DE1132919B - Process for the continuous production of hexachlorocyclohexane - Google Patents

Description

Process for the continuous production of hexachlorocyclohexane Addition to patent application St 100271V b / 120 (Auslegeschrift 1124 486) The patent application St 10027 IVb / 12O relates to a continuous process for the production of hexachlorocyclohexane by catalytically influenced chlorination of benzene in a liquid reaction mixture, containing benzene, acetic anhydride and carbon tetrachloride, at a temperature from 308 to 223 ° K, with chlorine entering the reaction mixture at a rate is initiated that the chlorine concentration between the value 0.241 0K-53.8 and the value 0.01776 0K-3.96 g of chlorine per liter of reaction mixture is. Degree means Kelvin the absolute temperature of the reaction mixture.

The invention aims to improve the patent application process St 10 027 IVb / 12 o.

According to the invention, the procedure is that the temperature of the Reaction mixture holds between 278 and 2480 K, continuously part of the reaction mass removed from the reaction zone, this part to volatilize the acetic acid and of the acetyl chloride from it and to the formation of acetic anhydride and hydrogen chloride heated, the hydrogen chloride removed, the acetic anhydride thus formed continuously returns, hexachlorocyclohexane wins from the withdrawn part and the Residual solutions are also fed back into the reaction mixture. Preferably the temperature is kept between 273 and 258 ° K.

The invention thus relates in particular to an advantageous one Separation and work-up of the solvent mixture used in the chlorination of benzene.

When carrying out the method according to the invention, the uniform Composition of the hexachlorocyclohexane solvent mixture by two factors adversely affected.

The first factor is that described in patent application St 10027 IVb / 12O "Oil formation", which leads to the formation of a small amount of acetyl chloride. The second Factor forms the chlorination of a small amount of acetic anhydride into one mixed monochloroacetic acid-acetic anhydride product, which together with the Hexachlorocyclohexane is removed. In the formation of the mixed monochloroacetic acid-acetic anhydride product hydrogen chloride is formed at the same time. The hydrogen chloride reacts with the existing acetic anhydride and forms acetic acid and acetyl chloride. If As this process goes on, the acetic anhydride present becomes gradually completely destroyed, and the circulating liquid solvent stream contains continuous operation acetic acid and acetyl chloride instead of the desired one Acetic anhydride. However, the use of such a solvent mixture leads to a reduction in the γ-isomer content of the crude product and a reduction the solubility of the hexachlorocyclohexane in the solvent mixture.

Also used as a co-solvent for the If hexachlorocyclohexane is used, the formation of oily substances is suppressed By-products, but at the same time falls as a result of increasing the volume of acetyl chloride and acetic acid, the total capacity of the reaction system, which is usually fixed.

It has now been found that the solvent mixture is continuous and the acetic anhydride content in relation to the benzene content can be kept at a constant, desired ratio. It is found that the acetic acid formed as by-products and the acetyl chloride with Success can be converted back to acetic anhydride by the hexachlorocyclohexane-containing reaction mixture for the formation of acetic anhydride and hydrogen chloride is heated and the hydrogen chloride is removed: CH3COOH + CH3COCl + (CH3CO) 2Ö + HCl This reaction is carried out in that the mixture consisting of exits the reaction zone, is distilled, the volatilized azeotropically boiling Mixture of acetic acid, acetyl chloride, carbon tetrachloride and benzene in one Reaction zone is introduced in which acetic acid and acetyl chloride follow each other Above scheme can react, and the liquid acetic anhydride formed drips back into the vessel in which the withdrawn reaction mixture is located, while the hydrogen chloride emerges as a gas.

In this way, the process can be carried out continuously and the Solvent mixture are kept at a uniform composition. It stays some acetyl chloride and acetic acid in the solvent mixture after heating back, but their concentration does not increase when the distillation heating stage runs continuously.

The solvent mixture of acetic anhydride, acetic acid and Acetyl chloride is an equilibrium mixture, with partial equilibrium depends on the amount of oxygen and water present in the system; the Ingress of air and water into the system is inevitable, even if one goes out of his way to turn it off. Even what is technically available Chlorine always contains a small amount of oxygen. If you can also use the procedure When pure acetic anhydride begins, a small amount of acetic acid soon appears and acetyl chloride in the system. By using the heating distillation stage the breakdown of acetyl chloride and acetic acid is prevented and their concentration kept below a value at which the yield of γ-isomer decreases will. The heating distillation stage can reduce the amount of acetic acid and acetyl chloride be kept to a minimum. It is preferred to use an amount of acetic acid and acetyl chloride no more than about 10% of the volume of the material added to the reaction vessel worked.

If the distillation heating step is not carried out, take in a short time the acetic anhydride concentration down to such a level which the yield of y-isomer is significantly lower and the acetic acid content becomes so large that the reaction mixture solidifies and the process is thereby disturbed can be. When performing the distillation heating step, the solvent mixture remains at constant composition if the process is kept running continuously will. The process is carried out continuously, with the only loss taking place Acetic anhydride is that which is produced by its solution in the hexachlorocyclohexane product is given which is removed.

In the drawing, a device and a flow diagram are schematically shown, which for the implementation of the invention in continuous more natural form is used can be. With a storage container for the solvent mixture is designated. The container is filled with an inert gas, such as argon or helium, over it a line 7 is kept at a pressure slightly above atmospheric pressure, to ensure that no oxygen penetrates into the solvent mixture. A benzene supply line 8 is provided through which fresh benzene is added to replace that which forms hexachlorocyclohexane. The benzene can can also be fed to another suitable location, e.g. B. through the line 25. From the container 6, the material is passed through a line 9 in which a control valve 11 is arranged, withdrawn into the reaction vessel 12. The one at working temperature The chlorine concentration to be kept in a constant state is determined in a known manner by periodically sampling the reaction mixture, reacting with excess Iodide ion and titration of the sample with thiosulfate solution set. A consistent one Chlorine concentration can also be adjusted by a photoelectric cell, which in turn determines the speed of the chlorine supply or the intensity of the lighting changes.

Means for cooling the reaction vessel 12, indicated generally at 13 are used to keep it at the desired temperature. chlorine is introduced through a line 16. There are suitable means (not shown) provided which stir the mixture in the reaction vessel to make it homogeneous Maintain mass in the reaction zone. The emerging from the reaction vessel 12 Products go through a line 17 to a second reaction vessel 20, where the existing excess chlorine is reduced to traces, and then through a line 25 to a solvent preheater 18. It is usually not necessary to use the second To cool reaction vessel 20; isolation has proven to be sufficient. Fresh acetic anhydride as required is added to line 25; an additional charge of anhydride is only required to replace that with the crude product is removed and that is slightly less than 1 percent by weight thereof.

On the solvent preheater 18 is a packed one Column section 51 is provided, the column having at least one theoretical plate is equivalent. A reflux cooler 19 is provided above the column 51, which has a gas line 52 which carries the hydrogen chloride and any present leads away inert gas into the fume cupboard. Sufficient heat is supplied to the preheater 18, to maintain constant conditions in column 51. From the preheater 18, the material is passed through a line 22 in which a control valve 24 is arranged is led to a still 23.

When the concentration of acetyl chloride with respect to acetic acid grows in the system, one can also add a small amount of water to the column 51, to hydrolyze the acetyl chloride. In practice, technical grade chlorine contains approximately 1 kg or more of water per ton, and this is usually used to regulate the amount of acetyl chloride-acetic acid sufficient in the reaction mixture.

In the volatilized still 23 materials will Discharged at the top through a line 26, condensed in a cooler 27 and then closed a receptacle 28 out, which has a barometric leg 29 with a valve 31 is connected to the storage container 6. The receptacle 28 is kept under vacuum generated by a vacuum pump (not shown) which is connected to a line 32.

The remaining liquid flows out of the still 23 a line 33, which is provided with a control valve 34, withdrawn and then in a vessel 36 transferred from which the product is provided with a valve 37 Line 38 is withdrawn. The solvent mixture from vessel 36 is over a steam line 39 passing through a condenser 41 into a receptacle 42, in which a vacuum is maintained that is generated by a pump (not shown) is generated. which is connected to a line 43. The solvent mixture from the receptacle 42 is withdrawn via a line 44, which is through a valve 46 can be regulated, and fed back into the line 24. The ones in the containers Solvent mixture collected 28 and 42 is in an oxygen-free atmosphere condenses.

It is the production of hexachlorocyclohexane by catalytic Addition chlorination of benzene known, with a reaction mixture of benzene and a polar inert solvent is used. In a known method can the hexachlorocyclohexane by distilling off the unreacted benzene and the solvent and finally by heating the reaction mixture a temperature of the liquid of 140 to 1500 C at a pressure of 10 mm Hg can be obtained in 10 minutes.

According to the invention, on the other hand, after the distillation volatile products obtained from a withdrawn portion of the reaction mixture The condensation is transferred to a reaction zone in which acetic acid and acetyl chloride Can react to acetic anhydride and hydrogen chloride, the hydrogen chloride removed and the acetic anhydride formed continuously recycled.

The following is an example of a practical implementation of the Invention given using the apparatus described. 10.532 kg per hour a benzene used for refreshment was fed to the storage container 6, during 8.891 per minute of a benzene-acetic anhydride-carbon tetrachloride mixture withdrawn and fed into the reaction vessel 12. 29.065 kg of chlorine per hour were introduced into the reaction vessel 12 kept at a temperature of 100.degree became. The stream emerging from reactor 12 contained 0.0213 g / l free chlorine. The stream was passed through the second reactor 20 to remove the free chlorine present further reduce by reaction with the benzene. The whole stream of the reaction mass, the benzene, hexachlorocyclohexane, carbon tetrachloride, acetic anhydride, acetic acid and acetyl chloride, was then passed into the solvent preheater 18, where the material is above its boiling point at the pressure used, e.g. 92 ° C Atmospheric pressure. The composition of the stream in Volume percentage, determined with an infrared spectrophotometer was the following: C6H6 ...... ..... 8.2 C6H6CI6 .. ... .. .. 5.0 (CH3COhO........ ....... 55.0 CH3COOH . . 5.7 CH3COC1. . 7.7 CC. ... 18.8 100.40 / 0 In the solvent preheater 18 Benzene, carbon tetrachloride, acetyl chloride and acetic acid evaporated as an azeotropic mixture into column 51, where the acetyl chloride and acetic acid reacted with each other to form acetic anhydride and hydrogen chloride. That Anhydride was returned to the preheater and the hydrogen chloride via the Line 52 removed.

In the example, 0.145 kg of hydrogen chloride were withdrawn per hour. The composition of the material passing through line 22 was substantial the same as that of the material entered the preheater since the in the column 51 caused change in the composition was too small to be with usual analytical methods to be measured. The effect of the heating distillation stage can only be observed after a certain period of work, if in absence a gradual decrease in acetic anhydride concentration during the heating distillation step occurs and at the same time the concentration of acetyl chloride and acetic acid increases.

The material in line 22 passed through the valve under control 24 to the distillation vessel 23, where the solvent mixture evaporates and passes through the line 26 to the condenser 27 was withdrawn. The receptacle 28 was held at a pressure of 120 to 200 mm Hg. The solvent mixture was through the barometric leg 29 is returned to the storage container 6.

The liquid collected in the still 23 was passed through the line 33 led into the vessel 36, where the existing solvent mixture was discharged through the line 39 to the receptacle 42. From the vessel 36 39.308 kg per hour of a product were withdrawn, of which 11.022 kg from the y-isomer of hexachlorocyclohexane, which corresponded to a content of 280/0 of y-isomer. The receptacle 42 was maintained under an absolute pressure of 25 to 35 mm Hg. The product contained 0.313 kg of acetic anhydride; an equal amount of acetic anhydride was fed to line 25 every hour.

The product withdrawn through line 38 was liquid and had a temperature of 1500 C.

It was stirred vigorously with water to remove any traces of acetic anhydride to remove and transform the material into the form of small spheres.

In the previous examples, light was used to activate the chlorine used. The method according to the invention does not rely on this means of activation of chlorine and to bring about its dissociation; you can do any use effective means for this purpose, such as a-particles, y-rays, ethylene, Propylene or a organic peroxide, the effect of which is known per se is.

Claims (1)

PATENT CLAIM: Process for the continuous production of hexachlorocyclohexane according to patent application St 10 027 IVb / l2 o by catalytic addition chlorination of benzene at 308 to 2230 K, a free chlorine concentration of 0.241 0K to 0.01776 - "K-3.96 gn in the presence of acetic anhydride and carbon tetrachloride, continuous removal of part of the reaction mixture, distillation of the same Condensation of the distillate, recycling of the condensed solvent mixture into the reaction zone and separating the hexachlorocyclohexane from the distillation residue, characterized by draws that one after the distillation of the withdrawn part the reaction mixture obtained volatile products before condensation in a Reaction zone converted into acetic anhydride in the acetic acid and acetyl chloride and hydrogen chloride can react, the hydrogen chloride removed and the formed Acetic anhydride is continuously recycled into the drawn off reaction mixture. References considered: U.S. Patent No. 2,558 363; French Patent No. 1,078,719; P. Karger, textbook of the organ. Chemistry, 12th edition, 1954, p.223; Houben-Weyl, Methods of the organ. Chemie, Vol. 3rd, 3rd edition, 1943, pp. 937 and 938.