Metal supported activated carbon catalyst for preparing aquacide dichloride

Abstract

The invention discloses a metal supported activated carbon catalyst for efficiently preparing aquacide dichloride and application of the metal supported activated carbon catalyst. The catalyst is prepared by taking activated carbon as a carrier, loading Lewis acid active components such as aluminum ions, zinc ions, iron ions, copper ions and the like through an impregnation method, and carrying out vacuum pyrolysis activation treatment at 300-600 DEG C. The catalyst synergistically catalyzes a nucleophilic substitution reaction of a pyridine derivative and alkyl halide in an aprotic polar solvent such as acetonitrile or nitrobenzene, and synthesis of diquat dichloride can be realized under the conditions that the temperature is 100-180 DEG C and the pressure is 1-3 MPa. In a reaction system, the mass ratio of the pyridine derivative to the catalyst to the solvent is 1: (0.01-0.05): (5-8), and real-time monitoring and regulation are performed through an online infrared spectrum, a liquid chromatograph and a gas chromatograph-mass spectrometer. The purity of the product is more than 99% after the product is subjected to filtration, recrystallization with an ethanol-water mixed solvent and vacuum drying. The catalyst provided by the invention has the characteristics of high activity, strong stability and recoverability, obviously improves the atom economy of the reaction, simplifies the production process, reduces the energy consumption and pollution, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention focuses on the field of organocatalytic synthesis, specifically a metal-loaded activated carbon catalyst for the preparation of diquat dichloride. This catalyst has high activity, high selectivity and good stability, and can significantly improve the synthesis yield and quality of diquat dichloride. At the same time, the present invention also provides a preparation method and application of this catalyst, providing new technologies for the development of related industries. Background Art

[0002] As an important member of the pyridine herbicide family, diquat dichloride has shown extremely extensive and important application value in the current agricultural field. Since its advent, it has been widely used in global agricultural production due to its unique advantages. Its herbicidal mechanism is mainly to be rapidly absorbed by the green tissues of plants, interfere with the photosynthetic electron transport chain, generate reactive oxygen free radicals in plants, and then damage the cell membrane structure, resulting in damage to weed cells, water loss and withering. The time from application to obvious poisoning symptoms in weeds is short, usually effective within a few hours. In agricultural production practice, the application scenarios of diquat dichloride are rich. In the no-till planting system, it can quickly kill surface weeds, create favorable conditions for sowing, and save labor, material and time costs in the tillage link; in orchards, it can effectively control the growth of inter-row weeds, reduce the competition for nutrients, water and light between weeds and fruit trees, and have little impact on the roots of fruit trees; in non-cultivated land weeding, such as along highways, railways and industrial sites, it can efficiently control various weeds and maintain the cleanliness and safety of the site.

[0003] However, there are a series of problems in the synthesis and application of existing diquat dichloride. In terms of the synthesis process, some traditional methods have cumbersome reaction steps, involving multiple complex chemical reactions, resulting in low production efficiency and increased costs; some processes have harsh reaction conditions, requiring high-temperature and high-pressure environments, which not only have high requirements for equipment, high energy consumption, but also pose safety hazards; moreover, the activity and selectivity of the catalyst in the synthesis process are poor, resulting in low product purity, many by-products, and difficult subsequent separation and purification. In the application link, the long-term and frequent use has caused some weeds to develop drug resistance, reducing the weeding effect; the residue problem of the drug in the environment has also gradually attracted attention, and its degradation rate in soil and water bodies and the potential impact on non-target organisms bring uncertainties to the ecological environment.

[0004] In this context, the use of metal-supported activated carbon catalysts for the catalytic synthesis of diquat dichloride is of great significance. Metal-supported activated carbon catalysts have a high specific surface area and adjustable surface properties, enabling effective screening and shape-selective catalysis of reactant molecules, reducing the activation energy of the reaction and allowing the reaction to proceed more precisely toward the formation of diquat dichloride. Furthermore, the supported metal active components can provide abundant active sites, significantly improving the activity and selectivity of the reaction. Therefore, the development of metal-supported activated carbon catalysts for the synthesis of diquat dichloride has become a key issue that needs to be urgently addressed in the industry. Summary of the Invention

[0005] This invention aims to provide a catalyst preparation technology for the gentle and efficient direct conversion of raw materials into diquat dichloride. This innovative method reduces the high energy consumption required for the reaction and increases the reaction rate, significantly lowering production costs, effectively improving atom economy, and significantly reducing environmental pollution. It provides a new, efficient and economical solution for the large-scale industrial production of diquat dichloride.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] Activated carbon pretreatment: Activated carbon is used as a carrier. Place the activated carbon in deionized water and clean it with an ultrasonic cleaner for 15 to 30 minutes to remove surface dust, impurities, and some soluble matter. Next, filter it with a Büchner funnel and repeatedly rinse it with deionized water until the filtrate is clear. The cleaned activated carbon is then placed in an oven and dried at 80 to 120°C for 2 to 6 hours to remove moisture.

[0008] Activated carbon activation: Mix the dried activated carbon with concentrated nitric acid in a mass ratio of 1:(3-5) and reflux in a water bath at 80-90°C for 2-6 hours. Afterwards, cool to room temperature, wash with plenty of deionized water until neutral, and dry again for later use to enhance the adsorption properties and surface activity of the activated carbon.

[0009] Preparation of metal salt solution: Dissolve accurately weighed metal salts (zinc chloride, ferric chloride, aluminum chloride, copper nitrate) in an appropriate amount of deionized water to prepare a solution of a certain concentration. To promote dissolution, stir or heat appropriately, but do not heat too high to prevent hydrolysis of the metal salts.

[0010] Metal loading: The metal precursor solution is loaded on the pretreated support by the equal volume impregnation method. The metal precursor is one or more of zinc chloride, ferric chloride, aluminum chloride, and copper nitrate, and the metal loading amount is 0.1-10.0% of the support mass. After impregnation, the loaded activated carbon is repeatedly washed with deionized water until no metal ions are detected in the washing liquid to remove unloaded metal salt impurities.

[0011] Catalyst activation: The washed activated carbon is dried at a low temperature of 60 - 80°C for 6 - 8 hours to avoid metal ion agglomeration or destruction of the activated carbon structure caused by high temperature. To further enhance the binding force between metal ions and activated carbon and change the existence form of metal ions (convert metal salts into metal oxides), the dried sample can be calcined in a muffle furnace. In an air atmosphere, it is heated to 250 - 550°C at a certain heating rate (2 - 5°C / min) and maintained for 2 - 4 hours, and then naturally cooled to room temperature to obtain the catalyst with metal ions supported on activated carbon.

[0012] Reaction system construction: Select pyridine derivatives with a purity of over 99% as the starting material. Under the protection of an inert gas, it is dried at 60 - 100°C for 2 - 3 hours. The pretreated pyridine derivatives, catalyst, and aprotic polar solvents such as acetonitrile and nitrobenzene are added to a specially designed reaction kettle. The material of the reaction kettle is a high-temperature and corrosion-resistant alloy material, equipped with an accurate temperature and pressure control system; the temperature of the reaction system is controlled at 100 - 180°C, the pressure is maintained at 1 - 3 MPa, and the mass ratio of pyridine derivatives, catalyst, and solvent is 1:0.01 - 0.05:5 - 8.

[0013] Product separation and purification: After the reaction is completed, the reaction solution is cooled to room temperature, and the mother liquor solvent is removed by pressure filtration. The mother liquor solvent is recycled after rectification treatment; the remaining solid crude product is purified by recrystallization. The recrystallization solvent is an ethanol - water mixed solvent with a volume ratio of 3:1 - 4:1. The crude product is dissolved under heating and stirring conditions, and then the recovered activated carbon catalyst is obtained by filtration. The product solution is slowly cooled to 0 - 5°C to precipitate diquat dichloride crystals. After filtration, washing with cold recrystallization solvent 2 - 3 times, and drying in a vacuum drying oven at 50 - 80°C for 3 - 6 hours, the diquat dichloride product is obtained; after the reaction is completed, the catalyst is recovered and activated for reuse. Specific implementation method

[0014] Example 1

[0015] Catalyst preparation: Weigh 20 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 100°C for 13 hours, and finally calcine it at 400°C for 3 hours in a nitrogen atmosphere. Preparation of metal salt solution: Weigh 0.5 g of zinc chloride and dissolve it in 50 mL of deionized water to prepare a zinc chloride solution with a concentration of 0.05 mol / L. Add the pretreated activated carbon to the zinc chloride solution, stir at room temperature for 10 hours, and then filter under reduced pressure to obtain activated carbon loaded with zinc ions. The activated carbon loaded with zinc ions is dried at 70°C for 8 hours, and then calcined at 300°C for 3 hours in an air atmosphere to obtain a zinc - loaded activated carbon catalyst with a zinc loading of 1%.

[0016] Raw material preparation: Weigh 100 g of pyridine derivative with a purity of 99.5%, and dry it at 70 °C for 2.5 hours under nitrogen protection. Select a metal ion-loaded catalyst based on activated carbon prepared with activated carbon and ZnCl2 as precursors, weigh 5 g, and prepare 500 g of acetonitrile as the solvent.

[0017] Reaction process: Add the dried pyridine derivative, the catalyst after activation and pyrolysis, and the acetonitrile solvent into the reaction kettle. Seal the reaction kettle, turn on the stirring device, and adjust the stirring speed to 400 r / min. Raise the temperature in the reaction kettle to 160 °C through the heating device, and at the same time maintain the pressure at 2 MPa through the pressure control system. Continuously add purified chloroethane with the flow rate controlled at 6 mL / min. During the reaction process, the reaction solution is detected every 2 hours by using an on-line infrared spectrometer and a gas chromatography-mass spectrometry combined instrument.

[0018] Product treatment: After reacting for 6 hours, turn off the heating device and cool the reaction solution to room temperature. Recover the acetonitrile solvent by vacuum distillation. Add the remaining solid crude product into 400 mL of ethanol-water (volume ratio of 3.5:1) mixed solvent, heat and stir until completely dissolved. Then slowly cool to 2 °C to precipitate diquat dichloride. After filtration, wash it 3 times with cold ethanol-water mixed solvent, and dry it in a vacuum drying oven at 60 °C for 3.5 hours to obtain 120 g of diquat dichloride product with a purity of 99.1% and a yield of 54.6%. After the reaction is completed, the catalyst is recovered. After detection, the activity retention rate of the recovered catalyst is 85%, and it can be used continuously for subsequent reactions after being pyrolyzed and activated again.

[0019] Example 2

[0020] Catalyst preparation: Weigh 10 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 110 °C for 11 hours, and finally calcine it at 400 °C for 3 hours under a nitrogen atmosphere. Metal salt solution preparation: Weigh 0.6 g of ferric chloride, dissolve it in 60 mL of deionized water to prepare a ferric chloride solution with a concentration of 0.06 mol / L. Add the pretreated activated carbon into the ferric chloride solution, stir at room temperature for 12 hours, and then filter it under reduced pressure to obtain activated carbon loaded with iron ions. Dry the activated carbon loaded with iron ions at 70 °C for 8 hours, and then calcine it at 350 °C for 3 hours under an air atmosphere to obtain an iron-loaded activated carbon catalyst with an iron loading of 2%.

[0021] Raw material preparation: Take 100 g of pyridine derivative with a purity of 99.8%, and dry it at 65 °C for 2 hours under argon protection. Weigh 4 g of a metal ion-loaded catalyst based on activated carbon derivative prepared with activated carbon and FeCl3, and this catalyst is obtained by loading iron ions in the pores of activated carbon. Prepare 600 g of nitrobenzene as the solvent.

[0022] Reaction process: Add the pyridine derivative, catalyst and solvent into the reaction kettle, start stirring, and set the speed to 350 r / min. Heat up to 150 °C, control the pressure at 1.8 MPa, add chloroethane, and the flow rate is 5.5 mL / min. Use an analytical instrument to monitor the reaction process in real time.

[0023] Product treatment: After reacting for 10 hours, cool, distill, recrystallize, wash and dry according to the method of Example 1. Obtain 128.0 g of diquat dichloride product, with a purity of 99.0% and a yield of 58.2%. The activity retention rate of the recovered catalyst is 81%, and it can be reused after activation.

[0024] Example 3

[0025] Catalyst preparation: Weigh 15 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 120 °C for 12 hours, and finally calcine it at 400 °C for 3 hours under a nitrogen atmosphere. Preparation of metal salt solution: Weigh 1.0 g of aluminum chloride, dissolve it in 80 mL of deionized water to prepare an aluminum chloride solution with a concentration of 0.09 mol / L. Add the pretreated activated carbon into the aluminum chloride solution, stir at room temperature for 12 hours, then filter under reduced pressure to obtain activated carbon loaded with aluminum ions. Dry the activated carbon loaded with aluminum ions at 70 °C for 8 hours, and then calcine it at 350 °C for 3 hours under an air atmosphere to obtain an iron-loaded activated carbon catalyst with an aluminum loading of 1.3%.

[0026] Raw material preparation: Weigh 100 g of pyridine derivative with a purity of 99.6%, and dry it at 75 °C for 3 hours under nitrogen protection. Select a metal ion-loaded catalyst based on activated carbon prepared with activated carbon and AlCl3 as precursors. This catalyst is prepared by loading aluminum ions in the pore channels of activated carbon. Weigh 3.5 g and prepare 400 g of acetonitrile as the solvent.

[0027] Reaction process: Add the raw materials into the reaction kettle, adjust the stirring speed to 450 r / min, heat up to 140 °C, maintain the pressure at 2.2 MPa, introduce chlorine gas, and the flow rate is 7 L / min, and monitor the reaction in real time.

[0028] Product treatment: After reacting for 3.5 hours, carry out subsequent treatment according to Example 1. Obtain 103 g of diquat dichloride product, with a purity of 98.5% and a yield of 7O.8%. After the recovered catalyst is detected, the activity retention rate is 87% and it can be put into use again.

[0029] Example 4

[0030] Catalyst preparation: Weigh 20g of activated carbon, wash it with deionized water 4 times, then dry it in an oven at 120℃ for 12 hours, and finally calcine it at 400℃ for 3 hours under a nitrogen atmosphere. Preparation of metal salt solution: Weigh 2.0g of copper nitrate, dissolve it in 100mL of deionized water to prepare a copper nitrate solution with a concentration of 0.10mol / L. Add the pretreated activated carbon to the copper nitrate solution, stir it at room temperature for 12 hours, and then filter it under reduced pressure to obtain activated carbon loaded with copper ions. The activated carbon loaded with copper ions was dried at 70℃ for 8 hours, and then calcined at 350℃ for 3 hours in an air atmosphere to obtain a copper-loaded activated carbon catalyst with a copper loading of 3.4%.

[0031] Raw material preparation: Weigh 100g of 99.6% pure pyridine derivative and dry it at 75℃ under nitrogen protection for 3 hours. Select activated carbon-based metal ion supported catalyst prepared with activated carbon and Cu(NO3)2 as precursors. The catalyst is prepared by loading copper ions in the activated carbon mesh. Weigh 4.0g and prepare 400g of acetonitrile as solvent.

[0032] Reaction process: The dried pyridine derivative, activated catalyst, and acetonitrile solvent are added to the reactor in sequence. The reactor is closed and sealed, and the stirring device is turned on and the stirring speed is set to 300r / min. The reactor is heated using an electric heating jacket, and the temperature inside the reactor is raised to 150°C at a heating rate of 2°C / min. At the same time, the pressure inside the reactor is maintained at 1.2MPa with the help of a pressure pump. Chloroethane that has undergone purification processes such as dehydration and drying is continuously introduced through a mass flow meter at a flow rate of 5mL / min. During the reaction, the reaction liquid is analyzed for composition every hour using an online infrared spectrometer and a gas chromatography-mass spectrometer.

[0033] Product Processing: After 4 hours of reaction, the heating device was turned off and the reaction mixture was allowed to cool naturally to room temperature in the reactor. The remaining crude solid product was transferred to a three-necked flask containing 500 mL of a 3:1 ethanol-water mixture. A stirrer and reflux condenser were installed, and the filtrate was heated and stirred in an 80°C oil bath until the crude product was completely dissolved. The flask was then slowly cooled in a 0°C ice bath to induce crystallization of diquat dichloride. The product was filtered through a Buchner funnel, and the filter cake was washed three times with a cold ethanol-water mixture. The filter cake was then dried in a vacuum oven at 50°C for 4 hours. This yielded 141 g of diquat dichloride, with a purity of 98.7% and a yield of 64.2% as determined by HPLC. After the reaction, the catalyst was recovered, showing an activity retention of 84%. It can be used in subsequent reactions after reactivation.

[0034] Example 5

[0035] Catalyst Preparation: Weigh 20 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 100 °C for 13 hours, and finally calcine it in a nitrogen atmosphere at 400 °C for 3 hours. Preparation of Metal Salt Solution: Weigh 1.0 g of zinc chloride, dissolve it in 50 mL of deionized water to prepare a zinc chloride solution with a concentration of 0.10 mol / L. Add the pretreated activated carbon to the zinc chloride solution, stir at room temperature for 10 hours, and then perform vacuum filtration to obtain activated carbon loaded with zinc ions. Dry the activated carbon loaded with zinc ions at 70 °C for 8 hours, and then calcine it in an air atmosphere at 300 °C for 3 hours to obtain a zinc-loaded activated carbon catalyst with a zinc loading of 2%.

[0036] Raw Material Preparation: Weigh 100 g of pyridine derivative with a purity of 99.5%, and dry it at 70 °C for 2.5 hours under nitrogen protection. Select an activated-carbon-based metal-ion-loaded catalyst prepared using activated carbon and ZnCl2 as precursors, weigh 3 g, and prepare 500 g of nitrobenzene as a solvent.

[0037] Reaction Process: Add the pyridine derivative, catalyst, and solvent into the reaction kettle together, start the stirring device, and adjust the stirring speed to 500 r / min. Using induction heating, raise the temperature in the reaction kettle to 150 °C at a heating rate of 3 °C / min, and stabilize the pressure at 1.5 MPa through the pressure control system. Continuously introduce purified chlorine gas into the reaction kettle at a flow rate of 8 L / min through a mass flowmeter. During the entire reaction process, use an automated on-line analysis system to monitor the temperature, pressure, and concentration changes of reactants and products in the reaction system in real time.

[0038] Product Treatment: After the reaction has lasted for 10 hours, turn off the heating system and let the reaction solution cool to room temperature. Use a vacuum distillation device to recover nitrobenzene under a vacuum degree of 0.09 MPa. Transfer the remaining solid crude product to a crystallizer, add 800 mL of ethanol-water (volume ratio 4:1) mixed solvent, and completely dissolve the crude product under the action of heating with a heating jacket and stirring with a stirring paddle. Subsequently, use a programmed cooling system to slowly lower the temperature in the crystallizer to 5 °C at a cooling rate of 0.5 °C / min to promote the crystallization of diquat dichloride. Use centrifugal separation to separate the crystallized product from the mother liquor, and perform 3 centrifugal washes of the product with cold ethanol-water mixed solvent. Finally, place the product in a vacuum drying oven at 60 °C and dry it for 3 hours to obtain 136 g of diquat dichloride product. After testing, the purity is 99.3% and the yield is 62.4%. The activity retention rate of the recovered catalyst is 86%, and it can be reused after activation.

[0039] Example 6

[0040] Catalyst Preparation: Weigh 20 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 110 °C for 11 hours, and finally calcine it at 400 °C for 3 hours under a nitrogen atmosphere. Preparation of Metal Salt Solution: Weigh 1.8 g of ferric chloride, dissolve it in 60 mL of deionized water to prepare a ferric chloride solution with a concentration of 0.10 mol / L. Add the pretreated activated carbon to the ferric chloride solution, stir at room temperature for 12 hours, then filter under reduced pressure to obtain activated carbon loaded with iron ions. Dry the activated carbon loaded with iron ions at 70 °C for 8 hours, and then calcine it at 350 °C for 3 hours under an air atmosphere to obtain an iron-loaded activated carbon catalyst with an iron loading of 3%.

[0041] Raw Material Preparation: Take 150 g of pyridine derivative with a purity of 99.8%, and dry it at 65 °C for 2 hours under argon protection. Weigh 4 g of a metal ion-loaded catalyst based on activated carbon-derived prepared with activated carbon and FeCl3 as precursors, which is prepared by loading iron ions into the pores of activated carbon. Prepare 600 g of nitrobenzene as a solvent.

[0042] Reaction Process: Add the raw materials to the reaction kettle, start stirring, and set the speed to 420 r / min. Through the heat transfer oil heating system, raise the temperature in the reaction kettle to 190 °C at a heating rate of 2.5 °C / min, and control the pressure at 2 MPa. Continuously introduce purified chloroethane with a stable flow rate of 6.5 mL / min, and at the same time use on-line monitoring equipment to track the reaction process in real time.

[0043] Product Treatment: After reacting for 12 hours, cool the reaction solution to room temperature. Perform operations such as distillation under reduced pressure, recrystallization, washing, and drying according to the method of Example 2. Finally, obtain 181.3 g of diquat dichloride product. After testing, the purity is 98.4% and the yield is 54.9%. After the catalyst is recovered and tested, the activity retention rate is 88% and it can be reused again.

[0044] Example 7

[0045] Catalyst Preparation: Weigh 15 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 120 °C for 12 hours, and finally calcine it at 400 °C for 3 hours under a nitrogen atmosphere. Preparation of Metal Salt Solution: Weigh 2.0 g of aluminum chloride, dissolve it in 80 mL of deionized water to prepare an aluminum chloride solution with a concentration of 0.19 mol / L. Add the pretreated activated carbon to the aluminum chloride solution, stir at room temperature for 12 hours, then filter under reduced pressure to obtain activated carbon loaded with aluminum ions. Dry the activated carbon loaded with aluminum ions at 70 °C for 8 hours, and then calcine it at 350 °C for 3 hours under an air atmosphere to obtain an aluminum-loaded activated carbon catalyst with an aluminum loading of 2.7%.

[0046] Raw material preparation: Weigh 100 g of pyridine derivative with a purity of 99.6%, and dry it at 75 °C for 3 hours under nitrogen protection. Select a metal ion-loaded catalyst based on activated carbon prepared using activated carbon and AlCl3 as precursors. This catalyst is prepared by loading aluminum ions into the pores of activated carbon. Weigh 3.5 g and prepare 400 g of acetonitrile as the solvent.

[0047] Reaction process: Add the dried pyridine derivative, the catalyst after activation and pyrolysis, and the acetonitrile solvent into the reaction kettle. Seal the reaction kettle, turn on the stirring device, and adjust the stirring speed to 400 r / min. Raise the temperature in the reaction kettle to 160 °C through the heating device, and at the same time maintain the pressure at 2 MPa through the pressure control system. Continuously add purified chloroethane with a flow rate controlled at 6 mL / min. During the reaction process, detect the reaction solution every 2 hours using an on-line infrared spectrometer and a gas chromatography-mass spectrometry combined instrument.

[0048] Product treatment: After reacting for 6 hours, turn off the heating device and cool the reaction solution to room temperature. Recover the acetonitrile solvent by vacuum distillation. Add the remaining solid crude product into 300 mL of ethanol-water (volume ratio 3.5:1) mixed solvent, heat and stir until completely dissolved. Then slowly cool to 2 °C to precipitate diquat dichloride crystals. After filtration, wash with cold ethanol-water mixed solvent 3 times, and dry in a vacuum drying oven at 55 °C for 3.5 hours to obtain 132.4 g of diquat dichloride product with a purity of 99.4% and a yield of 60.0%. After the reaction is completed, recover the catalyst. After detection, the activity retention rate of the recovered catalyst is 85%, and it can be reused for subsequent reactions after being pyrolyzed and activated again.

[0049] Example 8

[0050] Catalyst preparation: Weigh 20 g of activated carbon, wash it 4 times with deionized water, then dry it in an oven at 120 °C for 12 hours, and finally calcine it at 400 °C for 3 hours under a nitrogen atmosphere. Metal salt solution preparation: Weigh 2.0 g of copper nitrate, dissolve it in 100 mL of deionized water to prepare a copper nitrate solution with a concentration of 0.10 mol / L. Add the pretreated activated carbon into the copper nitrate solution, stir at room temperature for 12 hours, then filter under reduced pressure to obtain activated carbon loaded with zinc ions. Dry the activated carbon loaded with copper ions at 70 °C for 8 hours, and then calcine it at 350 °C for 3 hours under an air atmosphere to obtain a copper-loaded activated carbon catalyst with a copper loading of 3.4%.

[0051] Raw material preparation: Weigh 100 g of pyridine derivative with a purity of 99.6%, and under nitrogen protection, dry it at 75 °C for 3 hours. Select a metal ion-loaded catalyst based on activated carbon prepared using activated carbon and Cu(NO3)2 as precursors. This catalyst is prepared by loading copper ions into the pore channels of activated carbon. Weigh 4.0 g and prepare 400 g of acetonitrile as the solvent.

[0052] Reaction process: Add the pyridine derivative, catalyst, and solvent into the reaction kettle together, start the stirring device, and adjust the stirring speed to 500 r / min. Using induction heating, raise the temperature in the reaction kettle to 140 °C at a heating rate of 3 °C / min, and stabilize the pressure at 1.4 MPa through the pressure control system. Through the mass flowmeter, continuously introduce purified chlorine gas into the reaction kettle at a flow rate of 8 L / min. During the entire reaction process, use an automated on-line analysis system to monitor the temperature, pressure, and concentration changes of reactants and products in the reaction system in real time.

[0053] Product treatment: After the reaction has lasted for 12 hours, turn off the heating system and let the reaction solution cool to room temperature. Use a vacuum distillation device to recover nitrobenzene under a vacuum of 0.09 MPa. Transfer the remaining solid crude product to the crystallizer, add 800 mL of ethanol-water (volume ratio 4:1) mixed solvent, and under the action of heating with a heating jacket and stirring with a stirring paddle, completely dissolve the crude product. Subsequently, through the program cooling system, slowly lower the temperature in the crystallizer to 5 °C at a cooling rate of 0.5 °C / min to promote the crystallization of diquat dichloride. Use centrifugal separation to separate the crystallized product from the mother liquor, and wash the product 3 times by centrifugation with cold ethanol-water mixed solvent. Finally, place the product in a vacuum drying oven at 60 °C and dry it for 3 hours to obtain 131 g of diquat dichloride product. After testing, the purity is 99.3% and the yield is 60.1%. The activity retention rate of the recovered catalyst is 86%, and it can be reused after activation.

[0054] From different examples, it can be seen that the present invention can prepare qualified products under various parameter conditions by using a metal-loaded catalyst derived from activated carbon, with strong stability and operability. In actual production, the raw material selection and process parameters for catalyst preparation can be flexibly adjusted according to the characteristics of raw materials and product requirements to obtain the best catalytic performance and economic benefits.

Claims

1. A metal-loaded activated carbon catalyst for preparing diquat dichloride, characterized in that, It includes the following steps: Activated carbon pretreatment: Select activated carbon as the carrier. Place the activated carbon in deionized water and clean it with an ultrasonic cleaner for 15 - 30 minutes to remove surface dust, impurities and some soluble substances. Then, perform suction filtration with a Buchner funnel and repeatedly rinse with deionized water until the filtrate is clear. Subsequently, put the washed activated carbon into an oven and dry it at 105 - 120 °C for 4 - 6 hours to remove moisture. Activated carbon activation: Mix the dried activated carbon with concentrated nitric acid at a mass ratio of 1:(3 - 5), and reflux and stir in a water bath at 80 - 90 °C for 2 - 3 hours. After that, cool to room temperature, wash with a large amount of deionized water until neutral, and dry again for standby to enhance the adsorption performance and surface activity of the activated carbon. Metal salt solution preparation: Dissolve the accurately weighed metal salts (zinc chloride, iron chloride, aluminum chloride, copper nitrate) in an appropriate amount of deionized water to prepare a solution with a certain concentration. To promote dissolution, appropriate stirring or heating can be carried out, but the temperature should not be too high to prevent hydrolysis of metal salts. Metal loading: Use the equal-volume impregnation method to load the metal precursor solution onto the pretreated carrier. The metal precursors are one or more of zinc chloride, iron chloride, aluminum chloride, and copper nitrate, and the metal loading is 1 - 10% of the mass of the carrier; after impregnation, repeatedly wash the loaded activated carbon with deionized water until no metal ions can be detected in the washing solution to remove unloaded metal salt impurities. Catalyst activation: Low-temperature dry the washed activated carbon at 60 - 80 °C for 6 - 8 hours to avoid high temperature causing metal ion agglomeration or destruction of the activated carbon structure. To further enhance the binding force between metal ions and activated carbon and change the existence form of metal ions (convert metal salts into metal oxides), the dried sample can be calcined in a muffle furnace. In an air atmosphere, raise the temperature to 300 - 600 °C at a certain heating rate (such as 2 - 5 °C / min) and maintain for 2 - 4 hours, and then naturally cool to room temperature to obtain a catalyst with metal ions loaded on activated carbon. Reaction system construction: Select a pyridine derivative with a purity of over 99% as the starting material, dry it at 60 °C - 100 °C for 2 - 3 hours under inert gas protection. Add the pretreated pyridine derivative, catalyst, and aprotic polar solvents such as acetonitrile and nitrobenzene into a specially designed reaction kettle. The material of the reaction kettle is a high-temperature and corrosion-resistant alloy material with precise temperature and pressure control systems; control the reaction system temperature at 100 - 180 °C, maintain the pressure at 1 - 3 MPa, and the mass ratio of pyridine derivative, catalyst, and solvent is 1:0.01 - 0.05:5 - 8. Product separation and purification: After the reaction is completed, the reaction solution is cooled to room temperature, and the mother liquor solvent is removed by pressure filtration. The mother liquor solvent is recycled after rectification treatment; the remaining solid crude product is purified by recrystallization. The recrystallization solvent is an ethanol-water mixed solvent with a volume ratio of 3:1 to 4:

1. The crude product is dissolved under heating and stirring conditions, and then the recovered activated carbon catalyst is obtained by filtration. The product solution is slowly cooled to 0-5 °C to precipitate diquat dichloride crystals. After filtration, washing with cold recrystallization solvent 2-3 times, and drying in a vacuum drying oven at 50-80 °C for 3-4 hours, the diquat dichloride product is obtained; after the reaction is completed, the catalyst is recovered and activated to make it reusable.

2. The preparation method according to claim 1, characterized in that, The concentration of the impregnation solution used in the metal loading step is configured according to the effective metal loading amount.

3. A metal-loaded activated carbon catalyst prepared by the method according to claim 1, characterized in that: The catalyst contains active metal nanoparticles (particle size 3 - 8 nm) with a mass fraction of 1 - 10%, and the metal is Zn 2+ , Fe 3+ , Al 3+ , Cu 2+ , or a combination of one or more of them. The surface of the activated carbon carrier is grafted with carboxyl, hydroxyl, and amino functional groups with a density of 0.5 - 1.2 mmol / g, and the specific surface area of the catalyst is 500 - 1500 m 2 / g, and the average pore diameter is 0.8 - 1.2 nm.

4. The catalyst according to claim 3, characterized in that, The metal nanoparticles are uniformly dispersed in the zeolite pores. X-ray photoelectron spectroscopy (XPS) analysis shows that the metal exists in the form of Zn 2+ , Fe 3+ , Al 3+ , Cu 2+ .

5. The catalyst according to claim 4, characterized in that, The catalyst can be regenerated by the following steps: calcining in an air atmosphere at 300-600 °C for 1-3 hours to remove adsorbed organic substances, and then washing with a 0.1 mol / L nitric acid solution to restore the metal active sites. The activity recovery rate of the regenerated catalyst is ≥90%.

6. The catalyst according to claims 3 to 5, characterized in that, The catalyst shows better performance than traditional catalysts in the reaction for preparing quaternary ammonium salts by nucleophilic substitution reaction. In a closed stirred reactor, at a temperature of 100-180 °C and a stirring speed of 300-500 rpm, the reaction is carried out for 6-12 hours in an oxygen-free environment after nitrogen replacement, with a conversion rate of 50%-90%, a yield of 50%-95%, and a purity of ≥95%.