Method for preparing aniline through gas phase hydrogenation

Abstract

The invention relates to a method for preparing aniline through gas phase hydrogenation. The method comprises the following steps: reacting nitrobenzene and hydrogen under the action of a catalyst to obtain aniline, a carrier of the catalyst comprises modified silica gel, an active component of the catalyst comprises Cu, and an auxiliary active component of the catalyst comprises Co and / or Ce; the modification method of the modified silica gel comprises the following steps: carrying out alkali treatment on silica gel; the catalyst is prepared by the following steps: loading an active component Cu and an auxiliary active component on modified silica gel, and then carrying out heat treatment in an ammonia gas atmosphere to obtain the catalyst. The carrier silica gel of the catalyst is modified through alkali treatment, the surface and pore channel structure of the carrier is optimized, copper is used as an active component, Ce and / or Co are / is used as catalyst auxiliaries, and the catalyst is subjected to ammonia gas heat treatment modification; the catalyst is used for preparing aniline through gas-phase reduction of nitrobenzene and hydrogen, has excellent nitrobenzene conversion rate and aniline selectivity, and reduces the energy consumption and cost of aniline post-treatment.

Description

Technical Field

[0001] The invention belongs to the field of aromatic amine synthesis, and particularly relates to a method for preparing aniline by gas phase hydrogenation. Background Art

[0002] Aniline, also known as aminobenzene, is an organic compound with the chemical formula C6H7N. It is a colorless oily liquid that decomposes when heated to 370°C. It is slightly soluble in water and easily soluble in organic solvents such as ethanol and ether. Aniline is one of the most important amine substances. It is mainly used to make dyes, drugs, resins, and can also be used as a rubber vulcanization accelerator. It can also be used as a black dye. Its derivative methyl orange can be used as an indicator for acid-base titration.

[0003] Common preparation methods of aniline include nitrobenzene gas phase hydrogenation method and nitrobenzene liquid phase hydrogenation method, wherein the liquid phase hydrogenation method, for example, a method for preparing aniline by liquid phase hydrogenation of nitrobenzene with low phenol production disclosed in the prior art, relates to a method for preparing aniline by liquid phase hydrogenation of nitrobenzene with low phenol production, wherein raw material nitrobenzene is fed into a tower reactor at different heights, the nitrobenzene concentration in the reaction raw material liquid at the bottom of the reactor is controlled to be below 50%, and the mass ratio of nitrobenzene to hydrogen at the bottom of the tower is between 6:1 and 10:1, thereby reducing the production of by-product phenol raw material benzene in the tower, thereby reducing the production of phenol. Gas phase hydrogenation method, for example, the coupled reaction device and reaction method for hydrogenating nitrobenzene to produce aniline disclosed in the prior art, uses three reaction zones to finely control the reaction, and adopts the setting of two degassing tanks to solve the problem of online regeneration and activation of coking catalyst, achieving the technical solution of low nitrobenzene content in crude aniline, continuous reaction, regeneration and activation for a long period of production, which better solves the above technical problems and can be applied to the industrial production of hydrogenating nitrobenzene to produce aniline. Gas phase hydrogenation method, as one of the mainstream methods, still has problems such as insufficient activity of gas phase hydrogenation catalyst, long reaction temperature cycle, and many by-products.

[0004] Therefore, it is still of great significance to further improve the catalyst composition and structure to optimize the catalyst activity and aniline selectivity, thereby reducing the energy consumption and cost of subsequent separation of aniline. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing aniline by gas phase hydrogenation, comprising taking nitrobenzene and hydrogen as raw materials, adopting a specific catalyst to catalyze a reaction to obtain aniline, wherein the catalyst adopts modified silica gel treated with alkali as a carrier, and uses auxiliary active components Co and / or Ce to modify the active component Cu, and is modified by ammonia heat treatment; the catalyst is used for preparing aniline by gas phase hydrogenation of nitrobenzene, and has excellent nitrobenzene conversion rate and aniline selectivity, and reduces the energy consumption and cost of aniline post-treatment.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing aniline by gas phase hydrogenation, comprising reacting nitrobenzene and hydrogen in the presence of a catalyst to obtain aniline; the carrier of the catalyst comprises modified silica gel, the active component comprises Cu, and the auxiliary active component comprises Co and / or Ce;

[0008] The modification method of the modified silica gel comprises treating the silica gel with alkali;

[0009] The catalyst is prepared by the following method: loading the modified silica gel with active component Cu and auxiliary active component, and then performing heat treatment in an ammonia atmosphere to obtain the catalyst.

[0010] The synthesis of aniline by a gas phase process using nitrobenzene and hydrogen as raw materials is one of the main routes for the existing synthesis of aniline. Traditionally, silica gel supported Cu is generally used as a catalyst. However, due to the performance of the catalyst itself, there are still problems such as low reaction efficiency, high by-products, high light component separation cost, high energy consumption, etc. Based on the study of the above problems, the present invention provides a preparation method of aniline based on a specific catalyst composition improvement; the catalyst uses modified silica gel treated with alkali as a carrier, optimizes the surface and internal pore structure of the silica gel, and adds auxiliary active components Co and / or Ce to form a synergistic effect with the active component Cu, thereby optimizing the selectivity of aniline in the reaction process and reducing the by-products of phenol and other components.

[0011] Preferably, based on the mass of the modified silica gel as 100%, the loading amount of Cu is selected from 10wt% to 15wt%; for example, 11wt%, 12wt%, 13wt% or 14wt%, etc., and the loading amount of the co-active component is selected from 5wt% to 10wt%, for example, 6wt%, 7wt%, 8wt% or 9wt%, etc.

[0012] In the catalyst of the present invention, the loading amounts of the active component and the co-active component are selected within the above range, and the catalyst has good catalytic conversion rate and aniline selectivity.

[0013] Preferably, the alkali treatment method comprises: heat treating the silica gel under an inert atmosphere; the heat treatment temperature is selected from 300°C to 400°C, such as 320°C, 350°C or 370°C.

[0014] Then, the silica gel is immersed in an ammonia solution, washed and dried to obtain the modified silica gel.

[0015] Preferably, the concentration of the aqueous ammonia solution is selected from 15wt% to 30wt%, for example, 16wt%, 18wt%, 20wt%, 22wt%, 25wt% or 28wt%.

[0016] Preferably, the immersion temperature in the aqueous ammonia solution is 15°C to 30°C, such as 18°C, 20°C, 22°C, 25°C or 28°C.

[0017] Preferably, the immersion time in the aqueous ammonia solution is 0.5 h to 1.5 h, for example, 0.5 h, 1 h, 1.5 h, etc.

[0018] Preferably, the silica gel is selected from coarse-porous silica gel, preferably coarse-porous block silica gel;

[0019] Traditional nitrobenzene reduction catalyst Cu / SiO2 has a transition period at the beginning of the catalytic reaction. During the transition period, the reaction has low selectivity for aniline, and a large amount of by-product components such as phenol are generated. After the reaction has been carried out for a period of time, the selectivity for aniline will increase. Studies have found that the pore structure of the catalyst changes accordingly at this time, which further indicates that the surface and pore structure of the catalyst carrier have a great influence on the catalytic performance. The present invention has found through research that the above-mentioned alkaline treatment operation of the silica gel carrier before loading the active component is beneficial to optimizing the surface and pore structure of the catalyst, and is beneficial to improving the reaction selectivity of the catalyst in combination with the loading of the active component and the specific auxiliary active component.

[0020] Preferably, the catalyst is prepared by the following method, which comprises the following steps:

[0021] (1) treating silica gel with alkali to obtain modified silica gel;

[0022] (2) immersing the silica gel in a mixed solution of copper salt and auxiliary metal salt, and drying;

[0023] (3) calcining the product of step (2) at 200° C. to 300° C. (exemplarily including 220° C., 250° C. or 270° C., etc.) under an inert atmosphere, and then introducing ammonia gas for heat treatment to obtain the catalyst.

[0024] Preferably, the copper salt is selected from water-soluble copper salts, preferably copper nitrate.

[0025] Preferably, the temperature for heat treatment by introducing ammonia gas is selected from 200°C to 300°C, such as 220°C, 250°C, and 270°C.

[0026] Preferably, the time for introducing ammonia gas for heat treatment is selected from 1 h to 2 h, such as 1.2 h, 1.5 h or 1.8 h.

[0027] In the present invention, during the catalyst preparation process, the silica gel carrier modified by alkali treatment is impregnated with copper salt and auxiliary metal salt, and then calcined under the protection of an inert atmosphere, and the active components and auxiliary active components are highly dispersed on the surface of the carrier and in the pore structure; then ammonia is introduced for heat treatment reduction and surface modification to obtain the modified catalyst; then it is ground, screened and formed to obtain the granular catalyst.

[0028] The catalyst of the present invention is calcined in an inert atmosphere and heat-treated with ammonia for reduction modification, thereby optimizing the interaction between the main active component, the auxiliary active component and the carrier, further improving the selectivity of the catalyst for aniline during the catalytic reaction, and reducing the generation of by-products.

[0029] Preferably, the molar ratio of the nitrobenzene to the hydrogen is 1:5-15, such as 1:7, 1:10 or 1:13.

[0030] Preferably, the auxiliary active component is selected from Co; the loading ratio of Cu to Co is 1.5 to 2.5:1, such as 1.6:1, 1.8:1, 2:1, 2.2:1 or 2.4:1, etc.;

[0031] Or the auxiliary active component is selected from Ce, and the loading ratio of Cu to Ce is 1.5 to 2.5:1, such as 1.6:1, 1.8:1, 2:1, 2.2:1 or 2.4:1.

[0032] Preferably, the nitrobenzene and the hydrogen are reacted in a fluidized bed reactor or a fixed bed reactor.

[0033] Preferably, the particle size of the catalyst is selected from 60 mesh to 80 mesh, such as 60 mesh to 70 mesh or 70 mesh to 80 mesh.

[0034] Preferably, the reaction temperature of the nitrobenzene and the hydrogen is selected from 150°C to 210°C, such as 160°C, 170°C, 180°C, 190°C or 200°C.

[0035] Preferably, the reaction pressure of nitrobenzene and hydrogen is selected from 0.05 MPa to 0.3 MPa, for example, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa or 0.25 MPa, etc.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] In the aniline preparation method of the present invention, the carrier silica gel of the catalyst is modified by alkali treatment, the surface and pore structure of the carrier are optimized, copper is used as the active component and Ce and / or Co are used as catalyst promoters; the catalyst is modified by ammonia heat treatment, and the catalyst is used for preparing aniline by reduction of nitrobenzene and hydrogen, and has excellent nitrobenzene conversion rate and aniline selectivity, and reduces the energy consumption and cost of aniline post-treatment. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0039] Catalyst Preparation Example 1

[0040] The composition of the catalyst in this embodiment is as follows: the mass ratio of carrier, Cu, and Co is 1:0.125:0.06;

[0041] The catalyst is prepared by the following method, which comprises:

[0042] (1) In a tubular furnace, the coarse-porous silica gel is heat-treated at 350° C. for 20 min under a nitrogen atmosphere; then, it is immersed in a 25% ammonia solution at room temperature for 1 h, filtered, washed with deionized water, and dried to obtain modified silica gel;

[0043] (2) preparing a mixed salt solution of copper nitrate and cobalt nitrate, immersing the modified silica gel in the mixed salt solution, and then drying;

[0044] (3) The dried product in step (2) was calcined at 250° C. for 2 h under a nitrogen atmosphere; ammonia was then introduced and reduced at 250° C. for 1.5 h to obtain a modified catalyst; and the catalyst was ground and sieved to obtain catalyst particles of 60 to 80 mesh.

[0045] Catalyst Preparation Example 2

[0046] The difference between this embodiment and embodiment 1 is that the loading amount of the auxiliary active component is replaced by Co with Ce, and cerium nitrate is used as the raw material in the preparation process; the other parameters and conditions are exactly the same as those in embodiment 1.

[0047] Catalyst Preparation Example 3

[0048] The only difference between this embodiment and embodiment 1 is that the composition of the catalyst in this embodiment is as follows: the mass ratio of the carrier, Cu and Co is 1:0.14:0.08; the corresponding material parameters of the preparation process are adaptively adjusted, and the other parameters and conditions are exactly the same as those in embodiment 1.

[0049] Catalyst Preparation Example 4

[0050] The only difference between this embodiment and embodiment 1 is that the composition of the catalyst in this embodiment is as follows: the mass ratio of the carrier, Cu and Co is 1:0.2:0.13; the corresponding material parameters of the preparation process are adaptively adjusted, and the other parameters and conditions are exactly the same as those in embodiment 1.

[0051] Catalyst Preparation Comparative Example 1

[0052] The only difference between this embodiment and embodiment 1 is that the calcination under nitrogen atmosphere in step (3) is replaced by calcination under air atmosphere, and the ammonia reduction is replaced by hydrogen reduction; the other parameters and conditions are exactly the same as those in embodiment 1.

[0053] Catalyst Preparation Comparative Example 2

[0054] The only difference between this comparative example and comparative example 1 is that the operation in step (1) is not performed, and the other parameters and conditions are exactly the same as those in comparative example 1.

[0055] Catalyst Preparation Comparative Example 3

[0056] The only difference between this comparative example and comparative example 1 is that the catalyst does not contain any auxiliary active component, and the other parameters and conditions are exactly the same as those in comparative example 1.

[0057] Example:

[0058] A method for preparing aniline by gas phase hydrogenation, specifically, adding the catalyst prepared in the above catalyst preparation example and catalyst preparation comparative example into a fixed bed reactor, the particle size of the catalyst is selected from 60 mesh to 80 mesh, the catalyst filling volume is 5 mL, the feed inlet temperature is 180° C., and the pressure is set to 0.25 MPa; the molar ratio of nitrobenzene to hydrogen in the feed composition is 1:10; the feed flow rate of nitrobenzene is 0.2 ml / min. After the reaction is stable for 40 minutes, the gas composition after the reaction is tested by gas chromatography, and the nitrobenzene conversion rate and aniline yield are calculated. The test results are shown in Table 1.

[0059] Table 1

[0060] catalyst Nitrobenzene conversion rate (%) Aniline selectivity (%) Catalyst Preparation Example 1 99.3 99.1 Catalyst Preparation Example 2 99.6 99.5 Catalyst Preparation Example 3 99.5 99.2 Catalyst Preparation Example 4 98.8 98.7 Catalyst Preparation Comparative Example 1 91.4 92.1 Catalyst Preparation Comparative Example 2 88.1 91.5 Catalyst Preparation Comparative Example 3 84.1 89.4

[0061] It can be seen from the test results in the above table that the catalyst of the present invention has good catalytic activity and aniline selectivity. The catalyst of the present invention optimizes the carrier pores and surface structure by alkali-modified carrier, and combines the active component and ammonia reduction-modified active component and the active component to significantly improve the catalytic activity of the catalyst; it can be seen from the above table that after the reaction is stable for 40 minutes, the selectivity of nitrobenzene can reach up to 99.6%, and the selectivity of aniline can reach 98.7% and above, and further preferably can reach 99% and above, which reduces the generation of by-product components and is beneficial to reducing the subsequent purification cost and energy consumption of the product; and the catalyst used in the preparation method of the present invention has a simple composition and low preparation cost.

[0062] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing aniline by gas phase hydrogenation, comprising reacting nitrobenzene and hydrogen in the presence of a catalyst to obtain aniline; characterized in that: The catalyst carrier comprises modified silica gel, the active component comprises Cu, and the auxiliary active component comprises Co and / or Ce; The modification method of the modified silica gel comprises treating the silica gel with alkali; The catalyst is prepared by the following method: loading the modified silica gel with active component Cu and auxiliary active component, and then performing heat treatment in an ammonia atmosphere to obtain the catalyst.

2. The method for preparing aniline by gas phase hydrogenation according to claim 1, characterized in that: Based on the mass of the modified silica gel as 100%, the loading amount of Cu is selected from 10wt% to 15wt%; the loading amount of the co-active component is selected from 5wt% to 10wt%.

3. The method for preparing aniline by gas phase hydrogenation according to claim 1, characterized in that: The alkali treatment method comprises: heat treating the silica gel under an inert atmosphere; the heat treatment temperature is selected from 300° C. to 400° C.; Then, it is immersed in an ammonia solution, washed and dried to obtain the modified silica gel.

4. The method for preparing aniline by gas phase hydrogenation according to claim 3, characterized in that: The silica gel is selected from coarse pore silica gel.

5. The method for preparing aniline by gas phase hydrogenation according to any one of claims 1 to 4, characterized in that: The catalyst is prepared by the following method, which comprises the following steps: (1) treating silica gel with alkali to obtain modified silica gel; (2) immersing the silica gel in a mixed solution of copper salt and auxiliary metal salt, and drying; (3) calcining the product of step (2) at 200° C. to 300° C. under an inert atmosphere, and then introducing ammonia gas for heat treatment to obtain the catalyst.

6. The method for preparing aniline by gas phase hydrogenation according to claim 1, characterized in that: The molar ratio of the nitrobenzene to the hydrogen is 1:5-15.

7. The method for preparing aniline by gas phase hydrogenation according to claim 1 or 2, characterized in that: The auxiliary active component is selected from Co; the loading ratio of Cu to Co is 1.5 to 2.5:1; Or the auxiliary active component is selected from Ce, and the loading ratio of Cu to Ce is 1.5-2.5:

1.

8. The method for preparing aniline by gas phase hydrogenation according to claim 1, characterized in that: The nitrobenzene and the hydrogen are reacted in a fluidized bed reactor and / or a fixed bed reactor; The particle size of the catalyst is selected from 60 to 80 meshes.

9. The method for preparing aniline by gas phase hydrogenation according to claim 1, characterized in that: The reaction temperature of the nitrobenzene and the hydrogen is selected from 150°C to 210°C.

10. The method for preparing aniline by gas-phase hydrogenation according to claim 1, wherein the reaction pressure of the nitrobenzene and the hydrogen is selected from 0.05 to 0.3 MPa.