Low-dosage process for preparing aniline by liquid-phase hydrogenation of nitrobenzene and application thereof

Abstract

The present application relates to a kind of low-dosage process and application of nitrobenzene liquid phase hydrogenation to aniline, by monitoring the position of foam layer on the top of sieve plate tower type hydrogenation reactor, control gas phase residence time, and then reduce the loss amount of through the reactor top demister.Less temperature reduction is realized by the catalyst recovery tank of gas phase aniline through the tank internal cooling coil, promote the liquid drop wrapped catalyst to be further intercepted by wire mesh demister, so as to reduce the loss amount of catalyst.In addition, by monitoring the azobenzene in aniline slurry, N-cyclohexyl aniline can accurately evaluate the overall activity of system catalyst, timely adjust catalyst control strategy, so as to realize the great benefit of catalyst unit consumption to 1-2g / t aniline.

Description

Technical Field

[0001] This invention relates to a low-consumption process for the liquid-phase hydrogenation of nitrobenzene to produce aniline and its application. Background Technology

[0002] Aniline, as an important amine chemical raw material, is widely used in industries such as dyes, pharmaceuticals, resins, fragrances, and rubber vulcanization accelerators, and is especially an important raw material for MDI (4,4-diphenylmethane diisocyanate).

[0003] Currently, there are three methods for the industrial production of aniline: nitrobenzene catalytic hydrogenation, phenol amination, and iron powder reduction. The iron powder reduction method is gradually being phased out due to the poor quality of the aniline produced. The phenol amination method is highly dependent on the source of phenol. The nitrobenzene catalytic hydrogenation method is further divided into gas-phase hydrogenation and liquid-phase catalytic hydrogenation processes. The gas-phase hydrogenation process mainly uses copper-based catalysts, but its disadvantages include lower reaction capacity, greater catalyst wear requiring regular replacement, more complex operation, and higher maintenance costs. The liquid-phase hydrogenation process for nitrobenzene was first successfully developed by DuPont in the United States. It mainly uses precious metal catalysts under anhydrous conditions. The advantages of this process are low reaction temperature, high catalyst loading, long life and large equipment production capacity. The disadvantages are that the reactants and catalysts must be separated, the catalyst unit price and consumption are relatively high, and the excessive catalyst activity leads to more by-products. The system fluctuates greatly in the initial stage of start-up and is difficult to control. For example, literature CN113019270B discloses a liquid-phase nitrobenzene hydrogenation catalyst circulation process and device, which can realize catalyst circulation operation in the initial stage of start-up and provide a large buffer space. This reduces the operating variables in the initial stage of start-up and is conducive to the stable operation of the reactor, thereby improving the safety of the device.

[0004] Currently, the mainstream process for aniline production is the nitrobenzene liquid-phase hydrogenation method, which typically uses a supported noble metal catalyst. In a sieve plate reactor, nitrobenzene and hydrogen are reacted with a catalyst slurry to produce aniline. A measured amount of water is added to the reactor to control the reaction temperature. At the top of the reactor, a crude aniline / water gas phase product and a side stream slurry containing heavy components and catalyst are separated. The side stream slurry passes through a thickener to intercept the catalyst, and some of the heavy components are collected. The concentrated catalyst slurry is recycled to participate in the reaction.

[0005] In the operation of nitrobenzene liquid-phase hydrogenation units, the amount of fresh catalyst added is mainly adjusted based on the nitrobenzene content in the side stream slurry. Catalyst consumption is as high as 9-10 g catalyst / t aniline, with a catalyst price of 20,000-30,000 RMB / kg. For a 360,000-ton aniline production capacity, the catalyst cost reaches 60-110 million RMB. Breaking with conventional thinking, the inventors discovered through extensive experimental verification that the main factors affecting catalyst consumption are catalyst loss and catalyst activity. The catalyst mainly loses through entrainment in the gas phase at the top of the reactor, rather than due to a decrease in thickener filtration efficiency. Furthermore, characterizing catalyst activity solely through the nitrobenzene content in the side stream slurry has significant limitations. Therefore, the inventors developed a catalyst recovery technology and catalyst formulation scheme, achieving a dual effect of significantly reducing catalyst consumption and byproducts. Summary of the Invention

[0006] The purpose of this invention is to address the problem of high catalyst consumption in the existing liquid-phase hydrogenation process for producing aniline from nitrobenzene, and to provide a low-catalyst-consumption process and its application for producing aniline from nitrobenzene.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for reducing catalyst loss in the liquid-phase hydrogenation process of nitrobenzene to aniline, the method comprising the following steps:

[0008] (1) The raw material nitrobenzene and the catalyst-containing aniline slurry are mixed and fed into the bottom of the reactor, while hydrogen and water are injected into the bottom of the tower to control the reaction temperature.

[0009] (2) The gaseous and liquid slurry of aniline are separated in the space above the top tray of the reactor. The aniline slurry containing catalyst and heavy components is collected from the first tray. After the gaseous aniline stays in the top gaseous space for a certain period of time, it leaves the reactor after being intercepted by the top demister.

[0010] (3) The gaseous aniline coming out of the top of the reactor is sent to the catalyst recovery tank, and the liquid aniline obtained is sent to the catalyst slurry system, and the gaseous phase obtained is used as crude aniline product.

[0011] In this invention, the catalyst in step (1) is a metal-supported catalyst, which uses activated carbon as a support and palladium and platinum as active components. The catalyst particle size is 10-100 μm, and the median particle size is 7-10 μm.

[0012] In this invention, the catalyst-containing aniline slurry in step (1) comes from the catalyst slurry system to which the liquid aniline obtained by separation in step (3) is sent.

[0013] In this invention, in step (1), the reactor is a fluidized bed reactor, the mass ratio of hydrogen to nitrobenzene in the reactor is 6:1-10:1, the mass ratio of catalyst-containing slurry to hydrogen is controlled at 7:1-12:1, the catalyst content in the slurry is 0.2-2%, the number of sieve plates inside the reactor is 20-60, preferably 30-40; the reactor pressure is controlled at 14-20 barg, preferably 16-18 barg; the top temperature of the tower is 210-220℃, preferably 214-217℃; the bottom temperature of the tower is 70-120℃, preferably 85-95℃.

[0014] In this invention, in step (2), the reactor further includes a demister. The distance between the first tray at the top of the reactor and the demister is greater than 15% of the overall height of the reactor, preferably greater than 30%. The demister type is a blade type, a baffle plate type, or a wire mesh demister, preferably a blade type. A level gauge is also installed in the gas phase space to monitor the height of the foam layer. The level gauge type is a magnetic float level gauge or a differential pressure level gauge, preferably a differential pressure level gauge. The gas velocity of aniline in the gas phase space is 0.3-0.5 m / s. A regulating valve is installed on the liquid phase extraction pipeline of the first tray to control the height of the foam liquid layer at the top of the reactor, and further control the residence time of the foam liquid layer and the gas phase space between the demister to be >0.3s, preferably >5s.

[0015] In this invention, in step (3), the catalyst recovery tank is provided with a gas phase inlet, and a gas distributor is provided at the gas phase inlet, at a distance of 10%-30% of the overall height of the tank body from the bottom of the tank, preferably 15%-20%. A demister is provided at the top of the catalyst recovery tank. The demister type is a blade type, a baffle plate type, or a wire mesh demister, preferably a wire mesh demister, which can achieve an interception efficiency of 99.5% for droplets larger than 2μm. A horizontal cooling coil is provided between the gas phase inlet and the demister for precise temperature control of 0-2℃, preferably 0.5-1℃. The tank body is designed for a gas phase residence time of >1s, preferably >5s.

[0016] A second aspect of the present invention provides a method for monitoring and adjusting the overall activity of a system catalyst, the method comprising:

[0017] (1) Analyze the aniline slurry collected from the first tray at the top of the reactor, monitor the content of azobenzene, nitrobenzene, N-cyclohexylaniline and tar in the aniline slurry and compare it with the set content of azobenzene, nitrobenzene, N-cyclohexylaniline and tar;

[0018] (2) Determine the catalyst activity based on the content of azobenzene, nitrobenzene, N-cyclohexylaniline and tar in the aniline slurry, and extract or replenish the catalyst in the system.

[0019] In step (1), the contents of azobenzene, nitrobenzene, N-cyclohexylaniline, and tar in the aniline slurry are monitored. The azobenzene index is more sensitive to insufficient catalyst hydrogenation activity and is set at 10-150 ppm, preferably 20-50 ppm. The N-cyclohexylaniline index is more sensitive to excessive catalyst hydrogenation activity and is set at 50-200 ppm, preferably 80-120 ppm. The tar index affects the activity per unit catalyst and is set at 1%-10%, preferably 3-5%. The nitrobenzene index is used to assist in judging catalyst activity and is set at 0-1000 ppm, preferably 400-600 ppm.

[0020] In step (2), the filtrate output from the thickener is adjusted to maintain the tar content in the slurry at 1%-10%, preferably 3-5% (filtrate output = measured tar content in the slurry / 4% * reactor nitrobenzene feed rate * 5%, unit kg / h). The amount of fresh catalyst added is adjusted to control the nitrobenzene content in the slurry at 0-1000ppm, 400-600ppm (fresh catalyst added = measured nitrobenzene content in the slurry / 500 * reactor nitrobenzene feed rate * 0.3%, unit kg / h). When N-cyclohexylaniline exceeds the upper limit of the control range, part of the system catalyst slurry is extracted into the storage tank. Extraction can be done once or multiple times. There is no particular restriction on the amount extracted, as long as the content of N-cyclohexylaniline can be controlled within the index range. Preferably, the total amount of slurry extracted = measured N-cyclohexylaniline content / 50 * reactor volume * 2%, unit m³. 3 Then, resample and analyze the index until it returns to the control range. When the azobenzene content is higher than the upper limit of the control range, prioritize replenishing the catalyst slurry in the storage tank to the reactor. Replenishment can be done once or multiple times, and there is no particular limit to the amount replenished, as long as the azobenzene content can be controlled within the index range. The preferred total slurry replenishment amount is calculated as: (Actual azobenzene value / 50) * Reactor volume * 4%, in cubic meters. 3 If the catalyst is insufficient, fresh catalyst should be added, and the index should be resampled and analyzed until it returns to the control range.

[0021] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0022] (1) A new level gauge is added to the top of the reactor to monitor the height of the foam layer in real time, and to control the residence time of the gas phase at the top of the reactor to maintain 5-10 seconds, thereby reducing liquid splashing at the interface and thus preventing catalyst loss due to penetration of the demister. A catalyst recovery tank is added to the reactor outlet, and the temperature is precisely reduced slightly through the internal cooling coil, thereby further reducing the amount of catalyst loss.

[0023] (2) By monitoring azobenzene, the side-stream slurry can effectively determine the insufficient catalyst activity of the system, and by monitoring N-cyclohexylaniline, it can effectively monitor the excessive catalyst activity of the system, and can comprehensively monitor the overall hydrogenation quality.

[0024] (3) The side-stream slurry system is equipped with a slurry storage tank. When the system catalyst activity is too high, the slurry catalyst is promptly removed. When the system catalyst activity is insufficient, the slurry catalyst is promptly replenished. If the hydrogenation demand still cannot be met, fresh catalyst is added. This improves catalyst utilization efficiency and reduces the consumption of fresh catalyst.

[0025] (4) The present invention can reduce the catalyst consumption from 9-10 g / t aniline to 1-2 g / t aniline.

[0026] (5) This invention improves the economic benefits of hydrogenation process from aspects such as catalyst recovery and product quality improvement. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the liquid-phase hydrogenation of nitrobenzene to aniline according to the present invention.

[0028] Figure 2 A process flow diagram for the liquid-phase hydrogenation of nitrobenzene to aniline in existing technologies. Detailed Implementation

[0029] The specific implementation scheme of this method is further illustrated below with examples. However, the present invention is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims of the present invention.

[0030] Comparative Example 1

[0031] like Figure 1 The apparatus shown is for the liquid-phase hydrogenation of nitrobenzene and aniline. The catalyst is an activated carbon palladium-platinum catalyst with a particle size of 10 μm. The reactor has 35 trays, a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. The reactor top demister is a blade type, the residence time of gaseous aniline at the top of the reactor is 0.3 s, there is no catalyst recovery tank, and the catalyst consumption is 8 g / t aniline.

[0032] The tar content in the side stream slurry is controlled at 3%, and the amount of fresh catalyst added is adjusted to control the nitrobenzene content in the top side stream slurry of the reactor to 0 ppm. The catalyst consumption is 9 g / t aniline.

[0033] Comparative Example 2

[0034] like Figure 1The illustrated device is a liquid-phase hydrogenation apparatus for aniline from nitrobenzene. The catalyst is an activated carbon palladium-platinum catalyst with a particle size of 10 μm. The reactor has 35 trays, with a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a catalyst content of 0.2% in the slurry, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. A differential pressure level gauge at the top of the reactor monitors the foam layer height, and the residence time of the gaseous aniline at the top of the reactor is controlled by adjusting the flow rate of the side-stream slurry. The residence time of the gaseous aniline at the reactor top is 0 s. A catalyst recovery tank is added at the reactor outlet, with a gaseous residence time of 10 s. A wire mesh demister is installed at the top of the recovery tank, and the internal cooling coils of the catalyst recovery tank are controlled to cool the gaseous aniline by 1°C. The catalyst consumption is 6 g / t aniline.

[0035] The tar content in the side stream slurry is controlled at 3%, and the nitrobenzene content is controlled at 600 ppm. The catalyst extraction and replenishment strategy is adjusted according to the azobenzene and N-cyclohexylaniline content in the side stream slurry. When the N-cyclohexylaniline content is greater than 80 ppm, the system catalyst slurry is extracted to the storage tank. When the azobenzene content is greater than 20 ppm, the catalyst slurry in the storage tank is preferentially replenished to the reactor. Fresh catalyst is added only when the content is insufficient. The catalyst consumption per ton of aniline is further reduced to 5 g / t aniline.

[0036] Example 1

[0037] like Figure 1 The apparatus shown is for the liquid-phase hydrogenation of nitrobenzene and aniline. The catalyst is an activated carbon palladium-platinum catalyst (purchased from Evonik), with a particle size of 10 μm. The reactor has a total of 35 trays, with a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a catalyst content of 0.2% in the slurry, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. A differential pressure level gauge is installed at the top of the reactor to monitor the foam layer height, and the residence time of the gaseous aniline at the top of the reactor is controlled by adjusting the flow rate of the side stream slurry. The residence time of the gaseous aniline at the top of the reactor is 5 s. A catalyst recovery tank is added at the reactor outlet, with a gaseous residence time of 5 s in the recovery tank. A wire mesh demister is installed at the top of the recovery tank, and the internal cooling coils of the catalyst recovery tank are controlled to cool the gaseous aniline by 0.5°C. The catalyst consumption is 5 g / t aniline.

[0038] The tar content in the side stream slurry is controlled at 5%, and the nitrobenzene content is controlled at 400 ppm. The catalyst extraction and replenishment strategy is adjusted according to the azobenzene and N-cyclohexylaniline content in the side stream slurry. When the N-cyclohexylaniline content is greater than 120 ppm, the system catalyst slurry is extracted to the storage tank. When the azobenzene content is greater than 50 ppm, the catalyst slurry in the storage tank is preferentially replenished to the reactor. Fresh catalyst is added only when the content is insufficient. The catalyst consumption per ton of aniline is further reduced to 4 g / t aniline.

[0039] Example 2

[0040] like Figure 1 The illustrated device is a liquid-phase hydrogenation apparatus for aniline from nitrobenzene. The catalyst is an activated carbon palladium-platinum catalyst with a particle size of 10 μm. The reactor has 35 trays, with a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a catalyst content of 0.2% in the slurry, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. A differential pressure level gauge is installed at the top of the reactor to monitor the foam layer height, and the residence time of the gaseous aniline at the top of the reactor is controlled by adjusting the flow rate of the side-stream slurry. The residence time of the gaseous aniline at the reactor top is 10 s. A catalyst recovery tank is added at the reactor outlet, with a gaseous residence time of 10 s in the recovery tank. A wire mesh demister is installed at the top of the recovery tank, and the internal cooling coil is controlled to cool the gaseous aniline by 1°C. The catalyst consumption is 2 g / t aniline.

[0041] The tar content in the side stream slurry is controlled at 3%, and the nitrobenzene content is controlled at 600 ppm. The catalyst extraction and replenishment strategy is adjusted according to the azobenzene and N-cyclohexylaniline content in the side stream slurry. When the N-cyclohexylaniline content is greater than 80 ppm, the system catalyst slurry is extracted to the storage tank. When the azobenzene content is greater than 20 ppm, the catalyst slurry in the storage tank is preferentially replenished to the reactor. Fresh catalyst is added only when the content is insufficient. The catalyst consumption per unit is further reduced to 1 g / t aniline.

[0042] Example 3

[0043] like Figure 1 The apparatus shown is for the liquid-phase hydrogenation of nitrobenzene and aniline. The catalyst is an activated carbon palladium-platinum catalyst with a particle size of 10 μm. The reactor has a total of 35 trays, with a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a catalyst content of 0.2% in the slurry, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. A differential pressure level gauge is installed at the top of the reactor to monitor the foam layer height, and the residence time of the gaseous aniline at the top of the reactor is controlled by adjusting the flow rate of the side stream slurry. The residence time of the gaseous aniline at the reactor top is 7 s. A catalyst recovery tank is added at the reactor outlet, with a gaseous residence time of 7 s in the recovery tank. A wire mesh demister is installed at the top of the recovery tank, and the internal cooling coils of the catalyst recovery tank are controlled to cool the gaseous aniline by 0.7°C. The catalyst consumption is 4 g / t aniline.

[0044] The tar content in the side stream slurry is controlled at 4%, and the nitrobenzene content is controlled at 500 ppm. The catalyst extraction and replenishment strategy is adjusted according to the azobenzene and N-cyclohexylaniline content in the side stream slurry. When the N-cyclohexylaniline content is greater than 80 ppm, the system catalyst slurry is extracted to the storage tank. When the azobenzene content is greater than 20 ppm, the catalyst slurry in the storage tank is preferentially replenished to the reactor. Fresh catalyst is added only when the content is insufficient. The catalyst consumption per ton of aniline is further reduced to 1.5 g / t aniline.

[0045] Example 4

[0046] like Figure 1 The apparatus shown is for the liquid-phase hydrogenation of nitrobenzene and aniline. The catalyst is an activated carbon palladium-platinum catalyst with a particle size of 10 μm. The reactor has a total of 35 trays, with a hydrogen / nitrobenzene feed mass ratio of 8:1, a catalyst-containing slurry to hydrogen mass ratio of 9:1, a catalyst content of 0.2% in the slurry, a reaction pressure of 18 barg, a bottom temperature of 90°C, and a top temperature of 215°C. A differential pressure level gauge is installed at the top of the reactor to monitor the foam layer height, and the residence time of the gaseous aniline at the top of the reactor is controlled by adjusting the flow rate of the side stream slurry. The residence time of the gaseous aniline at the reactor top is 60 s. A catalyst recovery tank is added at the reactor outlet, with a gaseous residence time of 60 s in the recovery tank. A wire mesh demister is installed at the top of the recovery tank, and the internal cooling coil is controlled to cool the gaseous aniline by 2°C. The catalyst consumption is 1.5 g / t aniline.

[0047] The tar content in the side stream slurry is controlled at 3%, and the nitrobenzene content is controlled at 600 ppm. The catalyst extraction and replenishment strategy is adjusted according to the azobenzene and N-cyclohexylaniline content in the side stream slurry. When the N-cyclohexylaniline content is greater than 80 ppm, the system catalyst slurry is extracted to the storage tank. When the azobenzene content is greater than 20 ppm, the catalyst slurry in the storage tank is preferentially replenished to the reactor. Fresh catalyst is added only when the content is insufficient. The catalyst consumption per ton of aniline is further reduced to 0.7 g / t aniline.

Claims

1. A method for reducing catalyst loss in a liquid phase hydrogenation process of nitrobenzene to aniline, the method comprising the steps of: (1) mixing raw material nitrobenzene and catalyst-containing aniline slurry and feeding into the bottom of a reactor, while spraying hydrogen and water for controlling reaction temperature into the bottom of the reactor; (2) separating aniline gas phase and liquid phase slurry in the space above the top tray of the reactor, and collecting catalyst-containing and heavy component-containing aniline slurry at the first tray, and gas phase aniline staying in the top gas phase space for > 0.3 s, and then leaving the reactor after being intercepted by a demister at the top of the reactor; (3) feeding the gas phase aniline from the top of the reactor into a catalyst recovery tank, separating to obtain liquid phase aniline which is fed into a catalyst slurry system, and separating to obtain gas phase as a crude aniline product.

2. The method of claim 1, wherein, In the step (1), the catalyst is a metal-supported catalyst, which has activated carbon as a carrier and palladium platinum as an active component, and the catalyst particle size is 10-100 um and the median particle size is 7-10 um; the catalyst-containing aniline slurry in the step (1) comes from the catalyst slurry system to which the liquid phase aniline separated in the step (3) is fed.

3. The method of claim 1, wherein, In the step (1), the reactor is a fluidized bed reactor, and the number of internal screens in the reactor is 20-60; and / or, the mass ratio of hydrogen to nitrobenzene in the reactor is 6:1-10:1, the mass ratio of catalyst-containing slurry to hydrogen is controlled to be 7:1-12:1, and the catalyst content in the slurry is 0.2-2%; and / or, the pressure in the reactor is controlled to be 14-20 barg; and / or, the top temperature of the reactor is 210-220℃, and the bottom temperature of the reactor is 70-120℃.

4. The method of claim 1, wherein, In the step (1), the reactor is a fluidized bed reactor, and the number of internal screens in the reactor is 30-40; and / or, the pressure in the reactor is controlled to be 16-18 barg; and / or, the top temperature of the reactor is 214-217℃, and the bottom temperature of the reactor is 85-95℃.

5. The method according to any one of claims 1 to 4, characterized in that, In the step (2), the demister at the top of the reactor is a blade type, baffle type or wire mesh demister; and / or, a liquid level meter is further arranged in the gas phase space to monitor the height of the foam layer, and the liquid level meter is a magnetic flip plate liquid level meter or a differential pressure liquid level meter; and / or, the gas velocity of the gas phase aniline in the gas phase space is 0.3-0.5 m / s, and an adjusting valve is arranged in the liquid phase collecting pipeline of the first tray to control the height of the foam liquid layer at the top of the reactor.

6. The method according to any one of claims 1 to 4, wherein In the step (3), the catalyst recovery tank is provided with a gas phase inlet, the gas phase inlet is provided with a gas distributor, a demister is arranged at the top of the catalyst recovery tank, and the demister arranged at the top of the catalyst recovery tank is a blade type, baffle type or wire mesh demister.

7. The method of claim 6, wherein, A horizontal cooling coil is arranged between the gas phase inlet and the demister to accurately control the temperature to 0-2℃, and the gas phase residence time in the tank body is designed to be > 1 s.

8. The method of claim 6, wherein, A horizontal cooling coil is arranged between the gas phase inlet and the demister to accurately control the temperature to 0.5-1℃, and the gas phase residence time in the tank body is designed to be > 5 s.

9. A method for monitoring and adjusting the overall activity of a system catalyst, the method comprising: (1) analyzing the aniline slurry taken from the first tray of the reactor top in the process for reducing catalyst loss in liquid phase nitrobenzene hydrogenation to aniline according to any one of claims 1-8, monitoring the contents of azobenzene, nitrobenzene, N-cyclohexyl aniline and tar in the aniline slurry and comparing them with the set contents of azobenzene, nitrobenzene, N-cyclohexyl aniline and tar; (2) determining catalyst activity according to the contents of azobenzene, nitrobenzene, N-cyclohexyl aniline and tar in the aniline slurry, and taking or supplementing catalyst from the system.

10. The method of claim 9, wherein, The azobenzene is set at 10-150 ppm, the N-cyclohexyl aniline is set at 50-200 ppm, the tar is set at 1%-10%, and the nitrobenzene is set at 0-1000 ppm.

11. The method of claim 10, wherein, The azobenzene is set at 20-50 ppm, the N-cyclohexyl aniline is set at 80-120 ppm, the tar is set at 3-5%, and the nitrobenzene is set at 400-600 ppm.

12. The method according to any one of claims 9 to 11, characterized in that, In step (2), the thickener filtrate take-off amount is adjusted to control the tar content in the slurry to be 1%-10%, and / or the fresh catalyst addition amount is adjusted to control the nitrobenzene content in the slurry to be 0-1000 ppm, and / or when the N-cyclohexyl aniline exceeds the upper limit of the set range, the system catalyst slurry is partially taken off to a storage tank; and / or when the azobenzene content is higher than the upper limit of the control range, the catalyst slurry in the storage tank is preferentially supplemented to the reactor.

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