Patents

Abstract

The present invention relates to a method for destroying chlorine-containing products, especially aromatic and polyaromatic products.

This method consists in bringing the chlorine-containing product into contact with a sodium chloroaluminate bath containing aluminum powder.

Description

The present invention relates to a method for destroying chlorinated organic products, especially aromatic products and polychlorinated biphenyls.

Some dielectric fluids contain certain chlorinated organic products that decompose after a certain period of operation and need to be replaced. They may sometimes be fully or partially regenerated. Often a portion of such liquids has to be destroyed.

Chlorinated organic products, such as some pesticides, chlorinated aromatics such as hexachlorobenzene, or some polychlorinated biphenyls (PCBs), form toxic products when they are burned like ordinary combustible products.

These chlorine-containing products are destroyed at high temperatures and under specific conditions in order to avoid the formation of toxic products.

In an article in Sci.Total Environ.1987, Volume 10, No. 1, Page 51-59, the method of destroying polychlorinated biphenyls (PCBs) by incineration is described, and the residence time is slightly more than 2 seconds.

Another article, PROC.ANNU.MEET-AIR POLLUT.CONTROL ASSOC.1977, Volume 2, No. 33, describes the method of destroying 99.9995% PCBs at 1000°C with a residence time of 2 seconds.

European Patent EP170 714 describes the method of destroying PCBs by reacting with molten aluminum or an aluminum-based eutectic mixture, and the reaction is carried out above 382 ° C.

Journal of the Chemical Society of Japan 1977 (9) pp. 1407-1409 reported a method for decomposing polychlorinated biphenyls into carbon and hydrogen chloride using molten chloroaluminate. The reaction temperature of the method is 300-500 DEG C, and the reaction time is more than 10 hours. The initial concentration of chlorine-containing species is about 10,000-20,000 ppm. The decomposition rate of chlorine-containing substances is generally only 43%-85%. When the temperature is low (such as 350°C), PCBs with high chlorine content hardly decompose.

It can be seen that the method of the prior art requires high decomposition temperature, long treatment time and large initial concentration of chlorine-containing substances, but the decomposition effect is not ideal.

The purpose of the present invention is to overcome the shortcoming of prior art, provide a kind of method of destroying chlorine-containing product with low decomposition temperature, short treatment time, small initial concentration of chlorine-containing product.

The present inventors have discovered a simpler method of destroying these products, which can be operated at temperatures below 300°C.

The invention is a method of destroying chlorine-containing organic products containing more than 2 carbon atoms 2, characterized in that these products are brought into contact with at least one chloroaluminate bath.

Various chloroaluminates or mixtures thereof can be used. For example potassium chloroaluminate or lithium, sodium, calcium, strontium or ammonium chloroaluminate.

Any mixture of anhydrous aluminum chloride and one or more metal chlorides is referred to herein as a chloroaluminate.

More suitably used is sodium chloroaluminate, which refers to a mixture of aluminum chloride and sodium chloride in any proportion, not just equimolar. Sodium chloroaluminate may also contain lithium chloride and/or potassium chloride. Thus any mixture of aluminum chloride, sodium chloride and lithium chloride, known as lithium sodium chloroaluminate, can be used.

More preferably it contains at least 50 mole percent aluminum chloride and sodium chloroaluminate having a melting point below 200°C.

The present invention is applicable to all chlorine-containing organic products containing more than 2 carbon atoms, and is especially applicable to aliphatic, cyclic, monocyclic or polycyclic aromatic and heterocyclic products. The invention relates in particular to perchlorinated aliphatic products and, among aromatic products, to polychlorinated biphenyls.

The initial concentration of organic chloride product is preferably 5000 ppm (calculated as chloroaluminate), more preferably 2000 ppm.

These products can exist in any form. They can in particular be in a solid phase, for example absorbed on activated carbon.

The process of the invention consists in bringing the chlorine-containing product into contact with a chloroaluminate bath.

When the chlorine-containing product is in the solid phase, this solid phase can be poured into the chloroaluminate bath, such as It is even better if it is stirred. Take care to keep the salt bath molten, and heat the salt bath if necessary. Do the same if the chlorine-containing product is in the liquid phase.

In most cases the chlorinated product to be destroyed is in the gas phase alone or mixed with a lighter chlorinated product and/or carrier gas. This can be, for example, combustion gases, thus nitrogen containing carbon dioxide, carbon monoxide, chlorine-containing products and possibly oxygen. In short, it can be any gas mixture discharged from any process.

It is better if the chlorine-containing product is in an anhydrous phase. Gases containing chlorine-containing products can be dry-operated in contact with an absorbent such as alumina or ethylene glycol.

This gaseous phase containing the chlorine-containing products to be destroyed is then contacted with the chloroaluminate by any means of gas-liquid contact. This can be a tray column or a packed column. It is also possible to feed the gaseous phase in a stirred chloroaluminate vessel with a downcomer or a tube from the bottom of the vessel.

Various chlorine-containing organic products can be partitioned between the liquid and gas phases of the chloroaluminate bath. The same is true for products that accompany these chlorine-containing products. A plate tower or packed tower can be used to ensure continuous circulation and stirring of the liquid and gas phases and good contact between the gaseous product and the chloroaluminate bath. It is likewise possible to operate with stirred reactors in series. Keep chlorinated organic products in contact with the chloroaluminate bath for the time necessary to destroy them. The residence time can vary within wide ranges, but is usually between a few minutes and a few hours.

Although the chloroaluminate can be operated at any temperature as long as it is a liquid, it is preferably below 300°C, and most preferably at 200-300°C.

The destruction rate of chlorine-containing products, especially aromatic products, increases with the temperature of chloroaluminate.

Lighter products of decomposition of the chlorinated products to be destroyed can be found in the gas phase of the chloroaluminate bath; for example carbon tetrachloride and/or hexachloroethane. The chlorine-containing products originally to be destroyed cannot be found in the gas phase of the chloroaluminate bath. When the chloroaluminate bath was analyzed after the prescribed contact time between the chlorine-containing product and the chloroaluminate, no organic products were found to be destroyed.

The chloroaluminate bath may also be cleaned periodically to avoid deposits of undissolved products or products that cannot remain suspended in the bath. During cleaning, no traces of chlorine-containing organic products were found. It was thus confirmed that the chlorine-containing product to be destroyed disappeared.

In a preferred embodiment of the present invention, one or more reducing metal powders, such as aluminum powder or zinc powder, are added to the chloroaluminate bath. It is more preferable to use a powder with an average particle size of less than 500 microns. If metal is used, as mentioned above, the chlorine-containing organic products can be completely removed, but the speed is obviously increased, which is several times to dozens of times of the previous speed.

Consumption of metal (or metals) powders is observed, which indicates that chlorides are formed from chlorine derived from organic products containing chlorine when they are destroyed. There is no limit to the amount of metal powder passed into the chloroaluminate. Aluminum powder is better; up to 5% or 10% by weight of aluminum powder can be placed in the chloroaluminate bath. It was observed that the destruction rate of chlorine-containing products increased with the amount of aluminum powder and the temperature of the chloroaluminate bath. In order to disperse the metal powder well in the bath, it is better to carry out stirring. The resulting metal chloride(s) can be mixed into the chloroaluminate bath and partitioned between the liquid and gas phases. If desired, the metal chlorides can be removed therefrom by treating the gaseous phase with a hydroxide, such as sodium or potassium hydroxide.

The present invention can be illustrated by the following examples:

Example 1

In a 1-liter Pyrex round-bottomed flask equipped with a spiral stirrer with a rotating speed of 300 rpm and an electric heater, 500 grams of sodium chloroaluminate were charged, wherein the ratio of AlCl/NaCl was 1 in moles. The product was heated to 200°C, stirred, and then 0.2 g of hexachlorobenzene and 0.1 g of decachlorobiphenyl were added. After 1 hour at 200°C, the molten bath was purged for 15 minutes with a nitrogen stream of 50 liters/hour, which was scrubbed in a bubbler containing 100 ml of hexane.

The amount of chlorinated organic compounds in the final bath and in hexane was determined by gas chromatography.

The results are listed in Table 1.

Example 2

Carry out the same test, but add 5% fine aluminum powder (grade PECHI NEY XY 49). After 1 hour at 200°C, blow off with 50 liters/hour of nitrogen for 15 minutes, take salt bath and hexane samples for quantitative determination.

The results are listed in Table 1.

Table 1

Containing Chlorine No Aluminum Powder Added 5% Aluminum Powder

Hexane disappears in organic salt bath Hexane disappears in salt bath

Product Start Final Working Product % Start Final Working Product %

C ₆ Cl ₆ 200 111 13.2 37.7% 200 29 3.5 83.7

Decachlorobiphenyl 100 41.3 0.40 58.3% 100 3.8 0.2 96

The numbers in the table are expressed in milligrams

Example 3

Operation was carried out in the same equipment used in Examples 1 and 2, but the operating conditions were changed as follows:

Bath temperature: 250°C

Chloroaluminate bath weight: 500 grams

Add 5% aluminum powder (PECHI NEY XY 49)

Test time: 2 hours

After 2 hours blow off with nitrogen: 15 minutes

Start adding: 500 mg hexachlorobenzene, 500 mg decachlorobiphenyl

The results are listed in Table 2.

Example 4

The test was carried out in the same manner as in Example 3, but the test time was 4 hours.

The results are shown in Table 2.

Table 2

Chlorine After 2 hours After 4 hours

Hexane disappears in organic salt bath Hexane disappears in salt bath

Product Start Final Working Product % Start Final Working Product %

C ₆ H ₂ Cl ₄ 2.5 0.7 0.3 0.1

C ₆ HCl ₅ 10 5 1.5 1.3

C ₆ Cl ₆ 500 8 3 97.8 500 1.3 3 99.15

Decachlorobiphenyl 500 6 0.2 98.8 500 3 0.16 99.4

PS* 0.02 0.002 0.1 0.008

PS: polychlorinated styrene

The numbers in the table are expressed in milligrams

Claims (7)

1, destroys the method for the chloride organic products that contains 2 above carbon atoms, it is characterized in that being enough to destroy described chlorinated products below 300 ℃ these products being bathed to contact with at least a chloro-aluminate, best 1-4 of time hour, its concentration was below the 5000ppm, below the preferred 2000ppm.

2,, it is characterized in that chloro-aluminate is a Sodium Tetrachloroaluminate according to the method for claim 1.

3,, it is characterized in that Sodium Tetrachloroaluminate contains the 50%(mole at least according to the method for claim 2) aluminium chloride.

4, according to any one method in the claim 1 to 3, it is characterized in that the chloro-aluminate bath temperature is between 200 and 300 ℃.

5, according to any one method in the claim 1 to 3, it is characterized in that chloro-aluminate contains a kind of metal dust at least.

6,, it is characterized in that preferably aluminium of described metal according to the method for claim 5.

7, according to the method for claim 5, the particle mean size that it is characterized in that described metal dust is less than 500 microns.