JP7166770B2 - Method for producing acrylonitrile - Google Patents

Description

The present invention relates to a method for producing acrylonitrile.

Conventionally, a fluidized bed reactor has been widely used for gas-phase catalytic ammoxidation reaction of alkanes and/or alkenes in the presence of metal composite oxide catalysts. In a fluidized bed reactor used on an industrial scale, it is required to perform production operation with high yield while maintaining safety. From the viewpoint of safety, the oxygen concentration at the outlet of the fluidized bed reactor is lowered below the explosion limit, ammonia is moderately burned as a means, and the reaction temperature and raw material supply are controlled. . On the other hand, from the viewpoint of yield, the catalyst is exposed to a reducing environment by controlling the combustion of ammonia so that the synthesized acrylonitrile is not burned, or by making the oxygen concentration too low. , suppression of deterioration of catalyst performance, and the like. These controls are being studied respectively from the viewpoint of catalyst development and improvement of the production method.

For example, in Patent Document 1, in the production of acrylonitrile using propylene as a raw material, the object is to provide an oxide catalyst that achieves both an appropriate ammonia combustion rate during the ammoxidation reaction and a high acrylonitrile yield, and a method for producing the same. As an oxide containing molybdenum, bismuth, iron, cobalt, and a lanthanoid element A in a predetermined ratio, and a predetermined amount of a disorder phase composed of a crystal system containing molybdenum, bismuth, iron, and a lanthanoid element from these elements A catalyst is disclosed.

JP 2015-188802 A

As disclosed in Patent Document 1, a high acrylonitrile yield can be obtained by using a specific catalyst, but as disclosed in the document, when the ammonia combustion rate during the ammoxidation reaction is low On the other hand, if the ammonia combustion rate during the ammoxidation reaction becomes too high, the combustion reaction is excessively accelerated and the yield of acrylonitrile decreases. In addition, when the ammonia combustion rate during the ammoxidation reaction is low, it is conceivable to raise the reaction temperature in order to obtain a certain yield, but under such conditions, the decomposition products, mainly COx, increase, and the catalyst performance can occur.

As described above, from the viewpoint of catalytic properties, it is preferable to adjust the ammonia combustion rate during the ammoxidation reaction to an appropriate range. However, as a result of further studies by the present inventors, it has been found that by considering the production conditions in addition to the catalyst characteristics, the yield of acrylonitrile can be further improved, and safety such as explosion suppression can be ensured. rice field.

The present invention has been made in view of the above problems, and provides a method for producing acrylonitrile that can avoid the deterioration of catalyst performance that occurs in the initial stage of operation of a fluidized bed reactor and can obtain acrylonitrile in good yield throughout the operation. intended to

As a result of intensive studies to achieve the above object, the present inventors found that the above object can be solved by adjusting the ammonia combustion rate in the presence of oxygen and ammonia at a predetermined temperature, and completed the present invention. came to.

That is, the present invention is as follows.
[1]
A method for producing acrylonitrile by a gas-phase catalytic oxidation reaction of propylene, oxygen, and ammonia in the presence of a catalyst in a fluidized bed reactor, comprising:
a start-up step of supplying the oxygen and the ammonia to the fluidized bed reactor and raising the temperature in the fluidized bed reactor to 430 to 500° C.;
a reaction initiation step of supplying the propylene after the start-up step,
As the catalyst, an ammonium oxidation catalyst having an ammonia combustion rate of 80% or more when the reaction temperature is 490° C. and the contact time is 4.0 seconds in an atmosphere with an ammonia/air molar ratio of 15/100 is used. ,
A method for producing acrylonitrile.
[2]
Before starting the reaction initiation step, oxygen and ammonia are supplied to the fluidized bed reactor and the ammonia is burned, so that the oxygen concentration at the outlet of the fluidized bed reactor is 3 to 12% by volume.
The method for producing acrylonitrile according to [1] .
[3]
The temperature in the fluidized bed reactor at the start of the reaction initiation step is 430 to 500 ° C.
The method for producing acrylonitrile according to [1] or [2] .
[4]
The ammoxidation catalyst has a composition represented by the following general formula (1) and satisfies the following formula (2):
[1] The method for producing acrylonitrile according to any one of [3] .
_{Mo12BiaFebXcYdZeOf ( 1 ) _ _ _}
(wherein X is one or more elements selected from the group consisting of nickel, cobalt, magnesium, calcium, zinc, strontium and barium; Y is cerium, chromium, lanthanum, neodymium, yttrium, praseodymium, and samarium; , one or more elements selected from the group consisting of aluminum, gallium and indium, Z represents one or more elements selected from the group consisting of potassium, rubidium and cesium, a, b, c, d and e are 0.1≦a≦2.0, 0.1≦b≦3.0, 0.1≦c≦10.0, 0.1≦d≦3.0, and 0.01≦e≦2, respectively. .0 and f is the number of oxygen atoms required to satisfy the valence requirements of the other elements present.)
{(a+b+d)×1.5+c}<12.0 (2)

According to the present invention, it is possible to provide a method for producing acrylonitrile that can avoid the deterioration of catalytic performance that occurs in the initial stage of operation of a fluidized bed reactor and can obtain acrylonitrile in good yield throughout the entire operation.

1 is a schematic cross-sectional view of a fluidized bed reactor that can be used in the method for producing acrylonitrile of the present embodiment. FIG.

Hereinafter, an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described in detail, but the present invention is not limited to this, and various modifications are possible without departing from the gist thereof. is. In the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. In addition, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to the illustrated ratios.

[Method for producing acrylonitrile]
The method for producing acrylonitrile of the present embodiment is a method for producing acrylonitrile by subjecting propylene, oxygen, and ammonia to a gas-phase catalytic oxidation reaction in the presence of a catalyst in a fluidized bed reactor, wherein the catalyst is , an ammonium oxidation catalyst having an ammonia combustion rate of 80% or more when the reaction temperature is 490° C. and the contact time is 4.0 seconds in an atmosphere with an ammonia/air molar ratio of 15/100.

Normally, at the start-up of the ammoxidation reaction, it is necessary to adjust the oxygen concentration at the outlet of the fluidized bed reactor to be low before supplying propylene as a raw material from the viewpoint of explosion limit. As a method of lowering the oxygen concentration, there is a method of supplying air and ammonia to the reactor and burning the ammonia. Here, the ability to burn ammonia differs depending on the catalyst. For example, some catalysts burn ammonia 100% at a reaction temperature of 430°C, and some catalysts do not reach 100% ammonia combustion rate unless the reaction temperature is raised to 480°C. exist.

If the reactor is started up at a high reaction temperature to lower the oxygen concentration at the outlet and then feeds propylene, the reaction temperature in the fluidized bed reactor is already high, so decomposition products, mainly COx, increase. As a result, the outlet oxygen concentration becomes 0% by volume, the catalyst is exposed to a reducing atmosphere, and the catalytic performance is lowered before the reaction step.

On the other hand, in this embodiment, by using a catalyst with a high ammonia combustion rate, the outlet oxygen concentration at startup can be reduced even when the reaction temperature in the fluidized bed reactor is low. Since the reaction temperature in the fluidized bed reactor is low, the generation of decomposition products can be suppressed when propylene is fed, and the oxygen concentration at the outlet can be avoided from becoming 0% by volume, and the reactor is exposed to a reducing atmosphere. It becomes possible to avoid the deterioration of the catalyst performance due to this. That is, in the present embodiment, by using a catalyst with a high ammonia combustion rate, it is less likely to be affected by deterioration in catalytic performance due to reduction near the time of startup, and in that state, acrylonitrile can be continuously synthesized. .

The method for producing acrylonitrile of the present embodiment will be described in more detail below. First, FIG. 1 shows a schematic cross-sectional view of a fluidized bed reactor 1 that can be used in the method for producing acrylonitrile of the present embodiment.

The catalyst 2 is composed of the weight and volume of the catalyst itself, the raw material gas A oxygen-containing gas such as propylene and ammonia supplied from the dispersion pipe 5 through the raw material supply pipe 4, and the oxygen-containing gas supply pipe 6. The oxygen-containing gas B supplied from the dispersion plate 7 flows within the internal space 3 in balance with the supply amount and the like. The abundance (distribution) of the catalyst 2 per unit space in the internal space 3 tends to decrease from the bottom to the top of the internal space 3 (in the direction of arrow F) in the region above the dispersion tube 8 .

A vapor-phase catalytic oxidation reaction occurs within the internal space 3 . Propylene, oxygen, and ammonia are supplied to the flowing catalyst 2 in the internal space 3 to synthesize acrylonitrile, and a reaction product gas containing acrylonitrile is discharged from an outlet 9 via a cyclone 8 .

In the internal space 3, in addition to the cyclone 8 for separating and recovering the catalyst 2 from the reaction product gas C containing acrylonitrile, if necessary, mainly for removing the reaction heat of the dense layer in the internal space 3 and controlling the reaction temperature. cooling coil (not shown) and a member (not shown) for adjusting the gas superficial velocity in the internal space 3 . The gas superficial velocity in the internal space 3 varies depending on the cross-sectional area of the internal space 3 (the area in the direction perpendicular to the arrow F direction). For example, when assuming an internal space 3 with a non-uniform cross-sectional area, the gas superficial velocity is low at locations where the cross-sectional area is wide, and the gas superficial velocity is high at locations where the cross-sectional area is narrow.

The cyclone 8 enters the reaction product gas C entrained with the catalyst 2 from an inlet 8a. The catalyst 2 entering the cyclone 8 drops downward in the inner space 3 in a spiral manner at the conical portion of the cyclone 8, and the reaction product gas is led to the outlet 9 through a pipe extending upward from the upper part of the cyclone 8. go. Below the conical portion of the cyclone 8 there is also a pipe extending downward into the interior space 3, through which the catalyst 2 is guided downward into the interior space 3.

The method for producing acrylonitrile of the present embodiment is not particularly limited as long as acrylonitrile is produced by a vapor-phase catalytic oxidation reaction of propylene, oxygen, and ammonia in the presence of a catalyst. A catalyst filling step of filling the catalyst in the vessel, a startup step of supplying oxygen and ammonia to the fluidized bed reactor and raising the temperature in the fluidized bed reactor to 430 to 500 ° C., After the startup step, It has a reaction initiation step of supplying propylene and a reaction step of synthesizing acrylonitrile by carrying out a gas phase catalytic oxidation reaction while maintaining the supplied amounts of propylene, oxygen and ammonia. Each step will be described in detail below.

[Catalyst filling step]
The catalyst filling step is a step of filling the catalyst into the fluidized bed reactor. As the catalyst, an ammonium oxidation catalyst having an ammonia combustion rate of 80% or more when the reaction temperature is 490° C. and the contact time is 4.0 seconds in an atmosphere with an ammonia/air molar ratio of 15/100 is used. .

The ammonia combustion rate at a reaction temperature of 490° C. is 80% or higher, preferably 85% or higher, more preferably 90% or higher, still more preferably 95% or higher. An ammonia combustion rate of 80% or more tends to further improve the yield of acrylonitrile. Ammonia combustion rate can be improved by increasing the molybdenum ratio.

Note that the combustion rate of ammonia tends to decrease as the reaction temperature decreases. In this embodiment, it is preferred to use a catalyst that exhibits a high ammonia combustion rate at a lower reaction temperature. From this point of view, the ammonia combustion rate at a reaction temperature of 470° C. is preferably 85% or higher, more preferably 90% or higher, and even more preferably 95% or higher. Also, the ammonia combustion rate at a reaction temperature of 450° C. is preferably 85% or higher, more preferably 90% or higher, and still more preferably 95% or higher. Furthermore, the ammonia combustion rate at a reaction temperature of 430° C. is preferably 85% or higher, more preferably 90% or higher, still more preferably 95% or higher.

Such a catalyst is not particularly limited, but preferably has a composition represented by the following general formula (1) and satisfies the following formula (2). By using such a catalyst, the combustion rate of ammonia can be improved, and the yield of acrylonitrile tends to be further improved.
_{Mo12BiaFebXcYdZeOf ( 1 ) _ _ _}
(wherein X is one or more elements selected from the group consisting of nickel, cobalt, magnesium, calcium, zinc, strontium and barium; Y is cerium, chromium, lanthanum, neodymium, yttrium, praseodymium, and samarium; , one or more elements selected from the group consisting of aluminum, gallium and indium, Z represents one or more elements selected from the group consisting of potassium, rubidium and cesium, a, b, c, d and e are 0.1≦a≦2.0, 0.1≦b≦3.0, 0.1≦c≦10.0, 0.1≦d≦3.0, and 0.01≦e≦2, respectively. .0 and f is the number of oxygen atoms required to satisfy the valence requirements of the other elements present.)
{(a+b+d)×1.5+c}<12.0 (2)

X is one or more elements selected from the group consisting of nickel, cobalt, magnesium, calcium, zinc, strontium and barium. Among these, nickel and cobalt are preferred, and nickel and cobalt are preferably used in combination.

Y is one or more elements selected from the group consisting of cerium, chromium, lanthanum, neodymium, yttrium, praseodymium, samarium, aluminum, gallium and indium, and among these, cerium is preferred.

Z is one or more elements selected from the group consisting of potassium, rubidium and cesium, preferably potassium and rubidium, and preferably potassium and rubidium.

a is the atomic ratio of Bi to 12 molybdenum atoms, and is 0.1 to 2.0, preferably 0.1 to 1.5, more preferably 0.2 to 1.2, and further It is preferably 0.3 to 0.7.

b is the atomic ratio of Fe to 12 molybdenum atoms, and is 0.1 to 3.0, preferably 0.5 to 2.5, more preferably 0.8 to 2.0, and further It is preferably 1.0 to 1.8.

c is the atomic ratio of X to 12 molybdenum atoms, and is 0.1 to 10.0, preferably 5.0 to 10.0, more preferably 6.0 to 9.0, and further It is preferably 7.0 to 9.0. When a plurality of elements are used as X, it means the ratio of the total number of atoms of each element to 12 molybdenum atoms.

d is the atomic ratio of Y to 12 molybdenum atoms, and is 0.1 to 3.0, preferably 0.3 to 2.5, more preferably 0.5 to 2.0, and further It is preferably 0.5 to 1.5. When a plurality of elements are used as Y, it means the ratio of the total number of atoms of each element to 12 atoms of molybdenum.

e is the atomic ratio of Z to 12 molybdenum atoms, and is 0.01 to 2.0, preferably 0.1 to 1.5, more preferably 0.1 to 1.0, and further It is preferably 0.1 to 0.7. When a plurality of elements are used together as Z, it means the ratio of the total number of atoms of each element to 12 molybdenum atoms.

Formula (2) is a formula showing the atomic ratio of Bi, Fe, X, and Y to 12 molybdenum atoms, {(a + b + d) × 1.5 + c} is less than 12, preferably 11.8 or less. Yes, more preferably 11.5 or less. When {(a+b+d)×1.5+c} is less than 12, the ammonia combustion rate tends to be further improved. Although the lower limit of {(a+b+d)×1.5+c} is not particularly limited, it is preferably 10 or more, more preferably 10.5 or more, and still more preferably 11 or more.

The average particle size of the catalyst is preferably 20-100 μm, more preferably 30-90 μm, still more preferably 40-80 μm. The particle size range of the catalyst (the range including the minimum particle size and the maximum particle size) is preferably 1 to 500 μm, more preferably 5 to 400 μm, still more preferably 10 to 250 μm. When the average particle size and particle size range of the catalyst are within the above ranges, the yield of acrylonitrile tends to be further improved.

The catalyst of the present embodiment may be a metal oxide having the above composition supported on a carrier. The carrier is not particularly limited as long as it is commonly used as a catalyst carrier, and examples thereof include silica, alumina, titania, and zirconia. Among these, silica is preferable from the viewpoint of improving the abrasion resistance and particle strength of the catalyst particles. The amount of the carrier is preferably 20 to 70% by mass, more preferably 30 to 60% by mass, still more preferably 30 to 50% by mass, based on the total mass of the catalyst (metal oxide) and the carrier. be.

The method for producing the catalyst is not particularly limited, but a mixing step of mixing each raw material containing each atom constituting the catalyst and, if necessary, a chelating agent to obtain a raw material slurry, and drying the obtained raw material slurry and a method of calcining the resulting dried body. Firing may be performed in multiple steps.

[Startup process]
The start-up step is a step of supplying oxygen and ammonia to the fluidized bed reactor and raising the temperature inside the fluidized bed reactor to 430-500°C. Although the supply method is not particularly limited, oxygen can be supplied from the dispersion plate 7 via the oxygen-containing gas supply pipe 6 and ammonia can be supplied from the dispersion pipe 5 via the raw material supply pipe 4 . Also, oxygen and ammonia may be supplied together with an inert gas such as nitrogen or argon. In this embodiment, by having a catalyst with a high ammonia combustion rate, deterioration of catalyst performance can be avoided in the start-up step and the subsequent reaction initiation step.

Here, the temperature inside the fluidized bed reactor in the present embodiment refers to the temperature in the internal space 3, and when the height (distance in the flow direction) of the fluidized bed reactor is divided by 100, the temperature is 25 to 25, counting from the bottom. It can be measured as an average value of the temperature of the 30th division. The temperature rise in the fluidized bed reactor in the start-up step is preferably 430-500°C, more preferably 430-490°C, still more preferably 430-470°C. The yield of acrylonitrile tends to be further improved when the temperature within the reactor is within the above range.

In the start-up step, finally oxygen and ammonia are supplied, and
There are no restrictions as long as the temperature is within the above range. Therefore, in the process, oxygen and ammonia may be supplied stepwise or may be supplied simultaneously. Also, even if the temperature is raised after the supply of oxygen and ammonia; even if the temperature is raised before the supply; After supplying one, the temperature may be raised, then the other may be supplied, and the temperature may be further raised to the above temperature; or the supply and the temperature may be raised at the same time. Among these, it is preferable to supply oxygen, once raise the temperature to an intermediate temperature, then supply ammonia, and then further raise the temperature to the final temperature of the start-up step. By supplying oxygen before or at least simultaneously with ammonia, there is a tendency to suppress the reduction in activity of the catalyst due to being placed in a reducing atmosphere. Also, by raising the temperature to an intermediate temperature, there is a tendency that explosion in an oxygen-rich atmosphere can be suppressed.

[Reaction initiation step]
The reaction initiation step is a step of supplying propylene after the start-up step, more specifically, starting to supply propylene into the fluidized bed reactor after the start-up step, gradually increasing the amount of propylene supplied, and finally Generally, it refers to the process until the amount of propylene supplied in the reaction process is reached. In addition to propylene, the amount of oxygen and ammonia supplied may be increased or decreased in the reaction initiation step.

Before starting the reaction initiation step (after the start-up step), the oxygen concentration at the outlet of the fluidized bed reactor is preferably 3 to 12% by volume, more preferably 3.5 to 10% by volume, and still more preferably 4 to 7% by volume. By setting the outlet oxygen concentration to 3% by volume or more before the start of the reaction initiation step, there is a tendency to suppress the reduction in activity and acrylonitrile selectivity caused by placing the catalyst in a reducing atmosphere. Further, when the oxygen concentration at the outlet is 12% by volume or less before starting the reaction initiation step, explosion in an oxygen-rich atmosphere tends to be suppressed. The outlet oxygen concentration before the start of the reaction initiation step can be controlled by supplying oxygen and ammonia to the fluidized bed reactor and burning the ammonia, and additionally adjusting the amount of oxygen supplied. can also be controlled by The outlet oxygen concentration in the present embodiment means the oxygen concentration in the vicinity of the outlet 6, and can be obtained by measuring the oxygen concentration of the reaction product gas C containing acrylonitrile discharged from the outlet 6. Note that the reaction product gas C containing acrylonitrile does not contain a catalyst and has a lower temperature than the internal space, so downstream from the vicinity of the outlet 6, the composition of the reaction product gas C substantially changes. do not do. Therefore, the oxygen concentration at the outlet 6 can also be confirmed from the oxygen concentration of the reaction product gas C measured by an analyzer installed downstream from the vicinity of the outlet 6 . If the oxygen concentration is within the above range before starting the reaction initiation step, the oxygen concentration may temporarily exceed the upper limit of the above range during the start-up step.

The temperature in the fluidized bed reactor at the start of the reaction initiation step is preferably 430 to 510°C, more preferably 430 to 500°C, still more preferably 430 to 490°C, and particularly preferably 430 to 430°C. 470°C. The yield of acrylonitrile tends to be further improved when the temperature within the reactor is within the above range.

[Reaction step]
The reaction step is a step of synthesizing acrylonitrile by gas-phase catalytic oxidation reaction while maintaining the supplied amounts of propylene, oxygen, and ammonia.

In the reaction step, the oxygen concentration at the outlet of the fluidized bed reactor is preferably 0.1-1% by volume, more preferably 0.1-0.75% by volume, still more preferably 0.1-0. .5% by volume. When the oxygen concentration at the outlet of the reaction step is 0.1% by volume or more, it tends to suppress the reduction in activity of the catalyst due to being placed in a reducing atmosphere. In addition, since the outlet oxygen concentration in the reaction step is 1% by volume or less, explosion in an oxygen-rich atmosphere tends to be suppressed. In addition, when the outlet oxygen concentration in the reaction step is 1% by volume or less, the generation of peroxides can be suppressed. The outlet oxygen concentration in the reaction step can be controlled by adjusting the amount of oxygen supplied.

The temperature in the fluidized bed reactor in the reaction step is preferably 400-460°C, more preferably 410-450°C, still more preferably 420-440°C. In this embodiment, acrylonitrile can be obtained at a high yield even at a relatively low temperature by using a catalyst having a predetermined ammonia combustion rate. In particular, when the temperature in the reactor is within the above range, the generation of decomposition products that tend to occur at high temperatures is suppressed, and the yield of acrylonitrile tends to be further improved.

The sulfuric acid basic unit in the reaction step is preferably 12.5 to 27.5 kg/T-AN, more preferably 15 to 25 kg/T-AN, still more preferably 17.5 to 22.5 kg/T-AN. It is AN. The specific unit of sulfuric acid is an index represented by the following formula, and is a value obtained by the following formula from the amount of acrylonitrile in the reaction product gas and the amount of unreacted ammonia. In this embodiment, acrylonitrile can be obtained at a high yield even at a relatively low temperature by using a catalyst having a predetermined ammonia combustion rate. Basic unit of sulfuric acid = (Weight of sulfuric acid required to neutralize unreacted ammonia) / (Production weight of acrylonitrile)

[Reaction stop step]
The method for producing acrylonitrile of the present embodiment may have a reaction stopping step of stopping the vapor-phase catalytic oxidation reaction. Stopping the reaction means canceling the steady state operation of the fluidized bed reactor by reducing the supply of at least one of propylene, oxygen, and ammonia. Therefore, for the purpose of terminating the reaction, the point at which the supply of at least one of propylene, oxygen, and ammonia begins to be reduced is the starting point of the reaction terminating step, and the point at which the gas-phase catalytic oxidation reaction has completely terminated is the terminating of the reaction. end of the process.

Hereinafter, the present invention will be described more specifically using examples and comparative examples. However, the present invention is by no means limited by the following examples.

A fluidized bed reactor having at least the configuration shown in FIG. 1 as a basic configuration was used. Specifically, it is a vertical cylinder with an inner diameter of 8 m and a length of 20 m, and has an oxygen distribution plate 7 at a position 2 m from the bottom, a distribution pipe 5 for supplying propylene and ammonia thereon, and a heat removal pipe. I used the one with the interior. In addition, there are 8 pieces in a section at a height of 5 m from the bottom of the reactor (the 25th division counting from the bottom when the height of the fluidized bed reactor is divided into 100), and a section at a height of 6 m (fluidization When the height of the bed reactor is divided into 100 parts, 4 thermometers are provided in the 30th part counting from the bottom), and a total of 12 thermometers are provided, and the average value of these thermometers is taken as the temperature in the reactor. did. Also, the reaction product gas flowing out from the outlet 9 was sampled and its composition was measured by chromatography.

[Ammonia combustion rate]
In the fluidized bed reactor, no propylene was supplied, the atmosphere was such that the molar ratio of ammonia/air was 15/100, the reaction temperature was 490°C, and the contact time was 4.0 seconds. At this time, the reaction product gas flowing out from the outlet was sampled, its composition was measured, and the ammonia combustion rate of the catalyst was calculated by the following formula. Similarly, the ammonia combustion rate was also measured at reaction temperatures of 430°C, 450°C, and 470°C. At this time, the top pressure of the reactor was 0.17 MPa.
Ammonia combustion rate (%) = (number of moles of nitrogen produced) x 2/(number of moles of supplied ammonia) x 100

Incidentally, the contact time is obtained by the following formula.
Contact time (sec g/mL) = (W/F) x 273/(273 + T) x P/0.10
W: amount of catalyst F: total amount of supplied gas (in terms of NTP)
T: reaction temperature P: reaction pressure

[Yield of acrylonitrile (AN yield)]
The yield of acrylonitrile was calculated by the following formula after operating the fluidized bed reactor under the conditions described in Examples and Comparative Examples below, sampling the reaction product gas flowing out from the outlet, measuring its composition.
Yield of acrylonitrile (%) = (number of moles of acrylonitrile produced) / (number of moles of supplied propylene) x 100

[Production Example 1]
The _{bulk composition is Mo12.00Bi0.50Fe1.31Co4.05Ni3.10Ce0.87Rb0.10K0.08Of , where f is} the number of _oxygen atoms required to satisfy the valence requirements of the other elements present. A catalyst was produced in which 40 mass % of the metal oxide was supported on silica.

Specifically, ammonium heptamolybdate was dissolved in warm water, and 28% aqueous ammonia was added (solution A). Further, bismuth nitrate, iron nitrate, cobalt nitrate, nickel nitrate, cerium nitrate, rubidium nitrate, and potassium nitrate were dissolved in a 16.6% by mass nitric acid aqueous solution (solution B). An 8% by mass oxalic acid solution containing 2.5% by mass of oxalic acid dihydrate relative to the catalyst is added to a silica sol in which silica as a carrier is dispersed, then liquid A is added, and then Liquid B was added and mixed with stirring. After that, the obtained raw material slurry was dried using a rotary disc type spray dryer. At this time, the air temperature at the inlet of the dryer was set at 230°C, and the air temperature at the outlet was set at 110°C. The obtained dry particles were held at 200° C. for 5 minutes, heated from 200° C. to 450° C. at a rate of 2.5° C./min, and held at 450° C. for 20 minutes for denitrification. The obtained denitration powder was calcined at 590° C. for 2 hours to obtain the above catalyst. The particle size (including the carrier) of the obtained catalyst was 10 to 180 μm, and the average particle size (including the carrier) was 55 μm. The ammonia combustion rate of this catalyst at 490° C. was 100%.

[Production Examples 2 to 6]
A catalyst was produced in which a metal oxide having a bulk composition shown in Table 1 was supported on 40% by mass of silica. The specific operation was the same as in Production Example 1, except that the amount of nitrate used was adjusted. Note that although O is not described in Table 1, any of them depends on the metal composition Of ( _f is the number of oxygen atoms required to satisfy the valence requirements of other elements present.) have The particle size (including the carrier) of the obtained catalysts was 10 to 180 μm, and the average particle size (including the carrier) was 55 μm.

[Example 1]
The catalyst obtained in Production Example 1 was filled into a fluidized bed reactor by a static bed height of 2.7 m (catalyst filling step). Then, 25000 Nm ³ /hr of air from the dispersion plate and 3500 Nm ³ /hr of nitrogen from the dispersion tube were supplied, and the reactor temperature was raised to 400°C. Then, the supply of ammonia was started from the dispersion pipe. Specifically, the ammonia supply rate was increased to 5200 Nm ³ /hr at an increase rate of 75 Nm ³ /min. The reactor temperature was then adjusted to 435°C (start-up step). At this time, the oxygen concentration at the reactor outlet was 5.5%.

Next, the supply of propylene was started from the dispersion tube. Specifically, while increasing the propylene supply rate to 5400 Nm ³ /hr at an increasing rate of 45 Nm ³ /min, while maintaining the reactor outlet oxygen at 7% or less, the ammonia supply rate was increased to 6200 Nm ³ /hr, air was increased to 46000 Nm ³ /hr (reaction initiation step).

Finally, the supply of nitrogen from the dispersion pipe was stopped, and the reactor top pressure was 0.15 MPa, the reaction temperature was 430 ° C., the outlet oxygen concentration was 0.3%, and the sulfuric acid consumption rate was 20 ± 3 kg / T-AN. Acrylonitrile was produced by finely adjusting the supply amount (reaction step). The acrylonitrile yield was 83.8% 20 hours after the start of propylene supply (the beginning of the reaction initiation step).

[Example 2]
Each step was performed in the same manner as in Example 1 except that the reactor temperature in the startup step was adjusted to 455°C, and the yield of acrylonitrile after 20 hours from the start of propylene supply (the beginning of the reaction start step) was measured. got the rate. The yield of acrylonitrile in Example 2 was 83.7%.

[Example 3]
Each step was performed in the same manner as in Example 1 except that the reactor temperature in the startup step was adjusted to 475°C, and the yield of acrylonitrile after 20 hours from the start of propylene supply (the beginning of the reaction start step) was measured. got the rate. The AN yield in Example 3 was 83.6%.

[Example 4]
Each step was performed in the same manner as in Example 1 except that the reactor temperature in the start-up step was adjusted to 495 ° C., and the yield of acrylonitrile after 20 hours from the start of propylene supply (beginning of the reaction start step) was measured. got the rate. The AN yield in Example 4 was 83.5%.

[Example 5]
Each step was performed in the same manner as in Example 1 except that the reactor temperature in the start-up step was adjusted to 510 ° C., and the yield of acrylonitrile after 20 hours from the start of propylene supply (beginning of the reaction start step) was measured. got the rate. The AN yield in Example 5 was 83.0%.

[Example 6]
Each step was performed in the same manner as in Example 2, except that the oxygen concentration at the reactor outlet in the start-up step was adjusted to 9.1%, and 20 hours had passed since the start of propylene supply (the beginning of the reaction start step). A later yield of acrylonitrile was obtained. The AN yield in Example 6 was 83.6%.

[Example 7]
Each step was performed in the same manner as in Example 2, except that the oxygen concentration at the reactor outlet in the startup step was adjusted to 3.5%, and 20 hours had passed since the start of propylene supply (the beginning of the reaction initiation step). A later yield of acrylonitrile was obtained. The AN yield in Example 7 was 83.2%.

[Example 8]
Each step was performed in the same manner as in Example 2, except that the oxygen concentration at the reactor outlet in the startup step was adjusted to 2.7%, and 20 hours had passed since the start of propylene supply (the beginning of the reaction initiation step). A later yield of acrylonitrile was obtained. The AN yield in Example 8 was 83.1%.

[Example 9]
Each step was performed in the same manner as in Example 3, except that the catalyst obtained in Production Example 3 was used. got The AN yield in Example 9 was 83.5%.

[Example 10]
Each step was carried out in the same manner as in Example 4, except that the catalyst obtained in Production Example 4 was used. got The AN yield in Example 10 was 83.3%.

[Example 11]
Each step was performed in the same manner as in Example 4 except that the catalyst obtained in Production Example 7 was used and the oxygen concentration at the reactor outlet in the startup step was adjusted to 6.2%, and propylene supply was started. A yield of acrylonitrile was obtained after 20 hours from (the beginning of the reaction initiation step). The AN yield in Example 11 was 83.2%.

[Comparative Example 1]
Each step was performed in the same manner as in Example 1 except that the catalyst obtained in Production Example 2 was used as the catalyst, the reactor temperature was adjusted to 510 ° C. in the start-up step, and the outlet oxygen concentration was 5.8%. was carried out to obtain a yield of acrylonitrile 20 hours after the start of propylene supply (the beginning of the reaction initiation step). The AN yield in Comparative Example 1 was 82.0%.

[Comparative Example 2]
Each step was performed in the same manner as in Comparative Example 1 except that the catalyst obtained in Production Example 5 was used and the oxygen concentration at the reactor outlet in the startup step was adjusted to 5.6%, and propylene supply was started. A yield of acrylonitrile was obtained after 20 hours from (the beginning of the reaction initiation step). The AN yield in Comparative Example 2 was 81.9%.

[Comparative Example 3]
Each step was performed in the same manner as in Comparative Example 1 except that the catalyst obtained in Production Example 6 was used and the oxygen concentration at the reactor outlet in the startup step was adjusted to 5.9%, and propylene supply was started. A yield of acrylonitrile was obtained after 20 hours from (the beginning of the reaction initiation step). The AN yield in Comparative Example 3 was 81.7%.

INDUSTRIAL APPLICABILITY The present invention has industrial applicability as a method for producing acrylonitrile.

1: fluidized bed reactor, 2: catalyst, 3: inner space, 4: raw material supply pipe, 5: dispersion pipe, 6: oxygen-containing gas supply pipe, 7: dispersion plate, 8: cyclone, 8a: inlet, 9: Outlet, A: Raw material gas, B: Oxygen-containing gas, C: Reaction product gas

Claims (3)

A method for producing acrylonitrile by a gas-phase catalytic oxidation reaction of propylene, oxygen, and ammonia in the presence of a catalyst in a fluidized bed reactor, comprising:
a start-up step of supplying the oxygen and the ammonia to the fluidized bed reactor and raising the temperature in the fluidized bed reactor to 430 to 500° C.;
a reaction initiation step of supplying the propylene after the start-up step,
As the catalyst, an ammonium oxidation catalyst having an ammonia combustion rate of 80% or more when the reaction temperature is 490° C. and the contact time is 4.0 seconds in an atmosphere with an ammonia/air molar ratio of 15/100 is used. ,
The ammoxidation catalyst has a composition represented by the following general formula (1) and satisfies the following formula (2):
Mo12BiaFebXcYdZeOf ( 1 _{) _} _ _{_} _ _{_} _ _{_} _ _{_} _ _{_}
(wherein X is one or more elements selected from the group consisting of nickel, cobalt, magnesium, calcium, zinc, strontium and barium; Y is cerium, chromium, lanthanum, neodymium, yttrium, praseodymium, and samarium; , one or more elements selected from the group consisting of aluminum, gallium and indium, Z represents one or more elements selected from the group consisting of potassium, rubidium and cesium, a, b, c, d and e are 0.1≦a≦2.0, 0.1≦b≦3.0, 0.1≦c≦10.0, 0.1≦d≦3.0, and 0.01≦e≦2, respectively. .0 and f is the number of oxygen atoms required to satisfy the valence requirements of the other elements present.)
{(a+b+d)×1.5+c}<12.0 (2)
A method for producing acrylonitrile. Before starting the reaction initiation step, oxygen and ammonia are supplied to the fluidized bed reactor and the ammonia is combusted so that the oxygen concentration at the outlet of the fluidized bed reactor is 3 to 12%.
The method for producing acrylonitrile according to claim 1. The temperature in the fluidized bed reactor at the start of the reaction initiation step is 430 to 500 ° C.
The method for producing acrylonitrile according to claim 1 or 2.

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