JP2001172246A - Method for producing acrylonitrile - Google Patents

Abstract

(57) [Problem] To efficiently produce acrylonitrile by suppressing the adverse effect of acrylic acid, which is a by-product of producing acrylonitrile, on the production process. SOLUTION: In a method for producing acrylonitrile by a hydrocarbon ammoxidation reaction, unreacted ammonia is separated from an ammoxidation reaction gas generated by the ammoxidation reaction, and acrylic acid is separated from the ammoxidation reaction gas from which the unreacted ammonia is separated. A method for producing acrylonitrile, comprising a step of recovering acrylonitrile from an ammoxidation reaction gas from which unreacted ammonia and acrylic acid have been separated after separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing acrylonitrile, and more particularly to a method for efficiently producing acrylonitrile from propylene and / or propane by an ammoxidation reaction.

[0002]

2. Description of the Related Art Acrylonitrile is usually produced on a large scale by the ammoxidation of propylene. Also,
Recently, a method of performing an ammoxidation reaction using relatively inexpensive propane as a raw material instead of propylene has been developed. In a typical conventional method, propylene or propane, ammonia, and an oxygen-containing gas are supplied to a fluidized-bed reactor filled with a catalyst and reacted at a high temperature to produce acrylonitrile. The ammoxidation reaction gas containing acrylonitrile flowing out of the fluidized bed reactor includes ammonia,
By-products such as acrylic acid, acetic acid, hydrocyanic acid, acetonitrile and acrolein are present, and acrylonitrile is recovered by a recovery process as shown in FIG. First, the ammoxidation reaction gas flowing out of the fluidized bed reactor through the conduit 24 is supplied to the ammonia absorption tower 1, where the ammonia gas is washed and cooled with a sulfuric acid aqueous solution, and the unreacted ammonia is neutralized. It is absorbed as an aqueous ammonium sulfate solution and removed from the bottom of the ammonia absorption tower 1 through a conduit 25. On the other hand, the ammoxidation reaction gas from which unreacted ammonia flowing out from the top of the ammonia absorption tower 1 through the conduit 26 is cooled and supplied to the acrylonitrile absorption tower 2 where the acrylonitrile and acrylic By-products such as acid, acetic acid, hydrocyanic acid, acetonitrile, acrolein and the like are absorbed and dissolved in water, and extracted from a conduit 27 at the bottom of the tower to separate them from the ammoxidation reaction gas.
The gas not absorbed is supplied to a waste gas incinerator (not shown) through a conduit 28 and incinerated. The aqueous solution in which acrylonitrile and the like extracted from the conduit 27 are dissolved is supplied to the acrylonitrile recovery tower 3 after preheating, and the gaseous acrylonitrile is mainly contained in the acrylonitrile recovery tower 3 by means such as stripping or distillation. Water vapor having an azeotropic composition with acrylonitrile and acrylonitrile is recovered from the top of the tower through a conduit 30. In a subsequent purification system (not shown), hydrocyanic acid, water, and the like are removed and rectification is performed to obtain acrylonitrile as a product. On the other hand, the acrylonitrile wastewater containing acrylic acid and the like extracted from the bottom of the acrylonitrile recovery tower 3 through the conduit 29 is partially discharged from the conduits 31 and 3.
2 is recycled to the acrylonitrile absorption tower 2, another part is recycled to the acrylonitrile recovery tower 3 through conduits 31 and 33, and the rest is treated as wastewater or separately purified as product acrylic acid. Further, impurities such as acetonitrile are extracted from the middle stage of the acrylonitrile recovery tower 3 (not shown).

[0003]

However, in the above recovery process, acrylic acid is present in the acrylonitrile wastewater extracted from the bottom of the acrylonitrile recovery tower, and the acrylic acid is present in the water circulated to the acrylonitrile absorption tower and the acrylonitrile recovery tower. A large amount of acrylic acid is circulated through the acrylonitrile collection system composed of the acrylonitrile absorption tower and the acrylonitrile recovery tower because it is supplied together. As a result, the following problems occur in the conventional operation method in the acrylonitrile collection system.

1) The acrylic acid in acrylonitrile wastewater is polymerized at a later process, particularly at the bottom of an acrylonitrile recovery tower, and an acrylic acid polymer is generated, and the capacity of a heat exchanger and a distillation tower in the collection system is reduced. It becomes a factor that stains the drop and blockage.

2) As a conventional method for separating acrolein, which is one of the by-products of the ammoxidation reaction, an alkali is added to an extraction solvent water circulating in an acrylonitrile recovery tower to adjust pH (about pH 6). ) To increase the boiling point of acrolein and separate it from the crude acrylonitrile by distillation. However, when acrylic acid is present at a high concentration, the amount of alkali added for adjusting the pH needs a huge amount corresponding to the amount of acrylic acid. When the acrolein removal by this pH adjustment becomes uneconomical, and a large amount of acrylic acid is in the form of an alkali salt, when acrylic acid in acrylonitrile wastewater is purified to obtain product acrylic acid, It becomes difficult to isolate and purify acrylic acid in the subsequent step.

[0006] 3) The acrylic acid in the circulating water recycled to the acrylonitrile absorption tower and the acrylonitrile recovery tower is discharged outside the system from the top of the column or flows out to the acrylonitrile refining system, so that the acrylic acid is lost as product acrylic acid. As a result, the recovery rate of acrylic acid decreases, and further extra energy is required for separation from acrylonitrile in the acrylonitrile purification system.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, before the acrylonitrile absorption and separation of acrylonitrile from the ammoxidation reaction gas in the acrylonitrile absorption tower, acrylic acid was removed from the ammoxidation reaction gas. It has been found that the above-mentioned problems can be solved by selectively separating the above, and the present invention has been achieved. That is, the gist of the present invention is to provide a method for producing acrylonitrile by an ammoxidation reaction of hydrocarbons, wherein an unreacted ammonia is separated from an ammoxidation reaction gas generated by the ammoxidation reaction, and an ammoxidation reaction gas obtained by separating the unreacted ammonia. Acrylonitrile from an ammoxidation reaction gas from which unreacted ammonia and acrylic acid have been separated after selective separation of acrylic acid from acrylonitrile.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, acrylonitrile is synthesized by reacting a hydrocarbon, ammonia and an oxygen-containing gas in the presence of an ammoxidation catalyst. As the reactor, either a fluidized bed reactor or a fixed bed reactor may be used,
It is preferable to use a fluidized bed reactor because the heat of reaction can be easily removed. Propylene and / or propane can be used as the hydrocarbon. As the ammoxidation catalyst, a composite metal oxide catalyst containing at least one of molybdenum, vanadium, tellurium and antimony as an essential component is usually used. More specifically, molybdenum, vanadium, X, Y and oxygen (X is at least one of tellurium and antimony
Species, Y is niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, bismuth, boron, indium, phosphorus, germanium, rare earth element, alkali metal, (Indicating at least one element selected from the group consisting of alkaline earth metals) is preferred. The proportion of these catalyst constituent elements is determined by the following formula:

[0009]

## EQU2 ## 0.25 <rMo <0.98 0.003 <rV <0.5 0.003 <rX <0.50 ≦ rY <0.5

(However, rMo, rV, rX, rY represent the molar fraction of Mo, V, X and Y with respect to the total of the above essential components excluding oxygen). In the method for producing acrylonitrile of the present invention,
Unreacted ammonia is separated from the ammoxidation reaction gas generated by the ammoxidation reaction, acrylic acid is separated from the ammoxidation reaction gas from which the unreacted ammonia is removed, and then the unreacted ammonia and acrylic acid are separated from the ammoxidation reaction gas. A step of recovering acrylonitrile. Since most of the acrylic acid is separated from the ammoxidation reaction gas before acrylonitrile is recovered, polymerization of acrylic acid in the subsequent process and increase in alkali added to the extraction solvent water in the acrylonitrile recovery tower are suppressed, and acrylic acid is suppressed. When recovering as a product, the loss can be suppressed.

FIG. 1 shows an example of a process flow of an acrylonitrile recovery system applied to the present invention. Hereinafter, description will be made with reference to FIG. An ammoxidation reaction gas extracted from a reactor (not shown) is supplied to an ammonia absorption tower 1 (quenching tower) through a conduit 11, and is cooled by directly contacting a sulfuric acid aqueous solution in which a required amount of sulfuric acid is dissolved. Unreacted ammonia in the reaction gas is neutralized by contact with the aqueous sulfuric acid solution, absorbed into the aqueous solution, and removed as an aqueous ammonium sulfate solution from the conduit 12 to the outside of the system. The concentration of ammonium sulfate in the aqueous solution removed from the system through the conduit 12 is determined by the amount of liquid discharged from the bottom of the ammonia absorption tower 1, and the amount of the liquid discharged is determined by the amount of aqueous sulfuric acid added to the system or the amount of water removed by the ammonia absorption tower. It can be controlled by the amount of heat. If the amount of the extracted liquid is excessively increased, the amount of acrylic acid accompanying the aqueous ammonium sulfate solution increases, and when the acrylic acid separated in the subsequent process is purified to obtain the product acrylic acid, the amount of loss of acrylic acid is reduced. Therefore, it is necessary to adjust the amount of water to be added or the amount of heat removed in the quenching tower so that the concentration of ammonium sulfate in the bottoms withdrawn in the tower is in an appropriate range. Subsequently, acrylic acid is selectively separated from the ammoxidation reaction gas from which unreacted ammonia has been removed.

The ammoxidation reaction gas from which unreacted ammonia flows out from the top of the ammonia absorption tower 1 through the conduit 13 is supplied to the acrylic acid absorption tower 4. The supplied ammoxidation reaction gas comes into contact with the acrylic acid absorption solvent in the acrylic acid absorption tower 4, and most of the acrylic acid in the ammoxidation reaction gas is absorbed into the acrylic acid absorption solvent,
It is discharged from the bottom of the acrylic acid absorption tower 4 through the conduit 14 to the outside of the system, and is subjected to a separate treatment such as purification if necessary. The acrylic acid absorbing solvent may be any solvent that can absorb acrylic acid and does not adversely affect the subsequent process, and an aqueous solution and water in which an organic solvent is dissolved are preferably used. Acrylonitrile recovery tower 3 at the latter stage
The use of acrylonitrile wastewater extracted from the bottom of the column as an acrylic acid-absorbing solvent is particularly preferably used because it can suppress an increase in the amount of wastewater to the outside of the system and increase the amount of acrylic acid recovered. .

The acrylic acid-absorbing solvent is usually from 20 ° C to 90 ° C.
C., preferably 30 ° C. to 60 ° C., which is supplied from the top of the acrylic acid absorption tower 4 and is brought into countercurrent contact with the ammoxidation reaction gas rising in the acrylic acid absorption tower 4 and is sufficient for the ammoxidation reaction gas. By supplying an appropriate amount of the acrylic acid-absorbing solvent, most of the acrylic acid can be absorbed in the acrylic-acid-absorbing solvent, and preferably 99% or more of acrylic acid is absorbed in the acrylic-acid-absorbing solvent. Extract from the bottom of the column as an aqueous solution of acrylic acid. At this time, a small amount of an ammoxidation reaction product such as acrylonitrile, hydrocyanic acid, or acetonitrile accompanies the liquid extracted from the bottom of the column together with acrylic acid. These entrained components (corresponding to the light boiling point for acrylic acid) have a large difference in boiling point from acrylic acid and are components that form a low boiling azeotrope with water. Can be relatively easily separated from the aqueous solution of acrylic acid. The separated entrained component of acrylic acid can be recovered by adding it to the liquid supplied to the acrylonitrile recovery tower.

Here, as the operating conditions of the acrylic acid absorption tower, the temperature in the acrylic acid absorption tower must be kept as low as possible in order to prevent light-boiling components other than acrylic acid from being entrained on the acrylic acid (bottom) side as much as possible. preferable. Usually, the temperature in the acrylic acid absorption tower is maintained at 40 ° C. or higher, more preferably 60 ° C. or higher. Since cooling is performed by directly contacting the aqueous solution of sulfuric acid in the ammonia absorption tower 4 in the former stage, the ammoxidation reaction gas at the entrance of the acrylic acid absorption tower is supplied in a water-saturated state (that is, a dew point state). Therefore, if the temperature in the acrylic acid absorption tower is excessively lowered, the water vapor contained in the supplied ammoxidation reaction gas partially condenses, and as a result, the amount of liquid extracted from the bottom of the tower increases, and acrylonitrile and acetonitrile This is because the amount of light-boiling components such as hydrocyanic acid and the like dissolved in the bottom liquid also increases. On the other hand, regarding the absorption of acrylic acid, if a sufficient amount of water is supplied to absorb acrylic acid, even under relatively high temperature conditions, the solubility of acrylic acid in water is higher than that of other components. Therefore, acrylic acid can be selectively absorbed.

Subsequently, acrylonitrile is recovered from the ammoxidation reaction gas from which unreacted ammonia and acrylic acid have been separated by a conventionally known method. The ammoxidation reaction gas containing almost no acrylic acid flowing out from the top of the acrylic acid absorption tower 4 is cooled to about 30 ° C. and supplied to the bottom of the acrylonitrile absorption tower 2 through the conduit 15.
From the top of the acrylonitrile absorption tower 2, it is extracted from the bottom of the acrylonitrile recovery tower 3, and the pipes 18, 20, 2
Via 1 and 22 usually below 10 ° C., preferably 5 ° C.
Acrylonitrile wastewater cooled to ℃ is supplied and comes into countercurrent contact with the ammoxidation reaction gas supplied from the bottom of the tower, and most of the acrylonitrile in the ammoxidation reaction gas is absorbed into the supplied acrylonitrile wastewater. . From the viewpoint of absorption of acrylonitrile, which is hardly soluble in water, it is advantageous to lower the temperature in the absorption tower as much as possible.

The bottom liquid extracted through the conduit 16 from the bottom of the acrylonitrile absorption tower 2 having absorbed acrylonitrile and the like is supplied to a position slightly higher than the middle stage of the acrylonitrile recovery tower 3 after preheating. In this recovery tower, a portion of the acrylonitrile wastewater extracted from the bottom of the recovery tower is circulated to the top of the tower through conduits 18, 20, 21 and 23, and the extractive distillation using the wastewater as a solvent is performed, and acetonitrile is obtained. And other impurities are extracted from the middle stage of the recovery tower. From the top of the recovery tower, water vapor having an azeotropic composition with gaseous acrylonitrile as a main component and hydrocyanic acid and acrylonitrile flows out through a conduit 19, and after cooling and condensing in a heat exchanger, liquid-liquid separation in a decanter and then upper layer. Of crude acrylonitrile is supplied to an acrylonitrile purification system to remove hydrocyanic acid, water, etc., and to be rectified to obtain product acrylonitrile. On the other hand, water containing a small amount of acrylic acid (acrylonitrile wastewater) is extracted from the bottom of the recovery tower, and part of the water is circulated to the top of the acrylonitrile absorption tower 2 and the acrylonitrile recovery tower 3 as described above. You. Another part is circulated to the acrylic acid absorption tower 4 as an acrylic acid absorbing solvent, and the rest is discharged out of the system.

[0017]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Acrylonitrile was produced using the recovery process shown in FIG. Propane, ammonia and an oxygen-containing gas are supplied to the reactor, and the empirical formula Mo ₁ V _0.3 Te _0.17 Nb _0.12 O
pressure 190 in the presence of a composite metal oxide catalyst represented by _n.
An ammoxidation reaction was performed at kPa and a temperature of 460 ° C., and the ammoxidation reaction gas flowing out of the reactor was brought into contact with a sulfuric acid aqueous solution in an ammonia absorption tower to remove unreacted ammonia. An ammoxidation reaction gas from which unreacted ammonia removed from the ammonia absorption tower was removed (about 0.7 mol% of acrylic acid,
Acrylonitrile about 4.0 mol%, hydrocyanic acid about 2.0 mol%
And 0.6 mol% of acetonitrile) at a pressure of 17
It was supplied to the bottom of the acrylic acid absorption tower at 6 kPa and a temperature of about 84 ° C. From the top of the acrylic acid absorption tower, water of about 10 weight times the amount of acrylic acid in the raw material gas supplied to the bottom is supplied to the acrylic acid absorption tower at a temperature of about 40 ° C., and the water rises in the absorption tower. Counter-current contact with the ammoxidation reaction gas. At this time, the amount of acrylic acid contained in the absorption liquid withdrawn from the bottom of the acrylic acid absorption tower is determined by the ratio of the amount of acrylic acid in the absorption liquid to the amount of acrylic acid in the supply gas. (Hereinafter referred to as an absorption rate of acrylic acid) was 99.95%. The percentage of the ratio of the amount of each component to the amount of each component in the supply gas of acrylonitrile, hydrocyanic acid, and acetonitrile entrained in the absorption solution at the bottom (hereinafter referred to as the contamination rate of each component) is 1.8%, 5%, and 5%, respectively. .
8% and 2.7%. At this time, the lowest temperature in the acrylic acid absorption tower was about 82 ° C.

The ammoxidation reaction gas flowing out from the top of the acrylic acid absorption tower is further cooled to about 30 ° C. by a gas cooler.
After cooling the mixture to the acrylonitrile absorption tower. After cooling the aqueous solution extracted from the bottom of the acrylonitrile recovery tower at the top of the absorption tower to about 4 ° C., about 18 times the weight of acrylonitrile contained in the reaction gas supplied to the absorption tower Was supplied as an absorbing solvent, and acrylonitrile and other condensed components were absorbed and separated from the gas. Subsequently, the acrylonitrile absorption liquid extracted from the bottom of the absorption tower was supplied to the acrylonitrile recovery tower after preheating. Part of the aqueous solution withdrawn from the bottom of the recovery tower (about 9.5 times by weight of the supplied acrylonitrile)
Was adjusted to 38 ° C., and the mixture was supplied as an extraction solvent to carry out extractive distillation, and a gas stream containing acrylonitrile as a main component was discharged from the top of the recovery tower, and most of the light boiling components were stripped from the bottom of the column. A liquid stream mainly composed of water was extracted as waste water. At this time, the concentration of acrylic acid in the wastewater extracted from the bottom of the recovery tower was about 0.05% by weight.

Example 2 Acrylonitrile was recovered in the same manner as in Example 1 except that the wastewater extracted from the bottom of the acrylonitrile recovery tower was recycled to the acrylic acid absorption tower as an acrylic acid absorption solvent. The absorption rate of acrylic acid was 99.98%.

Comparative Example Acrylonitrile was produced using the recovery process shown in FIG. Propane, ammonia and an oxygen-containing gas are supplied to the reactor, and the empirical formula Mo ₁ V _0.3 Te _0.17 Nb _0.12 O
pressure 190 in the presence of a composite metal oxide catalyst represented by _n.
An ammoxidation reaction was performed at kPa and a temperature of 460 ° C., and the ammoxidation reaction gas flowing out of the reactor was brought into contact with a sulfuric acid aqueous solution in an ammonia absorption tower to remove unreacted ammonia. An ammoxidation reaction gas at 84 ° C. from which unreacted ammonia was removed from the ammonia absorption tower (about 0.7 mol% of acrylic acid, about 4.0 mol% of acrylonitrile, about 2.0 mol
Mol% and acetonitrile 0.6 mol%) was cooled to 30 ° C. by a gas cooler and fed to an acrylonitrile absorption tower. After cooling the aqueous solution extracted from the bottom of the acrylonitrile recovery tower at the top of the absorption tower to about 4 ° C., about 16 times by weight of acrylonitrile contained in the reaction gas supplied to the absorption tower Was supplied as an absorbing solvent, and acrylonitrile and other condensed components were absorbed and separated from the gas. Subsequently, the acrylonitrile absorption liquid extracted from the bottom of the absorption tower was supplied to the acrylonitrile recovery tower after preheating. At the top of the recovery tower, wastewater from the bottom of the acrylonitrile recovery tower, which is about 12 times the weight of acrylonitrile in the reaction gas supplied from the acrylonitrile absorption tower, was added to the top of the recovery tower.
After adjusting the temperature to 8 ° C., the mixture was supplied as an extraction solvent and subjected to extractive distillation. I was extracted as. The concentration of acrylic acid in the wastewater withdrawn from the bottom of the recovery tower was about 7.6% by weight.

[0021]

According to the method of the present invention, there is provided a step of separating acrylic acid from acrylic acid from the ammoxidation reaction gas after supplying unreacted ammonia from the ammoxidation reaction gas and before recovering acrylonitrile. By manufacturing acrylonitrile, it is possible to reduce the concentration of acrylic acid in the process fluid in the acrylonitrile recovery and purification steps, thereby preventing the polymerization of acrylic acid and lowering the pH of the process fluid, and recovering it as a product. And the energy required for distillation in the purification system can be reduced.

[Brief description of the drawings]

FIG. 1 is a process flow diagram showing an example of an acrylonitrile recovery system used in the method of the present invention.

FIG. 2 is a process flow chart showing an example of a conventional acrylonitrile recovery system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ammonia absorption tower 2 Acrylonitrile absorption tower 3 Acrylonitrile recovery tower 4 Acrylic acid absorption tower

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // C07B 61/00 300 C07B 61/00 300 F term (reference) 4H006 AA02 AC54 AD13 BA02 BA06 BA09 BA10 BA11 BA12 BA13 BA14 BA15 BA16 BA17 BA19 BA20 BA21 BA24 BA25 BA26 BA30 BC10 BC11 BD10 BD20 BE14 BE30 QN24 4H039 CA70 CL50

Claims (9)

[Claims] 1. A method for producing acrylonitrile by an ammoxidation reaction of a hydrocarbon, wherein unreacted ammonia is separated from an ammoxidation reaction gas generated by the ammoxidation reaction, and acrylic acid is separated from the ammoxidation reaction gas from which the unreacted ammonia is separated. A process for recovering acrylonitrile from an ammoxidation reaction gas from which unreacted ammonia and acrylic acid have been separated after separation of acrylonitrile. 2. Recovery of acrylonitrile from an ammoxidation reaction gas from which unreacted ammonia and acrylic acid have been separated, by absorbing the ammoxidation reaction gas into an aqueous solution in an acrylonitrile absorption tower and extracting and distilling the aqueous solution in an acrylonitrile recovery tower. The method for producing acrylonitrile according to claim 1, wherein 3. The method for producing acrylonitrile according to claim 1, wherein acrylic acid is separated from an ammoxidation reaction gas from which unreacted ammonia has been separated by contacting the solvent with an acrylic acid-absorbing solvent. 4. The method according to claim 3, wherein the contact between the acrylic acid-absorbing solvent and the ammoxidation reaction gas from which unreacted ammonia is separated is carried out in the acrylic acid-absorbing tower while maintaining the inside of the absorption tower at a temperature of 40 ° C. or higher. For producing acrylonitrile. 5. The method for producing acrylonitrile according to claim 3, wherein the acrylic acid-absorbing solvent is an aqueous solution. 6. The method for producing acrylonitrile according to claim 3, wherein the acrylic acid-absorbing solvent is acrylonitrile wastewater extracted from the bottom of an acrylonitrile recovery tower for recovering acrylonitrile. 7. The method for producing acrylonitrile according to claim 1, wherein the hydrocarbon is propylene and / or propane. 8. The catalyst used for the ammoxidation reaction is molybdenum, vanadium, X, Y and oxygen (X is at least one of tellurium and antimony, Y is niobium,
Made of tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, bismuth, boron, indium, phosphorus, germanium, rare earth elements, alkali metals, alkaline earth metals The method for producing acrylonitrile according to any one of claims 1 to 7, wherein the catalyst comprises one or more elements selected from the group) as an essential component. 9. An existing ratio of an essential component of a catalyst used in an ammoxidation reaction is represented by the following formula: 0.25 <rMo <0.98 0.003 <rV <0.5 0.003 <rX <0.5 0 ≦ rY <0.5 (where rMo, rV, rX, rY represent the mole fractions of Mo, V, X and Y with respect to the sum of the above essential components excluding oxygen) The method for producing acrylonitrile according to claim 8, wherein