NO118762B - - Google Patents

Description

Process for the production of benzonitrile.

It is known that from phthalic anhydride and ammonia or from the nitrogen-containing functional derivatives of phthalic acid, such as e.g. phthalimide or phthalic acid diamide by conduction in an ammonia stream over water-splitting catalysts, such as thorium oxide, silica gel, clay soil, clay soil silicates, clay soil phosphates etc. can produce phthalonitrile. When describing this procedure, it has already been mentioned that benzonitrile is thereby obtained in minor quantities as a by-product. When silica gel is used as a catalyst, a working temperature of 360° C is indicated as the favorable one for the production of phthalonitrile.

Based on this observation, a procedure for the production of benzonitrile is described, which is characterized by passing phthalic anhydride vapor in a mixture with ammonia gas at temperatures above 450° C over aluminum oxide, whereby a yield of 70-80 percent is obtained .of the theoretical of benzonitrile. This method was further developed by adding aluminum oxide to heavy metal oxides, especially zinc oxide or cobalt oxide, whereby the reaction temperature could be lowered and temperatures of 350-420° C could be used. The yields in this method are also indicated as 70-80 per cent of theoretical. In both procedures, a very considerable excess of ammonia is used, which amounts to approx. 100 times the theoretical amount (60 g of phthalic anhydride requires 1000 1 of ammonia gas).

It was now found that benzonitrile can be produced in excellent yield when phthalimide vapor is introduced either alone or in a mixture with inert gases, such as air, nitrogen, ammonia, carbonic acid, water vapor, benzene vapor or the like at temperatures between 360° C and approx. 500° C over a silica gel arm is wide-tracked and has a volume weight of less than 0.5. Instead of using an inert flushing agent, you can of course work at reduced pressure, e.g. at approx. 100-300 mm of mercury, whereby the phthalimide evaporates at the boiling temperature corresponding to the selected pressure, distills without any addition through the catalyst and is thereby decarboxylated. Finally, phthalimide can also be distilled through the catalyst at atmospheric pressure.

As phthalic anhydride reacts with ammonia according to the equation, the phthalimide vapor required for the new method can also be produced in a manner known per se by mixing at least one equivalent of ammonia gas to phthalic anhydride vapor with or without inert diluents.

The reaction temperature used for the formation of benzonitrile can be varied within wide limits. However, the turnover is still incomplete at temperatures below approx. 400° C, but the converted phthalimide cannot be fed back into the circuit. It is most appropriate to work at approx. 390-420° C. The nature of the silica gel used as catalyst has a significant effect on the course of the catalysis. The most active is the so-called wide-pored silica gel (see Fiat Final Report No. 1313, PB 85172, volume 1, pages 394—396, Sili-cagel B), which has a granular state with a grain size of 1—3 mm and a volumetric weight of 0.46-0.48. Narrow-pore silica gel is considerably less active. Acidic contaminants such as sodium or potassium bisulphate or phosphoric acid and the like have a particularly strong inhibitory effect on the catalysis, with the help of which the decomposition of water takes a strong place in the background directly opposite the decomposition of carbonic acid.

The following examples show the implementation of the method without limiting it. Between parts by volume and parts by weight, there is the same relationship as between liters and kilograms. Steam and gas volumes are converted to 20° C and 740 mm pressure.

Example 1: 1000 volume parts of nitrogen per hour is passed through an evaporation vessel, in which there was phthalimide that had been heated to 260° C, whereby per hour was evaporated approx. 1 part by weight of phthalimide. The nitrogen stream, which was charged with phthalimide, then passed a contact tube heated to 410° C in which there is 1-3 mm granular silica gel B (according to Fiat Final Report No. 1313, PB 85172, volume I, page 396, last paragraph ). The gases emerging from the contact furnace are cooled to room temperature whereby the benzonitrile formed, as well as approx. 2-5 per cent of the evaporated phthalimide is condensed. From 10 parts of evaporated phthalimide, 6.5-6.7 growth parts of benzonitrile are obtained, which corresponds to a yield of 93-95.5 per cent of the theoretical. Taking into account the separated phthalimide, which can be returned to the starting material, the yield is almost quantitative. Example 2: If ammonia gas is used instead of nitrogen in example 1, the results are approximately the same, as a mixture of phthalonitrile and phthalimide is obtained instead of the reacted phthalimide.

Example 3.

If instead of the nitrogen used in example 1, air is used as purge gas, the results are the same as in example 1.

Example 4: 12,000 parts by volume of air per hour is passed through an evaporation vessel in which there is phthalic anhydride heated to 230° C, whereby per hour evaporates approx. 36 parts by weight phthalic anhydride. The air flow which is charged with phthalic anhydride is added per hour 11 parts by weight gaseous ammonia. The formed gas mixture, preheated to 310° C, is then led through a contact tube which is heated to 415° C and in which there are 220 parts by volume of 2-5 mm grained silica gel, as indicated in example 1. The gases that emerge from the contact furnace are cooled to room temperature, whereby benzonitrile, some water and some unreacted phthalimide are condensed. The reaction mixture is taken up in ether, the water is separated, the remaining ether solution is dried over calcium chloride and filtered. The ether is then removed and the remaining benzonitrile is purified by means of vacuum distillation (boiling point 11 mm, 73° C). The yield is approximately 85 per cent of the theoretical.

Claims (2)

1 Process for the production of benzonitrile where gaseous phthalimide or such substances which manage to form this under the conditions of the process at temperatures between 360 and 500°, preferably between 390-420° C are passed over silica gel, characterized in that wide-pore silica gel with a volume weight of less than 0 .5 is used as a catalyst. 2. Method according to claim 1, characterized in that the phthalimide is mixed with inert gases or vapors, such as nitrogen, air, ammonia, water vapor, benzene vapor or the like.