Process method for preparing acrylonitrile through propylene ammoxidation

Abstract

A process method for preparing acrylonitrile through propylene ammoxidation belongs to the field of chemical engineering, and is characterized in that in a corresponding device and a reaction system of the method, propylene, ammonia gas and air (in terms of O2) enter a fluidized bed reactor at 400-450 DEG C and 0.01-0.15 MPa for reaction according to a ratio of 1: (1-1.5): (2-10) at a weight hourly space velocity of 0.04-0.1 h <-1 >; the micro-sphere catalyst with the particle size of 40-60 microns in the dense-phase section and the dilute-phase section has alpha-phase bismuth molybdate, gamma-phase bismuth molybdate and lattice oxygen active centers and meets the chemical formula MoaBibNicWdTleVfPgSixOy, the atomic ratio a in the formula is 21-22, the atomic ratio b in the formula is 1.5-2, the atomic ratio c in the formula is 4-5, the atomic ratio d in the formula is 0.8-1, the atomic ratio e in the formula is 0.09-0.1, the atomic ratio f in the formula is 0.15-0.2, the atomic ratio g in the formula is 0.8-1, the atomic ratio x in the formula is 70-71, and y is the number of oxygen atoms needed by the atomic valence of all elements; a product enters a quench tower and a water absorption tower to be neutralized and cooled, and then passes through a recovery tower, an acetonitrile tower, a decyanation tower, a layering device and a finished product tower to realize separation of a water phase and an organic phase, so that crude acetonitrile, hydrocyanic acid and refined acrylonitrile are further obtained. The process is good in conversion degree and product selectivity, stable and reliable in operation, energy-saving and environment-friendly.

Description

Technical Field

[0001] The present invention relates to a process for preparing acrylonitrile by ammoxidation of propylene, and more specifically to a process for preparing acrylonitrile by ammoxidation of propylene in a fluidized bed, a conversion device and a reaction system, and belongs to the technical field of chemical industry. Background Art

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

[0003] The industrial production of acrylonitrile has experienced the acetylene method, ethylene oxide method, propylene and propane ammoxidation method. Among them, the acetylene method and ethylene oxide method are the early acrylonitrile production methods, which have been eliminated due to serious environmental pollution and high production costs; the propane direct ammoxidation method, due to the low selectivity of the product acrylonitrile of the current technology, leads to low utilization rate of raw material propane, its propane conversion rate does not exceed 90%, and the acrylonitrile selectivity is less than 70%.

[0004] The current industrial production is mainly based on the direct ammoxidation process of propylene developed by Sohio Company in the United States in the 1960s. After more than 60 years of development and improvement, it has become increasingly mature, such as USP2481826, USP2904580, and USP5175334. In the mainstream existing technology, the catalyst mainly uses a Mo-Bi type catalyst for the ammoxidation of propylene to prepare acrylonitrile, as described in patent documents such as USP3746657, USP4264476, USP5093299, and USP5212137. In the process of industrial production of acrylonitrile, it is necessary to place the microsphere catalyst in a fluidized bed reactor, and convert propylene through an ammoxidation reaction process under the conditions of ammonia, air, and a relatively high reaction temperature, and obtain a purified acrylonitrile product through subsequent absorption, fractionation, and other processes.

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

[0006] In the further improvement of the prior art, a production system and production method of high-purity acrylonitrile are provided as in CN117463253A, and the production system comprises a reaction unit, a quenching deoxidation unit, a recovery unit, a dehydrocyanic acid removal unit and a product refining unit connected in sequence, which can realize the continuous industrial production of high-purity acrylonitrile prepared by ammoxidation of propylene. At the same time, the provided production method is matched with the production system, and a catalyst with a special ratio is provided to catalyze the ammoxidation process of propylene, so as to improve the yield of acrylonitrile and reduce the output of organic oxygen-containing byproducts. By removing impurities such as oxygen-containing compounds and hydrocyanic acid through the specific production process in the quenching deoxidation unit, the recovery unit and the dehydrocyanic acid removal unit, the purity of the acrylonitrile product finally prepared can reach more than 99.97wt%, and the content of total oxygen-containing compounds is below 5 micrograms / gram.

[0007] In addition to focusing on the reaction process of ammoxidation, USP3352764 also discloses the separation of crude olefinically unsaturated nitriles, such as acrylonitrile and methacrylonitrile, from aqueous solutions containing saturated aliphatic nitriles such as acetonitrile, relatively low molecular weight carbonyl compounds, and relatively high molecular weight soluble organic compounds. USP3885928, in the recovery and purification of acrylonitrile or methacrylonitrile obtained by ammoxidation of propylene or isobutylene, the water layer in the tower for removing hydrocyanic acid from the nitrile is recycled to the quenching tower, and the hot gas from the reactor is directly contacted with the recycled water flow, which is better utilized in the neutralization link.

[0008] USP3936360 saves a lot of operating costs and improves the recovery rate of acrylonitrile and methacrylonitrile by recycling the distillate at the bottom of the product cooling tower to the quench liquid of the reactor effluent quenching system. USP4234510 recovers the reactor effluent of propylene or isobutylene ammoxidation reaction by cooling the reactor effluent to a temperature of about 40°C to 100°C; by using direct contact cooling, preferably using a water-containing stream to obtain a gaseous stream containing acrylonitrile or methacrylonitrile, and using indirect contact cooling to cool it into a gaseous stream, and condense at least some acrylonitrile or formyl nitrile therefrom. USP6107509, in the method for preparing acrylonitrile and methacrylonitrile, purifies and recovers unsaturated nitrile by adjusting the absorption, separation and circulation links between multiple towers, and achieves the purpose of optimization. CN102659625B also discloses similar content, purifies and recovers unsaturated nitrile by optimizing the absorption, separation and circulation between multiple towers, and improves the reliability and energy utilization of the device.

[0009] USP5457223 also discloses a process for simultaneously eliminating waste in the process of manufacturing acrylonitrile, by preparing acrylonitrile by direct ammoxidation of propylene / propane, ammonia and an oxygen-containing gas, such as air, over a fluidized bed catalyst; wherein the improvement includes introducing methanol into the upper part of the reactor at a position where the methanol reacts with at least a portion of the exchange ammonia without affecting the acrylonitrile yield; preferably, the methanol is introduced into the reactor at a temperature below its coking temperature, and in particular, when an oxygen-deficient fluidized bed catalyst is used, additional oxygen-containing gas is introduced into the reaction at a distance of about 8 to 14 inches from the methanol feed position. USP5466857 also discloses a method for reducing the amount of waste generated in the process of preparing acrylonitrile, which is to introduce an additional amount of oxygen-containing gas, preferably air, into the upper part of the fluidized bed reactor in the absence of any oxygen-containing compound to react with at least some of the unreacted ammonia to reduce the amount of unreacted ammonia in the reactor effluent.

[0010] CN106430245A discloses an improved acrylonitrile sulfate-free ammonium process and reaction device, wherein a high-ammonia product gas stream contacts an absorption liquid in the lower section of a quench tower to absorb part of the unreacted ammonia in the high-ammonia product gas stream, contacts an ammonia-poor absorption liquid in the upper section of the quench tower to absorb the unabsorbed ammonia in the lower section of the quench tower, and the obtained lower section absorption liquid is stripped and then separated into light and heavy components in a three-phase separation device, and then reacted in a catalytic wet oxidation reactor to remove organic matter and ammonia nitrogen, and then returned to the lower section of the quench tower for absorption of unreacted ammonia; a high-purity ammonia stream is obtained after distillation of the crude ammonia gas stream; and the problem of easy blockage of the device in the prior art is solved.

[0011] In a method and device for producing acrylonitrile disclosed in CN113620839A, a rich liquid containing acrylonitrile is stripped and separated in a recovery tower, a gas phase stream containing acrylonitrile is obtained at the top of the recovery tower, and a high-temperature lean liquid substantially free of acrylonitrile is obtained at the bottom of the recovery tower, which is flashed, and the obtained steam is pressurized and recovered as a heat source for the recovery tower, wastewater evaporator, decyanation tower and finished product tower, and this low-grade heat source is utilized to achieve the purpose of energy saving and consumption 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 improved fluidized bed reactors for acrylonitrile production.

[0013] In summary, the direct ammoxidation of propylene to produce acrylonitrile has undergone significant improvements in its reaction process and catalysts since its initial industrialization, and has made significant progress over the past few decades. The yield of acrylonitrile has increased from 70% to 79% at the beginning of development to the current 80% to 86%. However, there is still much room for development and improvement in the reaction process route and the yield of acrylonitrile. The large amount of wastewater and waste gas, the hazards of toxic substances, and energy saving all need to be improved and optimized. Summary of the invention

[0014] The purpose of the present invention is to provide an industrial production method of acrylonitrile, which can improve the conversion efficiency and product selectivity of the propylene ammoxidation process through optimization and improvement of the traditional process flow, increase the yield of acrylonitrile products, improve the stability and reliability of the device during operation, and achieve energy saving and consumption reduction in the process.

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

[0016] In the corresponding device and reaction system of the process method, propylene, ammonia and air (in the form of O 2 The molar ratio is 1:(1-1.5):(2-10), and the weight hourly space velocity is 0.04-0.1h -1 The catalyst enters a fluidized bed reactor at 400-450°C and 0.01-0.15 MPa (gauge pressure) to carry out propylene ammoxidation reaction; the microsphere catalyst with a particle size of 40-60 μm in the dense phase section and the dilute phase section of the reactor has 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 , 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 atomic valence of each element; after the product enters the quench tower and the water absorption tower for cooling and neutralization, it is separated and purified by the recovery tower, acetonitrile tower, decyanation tower, classifier and finished product tower to further obtain crude acetonitrile, hydrocyanic acid and refined acrylonitrile products.

[0017] In a process for preparing acrylonitrile by propylene ammoxidation provided by the present invention, the fluidized bed reactor comprises a mixed feed port (42) for propylene and ammonia, an air feed port (43), a feed distributor (44) for propylene and ammonia, an air distribution pipe (45), a heat exchange coil (46) inside the reactor, 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 cyclone separator first feed leg (52), and a cyclone separator second feed leg (53).

[0018] In the process for preparing acrylonitrile by propylene ammoxidation provided by the present invention, the Mo / Bi atomic ratio of the α-phase and γ-phase bismuth molybdate active components contained in the catalyst is 0.5-3.

[0019] In the process for preparing acrylonitrile by propylene ammoxidation provided by the present invention, the catalyst component comprises V element and part of SiO 2 The invention discloses a pentasil type molecular sieve having a Si / V atomic ratio of 50 to 100 and forming a lattice oxygen active center in its framework structure.

[0020] In a process for preparing acrylonitrile by ammoxidation of propylene provided by the present invention, the reaction system is composed of a reaction part, a recovery and separation part, and a refining part; it comprises a fluidized bed reactor (1), a quenching tower (2), a water absorption tower (3), a recovery tower (4), an acetonitrile tower (5), a decyanation tower (6), a finished product tower (7), a tower top gas condenser (8-13), a tower bottom liquid pump (14-16), a tower top circulation and side line extraction pump (17, 20), an oil layer extraction pump (18, 19), a stratifier (21, 22), a tower bottom reboiler (23-25), a tower side line 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), sewage treatment (40), and acrylonitrile finished product (41).

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

[0022] In a process for preparing acrylonitrile by propylene ammoxidation provided by the present invention, the product gas is cooled and then enters a water absorption tower (3), where it absorbs organic materials contained therein with water to form a water absorption liquid, and then enters a recovery tower (4); acrylonitrile, hydrocyanic acid and water vapor evaporated from the top of the recovery tower are condensed and separated into an aqueous phase and an organic phase in a recovery tower separator (21).

[0023] In the process for preparing acrylonitrile by ammoxidation of propylene provided by the present invention, the gas phase containing acetonitrile extracted from the side line of the recovery tower is sent to an acetonitrile tower (5) to obtain a crude acetonitrile product.

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

[0025] In the process for preparing acrylonitrile by propylene ammoxidation provided by the present 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 finished 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 hydrocyanic acid are highly toxic, negative pressure operation can effectively prevent leakage of materials and improve safety.

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

[0027] The beneficial effects of the present invention are as follows: the process for preparing acrylonitrile by propylene ammoxidation provided by the present invention includes a corresponding device and reaction system, which can make the propylene ammoxidation reaction process have a very good conversion degree and product selectivity, a high yield of product acrylonitrile and low by-products, improve the operation stability and safety reliability of the acrylonitrile device, optimize the circulation and reuse of materials, achieve energy saving and consumption reduction, and is particularly suitable for industrialized acrylonitrile production processes. Other features and advantages of the present invention will also be described in more detail in the subsequent specific embodiments and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The content, implementation mode and use effect of the present invention will be further described with reference to the accompanying drawings, and other features, purposes and advantages of the present application will become clearer, but the broad interpretation of the present invention is not limited thereby.

[0029] Figure 1 The present invention is a schematic flow diagram of a process for preparing acrylonitrile by propylene ammoxidation.

[0030] Figure 2 The present invention is a schematic diagram of a fluidized bed reactor for a process for preparing acrylonitrile by propylene ammoxidation.

[0031] Figure 1 In: 1- fluidized bed reactor; 2- quenching tower; 3- water absorption tower; 4- recovery tower; 5- acetonitrile tower; 6- decyanation tower; 7- finished product distillation tower; 8, 9, 10, 11, 12, 13- top gas condenser; 14, 15, 16- bottom liquid pump; 17- quenching tower upper circulation pump; 18, 19- oil layer extraction pump; 20- absorption tower side line extraction pump; 21, 22- separator; 23, 24, 25- bottom reboiler; 26, 27- tower side line cooler; 28, 29- evaporator; 30- propylene; 31- ammonia; 32- air; 33- air; 34- sulfuric acid; 35, 36- extraction; 37- venting; 38- compressor; 39- ammonium sulfate recovery; 40- wastewater treatment; 41- acrylonitrile finished product.

[0032] Figure 2 In the figure: 42-mixed feed port for propylene and ammonia; 43-air feed port; 44-feed distributor for propylene and ammonia; 45-air distribution pipe; 46-heat exchange coil inside the reactor; 47-reaction product outlet; 48-dense phase reaction zone in the reactor; 49-dilute phase reaction zone in the reactor; 50-secondary cyclone separator; 51-cyclone separator inlet; 52-first-stage feed leg of cyclone separator; 53-second-stage feed leg of cyclone separator.

[0033] It should be noted that, for the purpose of simplicity, clarity and ease of description, the process schematic diagram and reactor schematic diagram used to illustrate the present invention only show the most core-related units and contents of the invention; and do not list in detail some other equipment and components that are also needed in the present invention. DETAILED DESCRIPTION

[0034] The following will be combined Figure 1 Flowchart and Figure 2 The specific implementation process of the present invention is explained by examples, and the content and use effect of the present invention are further described. The examples are used as illustrative explanations of the implementation mode of the present invention, but the broad interpretation of the present invention is not limited thereto.

[0035] Comparative Example

[0036] The invention contents in the more classic patent documents are used as a comparison, and the catalysts, conversion methods and recovery and purification process methods disclosed in the embodiments of USP3746657 and USP6107509 are referred to for comparison and explanation of the present invention.

[0037] Example

[0038] In this embodiment, firstly, referring to the steps in the embodiment of Chinese invention patent application No. 202411922598.X "A kind of acrylonitrile catalyst and its preparation method and application" applied by the inventor, the catalyst required by the content of the present invention is prepared and obtained. The chemical expression of the catalyst composition of the 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 average particle size of the microspheres is 50 microns. It contains α-phase bismuth molybdate with a Mo / Bi atomic ratio of 1.5 and γ-phase bismuth molybdate with a ratio of 0.5, and 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 catalytic ammonia oxidation reactions.

[0039] In the process of propylene ammoxidation, liquid propylene (30) and liquid ammonia (31) as reaction raw materials are mixed after passing through evaporators (28, 29) and then enter a fluidized bed propylene ammoxidation reactor (1) through a propylene and ammonia mixing feed port (42) and a feed distributor (44); air (32) is filtered and compressed by an air compressor (38) and then enters the reactor (1) through an air feed port (43) and an air distributor (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 so that the bed temperature reaches 435°C after the reaction is stably operated; the pressure in the reactor is 0.04 MPa; propylene: ammonia: air is 0 2 The molar ratio 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 are subjected to an ammoxidation reaction under the catalytic action of the active center of the catalyst of the present invention to produce acrylonitrile, and 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, etc. The water and coolant in the heat exchange coil (46) inside the reactor are used to remove heat from the highly exothermic reaction process to control the reaction temperature.

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

[0042] The reaction gas from the reactor (1) enters the quenching tower (2) from the lower section of the tower kettle, and is cooled and neutralized by circulating waste water and sulfuric acid solution (34) using circulating pumps (14, 17). The product gas after the reaction is quenched 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] The product gas after acid washing and neutralization is further cooled to about 30°C and sent to the bottom of the water absorption tower (3), where it is countercurrently absorbed with water to recover acrylonitrile, acetonitrile, hydrocyanic acid 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 pass through the top of the tower and are discharged after treatment (37).

[0044] In the recovery tower (4), water is used as a solvent to separate acrylonitrile, hydrocyanic acid and acetonitrile by extractive distillation. The acrylonitrile, hydrocyanic acid and water vapor at the top of the tower are passed through condensers (9, 10) and separated into an organic phase and an aqueous phase in a separator (21). The aqueous phase is circulated and the organic phase is mainly crude acrylonitrile, which is sent to a decyanation tower (6). The gas phase containing acetonitrile extracted from the side line of the recovery tower is sent to an acetonitrile tower (5). Through negative pressure operation, the top pressure of the tower is 60KPa and the bottom pressure of the tower is 80KPa. Acetonitrile is extracted from the top of the tower (35) and used to produce acetonitrile products.

[0045] The hydrogen cyanide is separated from the material entering the decyanation tower (6), and the dehydrated acrylonitrile is obtained in the bottom of the tower and sent to the finished product tower (7). Through negative pressure operation, the top pressure of the tower is 20KPa and the bottom pressure of the tower is 50KPa; the acrylonitrile and water obtained at the top of the tower are taken out from the side line to obtain the acrylonitrile product (41), which is sent to the product storage tank after cooling; the bottom liquid returns to the recovery tower (4) for circulation.

[0046] The conversion result data of preparing acrylonitrile by propylene ammoxidation obtained by the present invention and the results used for comparative examples can be seen in Table 1.

[0047] Table 1: Comparison of stable operation results of propylene ammoxidation process of Example and Comparative Example

[0048] project Acrylonitrile yield / % Acrylonitrile selectivity / % Carbon oxide yield / % Acrylic acid + acrolein yield / % Example 83.5 84.3 3.7 0.6 Comparative Example 80.7 81.8 4.5 0.8

[0049] By comparing the test results after stable operation of the embodiment and the comparative example, the propylene conversion degree and the product acrylonitrile selectivity are better than the comparative example. It is shown that compared with the prior art, the process method for preparing acrylonitrile by propylene ammoxidation provided by the present invention, including the corresponding reaction device and process system, has both a higher ammoxidation conversion degree and a better acrylonitrile product selectivity; by-products such as carbon monoxide and carbon dioxide are also relatively low; through negative pressure operation, wastewater reuse and other measures, the process operation is safer and more reliable; due to the full optimization of material circulation and heat utilization in the process, it is also more in line with the requirements of energy conservation and environmental protection; it shows that the process method of the present invention is more suitable for industrial production processes and can achieve better long-term stable operation results.

[0050] It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A process for preparing acrylonitrile by ammoxidation of propylene, characterized in that: In the corresponding device and reaction system of the method, propylene, ammonia and air (calculated as O2 molar ratio) are in a ratio of 1:(1-1.5):(2-10) at a weight hourly space velocity of 0.04-0.1h -1 The catalyst enters a fluidized bed reactor at 400-450°C and 0.01-0.15 MPa (gauge pressure) to carry out propylene ammoxidation reaction; the microsphere catalyst with a particle size of 40-60 μm in the dense phase section and the dilute phase section of the reactor has 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 , 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 atomic valence of each element; after the product enters the quench tower and the water absorption tower for cooling and neutralization, it is separated and purified by the recovery tower, acetonitrile tower, decyanation tower, classifier and finished product tower to further obtain crude acetonitrile, hydrocyanic acid and refined acrylonitrile products.

2. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The fluidized bed reactor comprises a mixed feed port (42) for propylene and ammonia, an air feed port (43), a feed distributor (44) for propylene and ammonia, an air distribution pipe (45), a heat exchange coil (46) inside the reactor, 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 cyclone separator first feed leg (52), and a cyclone separator second feed leg (53).

3. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The Mo / Bi atomic ratio of the α-phase and γ-phase bismuth molybdate active components contained in the catalyst is 0.5-3.

4. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The catalyst component composition comprises a pentasil type molecular sieve prepared from V element and part of SiO2 component at a Si / V atomic ratio of 50 to 100, and a lattice oxygen active center is formed in its skeleton structure.

5. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The reaction system is composed of a reaction part, a recovery and separation part, and a refining part; it includes a fluidized bed reactor (1), a quenching tower (2), a water absorption tower (3), a recovery tower (4), an acetonitrile tower (5), a decyanation tower (6), a finished product tower (7), a tower top gas condenser (8-13), a tower bottom liquid pump (14-16), a tower top circulation and side line extraction pump (17, 20), an oil layer extraction pump (18, 19), a stratifier (21, 22), a tower bottom reboiler (23-25), a tower side line 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), sewage treatment (40), and an acrylonitrile finished product (41).

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

7. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The product gas is cooled and enters a water absorption tower (3), where it absorbs the organic material contained therein with water to form a water absorption liquid, and then enters a recovery tower (4); acrylonitrile, hydrocyanic acid and water vapor evaporated from the top of the recovery tower are condensed and separated into an aqueous phase and an organic phase in a recovery tower separator (21).

8. The process for preparing acrylonitrile by propylene ammoxidation according to claim 1, characterized in that: The gas phase containing acetonitrile extracted from the side line of the recovery tower is sent to an acetonitrile tower (5) to obtain a crude acetonitrile product.

9. The process for preparing acrylonitrile by propylene ammoxidation 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 absorption water; the separated organic phase enters the decyanation tower (6) and the finished product tower (7) in sequence to obtain hydrocyanic acid and acrylonitrile finished product (41) after distillation and purification, respectively.

10. The process for preparing acrylonitrile by propylene ammoxidation 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 finished 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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