Preparation method of herbicide clopyralid

Abstract

The invention relates to the technical field of herbicides, and discloses a preparation method of herbicide clopyralid, which comprises the following steps: by taking 3, 4, 5, 6-tetrachloropicolinic acid as a raw material, adding a Ni-Fe-Mo / NC catalyst into a mixed solvent of ethanol and 1-butyl-3-methylimidazolium tetrafluoroborate, and carrying out high-pressure hydrodechlorination, concentration, acidification crystallization and drying to obtain the product. The catalyst is prepared by taking nitrogen-doped porous carbon prepared from corncobs as a carrier and loading Ni-Fe-Mo ternary alloy, the synergistic catalysis effect is achieved, the technological operation is simple and convenient, the raw materials are free of virulence, the catalyst can be recycled for 10-12 times, and the cumulative loss rate is 2.1-2.5%; the initial conversion rate of the product exceeds 95%, the selectivity is nearly 99%, the purity reaches 99% or above, and the method is suitable for large-scale industrial green production.

Description

Technical Field

[0001] This invention relates to the field of herbicide technology, and more particularly to a method for preparing the herbicide dichloropyridine acid. Background Technology

[0002] Dichloropyridine acid is a broad-spectrum herbicide with strong conductivity and low residue, suitable for various crop fields and lawns. It can effectively control broadleaf weeds and is widely used in agricultural production due to its unique mechanism of action and environmentally friendly characteristics.

[0003] Currently, there are various mainstream routes for the preparation of dichloropyridine acid, including multi-step reaction routes using methylpyridine as raw material, hydrazine hydrate reduction, electrochemical reduction, and chlorination-hydrolysis reduction routes using cyanopyridine and chlorine as raw materials. Among these, hydrazine hydrate reduction and electrochemical reduction are more widely used. However, hydrazine hydrate reduction requires highly toxic raw materials, generates large amounts of wastewater, and easily causes environmental pollution, while also resulting in low product yield and purity. Although electrochemical reduction is more environmentally friendly and produces better product quality, the product concentration in aqueous solution is low, the separation and recovery process is cumbersome, and the energy consumption and cost of mother liquor treatment are high. Traditional processes also suffer from problems such as electrode corrosion and difficulty in controlling side reactions. For example, patent number CN119592967B proposes an improved electrochemical reduction process. Its core is to use a diaphragm electrolytic cell, with an aqueous solution containing 3,4,5,6-tetrachloropyridinecarboxylic acid and a certain flow rate of CO2 continuously introduced as the catholyte. The catholyte is prepared by stirring and clarifying an aqueous solution of alkali metal carbonate or bicarbonate with 3,4,5,6-tetrachloropyridinecarboxylic acid. An aqueous solution of alkali metal hydroxide is used as the anode, and silver is selected as the cathode and nickel-based materials are used as the anode for the electrolytic reaction. The anode and cathode are isolated by a diaphragm to avoid corrosion. CO2 is used to regulate the pH of the catholyte to suppress the hydroxylation side reaction, thereby preparing dichloropyridinecarboxylic acid. However, this technology still has certain limitations: the cathode uses silver material, which is costly and not conducive to cost control in large-scale industrial production; CO2 needs to be continuously and stably introduced and the flow rate needs to be precisely controlled, which places high demands on the sealing and flow control accuracy of the production equipment, increasing the complexity of operation; although the corrosion resistance of nickel-based anodes is improved in the diaphragm system, slow wear may still occur during long-term electrolysis, affecting the service life of the device; and the electrolysis reaction is highly dependent on parameters such as temperature and current, making it difficult to control the stability of parameters during industrial scale-up, which may lead to fluctuations in product yield.

[0004] Therefore, there is an urgent need to develop a high-efficiency process that is cost-controllable, easy to operate, highly stable, and can simultaneously achieve high conversion rate, high selectivity, and high product purity, and is suitable for large-scale industrial green production. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing the herbicide dichloropyridine acid.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing the herbicide dichloropyridine acid includes the following steps: Step 1: Weigh 3,4,5,6-tetrachloropyridinecarboxylic acid and place it in a high-pressure reactor. Add the mixed solvent and stir until completely dissolved. Then add the Ni-Fe-Mo / NC catalyst, close the reactor, and replace the air in the reactor with H2 3-5 times. Each replacement pressure is 0.5-0.8 MPa. Hold the pressure for 1-2 minutes and then release the air. Step 2: High-purity H2 is introduced into the reactor until the reaction pressure reaches 1.3-1.5 MPa. The mixture is then allowed to stand for 5-10 minutes. The heating device and stirrer are then started, and the temperature is raised to 80-85℃. The stirring rate is 500-600 r / min, and the reaction is allowed to proceed for 4-6 hours. After the reaction is complete, the reactor is cooled to room temperature. The remaining H2 is slowly released, the reactor body is opened, and the Ni-Fe-Mo / NC catalyst and reaction solution are separated by vacuum filtration. The Ni-Fe-Mo / NC catalyst is recovered, and the filtrate is collected and placed in a rotary evaporator. In the concentration process, the concentration temperature is 45-55℃, the vacuum degree is 0.08-0.09MPa, and the solvent is removed by vacuum concentration. A hydrochloric acid solution with a molar concentration of 2-3mol / L is added to the concentrate to adjust the pH to 2.0-2.5. Then, the solution is placed in an ice-water bath at 0-5℃ and stirred and cooled for 2-4 hours to crystallize. The crystallized product is collected by vacuum filtration, washed 2-3 times with ice water, and the washed product is placed in a vacuum drying oven at 50-60℃ and 0.08-0.09MPa for 8-12 hours to obtain the herbicide dichloropyridine acid.

[0007] Preferably, in the first step, the mixed solvent is a mixture of ethanol and ionic liquid at a volume ratio of 1:(0.05-0.1), and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4).

[0008] Preferably, in the first step, the mass of the Ni-Fe-Mo / NC catalyst is 5-10% of the mass of 3,4,5,6-tetrachloropyridinecarboxylic acid.

[0009] Preferably, in the second step, the Ni-Fe-Mo / NC catalyst is recovered by washing it with ethanol 2-3 times and vacuum drying it at 55-60℃ for 8-10 hours, after which it can be recycled.

[0010] Preferably, the preparation principle of the herbicide dichloropyridine acid in this invention is explained as follows: Step 1: 3,4,5,6-Tetrachloropyridinecarboxylic acid is placed in a high-pressure reactor, and a mixed solvent consisting of ethanol and 1-butyl-3-methylimidazolium tetrafluoroborate is added. Ethanol serves as the main solvent to achieve initial dissolution of the substrate; the ionic liquid acts as a co-solvent, further enhancing the solubility and dispersibility of the substrate through ion association, reducing mass transfer resistance, and its excellent thermal stability and low volatility help minimize solvent loss. After the substrate is completely dissolved, the Ni-Fe-Mo / NC catalyst is added. This catalyst's nitrogen-doped porous carbon support, with its high specific surface area and abundant pores, can rapidly adsorb and enrich substrate molecules near the active sites. Subsequently, oxygen is completely removed from the reactor through multiple hydrogen purgings. This operation is crucial for ensuring reaction safety and catalyst activity, preventing oxygen from oxidizing the metal active sites and eliminating the risk of explosion from mixing with hydrogen.

[0011] The second step involves introducing high-purity hydrogen gas into the reactor to a set pressure to increase the solubility of hydrogen in the solvent, providing a sufficient hydrogen source for the reaction. A brief settling period allows for uniform hydrogen distribution, preventing excessive local concentrations that could lead to side reactions such as over-dechlorination. Subsequently, heating and stirring at suitable temperatures and speeds enhance gas-liquid-solid three-phase mass transfer, ensuring sufficient contact between the reactants and the catalyst. During this process, the Ni-Fe-Mo / NC catalyst plays a crucial synergistic role: Ni, as the main active component, chemically adsorbs and activates hydrogen molecules, generating active hydrogen species; Fe, by adjusting the electronic structure of the alloy, enhances the catalyst's adsorption selectivity for specific C-Cl bonds in the substrate molecules, thereby precisely breaking the target bonds and inhibiting over-dechlorination; Mo, strengthens the alloy's structural stability, inhibits metal particle sintering, and synergistically enhances the hydrogenation activity of Ni; the NC support, with its nitrogen sites forming strong coordination bonds with the alloy particles, enhances the metal-support interaction, prevents the loss of active components, and further modulates the electronic structure; and the carbon coating layer acts as a physical barrier, isolating the Cl generated in the reaction. - To prevent impurities from poisoning the active sites and ensure catalytic stability, the product is separated and purified through post-processing after the reaction. First, the product is concentrated under reduced pressure at low temperature to remove the solvent and prevent decomposition. Then, through acidification and low-temperature crystallization, the solubility of dichloropyridinic acid decreases sharply under acidic conditions, causing it to precipitate from the solution and separating it from soluble impurities. Finally, after washing and vacuum drying, high-purity dichloropyridinic acid is obtained. The reaction route is as follows: Preferably, the preparation method of the Ni-Fe-Mo / NC catalyst includes the following steps: A1: Take dried corn cobs, crush them, pass them through a 60-100 mesh sieve, place them in a beaker, add a ZnCl2 solution with a molar concentration of 4-6 mol / L and a nitrogen source, then ultrasonically disperse for 20-40 min, then transfer to a hydrothermal reactor, keep at 160-190℃ for 5-7 h, then cool naturally to room temperature, filter and collect the precursor, dry at 100-125℃ for 10-12 h, then place in a tube furnace, under a nitrogen atmosphere, heat at a rate of 4-6℃ / min, heat to 700-900℃ for 1.5-2.5 h, then cool and soak in a hydrochloric acid solution with a molar concentration of 1-2 mol / L for 2-4 h, stirring at a rate of 300-400 r / min, then wash with deionized water until the pH of the filtrate is 6.5-7.5, and finally vacuum dry at 60-80℃ for 10-14 h to obtain nitrogen-doped porous carbon (NC) support; A2: Weigh Ni(NO3)2・6H2O, Fe(NO3)3・9H2O, (NH4)6Mo7O 24 • Dissolve 4H₂O in deionized water and stir until completely dissolved to obtain a metal salt solution. Then add the NC support and stir magnetically for 40-80 min. Adjust the pH of the system to 9.0-10.0 with a 0.8-1.2 mol / L NaOH solution and stir for 10-20 min. Then add a 0.4-0.6 mol / L NaBH₄ solution dropwise at a rate of 0.6-0.8 mL / min and stir at room temperature for 1.5-2.5 h. Finally, add glucose and sonicate for 15-25 h. The solid was transferred to a hydrothermal reactor and kept at 150-170℃ for 3-5 hours. The solid was collected by vacuum filtration and washed 6-8 times with deionized water. Then, it was placed in a tube furnace in an H2 / Ar mixed atmosphere and reduced at 300-340℃ for 1.5-2.5 hours. After natural cooling to room temperature, it was soaked in a 3-7% (v / v) H2O2 solution for 20-40 minutes with a stirring rate of 200-300 r / min. It was washed with deionized water until neutral and dried under vacuum at 50-70℃ for 8-12 hours to obtain the Ni-Fe-Mo / NC catalyst.

[0012] Preferably, in step A1, the nitrogen source is a mixture of melamine and urea in a mass ratio of 1:(1-3).

[0013] Preferably, in step A2, the H2 / Ar mixed atmosphere is formed by mixing H2 and Ar in a volume ratio of 1:(4-9).

[0014] Preferably, in step A2, the molar ratio of Ni, Fe, and Mo metal ions in the metal salt solution is 1:(0.2-0.6):0.1.

[0015] Preferably, in step A2, the mass of the NC carrier is 0.8-1.2% of the mass of the metal salt solution; and the mass of the glucose is 20-30% of the mass of the NC carrier.

[0016] Preferably, in step A2, the number of moles of the NaBH4 solution is 12-16 times the total number of moles of Ni, Fe, and Mo metal ions in the metal salt solution.

[0017] Preferably, the preparation principle of the Ni-Fe-Mo / NC catalyst in this invention is explained as follows: The principle of step A1: This step uses corn cobs as a biomass carbon source. Through pretreatment, activation doping, hydrothermal molding, high-temperature calcination, and purification drying, a nitrogen-doped porous carbon (NC) support with high specific surface area and rich nitrogen active sites is prepared. The specific mechanism is as follows: First, the corn cobs are crushed and sieved to increase their specific surface area and ensure the uniformity of subsequent reactions. Then, they are ultrasonically dispersed with ZnCl2 activator and a melamine-urea mixed nitrogen source. The cavitation effect of ultrasound not only breaks up the agglomeration of the material but also promotes the dispersion of Zn... 2+ Ions penetrate into the interior of corn cob fibers, disrupting their cellulose crystalline structure and causing swelling, while simultaneously allowing for uniform dispersion of the nitrogen source, laying the foundation for in-situ doping. Next, a hydrothermal reaction (160-190℃) hydrolyzes and condenses the corn cob components, forming a structurally stable carbonaceous precursor. This process further promotes ZnCl2 penetration and initial nitrogen fixation. Subsequent drying aims to remove free moisture, preventing the collapse of the carbon skeleton structure due to rapid moisture vaporization during subsequent high-temperature calcination. The core high-temperature calcination is conducted under nitrogen protection. The slow heating rate ensures the smooth progress of the pyrolysis reaction. At high temperatures of 700-900℃, the following key processes occur: 1) ZnCl2 melts and vaporizes, acting as a template agent to form abundant microporous and mesoporous structures in the carbon matrix, i.e., pore-forming templates; 2) Hydrogen and oxygen elements in biomass are removed in the form of H2O, CO2, etc., further expanding the pores; 3) The nitrogen source is completely decomposed, and the nitrogen-containing active groups released react with the active sites of the carbon skeleton to form NC bonds, realizing in-situ doping of nitrogen elements.

[0018] The principle of step A2: Through multi-step synergistic regulation of "metal ion loading - reduction nucleation - carbon shell coating - high-temperature alloying - selective etching", uniform, highly dispersed, and structurally stable Ni-Fe-Mo ternary alloy nano-active sites are constructed on the surface of nitrogen-doped porous carbon (NC) support. First, Ni(NO3)2・6H2O, Fe(NO3)3・9H2O, and (NH4)6Mo7O are... 24 • Ni is dissolved in 4H₂O to form a homogeneous metal salt solution. Subsequently, an NC support is added, utilizing its high specific surface area and nitrogen-active sites on its surface, to adsorb Ni through physical adsorption and chemical coordination.2+ Fe 3+ Mo 6+ Plasma efficiently anchors onto the carrier surface. By adjusting the system pH to an alkaline environment of 9.0-10.0, the metal ions undergo in-situ hydrolysis to generate hydroxide precursors, further enhancing their binding force with the carrier. Next, by adding NaBH4 solution dropwise and controlling the drop rate, the metal hydroxide precursors are controllably reduced to elemental metals, forming dispersed primary nanocrystal nuclei. Subsequently, glucose is added and subjected to hydrothermal treatment (150-170℃), causing the glucose to dehydrate and polymerize on the nanoparticle surface, forming an amorphous carbon shell. This carbon layer effectively inhibits the aggregation and growth of nanoparticles during subsequent high-temperature processing. Then, thermal reduction is performed (300-340℃) in a H2 / Ar mixed atmosphere. In this step, H2 completely reduces the residual metal oxides and provides a high-temperature environment to promote the diffusion and rearrangement between Ni, Fe, and Mo atoms, ultimately forming a uniform Ni-Fe-Mo ternary alloy; Ar serves as a dilution and protective gas to prevent excessive oxidation. Finally, surface etching was performed using a low-concentration H2O2 solution. This process selectively removes unstable grains, exposes highly active alloy sites, and introduces abundant surface defects, thereby optimizing the surface chemistry of the catalyst. After washing with water to neutrality and vacuum drying, a Ni-Fe-Mo / NC catalyst with both high catalytic activity and excellent stability was obtained.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes a Ni-Fe-Mo / NC ternary alloy catalyst, leveraging the synergistic effect of Ni, Fe, and Mo components and the structural advantages of a nitrogen-doped porous carbon support to achieve highly efficient conversion of 3,4,5,6-tetrachloropyridine acid to dichloropyridine acid. The initial conversion rate can reach over 95%, the target product selectivity is close to 99%, and the final product purity exceeds 99%. It effectively suppresses side reactions such as excessive dechlorination, solving the problem of low product yield and purity in traditional processes.

[0020] 2. The Ni-Fe-Mo / NC catalyst prepared by this invention, after recycling, has a cumulative loss rate of only 2.1-2.5%, and can be recycled up to 10-12 times. During recycling, the conversion rate and selectivity remain at a high level. Compared to single-metal or binary alloy catalysts, its structural stability is significantly improved, which not only reduces the cost of catalyst use but also reduces the generation of solid waste, aligning with the concept of green production.

[0021] 3. The catalytic hydrogenation process employed in this invention operates within a mild and controllable range, controlling key parameters such as reaction temperature and pressure. Compared to traditional electrochemical processes that are highly sensitive to parameter changes, this method exhibits less impact on product yield and quality during industrial scale-up, demonstrating strong process stability and significantly improving the controllability and reliability of large-scale production.

[0022] 4. This invention embodies the concept of green chemistry from its very inception. The reaction uses an ethanol-ionic liquid mixed solvent, and the low volatility of the ionic liquid reduces solvent loss. The entire process eliminates the need for highly toxic reducing agents such as hydrazine hydrate, avoiding the generation of large amounts of saline wastewater, resulting in significant environmental advantages. Simultaneously, the catalyst can be efficiently recovered and reused, and there is no need for precious metals such as silver or complex gas flow control equipment, effectively reducing equipment investment, raw material costs, and production energy consumption. Compared to traditional chemical reduction and electrochemical methods, it demonstrates stronger economic viability for industrial application. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1: I. Preparation of Ni-Fe-Mo / NC catalyst: A1: Take 50g of dried corn cob, crush it and pass it through a 60-mesh sieve. Place it in a beaker, add 200mL of ZnCl2 solution with a molar concentration of 4mol / L and a nitrogen source made of 5g of melamine and 5g of urea in a mass ratio of 1:1. Then, ultrasonically disperse for 20min, transfer it to a hydrothermal reactor, keep it at 160℃ for 5h, and then cool it naturally to room temperature. Filter and collect the precursor, dry it at 100℃ for 10h, and then place it in a tube furnace under a nitrogen atmosphere. The heating rate is 4℃ / min, and the temperature is raised to 700℃ for 1.5h. After cooling, soak it in 1mol / L hydrochloric acid solution for 2h with a stirring rate of 300r / min. Then wash it with deionized water until the pH of the filtrate is 6.5. Finally, vacuum dry it at 60℃ for 10h to obtain nitrogen-doped porous carbon (NC) support. A2: Weigh out 29.08g of Ni(NO3)2·6H2O, 8.08g of Fe(NO3)3·9H2O, and 1.77g of (NH4)6Mo7O. 24• Dissolve 4H₂O in deionized water and bring the volume to 100g. Stir until completely dissolved to obtain a metal salt solution. Then add 0.8g of NC support and stir magnetically for 40min. Adjust the pH of the system to 9.0 with 0.8mol / L NaOH solution and stir for 10min. Then add 3.9L of 0.4mol / L NaBH₄ solution dropwise at a rate of 0.6mL / min. Stir at room temperature for 1.5h. Finally, add 0.16g of glucose and disperse by ultrasonication. After 15 min, the solid was transferred to a hydrothermal reactor and kept at 150℃ for 3 h. The solid was collected by vacuum filtration, washed 6 times with deionized water, and then placed in a tube furnace in a H2 / Ar mixed atmosphere (H2 and Ar mixed at a volume ratio of 1:4). The solid was reduced at 300℃ for 1.5 h, then naturally cooled to room temperature. The solid was soaked in a 3% H2O2 solution for 20 min with a stirring rate of 200 r / min, washed with deionized water until neutral, and dried under vacuum at 50℃ for 8 h to obtain the Ni-Fe-Mo / NC catalyst.

[0025] II. Preparation of the herbicide dichloropyridine acid: Step 1: Weigh 100g of 3,4,5,6-tetrachloropyridinecarboxylic acid and place it in a high-pressure reactor. Add 100mL of ethanol and 5mL of [BMIM]BF4 mixed in a volume ratio of 1:0.05 to form a mixed solvent. Stir until completely dissolved. Then add 5g of Ni-Fe-Mo / NC catalyst. Close the reactor and replace the air in the reactor with H2 three times. Each replacement pressure is 0.5MPa. Hold the pressure for 1 minute and then release the air. Step 2: High-purity H2 is introduced into the reactor until the reaction pressure reaches 1.3 MPa. After standing for 5 minutes, the heating device and stirrer are started, the temperature is raised to 80℃, the stirring rate is 500 r / min, and the reaction is carried out for 4 hours. After the reaction is completed, the reactor is cooled to room temperature, the remaining H2 is slowly released, the reactor body is opened, and the Ni-Fe-Mo / NC catalyst and the reaction solution are separated by vacuum filtration. The Ni-Fe-Mo / NC catalyst is recovered, the filtrate is collected, and it is concentrated in a rotary evaporator at a concentration temperature of 45℃ and a vacuum degree of 0.08 MPa to remove the solvent. A 2 mol / L hydrochloric acid solution is added to the concentrate to adjust the pH to 2.0. Then, it is placed in a 0℃ ice-water bath and stirred and cooled for 2 hours to crystallize. The crystallized product is collected by vacuum filtration, washed twice with ice water, and the washed product is placed in a 50℃, 0.08 MPa vacuum drying oven and dried for 8 hours to obtain the herbicide dichloropyridine acid.

[0026] Example 2: I. Preparation of Ni-Fe-Mo / NC catalyst: A1: Take 50g of dried corn cob, crush it and pass it through an 80-mesh sieve. Place it in a beaker, add 200mL of ZnCl2 solution with a molar concentration of 5mol / L and a nitrogen source composed of 5g of melamine and 10g of urea in a mass ratio of 1:2. Then, ultrasonically disperse for 30min, transfer it to a hydrothermal reactor, keep it at 175℃ for 6h, and then cool it naturally to room temperature. Filter and collect the precursor, dry it at 110℃ for 11h, and then place it in a tube furnace under a nitrogen atmosphere. The heating rate is 5℃ / min, and the temperature is raised to 800℃ for 2h. After cooling, soak it in 1.5mol / L hydrochloric acid solution for 3h with a stirring rate of 350r / min. Then wash it with deionized water until the pH of the filtrate is 7.0. Finally, vacuum dry it at 70℃ for 12h to obtain nitrogen-doped porous carbon (NC) support. A2: Weigh out 29.08g of Ni(NO3)2·6H2O, 16.16g of Fe(NO3)3·9H2O, and 1.77g of (NH4)6Mo7O. 24 • Dissolve 4H₂O in deionized water and bring the volume to 100g. Stir until completely dissolved to obtain a metal salt solution. Then add 1.0g of NC support and stir magnetically for 60min. Adjust the pH of the system to 9.5 with 1.0mol / L NaOH solution and stir for 15min. Then add 4.2L of 0.5mol / L NaBH₄ solution dropwise at a rate of 0.7mL / min. Stir at room temperature for 2.0h. Finally, add 0.25g of glucose and disperse by ultrasonication. After 20 min, the solid was transferred to a hydrothermal reactor and kept at 160℃ for 4 h. The solid was collected by vacuum filtration, washed 7 times with deionized water, and then placed in a tube furnace in a H2 / Ar mixed atmosphere (H2 and Ar mixed at a volume ratio of 1:6). The mixture was reduced at 320℃ for 2.0 h, then naturally cooled to room temperature. The solid was soaked in a 5% H2O2 solution for 30 min with a stirring rate of 250 r / min, washed with deionized water until neutral, and dried under vacuum at 60℃ for 10 h to obtain the Ni-Fe-Mo / NC catalyst.

[0027] II. Preparation of the herbicide dichloropyridine acid: Step 1: Weigh 100g of 3,4,5,6-tetrachloropyridinecarboxylic acid and place it in a high-pressure reactor. Add 100mL of ethanol and 7.5mL of [BMIM]BF4 mixed in a volume ratio of 1:0.075. Stir until completely dissolved. Then add 7.5g of Ni-Fe-Mo / NC catalyst. Close the reactor and replace the air in the reactor with H2 4 times. Each replacement pressure is 0.6MPa. Hold the pressure for 1.5min and then release the air. Step 2: High-purity H2 is introduced into the reactor until the reaction pressure reaches 1.4 MPa. After standing for 7 minutes, the heating device and stirrer are started, and the temperature is raised to 83℃. The stirring rate is 550 r / min, and the reaction is carried out for 5 hours. After the reaction is completed, the reactor is cooled to room temperature, and the remaining H2 is slowly released. The reactor body is opened, and the Ni-Fe-Mo / NC catalyst and reaction solution are separated by vacuum filtration. The Ni-Fe-Mo / NC catalyst is recovered, and the filtrate is collected and placed in a rotary evaporator. The concentration temperature is 50℃, and the vacuum degree is 0.085 MPa. The solvent is removed by vacuum concentration. A 2.5 mol / L hydrochloric acid solution is added to the concentrate to adjust the pH to 2.3. Then, the solution is placed in an ice-water bath at 2℃ and stirred and cooled for 3 hours to crystallize. The crystallized product is collected by vacuum filtration, washed twice with ice water, and the washed product is placed in a vacuum drying oven at 55℃ and 0.085 MPa for 10 hours to obtain the herbicide dichloropyridine acid.

[0028] Example 3: I. Preparation of Ni-Fe-Mo / NC catalyst: A1: Take 50g of dried corn cob, crush it and pass it through a 100-mesh sieve. Place it in a beaker, add 200mL of ZnCl2 solution with a molar concentration of 6mol / L and a nitrogen source composed of 5g of melamine and 15g of urea in a mass ratio of 1:3. Then, ultrasonically disperse for 40min, transfer it to a hydrothermal reactor, keep it at 190℃ for 7h, and then cool it naturally to room temperature. Filter and collect the precursor, dry it at 125℃ for 12h, and then place it in a tube furnace under a nitrogen atmosphere. The heating rate is 6℃ / min, and the temperature is raised to 900℃ for 2.5h. After cooling, soak it in 2mol / L hydrochloric acid solution for 4h with a stirring rate of 400r / min. Then wash it with deionized water until the pH of the filtrate is 7.5. Finally, vacuum dry it at 80℃ for 14h to obtain nitrogen-doped porous carbon (NC) support. A2: Weigh out 29.08g of Ni(NO3)2·6H2O, 24.24g of Fe(NO3)3·9H2O, and 1.77g of (NH4)6Mo7O. 24• Dissolve 4H₂O in deionized water and bring the volume to 100g. Stir until completely dissolved to obtain a metal salt solution. Then add 1.2g of NC support and stir magnetically for 80min. Adjust the pH of the system to 10.0 with 1.2mol / L NaOH solution and stir for 20min. Then add 4.53L of 0.6mol / L NaBH₄ solution dropwise at a rate of 0.8mL / min. Stir at room temperature for 2.5h. Finally, add 0.36g of glucose and sonicate. After 25 min of dispersion, the solid was transferred to a hydrothermal reactor and kept at 170℃ for 5 h. The solid was collected by vacuum filtration, washed 8 times with deionized water, and then placed in a tube furnace in a H2 / Ar mixed atmosphere (H2 and Ar mixed at a volume ratio of 1:9). The mixture was reduced at 340℃ for 2.5 h, then naturally cooled to room temperature. The solid was soaked in a 7% H2O2 solution for 40 min with a stirring rate of 300 r / min, washed with deionized water until neutral, and dried under vacuum at 70℃ for 12 h to obtain the Ni-Fe-Mo / NC catalyst.

[0029] II. Preparation of the herbicide dichloropyridine acid: Step 1: Weigh 100g of 3,4,5,6-tetrachloropyridinecarboxylic acid and place it in a high-pressure reactor. Add 100mL of ethanol and 10mL of [BMIM]BF4 mixed in a volume ratio of 1:0.1 and stir until completely dissolved. Then add 10g of Ni-Fe-Mo / NC catalyst, close the reactor, and replace the air in the reactor with H2 5 times at a pressure of 0.8MPa each time. Hold the pressure for 2 minutes and then release the air. Step 2: High-purity H2 is introduced into the reactor until the reaction pressure reaches 1.5 MPa. After standing for 10 minutes, the heating device and stirrer are started, the temperature is raised to 85℃, the stirring rate is 600 r / min, and the reaction is carried out for 6 hours. After the reaction is completed, the reactor is cooled to room temperature, the remaining H2 is slowly released, the reactor body is opened, and the Ni-Fe-Mo / NC catalyst and the reaction solution are separated by vacuum filtration. The Ni-Fe-Mo / NC catalyst is recovered, the filtrate is collected, and it is concentrated in a rotary evaporator at a concentration temperature of 55℃ and a vacuum degree of 0.09 MPa to remove the solvent. A 3 mol / L hydrochloric acid solution is added to the concentrate to adjust the pH to 2.5, and then it is placed in a 5℃ ice-water bath and stirred and cooled for 4 hours to crystallize. The crystallized product is collected by vacuum filtration, washed 3 times with ice water, and the washed product is placed in a 60℃, 0.09 MPa vacuum drying oven and dried for 12 hours to obtain the herbicide dichloropyridine acid.

[0030] Comparative Example 1: Based on Example 2, the difference is that in step A2, the H2 / Ar mixed atmosphere is replaced with a pure H2 atmosphere, and the rest is the same as in Example 2.

[0031] Comparative Example 2: Based on Example 2, the difference is that in the first step, 100 mL of ethanol and 7.5 mL of [BMIM]BF4 mixed solvent were replaced with 107.5 mL of single ethanol solvent, and the rest was the same as in Example 2.

[0032] Comparative Example 3: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Ni-Fe / NC catalyst. The preparation method of the Ni-Fe / NC catalyst is as follows: in step A2, 1.77g of (NH4)6Mo7O is removed. 24 • 4H2O: Weigh 29.08g of Ni(NO3)2·6H2O and 16.16g of Fe(NO3)3·9H2O, dissolve them in deionized water and bring the volume to 100g. The rest is the same as in Example 2.

[0033] Comparative Example 4: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Ni-Mo / NC catalyst. The Ni-Mo / NC catalyst is prepared by removing 16.16g of Fe(NO3)3・9H2O in step A2 and weighing 1.77g of (NH4)6Mo7O. 24 • 4H2O and 29.08g of Ni(NO3)2・6H2O were dissolved in deionized water and brought to a final volume of 100g. The rest of the process was the same as in Example 2.

[0034] Comparative Example 5: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Fe-Mo / NC catalyst. The Fe-Mo / NC catalyst is prepared by removing 29.08g of Ni(NO3)2・6H2O in step A2, and weighing 16.16g of Fe(NO3)3・9H2O and 1.77g of (NH4)6Mo7O. 24 • 4H2O, dissolved in deionized water and brought to a final volume of 100g, the rest is the same as in Example 2.

[0035] Comparative Example 6: Based on Example 2, the difference is that the nitrogen-doped porous carbon (NC) support is replaced with a common porous carbon support. The preparation method of the common porous carbon support is to remove the nitrogen source in step A1, and the rest is the same as Example 2.

[0036] Comparative Example 7: Based on Example 2, the difference is that glucose is removed in step A2, otherwise it is the same as Example 2.

[0037] Comparative Example 8: Based on Example 2, the difference is that the ion ratio of the metal salt solution in Example 2 is adjusted to Ni:Fe:Mo=1:0.8:0.1, that is, 32.32g of Fe(NO3)3・9H2O is weighed, and the rest is the same as in Example 2.

[0038] Comparative Example 9: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Ni / NC catalyst. The Ni / NC catalyst is prepared by removing 16.16g of Fe(NO3)3・9H2O and 1.77g of (NH4)6Mo7O from step A2. 24 • 4H2O: Weigh out 29.08g of Ni(NO3)2・6H2O and dissolve it in deionized water to a final volume of 100g. The rest is the same as in Example 2.

[0039] Comparative Example 10: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Fe / NC catalyst. The Fe / NC catalyst is prepared by removing 29.08g of Ni(NO3)2・6H2O and 1.77g of (NH4)6Mo7O from step A2. 24 • 4H2O: Weigh out 16.16g of Fe(NO3)3・9H2O and dissolve it in deionized water to a final volume of 100g. The rest is the same as in Example 2.

[0040] Comparative Example 11: Based on Example 2, the difference is that the Ni-Fe-Mo / NC catalyst is replaced with a Mo / NC catalyst. The preparation method of the Mo / NC catalyst is as follows: in step A2, 29.08g of Ni(NO3)2・6H2O and 16.16g of Fe(NO3)3・9H2O are removed, and only 1.77g of (NH4)6Mo7O is weighed. 24 • Dissolve 4H2O in deionized water and bring the volume to 100g. The rest is the same as in Example 2.

[0041] Test Example: This test example examines the performance of the herbicide dichloropyridine acid samples prepared in Examples 1-3 and Comparative Examples 1-11, including component analysis (conversion rate, selectivity), sample purity determination, and catalyst stability testing. Specific test methods and standards are as follows: 1. Component analysis was performed using gas chromatography. The concentrations of the substrate (3,4,5,6-tetrachloropyridine acid) before the reaction, the concentration of the remaining substrate after the reaction, and the concentrations of all products (dichloropyridine acid, byproducts such as monochloropyridine acid, non-chloropyridine acid, etc.) were calculated using the external standard method with a flame ionization detector (FID). The specific formulas are as follows: Conversion rate (%) = [1 - (substrate concentration after reaction / substrate concentration before reaction)] × 100%; the substrate concentration before reaction is the initial feed concentration of 3,4,5,6-tetrachloropyridine acid, and the substrate concentration after reaction is the concentration of unreacted 3,4,5,6-tetrachloropyridine acid in the filtrate.

[0042] Selectivity (%) = (target concentration / total concentration of all products) × 100%; the target is dichloropyridine acid, and the total concentration of the products used is the sum of the concentrations of all pyridine ring-containing products in the filtrate.

[0043] 2. Sample purity: determined by high performance liquid chromatography (HPLC): the final crystallized product of each test group, dichloropyridine acid, was dissolved and diluted with methanol to a concentration of 1 mg / mL, filtered through a 0.22 μm organic phase filter membrane, and injected into the HPLC instrument; a standard curve was plotted using dichloropyridine acid standard, and the mass fraction of dichloropyridine acid in the sample was calculated using the external standard method, which is the sample purity.

[0044] 3. Catalyst stability testing: The first reaction was completed according to the corresponding group's process. The initial conversion and initial selectivity were measured. The catalyst was recovered using the recovery process (washed twice with ethanol, vacuum dried at 58℃ for 9 hours). The recovered mass and loss rate were recorded. Cumulative loss rate (%) = [(initial catalyst mass - final recovered catalyst mass) / initial catalyst mass] × 100%; After the catalyst is recovered, it is fed back into the reaction. The number of times the catalyst is reused refers to the maximum number of times the catalyst can be reused when the reaction conversion rate and the reaction selectivity are reduced by less than or equal to 80%. Three parallel samples are set up for each test. The average value of the conversion rate, selectivity and number of reuses is taken as the final result. The higher the maximum number of reuses, the better the catalyst stability.

[0045] The test results are as follows: Table 1. Component analysis, purity, and catalyst stability test results of the herbicide dichloropyridine acid sample. Data Analysis: The herbicide dichloropyridine acid prepared in Examples 1-3 exhibits excellent comprehensive performance: the initial conversion rate is higher than 95%, the initial selectivity is close to 99%, and the product purity exceeds 99%. The Ni-Fe-Mo / NC catalyst used also shows excellent stability, with a cumulative loss rate as low as 2.1-2.5%, and can be recycled up to 10-12 times, fully demonstrating the advanced nature and practicality of the technical solution of this invention.

[0046] Compared with Example 2, the initial conversion rate, selectivity, sample purity and catalyst reuse times of Comparative Example 1 all decreased, while the cumulative catalyst loss rate increased. This is because Ar in the H2 / Ar mixed atmosphere of Example 2 plays a dilution and protection role, which can prevent the catalyst from being over-oxidized, while a pure H2 atmosphere will cause the active sites of the catalyst to agglomerate, reducing catalytic efficiency and stability. This highlights the importance of the H2 / Ar mixed atmosphere in maintaining the stability of the catalyst structure and high catalytic activity.

[0047] Compared with Example 2, all performance indicators of Comparative Example 2 declined. This is because the ethanol-ionic liquid mixed solvent in Example 2 can improve the solubility and dispersibility of the substrate, reduce the mass transfer resistance, and the thermal stability and low volatility of the ionic liquid can reduce solvent loss and protect the active sites of the catalyst. A single ethanol solvent cannot achieve these effects, highlighting the role of the ethanol-ionic liquid mixed solvent in improving reaction efficiency and catalyst stability.

[0048] Compared to Example 2, Comparative Example 3, which lacks Mo, showed a decrease in both catalytic effect and stability. This fully demonstrates that Mo plays the role of a "structural stabilizer" in the Ni-Fe-Mo ternary alloy. It can effectively inhibit the sintering and growth of metal nanoparticles during the reaction process and synergistically enhance the hydrogenation activity of Ni, making it a key component for ensuring the long-term stable operation of the catalyst.

[0049] Compared with Example 2, the catalytic performance and stability of Comparative Example 4 were reduced. This is because Fe can regulate the electronic structure of the alloy, enhance the adsorption selectivity of the target C-Cl bond, and inhibit excessive dechlorination. Without Fe, the catalytic selectivity decreased, side reactions increased, and the alloy structure was not stable enough, highlighting the important significance of Fe in optimizing the electronic structure of the catalyst and improving the reaction selectivity.

[0050] Compared with Example 2, the removal of Ni as the main active component significantly reduced the performance of Comparative Example 5. This is because Ni can chemically adsorb and activate hydrogen molecules to produce active hydrogen species. Without Ni, the hydrogen activation efficiency was greatly reduced, and the catalytic activity and stability were significantly decreased, highlighting the core role of Ni as the main active component in ensuring the efficient conduct of the reaction.

[0051] Compared to Example 2, Comparative Example 6 showed a decrease in performance. This is because the nitrogen sites on the NC support surface form strong coordination bonds with the alloy particles, enhancing the metal-support interaction and preventing the loss of active components. In contrast, ordinary porous carbon without nitrogen doping exhibits weak metal-support interaction, and the active sites are easily detached. This highlights the important role of nitrogen-doped porous carbon supports in anchoring active components and improving catalyst stability.

[0052] Compared with Example 2, the catalytic effect and stability of Comparative Example 7 were worse. This is because the carbon shell formed after glucose hydrothermation can inhibit the aggregation of nanoparticles. After removing glucose, the metal particles are prone to aggregation during high-temperature reduction, resulting in a reduction of active sites and a decrease in catalytic efficiency and stability. This highlights the key role of the carbon shell formed by glucose in inhibiting the aggregation of metal particles and maintaining the active structure of the catalyst.

[0053] Compared with Example 2, the performance of Comparative Example 8 is inferior to that of Example 2. This is because the molar ratio of Fe in Example 2 is appropriate and can optimize the electronic structure. However, an excessively high Fe ratio will destroy the synergistic effect of the ternary alloy, resulting in a decrease in catalytic selectivity and stability. This proves that optimizing the metal ratio is a necessary condition for achieving synergistic catalysis.

[0054] Compared with Example 2, Comparative Example 9 showed insufficient catalytic performance and stability. This is because the single Ni active site lacks the synergistic regulation of Fe and Mo, resulting in insufficient selective adsorption of the target C-Cl bond, easy over-dechlorination, and poor structural stability. This highlights the advantage of the synergistic effect of Ni-Fe-Mo ternary alloy in improving catalytic performance and stability.

[0055] Compared with Example 2, the performance of Comparative Example 10 declined significantly. This is because Fe alone cannot effectively activate hydrogen and lacks the synergistic support of Ni and Mo, resulting in low catalytic activity and poor stability. This highlights the synergistic advantages of ternary alloys compared to single metal catalysts.

[0056] Compared with Example 2, Comparative Example 11 had the worst performance. This is because the single Mo catalyst has weak catalytic activity, which cannot meet the requirements of the hydrodechlorination reaction. Moreover, it lacks the synergistic effect of other metals and has an extremely unstable structure. This further highlights the synergistic effect of the Ni-Fe-Mo ternary alloy and the indispensability of each component.

[0057] The above description is only 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 method for preparing the herbicide dichloropyridine acid, characterized in that, Includes the following steps: Step 1: Weigh 3,4,5,6-tetrachloropyridinecarboxylic acid and place it in a high-pressure reactor. Add the mixed solvent and stir until completely dissolved. Then add the Ni-Fe-Mo / NC catalyst, close the reactor, and replace the air in the reactor with H2 3-5 times. Each replacement pressure is 0.5-0.8 MPa. Hold the pressure for 1-2 minutes and then release the air. Step 2: High-purity H2 is introduced into the reactor until the reaction pressure reaches 1.3-1.5 MPa. The mixture is then allowed to stand for 5-10 minutes. The heating device and stirrer are then started, and the temperature is raised to 80-85℃. The stirring rate is 500-600 r / min, and the reaction is allowed to proceed for 4-6 hours. After the reaction is complete, the reactor is cooled to room temperature. The remaining H2 is slowly released, the reactor body is opened, and the Ni-Fe-Mo / NC catalyst and reaction solution are separated by vacuum filtration. The Ni-Fe-Mo / NC catalyst is recovered, and the filtrate is collected and placed in a rotary evaporator. In the concentration process, the concentration temperature is 45-55℃, the vacuum degree is 0.08-0.09MPa, and the solvent is removed by vacuum concentration. A hydrochloric acid solution with a molar concentration of 2-3mol / L is added to the concentrate to adjust the pH to 2.0-2.

5. Then, the solution is placed in an ice-water bath at 0-5℃ and stirred and cooled for 2-4 hours to crystallize. The crystallized product is collected by vacuum filtration, washed 2-3 times with ice water, and the washed product is placed in a vacuum drying oven at 50-60℃ and 0.08-0.09MPa for 8-12 hours to obtain the herbicide dichloropyridine acid.

2. The method for preparing the herbicide dichloropyridine acid according to claim 1, characterized in that, In the first step, the mixed solvent is ethanol and ionic liquid mixed at a volume ratio of 1:(0.05-0.1), and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4).

3. The method for preparing the herbicide dichloropyridine acid according to claim 1, characterized in that, In the first step, the mass of the Ni-Fe-Mo / NC catalyst is 5-10% of the mass of 3,4,5,6-tetrachloropyridinecarboxylic acid.

4. The method for preparing the herbicide dichloropyridine acid according to claim 1, characterized in that, In the second step, the Ni-Fe-Mo / NC catalyst is recovered by washing it with ethanol 2-3 times and then vacuum drying it at 55-60℃ for 8-10 hours, after which it can be recycled.

5. The method for preparing the herbicide dichloropyridine acid according to claim 1, characterized in that, The preparation method of the Ni-Fe-Mo / NC catalyst includes the following steps: A1: Take dried corn cobs, crush them, pass them through a 60-100 mesh sieve, place them in a beaker, add a ZnCl2 solution with a molar concentration of 4-6 mol / L and a nitrogen source, then ultrasonically disperse for 20-40 min, then transfer to a hydrothermal reactor, keep at 160-190℃ for 5-7 h, then cool naturally to room temperature, filter and collect the precursor, dry at 100-125℃ for 10-12 h, then place in a tube furnace, under a nitrogen atmosphere, heat at a rate of 4-6℃ / min, heat to 700-900℃ for 1.5-2.5 h, then cool and soak in a hydrochloric acid solution with a molar concentration of 1-2 mol / L for 2-4 h, stirring at a rate of 300-400 r / min, then wash with deionized water until the pH of the filtrate is 6.5-7.5, and finally vacuum dry at 60-80℃ for 10-14 h to obtain nitrogen-doped porous carbon (NC) support; A2: Weigh Ni(NO3)2・6H2O, Fe(NO3)3・9H2O, (NH4)6Mo7O 24 • Dissolve 4H₂O in deionized water and stir until completely dissolved to obtain a metal salt solution. Then add the NC support and stir magnetically for 40-80 min. Adjust the pH of the system to 9.0-10.0 with a 0.8-1.2 mol / L NaOH solution and stir for 10-20 min. Then add a 0.4-0.6 mol / L NaBH₄ solution dropwise at a rate of 0.6-0.8 mL / min and stir at room temperature for 1.5-2.5 h. Finally, add glucose and sonicate for 15-25 h. The solid was transferred to a hydrothermal reactor and kept at 150-170℃ for 3-5 hours. The solid was collected by vacuum filtration and washed 6-8 times with deionized water. Then, it was placed in a tube furnace in an H2 / Ar mixed atmosphere and reduced at 300-340℃ for 1.5-2.5 hours. After natural cooling to room temperature, it was soaked in a 3-7% (v / v) H2O2 solution for 20-40 minutes with a stirring rate of 200-300 r / min. It was washed with deionized water until neutral and dried under vacuum at 50-70℃ for 8-12 hours to obtain the Ni-Fe-Mo / NC catalyst.

6. The method for preparing the herbicide dichloropyridine acid according to claim 5, characterized in that, In step A1, the nitrogen source is a mixture of melamine and urea in a mass ratio of 1:(1-3).

7. The method for preparing the herbicide dichloropyridine acid according to claim 5, characterized in that, In step A2, the H2 / Ar mixed atmosphere is formed by mixing H2 and Ar in a volume ratio of 1:(4-9).

8. The method for preparing the herbicide dichloropyridine acid according to claim 5, characterized in that, In step A2, the molar ratio of Ni, Fe, and Mo metal ions in the metal salt solution is 1:(0.2-0.6):0.

1.

9. The method for preparing the herbicide dichloropyridine acid according to claim 5, characterized in that, In step A2, the mass of the NC carrier is 0.8-1.2% of the mass of the metal salt solution; the mass of the glucose is 20-30% of the mass of the NC carrier.

10. The method for preparing the herbicide dichloropyridine acid according to claim 5, characterized in that, In step A2, the number of moles of the NaBH4 solution is 12-16 times the total number of moles of Ni, Fe, and Mo metal ions in the metal salt solution.

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