A fixed-bed continuous catalytic hydrogenation system for preparing p-phenylenediamine

Abstract

This invention relates to the field of catalytic hydrogenation technology, and provides a fixed-bed continuous catalytic hydrogenation system for preparing p-phenylenediamine. The method includes: Step A, p-nitroaniline and solvent are mixed in a material mixing device in advance according to a certain proportion to obtain a p-nitroaniline solution, and then the p-nitroaniline solution and hydrogen are preheated separately in preheaters; Step B, the preheated reaction material is mixed in a gas-liquid mixer and then enters a fixed-bed reactor pre-loaded with a multilayer catalyst, where a catalytic hydrogenation reaction occurs to generate the product material; Step C, the product material is separated by a gas-liquid separator to obtain p-phenylenediamine solution and hydrogen gas, the p-phenylenediamine solution is post-treated to obtain p-phenylenediamine, and the solvent is recovered and reused. This invention effectively overcomes the pain point of the existing batch catalytic hydrogenation process, which has a single-batch reaction time of 4-14 hours, and achieves a significant reduction in the reaction time of continuous catalytic hydrogenation; it can also effectively ensure product selectivity, easy product separation, good safety, significantly reduced cost, and easy industrial application.

Description

Technical Field

[0001] This invention relates to the field of catalytic hydrogenation technology, and more specifically to a fixed-bed continuous catalytic hydrogenation system for the preparation of p-phenylenediamine. Background Technology

[0002] p-Phenylenediamine is an important chemical intermediate with a wide range of applications. Its downstream applications include high-performance materials and aramid fibers (para-aramid PPTA), as well as a raw material for rubber antioxidants. In the dye and pigment industry, it is a raw material for azo dyes and specialty dyes. It is an important intermediate in the synthesis of various direct dyes, acid dyes, and disperse dyes. These dyes are used for dyeing fibers such as cotton, wool, silk, and nylon. In the pharmaceutical field, it is a key intermediate in the synthesis of some drugs; 1,4-cyclohexanediamine, obtained by hydrogenation of its benzene ring, also has important applications in high-performance polyamides; CN 109503386 A / CN109867606 A provides a method for preparing p-phenylenediamine by hydrogenation in a batch reactor, but the batch reactor has low efficiency, the batch-produced products are unstable, and the Ni-based catalyst used is flammable with air, posing a significant safety risk; CN102701995 A / CN 105732396 A uses a mixed solution batch reactor to prepare p-phenylenediamine, which has low efficiency and the catalyst can only be reused 5-30 times, resulting in high catalyst usage costs; Currently, industrial production is based on batch-type processes, which are inefficient, have large quality fluctuations between production batches, cause serious waste of labor and energy, and require a large area. Furthermore, batch-type processes generally use nickel-based catalysts, which are highly flammable and pose significant safety risks, or palladium-based or platinum-based catalysts, which are used less frequently and result in high costs, or sulfide reduction, which generates a large amount of wastewater, thus failing to meet the concept of green environmental protection. Summary of the Invention

[0003] Based on this, the first aspect of the present invention provides a system for the continuous catalytic hydrogenation of p-phenylenediamine in a fixed bed, characterized in that the method comprises the following steps: Step S1: p-Nitroaniline and an organic solvent are mixed in a material mixing device to obtain a p-nitroaniline solution, and then the p-nitroaniline solution and hydrogen are preheated in a preheater respectively; Step S2: After the preheated reactants are mixed in a gas-liquid mixer, they enter a fixed-bed reactor pre-loaded with catalyst to carry out catalytic hydrogenation reaction and generate product materials. Step C: The product material is separated by a gas-liquid separator to obtain p-phenylenediamine solution and hydrogen gas; The fixed-bed reactor is characterized by having three layers of heterogeneous catalysts sequentially packed in sections along the material flow direction: Among them, the first layer, the second layer, and the third layer are each independently a supported Pt / Al2O3 catalyst, a supported Pt / C catalyst, and a supported Pt-Re / C catalyst; In some embodiments of the system, the first layer is a supported Pt / Al2O3 catalyst, the second layer is a supported Pt / C cloverleaf catalyst, and the third layer is a supported Pt-Re / C cylindrical catalyst.

[0004] In some embodiments of the method, the packing height ratios of the first, second, and third catalyst layers in the fixed-bed reactor are 20% for the first layer, 50% for the second layer, and 30% for the third layer, respectively; and / or, the supported Pt / Al2O3 is a spherical catalyst or a near-spherical catalyst.

[0005] In some embodiments of the system described, the supported Pt / C is a cloverleaf catalyst.

[0006] In some embodiments of the method, the Pt loading of the first layer catalyst is 0.5%.

[0007] In some embodiments of the system described, the Pt loading of the second catalyst layer is 1-5%, preferably 3%.

[0008] In some embodiments of the method, the third catalyst layer has a Pt loading of 1-5% and a Re loading of 0.5-2%, preferably a Pt loading of 3.0 wt% and a Re loading of 1.0 wt%.

[0009] In some embodiments of the system described, the gas-liquid mixer is selected from any one of a static mixer, a T-type mixer, a Y-type mixer, a cross-type mixer, a Venturi mixer, a porous media / sieve plate distributor, a Sitta ring distributor, and a coaxial flow mixer; and / or, the temperature of the preheater and the fixed bed reactor is controlled at 80~180°C, preferably 80~120°C.

[0010] In some embodiments of the system, the molar ratio of p-nitroaniline to hydrogen is 1:(3.0~10.0), preferably 1:(3.5~8).

[0011] In some embodiments of the system, the mass ratio of p-nitroaniline to organic solvent is 1:(1~20), preferably 1:(3.3~10).

[0012] In some embodiments of the system described, the organic solvent is selected from at least one of methanol, ethanol, isopropanol, water, toluene, acetone, tetrahydrofuran, dioxane, N,N-dimethylformamide, and dimethylacetamide, preferably isopropanol or N,N-dimethylformamide.

[0013] In some embodiments of the system, the residence time of the reactants in the fixed-bed reactor is 0.1 to 10 minutes, preferably 1 to 3 minutes.

[0014] In some embodiments of the system, the hourly feed mass of the reactants to the total mass of the catalyst packing has a space velocity ratio of (0.1~1.5):1, preferably (0.3~0.5):1.

[0015] In some embodiments of the system described, the reaction pressure is 0.1~5 MPa, preferably 0.6~1.0 MPa.

[0016] The second aspect of this invention provides a method for preparing the supported Pt-Re / C catalyst described in the first aspect, comprising the steps of... S1: Activated carbon powder is mixed with binder, water is added, extruded and molded, dried, calcined under an inert atmosphere, washed with nitric acid solution, washed with water until neutral, and dried to obtain the dried carrier; S2: Platinum salt and rhenium salt are dissolved in water, and acid is added to make an impregnation solution; S3: The dried carrier is mixed with the impregnation solution and then dried; S4: The dried sample was placed in a hydrogen atmosphere, and the temperature was increased by a programmed reduction. After cooling, the Pt-Re / C catalyst was obtained.

[0017] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the binder in step S1 is selected from any one of guar methyl cellulose (MC), carboxymethyl cellulose (CMC), starch, polyvinyl alcohol (PVA), kaolin, boehmite, silica sol, alumina sol, or lignin sulfonate.

[0018] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the mass ratio of the binder to the activated carbon powder in step S1 is 1:(15~25).

[0019] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the inert atmosphere is any one or a mixture of nitrogen, argon, and helium.

[0020] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the nitric acid solution is an aqueous solution of nitric acid.

[0021] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the aqueous solution of nitric acid has a mass concentration of 3-7%. In some embodiments of the preparation of the supported Pt-Re / C catalyst, the extrusion molding is performed by extruding into cylindrical strips with a diameter of 1.5-2.5 mm.

[0022] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the platinum salt in step S2 is selected from chloroplatinic acid, platinum nitrate, or nitrodiammineplatinum, or a mixture thereof.

[0023] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the rhenium salt in step S2 is selected from any one or a mixture of ammonium perrhenate, potassium perrhenate, sodium perrhenate, and calcium perrhenate.

[0024] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the acid in step S2 is selected from sulfuric acid, nitric acid, hydrochloric acid, or a mixture thereof.

[0025] In some embodiments of the preparation of the supported Pt-Re / C catalyst, after step S2, the concentration of acid added is 0.1~0.5 mol / L.

[0026] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the drying temperature of step S3 is 100~120°C.

[0027] In some embodiments of the preparation of the supported Pt-Re / C catalyst, the temperature program of step S4 is to slowly heat to 3-500°C at a heating rate of 1-3°C / min and maintain it for 3-6 hours.

[0028] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "furthermore," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] In the following content, all numbers disclosed herein, whether or not they use words such as "approximately" or "about," are approximate values. The value of each number may vary by 1%, 2%, 5%, 7%, 8%, 10%, 15%, or 20%. Whenever a number with a value of N is disclosed, any numbers with values ​​of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15%, or N+ / -20% will be explicitly disclosed, where "+ / -" indicates addition or subtraction.

[0030] The term “and / or” should be understood to mean any one of the options or any combination of two or more of the options.

[0031] The terms “optional,” “optional,” or “optionally” refer to events or situations that may, but are not necessarily, occur as described below.

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0033] All reagents used in this invention can be purchased commercially or prepared by the methods described in this invention.

[0034] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0035] Unless otherwise specified, the "loading amount" (such as Pt loading amount, Re loading amount, etc.) mentioned in this invention refers to the mass percentage of the active component element in the impregnation solution relative to the mass of the carrier. The calculation formula is as follows: ×100%.

[0036] Beneficial effects: This invention employs a three-layer heterogeneous catalyst gradient packing design. The first layer, a supported Pt / Al2O3 spherical catalyst, serves as a preliminary buffer and traps impurities. The second layer, a supported Pt / C clover-shaped catalyst, utilizes its irregular structure to increase the surface contact area, thereby optimizing mass transfer efficiency and effectively reducing bed pressure drop. The third layer, a supported Pt-Re / C cylindrical catalyst, introduces the Re promoter alloy synergistic effect, which not only enhances the deep hydrogenation capability but also effectively inhibits catalyst carbon deposition, ensuring an ultra-long stability of up to 800 hours.

[0037] This process significantly shortens the reaction time per batch through continuous production, effectively solving the inefficiency problem of traditional processes requiring 4 to 14 hours. It achieves a high level of output with a raw material conversion rate of over 99.7% and a selectivity of over 99.8%, and the catalyst can operate continuously and stably in the fixed bed for more than 800 hours without activity decay. Attached Figure Description

[0038] Figure 1 This is a flowchart of the preparation method of the present invention; Figure 2This is a schematic diagram of the segmented loading of the three-layer heterogeneous catalyst in the fixed bed of the present invention. Detailed Implementation

[0039] Certain embodiments of the invention will now be described in detail, examples of which are illustrated by the accompanying structural and chemical formulas. The invention is intended to cover all alternatives, modifications, and equivalents, all of which are included within the scope of the invention as defined in the claims. Those skilled in the art will recognize that many similar or equivalent methods and materials can be used to practice the invention. The invention is by no means limited to the methods and materials described herein. In the event that one or more of the incorporated documents, patents, and similar materials differ from or contradict this application (including, but not limited to, defined terminology, application of terminology, described techniques, etc.), this application shall prevail.

[0040] It should be further appreciated that certain features of the invention, for clarity, have been described in multiple independent embodiments, but may also be provided in combination in a single embodiment. Conversely, various features of the invention, for brevity, have been described in a single embodiment, but may also be provided individually or in any suitable sub-combination.

[0041] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. All patents and publications related to this invention are incorporated herein by reference in their entirety.

[0042] Example 1 The activated carbon powder and binder guar gum powder (5 wt%, based on the mass of activated carbon powder) are thoroughly mixed. Deionized water is added while stirring and kneaded until the mixture is plastic. The material is extruded into cylindrical strips with a diameter of 2.0 mm using an extruder. After drying at 110°C, the material is placed in a tube furnace and calcined at 600°C for 2 hours under nitrogen protection. The carbonized carrier is then washed with a 5% nitric acid solution, washed with deionized water until neutral, and dried.

[0043] Weigh 7.96g of chloroplatinic acid (calculated as H2PtCl6·6H2O) and 1.44g of ammonium perrhenate (calculated as NH4ReO4), dissolve them in deionized water, add deionized water to make the solution volume 100mL, adjust the hydrochloric acid concentration to 0.2 mol / L, and stir thoroughly to prepare the impregnation solution.

[0044] Take 100g of dried carbon carrier and place it in a container. Spray the impregnation solution evenly onto the surface of the carrier, allowing the liquid to completely penetrate into the pores of the carrier. Let it stand at room temperature for 18 hours, and then dry it at 110℃ to constant weight.

[0045] The dried sample was placed in a tube furnace and purged with pure hydrogen. Under a hydrogen atmosphere, it was slowly heated to 400°C at a heating rate of 2°C / min and maintained at a constant temperature for 5 hours. Then, it was naturally cooled to room temperature under hydrogen protection to obtain a cylindrical Pt-Re / C catalyst (Pt loading 3.0 wt% and Re loading 1.0 wt%).

[0046] Example 2 Activated carbon powder and binder guar gum powder (5 wt%, based on the mass of activated carbon powder) were thoroughly mixed. Deionized water was slowly added under continuous stirring and kneaded until the mixture reached a plastic state. The kneaded material was transferred to an extruder with a clover-shaped die (inscribed circle diameter 2.0 mm) for extrusion molding. The resulting clover-shaped wet strips were dried at 110°C for 12 hours, then placed in a tube furnace and calcined at 600°C for 2 hours under nitrogen protection. The carbonized carrier was then impregnated with a 5% nitric acid solution, finally washed with deionized water until neutral, and dried to obtain the clover-shaped carbon carrier.

[0047] Weigh 7.96g of chloroplatinic acid and dissolve it in deionized water. Adjust its concentration to 0.2 mol / L with hydrochloric acid and add water to 100mL to prepare the impregnation solution.

[0048] Place 100g of clover-shaped charcoal carrier in a container, spray 100mL of impregnation solution evenly onto the carrier to ensure complete absorption of the liquid, let stand at room temperature for 18 hours, and then dry at 110℃ to constant weight.

[0049] The dried sample was placed in a tube furnace and purged with hydrogen. Under a hydrogen atmosphere, it was heated to 400°C at a heating rate of 2°C / min and maintained at a constant temperature for 5 hours. After the reaction was completed, it was naturally cooled to room temperature under hydrogen protection to obtain a clover-shaped Pt / C catalyst (Pt loading 3.0 wt%).

[0050] Example 3 Select activated alumina balls with a diameter of 2.0~3.0mm and place them in a muffle furnace. Calcinate them in air at 550℃ for 4 hours. After calcination, allow the carrier to cool naturally to room temperature.

[0051] Weigh 1.32g of chloroplatinic acid (calculated as H2PtCl6·6H2O) and dissolve it in deionized water. Adjust its concentration to 0.2 mol / L with hydrochloric acid and add water to 100mL to prepare the impregnation solution.

[0052] 100g of pretreated spherical alumina carrier was placed in a container, and 100mL of impregnation solution was sprayed evenly onto the carrier to ensure complete absorption of the liquid. The carrier was left to stand at room temperature for 18 hours, and then dried at 110℃ to constant weight.

[0053] The dried sample was then placed in a tube furnace and heated to 450°C at a heating rate of 5°C / min under a hydrogen atmosphere. The temperature was maintained at a constant temperature for 4 hours. After the reduction was completed, the sample was cooled to room temperature under hydrogen protection to obtain a Pt / Al2O3 spherical catalyst (Pt loading 0.5wt%).

[0054] Example 4 This embodiment uses a three-layer heterogeneous catalyst segmented loading fixed bed. The specific loading process is as follows: The fixed-bed reactor is sequentially filled along the material flow direction with a first layer of 0.5% Pt / Al2O3 spherical catalyst (20% of the height), a second layer of 3% Pt / C clover-shaped catalyst (50% of the height), and a third layer of cylindrical Pt-Re / C catalyst (30% of the height).

[0055]

[0056] p-Nitroaniline and isopropanol were mixed at a mass ratio of 1:4 to form a mixture. The mixture and hydrogen (molar ratio of p-nitroaniline to hydrogen was 1:5) were simultaneously fed to a preheater and preheated to 80°C. After entering a gas-liquid mixer, the mixture was homogenized and then fed to a fixed bed containing three layers of heterogeneous catalysts. The temperature of the fixed bed was controlled at 80°C. The hourly feed mass of p-nitroaniline to the total mass of catalyst was space velocity ratio of 0.3:1, and the residence time was 1 minute. The reaction liquid flowing out of the fixed bed was condensed in a condenser and then flowed into a gas-liquid separator with a back pressure of 1.0 MPa. The residual p-nitroaniline and the yield of p-phenylenediamine in the separated product liquid were detected.

[0057] Comparative Example 1 The difference between Comparative Example 1 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 1 is as follows: The fixed-bed reactor is sequentially filled with a first layer of 0.5% Pt / Al2O3 spherical catalyst (40% of the height) and a second layer of 3% Pt / C clover-shaped catalyst (60% of the height) along the material flow direction.

[0058] Comparative Example 1 is the same as Example 4 in all other respects.

[0059] Comparative Example 2 The difference between Comparative Example 2 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 2 is as follows: The fixed-bed reactor is sequentially packed along the material flow direction with a first layer of cylindrical Pt-Re / C catalyst accounting for 30% of the height, a second layer of clover-shaped catalyst accounting for 3% of the height (50%), and a third layer of spherical catalyst accounting for 0.5% of the height (20%).

[0060] Comparative Example 2 is the same as Example 4.

[0061] Comparative Example 3 The difference between Comparative Example 3 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 3 is as follows: The fixed-bed reactor is sequentially filled with a first layer of clover-shaped catalyst (70% of the height) consisting of 3% Pt / C, and a second layer of cylindrical Pt-Re / C catalyst (30% of the height) along the material flow direction.

[0062] Comparative Example 3 is the same as Example 4.

[0063] Comparative Example 4 The difference between Comparative Example 4 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 4 is as follows: Filling method: The fixed bed reactor is filled sequentially along the material flow direction with a first layer of 0.5% Pt / Al2O3 spherical catalyst accounting for 20% of the height, and a second layer of 3% Pt / C clover-shaped catalyst accounting for 80% of the height.

[0064] Comparative Example 4 is the same as Example 4 in all other respects.

[0065] Comparative Example 5 The difference between Comparative Example 5 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 5 is as follows: Filling method: The fixed bed reactor was completely filled with the clover-shaped 3% Pt / C catalyst prepared in Example 2, with a filling height of 100%.

[0066] Comparative Example 5 is the same as Example 4.

[0067] Comparative Example 6 The difference between Comparative Example 6 and Example 4 lies in the loading method of the fixed bed. The loading method of Comparative Example 6 is as follows: Filling method: Replace the second layer of 3% Pt / C clover-shaped catalyst with a 3% Pt / C cylindrical catalyst of equal volume and height, with a diameter of 2.0 mm.

[0068] Comparative Example 6 is the same as Example 4.

[0069] Example 5 Examples 4 and Comparative Examples 1 to 6 were run continuously for T hours. The residual rate (%) of p-nitroaniline and the yield (%) of p-phenylenediamine in the product liquid separated in the gas-liquid separator were determined by gas chromatography. The results are shown in Table 1. Table 1

[0070] Example 4 of this invention employs a three-layer heterogeneous catalyst gradient loading process. The first layer uses a 0.5% Pt / Al2O3 spherical catalyst, which initially buffers and traps impurities. The second layer uses a 3% Pt / C clover-shaped catalyst. The clover-shaped catalyst's heterogeneous structure can significantly increase the external surface area, optimize mass transfer efficiency, and effectively reduce bed pressure drop. The supported Pt-Re / C cylindrical catalyst, through the introduction of Re metal, generates an alloy synergistic effect, enhances hydrogenation capacity, and effectively inhibits catalyst carbon deposition. During the reaction lasting up to 800 hours, the product output remained stable. As shown in Table 1, Comparative Examples 1 and 4, due to the lack of Re metal, showed a significant increase in p-nitroaniline residue after 400 hours of operation, indicating a certain degree of catalyst deactivation. Sampling revealed that the cause was insufficient anti-carbon deposition ability.

[0071] Compared to Example 4, Comparative Example 2 shows that the Pt-Re / C layer comes into contact with the raw material first, causing the Pt-Re / C layer to deactivate prematurely. Comparative Examples 3 and 5 either lack the first alumina buffer layer or use a single catalyst, resulting in low reaction conversion efficiency and shortened catalyst life. Compared to Example 4, Comparative Example 6 demonstrates that the clover-shaped structure is superior to the ordinary cylindrical structure in improving mass transfer efficiency.

[0072] The three-layer gradient design in Example 4 of this invention achieved excellent results with a reaction selectivity of over 99.8% and a raw material conversion rate of over 99.7% during a run of up to 800 hours.

[0073] The method of this invention has been described through preferred embodiments. Those skilled in the art will readily be able to modify or appropriately alter and combine the methods and applications described herein within the scope, spirit, and context of this invention to implement and apply the technology of this invention. Those skilled in the art can refer to the content herein to appropriately improve process parameters. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of this invention.

Claims

1. A system for the continuous catalytic hydrogenation of p-phenylenediamine in a fixed bed, characterized in that, include: Step S1: p-Nitroaniline and an organic solvent are mixed in a material mixing device to obtain a p-nitroaniline solution, and then the p-nitroaniline solution is preheated with hydrogen in a preheater; Step S2: The preheated nitroaniline solution and hydrogen are mixed in a gas-liquid mixer and then enter a fixed-bed reactor pre-loaded with catalyst to carry out a catalytic hydrogenation reaction to generate product materials including p-phenylenediamine. The fixed-bed reactor is characterized by having three layers of heterogeneous catalysts sequentially packed in sections along the flow direction of the reactants: Among them, the first layer, the second layer, and the third layer are each independently a supported Pt / Al2O3 catalyst, a supported Pt / C catalyst, and a supported Pt-Re / C catalyst.

2. The system according to claim 1, characterized in that, The first layer is a supported Pt / Al2O3 catalyst; the second layer is a supported Pt / C cloverleaf catalyst; the third layer is a supported Pt-Re / C cylindrical catalyst; and / or, the packing height ratios of the first, second, and third layers of catalyst in the fixed-bed reactor are respectively: first layer 20%, second layer 50%, and third layer 30%; and / or, the supported Pt / Al2O3 is a spherical or near-spherical catalyst; and / or, the supported Pt / C is a cloverleaf catalyst; and / or, the Pt loading of the first layer catalyst is 0.5%; and / or, the... The Pt loading of the second catalyst layer is 1-5%, preferably 3%; and / or, in the third catalyst layer, the Pt loading is 1-5%, the Re loading is 0.5-2%, preferably 3.0 wt% Pt loading and 1.0 wt% Re loading; and / or, the gas-liquid mixer is selected from any one of a static mixer, T-type mixer, Y-type mixer, cross-type mixer, Venturi mixer, porous media / sieve plate distributor, Sheta ring distributor, and coaxial flow mixer; and / or, the temperature of the preheater and fixed bed reactor is controlled at 80-180°C, preferably 80-120°C.

3. The system according to claim 1, characterized in that, The molar ratio of p-nitroaniline to hydrogen is 1:(3.0~10.0), preferably 1:(3.5~8); and / or the mass ratio of p-nitroaniline to organic solvent is 1:(1~20), preferably 1:(3.3~10); and / or the organic solvent is selected from at least one of methanol, ethanol, isopropanol, water, toluene, acetone, tetrahydrofuran, dioxane, N,N-dimethylformamide, and dimethylacetamide, preferably isopropanol or N,N-dimethylformamide.

4. The system according to claim 1, characterized in that, The residence time of the reactants in the fixed-bed reactor is 0.1 to 10 minutes, preferably 1 to 3 minutes.

5. The system according to claim 1, characterized in that, The hourly feed mass of the reactants to the total mass of the catalyst packing has a space velocity ratio of (0.1~1.5):1, preferably (0.3~0.5):

1.

6. The system according to claim 1, characterized in that, The reaction pressure is 0.1~5MPa, preferably 0.6~1.0MPa.

7. The preparation of a supported Pt-Re / C catalyst according to claims 1 to 6, characterized in that, Including steps, S1: Activated carbon powder is mixed with binder, water is added, extruded and molded, dried, calcined under an inert atmosphere, washed with nitric acid solution, washed with water until neutral, and dried to obtain the dried carrier; S2: Platinum salt and rhenium salt are dissolved in water, and acid is added to make an impregnation solution; S3: The dried carrier is mixed with the impregnation solution and then dried; S4: The dried sample was placed in a hydrogen atmosphere, and the temperature was increased by a programmed reduction. After cooling, the Pt-Re / C catalyst was obtained.

8. The preparation of the supported Pt-Re / C catalyst according to claim 7, characterized in that, The binder in step S1 is selected from any one of guar gum methylcellulose, carboxymethylcellulose, starch, polyvinyl alcohol, kaolin, boehmite, silica sol, alumina sol, or lignin sulfonate; and / or, the mass ratio of the binder to activated carbon powder in step S1 is 1:(15~25); and / or, the inert atmosphere is any one or a mixture of nitrogen, argon, and helium; and / or, the nitric acid solution is an aqueous solution of nitric acid; and / or, the mass concentration of the aqueous solution of nitric acid is 3~7%; and / or, the extrusion molding is extruding into a cylindrical strip with a diameter of 1.5~2.5 mm.

9. The preparation of the supported Pt-Re / C catalyst according to any one of claims 7 or 8, characterized in that, The platinum salt in step S2 is selected from chloroplatinic acid, platinum nitrate, or nitrodiamineplatinum, or a mixture thereof; and / or, the rhenium salt in step S2 is selected from ammonium perrhenate, potassium perrhenate, sodium perrhenate, or calcium perrhenate, or a mixture thereof; and / or, the acid in step S2 is selected from sulfuric acid, nitric acid, or hydrochloric acid, or a mixture thereof; and / or, after step S2, the concentration of the acid added is 0.1~0.5 mol / L.

10. The preparation of the supported Pt-Re / C catalyst according to any one of claims 7 to 9, characterized in that, The drying temperature in step S3 is 100~120°C; and / or the programmed heating method in step S4 is to slowly heat to 3~500°C at a heating rate of 1~3°C / min and maintain it for 3~6 hours.

Images