Process method for preparing acrylonitrile by means of propylene ammoxidation

Abstract

The present invention belongs to the field of the chemical industry. Disclosed is a process method for preparing acrylonitrile by means of propylene ammoxidation. The process method is characterized in that in a corresponding device and reaction system of the method, propylene, ammonia and air (calculated as O2), according to a ratio of 1:(1-1.5):(2-10), enter a fluidized bed reactor at 400-450°C and 0.01-0.15 MPa at a weight hourly space velocity of 0.04-0.1 h-1, so as to perform a reaction; a microsphere catalyst having a particle size of 40-60μm in a dense phase section and a dilute phase section has α- and γ-phase bismuth molybdate and a lattice oxygen active center, and satisfies the chemical formula MoaBibNicWdTleVfPgSixOy, wherein the atomic ratio a=21-22, b=1.5-2, c=4-5, d=0.8-1, e=0.09-0.1, f=0.15-0.2, g=0.8-1, x=70-71, and y is the number of oxygen atoms required to satisfy the valence of each element; and the product enters a quench tower and a water absorption tower to undergo neutralization and cooling, then passes through a recovery tower, an acetonitrile tower, a decyanation tower, a layer separator and a finished product tower to realize the separation of an aqueous phase and an organic phase, thereby further obtaining crude acetonitrile, hydrocyanic acid and refined acrylonitrile. The process conversion degree and product selectivity are good, the operation is stable and reliable, and the method is energy-saving and environmentally friendly.

Description

A process for producing acrylonitrile by ammoxidation of propylene Technical Field

[0001] This invention relates to a process for producing acrylonitrile by ammoxidation of propylene, and more specifically, to a process, conversion device, and reaction system for producing acrylonitrile from propylene by ammoxidation in a fluidized bed, belonging to the field of chemical technology. Background Technology

[0002] Acrylonitrile is a very important basic organic raw material. It is a monomer used to synthesize acrylic fibers, and it is also a raw material for thermoplastic synthetic resins such as acrylonitrile-butadiene-styrene and styrene-acrylonitrile, as well as nitrile rubber, adiponitrile, acrylamide and other derivatives.

[0003] The acrylonitrile industry has undergone several stages of production, including the acetylene process, the ethylene oxide process, and the propylene and propane ammoxidation process. The acetylene and ethylene oxide processes, being early methods, have been phased out due to severe environmental pollution and high production costs. The direct propane ammoxidation process, however, suffers from low acrylonitrile selectivity in current technology, resulting in low propane utilization (propane conversion rate not exceeding 90%) and acrylonitrile selectivity below 70%.

[0004] Current industrial production is primarily based on the direct ammoxidation of propylene process developed by Sohio Corporation in the United States in the 1960s. After more than sixty years of development and improvement, this process has become increasingly mature, as illustrated in patents such as USP2481826, USP2904580, and USP5175334. In mainstream existing technologies, Mo-Bi type catalysts are mainly used for the ammoxidation of propylene to produce acrylonitrile, as described in patent documents such as USP3746657, USP4264476, USP5093299, and USP5212137. In the industrial production of acrylonitrile, microsphere catalysts are placed in a fluidized bed reactor. Under conditions of ammonia, air, and relatively high reaction temperatures, propylene is converted through an ammoxidation reaction. The purified acrylonitrile product is then obtained through subsequent absorption and fractionation processes.

[0005] For example, earlier patent document USP2904580 discloses a method for producing acrylonitrile using a fluidized bed reactor, including steps such as contacting a mixture of propylene and oxygen in a stable phase with a catalyst selected from bismuth, tin, and antimony salts of phosphomolybdic acid and molybdic acid, as well as bismuth phosphotungstenate, to prepare acrylonitrile. In the ammoxidation process for producing acrylonitrile disclosed in USP4228098, a molybdenum-bismuth-iron catalyst is used to obtain a high acrylonitrile product yield.

[0006] Further improvements to existing technologies, such as those described in CN117463253A, provide a production system and method for high-purity acrylonitrile. This production system comprises a reaction unit, a rapid cooling deoxide unit, a recovery unit, a dehydrocyanic acid unit, and a product refining unit connected in sequence, enabling continuous industrial production of high-purity acrylonitrile through the ammoxidation of propylene. Simultaneously, the provided production method is matched to the production system, offering a specially formulated catalyst to catalyze the ammoxidation of propylene, thereby increasing the yield of acrylonitrile and reducing the production of organic oxygen-containing byproducts. Through specific production processes within the rapid cooling deoxide unit, recovery unit, and dehydrocyanic acid unit, impurities such as oxygen-containing compounds and hydrocyanic acid are removed, ultimately producing acrylonitrile products with a purity exceeding 99.97 wt% and a total oxygen content below 5 micrograms / gram.

[0007] In addition to focusing on the ammonia oxidation reaction process, USP 3352764 also discloses the separation of crude olefinic unsaturated nitrs, such as acrylonitrile and methacrylonitrile, from an aqueous solution containing saturated aliphatic nitrs such as acetonitrile, relatively low molecular weight carbonyl compounds, and relatively high molecular weight soluble organic compounds. USP 3885928, in the recovery and purification of acrylonitrile or methacrylonitrile obtained by the ammonia oxidation of propylene or isobutylene, describes a process where, in the tower for removing hydrogen cyanide from the nitrile, the aqueous layer is recycled to a quench tower, and the hot gas from the reactor is directly contacted with the recycled water flow, resulting in better utilization in the neutralization process.

[0008] USP3936360 significantly reduces operating costs and improves the recovery rate of acrylonitrile and methacrylonitrile by recycling the distillate from the bottom of the product cooling tower to the quench liquid in the reactor effluent quenching system. USP4234510 recovers reactor effluent from the ammoxidation reaction of propylene or isobutylene by cooling the reactor effluent to a temperature of approximately 40°C to 100°C; it obtains a gaseous stream containing acrylonitrile or methacrylonitrile through direct contact cooling, preferably using an aqueous stream, and then cools it into a gaseous stream using indirect contact cooling, condensing at least some acrylonitrile or formonitrile therefrom. USP6107509 optimizes the preparation of acrylonitrile and methacrylonitrile by adjusting the absorption, separation, and circulation processes between multiple towers to purify and recover unsaturated nitrile. CN102659625B also discloses a similar method that optimizes the absorption, separation, and circulation processes between multiple towers to purify and recover unsaturated nitrile, improving the reliability and energy efficiency of the apparatus.

[0009] USP5457223 also discloses a process for simultaneously eliminating waste during the production of acrylonitrile by directly ammoniatizing propylene / propane, ammonia, and an oxygen-containing gas, such as air, over a fluidized bed catalyst. An improvement includes introducing methanol into the upper part of the reactor at a location where it reacts with at least a portion of the exchanged ammonia without affecting the acrylonitrile yield. Preferably, the methanol is introduced into the reactor at a temperature below its coking temperature, particularly when using an oxygen-deficient fluidized bed catalyst, by introducing additional oxygen-containing gas into the reaction approximately 8 to 14 inches from the methanol feed location. USP5466857 also discloses a method for reducing the amount of waste generated during acrylonitrile production by introducing an additional amount of oxygen-containing gas, preferably air, into the upper part of a fluidized bed reactor without any oxygen-containing compounds, to react with at least some of the unreacted ammonia, thereby reducing the amount of unreacted ammonia in the reactor effluent.

[0010] CN106430245A discloses an improved acrylonitrile ammonium-free process and reaction apparatus. The high-ammonia product gas stream contacts the absorbent in the lower section of the quench tower, absorbing some of the unreacted ammonia in the gas stream. In the upper section of the quench tower, it contacts the lean ammonia absorbent, absorbing the ammonia not absorbed in the lower section. The resulting lower section absorbent is stripped and then separated into light and heavy components in a three-phase separation unit. It is then reacted in a catalytic wet oxidation reactor to remove organic matter and ammonia nitrogen, before being returned to the lower section of the quench tower for the absorption of unreacted ammonia. The crude ammonia gas stream is then distilled to obtain a high-purity ammonia stream. This process solves the problem of easy clogging in existing equipment.

[0011] In a method and apparatus for producing acrylonitrile disclosed in CN113620839A, a rich liquid containing acrylonitrile is stripped and separated in a recovery tower. A gaseous stream containing acrylonitrile is obtained at the top of the recovery tower, while a high-temperature lean liquid essentially free of acrylonitrile is obtained at the bottom. This lean liquid is then flash-evaporated, and the resulting steam is pressurized and used as a heat source for recovery in the recovery tower, wastewater evaporator, hydrogen cyanide removal tower, and product tower. This low-grade heat source is utilized to achieve energy conservation and emission reduction. CN204665978 also discloses heat recovery from reactor wastewater, optimizing and improving the manufacturing process of acrylonitrile and methacrylonitrile.

[0012] In addition, CN104693068A and CN205088162 U disclose an improved acrylonitrile manufacturing process involving the use of an effluent compressor; CN111918860A discloses a gas-phase conversion oxidation process for acrylonitrile conversion including a fluidized bed reactor; and CN114828995A and CN112823871A disclose an improved fluidized bed reactor for acrylonitrile production.

[0013] In summary, the direct ammoxidation of propylene to acrylonitrile technology has undergone significant development over the past few decades since its initial industrialization, with substantial improvements made to the reaction process and catalysts. The acrylonitrile yield has increased from 70%–79% at the beginning of development to the current 80%–86%. However, there is still considerable room for improvement in the reaction process and acrylonitrile yield. Issues such as large volumes of wastewater and waste gas, the presence of toxic substances, and energy conservation all require further improvement and optimization. Summary of the Invention

[0014] The purpose of this invention is to provide an industrial production method for acrylonitrile. By optimizing and improving the traditional process flow, the conversion efficiency and product selectivity of the propylene ammoxidation process can be improved, the yield of acrylonitrile products can be increased, the stability and reliability of the equipment during operation can be improved, and energy saving and consumption reduction can be achieved in the process.

[0015] The present invention provides a process for producing acrylonitrile by ammoxidation of propylene, comprising the following steps:

[0016] In the corresponding apparatus and reaction system of this process, propylene, ammonia, and air (in the molar ratio of O2) are reacted in a ratio of 1:(1-1.5):(2-10) at a weight hourly space velocity of 0.04-0.1 h⁻¹. -1 The propylene ammoxidation reaction is carried out in a fluidized bed reactor at 400–450℃ and 0.01–0.15 MPa (gauge pressure). The 40–60 μm microsphere catalyst in both the dense and dilute phase sections of the reactor contains α- and γ-phase bismuth molybdate and lattice oxygen active centers, and satisfies the chemical formula Mo… a Bi b Ni c W d Tl e V f P g Si x O y In the formula, the atomic ratios are a = 21–22, b = 1.5–2, c = 4–5, d = 0.8–1, e = 0.09–0.1, f = 0.15–0.2, g = 0.8–1, x = 70–71, and y is the number of oxygen atoms required to satisfy the valence of each element. After the product enters the quench tower and water absorption tower for cooling and neutralization, it is separated and purified by the recovery tower, acetonitrile tower, decyanation tower, separator and product tower to further obtain crude acetonitrile, hydrogen cyanide and refined acrylonitrile products.

[0017] The process for producing acrylonitrile by ammoxidation of propylene provided by the present invention includes a fluidized bed reactor comprising a mixed feed inlet (42) for propylene and ammonia, an air feed inlet (43), a feed distributor for propylene and ammonia (44), an air distribution pipe (45), an internal heat exchange coil (46), a reaction product gas outlet (47), a dense phase reaction zone (48), a dilute phase reaction zone (49), a secondary cyclone separator (50), a cyclone separator inlet (51), a primary feed leg of the cyclone separator (52), and a secondary feed leg of the cyclone separator (53).

[0018] In the process for producing acrylonitrile by ammoxidation of propylene provided by the present invention, the catalyst contains bismuth molybdate active components of α and γ phases with a Mo / Bi atomic ratio of 0.5 to 3.

[0019] In the process method for producing acrylonitrile by ammoxidation of propylene provided by the present invention, the catalyst composition includes a pentasil-type molecular sieve prepared by V element and part of SiO2 component with a Si / V atomic ratio of 50 to 100, and lattice oxygen active centers are formed in its framework structure.

[0020] The process for producing acrylonitrile by ammoxidation of propylene provided by the present invention comprises a reaction section, a recovery and separation section, and a refining section; including a fluidized bed reactor (1), a quench tower (2), a water absorption tower (3), a recovery tower (4), an acetonitrile tower (5), a decyanation tower (6), a product tower (7), a tower top gas condenser (8-13), a tower bottom liquid pump (14-16), a tower top circulation and side stream extraction pump (17, 20), an oil layer extraction pump (18, 19), a separator (21, 22), a tower bottom reboiler (23-25), a tower side stream cooler (26, 27); an evaporator (28, 29); propylene (30), ammonia (31), air (32), water (33), sulfuric acid (34), extraction (35, 36), venting (37), a compressor (38), ammonium sulfate recovery (39), wastewater treatment (40), and acrylonitrile product (41).

[0021] In the process method for producing acrylonitrile by ammoxidation of propylene provided by the present invention, the product gas coming out of the reactor contains acrylonitrile, hydrogen cyanide and acetonitrile components. It enters the quench tower (2) and is rapidly cooled to 70-90°C. The unreacted ammonia in the reaction gas is neutralized with sulfuric acid (34) added to the quench tower (2) to generate ammonium sulfate (39), which can be further recovered to obtain the ammonium sulfate product; the gas is further cooled to 30-50°C.

[0022] In the process of producing acrylonitrile by ammoxidation of propylene provided by the present invention, the product gas is cooled and enters a water absorption tower (3) to absorb the organic materials contained therein to form a water absorption liquid, which then enters a recovery tower (4). The acrylonitrile, hydrogen cyanide and water vapor distilled from the top of the recovery tower are condensed and then separated into an aqueous phase and an organic phase in a separator (21) of the recovery tower.

[0023] In the process method for producing acrylonitrile by ammoxidation of propylene provided by the present invention, the gas phase containing acetonitrile drawn from the side stream of the recovery tower is sent to the acetonitrile tower (5) to obtain crude acetonitrile product.

[0024] In the process method for producing acrylonitrile by ammoxidation of propylene provided by the present invention, the aqueous phase separated in the recovery tower separator (21) is subjected to heat exchange and circulation and used as absorbent water; the separated organic phase enters the decyanation tower (6) and the product tower (7) in sequence to obtain hydrogen cyanide and acrylonitrile product (41) after distillation and purification, respectively.

[0025] In the process for producing acrylonitrile by ammoxidation of propylene provided by this invention, the absolute pressure at the top of the decyanation tower (6) is 60-90 kPa, and the absolute pressure at the bottom of the tower is 80-110 kPa; the absolute pressure at the top of the product tower (7) is 20-60 kPa, and the absolute pressure at the bottom of the tower is 50-90 kPa. Since both acrylonitrile and hydrogen cyanide are highly toxic, negative pressure operation can effectively prevent material leakage and improve safety.

[0026] The chemicals involved in this invention are commonly used industrial chemical raw materials and products, which can be easily obtained through commercial purchase. The chemical unit operations involved in this invention are conventional operating techniques in the art, well known to those skilled in the art, and routinely used in industrial production processes.

[0027] The beneficial effects of this invention are as follows: The process for producing acrylonitrile by ammoxidation of propylene provided by this invention, including corresponding equipment and reaction systems, enables the ammoxidation reaction process to have a very high conversion rate and product selectivity, resulting in a high yield of acrylonitrile and low by-products. This improves the operational stability and safety of the acrylonitrile unit, optimizes material recycling and reuse, and achieves energy saving and consumption reduction. It is particularly suitable for industrial acrylonitrile production processes. Other features and advantages of this invention will be described in more detail in the following specific embodiments and examples. Attached image description:

[0028] The contents, embodiments, and effects of this invention will be further described with reference to the accompanying drawings. Other features, objectives, and advantages of this application will become clearer, but this does not limit the broad interpretation of this invention.

[0029] Figure 1 is a schematic flow diagram of a process for producing acrylonitrile by ammoxidation of propylene according to the present invention.

[0030] Figure 2 is a schematic diagram of a fluidized bed reactor for a process of producing acrylonitrile by ammoxidation of propylene according to the present invention.

[0031] In Figure 1: 1-Fluidized bed reactor; 2-Quick quench tower; 3-Water absorption tower; 4-Recovery tower; 5-Acetonitrile tower; 6-Decyanation tower; 7-Finish product distillation tower; 8, 9, 10, 11, 12, 13-Top gas condenser; 14, 15, 16-Bottom liquid pump; 17-Upper circulation pump of the quick quench tower; 18, 19-Oil extraction pump; 20-Side stream pump of the absorption tower; 21, 22-Separator; 23, 24, 25-Bottom reboiler; 26, 27-Side stream cooler; 28, 29-Evaporator; 30-Propylene; 31-Ammonia; 32-Air; 33-Air; 34-Sulfuric acid; 35, 36-Production; 37-Vent; 38-Compressor; 39-Ammonium sulfate recovery; 40-Wastewater treatment; 41-Acrylonitrile product.

[0032] In Figure 2: 42-Propylene and ammonia mixed feed inlet; 43-Air feed inlet; 44-Propylene and ammonia feed distributor; 45-Air distribution pipe; 46-Heat exchange coil inside the reactor; 47-Reaction product outlet; 48-Dense phase reaction zone inside the reactor; 49-Dilute phase reaction zone inside the reactor; 50-Secondary cyclone separator; 51-Cyclone separator inlet; 52-Primary feed leg of the cyclone separator; 53-Secondary feed leg of the cyclone separator.

[0033] It should be noted that, for the purposes of brevity, clarity and ease of description, the process diagrams and reactor diagrams used to illustrate the present invention only show the most core related units and contents; and do not list in detail other equipment and components that are also needed in the present invention. Detailed Implementation

[0034] The following will illustrate the specific implementation process of the present invention through examples, with reference to the flowchart in Figure 1 and the reactor diagram in Figure 2, and further describe the content and effects of the present invention. The examples are illustrative explanations of the implementation methods of the present invention, but do not limit the broad interpretation of the present invention.

[0035] Comparative Example

[0036] The invention content in relatively classic patent documents is used for comparison, and the catalysts, conversion methods and recovery and purification processes disclosed in the embodiments of USP3746657 and USP6107509 are used for comparative illustration of the present invention.

[0037] Example

[0038] In this embodiment, the steps in the embodiments of Chinese Invention Patent Application No. 202411922598.X, "An Acrylonitrile Catalyst and Its Preparation Method and Application," were first followed to prepare and obtain a catalyst that meets the requirements of this invention. The chemical formula of the catalyst in this embodiment is: Mo 21.6 Bi 1.8 Ni 4.2 W 0.9 Tl 0.1 V 0.1 P 0.9 Si 70 O 217 The microspheres have an average particle size of 50 micrometers and contain α-phase bismuth molybdate with a Mo / Bi atomic ratio of 1.5 and γ-phase bismuth molybdate with a Mo / Bi atomic ratio of 0.5, as well as a pentasil-type molecular sieve with a Si / V molar ratio of 77. The lattice oxygen active sites on the molecular sieve framework can be used as active centers for catalyzing the ammonia oxidation reaction process.

[0039] In the propylene ammoxidation process, the reactants, liquid propylene (30) and liquid ammonia (31), are mixed after passing through evaporators (28, 29) and then enter the fluidized bed propylene ammoxidation reactor (1) through the propylene and ammonia mixing inlet (42) and the feed distributor (44). Air (32) is filtered and compressed by an air compressor (38) and then enters the reactor (1) through the air inlet (43) and the air distribution pipe (45) to participate in the ammoxidation reaction. In the start-up reaction stage, the air needs to be mixed with the superheated gas after combustion provided in the start-up heater to increase the temperature in the reactor and make the bed temperature reach 435℃ after the reaction stabilizes. The pressure in the reactor is 0.04MPa. The molar ratio of propylene:ammonia:air with O2 is 1:1.2:10, and the weight hourly space velocity is 0.05h. -1 .

[0040] In the fluidized bed reactor (1) and under the above reaction conditions, propylene, ammonia, and air undergo an ammonia oxidation reaction under the catalytic action of the catalyst active center of the present invention to produce acrylonitrile. Simultaneously, hydrogen cyanide, acetonitrile, carbon monoxide, carbon dioxide, acrolein, acrylic acid, and water are also produced. The rising product gas also includes some unreacted propylene, ammonia, oxygen, and nitrogen. The reaction temperature is controlled by heat extraction from the highly exothermic reaction process using water and coolant in the heat exchange coil (46) inside the reactor.

[0041] The product gas generated by the reaction enters the cyclone separator (50) in the fluidized bed reactor (1) through the cyclone separator inlet (51) for gas-solid separation. The catalyst carried by the reaction gas returns to the dense phase reaction zone (48) and dilute phase reaction zone (49) in the reactor through the cyclone separator feed legs (52, 53). The reaction product gas effluent flows out from the reactor outlet (47), and after being cooled by heat exchange in the top gas condenser (8), it is sent to the quench tower (2).

[0042] The reaction gas from the reactor (1) enters the quench tower (2) from the bottom section of the tower. It is cooled and neutralized by circulating wastewater and sulfuric acid solution (34) using circulating pumps (14, 17). The product gas after the reaction is rapidly cooled to about 70°C by spray washing. The unreacted ammonia in the reaction gas is neutralized to generate ammonium sulfate for ammonium sulfate recovery (39).

[0043] After being acid-washed and neutralized, the product gas is further cooled to about 30°C and sent to the bottom of the water absorption tower (3). In the tower, water is used to absorb the acrylonitrile, acetonitrile, hydrogen cyanide and other organic matter. The solution is sent to the recovery tower (4). Most of the gas components, such as carbon monoxide, carbon dioxide, nitrogen and unreacted oxygen and hydrocarbons, are released through the top of the tower after treatment (37).

[0044] In the recovery tower (4), acrylonitrile, hydrogen cyanide and acetonitrile are separated by extractive distillation using water as a solvent. The acrylonitrile, hydrogen cyanide and water vapor at the top of the tower are condensed (9, 10) and separated into organic phase and aqueous phase in the separator (21). The aqueous phase is recycled and the organic phase, mainly crude acrylonitrile, is sent to the decyanation tower (6). The gas phase containing acetonitrile collected from the side stream of the recovery tower is sent to the acetonitrile tower (5). Through negative pressure operation, the pressure at the top of the tower is 60 kPa and the pressure at the bottom of the tower is 80 kPa. Acetonitrile is collected from the top of the tower (35) and used to produce acetonitrile products.

[0045] Hydrogen cyanide is separated from the material entering the decyanation tower (6), and the dehydrated acrylonitrile is obtained from the bottom of the tower and sent to the product tower (7). Under negative pressure operation, the pressure at the top of the tower is 20 kPa and the pressure at the bottom of the tower is 50 kPa. The acrylonitrile and water obtained at the top of the tower are used to obtain the acrylonitrile product from the side stream (41), which is then cooled and sent to the product storage tank. The bottom liquid is returned to the recovery tower (4) for recycling.

[0046] The conversion results of propylene ammoxidation to acrylonitrile obtained using the present invention, and the results used for comparative examples, can be found in Table 1.

[0047] Table 1: Comparison of stable operation results of propylene ammoxidation process in the examples and comparative examples

[0048] The experimental results after stable operation of the comparative examples and the control examples show that the propylene conversion degree and acrylonitrile selectivity are superior to those of the control examples. This demonstrates that, compared with existing technologies, the process for producing acrylonitrile by ammoxidation of propylene provided by this invention, including the corresponding reaction apparatus and process system, achieves both a high degree of ammoxidation conversion and good acrylonitrile product selectivity; byproducts such as carbon monoxide and carbon dioxide are also relatively low; and the process is made safer and more reliable through negative pressure operation and wastewater reuse; the optimized material circulation and heat utilization in the process also better meet the requirements of energy conservation and environmental protection. This indicates that the process method of this invention is more suitable for industrial production processes and can achieve better long-term stable operation results.

[0049] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A process for the ammoxidation of propylene to acrylonitrile, characterized in that, In the corresponding apparatus and reaction system of this method, propylene, ammonia, and air (in the molar ratio of O2) are reacted in a ratio of 1:(1-1.5):(2-10) at a weight hourly space velocity of 0.04-0.1 h⁻¹. -1 The propylene ammoxidation reaction is carried out in a fluidized bed reactor at 400–450℃ and 0.01–0.15 MPa (gauge pressure). The 40–60 μm microsphere catalyst in both the dense and dilute phase sections of the reactor contains α- and γ-phase bismuth molybdate and lattice oxygen active centers, and satisfies the chemical formula Mo… a Bi b Ni c W d Tl e V f P g Si x O y In the formula, the atomic ratios are a = 21–22, b = 1.5–2, c = 4–5, d = 0.8–1, e = 0.09–0.1, f = 0.15–0.2, g = 0.8–1, x = 70–71, and y is the number of oxygen atoms required to satisfy the valence of each element. After the product enters the quench tower and water absorption tower for cooling and neutralization, it is separated and purified by the recovery tower, acetonitrile tower, decyanation tower, separator and product tower to further obtain crude acetonitrile, hydrogen cyanide and refined acrylonitrile products.

2. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The fluidized bed reactor includes a mixed feed inlet (42) for propylene and ammonia, an air feed inlet (43), a feed distributor for propylene and ammonia (44), an air distribution pipe (45), an internal heat exchange coil (46), a reaction product gas outlet (47), a dense phase reaction zone (48), a dilute phase reaction zone (49), a secondary cyclone separator (50), a cyclone separator inlet (51), a primary feed leg of the cyclone separator (52), and a secondary feed leg of the cyclone separator (53).

3. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The catalyst contains α and γ phase bismuth molybdate active components with a Mo / Bi atomic ratio of 0.5 to 3.

4. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The catalyst composition includes a pentasil-type molecular sieve prepared by combining V and a portion of SiO2 with a Si / V atomic ratio of 50 to 100, and lattice oxygen active centers are formed in its framework structure.

5. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The reaction system consists of a reaction section, a recovery and separation section, and a refining section; it includes a fluidized bed reactor (1), a quench tower (2), a water absorption tower (3), a recovery tower (4), an acetonitrile tower (5), a decyanation tower (6), a product tower (7), a tower top gas condenser (8-13), a tower bottom liquid pump (14-16), a tower top circulation and side stream extraction pump (17, 20), an oil layer extraction pump (18, 19), a separator (21, 22), a tower bottom reboiler (23-25), a tower side stream cooler (26, 27); an evaporator (28, 29); propylene (30), ammonia (31), air (32), water (33), sulfuric acid (34), extraction (35, 36), venting (37), a compressor (38), ammonium sulfate recovery (39), wastewater treatment (40), and acrylonitrile product (41).

6. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The product gas from the reactor contains acrylonitrile, hydrogen cyanide and acetonitrile. It enters the quench tower (2) and is rapidly cooled to 70-90°C. Unreacted ammonia in the reaction gas is neutralized with sulfuric acid (34) added to the quench tower (2) to generate ammonium sulfate (39). The gas is further cooled to 30-50°C.

7. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The product gas is cooled and enters the water absorption tower (3) to absorb the organic materials contained therein to form a water absorption liquid, which then enters the recovery tower (4). The acrylonitrile, hydrogen cyanide and water vapor distilled from the top of the recovery tower are condensed and then separated into aqueous and organic phases in the separator (21) of the recovery tower.

8. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The gas phase containing acetonitrile extracted from the side stream of the recovery tower is fed into the acetonitrile tower (5) to obtain crude acetonitrile product.

9. The process for producing acrylonitrile by ammoxidation of propylene according to claim 1, characterized in that, The aqueous phase separated in the recovery tower separator (21) is heat exchanged and circulated, and used as absorbent water; the separated organic phase enters the decyanation tower (6) and the product tower (7) in sequence to obtain hydrogen cyanide and acrylonitrile product (41) after distillation and purification, respectively.

10. The process for producing acrylonitrile by ammoxidation of propylene according to claim 9, characterized in that, The absolute pressure at the top of the decyanation tower (6) is 60-90 kPa, and the absolute pressure at the bottom of the tower is 80-110 kPa; the absolute pressure at the top of the product tower (7) is 20-60 kPa, and the absolute pressure at the bottom of the tower is 50-90 kPa.

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