Hydrogenation catalyst for binitro compound and preparation process and application thereof

Abstract

The invention provides a binitro compound hydrogenation catalyst for a fixed bed and a preparation process and application thereof, and belongs to the technical field of catalysts. The preparation process comprises the following steps: (1) carrier modification: immersing a carrier into a polyethyleneimine solution for soaking to obtain the carrier; (2) loading a carrier of active metal: spraying a platinum salt-containing solution on the surface of the modified carrier by using an ultrasonic atomization spraying technology; (3) loading a citric acid protective layer: immersing the Pt / carrier in a citric acid solution for oscillation treatment; (4) loading a co-metal carrier: loading a co-metal precursor solution onto the citric acid-Pt / carrier by using an ultrasonic atomization spraying technology; and (5) reduction: carrying out three-stage reduction treatment on the catalyst precursor to obtain the catalyst. The hydrogenation catalyst with high activity, high selectivity and long service life is prepared by the preparation process; the catalyst is used for hydrogenation reaction of dinitro-compounds, and has high selectivity and conversion rate.

Description

Technical Field

[0001] This invention relates to the field of organic catalytic hydrogenation technology, specifically to a hydrogenation catalyst for dinitro compounds, its preparation process and uses, and particularly to a selective hydrogenation catalyst for dinitro compounds in a fixed bed. Background Technology

[0002] The hydrogenation of dinitro compounds to prepare corresponding diamine compounds is an important reaction process in chemical production, widely used in pharmaceuticals, dyes, pesticides, and other fields. Fixed-bed reactors are widely used in this reaction due to their advantages such as simple structure, convenient operation, and reusable catalysts. However, current catalysts used for the hydrogenation of fixed-bed dinitro compounds suffer from problems such as low activity, poor selectivity, and short lifespan, leading to harsh reaction conditions, low product yield and purity, and increased production costs. CN109569650B uses a microwave-assisted impregnation method to improve Pd dispersion, but it does not solve the problem of loss of active components from the support. Therefore, developing a high-performance preparation process for hydrogenation catalysts of fixed-bed dinitro compounds is of significant practical importance.

[0003] In existing technologies, catalyst preparation methods mainly include impregnation, co-precipitation, and sol-gel methods. Impregnation is one of the most commonly used methods, but traditional impregnation methods often suffer from uneven distribution of active components and weak interaction with the support, affecting catalyst performance. To improve catalyst performance, researchers have carried out various modification treatments on the support, such as surface modification and doping, and have also optimized the selection of active components and additives, as well as the loading process. However, current research results still cannot fully meet the needs of industrial production, and further improvements and innovations are needed. Summary of the Invention

[0004] Based on the above-mentioned technical objectives, the present invention provides a hydrogenation catalyst for dinitro compounds, its preparation process and application. The preparation process involves pretreating the support, optimizing the loading process of the active component and the auxiliary agent, and controlling the reduction conditions to prepare a hydrogenation catalyst with high activity, high selectivity and long lifespan. The catalyst exhibits high selectivity and conversion rate in the hydrogenation reaction of dinitro compounds.

[0005] In a first aspect, a process for preparing a hydrogenation catalyst for dinitro compounds is provided, comprising the following steps: (1) Carrier modification: The carrier is immersed in a polyethyleneimine solution to obtain the modified carrier; (2) Support for loading active metals: Platinum salt solution was sprayed onto the surface of the modified support using ultrasonic atomization spraying technology to obtain Pt / support; (3) Citric acid protective layer: Pt / support is immersed in citric acid solution and shaken to obtain citric acid-Pt / support; (4) Support for loading the auxiliary metal: The auxiliary metal precursor solution was loaded onto citric acid-Pt / support using ultrasonic atomization spraying technology to obtain the catalyst precursor; (5) Reduction: The catalyst precursor is subjected to a three-stage reduction process to obtain the hydrogenation catalyst.

[0006] In some embodiments, the carrier is selected from alumina, activated carbon, and silicon dioxide. Preferably, the carrier is spherical alumina, activated carbon, or silicon dioxide with a diameter of 1-5 mm, or strip-shaped alumina, activated carbon, or silicon dioxide with a size of 1-10 mm.

[0007] In some embodiments, the concentration of the polyethyleneimine solution is 0.5-2 mol / L, preferably 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, or any two of the above values ​​forming a range.

[0008] In some embodiments, the solid-liquid mass ratio of the carrier to polyethyleneimine is 1:(1-10), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values ​​forming a range.

[0009] In some embodiments, the soaking requires ultrasonic-assisted soaking for 2-5 hours, with ultrasonic conditions of 35-40 kHz. Preferably, the soaking time is 2 hours, 3 hours, 4 hours, 5 hours, or any two of these values ​​within a range. Preferably, the ultrasonic conditions are 35 kHz, 38 kHz, 40 kHz, or any two of these values ​​within a range.

[0010] In some embodiments, the modified carrier is vacuum dried at 80-150℃ (preferably 80℃, 90℃, 100℃, 110℃, 120℃, 140℃, 150℃) for 12-24h (preferably 12h, 14h, 15h, 16h, 18h, 20h, 22h, 24h).

[0011] In some embodiments, the platinum-containing salt solution is a chloroplatinic acid solution or a platinum nitrate solution.

[0012] In some embodiments, the concentration of the platinum salt solution is 0.1~0.5 mol / L, preferably 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any two of the above values ​​forming a range.

[0013] In some embodiments, the specific process of loading the active metal onto the carrier is as follows: using an ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm, a platinum salt solution of 0.1~0.5 mol / L is sprayed; during the spraying process, the pressure of the carrier gas nitrogen is set to 0.2 MPa to drive the atomized solution droplets; the temperature of the modified carrier is heated to 60°C to promote the evaporation of the solvent in the solution; the spraying speed is maintained at 2 mL / min, while the rotating platform on which the modified carrier is placed rotates at a constant speed of 10±1 rpm; after the spraying is completed, the Pt / carrier is subjected to a static aging treatment at room temperature for 2 h.

[0014] In some embodiments, the solid-liquid mass ratio of the platinum salt solution to the modified carrier is 1:(1-10), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values ​​forming any one of the ranges.

[0015] In some embodiments, a citric acid protective layer is loaded: Pt / support is immersed in a 0.1 mol / L citric acid solution, with the solid-liquid mass ratio controlled at 1:(1-10) (preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the above values ​​within a range), and subjected to shaking treatment at 25°C for 30 min. Subsequently, centrifugation is performed at 8000 rpm for 5 min; after separation, the sample is placed in a 60°C environment for vacuum drying for 2 h to obtain citric acid-Pt / support. The protective layer formed by the citric acid facilitates the subsequent blocking of mutual interference between the two metal precursors, achieving distributed and localized loading of Pt and Cu.

[0016] In some embodiments, the auxiliary metal precursor solution is selected from copper nitrate solution, cobalt nitrate solution, or nickel nitrate solution.

[0017] In some embodiments, the concentration of the auxiliary metal precursor solution is 0.1~0.5 mol / L, preferably 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, or any two of the above values ​​forming a range.

[0018] In some embodiments, the solid-liquid mass ratio of the auxiliary metal precursor solution to citric acid-Pt / carrier is 1:(1-10), preferably 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, and any two of the above values ​​constitute any one of the ranges.

[0019] In some embodiments, the support for the auxiliary metal is prepared by: using an ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm to spray a 0.1~0.5 mol / L auxiliary metal precursor solution; during the spraying process, the pressure of the carrier gas nitrogen is set to 0.2 MPa to drive the atomized solution droplets; the temperature of citric acid-Pt / support is controlled at 60°C to promote the evaporation of the solvent in the solution; the spraying rate is maintained at 2 mL / min, while the rotating platform holding the citric acid-Pt / support rotates at a constant speed of 10±1 rpm, and the entire spraying process lasts for 30 min; after the spraying is completed, the sample is subjected to static aging treatment at room temperature for 2 h, and then dried at 100-150°C (preferably 100, 110, 120, 130, 140 or 150°C) for 12-24 h (preferably 12 h, 14 h, 15 h, 16 h, 18 h, 20 h, 22 h, 24 h) to obtain the catalyst precursor.

[0020] In some embodiments, the three-stage restoration process includes: Stage 1: The catalyst precursor is activated using vapors of acetic acid and argon. Phase 2: Step reduction using a mixture of hydrogen and argon; Stage 3: The catalyst is obtained by reduction treatment with pure H2.

[0021] The catalyst precursor is subjected to a three-stage reduction process, and the alloying process is controlled by a three-step gradient reduction process; acetic acid vapor is used to activate and dissolve part of the citric acid layer; the alloying rate is controlled by gradient reduction of hydrogen (H2) and argon (Ar); and organic residues are removed by pure hydrogen to achieve rapid shaping.

[0022] In some embodiments, the acetic acid and argon vapor refers to a mixture of acetic acid vapor (after heating and vaporizing) and argon gas, wherein the concentration of acetic acid is 1-5 vol%, preferably any two values ​​from 1 vol%, 2 vol%, 3 vol%, 4 vol%, or 5 vol%. In some embodiments, the temperature of the acetic acid and argon vapor is any two values ​​from 80°C, 90°C, 100°C, or 110°C. In some embodiments, the stage 1 control pressure is any two values ​​from 5 kPa, 10 kPa, 15 kPa, or 20 kPa. In some embodiments, the carrier gas argon (Ar) flow rate is any two values ​​from 10 mL / min, 20 mL / min, 30 mL / min, 40 mL / min, or 50 mL / min.

[0023] In some embodiments, the volume ratio of hydrogen (H2) to argon (Ar) is 1:1 to 5, preferably 1:1, 1:2, 1:3, 1:4, 1:5, or any two of the above values. In some embodiments, the temperature of stage 2 is 200°C, 210°C, 220°C, 230°C, 240°C, or any two of the above values. In some embodiments, the reduction duration of stage 2 is 60 min, 70 min, 80 min, 90 min, 100 min, or any two of the above values.

[0024] In some embodiments, the reduction duration in stage 3 is 30 min, 40 min, 50 min, 60 min, or any two of the above values ​​forming a range. In some embodiments, the H2 flow rate in stage 3 is controlled at 20 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 80 mL / min, 100 mL / min, or any two of the above values ​​forming a range.

[0025] In some embodiments, the three-stage restoration process includes: Stage 1: The catalyst precursor is placed in a steam generator and activated by steam containing acetic acid and argon at a temperature of 80-110℃ and a concentration of 1-5 vol%. The pressure is controlled at 5-20 kPa, the flow rate of the carrier gas argon (Ar) is 10-50 mL / min, and the activation time is 60 min. Phase 2: At 200-240℃, reduction is carried out using a mixed gas of hydrogen and argon (Ar) with a volume ratio of 1:4 (H2 flow rate of 20 mL / min and Ar flow rate of 80 mL / min) for 60-100 min; during this period, the proportion of H2 is increased by 5% every 15 min, until the H2 / Ar ratio reaches 1:1. Stage 3: In an environment of 300℃, pure H2 is used for treatment for 30-60 minutes, with the H2 flow rate controlled at 20-100 mL / min; when the carbon dioxide (CO2) concentration in the exhaust gas is below 10 ppm, the reduction process is considered to have reached its endpoint, and the catalyst is finally obtained.

[0026] Secondly, a hydrogenation catalyst is provided, which is prepared by the method described in this invention.

[0027] Thirdly, the present invention provides an application of the hydrogenation catalyst described herein in the hydrogenation reaction of dinitro compounds, the application comprising: loading the hydrogenation catalyst described herein into a fixed-bed reactor, pretreating it with hydrogen gas, then introducing raw materials to carry out a catalytic reaction, and separating the amino compound after the reaction is completed.

[0028] In some embodiments, the dinitro compound includes one of 1,3-dinitrobenzene, 2,4-dinitrochlorobenzene, 3,5-dinitropyridine, 2,4-dinitrobenzene, and m-dinitrobenzene.

[0029] In some embodiments, the temperature during hydrogen pretreatment is 100-200℃, the pressure during hydrogen pretreatment is 0.1-2MPa, and the temperature and pressure are maintained for 1-5 hours. Preferably, the temperature during hydrogen pretreatment is any one of the following ranges: 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 180℃, 190℃, 200℃, or any two of the above values. Preferably, the temperature and pressure maintenance time is any one of the following ranges: 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any two of the above values. Preferably, the pressure during hydrogen pretreatment is any one of the following ranges: 0.1MPa, 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, 2MPa, or any two of the above values.

[0030] In some embodiments, the catalytic reaction is carried out at a temperature of 40-120°C, a catalytic pressure of 0.5-2 MPa, and a feed space velocity of 0.1-1.2 h⁻¹. -1The hydrogen ratio is 5-50. Preferably, the temperature of the catalytic reaction is 40℃, 60℃, 80℃, 100℃, 120℃, or any two of the above values. Preferably, the catalytic pressure is 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, 2MPa, or any two of the above values. Preferably, the feed space velocity is 0.1 h⁻¹. -1 0.2h -1 0.4h -1 0.6h -1 0.8h -1 1h -1 1.2h -1 And any two of the above values ​​constitute any one of the ranges. Preferably, the hydrogen ratio is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, and any two of the above values ​​constitute any one of the ranges.

[0031] Feed space velocity refers to the feed mass divided by (catalyst mass × hour). Hydrogen ratio refers to the molar ratio of hydrogen to feed.

[0032] In this invention, room temperature refers to 10-40°C, preferably 20-35°C.

[0033] Compared with the prior art, one of the above technical solutions has the following advantages or beneficial effects: This invention modifies the support with polyethyleneimine (PEI) to assist in the distribution and positioning of bimetals, solving the problem of uneven bimetal alloying. Through a two-step spraying of active metal and auxiliary metal precursors, combined with a protective layer formed by citric acid, the electronic structure and surface properties of the active metal are adjusted, improving the dispersibility and anti-sintering ability of the bimetal. Simultaneously, it promotes the adsorption and activation of molecules during subsequent catalytic hydrogenation reactions, thereby enhancing the activity and selectivity of the catalyst and achieving interaction between the bimetal and the support. Through a three-step reduction process, the catalyst precursor surface is reconstructed by acetic acid activation, overcoming the limitations of traditional hydrogen reduction and achieving a synergistic improvement in activity and stability.

[0034] In summary, this invention prepares a hydrogenation catalyst with good metal particle dispersion, high activity, high selectivity, and long lifespan by pretreating the support with PEI, optimizing the loading process of spraying chloroplatinic acid and copper nitrate, and controlling the reduction conditions of acetic acid, H2 / Ar mixed gas, and hydrogen.

[0035] The catalyst of this invention exhibits excellent catalytic performance in the hydrogenation reaction of dinitro compounds in a fixed-bed reactor, significantly improving the yield and purity of the target product while reducing reaction energy consumption and cost. When applied to the hydrogenation of dinitro compounds such as 1,3-dinitrobenzene, 2,4-dinitrochlorobenzene, 3,5-dinitropyridine, 1,4-dinitrobenzene, and 1,2-dinitrobenzene, the catalyst achieves a conversion rate >99%, a target amine selectivity >99%, and operates stably in a fixed bed for over 500 hours. Attached Figure Description

[0036] Figure 1 This is a transmission electron microscope (TEM) image of catalyst A prepared in Example 1. From... Figure 1 It is evident that the metal particles are well dispersed.

[0037] Figure 2 This is a transmission electron microscope (TEM) image of catalyst G prepared in Comparative Example 2. From... Figure 2 The agglomeration of metal particles is clearly visible, and the dispersion of metal particles is poor.

[0038] Terminology Explanation 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.

[0039] 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.

[0040] 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.

[0041] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," 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. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the features of the embodiments or examples in this specification without contradiction.

[0042] Unless otherwise expressly indicated, the descriptive terms “each…independently”, “…each…independently”, and “…independently” used in this invention are interchangeable and should be interpreted broadly. They can mean that the specific options expressed by the same symbols in different groups do not affect each other, or that the specific options expressed by the same symbols in the same group do not affect each other.

[0043] The terms “optional,” “optionally,” or “arbitrarily” mean that the event or situation described below may, but is not necessarily, occur, and the description includes both the occurrence and non-occurrence of the event or situation. For example, “optionally replaced by…” means that the replacement may or may not occur.

[0044] When the terms “independent” and “arbitrarily” are used together, for example, “independently and arbitrarily replaced by…”, it means that specific options are replaced by or not replaced by each other without affecting each other. Detailed Implementation

[0045] The following provides various embodiments or examples to enable those skilled in the art to implement the invention based on the description. These are merely examples and not intended to limit the invention. The endpoints and values ​​of the ranges disclosed herein are not limited to precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," 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 invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] 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.

[0048] All reagents used in this invention can be purchased commercially or prepared by the methods described in this invention.

[0049] Polyethyleneimine was added to deionized water and stirred until homogeneous to obtain a 0.5-2 mol / L polyethyleneimine (PEI) solution.

[0050] Example: Preparation of catalyst (1) Carrier modification: 10g of carrier is immersed in 0.5-2mol / L polyethyleneimine solution (100g), ultrasonically assisted (40kHz) for 2-5h, and vacuum dried at 80-150℃ for 12-24h to obtain the modified carrier; (2) Support for active metals: An ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm was used to spray a platinum salt solution containing 0.1~0.5 mol / L, controlling the solid-liquid ratio at 1:3. During the spraying process, the pressure of the carrier gas nitrogen was set to 0.2 MPa to drive the atomized solution droplets; the temperature of the modified support was controlled at 60 ℃ to promote the evaporation of the solvent in the solution; the spraying speed was maintained at 2 mL / min, while the rotating platform holding the modified support was rotated at a constant speed of 10±1 rpm. After spraying, the Pt / support was subjected to a static aging treatment at room temperature for 2 h.

[0051] (3) Citric acid protective layer: The obtained Pt / support was immersed in a 0.1 mol / L citric acid solution with a solid-liquid ratio of 1:10 and shaken at 25°C for 30 min. Then, centrifugation was performed at 8000 rpm for 5 min. After separation, the sample was vacuum dried at 60°C for 2 h to obtain citric acid-Pt / support.

[0052] (4) Support for the auxiliary metal: An ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm was used to spray a 0.1~0.5 mol / L auxiliary metal solution, controlling the solid-liquid ratio at 1:2. During the spraying process, the pressure of the carrier gas nitrogen (N2) was set to 0.2 MPa to drive the atomized solution droplets; the temperature of the obtained citric acid-Pt / support was controlled at 60 ℃ to promote the evaporation of the solvent in the solution; the spraying speed was maintained at 2 mL / min, while the rotating platform holding the citric acid-Pt / support was rotated at a constant speed of 10±1 rpm. After the spraying was completed, the obtained product was subjected to static aging treatment at room temperature for 2 h, and then dried at 100-150℃ for 12-24 h to obtain the catalyst precursor.

[0053] (5) Restoration: The specific steps are as follows: Stage 1: The obtained catalyst precursor is placed in a steam generator and activated by introducing acetic acid and argon steam at a temperature of 80-110 °C and a concentration of 1-5 vol%. The pressure is controlled at 5-20 kPa, the argon (Ar) carrier gas flow rate is 50 mL / min, and the activation time is 60 min. Stage 2: Reduction is carried out at 200-240 °C using a hydrogen to argon (Ar) mixture with a volume ratio of 1:4 (H2 flow rate 20 mL / min, Ar flow rate 80 mL / min) for 90 min. During this period, the H2 ratio is increased by 5% every 15 min until the H2 / Ar ratio reaches 1:1. Stage 3: Treatment is carried out at 300 °C using pure H2 for 30 min, with the H2 flow rate controlled at 20-100 mL / min. The reduction process is considered complete when the carbon dioxide (CO2) concentration in the exhaust gas is below 10 ppm, and the catalyst is finally obtained.

[0054] The preparation conditions of the catalyst are shown in Table 1: Table 1. Variations in catalyst preparation conditions

[0055] Comparative Example 1 The difference from Example 1 is that the support modification step is omitted, while the rest of the steps are the same as in Example 1, to obtain catalyst F.

[0056] Comparative Example 2 The difference from Example 1 is that the platinum salt solution and the auxiliary metal solution are mixed and then sprayed, while the rest of the steps are the same as in Example 1, to obtain catalyst G.

[0057] Comparative Example 3 The difference from Example 1 is that the step of supporting the citric acid protective layer is omitted, while the rest of the steps are the same as those in Example 1, to obtain catalyst H.

[0058] Comparative Example 4 The difference from Example 1 is that a mixture of hydrogen and argon gas was used for reduction of acetic acid, while the rest of the steps were the same as in Example 1, to obtain catalyst I.

[0059] Application Examples: Hydrogenation of Dinitro Compounds 10g of catalyst was packed into a 20ml fixed bed, and the gas in the bed was replaced with hydrogen. The temperature was then raised to 100-200℃, and the hydrogen pressure was increased to 0.1-2MPa. The temperature and pressure were maintained for 3 hours. 100g of a dinitro compound (such as m-dinitrobenzene, 3,5-dinitropyridine, 1,2-dinitrobenzene) was dissolved in 900g of solvent (methanol, ethanol, or tetrahydrofuran) to prepare a 10wt% solution. The mass hourly space velocity (WHSV) was 0.1-1.2h. -1 Aniline was obtained by catalytic reaction with a hydrogen ratio of 5-50, a catalytic temperature of 80-85℃, and a hydrogen gas pressure of 0.5-2 MPa. The conversion rate and selectivity of aniline were calculated by gas chromatography analysis of samples taken after 500 hours of stable catalyst operation. The reaction conditions and results are shown in Table 2.

[0060] Table 2 Hydrogenation reaction conditions and results

[0061] The results are shown in Table 2. The catalyst prepared in the embodiments of the present invention converts nitro compounds into aniline, and the conversion rate of the obtained product is >99% and the selectivity is >99%. Even after running for 500 hours, aniline with high conversion rate and high selectivity is still obtained.

[0062] Example 11 used an unmodified support for hydrogenation catalysis, and the conversion rate and selectivity of the resulting product were significantly lower than those of the embodiments of the present invention. The PEI-modified support solves the problem of uneven bimetallic alloying to a certain extent, therefore the embodiments of this application show better catalytic performance.

[0063] Example 12 involved directly mixing platinum and a fluxing metal before spraying. The resulting product exhibited significantly lower conversion and selectivity compared to the examples of this invention, and the catalyst's metal particles agglomerated (e.g., Figure 2In this embodiment of the invention, the active metal platinum and the auxiliary metal are sprayed separately and then attached sequentially, thereby adjusting the electronic structure and surface properties of the metal and improving its dispersibility (e.g., Figure 1 The catalyst's activity and selectivity are enhanced by its resistance to sintering and its ability to facilitate the adsorption and activation of reaction molecules in subsequent hydrogenation catalysis.

[0064] In Example 13, no citric acid protective layer was used during the separate spraying of the active metal platinum and the auxiliary metal. The two metals may interfere with each other after spraying. In catalytic applications, the conversion rate and selectivity are slightly better than those in Example 12, but still inferior to the catalytic effect of the catalyst in the embodiments of the present invention.

[0065] Example 14 used a conventional hydrogen reduction mode, and the resulting catalyst underwent dinitro reduction, resulting in lower conversion and selectivity than the examples of this invention. The examples of this invention use acetic acid to activate and reconstruct the catalyst surface, followed by a two-stage reduction with hydrogen, achieving a synergistic improvement in both activity and stability.

[0066] In this embodiment of the invention, the support is first modified, an active metal and a citric acid protective layer are first sprayed on, and then a helper metal is sprayed on. The hydrogenation catalyst is prepared by three-stage reduction. The resulting catalyst exhibits excellent catalytic performance in the hydrogenation catalytic reaction of dinitro compounds, which can significantly improve the yield and purity of the target product and reduce the reaction energy consumption and cost.

[0067] 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 process for preparing a hydrogenation catalyst for dinitro compounds, characterized in that, Includes the following steps: (1) Carrier modification: The carrier is immersed in a polyethyleneimine solution to obtain the modified carrier; (2) Support for loading active metals: Platinum salt solution was sprayed onto the surface of the modified support using ultrasonic atomization spraying technology to obtain Pt / support; (3) Citric acid protective layer: Pt / support is immersed in citric acid solution and shaken to obtain citric acid-Pt / support; (4) Support for loading auxiliary metal: The auxiliary metal precursor solution is loaded onto citric acid-Pt / support using ultrasonic atomization spraying technology to obtain the catalyst precursor; (5) Reduction: The catalyst precursor is subjected to a three-stage reduction process to obtain the hydrogenation catalyst.

2. The preparation process according to claim 1, characterized in that, The carrier is selected from alumina, activated carbon, and silicon dioxide; And / or, the concentration of the polyethyleneimine solution is 0.5-2 mol / L; And / or, the solid-liquid mass ratio of the carrier to polyethyleneimine is 1:(1-10). And / or, the soaking requires ultrasonic-assisted soaking for 2-5 hours, with ultrasonic conditions of 35-40 kHz; the carrier is modified and then vacuum-dried at 80-150℃ for 12-24 hours.

3. The preparation process according to claim 1, characterized in that, The platinum-containing salt solution is a chloroplatinic acid solution or a platinum nitrate solution. And / or, the solid-liquid mass ratio of the platinum salt solution to the modified support is 1:(1-10). And / or, the specific process of the carrier loaded with active metal is as follows: using an ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm, a platinum salt solution of 0.1~0.5 mol / L is sprayed; during the spraying process, the pressure of the carrier gas nitrogen is set to 0.2 MPa, and the temperature of the modified carrier is heated to 60℃; the spraying rate is maintained at 2 mL / min, while the rotating platform on which the modified carrier is placed rotates at a constant speed of 10±1 rpm; after the spraying is completed, the Pt / carrier is subjected to a static aging treatment for 2 hours.

4. The preparation process according to claim 1, characterized in that, Citric acid protective layer loading: The obtained Pt / support was immersed in 0.1 mol / L citric acid solution, and the solid-liquid mass ratio was controlled at 1:(1-10). The mixture was shaken at 25℃ for 30 min. Then, centrifugation was performed at 8000 rpm for 5 min. After separation, the sample was placed in a 60℃ environment for vacuum drying for 2 h to obtain citric acid-Pt / support.

5. The preparation process according to claim 1, characterized in that, Support for the co-metal: An ultrasonic atomization spraying system with a nozzle diameter of 0.3 mm was used to spray a 0.1~0.5 mol / L co-metal precursor solution. During the spraying process, the pressure of the carrier gas nitrogen was set to 0.2 MPa to drive the atomized solution droplets. The temperature of the obtained citric acid-Pt / support was controlled at 60 ℃ to promote the evaporation of the solvent in the solution. The spraying rate was maintained at 2 mL / min, while the rotating platform holding the citric acid-Pt / support was rotated at a constant speed of 10±1 rpm. After the spraying was completed, the sample was subjected to a static aging treatment for 2 h and then dried at 100-150℃ for 12-24 h to obtain the catalyst precursor. And / or, the auxiliary metal precursor solution is selected from copper nitrate solution, cobalt nitrate solution, or nickel nitrate solution. And / or, the solid-liquid mass ratio of the auxiliary metal precursor solution to the citric acid-Pt / carrier is 1:(1-10).

6. The preparation process according to claim 1, characterized in that, The three-stage restoration process includes: Stage 1: The catalyst precursor is activated using vapors of acetic acid and argon. Phase 2: Step reduction using a mixture of hydrogen and argon; Stage 3: The catalyst is obtained by reduction treatment with pure H2.

7. The preparation process according to claim 6, characterized in that, The three-stage restoration process includes: Stage 1: The catalyst precursor is placed in a steam generator and activated by steam containing acetic acid and argon at a temperature of 80-110℃ and a concentration of 1-5 vol%. The pressure is controlled at 5-20 kPa, the flow rate of the carrier argon is 10-50 mL / min, and the activation time is 60 min. Phase 2: At 200-240℃, reduction is carried out using a mixed gas with a hydrogen to argon volume ratio of 1:4 (H2 flow rate of 20 mL / min and Ar flow rate of 80 mL / min) for 60-100 min; during this period, the proportion of H2 is increased by 5% every 15 min, until the H2 / Ar ratio reaches 1:

1. Stage 3: In an environment of 300℃, pure H2 is used for treatment for 30-60 minutes, with the H2 flow rate controlled at 20-100 mL / min; when the carbon dioxide concentration in the exhaust gas is below 10 ppm, the reduction process is considered to have reached its endpoint, and the catalyst is finally obtained.

8. A hydrogenation catalyst prepared by the method according to any one of claims 1 to 7.

9. Use of a hydrogenation catalyst prepared by the method according to any one of claims 1 to 7 in the hydrogenation reaction of dinitro compounds, the use comprising: The hydrogenation catalyst prepared by the method according to any one of claims 1 to 7 is packed into a fixed-bed reactor, pretreated with hydrogen, and then fed with raw materials to carry out a catalytic reaction. After the reaction is completed, amino compounds are separated.

10. The use according to claim 9, characterized in that, The dinitro compound includes one of 1,3-dinitrobenzene, 2,4-dinitrochlorobenzene, 3,5-dinitropyridine, 2,4-dinitrobenzene, and m-dinitrobenzene; And / or, the temperature during hydrogen pretreatment is 100-200℃, the pressure during hydrogen pretreatment is 0.1-2MPa, and the temperature and pressure are maintained for 1-5 hours; And / or, the reaction temperature is 40-120℃, the pressure is 0.5-2MPa, and the feed space velocity is 0.1-1.2h. -1 The hydrogen ratio is 5-50.

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