A method of reducing acrylonitrile loss

Abstract

The application provides a method for reducing acrylonitrile loss, which comprises the following steps: S1: introducing the product of propylene ammoxidation reaction and quenching liquid into a gas-liquid static mixer, so that the product of propylene ammoxidation reaction and the quenching liquid generate shearing force and tangential stress under the action of the mixer to form turbulent flow, and a gas-liquid mixture flow I is obtained; S2: the gas-liquid mixture flow I is introduced from the upper part of a high-efficiency quencher which is vertically placed, the product of the reaction is quenched in the high-efficiency quencher, and a flow II is obtained after ammonia in the reaction gas is absorbed. The product of propylene ammoxidation reaction and the quenching liquid generate shearing force and tangential stress under the action of the flow velocity and the internal structure of the mixer to form turbulent flow, so that the flow is fully mixed to promote the full mixing of the two materials. By using the method, the acrylonitrile loss can be reduced to less than 2.5 wt% during the quenching of the product of propylene ammoxidation reaction, and a good technical effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of acrylonitrile recovery processes, and more particularly to methods for reducing acrylonitrile loss. Background Technology

[0002] Acrylonitrile is an important organic chemical raw material, mainly used in the synthesis of materials such as acrylonitrile-butadiene-styrene copolymer, acrylic fiber, acrylamide, nitrile latex, polymer polyol, nitrile rubber and carbon fiber.

[0003] Currently, the main method for producing acrylonitrile is the propylene ammoxidation process. In a fluidized bed reactor, propylene undergoes an ammoxidation reaction with ammonia and air under the action of a catalyst, yielding acrylonitrile and main byproducts such as acetonitrile, hydrogen cyanide, acrylic acid, and acrolein. The gaseous products exiting the reactor are cooled in a quench tower, then enter an absorption tower to absorb acrylonitrile and other byproducts. Finally, the product is purified and separated to obtain the acrylonitrile product. Low acrylonitrile recovery rate is a common problem in many domestic acrylonitrile plants, especially with a 5-10% loss in the quench tower, significantly impacting the recovery rate and efficiency of the acrylonitrile plant.

[0004] The main function of the quench tower is to cool the acrylonitrile-containing reaction gas at 200°C using water, absorb unreacted ammonia, and remove catalyst particles and some oligomers and other impurities. During the ammoxidation of propylene, to increase propylene yield, unreacted ammonia in the aqueous solution polymerizes with acrylonitrile during quenching. Especially under conditions of high local pH, acrylonitrile and hydrogen cyanide can self-polymerize, which is a significant factor affecting the acrylonitrile yield. Therefore, removing ammonia from the reaction gas is beneficial for improving the acrylonitrile yield.

[0005] CN 116531929 discloses a quench tower device for improving acrylonitrile recovery rate. This patent designs a quench tower device including a cooling tower, a precooling mechanism, a water distribution assembly, and a spray rack. By adjusting the water spray state through a sawtooth groove structure to increase the coverage area, and by using sawtooth filter plates and rotating drive blades to improve filtration and precooling efficiency, it ensures the effective neutralization of ammonia by acid and improves the recovery efficiency of acrylonitrile.

[0006] However, the method described in the aforementioned patent only improved the ammonia removal rate. Research revealed that the ammonia removal rate in the reaction gas is not the sole factor affecting acrylonitrile yield; the greater influence lies in the ammonia removal rate during the quenching process. This is because the sulfuric acid added during quenching reacts with the ammonia in the reaction gas phase in a neutralization reaction, which occurs very rapidly. Compared to the acrylonitrile-related side reactions under the aforementioned ammonia-containing conditions, the neutralization reaction proceeds preferentially. In practice, the slow diffusion between the gas and liquid phases affects the neutralization reaction rate of ammonia and sulfuric acid, thus providing opportunities for acrylonitrile and other substances to react with ammonia and for self-polymerization under alkaline conditions. Summary of the Invention

[0007] The technical problem this invention aims to solve is the high acrylonitrile loss rate in the quenching process of existing technologies. This invention provides a method to reduce the acrylonitrile loss rate in the quenching process. The method provided by this invention features rapid and effective ammonia removal from the reaction gas, low acrylonitrile loss rate, and compact equipment size.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for reducing acrylonitrile loss includes the following steps:

[0010] S1: The products of propylene ammoxidation reaction and the quench liquid are introduced into a gas-liquid static mixer. Under the action of the mixer, the products of propylene ammoxidation reaction and the quench liquid generate shear force and tangential stress, forming turbulence and obtaining gas-liquid mixture flow I. The gas-liquid static mixer is equipped with a mixing component with a spiral structure. When the gas phase products of propylene ammoxidation reaction and the liquid quench liquid enter, the spiral structure controls the gas-liquid mixture to generate shear force and tangential stress, forming turbulence, so that the gas and liquid two-phase materials are fully mixed.

[0011] S2: Gas-liquid mixture stream I enters from the top of the vertically placed high-efficiency quencher. The reaction products are quenched in the high-efficiency quencher, and at the same time, the ammonia in the reaction gas is absorbed to obtain stream II. The reaction products are quenched in the quencher, and at the same time, the sulfuric acid and ammonia in the quench liquid react and are absorbed, thereby reducing the polymerization reaction between ammonia and acrylonitrile and reducing the loss of acrylonitrile.

[0012] S3: Logistics II enters the gas-liquid separation equipment to separate the reaction gas and the quench liquid. At the same time, some catalyst dust particles and a small amount of polymer in the reaction gas precipitate here and are discharged from the system.

[0013] S4: The separated gaseous effluent goes to the subsequent absorption tower, and the separated liquid phase goes to the subsequent ammonia salt recovery unit.

[0014] Preferably, the gas-liquid static mixer in S1 has a length-to-diameter ratio of 5:8, and the internal mixing unit is spiral-shaped.

[0015] Preferably, the velocity of the propylene ammoxidation product gas in the static mixer in S1 is 2-15 m / s, and the mass ratio of the propylene ammoxidation product to the quench liquid is 1:4-8.

[0016] Preferably, the quenching liquid in S1 is composed of deionized water and sulfuric acid.

[0017] Preferably, the residence time of the gas-liquid mixture flow I in S2 in the quench cooler is 10s to 60s, the temperature is 90 to 95℃, and the pressure is 0.03 to 0.05MPa.

[0018] Preferably, in S2, the high-efficiency quencher includes a fluid distributor and multiple vertically arranged small-diameter quenching reaction channels. The small-diameter quenching reaction channels are used to reduce the reaction process of acrylonitrile, acrylic acid, and ammonia, as well as the self-polymerization reaction. By setting the fluid distributor as a small-diameter channel, the diameter of the small-diameter quenching reaction channel is 1.5~3.5mm and the length is 2000~5000mm. This confines the gas and liquid phase materials within a very small range during the quenching process, accelerating the mass and heat transfer between the two phases. This is beneficial to the rapid neutralization reaction of the main reaction, ammonia and sulfuric acid.

[0019] Preferably, the inlet portion of the quench reaction channel is S-shaped, and the connection with the inlet is straight. The S-shaped portion of the reaction channel accounts for 20-40% of the total length. The S-shaped structure can increase the residence time of the gas-liquid mixture I inside, promoting the absorption reaction of ammonia.

[0020] Preferably, the pH value of the material II in S2 is 6.2 to 6.6, in order to reduce the self-polymerization of acrylonitrile, hydrogen cyanide, etc.

[0021] The method for reducing acrylonitrile loss proposed in this invention has the following beneficial effects: This invention uses a static mixer to generate shear force and tangential stress in the propylene ammoxidation gaseous product and the quench liquid under the action of the flow rate and the internal structure of the mixer, forming turbulence, which makes the flow fully mixed and promotes the full mixing of the two materials.

[0022] This invention also innovatively utilizes a high-efficiency quenching device with a multi-channel, small-diameter pipe structure. The radial dimension of a single channel in this device is much smaller than that of a conventional quenching tower. This confines the gas-liquid two-phase materials within a very small area during quenching, accelerating mass and heat transfer between the two phases. This is beneficial for the rapid neutralization reaction of the main reaction, ammonia and sulfuric acid. Simultaneously, by controlling the reaction channel length and residence time, the progress of the main reaction, ammonia and sulfuric acid neutralization, as well as the side reactions of acrylonitrile, acrylic acid, and ammonia, and the self-polymerization reaction, is further controlled, thereby reducing acrylonitrile loss during quenching. Using the method of this invention, the mass transfer efficiency between gas and liquid is improved, the ammonia neutralization reaction rate is accelerated, and the acrylonitrile loss rate in the quenching process is effectively reduced. During the quenching of propylene ammoxidation products, acrylonitrile loss can be reduced to below 2.5 wt%, achieving significant technical results. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0024] Figure 1 This is a schematic diagram of the process of the present invention;

[0025] The components include: 1. Gas-liquid static mixer; 2. High-efficiency quench cooler; 3. Gas-liquid separation equipment; 4. Quenching liquid; 5. Propylene ammoxidation reaction products; 6. Gas phase absorption unit; 7. Ammonia salt recovery unit; and 8. Solid waste discharge. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] The test materials used in the embodiments of the present invention, unless otherwise specified, are all conventional test materials in the art and can be purchased through commercial channels.

[0028] Gas phase products were analyzed using a gas chromatograph, a TCD detector, and a Poropak-N column.

[0029] Example 1

[0030] See appendix Figure 1 The process shown is as follows:

[0031] 200 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of sulfuric acid-containing quenched liquid at a gas velocity of 10 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 6.

[0032] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 1500 mm long and 2 mm in diameter. The quencher is vertically positioned, with the first 25% of its length forming an S-shape and the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0033] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0034] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 1.74%.

[0035] Example 2

[0036] As attached Figure 1 The process is shown below.

[0037] 200 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of sulfuric acid-containing quenched liquid at a gas velocity of 10 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 6.

[0038] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 150 circular channels, each 1500 mm long and 3.5 mm in diameter. The quencher is vertically positioned, with the first 25% of its channels forming an S-shape, the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0039] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0040] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 2.4%.

[0041] Example 3

[0042] As attached Figure 1 The process is shown below.

[0043] 200 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of sulfuric acid-containing quenched liquid at a gas velocity of 10 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 6.

[0044] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 450 circular channels, each 1500 mm long and 1.5 mm in diameter. The quencher is vertically positioned, with the first 25% of its channels forming an S-shape, the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0045] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0046] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 1.63%.

[0047] Example 4

[0048] Adopting attachment Figure 1 The process is shown below.

[0049] 200 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of sulfuric acid-containing quenched liquid at a gas velocity of 10 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 6.

[0050] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 2000 mm long and 2 mm in diameter. The quencher is vertically positioned, with the first 40% of its channel length forming an S-shape, and the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0051] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0052] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 1.56%.

[0053] Example 5

[0054] Adopting attachment Figure 1 The process is shown below.

[0055] 300 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200°C and then introduced into a gas-liquid static mixer with 2400 kg of quenched liquid containing sulfuric acid at a gas velocity of 15 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 8.

[0056] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 1500 mm long and 2 mm in diameter. The quencher is vertically positioned, with the first 25% of its length forming an S-shape and the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0057] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0058] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 1.95%.

[0059] Example 6

[0060] Adopting attachment Figure 1The process is shown below.

[0061] 200 kg of propylene ammoxidation product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of sulfuric acid-containing quenched liquid at a gas velocity of 10 m / s. The mixer had a spiral internal structure and a length-to-diameter ratio of 6.

[0062] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 1500 mm long and 2 mm in diameter. The quencher is vertically positioned, with the first 25% of its length forming an S-shape, and the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.2 by adjusting the amount of sulfuric acid in the quenching liquid.

[0063] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0064] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 1.87%.

[0065] Comparative Example 1

[0066] The experimental method of Example 1 was followed, except that the mixing of the gaseous product and the quench liquid was changed to ordinary three-way mixing. Specifically, 200 kg of propylene ammoxidation reaction product containing 12.5% ​​acrylonitrile was cooled to 200°C and then mixed with 1200 kg of quench liquid containing sulfuric acid through a three-way pipe.

[0067] After mixing through the three-way pipe, the material enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 1500 mm long and 2 mm in diameter. The quencher is vertically positioned, with the first 25% of its channel length forming an S-shape and the remainder being straight circular channels. The reaction products are quenched within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0068] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0069] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 3.76%.

[0070] Comparative Example 2

[0071] The experimental method of Example 1 was followed, except that the outlet material of the gas-liquid static mixer was changed to enter a conventional plate quench tower for quenching and ammonia absorption. Specifically, 200 kg of propylene ammoxidation reaction product containing 12.5% ​​acrylonitrile was cooled to 200°C and then introduced into the gas-liquid static mixer with 1200 kg of quench liquid containing sulfuric acid under a gas velocity of 10 m / s. The mixer had a spiral shape inside and a length-to-diameter ratio of 6.

[0072] The static mixer outlet stream then enters from the middle of a conventional plate quench tower. The reaction products are quenched in the quench tower, while sulfuric acid and ammonia in the quench liquid react and are absorbed. The pH of the liquid phase outlet at the bottom of the tower is controlled to be 6.5 by adjusting the amount of sulfuric acid in the quench liquid.

[0073] Some catalyst dust particles and a small amount of polymer and liquid products are discharged from the bottom of the tower to the ammonia salt recovery unit; gaseous products flow out from the top of the tower to the subsequent absorption tower.

[0074] Based on the flow meter and sample analysis of the gaseous products at the top of the tower, the acrylonitrile loss was calculated to be 6.79%.

[0075] Comparative Example 3

[0076] The experimental method of Example 1 was followed, except that all the channels in the high-efficiency quencher were straight circular channels. 200 kg of propylene ammoxidation reaction product containing 12.5% ​​acrylonitrile was cooled to 200°C and then introduced into a gas-liquid static mixer with 1200 kg of quench liquid containing sulfuric acid at a gas velocity of 10 m / s. The mixer was spiral-shaped with a length-to-diameter ratio of 6.

[0077] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 vertically placed, straight, circular channels, each 1500 mm long and 2 mm in diameter. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0078] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0079] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 3.04%.

[0080] Comparative Example 4

[0081] The experimental method of Example 1 was followed, except that the channel diameter in the high-efficiency quencher was changed to 5 mm. 200 kg of propylene ammoxidation reaction product containing 12.5% ​​acrylonitrile was cooled to 200 °C and then introduced into a gas-liquid static mixer with 1200 kg of quench liquid containing sulfuric acid at a gas velocity of 10 m / s. The mixer was spiral-shaped with a length-to-diameter ratio of 6.

[0082] The effluent from the static mixer then enters from the top into a high-efficiency quencher consisting of 250 circular channels, each 1500 mm long and 50 mm in diameter. The quencher is vertically positioned, with the first 25% of its channel length forming an S-shape, and the remainder being straight circular channels. The reaction products are rapidly cooled within the quencher, while sulfuric acid and ammonia in the quenching liquid react and are absorbed. The pH at the quench outlet is controlled to 6.5 by adjusting the amount of sulfuric acid in the quenching liquid.

[0083] The product from the high-efficiency quench cooler enters the gas-liquid separation equipment, where some catalyst dust particles and a small amount of polymer precipitate and are discharged from the system; the separated gaseous effluent goes to the subsequent absorption tower; and the liquid product goes to the ammonia salt recovery unit.

[0084] Based on the analysis of the gas phase product flow meter and samples taken from the top of the gas-liquid separator, the acrylonitrile loss was calculated to be 3.26%.

Claims

1. A method for reducing acrylonitrile loss, characterized in that, Includes the following steps: S1: The products of propylene ammoxidation reaction and the quench liquid are fed into the gas-liquid static mixer. Under the action of the gas-liquid static mixer, the products of propylene ammoxidation reaction and the quench liquid generate shear force and tangential stress, forming turbulence, and obtaining gas-liquid mixture flow I. S2: Gas-liquid mixture stream I enters from the top of the vertically placed high-efficiency quencher. The reaction products are quenched in the high-efficiency quencher and simultaneously absorb ammonia from the reaction gas to obtain stream II. S3: Logistics II enters the gas-liquid separation equipment to separate the reaction gas and the quench liquid. At the same time, some catalyst dust particles and a small amount of polymer in the reaction gas precipitate here and are discharged from the system. S4: The separated gaseous effluent goes to the subsequent absorption tower, and the separated liquid phase goes to the subsequent ammonia salt recovery unit.

2. The method for reducing acrylonitrile loss according to claim 1, characterized in that, The gas-liquid static mixer in S1 has a length-to-diameter ratio of 5:8, and its internal mixing unit is spiral-shaped.

3. The method for reducing acrylonitrile loss according to claim 1, characterized in that, In S1, the velocity of the propylene ammoxidation product gas in the static mixer is 2-15 m / s, and the mass ratio of the propylene ammoxidation product to the quench liquid is 1:4-8.

4. The method for reducing acrylonitrile loss according to claim 1, characterized in that, The quenching liquid in S1 consists of deionized water and sulfuric acid.

5. The method for reducing acrylonitrile loss according to claim 1, characterized in that, The residence time of the gas-liquid mixture flow I described in S2 in the quench cooler is 10s to 60s, the temperature is 90 to 95℃, and the pressure is 0.03 to 0.05MPa.

6. The method for reducing acrylonitrile loss according to claim 1, characterized in that, In S2, the high-efficiency quencher includes a fluid distributor and multiple vertically arranged small-diameter quenching reaction channels, which are used to reduce the reaction process of acrylonitrile, acrylic acid and ammonia and the self-polymerization reaction.

7. The method for reducing acrylonitrile loss according to claim 6, characterized in that, The small-diameter quenching reaction channel has a diameter of 1.5~3.5mm and a length of 2000~5000mm.

8. The method for reducing acrylonitrile loss according to claim 6 or 7, characterized in that, The inlet of the quench reaction channel is S-shaped, and the connection with the inlet is straight. The S-shaped part of the reaction channel accounts for 20-40% of the total length.

9. The method for reducing acrylonitrile loss according to claim 1, characterized in that, The pH value of the material II described in S2 is 6.2~6.6.

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