CH641425A5 - Process for preparing anhydrous aluminium chloride - Google Patents

Description

The present invention relates to a process for the production of anhydrous aluminum chloride by reacting aluminum oxide, in particular gamma earth (y-Al203) with chlorine in the presence of carbon.

The production of aluminum chloride by chlorination of materials containing aluminum oxide, such as bauxite or gamma earth with coal, has been known for a long time. The reaction components are initially at high temperatures of above 650 ° C, e.g. 1000 ° C, with each other according to the following reaction equation

A1203 + 3 C + 3 Cl2 -> 2 A1C13 + 3 CO-C quay implemented together. Since this reaction is endothermic, attempts have been made to maintain lower temperatures below 650 ° C and below. At these temperatures, the Boudouard equilibrium is shifted in favor of carbon dioxide, and the now exothermic reaction proceeds according to the following equation:

A1203 + 3/2 C + 3 Cl2 -> A12C16 + 3/2 C02 + X Kai.

In order to allow the reaction to proceed at these low temperatures, special requirements are placed on the starting materials.

It is known from DE-PS I 237 995 to use a low-ash coal, the ash content of which should not exceed 2.5%.

According to another known process DE-OS 2 244 041, the aluminum component used is a porous aluminum oxide with an enlarged effective surface and an average α-aluminum oxide content of less than 5%. This aluminum oxide is either used mixed with carbon or is preferably coated or impregnated with it. For this purpose, a hydrocarbon is cracked in the presence of aluminum oxide in a separate process step and the carbon formed is deposited in situ on the aluminum oxide particles. Based on the total content of the mixture, which should have an average carbon content of 15 to 24%, the hydrogen content should be less than 0.5%. This process is cumbersome because of the additional process step, combined with the additional processing of the resulting still hydrocarbon-containing exhaust gases, quite apart from the fact that the activity of the aluminum oxide can be damaged as a result of the high temperatures used during cracking.

Studies with the aim of carrying out the reaction at temperatures as low as possible have shown that the ash content of the coal, as important as it may be for keeping a continuously operated fluidized bed in which the reaction is preferably carried out, just as little as the low hydrogen content of the carbon have an immediate impact on the completeness of the reaction. Such a complete implementation is not only desirable for reasons of intensive use of the starting materials, but also because the A1203 / C / CI2 system is very corrosive and the reactor linings have to be replaced more or less frequently depending on the temperature.

The present invention was therefore based on the object of specifying a process for the production of anhydrous aluminum chloride by reacting aluminum oxide with carbon and chlorine, in which a high chlorine yield is ensured. It has been found that this object can be achieved by using carbon with an inner surface of 20 to 100 m2 / g.

The carbon should preferably have an inner surface area of 40 to 70 m 2 / g (N2 surface area according to BET). A coal that meets these conditions is produced, for example, in the production of acetylene. As aluminum oxide, it is expedient to use y-Al203 which has the lowest possible a-Al203 content of e.g. should have less than 5 wt .-%. When using a fluidized bed reactor as the preferred reactor, the grain sizes of the two solids used as starting materials should be such that they mix well and no separation is effected. It is advantageous if the grain size of the carbon is approximately 1.75 to 2.25 times the grain size of the aluminum oxide, the grain size of the aluminum oxide being e.g. B. can be 0.1 to 0.3 mm.

In the fluidized bed, the carbon content (based on A1203 + C) is expediently kept at 15 to 50%, which is brought about by appropriate mixing ratios of the reaction components to be metered.

The reaction is preferably carried out at from 500 to 800.degree. C., in particular from 530 to 650.degree. C., it being generally possible to say that the greater the surface area of the carbon used, the higher the chlorine yield Reaction with the same chlorine yield can also be carried out at lower temperatures if a carbon with a correspondingly increased inner surface is used. This has the advantage that it is possible to work with a high chlorine yield even at temperatures of 500 to 600 ° C., which are preferred in this temperature range because of the favorable position of the Boudouard equilibrium.

The relatively low heat development in the reaction of aluminum oxide with carbon and chlorine can be increased without reducing the chlorine yield by additionally introducing oxygen into the reaction zone with the chlorine if the use of carbon is increased accordingly. It is therefore possible to operate even smaller reactors in stationary fashion at the desired reaction temperature without additional heating.

A particularly preferred method of increasing and maintaining the temperature in the reactor to a certain value is to combine the reaction according to the invention with carbon with the strongly heat-producing reaction between aluminum oxide and phosgene or an equimolar mixture of carbon monoxide and chlorine, which according to the following Reaction equation expires:

2 A1203 + 6 CO + 6 Cl2 -> 4 AIC13 + 6C02.

5

10th

15

20th

25th

30th

35

40

45

50

55

fiO

65

3rd

641 425

This procedure has the advantage over the addition of oxygen that no additional carbon has to be used, which is burned to carbon dioxide, which additionally dilutes the reaction gases, but that the carbon monoxide introduced is also used for the formation of aluminum chloride. If the temperature in the reactor does not reach the desired value, part of the chlorine can be replaced by appropriate amounts of phosgene or an equimolar mixture of carbon monoxide and chlorine, which are dimensioned so that the desired temperature is maintained.

Examples

example 1

A. In a heated fluidized bed apparatus, 400 g of carbon with a surface area of 7.2 m 2 / g and 600 g of y-Al 2 O 3 are converted at 501 chlorine / h at temperatures between 500 and 600 ° C. A mixture of 8% by weight of A1203 and 19% by weight of C is metered in, so that the carbon content in the bed remains constant (40%). The chlorine content in the exhaust gas is determined, which is still 33% by volume at 500 ° C and drops to 4% by volume at 600 ° C.

B. As indicated under A, carbon and y-A1203 are reacted with chlorine. This time, however, the carbon has a surface area of 51 m2 / g. The chlorine content in the exhaust gas is 27% by volume at 500 ° C and 0.8% by volume at 600 ° C.

Table 1

Carbon temp. Cl2.m exhaust

Surface m2 / g ° C vol.%

Example 1A 7.2 500 33

7.2 550 20

7.2 600 4

Example 1B 51 500 27

51 530 18

51 550 3.5

51 600 0.8

Example 2

As described in Example I, carbon (51 m2 / g) and y-Al203 are reacted with chlorine. Different amounts of oxygen are added to the chlorine. At CI2 oxygen concentrations between 8.2: 1 to

2.3: 1 (volume ratio), no reduction in the chlorine yield (calculated after A1C13 obtained) was found.

The discrepancy between the chlorine yield and the chlorine content in the exhaust gas compared to Example 1B is explained by the H20 content of the y-Al203 used.

Table 2

10th

Carbon temp.

CH2: 02

Chloraus

surface

prey

m2 / g

"C

%

Example 2

51

600

-

80.5

15

51

600

8.2: 1

78.2

51

600

3.5: 1

78.9

51

600

2.3: 1

80.4

Example 3

20 A fluidized bed reactor with a total height of 10 m and a diameter of 3.50 m is 60% filled with a mixture of gamma earth and carbon black (weight ratio: 7: 3). The reactor is lined with ceramic stones of 350 mm thickness (R = 1.13 Kcal / m and ° C) 25 and sealed gas-tight to the outside with a 10 mm thick steel jacket. If chlorine gas is introduced into this reactor for a swirl speed of 2.4 m / sec (based on normal conditions), the desired conversion to aluminum chloride cannot be achieved, since the minimum reaction temperature of 550 ° C. is far from being reached. Even if the reaction contents were preheated to 550 ° C, the reaction could not be kept going. In less than an hour the temperature has already dropped so far that a reaction practically does not take place, so that the chlorine introduced leaves the reactor unreacted.

If half of the chlorine gas introduced into the reactor is now replaced by the corresponding amount of phosgene, it is possible to operate the above-described reactor continuously at the desired reaction temperature of 600 ° C., even if the reactor is charged with cold gamma -Aluminium oxide takes place. The heat released by the reaction of the phosgene with gamma aluminum oxide is sufficient to compensate for the heat energy dissipated through the reaction wall and the process gas.

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Claims (3)

641 425 1. A process for the preparation of anhydrous aluminum chloride by reacting aluminum oxide with carbon and chlorine, characterized in that the carbon has an inner surface of 20 to 100 m2 / g. 2. The method according to claim 1, characterized in that one carries out the reaction at a temperature of 500 to 800 ° C. 2nd PATENT CLAIMS 3. Process according to claims 1 and 2, characterized in that to maintain the reaction temperature, part of the chlorine is replaced by a corresponding amount of phosgene or an equimolar mixture of carbon monoxide and chlorine.