Preparation method of catalyst for preparing cyclohexene through benzene hydrogenation

Abstract

The invention discloses a preparation method of a catalyst for preparing cyclohexene through benzene hydrogenation, and belongs to the technical field of catalyst preparation. Comprising the following steps: dropwise adding a metal salt solution containing ruthenium salt and zinc salt and a precipitant solution into an alcohol solution at the same time, and carrying out a co-precipitation reaction; carrying out in-situ reduction on a solid product obtained by the coprecipitation reaction; a product obtained after in-situ reduction is put into alkali liquor to be stirred; according to the method, the alcoholic solution is used as a coprecipitation reaction medium, does not participate in the reaction, but can adjust the microenvironment of the reaction medium, so that the microenvironment fluctuation of the solution in the precipitation process is relatively small; the catalyst with relatively uniform precipitation can be obtained, so that the activity of the prepared Ru-Zn catalyst can be improved; the problems of single precipitation process, insufficient catalyst structure uniformity, poor preparation reproducibility and the like of a traditional water phase coprecipitation method are solved; the catalyst is applied to a reaction for generating cyclohexene through selective hydrogenation of benzene.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically a method for preparing a catalyst for the hydrogenation of benzene to cyclohexene. Background Technology

[0002] The partial hydrogenation of benzene to cyclohexene is a key reaction in the manufacture of bulk chemicals, especially providing an important intermediate for the production of nylon-6 and nylon-66. These two nylon materials are widely used as indispensable raw materials in the automotive, electronics, and construction industries. The traditional cyclohexane route based on free radical oxidation is gradually being replaced by the cyclohexene route due to significant safety hazards and insufficient production efficiency. In contrast, the cyclohexene route only produces cyclohexane as a byproduct, and reduces hydrogen consumption by about one-third. It offers advantages such as safer reaction process, simplified process flow, good economics, and environmental friendliness, demonstrating broad application prospects.

[0003] However, the development of catalysts with both high activity and high selectivity remains a key challenge for the industry in the selective hydrogenation of benzene to cyclohexene. The main difficulties are: (1) From the perspective of reaction thermodynamics, cyclohexane is more stable than cyclohexene, which makes the hydrogenation reaction of benzene more likely to produce cyclohexane, thus limiting the selectivity of cyclohexene; (2) From the perspective of reactant activity, benzene molecules are more stable due to their large π-bond structure, while cyclohexene molecules contain a carbon-carbon double bond, and their reactivity is significantly higher than that of benzene. Therefore, cyclohexene is more likely to be further hydrogenated to produce cyclohexane during the hydrogenation process.

[0004] To address these challenges, numerous research institutions and companies both domestically and internationally have initiated related catalyst development and filed patents. For example, Zhengzhou University (CN01122208, CN200410060451.0), Fudan University (CN03115666.5), the Dalian Institute of Physical Chemistry, Chinese Academy of Sciences (CN200410101806.6), and the China Petroleum & Chemical Research Institute (CN200510126062.8) have successively applied for patents on amorphous alloy catalysts for the selective hydrogenation of benzene to cyclohexene. Asahi Kasei Corporation of Japan has also applied for a series of Ru-Zn catalyst-related patents in China, such as CN1159269C. Currently, catalyst preparation primarily employs traditional methods such as co-precipitation and impregnation. Among them, the co-precipitation method, which is widely used in industry, is prone to problems such as uneven precipitation of precursors and significant changes in solution concentration during the reaction process when using pure water as the reaction medium. This can lead to single-phase precipitation of active components such as ruthenium and zinc, which in turn affects the uniformity of the catalyst structure and the reproducibility of the preparation process. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and proposes a method for preparing a catalyst for the hydrogenation of benzene to cyclohexene; it solves the problems of the aqueous coprecipitation method, such as the single precipitation process, insufficient uniformity of catalyst structure, and poor reproducibility of preparation.

[0006] This invention is achieved through the following technical solution: A method for preparing a catalyst for the hydrogenation of benzene to cyclohexene includes the following steps: S1. A metal salt solution containing ruthenium salt and zinc salt and a precipitant solution are simultaneously added dropwise to an alcohol solution to carry out a co-precipitation reaction; S2. In-situ reduction of the solid product obtained from the coprecipitation reaction; S3. The product obtained after in-situ reduction is placed in an alkaline solution and stirred.

[0007] Preferably, the ruthenium salt is ruthenium trichloride or ruthenium nitrite, and the zinc salt is zinc sulfate or zinc chloride.

[0008] Preferably, the precipitant is one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0009] Preferably, the alcohol in the alcohol solution is a low-carbon alcohol of C1 to C4.

[0010] Preferably, the alcohol is one or more selected from methanol, ethanol, isopropanol, n-propanol, and n-butanol.

[0011] Preferably, the alcohol in the alcohol solution has a mass fraction of 5% to 70%.

[0012] Preferably, the mass fraction of the alcohol solution in the coprecipitation reaction system is 5% to 30%.

[0013] Preferably, the coprecipitation reaction conditions are: 40-80℃, with continuous stirring for 1-6 hours.

[0014] Preferably, the solid product is washed to pH 7-11 and then reduced in situ under the following conditions: 120-150℃, 2-5 MPa H2, 4-12 h.

[0015] Preferably, in step S3, the stirring process uses a 5-25 wt% NaOH aqueous solution, stirred at 40-80°C for 2-4 hours, and then washed until the pH reaches 8-11.

[0016] The prepared catalyst was used for the hydrogenation of benzene to cyclohexene. Specifically, 0.5 g of catalyst, 28 mL of benzene, 56 mL of water, 2.3 g of zirconium dioxide, and 10 g of zinc sulfate heptahydrate were weighed out, and the reaction temperature was 100-180°C. o C. Under hydrogen pressure of 2-6 MPa, samples were taken every 5 minutes to calculate benzene selectivity and cyclohexene yield.

[0017] The beneficial effects of this invention compared to the prior art are as follows: This invention uses an alcohol solution as the coprecipitation reaction medium. The alcohol solution does not participate in the reaction, but it can adjust the microenvironment of the reaction medium, thereby ensuring that the microenvironment of the solution fluctuates less during the precipitation process. This allows for the acquisition of a catalyst with more uniform precipitation, thereby improving the activity of the prepared Ru-Zn catalyst.

[0018] This invention effectively overcomes the problems of traditional aqueous coprecipitation methods, such as a single precipitation process, insufficient catalyst structural uniformity, and poor reproducibility. In the performance evaluation of selective hydrogenation of benzene to cyclohexene, the catalyst prepared by this method achieved a cyclohexene selectivity of 82% at a benzene conversion rate of 40%. Attached Figure Description

[0019] Figure 1 The XRD pattern of the Ru-Zn catalyst prepared in Example 1 is shown below. Figure 2 The image shows the N2 adsorption-desorption isotherm of the Ru-Zn catalyst prepared in Example 1. Figure 3 The images shown are TEM and SEM images of the Ru-Zn catalyst prepared in Example 1, where ac is the TEM image and de is the SEM image. Figure 4 The results show the cycle stability test results of the Ru-Zn catalyst prepared in Example 1. Detailed Implementation

[0020] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto. Example 1

[0021] S1. Weigh 1.00 g RuCl3•3H2O (ruthenium salt) and 0.4 g ZnCl2 (zinc salt) and dissolve them in 100 mL of deionized water to prepare solution A; S2. Prepare the precipitant solution: Prepare 3 mL of 30 wt% NaOH solution; S3. Simultaneously add solution A and NaOH solution to 15 mL of ethanol-water solution (ethanol mass fraction 10%), and coprecipitate under the following conditions: react at 80℃ for 2 h. After the reaction is complete, separate the black solid product and wash with water until neutral. S4. Then the solid product is reduced in situ under the following conditions: 150℃ for 12 h and hydrogen pressure of 4 MPa. S5. Finally, the product obtained after in-situ reduction is placed in an alkaline solution and stirred. The alkaline solution treatment conditions are: 15wt% NaOH aqueous solution, stirring at 50℃ for 3h, and washing until pH=11; thus, a catalyst for the selective hydrogenation of benzene to cyclohexene is prepared.

[0022] S6. Catalyst evaluation system: 0.5 g catalyst, 56 mL water, 28 mL benzene, 2.3 g zirconium dioxide, 9.96 g zinc sulfate heptahydrate, 140℃, hydrogen pressure 4 MPa, samples taken every 5 min. Under these conditions, the cyclohexene selectivity was 82% when the benzene conversion rate was 40%. Example 2

[0023] The catalyst was synthesized under the conditions of Example 1, except that the alcohol solution was 30 wt% methanol-30 wt% isopropanol-40 wt% water, in 40 mL. The cyclohexene selectivity was 76% when the benzene conversion was 40%. Example 3

[0024] The reaction was carried out under the conditions of Example 1, except that the alcohol solution was 10 wt% ethanol - 10 wt% n-propanol - 10 wt% n-butanol - 70 wt% water, 30 mL. The cyclohexene selectivity was 69% when the benzene conversion was 40%. Example 4

[0025] The reaction was carried out under the conditions of Example 1, except that the alcohol solution was 10 wt% methanol - 90 wt% water, 30 mL. The cyclohexene selectivity was 71% when the benzene conversion was 40%. Example 5

[0026] The reaction was carried out under the conditions of Example 1, except that the alcohol solution was 30 wt% isopropanol-70 wt% water, 20 mL. The cyclohexene selectivity was 75% at a benzene conversion of 40%. Example 6

[0027] The reaction was carried out under the conditions of Example 1, except that the co-precipitation conditions were: 40°C for 6 h. The black solid product was separated and washed with water until neutral. The selectivity for cyclohexene was 61% when the benzene conversion was determined to be 40%. Example 7

[0028] The reaction was carried out under the conditions of Example 1, except that the reduction conditions were: in-situ reduction at 150°C for 4 h, and hydrogen pressure of 3 MPa. The cyclohexene selectivity was 65% when the benzene conversion was 40%. Example 8

[0029] The reaction was carried out under the conditions of Example 1, except that the alkaline treatment conditions were: 20 wt% NaOH aqueous solution, stirring at 60°C for 2 h, and washing until pH=8. The cyclohexene selectivity was 44% when the benzene conversion rate was 40%. Example 9

[0030] The reaction was carried out under the conditions of Example 1, except that the selected ruthenium salt was ruthenium nitrite nitrate. The cyclohexene selectivity was 76% at a benzene conversion rate of 40%. Example 10

[0031] The reaction was carried out under the conditions of Example 1, except that the zinc salt was zinc sulfate. The cyclohexene selectivity was 74% at a benzene conversion rate of 40%. Example 11

[0032] The reaction was carried out under the conditions of Example 1, except that potassium hydroxide was used as the precipitant. The cyclohexene selectivity was 69% when the benzene conversion was 40%.

[0033] Comparative Example The reaction was carried out under the conditions of Example 1, except that the alcohol solution was replaced with deionized water. The cyclohexene selectivity was 72% when the benzene conversion was 40%.

[0034] ; ; ; As can be seen from the above examples, when using ethanol as the coprecipitation reaction medium, the Ru-Zn catalyst exhibits the best selectivity (S 40 =82%).

[0035] Catalyst recycling: The catalyst prepared according to Example 1 was used in hydrogenation experiments. After hydrogenation, the organic phase was separated, and the catalyst, zirconium dioxide, and slurry could be directly used for the next hydrogenation reaction. Thus, the catalyst was recycled 8 times. The evaluation results are shown below. Figure 4 The selectivity data is the cyclohexene selectivity when the benzene conversion rate is 40%, i.e., S40 (%).

[0036] from Figure 4 It can be seen that during the 8 reuses, the cyclohexene selectivity remained constant when the benzene conversion rate was 40%, indicating that the Ru-Zn catalyst prepared by ethanol treatment in this invention has excellent reusability.

[0037] As demonstrated by the examples above, using alcohol solutions as the co-precipitation reaction medium allows for effective control of the microscopic chemical environment of the reaction system by leveraging the unique polar characteristics and spatial structure of alcohol molecules. This method not only optimizes the solvation state of metal ions but also suppresses drastic fluctuations in reactant concentrations in localized areas, thereby significantly reducing the instability of the microscopic environment during precipitation and providing stable conditions for the uniform growth of the precipitate phase. In this stable reaction environment, problems such as particle agglomeration and component segregation caused by localized supersaturation can be effectively avoided, ultimately yielding a catalyst with uniform particle size, uniform distribution of active components (Ru and Zn), and a regular crystal structure. The uniformity of the catalyst directly determines the exposure degree of active sites and their synergistic catalytic efficiency, which not only helps to promote the participation of more Ru-Zn active centers in the reaction but also allows for precise control of the degree of benzene hydrogenation through an ordered microstructure, thereby significantly improving the intrinsic activity and cyclohexene selectivity of the Ru-Zn catalyst.

[0038] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0039] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this invention.

Claims

1. A process for the preparation of a catalyst for the hydrogenation of benzene to cyclohexene, characterized in that The method comprises the following steps: S1, simultaneously adding a metal salt solution containing a ruthenium salt and a zinc salt and a precipitant solution into an alcohol solution to perform a coprecipitation reaction; S2, in-situ reducing a solid product obtained in the coprecipitation reaction; S3, stirring the product obtained after the in-situ reduction in a lye.

2. The method for preparing a catalyst for the hydrogenation of benzene to cyclohexene according to claim 1, characterized in that, The ruthenium salt is ruthenium trichloride or ruthenium nitrosyl nitrate, and the zinc salt is zinc sulfate or zinc chloride.

3. The method for preparing a catalyst for the hydrogenation of benzene to cyclohexene according to claim 1, characterized in that, The precipitant is one of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate.

4. The method of claim 1, wherein the catalyst is prepared by the steps of: (a) preparing a solution of a transition metal compound in a solvent; (b) adding a reducing agent to the solution; (c) adding a ligand to the solution; (d) adding a base to the solution; and (e) recovering the catalyst. The alcohol in the alcohol solution is a low-carbon alcohol with 1-4 carbon atoms.

5. The method of claim 4, wherein the catalyst is prepared by the steps of: (a) preparing a solution of the catalyst precursor; (b) adding the solution of the catalyst precursor to the solvent; (c) adding the reducing agent to the solution of the catalyst precursor; and (d) recovering the catalyst. The alcohol is one or more of methanol, ethanol, isopropyl alcohol, n-propanol and n-butanol.

6. The method for preparing a catalyst for the hydrogenation of benzene to cyclohexene according to claim 1 or 4 or 5, characterized in that, The mass fraction of the alcohol in the alcohol solution is 5%-70%.

7. The method of claim 6, wherein the catalyst is prepared by the steps of: (a) preparing a solution of the catalyst precursor; (b) adding the solution of the catalyst precursor to the solvent; (c) adding the reducing agent to the solution of the catalyst precursor; and (d) recovering the catalyst. The mass fraction of the alcohol solution in the coprecipitation reaction system is 5%-30%.

8. The method for preparing a catalyst for the hydrogenation of benzene to cyclohexene according to claim 1 or 7, characterized in that, The coprecipitation reaction condition is 40-80℃, and the stirring lasts for 1-6h.

9. The method of claim 1, wherein the catalyst is prepared by the steps of: (a) preparing a solution of a transition metal compound in a solvent; (b) adding a reducing agent to the solution; (c) adding a ligand to the solution; (d) adding a base to the solution; and (e) recovering the catalyst. The solid product is washed to pH=7-11, and then in-situ reduced, and the in-situ reduction condition is 120-150℃, 2-5 MPa H2 and 4-12h.

10. The method of claim 1, wherein the catalyst is prepared by the steps of: (a) preparing a solution of a transition metal compound in a solvent; (b) adding a reducing agent to the solution; (c) adding a ligand to the solution; (d) adding a base to the solution; and (e) recovering the catalyst. In S3, a 5-25wt% NaOH aqueous solution is used for stirring at 40-80℃ for 2-4h, and the washing is performed until the pH is 8-11.

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