DE937347C - Process for the production of hexachlorobenzene - Google Patents

Description

Process for the production of hexachlorobenzene The invention relates to a process for the production of hexachlorobenzene.

Hexachlorocyclohexane or Benzene Hexachloride is now available in a great deal Manufactured on a scale because this substance or its y-isomer is an excellent Has insecticidal effectiveness. Because the raw material is about five times as much a- as y-isomer contains, necessarily goes with the concentration or separation of the latter hand in hand the production of a large amount of the undesirable α-isomer. It it is known that polychlorobenzenes are produced from this waste material by dehydrochlorination can be obtained with the help of sodium hydroxide, as a result of which trichlorobenzene is formed, whereupon, if desired, the latter substance is further chilorated.

However, this process results in a significant loss of chlorine as a result of the formation of hydrogen chloride in the first stage.

It has now been found that polychlorobenzenes can be used directly and economically can be prepared from benzene hexachloride in one operation without a significant loss of chlorine occurs.

Although an appropriate setting of the reaction conditions Mixture of tetra-, penta- and hexachlorobenzenes in different proportions can be obtained, the hexachlorobenzene generally makes up the largest proportion of this product. The less chlorinated compounds can if desired can be deposited, but the production of these substances cannot be done in this way to seriously compete with other known manufacturing processes. on the other hand that delivers the subject of Invention forming a method satisfactory and economical way of working for the production of hexachlorobenzene.

According to the invention there is thus a process for the preparation of hexachlorobenzene proposed which consists in that benzene hexachloride with an excess of oxygen or an oxygen-containing gas at an elevated temperature in a reaction zone containing a catalyst which is appropriate is to oxidize hydrogen chloride to chlorine, whereupon the product obtained from the The reaction zone is removed and the chlorinated benzene thus formed is condensed.

In a preferred embodiment of the method, the reactants are passed through a bed of finely divided heated catalyst, which is constantly in more uniform suspension is maintained by a stream of oxygen through it or a gas containing oxygen.

The overall reaction that occurs here can be broken down into the following Expressing the equation: 2 C6 H6 C16 + 3 02+ 2 C6 C16 + 6 H2 ° Find in reality however, three main reactions take place at the same time, namely C6 H6 Cl6 + C6 H3 C13 + 3 H C1 (I) 4HCl + 02t2C12 + 2H20 (2) C6 H3 C13 + 3 C12 + C, C6 C16 + 3 Hcl (3) In theory, all of the hydrogen chloride formed during reactions (I) and (3) should be can be converted into chlorine by reaction (2), which is then used for reaction (3) is available. However, this ideal result cannot easily be achieved because the reactions mentioned take place at different speeds and the Reaction (2) is slower than reactions (i) and (3), with the addition of that reaction (i) is somewhat endothermic, while reaction (3) is strongly exothermic is. It is therefore necessary to choose the reaction conditions so that they are mutually exclusive opposing properties are balanced as far as possible to create a maximum yield of polychlorobenzenes and a maximum yield of hexachlorobenzene get in the product.

In addition to hexachlorobenzene, there is also a certain amount of partially chlorinated Benzenes, namely tri-, tetra- and pentachlorethylene, which depends on the flow rate, the reaction temperature and the amount of oxygen used depends. Do you want A larger proportion of these imperfectly chlorinated products can be obtained you get this result through high throughput speeds, relatively low Temperatures and a restriction in the supply of air or oxygen too favor the reaction vessel. Usually, however, this procedure is very good useful for the production of hexachlorobenzene, and the reaction conditions can be adjusted so that this substance is practically the only product.

The throughput speed is understood to mean the total volume of the gases, that measured at the prevailing reaction temperature by a not in the flow state Unit volume of the catalyst per hour are passed through.

Any substance which is more satisfactory can be used as a catalyst Way according to the well-known Deacon process for the production of chlorine from hydrogen chloride is applied. In general, such a catalyst consists of a chloride a polyvalent metal such as copper supported by an inert carrier such as aluminum oxide or silica gel, can be worn; sometimes a mixture of chlorides is used used, one of which has little or no catalytic activity owns.

The catalyst can be in the form of fine particles and is preferred applied in the form of a fluidized bed.

The "pyrolysis of benzene hexachloride [reaction (I)] goes at elevated levels Temperatures in the presence of the catalyst proceed smoothly during the reaction (2) leads to an equilibrium such that the formation of chlorine is caused by temperatures within the range of about 200 to 8000, depending on the catalyst used, is favored. It is known that the production of chlorine from hydrogen chloride is greatest at temperatures below about 5770, and the best working temperature this is likely to be within the range of 480 to 5000. The response However, (3) is favored by the use of higher temperatures. The general reaction temperature should therefore be as high as possible corresponding to an optimal generation of Chlorine according to equation (2), and it is advantageous to use a temperature between 450 and 5500 to be used when working with a copper catalyst.

The required throughput speed depends to a certain extent on the type of catalyst used and the reaction temperature; it was however, found that if the other conditions are held constant, the Hexachlorobenzene content of the product increases with decreasing flow rate. As a result, it is advantageous to work with low throughput speeds. If, for example, benzene hexachloride together with an I 10% of the theoretical 5 the amount of air that corresponds to the oxygen requirement by keeping it at around 450 to 5000 Fluidized bed of a supported copper catalyst is passed, the space velocity should preferably be 60 parts by volume of the mixture of vapor Benzene hexachloride and air, measured at the working temperature, per hour and unit of space of the catalyst measured in the non-flowing state. In general should per hour and unit of space of the catalyst measured in the non-flowing state 20 to 300, preferably 50 to 200 parts by volume of a mixture vaporous benzene hexachloride and oxygen or a gas containing oxygen, measured at the working temperature, are passed over the flow catalyst.

To achieve a satisfactory conversion to hexachlorobenzene, the amount of oxygen or oxygen-containing gas must be in excess to that from of the equation 2 CoH6C16 + 3 02 + 2 C6C16 + 6H2O, and should be available be between 110 and 200% of this theoretical amount. A more perfect one The trichlorobenzene is reacted with the chlorine by using a large 5 excess of oxygen obtained, but this has the disadvantage that the overall yield of polychlorobenzene something sinks because part of the organic matter is completely oxidized to carbon dioxide will. It is therefore advantageous to use only a small excess of oxygen and to change the other reaction conditions so that the hexachlorobenzene is as high as possible.

The oxidation can be carried out with either pure oxygen or with a Mixture of oxygen and an inert gas of known properties carried out become, such as B. air, the most common oxygen-containing gas in question comes. If the other factors are kept constant, an increase is made the oxygen concentration in the gas fed in, the yield of hexachlorobenzene increased.

In one embodiment of the subject matter of the invention In the process, the finely divided catalyst is placed in a vertical reaction vessel entered that on its underside with separate supply pipes for air and Benzene hexachloride is equipped. As a result of the corrosive action of some of the reactants the apparatus should be made of suitable resistant material, for example made of nickel or a nickel-chromium alloy (79 0 / o Ni, I3 0 / o Cr, 60/0 each) or made of brick-lined steel. The catalyst will brought to the desired reaction temperature, at the same time air with a linear velocity which is sufficient to make it more uniform To keep suspension. Then molten a-benzene hexachloride residues are in The catalyst bed is introduced where they evaporate and go up with the air be led through the bed. Optionally, the benzene hexachloride can be added to the reaction vessel can also be supplied in vapor form. This can be achieved for example be that the air is first passed through the molten material, so that it saturates with the benzene hexachloride vapor before it enters the catalyst bed is introduced.

The reaction products, which are at the top of the reaction vessel are discharged, are then fed to the top of a second cooling vessel, which is equipped with cooling devices and in which the cooled product is collected will. This cooling vessel can consist of a tower in which water is sprayed downwards so that the solid polychlorobenzenes collect at the bottom of the tower while unreacted hydrogen chloride is dissolved. If desired, the product can be further purified in a known manner, for example by extraction with suitable Solvents or by fractional distillation or crystallization.

The process according to the invention is illustrated in the following examples.

Example I The catalyst is prepared as follows.

3000 g of finely divided aluminum oxide become one with stirring boiling solution of 400 g cup trichloride and 200 g potassium chloride in 2070 g water given. The resulting suspension is heated until it is semi-solid and finally dried in an oven at 250-3000 until the product is free flowing. Of the the catalyst thus obtained is sieved through a sieve that is 20 meshes per centimeter and retained on a sieve that has 79 meshes per centimeter, being go ° / o of the material pass through a sieve that is 40 meshes per centimeter Has.

2400 g of this catalyst are placed in a vertical reaction vessel 1.50 m high and 50 mm in diameter, which is provided with a jacket to pass through is provided with heating or cooling means. Ddr catalyst is then brought to a temperature of 470, and at the bottom of the reaction vessel is heated at such a linear velocity Air is introduced so that the catalyst takes the form of a fluidized bed; if these conditions are set, the air flow is diverted so that it is initially is passed through molten benzene hexachloride of 2500 before entering the reaction vessel entry. Under these conditions were of a stream of air going at one speed of 151 1 flows per hour, entrained 215 g of benzene hexachloride per hour and passed upwards through the hot fluidized bed of the catalyst, the flow rate 1 So parts of the volume of the mixture of air and benzene hexachloride vapor, measured at the Working temperature, measured per hour and unit of space in the non-flowing state Catalyst is. The amount of oxygen used was I200 / e of the theoretical Lot.

The gaseous exiting at the top of the reaction vessel Product was passed into a separator to remove any entrained particles of the To separate the catalyst, and then fed directly to a water-cooled tower, in which the polychlorobenzenes solidified and were collected at the bottom of the tower. The water spraying down removed any hydrogen chloride that was still present. After drying, 341 g of organic product were obtained, the 84.40 / 0 Hexachlorobenzene contained; the remainder consisted of a mixture of tri-, tetra- and pentachlorobenzenes. The total yield of polychlorobenzenes based on benzene hexachloride was 67 0 / o and the yield of hexachlorobenzene 55 0 / o.

Example 2 The procedure was the same as described in Example 1, except that the air through the molten benzene hexachloride among such Conditions were passed that only 137 g per hour in vapor form through 151 l of air were carried away per hour, so that the ratio of oxygen to benzene hexachloride was greater than in example 1. The throughput speed was therefore only 172 parts of space of the benzene hexachloride vapor-air mixture, measured at the working temperature, per hour and unit of space of the catalyst measured in the non-flowing state, and the reaction temperature was maintained at 4700. The amount of oxygen used was 190 per cent of theory. The yield of benzene hexachloride was here again about 55%, but the product contained 95 ovo of this substance, and the remainder consisted mainly of pentachlorobenzene.

Claims (7)

PATENT CLAIMS I. Process for the production of hexachlorobenzene, characterized in that benzene hexachloride with an excess of oxygen or an oxygen-containing gas at an elevated temperature in a reaction zone which contains a catalyst suitable for hydrogen chloride to oxidize to chlorine, whereupon the product is removed from the reaction zone and the chlorinated benzene formed is condensed. 2. The method according to claim 1, characterized in that the catalyst is in finely divided form and the oxygen-containing gas through a bed of the catalyst is passed at such a rate as is sufficient is the amount of the catalyst in a state of continuous and uniform To keep suspension. 3. The method according to claim I or 2, characterized in that the catalyst consists of a copper chloride. 4. The method according to claim I to 3, characterized in that the Reaction temperature between 200 and 8000 and preferably between 450 and 550 " lies. 5. The method according to claim I to 4, characterized in that the Oxygen or the oxygen-containing gas is applied in an amount that between 110 and 200 per cent of the stoichiometric amount required for a perfect Conversion of the benzene hexachloride to hexachlorobenzene is required. 6. The method according to claim I to 5, characterized in that the Reaction zone 20 to 300, preferably 50 to 200 parts by volume of a mixture of Benzene hexachloride vapor and oxygen or an oxygen-containing gas at the - working temperature, per hour and unit of space of the in not flowing Condition measured catalyst are supplied. 7. The method according to claim 6, characterized in that the from The gases exiting the reaction zone are passed through a tower in the water is sprayed downwards, and the hexachlorobenzene at the bottom of the tower is collected. Attached publications: German patent specifications No. 539 176, 58o 512.