JP2000327651A - Production of acrylonitrile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for industrially producing acrylonitrile by ammoxidation of propane. SOLUTION: In this method for producing acrylonitrile by reacting propane with ammonia and oxygen to form acrylonitrile, recovering acrylonitrile from a reaction product gas and propane from the residual gas and reusing them, the reaction is carried out in a molar ratio of ammonia to propane in a gas fed to the reaction of 0.1-5, that of oxygen of 1-10 at 10-70% degree of conversion of propane, 1-9 volume % oxygen concentration in a reaction product gas and 0-30 volume % ammonia concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing acrylonitrile by the ammoxidation of propane, ammonia and oxygen. In particular, the present invention relates to a method for producing acrylonitrile by a propane circulation system in which a reaction is carried out so that a large amount of propane remains in a reactor effluent gas, propane is recovered from the reactor effluent gas, and then subjected to the reaction again. .

[0002]

2. Description of the Related Art Although a number of processes for producing acrylonitrile are known, at present, industrially large-scale processes are carried out by reacting propylene, ammonia and oxygen in the presence of a solid oxidation catalyst. This is the method of dating. This method is an excellent method because the process is relatively simple and the yield of acrylonitrile relative to propylene is high. However, propylene is in great demand and expensive as a raw material for polypropylene and other materials. Therefore, a method for producing acrylonitrile by using an inexpensive propane as a raw material instead of propylene, that is, a method in which propane, ammonia and oxygen are reacted in the presence of a solid oxidation catalyst, and an ammoxidation method using propane as a raw material, has been developed. Is underway.

[0003]

The biggest problem of the ammoxidation method using propane as a raw material is that propane is less reactive than propylene, so that a side reaction easily occurs, and the yield of acrylonitrile relative to propane is high. Is low. Improvements in solid oxidation catalysts have significantly improved the yield of acrylonitrile relative to propane, but still fall short of the propylene process.

One of the solutions to the problem of the ammoxidation method using propane as a raw material is to suppress the combustion reaction and other side reactions mainly due to the sequential reaction by reducing the reaction rate of propane, Is to use a propane circulation system in which unreacted propane in the reaction product gas flowing out of the reactor is recovered and reused in the reaction. In the propane circulation method, since the cost required for circulation greatly affects the economics of the process, the reaction conditions are set so that the entire process including the recovery of unreacted propane and the circulation of the recovered propane is optimized. It is important that such reaction conditions have not yet been found. Accordingly, an object of the present invention is to provide a method for industrially and efficiently producing acrylonitrile from propane by an optimized propane circulation system.

[0005]

According to the present invention, there is provided a reaction step of reacting a raw material gas consisting mainly of propane, ammonia and oxygen in a reactor containing a solid oxidation catalyst to produce acrylonitrile. Acrylonitrile recovery step of separating acrylonitrile generated from the reaction product gas flowing out, propane recovery step of obtaining a circulating gas mainly containing propane by removing carbon dioxide gas and other non-hydrocarbons from the gas after separating acrylonitrile, and In the method for producing acrylonitrile by ammoxidation of propane, the method comprises the steps of a raw gas supply step of continuously supplying the circulating gas to the reactor together with new propane, ammonia and oxygen supplied from outside the system. Propane in the gas supplied to the reactor in the process The molar ratio of ammonia is 0.1 to
5. The composition of the supplied gas is controlled so that the molar ratio of oxygen is 1 to 10, and the reaction rate of propane in the reactor is 1
Acrylonitrile is industrially advantageously produced from propane by allowing the reaction to proceed at 0 to 70% so that the oxygen concentration in the reactor effluent gas is 1 to 9% by volume and the ammonia concentration is 0 to 3% by volume. be able to.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The present invention will be described in detail. In the present invention, acrylonitrile is produced by reacting propane, ammonia and oxygen in the presence of a solid oxidation catalyst. This reaction itself is known, and many catalysts are known. Usually, a metal oxide catalyst containing molybdenum and / or vanadium is used. Examples of this type of catalyst include V-Sb-W-based oxides and Mo-Bi-Ce
Catalyst obtained by mechanically mixing -W type oxide
-38051), Mo-Ag-Bi-V based catalyst (JP-A-3-58961, Mo-V-Sn-Bi-P-based catalyst (JP-A-4-247060)), Mo-Cr-Te-based catalyst ( U.S.P. 5,171,876), Mo and M
composite metal oxide catalysts comprising elements such as n, Co, etc. (JP-A-5-194347), Mo-V-Te-X-based catalysts (JP-A-2-257, JP-A-5-148212), X -Cr-Mo-Bi-Y based catalyst (Japanese Unexamined Patent Publication No.
No. 16225), V-Sb-based catalysts (JP-A 1-2686)
No. 68, JP-A-2-180637), V-Sb-W-
P (JP-A-2-95439), V-Sb-Sn-Cu
A system catalyst (JP-A-4-275266) has been proposed. In the present invention, the Mo-VT disclosed in JP-A-2-257 and JP-A-3-104382 are disclosed.
e-X-based catalysts and Mo-V-Sb-X-based catalysts disclosed in JP-A-9-157291 are disclosed in Japanese Patent Application Laid-Open No. H09-157291.
It is preferred because it gives acrylonitrile with a high selectivity at a relatively low reaction temperature of ° C.

The catalyst preferably used in the present invention is described in more detail. Molybdenum, vanadium, X, Y and oxygen (X is at least one of tellurium and antimony, and Y is niobium, tantalum, tungsten, titanium, aluminum , Zirconium, chromium, manganese,
Iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, bismuth, boron, indium, phosphorus,
One or more elements selected from the group consisting of germanium, rare earth elements, alkali metals, and alkaline earth metals)
Is an essential component, more specifically, the proportion of the essential component is represented by the following formula: 0.25 <rMo <0.98 0.003 <rV <0.5 0.003 <rX <0. 50 ≦ rY <0.5 (where rMo, rV, rX and rY represent the mole fractions of Mo, V, X and Y with respect to the sum of the above essential components excluding oxygen) The catalyst shows better performance. The method for producing these catalysts is not particularly limited, and is produced by drying a solution or a slurry containing the constituent elements and subjecting the dried product to heat treatment. Also,
Well-known carrier components such as silica, alumina, titania, zirconia, aluminosilicate, diatomaceous earth, etc.
It can be used as a mixture containing about 90% by weight.

In the present invention, the composition of the gas supplied to the reactor is adjusted so that the molar ratio of ammonia to propane is 0.1 to 0.1.
5, preferably 0.3 to 2 and a molar ratio of oxygen of 1 to 1
It is controlled to be 0, preferably 1.5 to 5. The reaction rate of propane in the reactor is 10 to 70%,
Preferably, the reaction temperature and other conditions are controlled so as to be 20 to 60%. In the case of the propane circulation system, propylene by-produced in a molar ratio of usually about 0.01 to 0.5 with respect to propane and propane in the residual gas from the residual gas after recovering acrylonitrile from the reaction product gas. (In the present invention, both are collectively referred to as propane.) From the economic viewpoint, it is important to minimize the ratio of the amount of gas to be treated in the propane recovery system to the amount of acrylonitrile recovered. Therefore, in order not to introduce inert gas into the system as much as possible, use not oxygen as air but oxygen obtained by air separation or oxygen-enriched air, such as nitrogen or carbon dioxide in the gas supplied to the reactor. It is preferable that the ratio of the inert gas be 60% by volume or less, particularly 40% by volume or less. Also, if the reaction rate of propane in the reactor is reduced, the selectivity of acrylonitrile is improved, but the amount of propane to be recovered and circulated is increased, which leads to an increase in the size of the recovery system and the circulation system, and also increases operating costs. Increase. The relationship between the reaction rate of propane and the selectivity of acrylonitrile varies depending on the catalyst used. However, if the reaction rate of propane is less than 10%, the amount of circulating gas becomes excessively large, which is disadvantageous. Above this, the selectivity of acrylonitrile is reduced and the advantages of the propane cycle are lost. The reaction rate of propane is preferably 20 to 60%.

In the present invention, as described above, the supply ratio of oxygen and ammonia to propane is made significantly smaller than in the normal case, and the reaction is carried out so that a considerable amount of propane remains unreacted. Easily. However, the solid oxidation catalyst used for ammoxidation is a metal oxide, and is generally inactivated when it is in a reduced state. Therefore, it is necessary to keep molecular oxygen in the reactor at all times. The oxygen in the reactor needs to be at least 1% by volume as the oxygen concentration in the gas discharged from the reactor, and is usually preferably 2% by volume or more. On the other hand, leaving a large amount of oxygen in the reactor effluent gas is not preferable because it increases the processing gas amount and wastes oxygen. The upper limit of the oxygen concentration in the reactor effluent gas should be 9% by volume or less, preferably 7% by volume or less.

The ammonia concentration in the reactor effluent gas is 0 to
It should be 3% by volume or less. Acrylonitrile is liable to decompose under reaction conditions where a large amount of ammonia is present in the reactor effluent gas. Ammonia in the reactor effluent gas is usually absorbed with an aqueous acid at the time of acrylonitrile recovery, separated from the gas, and discarded. Therefore, the ammonia in the effluent gas is not only wasted, but also requires disposal.

One example of producing acrylonitrile from propane by the method of the present invention will be described with reference to the drawings. A raw material gas mainly comprising propane, ammonia and oxygen is continuously supplied to a reactor (1) containing a solid oxidation catalyst. And react to produce acrylonitrile. It is preferable to use a fluidized-bed reactor that can easily remove heat as the reactor. The reaction temperature varies depending on the catalyst used, but usually 4
50-550 ° C. The reaction pressure is usually from normal pressure to 196 kPa as a gauge pressure. The raw material gas supplied to the reactor was supplied from a circulating gas supplied from a propane recovery step via a conduit (4), and a circulating gas supplied from outside the system to a conduit (5),
It consists of propane, ammonia and oxygen supplied via (6) and (7). The circulation gas and the newly supplied propane and ammonia may be separately supplied to the reactor as shown in the figure, or they may be partially or wholly mixed and supplied to the reactor. Oxygen is usually
From the safety point of view, supply the gas to the reactor separately from other gases,
Mix with other gases in the reactor. Of course, if a mixing means capable of ensuring safety is used, the mixture may be supplied outside the reactor. Preferably, the composition of the circulating gas, particularly its propane concentration, is measured on-line, and based on the results, the supply of at least one of newly supplied propane and oxygen is controlled, and the amount of oxygen relative to propane supplied to the reactor is controlled. Keep the ratio constant.

The reaction product gas flowing out of the reactor (1) is sent to an acrylonitrile recovery unit (2). Preferably, the oxygen concentration of the reaction product gas is measured online on the way to the acrylonitrile recovery device, and based on the result, the composition of the raw material gas supplied to the reactor is controlled. To be maintained.
In the acrylonitrile recovery device, a common acrylonitrile recovery method can be used, such as washing the reaction product gas with water and recovering acrylonitrile in the gas as an aqueous solution together with acrylic acid as a by-product. The residual gas after the separation of acrylonitrile is sent to a propane recovery device (3) to remove non-hydrocarbons such as carbon dioxide and recover propane containing propylene as a by-product. As the propane recovery device, one having a plurality of pressure swing type adsorption / separation devices is preferably used.
By sequentially switching the desorption, propane in the gas is continuously recovered to generate a circulating gas. The adsorbent of the adsorption / separation device may be any adsorbent that adsorbs propane and does not adsorb non-hydrocarbons such as carbon dioxide, and usually uses an inorganic adsorbent such as zeolite. Since the composition of the circulating gas obtained from the adsorption / separation apparatus changes periodically, in order to alleviate this change, a gas storage tank is provided on the way to send the circulating gas to the reactor, or a large number of adsorption / separation apparatuses are used. It is preferable that the phases of the adsorption and desorption of each apparatus are slightly shifted.

As an example of the production of acrylonitrile from propane according to the method of the present invention, a catalyst (Mo ₁ -V _0.4 -Nb _0.1 -Te _0.2 -O _x ) is contained in a fluidized bed reactor, and circulating gas is added thereto. And a new raw material gas consisting of propane, ammonia and oxygen is supplied in a molar ratio of propane: ammonia: oxygen = 1: 0.75: 1.8, at a temperature of 430 ° C. and a pressure of 98 kPa (gauge pressure).
And propane is reacted so as to have a reaction rate of about 50%. One example of the composition of the reaction product gas flowing out of the reactor is:
Acrylonitrile 5.6-6.1%, propane 8.5-
8.7%, oxygen 6.2-7.0%, carbon dioxide 8.2-
9.2% and nitrogen 21.8-22.1%. The reaction product gas is washed with an acrylonitrile recovery device to recover acrylonitrile. The gas from which acrylonitrile has been separated is sent to a pressure swing adsorption / separation device to recover propane and circulate through the reactor. In this way, acrylonitrile can be obtained in a yield of 65 to 70 mol% based on propane and 42 to 45 mol% based on ammonia.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing an example of a process for producing acrylonitrile according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor 2 Acrylonitrile recovery device 3 Propane recovery device 4 Circulating gas conduit 5 Propane supply conduit 6 Ammonia supply conduit 7 Oxygen supply conduit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C07B 61/00 300 C07B 61/00 300 (72) Inventor Iwao Hatano Shiotsume 3-chome, Kurashiki City, Okayama Prefecture No. 10 Mitsubishi Chemical Corporation Mizushima Plant F-term (reference) 4G069 AA03 BA01B BA02B BA03B BA04B BA05B BB06A BB06B BC01A BC01B BC08A BC08B BC16A BC16B BC18A BC18B BC23A BC23B BC24A BC24B BC25A BC25B BC38A BCB BCBC BCA BCBC BC56B BC58A BC58B BC59A BC59B BC60A BC60B BC62A BC62B BC66A BC66B BC67A BC67B BC68A BC68B BC70A BC70B BC71A BC71B BC72A BC72B BC75A BC75B BD02A BD02B BD03A BD03B BD07A BD07B CB78 BA12 BA15 BA12 BA15 BA18 BA26 BA30 BA31 BA35 BB61 BC31 BC35 BC40 BD33 BD51 B D80 BE14 BE30 QN24 4H039 CA70 CL50

Claims (8)

[Claims] 1. A reaction process in which a raw material gas mainly composed of propane, ammonia and oxygen is reacted in a reactor containing a solid oxidation catalyst to produce acrylonitrile, and acrylonitrile produced from a reaction product gas flowing out of the reactor is converted into acrylonitrile. Acrylonitrile recovery step to separate, propane recovery step to remove carbon dioxide gas and other non-hydrocarbons from gas after separating acrylonitrile to obtain propane-based circulating gas, and to supply this circulating gas from outside the system In a method for producing acrylonitrile by ammoxidation of propane, which comprises the steps of a raw gas supply step of continuously supplying new propane, ammonia and oxygen to the reactor together with the gas supplied to the reactor in the raw gas supply step The molar ratio of ammonia to propane is 0.1 -5, the composition of the feed gas is controlled so that the molar ratio of oxygen is 1-10, the reaction rate of propane in the reactor is 10-70%, and the oxygen concentration in the effluent gas of the reactor is 1-9. Volume%, ammonia concentration 0-3
A method for producing acrylonitrile, wherein the reaction is carried out so as to give a volume%. 2. The reaction rate of propane in the reactor is 20.
The method for producing acrylonitrile according to claim 1, wherein the reaction is carried out so as to be up to 60%. 3. The method according to claim 1, wherein an oxygen concentration in the gas is measured while the gas discharged from the reactor is guided to an acrylonitrile recovery step, and a composition of the gas supplied to the reactor is controlled based on a result of the measurement. Item 3. The method for producing acrylonitrile according to Item 1 or 2. 4. The method according to claim 1, wherein the composition of the circulating gas is analyzed, and at least one of the supply amounts of propane and oxygen supplied from outside the system is controlled based on the measurement result.
4. The method for producing acrylonitrile according to any one of items 3 to 3. 5. The method according to claim 1, wherein the composition of the supply gas is controlled so that the ratio of the inert gas in the gas supplied to the reactor in the raw material gas supply step is 60% by volume or less. A method for producing acrylonitrile according to any one of the preceding claims. 6. The process for producing acrylonitrile according to claim 1, wherein the reaction is carried out in a fluidized bed reactor. 7. A solid oxidation catalyst comprising molybdenum, vanadium, X, Y and oxygen (X is at least one of tellurium and antimony, and Y is niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, Iron, ruthenium, cobalt, rhodium,
A metal oxide catalyst comprising at least one element selected from the group consisting of nickel, palladium, platinum, bismuth, boron, indium, phosphorus, germanium, rare earth elements, alkali metals and alkaline earth metals) The method for producing acrylonitrile according to any one of claims 1 to 6, wherein 8. The solid oxidation catalyst according to claim 1, wherein an essential component is present in an amount of:
The following formula: 0.25 <rMo <0.98 0.003 <rV <0.5 0.003 <rX <0.50 ≦ rY <0.5 (However, rMo, rV, rX and rY exclude oxygen) The method for producing acrylonitrile according to claim 7, wherein the molar fraction of Mo, V, X, and Y with respect to the total of the essential components is represented by: