DE1468702B2 - PROCESS FOR THE CONTINUOUS MANUFACTURING OF ACRYLIC NITRILE - Google Patents

Description

The present invention relates to a process for the continuous production of acrylonitrile by catalytic conversion of propylene, ammonia and oxygen, with the conversion of propylene too Acrylonitrile can be carried out in consistently high yields on an industrial scale.

From the published documents of the Belgian patent 5 71 200 it is known acrylonitrile from propylene, ammonia and oxygen at elevated temperature under the action of a catalyst to manufacture. According to this process, the reaction mixture can also contain water vapor, if it is proves to be expedient. The method according to the invention relates to a modified embodiment of the known method described in the aforementioned patent application.

According to the known process, bismuth, tin and antimony salts of phosphomolybdic acid can be used as catalysts and molybdic acid and the bismuth salt of phosphotungstic acid can be used. For the known method has been proposed, the molar ratio between oxygen and olefin in the reaction mixture fed to the reactor from 0.5: 1 to 5: 1, preferably from about 1: 1 to 2.5: 1 keep. The molar ratio of ammonia to olefin in the reaction mixture fed to the reactor can range from 0.05: 1 to 5: 1. The optimal ratio for the production of the acrylonitrile should then be approximately 1: 1.

When the known process was carried out on an industrial scale, the observation made that during the implementation of the process the degree of conversion of propylene increases Acrylonitrile often declines gradually when the process is with an ammonia-to-propylene ratio of about 1: 1 and an oxygen to olefin ratio on the order of about 1.5: 1 to about 2: 1. This disadvantage occurs when Dilute the reaction mixture with steam as well as when working without steam. This a gradual decrease in the degree of conversion of propylene to acrylonitrile appears to be due to a decrease in activity caused by the catalyst. According to the known process, a catalyst can generally are restored to their original state by treatment with air at elevated temperatures, if you notice a decrease in activity while using it. This regeneration however, the catalyst is unproductive due to time outage, and so it is for economic reasons it is desirable to avoid these regeneration periods or at least to keep them to a minimum.

It has now been found that the conversion to acrylonitrile over long periods of time without substantial Decrease in the degree of conversion of propylene to acrylonitrile can be carried out if special Process conditions are applied.

The inventive method for the continuous production of acrylonitrile in technical Scale by converting a gaseous mixture of propylene, ammonia and oxygen into Presence of a bismuth molybdate or bismuth phosphorus molybdate catalyst at an elevated temperature without the addition of water, if necessary at elevated pressure, is characterized in that the reaction vessel leaving gaseous reaction product continuously or at suitable time intervals for its oxygen content is analyzed and oxygen to the gas mixture supplied to the reaction vessel in such an amount it is added that the oxygen content in the gaseous reaction product leaving the reaction vessel is always in the range from more than 0.1 to about 7 mole percent.

The oxygen content of the reaction mixture leaving the reactor can be determined according to the various methods known per se for determining the oxygen content of a gas will. If these measurements show that the oxygen content in the leaving the reactor Reaction mixture below the desired amount, d. H. falls to 0.1 mol% and below, it is only necessary to increase the amount of oxygen in the reaction mixture fed to the reactor to the desired To achieve effect.

In the technical implementation of the acrylonitrile manufacturing process the oxygen content in the reaction mixture leaving the reactor is reduced influenced several factors. Apart from the amount of air or oxygen that goes into the reactor is supplied, the amount of oxygen consumed can depend on the temperature and the contact time be dependent. If a mixture of propylene and propane is used as the starting product, The amount of oxygen consumed in the reaction fluctuates when there is a change in the ratio of these two components occurs. Some of these factors cannot be fully assessed. It will therefore the oxygen content in the reaction mixture leaving the reactor is continuously monitored. In this way, one quickly becomes aware of a possible reduction in the oxygen content in the Reactor leaving the reaction mixture, regardless of the cause, the change in the

Oxygen content is based. If the technical system is to be largely automated, a continuous oxygen determination apparatus can be used. It will then be easy to use a continuous measurement of the oxygen content in the reaction mixture leaving the reactor achieved. Various types of continuous oxygen meters are commercially available available. Such continuously working oxygen

Determination apparatus can control automatic control valves that regulate the amount of oxygen added to the reactor. In this way, the amount of oxygen supplied to the reactor and thus also the amount of oxygen contained in the reaction mixture leaving the reactor can be kept at the desired level automatically and largely independently of the operating personnel.

The technical progress achieved by the method according to the invention is based on the explained in the following table.

In a small laboratory reactor with a fluidized bed arrangement of the catalyst of Example 17 of FIG Belgian patent 5 71200 the following reactions were carried out at 449 ° C:

Molar ratio NH3 H2O yield Excess acrylic Attempt nitrile duration Propylene air NH3 O2 % total Hours.

According to the present
invention

Example 17 of the
BE-PS 5 71 200

10 1 0 72.2 14.4 1.67 67.0 60.5 10 1 0 75.1 10.3 2.15 70.9 78 10 1 3 71.0 23.5 2.39 66.3 121

The bismuth phosphomolybdate catalyst of the tables was prepared by the following procedure.

A solution containing 9.3 ecm of 85% phosphoric acid, 272 g of molybdic acid (85% MoCb), 40 ecm of nitric acid and 582 g of bismuth nitrate, Bi (NO3) 3 · 5 H2O, in 400 ecm of water became 750 g of one given aqueous, colloidal, 30% silica containing silica sol. The mixture then became evaporated to dryness and heated to 538 ° C for 16 hours. Then it was married and through Seven brought to a particle size corresponding to 235 to 1460 meshes per square centimeter.

325 g of this catalyst was placed in a conventional oxidizer.

Claims (1)

Claim: Process for the continuous production of acrylonitrile on an industrial scale by reaction a gaseous mixture of propylene, ammonia and oxygen in the presence of a Bismuth molybdate or bismuth phosphorus molybdate catalyst at elevated temperature without the addition of water, optionally at elevated pressure, characterized in that the reaction vessel leaving gaseous reaction product continuously or at suitable time intervals its oxygen content is analyzed and oxygen is analyzed in the gas mixture supplied to the reaction vessel is added in such an amount that the oxygen content in the reaction vessel leaving gaseous reaction product is always in the range of more than 0.1 to about 7 mol%.