A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline

Abstract

The present invention discloses a method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline; aiming to provide a method for synthesizing p-fluoroaniline with less environmental pollution, high catalytic activity, good selectivity and low cost; its technical solution successively includes the following steps: (1) adding p-fluoronitrobenzene, ethanol and a catalyst into a hydrogenation reaction kettle to form a reaction precursor solution; (2) replacing the gas inside the reaction kettle with hydrogen, and reacting the reaction precursor solution and hydrogen at a catalytic temperature of 50-80 °C and a catalytic pressure of 2 MPa for 3-7 h to synthesize p-fluoroaniline.

Description

Technical Field

[0001] The present invention belongs to the field of synthesis and relates to a method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline. Background Art

[0002] p-Fluoroaniline is an important intermediate widely used in the synthesis of fluorine-containing pesticides, pharmaceuticals and dyes. Aniline compounds are mainly prepared by reducing aromatic nitro compounds. The industrial methods for reducing aromatic nitro compounds to produce aniline compounds mainly include metal reduction, alkali sulfide reduction, catalytic hydrogenation reduction, hydrazine hydrate reduction and electrochemical reduction, etc. Among them, the application of metal catalysis is the most extensive and has high catalytic activity, but its disadvantage is that it is easy to be poisoned. Widely used metal catalysts are precious metal catalysts such as palladium, platinum and rhodium, with too high production costs and problems of difficult recovery and separation. Therefore, due to its rich reserves, low price and excellent dehydrogenation performance, transition metal Ni is expected to become a substitute for precious metal catalysts.

[0003] Currently, the industrial production of p-fluoroaniline is mainly by one-step synthesis. Among the one-step synthesis processes, the nitrobenzene method is a better process, which involves hydrogenating p-fluoronitrobenzene to prepare p-fluoroaniline. Chinese Patent CN111659400A discloses a preparation method of a supported CuNi bimetallic Cu1Ni1 / rGO catalyst and its application in the synthesis of p-fluoroaniline, which has the characteristics of stable chemical structure, good conductivity and high catalytic activity, but requires a certain Ni loading amount. Chinese Patent CN104710316A discloses a method for continuous catalytic hydrogenation of fluoronitrobenzene to prepare fluoroaniline, which can be used for continuous reactions and has relatively high catalytic activity, but the catalyst preparation process is relatively complex, resulting in high production costs.

[0004] Therefore, in order to improve the activity of the catalyst, simplify the catalyst preparation process, reduce costs and environmental pollution, meet the current environmental protection requirements, and improve the production efficiency of p-fluoroaniline, it is particularly important to prepare a suitable highly selective hydrogenation catalyst. The selection of the carrier also affects the catalytic activity of the catalyst. For example, transition metal Mn element has variable d electrons and shows a special influence on hydrogenation, which can promote the dispersion of the active phase, inhibit catalyst sintering and surface carbon deposition, and modulate the metal electron density and basicity effect. Summary of the Invention

[0005] To solve the above technical problems, the present invention discloses a method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, aiming to provide a method for synthesizing p-fluoroaniline with less environmental pollution, high catalytic activity, good selectivity and low cost.

[0006] For this reason, the first technical solution provided by the present invention is as follows:

[0007] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline successively includes the following steps:

[0008] (1) Add p-fluoronitrobenzene, ethanol and a catalyst into a hydrogenation reactor to form a reaction precursor solution;

[0009] (2) Replace the gas inside the reactor with hydrogen, and react the reaction precursor solution and hydrogen at a catalytic temperature of 50 - 80 °C and a catalytic pressure of 2 MPa for 3 - 7 h to synthesize p-fluoroaniline;

[0010] The mass ratio of the p-fluoronitrobenzene∶ethanol∶catalyst is 1∶(10 - 15)∶(0.1 - 0.3).

[0011] Furthermore, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the catalyst is a nickel catalyst supported on manganese oxide

[0012] Furthermore, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the catalytic temperature in step (2) is 60 - 70 °C.

[0013] Furthermore, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the reaction time in step (2) is 4 - 6 h.

[0014] Furthermore, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the catalyst is prepared by the following method:

[0015] (1) Mix nickel oxide and manganese oxide in a molar ratio of 1∶(1 - 3), grind them into powder to obtain a mechanically mixed powder of NiMn oxide;

[0016] (2) Reduce the NiMn oxide powder described in step (1) in a reducing gas atmosphere at 450 - 700 °C for 5 - 6 h to obtain a nickel catalyst supported on manganese oxide.

[0017] Even further, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the nickel oxide in step (1) is nickel oxide.

[0018] Even further, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the manganese oxide in step (1) is manganese dioxide.

[0019] Even further, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the molar ratio of nickel oxide and manganese oxide in step (1) is 1∶(1 - 3).

[0020] Even further, in the above method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, the reducing gas in step (2) is hydrogen.

[0021] Further, in the preparation method of the nickel-loaded manganese oxide catalyst described above, the reduction temperature in step (2) is 550 - 600 °C.

[0022] Further, in the preparation method of the nickel-loaded manganese oxide catalyst described above, the reduction time in step (2) is 4 h.

[0023] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0024] 1. The technical solution provided by the present invention uses a nickel-loaded manganese oxide catalyst to catalytically synthesize p-fluoroaniline. The addition of manganese significantly increases the active specific surface area of the catalyst, promotes the dispersion of the active components, and increases the number of active centers generated after reduction, thereby improving the hydrogenation activity.

[0025] 2. The preparation method of the technical solution provided by the present invention is simple and easy to implement. The synthesis process of p-fluoroaniline is simple, with the advantages of mild reaction conditions, high catalytic activity, and low production cost, and has the prospect of realizing industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the XRD pattern of the nickel-loaded manganese oxide catalyst and the manganese oxide standard card used in Examples 1 - 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below by way of examples, but it does not constitute any limitation to the present invention. Any limited modifications made by anyone within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0028] Example 1

[0029] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively includes the following steps:

[0030] (1) Weigh 0.01 mol of nickel oxide and 0.01 mol of manganese dioxide, mix them and grind them into powder with a mortar, and calcine them at 450 °C for 4 h in a hydrogen atmosphere for reduction treatment to obtain a nickel-loaded manganese oxide catalyst, and its XRD pattern is referred to Figure 1 ;

[0031] (2) Weigh 2 g of p-fluoronitrobenzene, 20 g of ethanol and 0.2 g of the catalyst prepared in step (1) and add them to a hydrogenation reactor, then replace the gas inside the reactor with hydrogen, the reaction temperature is 50 °C, the catalytic pressure is 2 MPa, and the reaction time is 7 h. After the reaction is completed, a sample is taken for analysis by gas chromatography (GC), and quantitative analysis is carried out by the internal standard method. The reaction conversion rate is 96.9%, and the reaction selectivity is 100%.

[0032] Example 2

[0033] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively comprises the following steps:

[0034] (1) Weigh 0.01 mol of nickel oxide and 0.03 mol of manganese dioxide, mix them and grind them into powder with a mortar, and calcine them at 450 °C for 4 h in a hydrogen atmosphere for reduction treatment to obtain a manganese oxide-supported nickel catalyst, and its XRD pattern is referred to Figure 1 ;

[0035] (2) Weigh 2 g of p-fluoronitrobenzene, 30 g of ethanol and 0.6 g of the catalyst prepared in step (1) and add them to a hydrogenation reactor, then replace the gas inside the reactor with hydrogen, the reaction temperature is 80 °C, the catalytic pressure is 2 MPa, the reaction time is 3 h, and after the reaction is completed, a sample is taken for analysis by gas chromatography (GC), and quantitative analysis is carried out by the internal standard method. The reaction conversion rate is 99.0%, and the reaction selectivity is 96.5%.

[0036] Example 3

[0037] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively comprises the following steps:

[0038] (1) Weigh 0.01 mol of nickel oxide and 0.02 mol of manganese dioxide, mix them and grind them into powder with a mortar, and calcine them at 450 °C for 4 h in a hydrogen atmosphere for reduction treatment to obtain a manganese oxide-supported nickel catalyst, and its XRD pattern is referred to Figure 1 ;

[0039] (2) Weigh 2 g of p-fluoronitrobenzene, 25 g of ethanol and 0.4 g of the catalyst prepared in step (1) and add them to a hydrogenation reactor, then replace the gas inside the reactor with hydrogen, the reaction temperature is 70 °C, the catalytic pressure is 2 MPa, the reaction time is 5 h, and after the reaction is completed, a sample is taken for analysis by gas chromatography (GC), and quantitative analysis is carried out by the internal standard method. The reaction conversion rate is 99.5%, and the reaction selectivity is 99.7%.

[0040] Example 4

[0041] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively comprises the following steps:

[0042] (1) Weigh 0.01 mol of nickel oxide and 0.01 mol of manganese dioxide, mix them and grind them into powder with a mortar, and calcine them at 700 °C for 4 h in a hydrogen atmosphere for reduction treatment to obtain a manganese oxide-supported nickel catalyst;

[0043] (2) Weigh 2 g of p-fluoronitrobenzene, 20 g of ethanol, and 0.2 g of the catalyst prepared in step (1) and add them to the hydrogenation reactor. Then, replace the gas inside the reactor with hydrogen. The reaction temperature is 70 °C, the catalytic pressure is 2 MPa, and the reaction time is 5 h. After the reaction ends, take a sample for analysis by gas chromatography (GC), and use the internal standard method for quantification. The reaction conversion rate is 94.2%, and the reaction selectivity is 95.3%.

[0044] Example 5

[0045] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively includes the following steps:

[0046] (1) Weigh 0.01 mol of nickel oxide and 0.01 mol of manganese dioxide, mix them and grind them into powder with a mortar, and calcine them at 550 °C for 4 h in a hydrogen atmosphere for reduction treatment to obtain a manganese dioxide-supported nickel catalyst.

[0047] (2) Weigh 2 g of p-fluoronitrobenzene, 20 g of ethanol, and 0.2 g of the manganese dioxide-supported nickel catalyst prepared in step (1) and add them to the hydrogenation reactor. Then, replace the gas inside the reactor with hydrogen. The reaction temperature is 70 °C, the catalytic pressure is 2 MPa, and the reaction time is 5 h. After the reaction ends, take a sample for analysis by gas chromatography (GC), and use the internal standard method for quantification. The reaction conversion rate is 99.8%, and the reaction selectivity is 100%.

[0048] Comparative Example 1

[0049] A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline provided by the present invention successively includes the following steps:

[0050] (1) Weigh 2 g of p-fluoronitrobenzene, 20 g of ethanol, and 0.2 g of pure nickel and add them to the hydrogenation reactor. Then, replace the gas inside the reactor with hydrogen. The reaction temperature is 70 °C, the catalytic pressure is 2 MPa, and the reaction time is 5 h. After the reaction ends, take a sample for analysis by gas chromatography (GC), and use the internal standard method for quantification. The conversion rate is 83.2%, and the selectivity is 80.6%.

[0051] From Examples 1-6 and Comparative Example 1, it can be seen that the manganese dioxide-supported nickel catalyst provided by the present application significantly improves the conversion rate and selectivity of catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline.

[0052] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline, which is characterized in that it successively includes the following steps: (1) Add p-fluoronitrobenzene, ethanol and a catalyst into a hydrogenation reactor to form a reaction precursor solution; (2) Replace the gas inside the reactor with hydrogen, and react the reaction precursor solution and hydrogen at a catalytic temperature of 50 - 80 °C and a catalytic pressure of 2 MPa for 3 - 7 h to synthesize p-fluoroaniline; The mass ratio of the p-fluoronitrobenzene:ethanol:catalyst is 1:(10 - 15):(0.1 - 0.3); The catalyst is a nickel supported on manganese oxide catalyst, which is prepared by the following method: S1: Mix nickel oxide and manganese oxide according to a molar ratio of 1:(1 - 3), grind them into powder to obtain a powder of mechanically mixed NiMn oxide; S2: Subject the NiMn oxide powder described in S1 to a reduction treatment at 450 - 700 °C in a reducing gas atmosphere for 4 h to obtain a nickel supported on manganese oxide catalyst.

2. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the catalytic temperature described in step (2) is 60 - 70 °C.

3. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the reaction time described in step (2) is 4 - 6 h.

4. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the nickel oxide in step S1 is nickel oxide.

5. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the manganese oxide in step S1 is manganese dioxide.

6. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the reducing gas in step S2 is hydrogen.

7. The method for catalytic hydrogenation of p-fluoronitrobenzene to synthesize p-fluoroaniline according to claim 1, which is characterized in that the reduction temperature in step S2 is 550 - 600 °C.

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