JPS6113700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ammoxidation method for efficiently and safely producing an acrylonitrile compound by a fluidized bed method.

In the presence of a catalyst, one molecule of α and β is produced from one molecule of raw material olefin and ammonia and 3/2 molecules of oxygen.
The so-called ammoxidation reaction, which produces an unsaturated nitrile and three molecules of water, is a very widely used reaction method throughout the world, especially in the production of acrylonitrile, since the advent of the Sohio process. As a manufacturing process for acrylonitrile, a fixed bed reaction method is also used in some cases, but a fluidized bed reaction method represented by the Sohio method is more common.
That is, a mixed gas of raw material olefin and ammonia is blown separately from the molecular oxygen-containing gas into a catalyst that is fluidized using a molecular oxygen-containing gas as a fluidizing gas to cause a reaction at high temperature.
This is a method for producing unsaturated nitriles.

However, in this reaction, the main objective is usually α・
In addition to β-unsaturated nitriles, nitrile compounds such as hydrogen cyanide, aldehyde compounds such as acrolein, carboxylic acid compounds such as acrylic acid,
It is accompanied by a large number of by-products such as CO, carbon oxides of _CO2 , etc., and it is very important to increase the selectivity by suppressing these undesirable products. On the other hand, various discussions have been made regarding this ammoxidation mechanism, but in order to obtain the desired α/β-unsaturated nitrile, it is necessary to contact the three reaction components of raw material olefin, ammonia, and oxygen on a catalyst. are necessary, and for this purpose, their complete mixing is essential. That is, each reaction component supplied into the catalyst layer needs to be well mixed to a predetermined mixing degree at or before the activation stage. However, no matter how many modifications are made to the structure of the reactor and the raw material gas supply equipment, the method in which the reactants are mixed only after entering the reactor cannot essentially improve the mixing of the reactant gases themselves. However, the effect is small. Therefore, a method can be considered in which the entire amount of gas containing these three types of reaction components is mixed in advance before being supplied to the reactor, but such a mixed gas is not suitable for achieving good reaction results. Under optimal conditions, this would be difficult to achieve because it would fall within the explosion range of flammable gas, and even if it were possible,
This would be extremely unsafe.

Furthermore, although a large number of ammoxidation catalysts have been researched and developed to date, their selectivity is not sufficient, so in order to improve the production unit consumption, it is necessary to It is necessary to improve the reaction results by improving the mixing method. Moreover, these catalysts inevitably lose their activity gradually during the reaction, and therefore must be replaced with new catalysts, which is not desirable from an industrial implementation point of view due to the high cost of the catalyst. Ta.

The present inventors have conducted intensive research to overcome the drawbacks of these conventional methods. As a result, a predetermined proportion of the air supplied to the fluidized bed reactor is mixed with olefin and ammonia in advance, and this is mixed with molecular oxygen. It has been shown that when supplied into a catalytic reaction bed that has already been fluidized with a containing gas, explosive limits can be avoided, the reaction performance can be improved over conventional ammoxidation methods, and the catalyst life can be extended. I found it. The present invention has been made based on this knowledge.

That is, the present invention provides a method for producing acrylonitrile or methacrylonitrile by reacting at least one olefin selected from propylene and isobutylene, ammonia, and oxygen using a fluidized bed reactor. Of this, an amount equivalent to 10 to 110 mol% of the olefin is mixed in advance with at least one of olefin and ammonia, and this mixed gas of olefin, ammonia, and oxygen is placed in a catalytic reaction layer fluidized with an oxygen-containing gas. The present invention provides an ammoxidation method characterized by supplying.

The oxygen used in the present invention means molecular oxygen, and any oxygen-containing gas other than air may be used as the oxygen source, but air is preferably used because it is economical. Furthermore, in order to achieve the object of the present invention, the amount of oxygen-containing gas mixed with propylene, isobutylene or a mixture thereof and ammonia may be in a range equal to or higher than the upper limit of explosion of these flammable gases or mixed flammable gases, and ammonia oxidation This is not enough to mix the entire amount of raw material gas required for the reaction, and there is no need to do so. The upper limit is propylene,
Oxygen amount 110 for isobutylene or its mixture
It is the amount of gas containing mol%, and the lower limit is 10 mol% of oxygen.
This is the amount of gas included. When the amount of oxygen exceeds 110 mol%, the amount of oxygen-containing gas used as fluidizing gas decreases, while the amount of mixed gas consisting of raw material olefin, ammonia, and oxygen-containing gas supplied to the reactor increases too much. , which will have an adverse effect on the fluidization and mixing conditions in the reactor and may enter the explosive range. Also, 10 mol%
If it is less than , the desired effect of the present invention will be less and undesirable.

Next, an example of a flow sheet suitable for carrying out the method of the present invention will be explained according to the drawings. Oxygen-containing gas C is introduced from pipe 3 into mixer 6, where it is mixed with propylene, isobutylene or a mixture thereof A and ammonia B introduced from pipes 1 and 2, respectively, and then blown into fluidized bed reactor 7. . On the other hand, the remaining oxygen-containing gas is blown into the fluidized bed reactor 7 from the acid pipe 4 to fluidize the catalyst. The interior of the fluidized bed reactor is maintained under predetermined reaction conditions to carry out the ammoxidation reaction.
The reaction product is taken out from pipe 5. The order in which the raw materials A, B, and C are mixed is not limited to that shown in the drawings, and may be mixed at one location or in stages, for example. The mixer 6 may be any of various static mixers, as well as baffles such as a bench turret or an orifice, and is not particularly limited. Preferably, propylene, isobutylene or a mixture thereof, ammonia and the oxygen-containing gas are thoroughly mixed before entering the catalyst bed of the reactor, and turbulent mixing in the piping is performed without using a mixer. Good too.

As described above, according to the method of the present invention, a predetermined proportion of the oxygen-containing gas blown into the fluidized bed reactor is mixed with olefin and ammonia in advance. - The amount of β-unsaturated nitrile produced increases, that is, the selectivity increases. In addition, the ammoxidation catalyst is thought to have low durability against reducing atmospheres, and the conventional method had a problem in that its activity gradually decreased due to this, but according to the method of the present invention, a reducing atmosphere is generated within the catalyst layer. is suppressed, thereby significantly extending its service life. Moreover, according to the method of the present invention, the danger of explosion due to mixed gas is avoided, and the method is extremely superior in terms of operational safety.

Next, the present invention will be explained in more detail based on examples.

Example 1 Acrylonitrile was produced according to the illustrated flow sheet. First, fluidized bed reactor 7 (inner diameter 55 mm)
is filled with an ammoxidation catalyst (e.g. molybdate catalyst), and when reacting by supplying air:ammonia:propylene at a molar ratio of 11:1.15:1.0, 10% by volume of the supplied air is added to the mixer from pipe 3. 6 and premixed with propylene and ammonia introduced through pipes 1 and 2, respectively. This mixed gas was blown into the reactor from a superjar provided above the distribution plate of the reactor. on the other hand,
The remaining air was blown into the distribution plate in the reactor through pipe 4. When the ammoxidation reaction was carried out at 440°C in this way, the conversion rate of acrylonitrile in one pass (number of moles of acrylonitrile produced/
The number of moles of propylene supplied x 100) was 75.3%. In this case, the premix ratio of molecular oxygen to propylene was 23.1 mol%.

Example 2 The amount of air fed to the reactor from the super jar by premixing with propylene and ammonia is 40
Acrylonitrile was produced in exactly the same manner as in Example 1, except that the conversion rate was 75.5% in one pass, and the conversion rate remained almost unchanged even after 100 hours of operation. In this case, the premix ratio of molecular oxygen to propylene was 92.4 mol%.

Example 3 Acrylonitrile was produced in the same manner as in Example 1 except that the molar ratio of supplied air: ammonia: propylene was 9.0:1.15:1.0. No change was observed even when the conversion rate was measured after continuous operation for hours.
It was found that good catalytic activity was maintained. In this case, the premix ratio of molecular oxygen to propylene was 18.9 mol%.

Comparative example (conventional ammoxidation method) Using the same fluidized bed reactor as in Example 3, pipe 3
The entire amount of supplied air is blown into the dispersion plate of the reactor through the pipe 4 without introducing air into the mixer 6,
In mixer 6, only ammonia and propylene were mixed, and the reaction was carried out in the same manner as in Example 3 except that this was blown into the super jar.The conversion rate of acrylonitrile in the first pass was 73%, but after that After 75 hours of continuous operation, the conversion rate was 68.8%.
It declined to .

[Brief explanation of the drawing]

The drawing shows one example of a flow sheet suitable for carrying out the invention. Explanation of symbols, 1 to 5... Piping, 6... Mixer,
7...Fluidized bed reactor, A...Propylene, isobutylene or a mixture thereof, B...Ammonia, C...
...Oxygen-containing gas.

Claims (1)

[Claims] 1. When producing acrylonitrile or methacrylonitrile by reacting at least one olefin selected from propylene and isobutylene, ammonia, and oxygen using a fluidized bed reactor, among the oxygen, olefin Against 10~
An amount equivalent to 110 mol% is mixed in advance with at least one of olefin and ammonia,
An ammoxidation method characterized by supplying this mixed gas of olefin, ammonia, and oxygen into a catalytic reaction bed fluidized with an oxygen-containing gas.