JP7012523B2 - Method for producing (meth) acrylonitrile - Google Patents

Description

The present invention relates to a method for producing (meth) acrylonitrile.

Ammooxidation using a fluidized bed reactor has been industrially practiced for a long time. For the purpose of improving the reaction yield of α, β-unsaturated nitrile, for example, the raw material gas distribution tube and the dispersion plate have been improved as the development of the catalyst and the improvement of the reactor internal apparatus. Iwao, Shigekatsu Mori, Masatoshi Horio "Reaction Engineering of Fluidized Beds" (published by Fudokan (1984)) and Fluidization Engineering (Fluidized Bed Engineering); (Published) describes a very common fluidized bed reaction technique.

When a monomer is produced by a gas-phase contact reaction using a fluidized bed reactor, unsaturated nitrile is produced by reacting with ammonia, oxygen (often air is often used), and an olefin or a tertiary alcohol. At this time, a heat exchanger is generally installed at the outlet of the reactor in order to cool the generated high-temperature reaction gas. However, the high boiling point by-products generated by the reaction and a small amount of catalyst scattered from the fluidized layer reactor adhere to the heat exchanger, causing clogging, the reactor pressure rising, and stable operation for a long period of time. It can be difficult to do.

As a technique for solving the above-mentioned problems, in Patent Document 1, in a reactor having a heat exchanger used for cooling the reaction gas, the reaction gas between the reactor outlet and the heat exchanger is operated during operation. A technique for removing clogging substances in the heat exchanger by introducing powder into the lead-out tube or introducing a fluidized layer reaction catalyst deposited in the reactor into the above-mentioned reaction gas lead-out tube. It has been disclosed.

Japanese Unexamined Patent Publication No. 5-301040

According to the cleaning method described in Patent Document 1, it is said that the rate of increase in pressure loss of the heat exchanger can be suppressed, and the fluidized bed reactor can be operated stably for a long period of time as compared with the case where the heat exchanger is not implemented. The reaction results tend to decrease over time. As described above, there is still room for improvement in the technique described in Patent Document 1 from the viewpoint of stable operation for a long period of time without impairing the reaction results.

The present invention has been made in view of the above-mentioned problems of the prior art, and in the production of (meth) acrylonitrile using a fluidized bed reactor, it can be stably produced for a long period of time and the reaction results can be maintained. , (Meta) It is an object of the present invention to provide a method for producing acrylonitrile.

As a result of diligent studies, the present inventor has found that the above problems can be solved by adjusting the introduction position of the powder, and has completed the present invention.

That is, the present invention is as follows.
[1]
A method for producing (meth) acrylonitrile using a fluidized bed reactor including a fluidized bed reactor and a heat exchanger connected by a reaction gas lead-out pipe of the fluidized bed reactor.
A step of introducing the raw material gas into the fluidized bed reactor and performing an ammoxidation reaction in the presence of a catalyst to obtain a reaction gas.
A step of introducing powder into the reaction gas lead-out pipe and leading out the reaction gas to the heat exchanger while cleaning the heat exchanger.
Have,
The reaction gas lead-out pipe extends from the upper part of the fluidized bed reactor in the height direction of the fluidized bed reactor, reaches the highest point of the reaction gas lead-out pipe, and is connected to the highest point. And has a second portion extending towards the heat exchanger
A method for producing (meth) acrylonitrile, wherein the introduction position of the powder is a position in the second portion and is a position lower than the highest point.
[2]
The second portion, at least in part thereof, has an intermediate portion extending downward in the height direction.
The method for producing (meth) acrylonitrile according to [1], wherein the powder introduction position is the intermediate portion.
[3]
The method for producing (meth) acrylonitrile according to [1] or [2], wherein the angle formed by the first portion and the line connecting the highest point and the introduction position of the powder is 89 ° or less. ..
[4]
The method for producing (meth) acrylonitrile according to any one of [1] to [3], wherein the distance from the powder introduction position in the second portion to the heat exchanger is 10 m or more.

INDUSTRIAL APPLICABILITY According to the present invention, in the production of (meth) acrylonitrile using a fluidized bed reactor, a method for producing (meth) acrylonitrile that can be stably produced for a long period of time and can maintain reaction results is provided.

FIG. 1 is a schematic explanatory view illustrating a fluidized bed reactor according to an embodiment of the present embodiment. FIG. 2 is a schematic explanatory view illustrating the fluidized bed reaction apparatus according to another aspect of the present embodiment. FIG. 3 is a schematic cross-sectional view illustrating the fluidized bed reactor that can be used in this embodiment. FIG. 4 is a schematic explanatory view of the fluidized bed reactor used in Comparative Example 1.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail with reference to the drawings as necessary. The following embodiments are examples for explaining the present invention, and the present invention is not intended to be limited to the following contents. The present invention can be variously modified and carried out within the scope of the gist thereof. In the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the positional relationship such as up, down, left, and right shall be based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

The method for producing (meth) acrylonitrile according to the present embodiment uses a fluidized bed reactor including a fluidized bed reactor and a heat exchanger connected by a reaction gas lead-out pipe of the fluidized bed reactor (meth). ) A method for producing acrylonitrile. Further, in the method for producing (meth) acrylonitrile according to the present embodiment, a step of introducing a raw material gas into the fluidized layer reactor and performing an ammooxidation reaction in the presence of a catalyst to obtain a reaction gas, and a step of deriving the reaction gas. It has a step of introducing powder into a pipe and leading out the reaction gas to the heat exchanger while cleaning the heat exchanger, and the reaction gas out-drawing pipe is from the upper part of the fluidized layer reactor. A first portion extending in the height direction of the fluidized layer reactor and reaching the highest point of the reaction gas outlet pipe, and a second portion connected to the highest point and extending toward the heat exchanger. The position where the powder is introduced is the position in the second portion, which is lower than the highest point.
Since it is configured as described above, according to the method for producing (meth) acrylonitrile according to the present embodiment, in the production of (meth) acrylonitrile using a fluidized bed reactor, it can be stably produced for a long period of time, and at the same time, it can be stably produced. The reaction results can also be maintained.

The method for producing (meth) acrylonitrile according to the present embodiment uses a fluidized bed reactor including a fluidized bed reactor and a heat exchanger connected by a reaction gas lead-out pipe of the fluidized bed reactor. The step of introducing the raw material gas into the fluidized bed reactor and performing an ammoxidation reaction in the presence of a catalyst to obtain a reaction gas is included.
Hereinafter, an example of the fluidized bed reaction apparatus that can be used in the present embodiment will be described, but the configuration is not particularly limited as long as it is an apparatus capable of carrying out each step in the present embodiment, and a fluidized bed reactor having various configurations can be used. Can be applied.

The fluidized bed reactor in the present embodiment includes a fluidized bed reactor and a heat exchanger connected by a reaction gas lead-out pipe of the fluidized bed reactor.
As one aspect of such a fluidized bed reactor, the fluidized bed reactor shown in FIG. 1 can be mentioned. The fluidized bed reactor 1 in FIG. 1 includes a reactor 2, a heat exchanger 3, and a reaction gas lead-out pipe 4 for connecting the reactor 2 and the heat exchanger 3.
The reaction gas lead-out pipe 4 has a first portion 4A and a second portion 4B.
The first portion 4A is a portion extending from the upper part of the reactor 2 substantially parallel to the height direction of the reactor 2 until reaching the highest point 5 of the reaction gas lead-out pipe 4. Approximately parallel means a state within ± 10 ° from the parallel direction.
Further, the second portion 4B is a portion connected to the above-mentioned highest point 5 and extends toward the heat exchanger 3.
The first portion 4A and the second portion 4B described above divide the reaction gas lead-out pipe 4 into two regions with the highest point 5 as a boundary, and the members are not intended to be different in these regions. do not have. That is, the first portion 4A and the second portion 4B in the reaction gas lead-out pipe 4 may be integrally formed of the same member, or may be formed by connecting different members.
In the embodiment shown in FIG. 1, the angle α formed by the line connecting the first portion 4A and the highest point 5 and the powder introduction position 6 is less than 90 °, and the second portion 4B is the heat exchanger 3. The reactor 2 is configured to incline downward in the height direction toward the direction of the reactor 2.
The reaction gas passes through the reaction gas lead-out pipe 4 and is introduced into the heat exchanger 3. Further, the reaction gas that has passed through the heat exchanger 3 is introduced into a quenching tower (not shown), and then recovered as a product ((meth) acrylonitrile) through various known purification steps and the like.
In the present embodiment, as described above, the second portion of the reaction gas lead-out pipe is configured to have a portion lower than the highest point, and the powder can be introduced into the portion. In this case, even if a force in the direction opposite to the derivation direction of the reaction gas is applied to the powder, in order for the powder to move to the reactor side, not only the force in the opposite direction but also the highest point is reached. A force equivalent to the potential energy up to is also required. Therefore, according to the method for producing (meth) acrylonitrile according to the present embodiment, it is prevented that the introduced powder flows back and moves to the fluidized bed reactor side, and therefore occurs due to the movement of the powder. It is possible to effectively prevent catalyst deterioration such as catalyst poisoning.

In the above, as a typical example of this embodiment, the reaction gas lead-out pipe (first portion and second portion) and the powder introduction position shown in FIG. 1 have been described, but the powder introduction position is the second. The position in the portion is not limited to such an example as long as it is a position lower than the highest point. As another typical example in this embodiment, the configuration shown in FIG. 2 can be mentioned.
The aspect shown in FIG. 2 is different from the aspect shown in FIG. 1 in the configuration of the second portion 4B in the reaction gas lead-out pipe 4, and the other configurations are the same as those in FIG. That is, in the embodiment shown in FIG. 2, the connection angle between the first portion 4A and the second portion 4B is 90 °, but the second portion 4B is an intermediate extending downward in the height direction of the reactor 2. It has a portion 4C and the powder is introduced at any position in the intermediate portion 4C. Therefore, the angle α formed by the line connecting the first portion 4A, the highest point 5 and the powder introduction position 6 is less than 90 ° even in the embodiment shown in FIG.
The intermediate portion 4C extends substantially parallel to the height direction of the reactor 2. Approximately parallel means a state within ± 10 ° from the parallel direction.
As described above, in the present embodiment, the second portion has an intermediate portion extending downward in the height direction of the reactor in at least a part thereof, and the powder introduction position is the intermediate portion. Is preferable. With such a configuration, the introduced powder tends to be more effectively prevented from flowing back and moving to the fluidized bed reactor side.

The reactor 2 in the fluidized bed reactor 1 of FIG. 1 corresponds to the main body portion of the gas phase reactor that separates the reaction system of the fluidized bed reaction from the outside, and the shape thereof is not particularly limited and various known shapes. Can be applied.
The reactor 2 is, for example, in its internal space, as illustrated in FIG.
Cooling coils 7A, 7B and 7C provided in the lower part of the internal space of the reactor 2 and controlling the temperature (reaction temperature) of the internal space by removing the heat of reaction.
Cyclones 8A, 8B and 8C arranged in the upper part of the reactor 2 internal space, and
Cyclone entrance 9 corresponding to the entrance of the cyclone 8A and
With the deplegs 10A, 10B and 10C connected to the cyclones 8A, 8B and 8C,
Can be configured to include.
Further, although not shown in FIG. 3, the reactor 2 is usually used.
An air (oxygen) introduction tube connected to the bottom of the reactor 2 and introducing air (oxygen) into the reaction system,
An air (oxygen) dispersion plate provided in the lower part of the internal space of the reactor 2 to disperse air (oxygen) as a reaction raw material in the reaction system.
A raw material introduction pipe that is connected to the upper part of the raw material distribution pipe, which will be described later, and introduces raw materials other than air (oxygen) into the reaction system.
A raw material distribution tube provided in the lower part of the internal space of the reactor 2 to disperse the raw material in the reaction system,
A catalyst layer composed of a fluidized bed catalyst filled in the upper part of the raw material dispersion tube, and
It is equipped with.

Specifically, the fluidized bed reaction includes a step of supplying a raw material gas to a fluidized bed reactor including a catalyst layer to flow the catalyst layer, and a step of passing the raw material gas through the catalyst layer to obtain a reaction-producing gas. After discharging the generated gas from the catalyst layer and introducing it into the cyclone, the step of discharging the reaction generated gas from the fluidized bed reactor and the catalyst accompanying when the reaction generated gas is introduced into the cyclone are recovered and the said. It can include a step of returning the catalyst from the depreg to the catalyst layer.

The oxygen-containing gas supplied to the reactor is not particularly limited, and examples thereof include air and an oxygen-containing inert gas, and air is generally used. The supply amount of the oxygen-containing gas is preferably 5 to 15 mol ratio, more preferably 7 to 14 mol ratio with respect to the hydrocarbon or the tertiary alcohol. The amount of ammonia supplied may be preferably in the range of 0.5 to 2 molar ratio, more preferably 1 to 1.5 molar ratio with respect to the hydrocarbon or the tertiary alcohol.

The temperature in the catalyst layer is preferably 300 to 600 ° C., more preferably 400 to 500 ° C., and the pressure is preferably 3 kg / cm ² -G or less, more preferably 0.2 to 1.5 kg / cm ² -G. It is done under the condition of. Regarding the flow layer catalyst, it is described in many documents and patents such as Yutaka Kiyomiya et al., "Acrylonitrile" (Chemical Engineering, vol. 48, 11, pp. 873-881 (1984)) and JP-A-51-40391. A supported catalyst containing molybdenum can be used, and examples thereof include molybdenum-bismuth-iron catalysts.

During the fluidized bed reaction in the present embodiment, the catalyst thick layer exists in the lower part of the reactor and the catalyst dilute layer exists in the upper part of the reactor. That is, when the fluidized bed catalyst is in a fluidized state in the reactor, the spatial density of the catalyst tends to decrease toward the upper side. As stated in Daizo Kunii's "Fluidization Law" (published by Nikkan Kogyo Shimbun (1962)), in gas systems, the height of the fluidized bed is not always as definite as the liquid level. Since there are protrusions due to large and small fluttering, it is only approximate and averagely specified.

In the present embodiment, the upper and lower limit ranges of the catalyst thick layer are set to the upper limit of the catalyst layer height calculated from the following formula using the differential pressure that can be measured from the pressure nozzle attached to the reactor, and the lower limit is the oxygen-containing gas dispersion. It can be specified as the installation position of the pipe or dispersion plate.
Catalyst layer height Lr = (differential pressure between bh) / ((differential pressure between bc) / (distance between bc)) + (distance between ab)
Here, a is the installation height of the oxygen-containing gas dispersion pipe or the dispersion plate, b is the height of the midpoint between the oxygen-containing gas distribution plate and the raw material gas distribution pipe, c is the height 1 m above b, and h is the cyclone. The height of the entrance.

The upper region of the catalyst thick layer has a relatively small catalyst density in the fluid and is called a catalyst dilute layer. In the reactor, the catalyst dilute layer region generally has a wider region than the catalyst thick layer region. The catalyst accompanying the reaction product gas flows into the cyclone installed in the upper part of the reactor. Most of the accompanying catalyst is then separated from the reaction-producing gas and returned to the bottom of the reactor by the depleg attached to the cyclone. Although the reaction-producing gas separated from the catalyst is not shown in FIG. 3, it can be taken out of the reactor from the lead-out tube. Further, in FIG. 3, only one series (three) of cyclones is drawn, but the number of cyclones is determined by the size of the reactor, the catalyst particle size and the amount of reaction-producing gas, and usually a plurality of cyclones are installed. To. Further, when two or more cyclones are installed in series, the catalyst collection efficiency tends to increase.

In the catalyst thick layer, the ammooxidation reaction of most of the feedstock gas proceeds, and heat of reaction is generated. The catalyst thick layer has good heat exchange efficiency because the catalyst is present at a high density. In order to reduce the burden on the equipment that controls the reaction temperature, a cooling coil having at least 40% or more of the heat transfer area is installed in the catalyst thick layer that can efficiently remove the reaction heat and control the temperature. In order to reduce the local imbalance of reaction temperature, the cooling coil can be composed of a plurality of independent series having heat transfer areas of various sizes.

As the cooling coil in the present embodiment, various known types of indirect heat exchangers installed in the fluidized bed reactor can be applied, and the type, size and shape thereof are not limited. The low-temperature fluid to be passed through the cooling coil is a fluid having an ammonium oxidation reaction temperature or lower, preferably 100 to 300 ° C., and for example, hot water, high-pressure hot water, steam, the above-mentioned mixture, or a molten salt is used.

The step of introducing the raw material gas into the fluidized layer reactor and performing the ammoxidation reaction in the presence of a catalyst to obtain the reaction gas in the present embodiment is not particularly limited, but for example, a reactor filled with a catalyst. For example, propane or propylene, ammonia and oxygen may be supplied as raw materials, and acrylonitrile may be obtained as a reaction gas by a gas phase ammoxidation reaction. Isobutene, tertiary butanol or isobutane, ammonia and oxygen may be obtained. It may be a step of supplying as a raw material and obtaining metaacrylonitrile as a reaction gas by a vapor phase ammoxidation reaction.
In the fluidized bed reaction, it is necessary that the catalyst particles are kept in a fluidized state. As the catalyst, conventionally known catalysts may be used for producing unsaturated nitriles from the above raw material gas by an ammoxidation reaction. For example, in the ammoxidation reaction of an olefin, a composite oxide containing molybdenum and / or antimony as a main component may be used. Examples of the catalyst used for the ammoxidation reaction of paraffin include a composite oxide containing molybdenum or vanadium as a main component. The reaction pressure in the fluidized bed reactor is not particularly limited and may be, for example, 1.5 kg / cm ² G or less. The reaction temperature is not particularly limited as long as the raw materials react in a gas phase state, and may be 400 to 500 ° C.

In the present embodiment, in the step of introducing the powder into the reaction gas outlet pipe and leading the reaction gas to the heat exchanger while cleaning the heat exchanger, the reaction gas is cooled and the heat exchange accompanying the cooling is performed. This is done from the viewpoint of preventing the adhesion of the reaction gas-derived components to the inside of the vessel. That is, in this step, the reaction-generated gas generated by the ammoxidation reaction is introduced into the heat exchanger and cooled by the refrigerant. The method and structure of the heat exchanger are not particularly limited as long as it has an appropriate cooling capacity. However, from the viewpoint of cooling efficiency in the heat exchanger, a shell / tube type heat exchanger is preferable. The gas generated from the reactor is introduced into the tube side (inside the tube), which is the heat transfer member of this heat exchanger, and the refrigerant is introduced into the shell side (outside the tube) by heat exchange between them. , The heat of the generated gas is recovered.

The temperature of the refrigerant introduced into the heat exchanger is 110 ° C. or higher, and a refrigerant that has been heated to that temperature in advance may be used. By using a refrigerant heated to 110 ° C. or higher, the temperature of the high boiling point by-product in the produced gas is maintained higher than the temperature of the high boiling point by-product, and the blockage due to the condensation of the high boiling point by-product in the heat exchanger of the reactor outlet line is prevented. be able to.

The catalyst used in the reaction step is, for example, fine particles having an average particle size of about 50 μm, and the generated gas contains the catalyst particles. From the viewpoint of more effectively preventing such catalyst particles from accumulating in the heat exchanger, when a shell / tube heat exchanger is used, the tube is preferably a straight tube, and the inside of the tube is preferable. A structure in which the generated gas passes through in one pass is preferable.

From the viewpoint of effectively and surely preventing the adhesion of high boiling point by-products to the wall surface of the generated gas flow path of the heat exchanger, it is preferable to monitor and control the temperature of the refrigerant introduced into the heat exchanger. The gas temperature in the generated gas flow path becomes lower toward the downstream, and high boiling point by-products tend to adhere. Therefore, if the refrigerant is introduced from the downstream side of the generated gas flow path, that is, a countercurrent type is used to control the inlet temperature (supply temperature) of the refrigerant to the heat exchanger, the temperature on the downstream side of the generated gas is also controlled. It is preferable because it is easy to manage. From the same viewpoint, it is also possible to monitor the temperature of the heat exchanger outlet of the generated gas and control the temperature and / or flow rate of the refrigerant introduced into the heat exchanger so that the temperature exceeds a certain temperature. preferable. However, it is not always necessary to accurately measure the temperature of the heat exchanger outlet of the produced gas, and there is a certain relationship between the temperature of the heat exchanger outlet of the produced gas and the temperature of the refrigerant introduced into the heat exchanger. If is known, the temperature of the refrigerant introduced into the heat exchanger may be monitored to control the temperature and / or flow rate of the refrigerant.

The refrigerant introduced into the heat exchanger may be a liquid or a gas. The liquid used as the refrigerant is preferably water, and examples thereof include pure water, industrial water, seawater, and a mixture of two or more thereof. Such a refrigerant may be pressurized and heated by a boiler to adjust the temperature to 110 ° C. or higher. Examples of the gas used as the refrigerant include water vapor, air, nitrogen, carbon dioxide, or a mixture of two or more thereof. Such a refrigerant may be heated to 110 ° C. or higher by heating it with a boiler or the like. From the viewpoint of more effectively and surely suppressing the adhesion of high boiling point by-products contained in the generated gas to the inner wall of the heat exchanger (for example, the surface of the heat transfer member), the temperature of the refrigerant introduced into the heat exchanger is set. It is preferably 140 to 260 ° C, more preferably 170 to 240 ° C. In order to control the temperature of the refrigerant to a desired temperature, the amount and temperature of the preheated refrigerant supplied to the heat exchanger may be adjusted. Since the temperature of the generated gas flowing out of the reactor is almost the same as the reaction temperature, it is generally 400 to 500 ° C. Therefore, even if the temperature of the refrigerant is in the above range, the generated gas can be cooled without any problem.

Further, from the viewpoint of more effectively and surely preventing the adhesion of high boiling point by-products to the wall surface of the generated gas flow path of the heat exchanger, in the present embodiment, when the reaction gas is led out to the heat exchanger, the reaction is carried out. By introducing powder into the gas outlet pipe, the heat exchanger is cleaned in parallel.
The powder is not particularly limited, but for example, sand, waste catalyst, ammonium sulfate, sodium sulfate and the like can be used, and sodium sulfate is preferable from the viewpoint of cleaning efficiency.

As shown in FIGS. 1 and 2, the angle α formed by the line connecting the first portion, the highest point and the powder introduction position is less than 90 ° as long as the configuration of the present embodiment is satisfied. .. In the present embodiment, the angle formed by the line connecting the first portion and the highest point and the powder introduction position is preferably 89 ° or less. With such a configuration, the introduced powder tends to be more effectively prevented from flowing back and moving to the fluidized bed reactor side.

In the present embodiment, from the viewpoint of further improving the cleaning efficiency, the distance from the powder introduction position in the second portion to the heat exchanger is preferably 10 m or more, more preferably 30 m or more. The distance from the powder introduction position in the second portion to the heat exchanger here is determined based on the length of the pipe in the second portion, and in the embodiment shown in FIGS. 1 and 2, it is L2. It is given as the total value of L3.

In the present embodiment, the distance from the highest point to the powder introduction position is preferably 0.5 m or more, more preferably 3 m or more. With such a configuration, the introduced powder tends to be more effectively prevented from flowing back and moving to the fluidized bed reactor side. The distance from the highest point to the powder introduction position here is obtained based on the length of the pipe in the second portion, is given as L1 in the embodiment shown in FIG. 1, and is given as L1 in the embodiment shown in FIG. Is given as the total value of L1a and L1b.

Next, this embodiment will be described in more detail with reference to Examples and Comparative Examples. However, this embodiment is not limited to the following examples as long as it does not deviate from the gist.

(Example 1)
In Example 1, acrylonitrile was produced using the fluidized bed reactor shown in FIG. A line extending from the upper part of the fluidized bed reactor in the height direction of the fluidized bed reactor and reaching the highest point of the reaction gas outlet pipe, and a line connecting the highest point and the introduction position of the powder. The angle formed by, was 89 ° or less.
As the reactor 2, the reactor having the configuration shown in FIG. 3 was used. That is, a dispersion tube and a dispersion plate for gas as a reaction raw material are provided in the lower part of the reactor 2 (not shown), and cooling coils 7A to 7C are arranged in the lower part of the fluidized bed reactor to flow. Cyclones 8A to 8C for collecting the catalyst mixed in the generated gas flowing out of the reactor were placed in the upper part of the layer reactor, and the catalyst was returned to the lower part by the depreg 10A to 10C.
As shown in FIG. 3, the cyclones were arranged in three stages in series as one series, and similar cyclones were arranged in a total of eight series. Instruments and ancillary equipment were normally used.

Propylene, ammonia and air were supplied to a reactor 2 having a diameter of 7.8 m filled with a catalyst having an average particle size of 50 μm, and an ammoxidation reaction was carried out. In order to confirm the state of the catalyst, the composition analysis of the catalyst before the start of the reaction was carried out by atomic absorption spectroscopy, and the Na concentration in the catalyst was 1500 ppm. The reaction gas generated in the reactor 2 was cooled by passing through the heat exchanger 3 via the reaction gas lead-out pipe 4. The heat exchanger 3 was a multi-tube cylindrical heat exchanger with a diameter of 1.8 m and a length of 2.2 m and one pass on the tube side, and water was used as the refrigerant.
When the pressure loss of the heat exchanger 3 increased to 1700 mmH ₂ O, sodium sulfate (powder) having an average particle size of 0.1 mm was introduced at position 6 in the intermediate portion 4C of the reaction gas lead-out pipe 4. The powder introduction position 6 is a position lower than the highest point 5. A significant reduction in pressure loss was confirmed before and after the introduction of such powder. In this way, the reaction was continued for 2 years from the start of the reaction. After completion of the reaction, the catalyst packed in the reactor 2 was taken out, and the composition of the catalyst was analyzed by atomic absorption spectroscopy in order to confirm the state of the catalyst. As a result, the Na concentration in the catalyst was 1500 ppm. That is, no change was observed in the Na concentration of the catalyst after the reaction was completed as compared with the catalyst before the reaction was started.
Furthermore, the reaction results after the plant start (reaction results when the pressure loss of the heat exchanger 3 described above rises to 1700 mmH ₂ O) and the reaction immediately before the plant is stopped by continuing blasting with powder for 2 years. I asked for grades. That is, as a result of calculating the ratio of acrylonitrile produced to the propylene supplied to the reactor by sampling the gas at the outlet of the reactor and analyzing the reaction gas with a gas chromatograph, 81.5% and 81.3, respectively. %, And no change in the reaction results was observed after the powder introduction was continued for 2 years.
From the above results, it was found that according to the method of the present embodiment, acrylonitrile can be stably produced for a long period of time and the reaction results can be maintained.

(Comparative Example 1)
In Comparative Example 1, acrylonitrile was produced in the same manner as in Example 1 except that the fluidized bed reactor shown in FIG. 4 was used. The fluidized bed reactor shown in FIG. 4 has the same configuration as the fluidized bed reactor shown in FIG. 2, except for the shape of the reaction gas lead-out pipe. That is, in the fluidized bed reactor shown in FIG. 4, the first portion 4A and the second portion 4B are connected at right angles, and the intermediate portion 4C in FIG. 2 is not formed.
When the pressure loss of the heat exchanger 3 increased to 1700 mmH ₂ O, sodium sulfate (powder) having an average particle size of 0.1 mm was introduced at position 6 in the first portion 4A of the reaction gas lead-out pipe 4. .. The powder introduction position 6 is a position lower than the highest point 5, but is a position in the first portion 4A. After the introduction of such powder, it was confirmed that the pressure loss was reduced as compared with that before the introduction. In this way, the reaction was continued for 2 years from the start of the reaction. After completion of the reaction, the catalyst packed in the reactor 2 was taken out and analyzed in the same manner as in Example 1 in order to confirm the state of the catalyst. As a result, the Na concentration in the catalyst was 4900 ppm. Thus, it was confirmed that the catalyst was poisoned by sodium. From these results, it was suggested that a part of the introduced powder flowed back to the reactor side.
Furthermore, as a result of obtaining the reaction results after the start of the plant and the reaction results immediately before the plant was stopped by continuing the blasting with powder for 2 years in the same manner as in Example 1, 81.5% and 79.2%, respectively. Therefore, deterioration of the reaction results was observed after the powder introduction was continued for 2 years. From these results, it was suggested that the reaction results deteriorated because the catalyst was poisoned by the introduced powder.

INDUSTRIAL APPLICABILITY The present invention can be effectively used when carrying out a fluidized bed reaction using a fluidized bed reaction apparatus.

1 Fluidized bed reactor 2 Reactor 3 Heat exchanger 4 Reaction gas outlet piping 4A 1st part 4B 2nd part 4C Intermediate part 5 Highest point 6 Powder introduction position 7A Cooling coil 7B Cooling coil 7C Cooling coil 8A Cyclone 8B Cyclone 8C Cyclone 9 Cyclone entrance 10A Depleg 10B Depleg 10C Depleg

Claims (4)

A method for producing (meth) acrylonitrile using a fluidized bed reactor including a fluidized bed reactor and a heat exchanger connected by a reaction gas lead-out pipe of the fluidized bed reactor.
A step of introducing the raw material gas into the fluidized bed reactor and performing an ammoxidation reaction in the presence of a catalyst to obtain a reaction gas.
A step of introducing powder into the reaction gas lead-out pipe and leading out the reaction gas to the heat exchanger while cleaning the heat exchanger.
Have,
The reaction gas lead-out pipe extends from the upper part of the fluidized bed reactor in the height direction of the fluidized bed reactor, reaches the highest point of the reaction gas lead-out pipe, and is connected to the highest point. And has a second portion extending towards the heat exchanger
A method for producing (meth) acrylonitrile, wherein the introduction position of the powder is a position in the second portion and is a position lower than the highest point. The second portion, at least in part thereof, has an intermediate portion extending downward in the height direction.
The method for producing (meth) acrylonitrile according to claim 1, wherein the introduction position of the powder is the intermediate portion. The method for producing (meth) acrylonitrile according to claim 1 or 2, wherein the angle formed by the first portion and the line connecting the highest point and the introduction position of the powder is 89 ° or less. The method for producing (meth) acrylonitrile according to any one of claims 1 to 3, wherein the distance from the powder introduction position in the second portion to the heat exchanger is 10 m or more.

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