Catalyst for synthesizing aniline through direct amination of benzene as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for synthesizing aniline through direct amination of benzene and a preparation method and application of the catalyst, the catalyst takes gamma-Al2O3 as a carrier, active components comprise vanadium oxide, molybdenum oxide and cerium oxide, and the catalytic performance is remarkably improved through the synergistic effect of the components. The preparation method adopts a complexing-equivalent-volume impregnation method, and the process is simple. The catalyst is used for a direct amination reaction taking benzene and hydroxylamine salt as raw materials, has the characteristics of mild reaction conditions, high benzene conversion rate, good aniline selectivity, excellent catalyst stability, recyclability and the like, overcomes the defects of an existing single vanadium-based catalyst, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of industrial catalysis and organic synthesis technology, specifically relating to a catalyst for the direct amination of benzene to aniline, its preparation method, and its application. Background Technology

[0002] Aniline is an important organic chemical raw material and intermediate, widely used in industries such as polyurethane, rubber additives, dyes, pesticides, and pharmaceuticals. Industrially, aniline is mainly produced using the nitrobenzene catalytic hydrogenation method. While this technology is mature, it suffers from drawbacks such as lengthy steps (requiring prior nitration followed by hydrogenation), high energy consumption, the use of large amounts of strong acid, and the generation of significant amounts of waste acid, which contradicts the environmentally friendly concept of green chemistry.

[0003] To address this, researchers have developed a process for the direct amination of benzene to produce aniline. This method uses benzene and hydroxylamine salts as raw materials, producing aniline in a single step, offering high atom economy and a clean process. However, the core challenge of this reaction lies in developing efficient, stable, and inexpensive catalysts. Current research mainly focuses on single vanadium-based, copper-based, or palladium-based catalysts. Taking V₂O₅ / γ-Al₂O₃ catalysts as an example, while they exhibit some activity in this reaction, the conversion rate of benzene and the selectivity of aniline still need improvement. Furthermore, the active components of the catalyst are easily lost during recycling, resulting in insufficient stability. Single vanadium oxide catalysts are prone to over-oxidation of the benzene ring, producing byproducts such as quinones, and the reaction requires relatively high temperatures.

[0004] Therefore, developing a highly active, highly selective, highly stable, and low-cost catalyst for the direct amination of benzene has significant industrial application value and market prospects. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings of existing technologies and provide a catalyst, its preparation method, and its application for the direct amination of benzene to aniline. Specifically, it relates to a highly active, highly selective, and highly stable catalyst for the direct amination of benzene to aniline. This supported multi-metal oxide catalyst for the direct amination of benzene and hydroxylamine compounds to aniline particularly relates to a ternary catalyst supported on γ-alumina with vanadium, molybdenum, and cerium oxides, its preparation method, and its application in green synthesis of aniline from benzene.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention discloses a catalyst for the direct amination of benzene to aniline, which is a supported polymetallic oxide catalyst with γ-Al2O3 as the support. The active components include vanadium oxide, molybdenum oxide and cerium oxide. Based on the total mass of the catalyst, the loading of vanadium oxide is 5-10 wt% based on V, the loading of molybdenum oxide is 5-14 wt% based on Mo, and the loading of cerium oxide is 1-5 wt% based on Ce.

[0008] The present invention also discloses a method for preparing the catalyst as claimed in claim 1, comprising the following steps:

[0009] 1) Preparation of complexing impregnation solution: Dissolve vanadium source, molybdenum source and complexing agent together in hot water, stir to form a clear solution, then add cerium source and stir until completely dissolved to obtain mixed impregnation solution;

[0010] 2) Equal volume impregnation: The mixed impregnation solution is loaded onto the γ-Al2O3 support using the equal volume impregnation method;

[0011] 3) Aging: Let the impregnated carrier stand for 12-24 hours to age;

[0012] 4) Drying: Drying the aged solid product;

[0013] 5) Calcination: The dried solid product is calcined at 400-600℃ for 2-6 hours to obtain the catalyst.

[0014] As a further improvement, the vanadium source in this invention is ammonium metavanadate, the molybdenum source is ammonium molybdate, the cerium source is cerium nitrate, and the complexing agent is oxalic acid.

[0015] As a further improvement, the present invention describes dissolving the vanadium source, molybdenum source, and complexing agent together in hot water at 50-70°C.

[0016] As a further improvement, in step 4) of the present invention, the aged solid product is dried at 80-120°C for 6-12 hours.

[0017] The present invention also discloses an application of a catalyst for the direct amination of benzene to synthesize aniline. The method of using the catalyst to synthesize aniline involves using the catalyst, with benzene and hydroxylamine compounds as raw materials, reacting in an acetic acid-water medium at 70-90°C for 3-6 hours to directly synthesize aniline.

[0018] As a further improvement, the hydroxylamine compound described in this invention is hydroxylamine hydrochloride or hydroxylamine sulfate.

[0019] As a further improvement, the amount of catalyst used in this invention is 5-10% of the mass of benzene.

[0020] Compared with the prior art, the present invention has the following significant advantages:

[0021] 1. Significant synergistic effect and excellent catalytic performance: The introduction of molybdenum and cerium components resulted in a strong synergistic effect with vanadium. Mo modulated the electronic structure and redox properties of V, suppressed excessive oxidation side reactions, and significantly improved the selectivity of aniline. The addition of Ce greatly improved the dispersion of V and Mo active components, stabilized the catalyst structure, and enhanced the redox ability of the catalyst, thereby improving the conversion rate of benzene and the stability of the catalyst.

[0022] 2. Green and efficient: This catalyst is used for the direct amination reaction of benzene and can achieve high conversion rate and high selectivity under milder conditions (atmospheric pressure, <90℃), avoiding the high energy consumption and high pollution problems of traditional processes.

[0023] 3. Good stability and long lifespan: The introduction of Ce acts like a "structural nail," effectively preventing the aggregation and loss of active components during the reaction and regeneration process, giving the catalyst excellent recyclability and reducing the cost of industrial applications.

[0024] 4. The preparation method is simple and easy to industrialize: The preparation method adopts the mature equal volume impregnation method, which is simple, has low equipment requirements, good repeatability, and is very suitable for large-scale industrial production. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0026] Example 1:

[0027] Catalyst preparation

[0028] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0029] Based on a V loading of 5 wt%, a Mo loading of 5 wt%, and a Ce loading of 1 wt%, accurately weigh out: 1.147 g of ammonium metavanadate, 0.883 g of ammonium molybdate, 0.310 g of cerium nitrate hexahydrate, and 4.94 g of oxalic acid dihydrate.

[0030] Oxalic acid was dissolved in 30 mL of hot water at 50 °C. Ammonium metavanadate was added with stirring to obtain a deep blue transparent solution. Ammonium molybdate was then added and stirred until clear. Finally, cerium nitrate was added and stirred until completely dissolved. After cooling to room temperature, water was added to bring the volume to 6 mL (the pore volume of the carrier was measured to be 0.6 mL / g).

[0031] The above solution was added dropwise to the γ-Al₂O₃ support using an equal-volume impregnation method and aged at room temperature for 24 hours. It was then dried at 80°C for 12 hours. Finally, it was calcined in a muffle furnace at 400°C for 6 hours, and after natural cooling, the catalyst VMoCe-1 was obtained.

[0032] Catalytic performance evaluation

[0033] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (5% of the benzene mass) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 70 °C. 8.90 g hydroxylamine hydrochloride was quickly added, and the reaction was started. The reaction was carried out at 70 °C and atmospheric pressure for 6 hours.

[0034] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0035] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the evaluation experiment described above. A total of 5 cycles were performed.

[0036] Example 2:

[0037] Catalyst preparation

[0038] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0039] Based on a V loading of 10 wt%, a Mo loading of 14 wt%, and a Ce loading of 5 wt%, accurately weigh the following: ammonium metavanadate 2.294 g, ammonium molybdate 2.472 g, cerium nitrate hexahydrate 1.550 g, and oxalic acid dihydrate 9.88 g.

[0040] The preparation steps were the same as in Example 1, but the hot water temperature was 70°C, the aging time was 12 hours, the drying temperature was 120°C for 6 hours, and the calcination conditions were 600°C for 2 hours to obtain catalyst VMoCe-2.

[0041] Catalytic performance evaluation

[0042] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (10% of the mass of benzene) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 90 °C. 10.50 g hydroxylamine sulfate was quickly added, and the reaction was started. The reaction was carried out at 90 °C and atmospheric pressure for 3 hours.

[0043] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0044] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the evaluation experiment described above. A total of 5 cycles were performed.

[0045] Example 3:

[0046] Catalyst preparation

[0047] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0048] Based on a V loading of 8 wt%, a Mo loading of 10 wt%, and a Ce loading of 3 wt%, accurately weigh out: 1.835 g of ammonium metavanadate, 1.765 g of ammonium molybdate, 0.930 g of cerium nitrate hexahydrate, and 7.91 g of oxalic acid dihydrate.

[0049] The preparation steps were the same as in Example 1, but the hot water temperature was 60°C, the aging time was 18 hours, the drying conditions were 100°C for 10 hours, and the calcination conditions were 500°C for 4 hours to obtain catalyst VMoCe-3.

[0050] Catalytic performance evaluation

[0051] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (8% of the benzene mass) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 80 °C. 8.90 g hydroxylamine hydrochloride was quickly added, and the reaction was started. The reaction was carried out at 80 °C and atmospheric pressure for 5 hours.

[0052] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0053] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the catalytic performance evaluation experiment. A total of 5 cycles were performed.

[0054] Comparative Example 1: Vanadium-only catalyst

[0055] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0056] Based on a V loading of 8wt%, accurately weigh out: 1.835g of ammonium metavanadate and 4.94g of oxalic acid dihydrate.

[0057] Oxalic acid was dissolved in 30 mL of hot water at 60 °C. Ammonium metavanadate was added with stirring to obtain a deep blue transparent solution. After cooling to room temperature, water was added to bring the volume to 6 mL. The support was impregnated using an equal-volume impregnation method, and the subsequent aging, drying, and calcination steps were exactly the same as in Example 3, yielding comparative catalyst V.

[0058] Catalytic performance evaluation

[0059] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (8% of the benzene mass) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 80 °C. 8.90 g hydroxylamine hydrochloride was quickly added, and the reaction was started. The reaction was carried out at 80 °C and atmospheric pressure for 5 hours.

[0060] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0061] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the catalytic performance evaluation experiment. A total of 5 cycles were performed.

[0062] Comparative Example 2: Binary Vanadium-Mo Catalyst (V-Mo)

[0063] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0064] Based on a V loading of 8 wt% and a Mo loading of 10 wt%, accurately weigh out: 1.835 g of ammonium metavanadate, 1.765 g of ammonium molybdate, and 7.91 g of oxalic acid dihydrate.

[0065] The preparation steps were the same as in Example 3, but without the addition of cerium nitrate, resulting in the comparative catalyst VMo.

[0066] Catalytic performance evaluation

[0067] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (8% of the benzene mass) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 80 °C. 8.90 g hydroxylamine hydrochloride was quickly added, and the reaction was started. The reaction was carried out at 80 °C and atmospheric pressure for 5 hours.

[0068] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0069] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the catalytic performance evaluation experiment. A total of 5 cycles were performed.

[0070] Comparative Example 3: Binary Vanadium-Ce Catalyst (V-Ce)

[0071] Weigh 10g of γ-Al2O3 support (20-40 mesh) that has been calcined at 500℃ for 4 hours and set aside.

[0072] Based on a V loading of 8wt% and a Ce loading of 3wt%, accurately weigh out: 1.835g of ammonium metavanadate, 0.930g of cerium nitrate hexahydrate, and 4.94g of oxalic acid dihydrate.

[0073] The preparation steps were the same as in Example 3, but ammonium molybdate was not added, resulting in the comparative catalyst VCE.

[0074] Catalytic performance evaluation

[0075] The reaction was carried out in a 100 mL three-necked flask. 10.0 g benzene, 20.0 g glacial acetic acid, 10.0 g water, and a certain amount of catalyst (8% of the benzene mass) were added sequentially. A condenser and thermometer were installed, and the mixture was stirred and heated to 80 °C. 8.90 g hydroxylamine hydrochloride was quickly added, and the reaction was started. The reaction was carried out at 80 °C and atmospheric pressure for 5 hours.

[0076] After the reaction was complete, the mixture was cooled, and the catalyst was recovered by filtration. The filtrate was adjusted to pH 11 with NaOH solution, and then extracted three times with dichloromethane. The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed by rotary evaporation to obtain the crude product. The product composition was analyzed by gas chromatography (GC), and the benzene conversion and aniline selectivity were calculated.

[0077] Stability evaluation method: The recovered catalyst after the reaction was washed with water, dried, and then calcined in a muffle furnace at 500℃ for 3 hours for regeneration. The regenerated catalyst was then used in a new round of reaction under the same conditions as the catalytic performance evaluation experiment. A total of 5 cycles were performed.

[0078] The catalytic performance of catalysts VMoCe-1, VMoCe-2, and VMoCe-3 prepared in Examples 1-3 and catalysts V, VMo, and VCe prepared in Comparative Examples 1-3 is compared in Table 1.

[0079] Table 1: Comparison of catalytic performance of different catalysts

[0080]

[0081]

[0082] Results analysis:

[0083] It can be seen from the above table:

[0084] 1. The ternary catalysts (VMoCe series) provided by this invention are significantly superior to single vanadium catalysts (V) and binary catalysts (VMo,VCe) in terms of initial activity, selectivity and stability.

[0085] 2. The catalyst VMoCe-3 (V 8wt%, Mo 10wt%, Ce 3wt%) prepared in Example 3 showed the best performance, with a benzene conversion rate of 95.8% and an aniline selectivity of 98.5%.

[0086] 3. The three-way catalyst exhibits excellent stability. After four regeneration cycles (i.e., the fifth reaction), the activity retention rate is as high as 95% or more (e.g., VMoCe-3 decreased from 95.8% to 91.8%, a decrease of only 4.2%).

[0087] 4. The comparative single vanadium catalyst V had low initial activity and selectivity (conversion rate 48.3%, selectivity 69.2%) and extremely poor stability. After the fifth cycle, the conversion rate dropped to 21.5%, the activity retention rate was only 44.5%, and the activity loss exceeded 55%.

[0088] 5. Although the performance of binary catalysts (VMo, VCe) is better than that of single vanadium catalysts, it is still significantly inferior to that of ternary catalysts. Furthermore, the cycle stability (activity retention rates of 80.0% and 75.6%) is far lower than that of ternary catalysts, which proves that there is a significant synergistic effect among V, Mo, and Ce, rather than a simple additive effect.

[0089] The above results demonstrate that this invention successfully prepared a highly active, highly selective, and highly stable catalyst through the optimized combination and synergistic effect of V, Mo, and Ce. This solves the core problems of low activity, poor selectivity, and insufficient stability of existing single vanadium-based catalysts in the direct amination reaction of benzene, and has great potential for industrial application.

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A catalyst for the direct amination of benzene to aniline, characterized in that, It is a supported multi-metal oxide catalyst with γ-Al2O3 as the support. The active components include vanadium oxide, molybdenum oxide and cerium oxide. Based on the total mass of the catalyst, the loading of vanadium oxide is 5-10 wt% based on V, the loading of molybdenum oxide is 5-14 wt% based on Mo, and the loading of cerium oxide is 1-5 wt% based on Ce.

2. A method for preparing the catalyst as described in claim 1, characterized in that, Includes the following steps: 1) Preparation of complexing impregnation solution: Dissolve vanadium source, molybdenum source and complexing agent together in hot water, stir to form a clear solution, then add cerium source and stir until completely dissolved to obtain mixed impregnation solution; 2) Equal volume impregnation: The mixed impregnation solution is loaded onto the γ-Al2O3 support using the equal volume impregnation method; 3) Aging: Let the impregnated carrier stand for 12-24 hours to age; 4) Drying: Drying the aged solid product; 5) Calcination: The dried solid product is calcined at 400-600℃ for 2-6 hours to obtain the catalyst.

3. The method for preparing the catalyst according to claim 2, characterized in that, The vanadium source is ammonium metavanadate, the molybdenum source is ammonium molybdate, the cerium source is cerium nitrate, and the complexing agent is oxalic acid.

4. The method for preparing the catalyst according to claim 2, characterized in that, The vanadium source, molybdenum source, and complexing agent are dissolved together in hot water at 50-70°C.

5. The method for preparing the catalyst according to claim 2, characterized in that, In step 4), the aged solid product is dried at 80-120°C for 6-12 hours.

6. The application of the catalyst as described in claim 1 for the direct amination of benzene to aniline, characterized in that, The method for synthesizing aniline using the catalyst described herein: Using the catalyst described herein, aniline is directly synthesized by reacting benzene and hydroxylamine compounds as raw materials in an acetic acid-water medium at 70-90°C for 3-6 hours.

7. The application according to claim 6, characterized in that, The hydroxylamine compound is hydroxylamine hydrochloride or hydroxylamine sulfate.

8. The application according to claim 6, characterized in that, The amount of catalyst used is 5-10% of the mass of benzene.

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