A method for reducing the content of phenol in the byproduct of nitrobenzene MNB liquid phase hydrogenation

Abstract

The present application provides a method for reducing the content of phenol in the byproduct of nitrobenzene MNB liquid phase hydrogenation. The method comprises the following steps: after the raw material nitrobenzene is mixed with aniline slurry containing catalyst, it is sent into a hydrogenation reactor together with hydrogen, and the reaction temperature is adjusted; after the heavy component tar in the side line catalyst slurry is removed, it is returned to the reactor for recycling, and fresh catalyst is supplemented from the side line; nitrobenzene and hydrogen are catalytically reacted to generate aniline crude product, and aniline is co-boiled with water to be collected in gas phase from the top of the reactor; wherein the mass content of phenylhydroxylamine in the side line of the reactor is controlled to be 200-1000 ppm based on the total mass of the side line catalyst slurry by the amount of fresh catalyst supplement. The method can significantly reduce the content of phenol, a key impurity in the aniline product of nitrobenzene liquid phase hydrogenation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aniline, and particularly relates to a method for reducing the content of phenol in by-product of liquid-phase hydrogenation of nitrobenzene. BACKGROUND

[0002] Aniline is an important organic synthetic raw material, which is widely used in the industries of polyurethane, medicine, pesticide, rubber additive, etc., and is mainly used for preparing 4,4-diphenyl methane diisocyanate (MDI) which is a raw material for preparing polyurethane. At present, aniline is generally prepared by a liquid-phase hydrogenation process of nitrobenzene, which has the advantages of large production capacity and low production cost. However, a series of by-products such as benzene, cyclohexanol, cyclohexylamine, phenol and tar are generated due to the inevitable accompanying side reactions, thereby affecting the quality of aniline product. In the preparation of MDI-grade aniline, the content of phenol impurity is strictly required to be less than 20 ppm. Since the boiling point of phenol is 181.9℃ and the boiling point of aniline is 184.4℃, which are very close, the current process needs to consume a large amount of steam to remove phenol from the product by distillation separation. If the generation of phenol can be reduced by optimizing the reaction parameters from the reaction end, the energy consumption of the downstream refining can be greatly reduced, and the production cost can be saved.

[0003] Patent CN 113943223 A controls the concentration of nitrobenzene in the reaction raw material liquid at the bottom of the reactor to be less than 50% by feeding the raw material nitrobenzene to different height positions of the tower reactor in different streams, thereby inhibiting the generation of phenol from benzene in the tower, and further reducing the generation amount of phenol. However, this method ignores that phenol can also be generated through other reaction paths, and the generation of phenol from benzene is not the only reaction path. In addition, the nitrobenzene introduced into the upper part of the reactor tower may not be completely reacted due to insufficient residence time, thereby increasing the catalyst consumption. Patent CN 110627651 A increases a catalytic reactor after a hydrogen heat exchanger on the basis of the existing process of preparing aniline by gas-phase hydrogenation of nitrobenzene, and provides a method for further catalytically hydrogenating phenol in aniline into light components which are easy to remove by using the waste heat of gas-phase hydrogenation of nitrobenzene and excess hydrogen, thereby reducing the content of phenol in aniline product. However, this method needs to additionally increase a reactor, which greatly changes the original device, and the conversion efficiency of phenol is limited.

[0004] For the current process of preparing aniline by liquid-phase hydrogenation of nitrobenzene, the generation amount of key impurity phenol fluctuates greatly due to the control of multiple factors, and the product distillation tower needs to maintain a high steam input for a long time to ensure the product quality to be qualified, thereby causing waste of energy consumption. Moreover, in the face of high generation amount of phenol, it is always blindly adjusted according to experience, and lacks systematic regulation means.

[0005] In summary, the stable control of the content of phenol in by-product in the preparation of aniline is still a problem to be solved. SUMMARY

[0006] One of the purposes of the present application is to provide a method for reducing the content of phenol in the byproduct of nitrobenzene MNB liquid phase hydrogenation, which can significantly reduce the content of phenol, a key impurity in the aniline product of nitrobenzene liquid phase hydrogenation.

[0007] To achieve the above purposes, the technical solutions of the present application are as follows:

[0008] A method for reducing the content of phenol in the byproduct of nitrobenzene MNB liquid phase hydrogenation, the method comprising the following steps:

[0009] S1: After the raw material nitrobenzene is mixed with aniline slurry containing catalyst, it is sent into a hydrogenation reactor together with hydrogen, and the reaction temperature is adjusted;

[0010] S2: After the side-line catalyst slurry is removed from the heavy component tar, it is returned to the reactor for recycling and fresh catalyst is supplemented from the side-line;

[0011] S3: Nitrobenzene and hydrogen are catalytically reacted to generate aniline crude product, and aniline is co-boiled with water to be taken out from the top of the reactor in gas phase;

[0012] Wherein, the mass content of phenylhydroxylamine in the side-line of the reactor is controlled to be 200-1000 ppm, based on the total mass of the side-line catalyst slurry, by the amount of fresh catalyst supplement.

[0013] The inventors have surprisingly found that phenol is a byproduct of over-hydrogenation of nitrobenzene, and phenylhydroxylamine is an intermediate product in the reaction, which can control the degree of hydrogenation by controlling the degree of hydrogenation of phenylhydroxylamine, thereby achieving the purpose of reducing the content of phenol.

[0014] In an embodiment of the present application, the temperature of nitrobenzene feed in S1 is 110-140°C, preferably 120-140°C.

[0015] In an embodiment of the present application, the temperature of hydrogen and aniline containing catalyst feed in S1 is 60-90°C, preferably 70-85°C.

[0016] In an embodiment of the present application, the catalyst in S1 is one or more of Pd-Pt / C, Pd-Pt / Al2O3, Pd-Pt / SiO2, nickel-based catalyst, copper-based catalyst, preferably noble metal catalyst, more preferably noble metal catalyst with a noble metal loading of 4-6 wt%.

[0017] For example, in one scheme, the ratio of noble metal Pd / Pt is 0-4, preferably 0.25-1.5; the catalyst additive is one or more of Fe, Zn, Cr, Zr, and the additive loading of the catalyst is 5%-10 wt%.

[0018] In one embodiment of the present application, the catalyst-containing aniline slurry in S1 has a solid content of 0.1-3.0 wt% of the catalyst, based on the total mass of the aniline slurry at the bottom of the reactor; preferably, the mass ratio of the catalyst-containing aniline slurry to nitrobenzene is 1:1.5-2.

[0019] In one embodiment of the present application, the amount of hydrogen fed in S1 is such that the pressure in the reactor is 1500-2000 kpag, preferably 1600-1800 kpag.

[0020] In one embodiment of the present application, the mass ratio of hydrogen to nitrobenzene fed into the reactor in S1 is 1:15-18.

[0021] In one embodiment of the present application, the nitrobenzene, catalyst-containing aniline slurry and hydrogen are fed into the bottom of the hydrogenation reactor in S1.

[0022] In one embodiment of the present application, the quenching water is fed into the bottom and middle of the column in S1 to regulate the reaction temperature; preferably, the temperature of the quenching water is 25-40°C, preferably 30-35°C; preferably, the feeding position of the quenching water in the middle is between 18-25 plates, preferably 20-23 plates, of the reactor.

[0023] In one embodiment of the present application, the temperature at the top of the reactor in S1 is controlled to be 190-230°C.

[0024] In one embodiment of the present application, the catalyst slurry in S2 is passed through a thickener to remove heavy tar; preferably, the mass content of tar in the system is controlled to be 2%-6%, based on the total mass of the crude aniline in the reactor.

[0025] In one embodiment of the present application, the fresh catalyst-containing aniline slurry is added in S2.

[0026] In one embodiment of the present application, the mass ratio of the catalyst slurry returned to the reactor from the side line to the fresh catalyst slurry added from the side line in S2 is 65-95:1.

[0027] In one embodiment of the present application, the mass content of the catalyst in the reaction liquid in S3 is 0.1-3.0 wt%, preferably 0.5-2.5 wt%.

[0028] In one embodiment of the present application, the reactor in S3 is a slurry bed reactor; preferably, the number of internal screens in the reactor is 25-45, preferably 28-35.

[0029] In one embodiment of the present application, the mass concentration of phenol in the crude aniline product in S3 is less than 30 ppm, based on the total mass of the gaseous crude aniline.

[0030] Another object of the present application is to provide a crude aniline product.

[0031] A crude aniline product, the crude aniline product being prepared by the above method, and a mass concentration of phenol in the crude aniline product being less than 30 ppm, based on the total mass of the crude aniline.

[0032] Compared with the prior art, the technical solution of the present application has the following positive effects:

[0033] (1) The mass concentration of phenol in the crude aniline product is less than 30 ppm;

[0034] (2) The problem of high phenol content under different working conditions can be solved, and the system is subjected to minimal fluctuation;

[0035] (3) The generation amount of key impurities is reduced from the reaction end, without the need to modify the equipment, introduce a reaction inhibitor, or replace the catalyst, without modifying the original process, and the process adjustment is simple. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A process flow diagram for the production method of nitrobenzene liquid phase hydrogenation to aniline. DETAILED DESCRIPTION

[0037] The specific implementation of the present method will be further described below in conjunction with examples, and it should be noted that each example is a specific description of a preferred embodiment of the present application, and does not limit the protection scope of the present application.

[0038] The sample analysis instrument is a 7890 series gas chromatograph produced by Agilent, using an HP-5 capillary column, and the FID detector temperature is 260℃, the initial column temperature is 50℃, the temperature is programmed to rise at 15℃ / min to 80℃, and the temperature is programmed to rise at 1℃ / min to 255℃, and the temperature is held for 5 min.

[0039] Example 1

[0040] The aniline reactor is a slurry bed reactor using 32 trays, and a Pd-Pt / C noble metal catalyst (Pd:Pt mass ratio = 3:2, Fe as a catalyst promoter, total noble metal loading 5%, and promoter loading 10%, based on the total mass of the catalyst) is used.

[0041] The flow rate of nitrobenzene at 135℃ is 33500 kg / h, and the flow rate of aniline slurry containing 2.6wt% catalyst at 85℃ is 18400 kg / h, which is mixed and fed into the reactor tank, and at the same time, hydrogen gas with a flow rate of 1920 kg / h at 85℃ is introduced into the reactor bottom. The temperature of the reactor top is controlled at 223℃ by introducing 40℃ quenching water at the reactor bottom and 19 plates in the column.

[0042] The thickener filtrate was controlled to maintain the tar content of the reaction system at 3.68%. The fresh catalyst make-up was 250 kg / h, and the phenylhydroxylamine content in the slurry of the reactor side line was analyzed to be 453 ppm.

[0043] The reactor pressure was controlled at 1750 kpag during the reaction, and the phenol content in the gaseous crude aniline at the top of the column was analyzed by chromatography to be 28 ppm.

[0044] Example 2

[0045] The aniline reactor was a slurry bed reactor with 30 trays, and a Pd-Pt / Al203 noble metal catalyst (Pd:Pt mass ratio = 4.5:0.5, Fe as a promoter, total noble metal loading 6%, and promoter loading 8%, based on the total mass of the catalyst) was used.

[0046] The nitrobenzene with a flow rate of 33000 kg / h and a temperature of 135°C was mixed with the aniline slurry containing 2.0 wt% catalyst with a flow rate of 17000 kg / h and a temperature of 85°C, and was fed into the reactor tank, while hydrogen with a flow rate of 1920 kg / h and a temperature of 90°C was fed into the bottom of the reactor. Cooling water at 25°C was fed into the bottom of the reactor and 23 plates in the column, and the temperature at the top of the reactor was controlled at 192°C.

[0047] The thickener filtrate was controlled to maintain the tar content of the reaction system at 3.72%. The fresh catalyst make-up was 180 kg / h, and the phenylhydroxylamine content in the slurry of the reactor side line was analyzed to be 850 ppm.

[0048] The reactor pressure was controlled at 1530 kpag during the reaction, and the phenol content in the gaseous crude aniline at the top of the column was analyzed by chromatography to be 25 ppm.

[0049] Example 3

[0050] The aniline reactor was a slurry bed reactor with 28 trays, and a Pd-Pt / C noble metal catalyst (Pd:Pt mass ratio = 4.5:0.5, Fe as a promoter, total noble metal loading 7%, and promoter loading 5%, based on the total mass of the catalyst) was used.

[0051] The nitrobenzene with a flow rate of 34200 kg / h and a temperature of 115°C was mixed with the aniline slurry containing 0.9 wt% catalyst with a flow rate of 18400 kg / h and a temperature of 65°C, and was fed into the reactor tank, while hydrogen with a flow rate of 2150 kg / h and a temperature of 65°C was fed into the bottom of the reactor. Cooling water at 30°C was fed into the bottom of the reactor and 23 plates in the column, and the temperature at the top of the reactor was controlled at 225°C.

[0052] The thickener filtrate was controlled to maintain the tar content of the reaction system at 2.54%. The fresh catalyst make-up was 280 kg / h, and the phenylhydroxylamine content in the slurry of the reactor side line was analyzed to be 980 ppm.

[0053] The reactor pressure was controlled at 1950 kpag, and the phenol content in the gaseous crude aniline at the top of the column was analyzed by chromatography to be 28 ppm.

[0054] Example 4

[0055] The aniline reactor was a slurry bed reactor with 43 plates, and a Pd-Pt / C noble metal catalyst (Pd:Pt mass ratio = 3:2, Zn as a promoter, total noble metal loading 5%, and promoter loading 10% based on the total mass of the catalyst) was used.

[0056] Nitrobenzene with a flow rate of 32150 kg / h and a temperature of 120°C was mixed with aniline slurry containing 1.9wt% catalyst with a flow rate of 17800 kg / h and a temperature of 75°C, and was fed into the reactor at the bottom of the column. Hydrogen with a flow rate of 1890 kg / h and a temperature of 70°C was also fed into the reactor at the bottom of the column. Cooling water with a temperature of 28°C was fed into the reactor at the bottom of the column and at the 20th plate of the column, and the temperature at the top of the column was controlled at 220°C.

[0057] The thickener filtrate was controlled to maintain the tar content of the reaction system at 5.21%. The fresh catalyst make-up was 220 kg / h, and the phenylhydroxylamine content in the slurry of the reactor side line was analyzed to be 300 ppm.

[0058] The reactor pressure was controlled at 1655 kpag, and the phenol content in the gaseous crude aniline at the top of the column was analyzed by chromatography to be 21 ppm.

[0059] Example 5

[0060] The aniline reactor was a slurry bed reactor with 35 plates, and a Pd-Pt / C noble metal catalyst (Pd:Pt mass ratio = 3:2, Fe as a promoter, total noble metal loading 5%, and promoter loading 10% based on the total mass of the catalyst) was used.

[0061] Nitrobenzene with a flow rate of 33800 kg / h and a temperature of 140°C was mixed with aniline slurry containing 2.8wt% catalyst with a flow rate of 22000 kg / h and a temperature of 90°C, and was fed into the reactor at the bottom of the column. Hydrogen with a flow rate of 2180 kg / h and a temperature of 90°C was also fed into the reactor at the bottom of the column. Cooling water with a temperature of 30°C was fed into the reactor at the bottom of the column and at the 21st plate of the column, and the temperature at the top of the column was controlled at 228°C.

[0062] The thickener filtrate yield was controlled to maintain the tar mass content of the reaction system at 4.69%. The fresh catalyst make-up rate was 380 kg / h, and the phenylhydroxylamine mass content in the reactor side-line slurry was 220 ppm.

[0063] The reactor pressure was controlled at 1980 kpag, and the phenol content in the crude aniline gas phase at the top of the chromatographic column was 29 ppm.

[0064] Comparative Example 1

[0065] Compared with Example 1, the fresh catalyst make-up rate was 400 kg / h, and the phenylhydroxylamine mass content in the reactor side-line slurry was not detected. The catalyst solid content of the reaction system was 2.8 wt%. Other conditions were the same as in Example 1, and the phenol content in the crude aniline gas phase at the top of the chromatographic column was 98 ppm.

[0066] Comparative Example 2

[0067] Compared with Example 1, the fresh catalyst make-up rate was 150 kg / h, and the phenylhydroxylamine mass content in the reactor side-line slurry was 1300 ppm. The catalyst solid content of the reaction system was 0.5 wt%. Other conditions were the same as in Example 1, and the phenol content in the crude aniline gas phase at the top of the chromatographic column was 72 ppm.

[0068] The above description is only a specific description of the preferred embodiments of the present application and does not limit the scope of protection of the present application.

Claims

1. A method for reducing the phenol content in the by-products of the liquid phase hydrogenation of nitrobenzene (MNB), characterized in that, The method comprises the following steps: S1: the raw material nitrobenzene is mixed with the aniline slurry containing catalyst, and is sent into a hydrogenation reactor together with hydrogen, and the reaction temperature is adjusted; S2: after the heavy component tar in the side line catalyst slurry is removed, the catalyst slurry is returned to the reactor for recycling, and fresh catalyst is supplemented from the side line; S3: the nitrobenzene and hydrogen are catalytically reacted to generate a crude aniline product, and the aniline is azeotroped with water and is taken out from the top of the reactor in a gas phase; In S2, the mass content of phenylhydroxylamine in the reactor side line is controlled to be 200-1000 ppm, based on the total mass of the side line catalyst slurry.

2. The method of claim 1, wherein, The nitrobenzene feed temperature in S1 is 110-140 DEG C; And / or, the hydrogen and aniline containing catalyst feed temperature in S1 is 60-90 DEG C; And / or, the catalyst in S1 is one or more of Pd-Pt / C, Pd-Pt / Al2O3, Pd-Pt / SiO2, a nickel catalyst and a copper catalyst; And / or, the solid content of the catalyst in the aniline slurry containing catalyst in S1 is 0.1-3.0 wt%, based on the total mass of the aniline slurry at the bottom of the reactor; And / or, the hydrogen feed amount in S1 makes the reactor pressure 1500-2000 kpag; And / or, the mass ratio of hydrogen to nitrobenzene in the reactor feed in S1 is 1:15-18; And / or, the nitrobenzene, the aniline slurry containing catalyst and hydrogen are sent into the bottom of the hydrogenation reactor in S1; And / or, the quenching water is sent into the bottom and the middle of the tower in S1 to adjust the reaction temperature; And / or, the reactor top temperature in S1 is controlled to be 190-230 DEG C.

3. The method of claim 2, wherein, The nitrobenzene feed temperature in S1 is 120-140 DEG C; And / or, the hydrogen and aniline containing catalyst feed temperature in S1 is 70-85 DEG C; And / or, the catalyst in S1 is a noble metal catalyst; The mass ratio of the aniline slurry containing catalyst to nitrobenzene in S1 is 1:1.5-2; And / or, the hydrogen feed amount in S1 makes the reactor pressure 1600-1800 kpag; The temperature of the quenching water in S1 is 25-40 DEG C; The middle quenching water feed position in S1 is between the 18th and the 25th plate of the reactor.

4. The method of claim 3, wherein, The catalyst in S1 is a noble metal catalyst with a noble metal loading of 4-6 wt%; The temperature of the quenching water in S1 is 30-35 DEG C; The middle quenching water feed position in S1 is between the 20th and the 23rd plate of the reactor.

5. The method of claim 1, wherein, The catalyst slurry in S2 removes heavy component tar through a thickener; And / or, the fresh catalyst containing aniline slurry is added in S2; And / or, the mass ratio of the catalyst slurry returned to the reactor in the side line to the fresh catalyst slurry supplemented in the side line in S2 is 65-95:

1.

6. The method of claim 5, wherein, The mass content of tar in the system in S2 is controlled to be 2%-6%, based on the total mass of the crude aniline in the reactor.

7. The method of claim 1, wherein, The catalyst mass content in the reaction liquid in S3 is 0.1-3.0 wt%; And / or, the reactor in S3 is a slurry bed reactor; And / or, the mass concentration of phenol in the crude aniline product in S3 is less than 30 ppm, based on the total mass of the gas phase crude aniline.

8. The method of claim 7, wherein, The catalyst mass content in the reaction liquid in S3 is 0.5-2.5 wt%; The number of sieve plates in the reactor in S3 is 25-45.

9. The method of claim 8, wherein, S3 28-35 trays in the reactor.

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