JPH0940628A - Production of acrylonitrile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily remove unreacted ammonia from crude acrylonitrile and produce acrylonitrile in high yield while suppressing the loss of valuable materials in the reaction gas and scarcely generating wastes to be treated. SOLUTION: Acrylonitrile is synthesized by reacting propylene and/or propane with ammonia and oxygen and the reaction gas is contacted with a catalyst composed mainly of a double oxide containing an element selected from vanadium, molybdenum, tungsten, antimony and bismuth (e.g. V2 O5 -MoO3 , Pmo-V or Bi2 O3 -MoO3 catalyst) at 200-550 deg.C to remove unreacted ammonia from the reaction gas and obtain acrylonitrile in high yield. The content of propylene and/or propane in the reaction gas for the synthesis of acrylonitrile is preferably <=0.5vol.% and the catalyst is formed in honeycomb form to minimize the pressure drop.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing acrylonitrile, and more specifically, in producing acrylonitrile by an ammoxidation method of propylene or propane, by contacting the mixed gas obtained by the acrylonitrile synthesis reaction with a catalyst again, The present invention relates to a method for reducing unreacted ammonia in a reaction gas.

[0002]

2. Description of the Related Art A method for synthesizing acrylonitrile by reacting propylene, ammonia and air in the presence of a catalyst is well known (K. Weissermel, HJ Arpe, translated by Mitsuaki Mukaiyama, "Industrial Organic Chemistry-Main Raw Materials and Intermediates". "Tokyo Kagaku Doujinshi P-290,291 (1978)). Some reactors adopt a fixed bed type, but generally, a fluidized bed reactor is used to carry out the reaction while flowing the catalyst with the source gas.

The reaction conditions are somewhat different depending on the structure of the reactor and the catalyst used, but the molar ratio of ammonia to the raw material propylene is usually 1.05 to 1.25, which is a slight excess of ammonia, and the ratio of oxygen to propylene is stoichiometric. Is several tens of percent over. The reaction temperature is 400 to 500 ° C. Under such conditions, the conversion of raw material propylene generally reaches 98% or more. Usually, the components in the reactor outlet gas are acrylonitrile and water, which are the main reaction products, and nitrogen and argon in the air used as an oxidizing gas, as well as hydrocyanic acid and acetonitrile, which are side reaction products.
It contains acrylic acid, acetic acid, acrolein, carbon dioxide, carbon monoxide, unreacted propylene or ammonia, oxygen and other propane.

In recent years, a method for producing acrylonitrile using cheaper propane instead of propylene has been developed (JP-A-5-279313, etc.). In both the method using propylene and the method using propane, the raw material ammonia is supplied in excess with respect to propylene or propane, so that some unreacted ammonia is present in the reactor outlet gas together with the residual oxygen. Normally, about 1 to 10 g of ammonia remains per 1 Nm ^{3 of the} reactor outlet gas.

When recovering and purifying acrylonitrile and hydrocyanic acid from the reaction gas, when ammonia is washed with water, absorbed by water and distilled without being treated, acrylonitrile and hydrocyanic acid cause a remarkable decrease in recovery rate due to polymerization and hydrolysis reaction. Moreover, the quality of the product deteriorates due to the inclusion of these polymers and hydrolysates. Furthermore, the adherence and accumulation of the polymer result in blockage of the tower, heat exchanger, etc., which makes stable operation difficult. Therefore, in order to efficiently recover acrylonitrile and hydrocyanic acid from the reaction gas and perform stable operation, a step of removing unreacted ammonia is provided.

For example, in Japanese Examined Patent Publication No. 44-15645, the reaction gas is washed with water to remove high boiling point compounds such as polymers, and then unreacted ammonia is separated from the reaction gas by contacting with sulfuric acid to produce ammonium sulfate. Is proposed to be recovered. Further, an improved patent thereof is proposed by Standard Oil Co., Ltd. as Japanese Patent Laid-Open No. 52-65219.

[0007]

However, in the above method of removing ammonia with sulfuric acid, acrylonitrile in the reaction gas reacts with by-produced hydrocyanic acid, acetonitrile and aldehydes having 2 and 3 carbon atoms, A few percent of the acrylonitrile produced is lost. It is considered that when the polymer is removed by washing with water in the washing step, a part of the unreacted ammonia is absorbed by the washing water and the washing water becomes alkaline so that the reaction is promoted. The products of such secondary reactions include, for example, polymers of hydrocyanic acid, pyridine bases formed by aldehydes and ammonia, and the reaction of ammonia with acrylonitrile, hydrocyanic acid, acrylic acid and polymers thereof. A compound can be mentioned.

Besides, the cost of sulfuric acid for neutralizing and removing ammonia in the reaction gas is high, and discharging a large amount of ammonium sulfate produced by the neutralization reaction without treatment may cause a problem of environmental pollution. The cost of preventing this increases the production cost of acrylonitrile. It is an object of the present invention to provide a method for producing acrylonitrile which has less loss of acrylonitrile and less cost for removing ammonia than the conventional techniques.

[0009]

The present inventors have completed the present invention as a result of intensive research to solve the above problems. That is, in the method for producing acrylonitrile of the present invention, propylene and / or propane, ammonia and oxygen are reacted in the presence of a catalyst to perform an acrylonitrile synthesis reaction, and then this reaction gas is mixed with vanadium, molybdenum, tungsten, antimony and bismuth. The non-reacted ammonia in the reaction gas is reduced by bringing the complex oxide containing at least one element selected from the above into contact with a catalyst having a main catalyst at 200 to 550 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Ammonia reduction by the method of the present invention
The catalysts used as are vanadium, molybdenum, and
At least one type of ungsten, antimony, or bismuth
It is a catalyst whose main catalyst is a complex oxide containing it. Complex oxide
In vanadium, molybdenum, tungsten, anti
At least one element selected from mon and bismuth
Other elements may be contained as long as they are contained.
V as such a complex oxide ₂O_Five-MoO_ThreeSystem, P
-Mo-V system, Bi₂O_Three-MoO_ThreeSystem, Bi₂O_Three−
WO_ThreeSystem, Fe₂O_Three-Sb₂O_FiveSystem, SnO₂-Sb
₂O_FourThere are systems, etc. Furthermore, the catalyst life was extended.
Improve the mechanical strength of the catalyst and improve the catalytic activity.
Control the decomposition of valuable materials such as acrylonitrile.
Other components may be added for the purpose of the above.

In the reactor for synthesizing acrylonitrile,
A fluidized bed reactor is used in which the reaction temperature is uniform and the heat can be easily removed. The reactor for ammonia decomposition can reduce unreacted ammonia by using either a fluidized bed or a fixed bed, but in the acrylonitrile synthesis reaction, the selectivity of acrylonitrile decreases as the pressure increases, so the ammonia decomposition reactor For this purpose, a fixed bed reactor having a relatively small pressure loss is used, or more preferably, a catalyst is supported on a honeycomb type carrier, or a catalyst formed into a honeycomb type is used to minimize the pressure loss.

The reaction temperature for the decomposition of ammonia varies depending on the catalyst used, but is 200 to 550 ° C, preferably 250 to 520 ° C, more preferably 350 to 500 ° C.
It is. When the temperature of the acrylonitrile synthesis gas is 200 ° C. or higher, it is possible to prevent the precipitation trouble of the high boiling point between the acrylonitrile synthesis reactor and the ammonia decomposition reactor. The ammonia decomposition reaction temperature is 55
When the temperature is 0 ° C. or less, heating before supplying the gas stream from the acrylonitrile synthesis reactor to the ammonia decomposition reactor is almost unnecessary, which is economically advantageous. Furthermore 55
When the temperature is 0 ° C. or lower, the amount of valuable substances such as acrylonitrile decomposed is relatively small.

Acrylonitrile synthesis reaction is multi-component Mo-B
Using known i-type, Fe-Sb-type, etc., catalysts for synthesizing arylonitrile, various conditions for maximizing the yield of acrylonitrile, that is, reaction temperature, air / propylene molar ratio, ammonia / propylene molar ratio, etc. You can choose. Under these conditions, the conversion of propylene is 9
Reach over 8%.

In the ammonia decomposition reactor, if propylene, ammonia and oxygen are present, a part of propylene is converted into acrylonitrile, but the yield is low. Therefore, the reaction conditions that maximize the yield of acrylonitrile are selected in the same manner as in a normal process without an ammonia decomposition reactor in the acrylonitrile synthesis reactor, and the propylene concentration at the inlet of the ammonia decomposition reactor is 0.5.
% Or less, preferably 0.3% or less, and more preferably 0.1% or less.

Since ammonia is excessively supplied to the acrylonitrile synthesis reactor, the reaction gas contains 1 to 10 g of unreacted ammonia per 1 Nm ³ . This unreacted ammonia is decomposed in the ammonia decomposition reactor. The term "decomposition" used herein means both an oxidation reaction by ammonia and oxygen and a decomposition reaction by which ammonia is decomposed into nitrogen and hydrogen. The loss of acrylonitrile in the ammonia decomposition reactor is less than 2% of the amount produced in the acrylonitrile synthesis reactor.

When decomposing ammonia in the ammonia decomposition reactor, oxygen is supplied at the reactor inlet, if necessary.
The oxygen supplied at this time may be pure oxygen or may contain an inert gas such as nitrogen such as nitrogen. The substances produced by the decomposition of ammonia are mainly nitrogen and water, and the amount thereof is 1/10 or less of the total gas amount. Since the reaction gas before treating ammonia originally contained about 60 vol% of nitrogen and about 10 to 30 vol% of water, the nitrogen and water produced by the oxidation of ammonia were not contained in the refining process at all. Has no effect. As described above, according to the method of the present invention, the ammonia component can be reduced with almost no loss of acrylonitrile in the acrylonitrile synthesis gas, and the cost of treating sulfuric acid for neutralization and waste water can be reduced.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Examples 1 to 6 [Acrylonitrile synthesis reaction] In a fluidized bed reactor filled with a multi-component Mo-Bi catalyst, the molar ratio of propylene, ammonia and air was propylene: ammonia: air = 1: 1.
A mixed gas of 1.2: 9.8 was inserted so that the contact time was 10 seconds, and the reaction was performed at a reaction temperature of 450 ° C. The pressure of the reactor inlet gas was 1.68 kg / cm ³ . Analysis of the reaction gas from the reactor outlet revealed that acrylonitrile was 6.1 vol%, hydrocyanic acid was 0.8 vol%, and ammonia was 1.0 v.
It was ol%, 1.1 vol% oxygen, 0.03 vol% propylene, and included nitrogen, water vapor, propane, carbon monoxide, carbon dioxide, acetonitrile, acrylic acid and the like. The conversion rate of propylene was 99.7%.

[Ammonia Decomposition Reaction] As shown in Table 1, each of the above acrylonitrile synthesis reaction gases was mixed with a catalyst containing various complex oxides as main catalysts at 6 mmφ × 3 mmt.
SV = in a reactor that was molded into a tablet and packed in a fixed bed
It was fed at 5000 h ⁻¹ and operated for 4 hours at the temperatures shown in Table 1, and the outlet gas was analyzed to measure the ammonia decomposition rate and the acrylonitrile loss rate. The ammonia decomposition rate and the acrylonitrile loss rate were calculated by the following formulas.

[0020] The results are shown in Table 1.

[0021]

[Table 1]

[0022]

EFFECTS OF THE INVENTION According to the present invention, the loss of acrylonitrile in the acrylonitrile synthesis reaction gas is made extremely small as compared with the conventional method, and unreacted ammonia is efficiently decomposed and removed to produce acrylonitrile with less waste. A method can be provided, which is industrially advantageous.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 27/199 B01J 27/199 X C07C 253/24 C07C 253/24 // C07B 61/00 300 C07B 61/00 300 (72) Inventor Ken Takeshita 1-6 Takasago, Takaishi-shi, Osaka Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. Acrylonitrile synthesis reaction is carried out by reacting propylene and / or propane, ammonia and oxygen in the presence of a catalyst, and this reaction gas is then at least selected from vanadium, molybdenum, tungsten, antimony and bismuth. A method for producing acrylonitrile, which comprises contacting with a catalyst having a complex oxide containing one kind of element as a main catalyst at 200 to 550 ° C. to reduce unreacted ammonia in a reaction gas. 2. The complex oxide is V₂O_Five-MoO_ThreeSystem, P-
Mo-V system, Bi₂O_Three-MoO_ThreeSystem, Bi₂O_Three-W
O_ThreeSystem, Fe₂O_Three-Sb₂O_FiveSystem, SnO ₂-Sb₂
O_FourThe method of claim 1 which is a system. 3. The method according to claim 1, wherein the content rate of propylene and / or propane in the acrylonitrile synthesis reaction gas is 0.5 vol% or less.