Multistage fluidized bed device for efficiently preparing pyridine base

Abstract

The invention discloses a multi-stage fluidized bed device for efficiently preparing pyridine base, which belongs to the field of chemical production and comprises a gas feeding system, a liquid feeding system, a reaction system, a post-treatment system and a valve assembly, the reaction system comprises a reactor I, a reactor II and a reactor III which are connected in series end to end; tail gas treatment pipelines and material outlet pipelines are arranged at the tops of the reactor I, the reactor II and the reactor III; the material outlet pipelines are communicated with a post-treatment system; the gas feeding system is respectively communicated with bottom inlets of the reactor I, the reactor II and the reactor III, and the liquid feeding system is respectively communicated with side surface inlets of the reactor I, the reactor II and the reactor III. The device can improve the pyridine yield, increase the raw material utilization rate and the production efficiency, and is convenient for industrial production and automation.

Description

Technical Field

[0001] The present invention relates to the technical field of pyridine base production, and particularly relates to a high-efficiency multi-stage fluidized bed production device for pyridine base. Background Art

[0002] Pyridine is an organic compound, which is used in the manufacture of vitamins, sulfonamides, insecticides, plastics, etc.; it can also be used as an alkaline solvent, and is also an excellent solvent for deacidification agents and acylation reactions; it can also be used as a catalyst for polymerization reactions, oxidation reactions, carbonylation reactions of acrylonitrile, etc.; it can also be used as a silicone rubber stabilizer, a raw material for anion exchange membranes, etc.

[0003] At present, most fluidized beds for producing pyridine base adopt the mode of loading - reaction - unloading - roasting - loading for production, and this method has the problem of low efficiency. Chinese Patent CN102219731B relates to a method for producing pyridine base. In a fluidized bed reactor, raw materials contact with a molecular sieve catalyst to generate a product stream containing pyridine base. The product stream and entrained catalyst enter a settler, and a part of the catalyst in the settler returns to the reactor through a circulation pipeline, and the rest of the catalyst returns to the reactor after regeneration. Although this method can increase the selectivity of the product to a certain extent, its low pyridine yield and raw material utilization rate make it difficult to be applied on a large scale. Summary of the Invention

[0004] To solve the problems of low efficiency, low pyridine yield, and low raw material utilization rate in the prior art, the present invention provides a high-efficiency multi-stage fluidized bed device for producing pyridine base, which has the advantages of high yield, high degree of automation, high efficiency, and low cost.

[0005] To achieve the above object, the technical solutions adopted by the present invention include: The present invention provides a high-efficiency multi-stage fluidized bed device for producing pyridine base, and the device includes a gas feeding system, a liquid feeding system, a reaction system, a post-treatment system, and a valve assembly; The reaction system includes Reactor I, Reactor II, and Reactor III connected in series from beginning to end; Tail gas treatment pipelines and material outlet pipelines are provided at the tops of Reactor I, Reactor II, and Reactor III, and the material outlet pipelines are communicated with the post-treatment system; The gas feeding system is respectively communicated with the bottom inlets of Reactor I, Reactor II, and Reactor III, and the liquid feeding system is respectively communicated with the side inlets of Reactor I, Reactor II, and Reactor III; The valve assembly is used to control the opening and closing of each connecting pipeline.

[0006] Optionally, the gas feeding system includes an air feeding pipeline, a nitrogen feeding pipeline, and an ammonia feeding pipeline; an air flowmeter is provided on the air feeding pipeline, a nitrogen flowmeter is provided on the nitrogen feeding pipeline, and an ammonia flowmeter is provided on the ammonia feeding pipeline.

[0007] Optionally, the liquid feeding system includes a raw material tank and a liquid-phase feeding pump.

[0008] Optionally, the valve assembly includes connecting valve 1-1, connecting valve 1-2, connecting valve 1-3, connecting valve 2-1, connecting valve 2-2, connecting valve 2-3, connecting valve 3-1, connecting valve 3-2, connecting valve 3-3, connecting valve 4-1, connecting valve 4-2, connecting valve 4-3, connecting valve 5, feed valve 1-1, feed valve 1-2, and feed valve 1-3; The connecting valve 1-1 connects the material outlet pipeline of reactor I and the bottom inlet of reactor II, the connecting valve 1-2 connects the material outlet pipeline of reactor II and the bottom inlet of reactor III, and the connecting valve 1-3 connects the material outlet pipeline of reactor III and the bottom inlet of reactor I. The connecting valve 2-1 is located on the material outlet pipeline of reactor I and between the top of reactor I and the connecting valve 1-1, the connecting valve 2-2 is located on the material outlet pipeline of reactor II and between the top of reactor II and the connecting valve 1-2, and the connecting valve 2-3 is located on the material outlet pipeline of reactor III and between the top of reactor III and the connecting valve 1-3. The connecting valve 3-1 is located on the tail gas treatment pipeline of reactor I, the connecting valve 3-2 is located on the tail gas treatment pipeline of reactor II, and the connecting valve 3-3 is located on the tail gas treatment pipeline of reactor III. The connecting valve 4-1 is located between the connecting valve 2-1 and the connecting valve 2-2 and is used to connect the material outlet pipelines of reactor I and reactor II, the connecting valve 4-2 is located between the connecting valve 2-2 and the connecting valve 2-3 and is used to connect the material outlet pipelines of reactor II and reactor III, and the connecting valve 4-3 is located between the connecting valve 2-3 and the post-treatment system and is used to connect the material outlet pipeline of reactor III and the post-treatment system. The feed valve 1-1 connects the liquid-phase feeding pump and the side inlet of reactor I, the feed valve 1-2 connects the liquid-phase feeding pump and the side inlet of reactor II, and the feed valve 1-3 connects the liquid-phase feeding pump and the side inlet of reactor III. The connecting valve 5 is located between the connecting valve 2-1 and the post-treatment system and is used to connect the material outlet pipeline of reactor I and the post-treatment system.

[0009] Optionally, the device further includes a PLC controller, and both the valve assembly and the liquid-phase feeding pump are electrically connected to the PLC controller.

[0010] Optionally, a one-way valve is provided on the connecting pipeline between adjacent reactors to prevent backflow.

[0011] Optionally, the post-treatment system includes a condensation tank and an off-gas treatment tank. After the reaction gas is condensed in the condensation tank, it is discharged through the off-gas treatment tank, and a discharge valve is connected between the off-gas treatment tank and the condensation tank.

[0012] The present invention also provides a method for preparing pyridine base using the above device. When one of the reactors is used for catalyst regeneration, the other two reactors are used for the reaction to prepare pyridine base.

[0013] Optionally, when Reactor II and Reactor III are used for the reaction to prepare pyridine base and Reactor I is used for catalyst regeneration, Air enters from the bottom of Reactor I through an air flowmeter, and the reaction gas enters the off-gas treatment pipeline through the connection valve 3-1. The raw materials sequentially pass through a liquid feed pump and a feed valve 1-2, and then enter from the side of Reactor II. At the same time, ammonia enters from the bottom of Reactor II through an ammonia flowmeter. The reaction gas sequentially passes through the connection valve 2-2 and the connection valve 1-2, and then enters from the bottom of Reactor III. The reaction gas sequentially passes through the connection valve 2-3 and the connection valve 4-3, and then enters the post-treatment system. The remaining connection valves and feed valves are all in the closed state. After one cycle is completed, the reactor is purged with nitrogen, and all the connection valves and feed valves are switched to the next cycle as required.

[0014] Optionally, the molar ratio of formaldehyde: acetaldehyde: ammonia in the raw materials is 1: 0.6-0.8: 2-3, preferably 1: 0.7: 3.

[0015] The beneficial effects of the present invention include: (1) By adopting the series connection mode of multiple reactors, the pyridine yield and the raw material utilization rate are improved.

[0016] (2) An air pipeline is added, which can directly carry out regeneration in the reactor, and at the same time other reactors carry out reactions, improving the efficiency.

[0017] (3) Controlled by the PLC program, the present invention can continuously and periodically switch the internal channels of the valves and start and stop in zones, with a high degree of automation.

[0018] (4) The present invention uses a multi-stage fluidized bed reactor, which can improve the efficiency without preheating the gas, saving energy consumption.

[0019] After the multi-stage fluidized beds used in the present invention are connected in series through multiple reactors, the raw materials in the reactors undergo reactions in two cycles. Compared with a single reactor, excessive ammonia can shift the ammonia-aldehyde condensation reaction towards the direction of pyridine formation. Therefore, when the yield is the same, the content of acetaldehyde, which has a relatively high cost in the raw material ratio, can be reduced, and the content of ammonia can be increased, thus saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a schematic structural diagram of a multi-stage fluidized bed device for efficiently producing pyridine base of the present invention; In the figure: 1, connection valve 4-1; 2, connection valve 4-2; 3, connection valve 4-3; 4, raw material tank; 5, air flowmeter 1; 6, nitrogen flowmeter 1; 7, ammonia flowmeter 1; 8, air flowmeter 2; 9, nitrogen flowmeter 2; 10, ammonia flowmeter 2; 11, air flowmeter 3; 12, nitrogen flowmeter 3; 13, ammonia flowmeter 3; 14, air feed pipeline; 15, nitrogen feed pipeline; 16, ammonia feed pipeline; 17, distribution plate 1; 18, reactor I; 19, reactor II; 20, reactor III; 21, connection valve 1-1; 22, connection valve 1-2; 23, connection valve 1-3; 24, connection valve 2-1; 25, connection valve 2-2; 26, connection valve 2-3; 27, distribution plate 2; 28, distribution plate 3; 29, connection valve 3-1; 30, connection valve 3-2; 31, connection valve 3-3; 32, tail gas treatment pipeline; 33, condensation tank; 34, tail gas treatment tank; 35, discharge valve; 36, liquid feed pump; 37, feed valve 1-1; 38, feed valve 1-2; 39, feed valve 1-3; 40, connection valve 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The following embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0023] Such as Figure 1As shown in the figure, the device of the present invention includes a gas feeding system, a liquid feeding system, a reaction system, a post-treatment system, and a valve assembly; the reaction system includes reactors I, II, and III connected in series from beginning to end; the tops of reactors I, II, and III are all provided with tail gas treatment pipelines and material outlet pipelines, and the material outlet pipelines are communicated with the post-treatment system; the gas feeding system is respectively communicated with the bottom inlets of reactors I, II, and III, and the liquid feeding system is respectively communicated with the side inlets of reactors I, II, and III; the valve assembly is used to control the opening and closing of each connecting pipeline.

[0024] A distribution plate is provided in the middle of each reactor of the present invention, and the side inlet of the reactor is located above the distribution plate.

[0025] After each cycle of reaction of the device of the present invention is completed, through the control of the valve assembly, the reactor is switched to the corresponding state of the next cycle.

[0026] The gas feeding system includes an air feeding pipeline, a nitrogen feeding pipeline, and an ammonia feeding pipeline; an air flowmeter is provided on the air feeding pipeline, a nitrogen flowmeter is provided on the nitrogen feeding pipeline, and an ammonia flowmeter is provided on the ammonia feeding pipeline.

[0027] The liquid feeding system includes a raw material tank and a liquid phase feeding pump.

[0028] The valve assembly includes connection valves 1-1, 1-2, 1-3, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 4-1, 4-2, 4-3, connection valve 5, feeding valves 1-1, 1-2, and 1-3; The connection valve 1-1 connects the material outlet pipeline of reactor I and the bottom inlet of reactor II, the connection valve 1-2 connects the material outlet pipeline of reactor II and the bottom inlet of reactor III, and the connection valve 1-3 connects the material outlet pipeline of reactor III and the bottom inlet of reactor I. The connection valve 2-1 is located on the material outlet pipeline of reactor I and between the top of reactor I and the connection valve 1-1, the connection valve 2-2 is located on the material outlet pipeline of reactor II and between the top of reactor II and the connection valve 1-2, and the connection valve 2-3 is located on the material outlet pipeline of reactor III and between the top of reactor III and the connection valve 1-3. The connection valve 3-1 is located on the tail gas treatment pipeline of reactor I, the connection valve 3-2 is located on the tail gas treatment pipeline of reactor II, and the connection valve 3-3 is located on the tail gas treatment pipeline of reactor III. The connection valve 4-1 is located between the connection valves 2-1 and 2-2 and is used to connect the material outlet pipeline of Reactor I and the material outlet pipeline of Reactor II. The connection valve 4-2 is located between the connection valves 2-2 and 2-3 and is used to connect the material outlet pipeline of Reactor II and the material outlet pipeline of Reactor III. The connection valve 4-3 is located between the connection valve 2-3 and the post-treatment system and is used to connect the material outlet pipeline of Reactor III and the post-treatment system. The feed valve 1-1 connects the liquid feed pump and the side inlet of Reactor I. The feed valve 1-2 connects the liquid feed pump and the side inlet of Reactor II. The feed valve 1-3 connects the liquid feed pump and the side inlet of Reactor III. The connection valve 5 is located between the connection valve 2-1 and the post-treatment system and is used to connect the material outlet pipeline of Reactor I and the post-treatment system.

[0029] The device further includes a PLC controller, and both the valve assembly and the liquid feed pump are electrically connected to the PLC controller.

[0030] The post-treatment system includes a condensation tank and a tail gas treatment tank. After the reaction gas is condensed in the condensation tank, it is discharged through the tail gas treatment tank. An outlet valve is connected between the tail gas treatment tank and the condensation tank.

[0031] The pyridine yield of the present invention = (mass of raw materials required to produce pyridine / mass of raw material feed) * 100%.

[0032] Example 1

[0033] 3000 g of ZSM-5 molecular sieve catalyst is installed in each of the three reactors. The molar ratio of the raw materials formaldehyde, acetaldehyde, and ammonia is 1:0.8:3.

[0034] Reactor I is subjected to regeneration treatment: air enters from the lower end of Reactor I through an air flow meter and enters the tail gas treatment pipeline through the connection valve 3-1. The temperature inside Reactor I is controlled at 550°C and at normal pressure.

[0035] Reactor II undergoes a reaction: the raw materials pass through the liquid feed pump and enter from the side of Reactor II through the feed valve 1-2. At the same time, ammonia enters from the lower end of Reactor II through an ammonia flow meter. After mixing, it enters from the lower end of Reactor III through the connection valve 2-2 and the connection valve 1-2. The temperature inside Reactor II is 470°C and at normal pressure.

[0036] Reactor III undergoes a reaction: the mixed gas enters from the lower end of Reactor III and enters the condensation tank through the connection valve 2-3 and the connection valve 4-3. The temperature inside Reactor III is 470°C and at normal pressure.

[0037] After a cycle is completed, each reactor is purged with nitrogen, and then the PLC controller controls the channel switching of the selection valve to switch to the valve state corresponding to the next cycle according to Table 1.

[0038] The reaction gas is condensed in the condensation tank and then discharged from the discharge valve. The excess tail gas is discharged after passing through the tail gas treatment tank. The discharged sample is subjected to chromatographic analysis to calculate the yield. The pyridine yield in this example is 66.5%.

[0039] Example 2 3000 g of ZSM-5 molecular sieve catalyst is installed in each of the three reactors, and the molar ratio of the raw materials formaldehyde, acetaldehyde, and ammonia is 1:0.8:2.5.

[0040] Reactor I is regenerated: Air enters from the lower end of Reactor I through the air flowmeter 1 and enters the tail gas treatment pipeline through the connection valve 3-1. The temperature in Reactor I is controlled at 550 °C under normal pressure.

[0041] Reactor II undergoes a reaction: The raw materials pass through the liquid feed pump and enter from the side of Reactor II through the feed valve 1-2. At the same time, ammonia enters from the lower end of Reactor II through the ammonia flowmeter. After mixing, it enters from the lower end of Reactor III through the connection valve 2-2 and the connection valve 1-2. The temperature in Reactor II is 470 °C under normal pressure.

[0042] Reactor III undergoes a reaction: The mixed gas enters from the lower end of Reactor III and enters the condensation tank through the connection valve 2-3 and the connection valve 4-3. The temperature in Reactor III is 470 °C under normal pressure.

[0043] After a cycle is completed, each reactor is purged with nitrogen, and then the PLC controller controls the channel switching of the selection valve to switch to the valve state corresponding to the next cycle according to Table 1.

[0044] The reaction gas is condensed in the condensation tank and then discharged from the discharge valve. The excess tail gas is discharged after passing through the tail gas treatment tank. The discharged sample is subjected to chromatographic analysis to calculate the yield. The pyridine yield in this example is 64.2%.

[0045] Example 3 3000 g of ZSM-5 molecular sieve catalyst is installed in each of the three reactors, and the molar ratio of the raw materials formaldehyde, acetaldehyde, and ammonia is 1:0.8:2.

[0046] Reactor I is regenerated: Air enters from the lower end of Reactor I through the air flowmeter 1 and enters the tail gas treatment pipeline through the connection valve 3-1. The temperature in Reactor I is controlled at 550 °C under normal pressure.

[0047] Reactor II conducts the reaction: The raw materials enter from the side of Reactor II through the liquid feed pump and the feed valve 1-2. At the same time, ammonia enters from the lower end of Reactor II through the ammonia flowmeter. After mixing, it enters from the lower end of Reactor III through the connection valve 2-2 and the connection valve 1-2. The temperature in Reactor II is 470 °C and the pressure is atmospheric pressure.

[0048] Reactor III conducts the reaction: The mixed gas enters from the lower end of Reactor III and enters the condensation tank through the connection valve 2-3 and the connection valve 4-3. The temperature in Reactor III is 470 °C and the pressure is atmospheric pressure.

[0049] When a cycle is completed, each reactor is purged with nitrogen, and then the PLC controller controls the channel switching of the selection valve and switches to the valve state corresponding to the next cycle according to Table 1.

[0050] After the reaction gas is condensed in the condensation tank, it is discharged from the discharge valve. The excess tail gas is discharged after passing through the tail gas treatment tank. The discharged sample is analyzed by chromatography to calculate the yield. The pyridine yield in this example is 63.5%.

[0051] Example 4 3000 g of ZSM-5 molecular sieve catalyst is installed in each of the three reactors. The molar ratio of the raw materials formaldehyde, acetaldehyde, and ammonia is 1:0.7:3.

[0052] Reactor I conducts the regeneration treatment: Air enters from the lower end of Reactor I through the air flowmeter 1 and enters the tail gas treatment pipeline through the connection valve 3-1. The temperature in Reactor I is controlled at 550 °C and the pressure is atmospheric pressure.

[0053] Reactor II conducts the reaction: The raw materials enter from the side of Reactor II through the liquid feed pump and the feed valve 1-2. At the same time, ammonia enters from the lower end of Reactor II through the ammonia flowmeter. After mixing, it enters from the lower end of Reactor III through the connection valve 2-2 and the connection valve 1-2. The temperature in Reactor II is 470 °C and the pressure is atmospheric pressure.

[0054] Reactor III conducts the reaction: The mixed gas enters from the lower end of Reactor III and enters the condensation tank through the connection valve 2-3 and the connection valve 4-3. The temperature in Reactor III is 470 °C and the pressure is atmospheric pressure.

[0055] When a cycle is completed, each reactor is purged with nitrogen, and then the PLC controller controls the channel switching of the selection valve and switches to the valve state corresponding to the next cycle according to Table 1.

[0056] After the reaction gas is condensed in the condensation tank, it is discharged from the discharge valve. The excess tail gas is discharged after passing through the tail gas treatment tank. The discharged sample is analyzed by chromatography to calculate the yield. The pyridine yield in this example is 67.7%.

Claims

1. A multi-stage fluidized bed device for efficiently preparing pyridine base, characterized in that: The device comprises a gas feed system, a liquid feed system, a reaction system, a post-processing system and a valve assembly; The reaction system comprises a reactor I, a reactor II and a reactor III connected in series end to end; The tops of the reactors I, II and III are all provided with tail gas treatment pipelines and material outlet pipelines, and the material outlet pipelines are connected to the post-processing system; The gas feed system is communicated with the bottom inlet of the reactor I, the reactor II and the reactor III respectively, and the liquid feed system is communicated with the side inlet of the reactor I, the reactor II and the reactor III respectively; The valve assembly is used to control the opening and closing of each connecting pipeline.

2. The device according to claim 1, characterized in that The gas feeding system comprises an air feeding pipeline, a nitrogen feeding pipeline and an ammonia feeding pipeline; the air feeding pipeline is provided with an air flow meter, the nitrogen feeding pipeline is provided with a nitrogen flow meter, and the ammonia feeding pipeline is provided with an ammonia flow meter.

3. The device according to claim 1 or 2, characterized in that: The liquid feed system comprises a raw material tank and a liquid phase feed pump.

4. The device according to any one of claims 1 to 3, characterized in that The valve assembly includes a connecting valve 1-1, a connecting valve 1-2, a connecting valve 1-3, a connecting valve 2-1, a connecting valve 2-2, a connecting valve 2-3, a connecting valve 3-1, a connecting valve 3-2, a connecting valve 3-3, a connecting valve 4-1, a connecting valve 4-2, a connecting valve 4-3, a connecting valve 5, a feed valve 1-1, a feed valve 1-2 and a feed valve 1-3; The connecting valve 1-1 connects the material outlet pipeline of the reactor I and the bottom inlet of the reactor II, the connecting valve 1-2 connects the material outlet pipeline of the reactor II and the bottom inlet of the reactor III, and the connecting valve 1-3 connects the material outlet pipeline of the reactor III and the bottom inlet of the reactor I. The connecting valve 2-1 is located on the material outlet pipeline of the reactor I and between the top of the reactor I and the connecting valve 1-1. The connecting valve 2-2 is located on the material outlet pipeline of the reactor II and between the top of the reactor II and the connecting valve 1-2. The connecting valve 2-3 is located on the material outlet pipeline of the reactor III and between the top of the reactor III and the connecting valve 1-3. The connecting valve 3-1 is located on the tail gas processing pipeline of reactor I, the connecting valve 3-2 is located on the tail gas processing pipeline of reactor II, and the connecting valve 3-3 is located on the tail gas processing pipeline of reactor III. The connecting valve 4-1 is located between the connecting valve 2-1 and the connecting valve 2-2, and is used to connect the material outlet pipeline of the reactor I and the material outlet pipeline of the reactor II. The connecting valve 4-2 is located between the connecting valve 2-2 and the connecting valve 2-3, and is used to connect the material outlet pipeline of the reactor II and the material outlet pipeline of the reactor III. The connecting valve 4-3 is located between the connecting valve 2-3 and the post-processing system, and is used to connect the material outlet pipeline of the reactor III and the post-processing system. The feed valve 1-1 is connected to the liquid-phase feed pump and the side inlet of the reactor I, the feed valve 1-2 is connected to the liquid-phase feed pump and the side inlet of the reactor II, and the feed valve 1-3 is connected to the liquid-phase feed pump and the side inlet of the reactor III. The connecting valve 5 is located between the connecting valve 2-1 and the post-processing system, and is used to connect the material outlet pipeline of the reactor I and the post-processing system.

5. The device according to any one of claims 1 to 4, characterized in that: The device also includes a PLC controller, and the valve assembly and the liquid-phase feed pump are both electrically connected to the PLC controller.

6. The device according to any one of claims 1 to 5, characterized in that One-way valves are arranged on the connecting pipelines between adjacent reactors.

7. The device according to any one of claims 1 to 6, characterized in that The post-processing system comprises a condensation tank and a tail gas treatment tank. The post-reaction gas is condensed by the condensation tank and then discharged through the tail gas treatment tank. A discharge valve is connected between the tail gas treatment tank and the condensation tank.

8. A method for preparing pyridine base using the device according to any one of claims 1 to 7, characterized in that: When one of the reactors is used for catalyst regeneration, the other two reactors are used for reaction to prepare pyridine base.

9. The method according to claim 8, characterized in that When reactor II and reactor III are used for the reaction to prepare pyridine base, and reactor I is used for catalyst regeneration, Air enters from the bottom of reactor I through an air flow meter, and the gas after reaction enters the tail gas treatment pipeline from connecting valve 3-1. The raw materials pass through the liquid feed pump and feed valve 1-2 in sequence, and then enter from the side of reactor II. At the same time, ammonia enters from the bottom of reactor II through an ammonia flow meter. After the reaction, the gas passes through connecting valve 2-2 and connecting valve 1-2 in sequence, and then enters from the bottom of reactor III. The post-reaction gas passes through connecting valve 2-3 and connecting valve 4-3 in turn and enters the post-treatment system. The other connecting valves and feed valves are all in closed state. After one cycle is completed, the reactor is purged with nitrogen, and all connecting valves and feed valves are switched to the next cycle as needed.

10. The method according to claim 8 or 9, characterized in that: The molar ratio of formaldehyde: acetaldehyde: ammonia in the raw material is 1: 0.6-0.8: 2-3, preferably 1: 0.7: 3.

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