Process and device for the continuous preparation of 2,6-difluorobenzonitrile under mild conditions

Abstract

This invention discloses a process and apparatus for the continuous fluorination preparation of 2,6-dichlorobenzonitrile under mild conditions. The apparatus includes sequentially connected units for 2,6-dichlorobenzonitrile preparation, raw material preparation, online dehydration, continuous metering feeding, continuous reaction, and post-treatment, with a supporting control system for precise parameter control. The process first involves the continuous preparation and purification of 2,6-dichlorobenzonitrile at 70–90℃ and 0.1–0.3 MPa. Then, a raw material solution and a fluorination suspension are prepared and deeply dehydrated. Subsequently, a continuous fluorination reaction is carried out at 80–150℃ and 0.1–1.0 MPa. Finally, the finished product is obtained through post-treatment. This invention achieves continuous production throughout the entire process, with mild reaction conditions, a solvent recovery rate ≥95%, a finished product purity ≥99.8%, high production efficiency, low cost, wide equipment adaptability, and easy industrialization.

Description

Technical Field

[0001] This invention relates to the field of fine chemical intermediate synthesis technology, and in particular to a process and apparatus for the continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions. Background Technology

[0002] 2,6-Difluorobenzonitrile is a core intermediate in the synthesis of fluorinated benzamide urea-based green pesticides such as flufenoxuron and diflubenzuron. It is also widely used in pharmaceutical synthesis and liquid crystal material preparation, showing promising market prospects. Currently, the mainstream preparation method for this product is the halogen exchange method, which involves reacting 2,6-dichlorobenzonitrile with fluoride salts or hydrogen fluoride via a halogen exchange reaction. However, existing processes still have many technical shortcomings, making it difficult to meet the demands of efficient, low-cost, and green industrial production.

[0003] In existing technologies, the methods for preparing 2,6-difluorobenzonitrile disclosed in patents such as CN104788341A and CN101456827A all use 2,6-dichlorobenzonitrile and potassium fluoride as raw materials, and complete the fluorination reaction in an aprotic polar solvent with a quaternary ammonium salt phase transfer catalyst. In this type of process, although the catalyst can reduce the activation energy of the reaction, it has the problems of high toxicity, high cost and difficulty in recovery. This not only increases the cost of raw material procurement and post-processing, but catalyst residue can also easily affect the purity of the product. At the same time, the complicated post-processing process significantly reduces the production efficiency. Some processes use hydrogen fluoride as the fluorinating agent, such as the method disclosed in CN112851539A. Hydrogen fluoride is extremely corrosive, the production process has a high risk factor, and its storage and transportation conditions are harsh, which greatly increases the difficulty of preparation and production input, making it unsuitable for large-scale industrial production.

[0004] In summary, developing a process and apparatus for preparing 2,6-difluorobenzonitrile with mild reaction conditions, continuous operation throughout the entire process, efficient solvent recycling, and stable product quality has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing 2,6-difluorobenzonitrile preparation technologies, this invention provides a continuous, end-to-end process and apparatus for preparing 2,6-difluorobenzonitrile under mild conditions. This invention aims to achieve low-temperature, mild reaction, efficient solvent circulation, and continuous operation throughout the entire process, thereby improving product purity and yield while reducing equipment requirements and production costs, minimizing waste emissions, and adapting to the needs of large-scale industrial production.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The apparatus provided by this invention comprises, in sequence, an interconnected 2,6-dichlorobenzonitrile preparation unit, a raw material preparation unit, an online dehydration unit, a continuous metering feed unit, a continuous reaction unit, and a post-treatment unit. Each unit is connected to a control valve via corrosion-resistant pipes. The apparatus is also equipped with a control system to achieve precise control of various process parameters. The reaction temperature for 2,6-dichlorobenzonitrile preparation is 70–90℃ and the pressure is 0.1–0.3 MPa, while the fluorination reaction temperature is 80–150℃ and the pressure is 0.1–1.0 MPa.

[0008] As a preferred embodiment of the present invention, the 2,6-dichlorobenzonitrile preparation unit includes a continuous reactor and a distillation purification column. The continuous reactor is equipped with a stirring device, a temperature control device, and a catalyst feed port, with a temperature control accuracy of ±1℃. The distillation purification column is a packed column, with a condensation recovery device on one side of the top. After purification by this unit, 2,6-dichlorobenzonitrile with a purity ≥99.5% can be obtained. The volume of the continuous reactor is 500–5000L, and the stirring speed of the stirring device is 60–120 r / min. The theoretical number of plates in the distillation purification column is 15–30, and the reflux ratio is 1:1–3:1.

[0009] As a preferred embodiment of the present invention, the raw material preparation unit includes a raw material liquid preparation tank and a fluorinated suspension preparation tank. The raw material liquid preparation tank is connected to a distillation purification tower. The fluorinated suspension preparation tank is used to prepare a fluorinated suspension of anhydrous potassium fluoride and a phase transfer catalyst. The raw material liquid preparation tank is equipped with a first constant temperature jacket and a first stirrer. The fluorinated suspension preparation tank is equipped with a second constant temperature jacket and a second stirrer. The first and second constant temperature jackets maintain a constant temperature environment of 25–60°C. The stirring speed of the first and second stirrers is 40–80 r / min.

[0010] As a preferred embodiment of the present invention, the online dehydration unit is a dehydration vessel connected to the fluorinated suspension preparation tank. The dehydration vessel is equipped with a vacuum system and a condensation recovery system, and the dehydration pressure is -0.06 to -0.095 MPa, thereby achieving deep dehydration of the fluorinated suspension.

[0011] As a preferred technical solution of the present invention, the continuous metering feeding unit includes a first metering pump and a second metering pump, which are respectively connected to the raw material liquid preparation tank and the dehydration kettle, so as to realize the accurate metering and proportional synchronous feeding of the raw material liquid and the dehydrated fluorinated suspension.

[0012] As a preferred embodiment of the present invention, the post-processing unit includes a cooler, a phase separator, a desolventizing column, and a distillation column connected in sequence; the desolventizing column is a vacuum desolventizing column with an operating pressure of -0.08 to -0.095 MPa and an operating temperature of 80–120°C; the distillation column is a precision distillation column with 20–40 theoretical plates and a reflux ratio of 2:1–4:1.

[0013] As a preferred technical solution of the present invention, the control system is electrically connected to the temperature control device, the first metering pump, the second metering pump, the control valve, and the temperature sensor of each unit, so as to realize real-time monitoring and precise control of each key process parameter.

[0014] The present invention also provides a process for the continuous preparation of 2,6-difluorobenzonitrile using the above-described apparatus, the process comprising the following steps: Continuous preparation and purification of 2,6-dichlorobenzonitrile: o-Dichlorobenzene, a cyaniding agent, and a catalyst were added to a continuous reactor and reacted under nitrogen protection at 70–90℃ and 0.1–0.3 MPa for 3–5 h, with a nitrogen flow rate of 0.5–1.5 L / min. The cyaniding agent was either cuprous cyanide or potassium cyanide, with a molar ratio of o-dichlorobenzene to cyaniding agent of 1:(1.05–1.15). The catalyst was either palladium chloride or nickel chloride, and its addition amount was 0.8%–1.5% of the mass of o-dichlorobenzene. The reaction product was purified by distillation to obtain 2,6-dichlorobenzonitrile with a purity ≥99.7%.

[0015] Material preparation and online deep dehydration: The purified 2,6-dichlorobenzonitrile is prepared into a raw material solution with an aprotic polar solvent selected from one or more of sulfolane and γ-butyrolactone; anhydrous potassium fluoride is prepared into a fluorinated suspension with a phase transfer catalyst selected from one of quaternary ammonium salt, quaternary phosphonium salt, and crown ether, with an addition amount of 0.1%–5% of the mass of 2,6-dichlorobenzonitrile, and a molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride of 1:(2.0–3.0); the fluorinated suspension is fed into a dehydration reactor and dehydrated online under a negative pressure of -0.06 to -0.095 MPa.

[0016] The continuous fluorination reaction involves feeding the raw material liquid and the dehydrated fluorinated suspension into a continuous reactor simultaneously via a first metering pump and a second metering pump. The reaction is carried out continuously for 10–120 minutes at 80–150℃ and 0.1–1.0MPa to complete the halogen exchange fluorination reaction.

[0017] The effluent from the continuous post-treatment and solvent recycling reaction is cooled by a cooler and separated by a phase separator, and then sent to a vacuum desolventizing tower to remove the solvent. The removed solvent is condensed and recovered and recycled for the preparation of the raw material solution, with a solvent recovery rate of ≥95%. The product after desolventizing is sent to a precision distillation tower for purification to obtain 2,6-difluorobenzonitrile product with a purity of ≥99.8%.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention controls the fluorination reaction temperature at 80–150℃, which is far lower than the high temperature requirement of 190–230℃ for existing catalyst-free processes. This avoids the problems of increased product impurities and decreased purity caused by high temperatures, and also significantly reduces the requirements for the high temperature and high pressure resistance of the reaction equipment, thereby reducing the procurement and maintenance costs of the equipment. The fluorination reaction pressure is in the range of atmospheric pressure to low pressure, which is 0.1–1.0 MPa. The production process is easy to operate and the safety is significantly improved. 2. This invention, through the series connection design of each functional unit and the precise control of metering pumps and continuous reactors, realizes a continuous operation of the entire process from the preparation of 2,6-dichlorobenzonitrile to the purification of 2,6-difluorobenzonitrile, replacing the intermittent batch operation of the existing process; the residence time of the material in the continuous reactor can be flexibly adjusted to 10–120 min, the reaction efficiency is significantly improved, and it can meet the capacity requirements of large-scale industrial production. 3. The depressurization stripping tower of the post-processing unit of the present invention can achieve efficient condensation and recovery of solvent with a recovery rate of ≥95%. The recovered solvent can be directly recycled for the preparation of raw material liquid, which solves the problems of poor solvent reuse stability and significant yield drop after multiple reuses in the existing catalyst-free process, greatly reduces solvent waste, and further reduces production and environmental protection costs. 4. The control system of this invention is electrically connected to the temperature control device, metering pump, regulating valve and temperature sensor of each unit, which can realize the precise control and real-time monitoring of key process parameters such as reaction temperature, pressure, material feed rate and residence time. It has a high degree of automation, reduces human operation error, facilitates the control and optimization of the production process, improves the stability and controllability of the production process, and reduces labor costs. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is the front view of the present invention; In the diagram: 1. Continuous reaction vessel; 2. Distillation and purification column; 3. Stirring device; 4. Temperature control device; 5. Catalyst feed port; 6. Condensation and recovery device; 7. Raw material liquid preparation tank; 8. Fluorinated suspension preparation tank; 9. Dehydration vessel; 10. Vacuum system; 11. Condensation and recovery system; 12. First metering pump; 13. Second metering pump; 14. Continuous reactor; 15. Heat exchange channel; 16. Temperature sensor; 17. Corrosion-resistant pipe; 18. Control valve; 19. First thermostatic jacket; 20. Second thermostatic jacket; 21. First stirrer; 22. Second stirrer; 23. Control system. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] In the attached diagram, all identical reference numerals refer to the same components.

[0022] The apparatus for the continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions described in this invention is such that each unit is sealed and connected to the control valve 18 via corrosion-resistant pipes 17. The control system 23 is electrically connected to the temperature control device 4, the first metering pump 12, the second metering pump 13, the control valve 18, and the temperature sensor 16 of each unit, realizing real-time monitoring and precise control of the process parameters throughout the entire process. The following describes in detail the structural connection relationship, function, and process implementation of the apparatus with reference to the embodiments.

[0023] Example 1 Device structure connection and functional implementation like Figure 1 , Figure 2 As shown, the 2,6-dichlorobenzonitrile preparation unit consists of a continuous reactor 1 and a distillation purification column 2 connected sequentially. The continuous reactor 1 is equipped with a fixed stirring device 3, a temperature control device 4, and a catalyst feed port 5. The temperature control device 4 can achieve precise temperature control within ±1℃, stably maintaining a reaction temperature of 70-90℃ and a reaction pressure of 0.1-0.3MPa within the reactor. The stirring device 3 can drive uniform mixing of materials within the reactor, improving reaction efficiency. The catalyst feed port 5 allows for quantitative and continuous addition of catalyst. The distillation purification column 2 is a packed column, with its inlet connected to the outlet of the continuous reactor 1 via a corrosion-resistant pipe 17. A condensation recovery device 6 is fixedly installed on one side of the column top, which can purify the reaction products of the continuous reactor 1 through distillation and simultaneously condense and recover light components, ultimately obtaining 2,6-dichlorobenzonitrile with a purity ≥99.5%. The reflux ratio of the distillation purification column is 2:1, and the reflux ratio of the precision distillation column is 3:1.

[0024] The raw material preparation unit includes a raw material liquid preparation tank 7 and a fluorinated suspension preparation tank 8. The feed end of the raw material liquid preparation tank 7 is connected to the discharge end of the distillation and purification tower 2 through a corrosion-resistant pipe 17. It can receive 2,6-dichlorobenzonitrile after distillation and purification, and mix it with an aprotic polar solvent to prepare a homogeneous raw material liquid. The fluorinated suspension preparation tank 8 is used to prepare a fluorinated suspension of anhydrous potassium fluoride and a phase transfer catalyst. The raw material liquid preparation tank 7 is externally fitted with a first thermostatic jacket 19 and internally fitted with a first stirrer 21. The fluorinated suspension preparation tank 8 is externally fitted with a second thermostatic jacket 20 and internally fitted with a second stirrer 22. The first thermostatic jacket 19 and the second thermostatic jacket 20 can stably maintain a constant temperature environment of 25-60°C inside the tank. The first stirrer 21 and the second stirrer 22 can achieve full mixing of the materials inside the tank, ensuring the homogeneity of the raw material liquid and the fluorinated suspension, laying the foundation for subsequent reactions.

[0025] The online dehydration unit is a dehydration kettle 9, whose feed end is connected to the discharge end of the fluorinated suspension preparation tank 8 through a corrosion-resistant pipe 17. A vacuum system 10 and a condensation recovery system 11 are fixedly installed on the dehydration kettle 9. The vacuum system 10 can create a negative pressure environment of -0.06 to -0.095 MPa inside the dehydration kettle 9, so as to achieve deep dehydration of the fluorinated suspension. The removed water is condensed and collected by the condensation recovery system 11, which effectively reduces the water content of the fluorinated suspension and improves the conversion rate of the subsequent fluorination reaction.

[0026] The continuous metering feeding unit includes a first metering pump 12 and a second metering pump 13. The feed end of the first metering pump 12 is connected to the discharge end of the raw material liquid preparation tank 7 and the feed end of the continuous reaction unit. The feed end of the second metering pump 13 is connected to the discharge end of the dehydration kettle 9 and the feed end of the continuous reaction unit. The two metering pumps can precisely control the material conveying rate according to the process requirements to realize the synchronous and continuous feeding of the raw material liquid and the dehydrated fluorinated suspension in proportion, ensuring the stability of the reaction material ratio.

[0027] The continuous reaction unit is a temperature-controlled continuous reactor 14, which is a tubular reactor. Its feed end is connected to the discharge ends of the first metering pump 12 and the second metering pump 13. A heat exchange channel 15 and a temperature sensor 16 are fixedly installed inside the reactor. The temperature control accuracy can reach ±1℃. The heat exchange channel 15 can achieve temperature regulation of the reaction system through the heat exchange medium. The temperature sensor 16 can collect the reaction temperature in the reactor in real time and transmit it to the control system 23. The control system 23 completes the real-time temperature adjustment. The continuous reactor 14 can stably regulate the reaction temperature of 80-150℃ and the reaction pressure of 0.1-1.0MPa to realize the continuous fluorination reaction of materials. The residence time of materials in the reactor can be flexibly adjusted within the range of 10-120min.

[0028] The post-processing unit consists of a cooler, a phase separator, a solvent removal tower, and a distillation tower connected sequentially via corrosion-resistant pipe 17. The feed end of the cooler is connected to the discharge end of the continuous reactor 14, which can rapidly cool the reaction effluent and reduce the viscosity of the material. The phase separator receives the discharge from the cooler and can achieve efficient solid-liquid separation of the cooled material. The solvent removal tower is a vacuum solvent removal tower, which can remove aprotic polar solvents from the material at an operating pressure of -0.08 to -0.095 MPa and an operating temperature of 80-120℃. The removed solvent can be recycled to the raw material preparation tank 7 after condensation and recovery, with a solvent recovery rate of ≥95%. The distillation tower is a precision distillation tower, which can perform high-precision distillation purification on the desolventized material to remove trace impurities and finally obtain high-purity 2,6-difluorobenzonitrile product.

[0029] The control system 23 is the core of the entire device. It is electrically connected to the temperature control device 4, the first metering pump 12, the second metering pump 13, the control valve 18, and the temperature sensor 16 of each unit. It can collect process parameters such as temperature, pressure, and material flow rate of each unit in real time. At the same time, it can accurately control each piece of equipment according to the preset process requirements to achieve automated continuous production throughout the entire process and reduce human operation errors.

[0030] The process implementation is as follows: Continuous preparation and purification of 2,6-dichlorobenzonitrile: o-dichlorobenzene, potassium cyanide, and palladium chloride are added to continuous reaction vessel 1 through their respective feed inlets. The molar ratio of o-dichlorobenzene to potassium cyanide is 1:1.1, and the amount of palladium chloride added is 1.0% of the mass of o-dichlorobenzene. Stirring device 3 is turned on, and the stirring speed is adjusted to 80 r / min. The temperature inside the vessel is controlled at 80℃ and the pressure is controlled at 0.2 MPa by temperature control device 4. At the same time, nitrogen gas is introduced into the vessel for protection at a nitrogen introduction rate of 1.0 L / min. The reaction is carried out continuously for 4 hours. The reaction product is continuously transported to distillation purification tower 2 through corrosion-resistant pipeline 17. After light component recovery by distillation purification and condensation recovery device 6, 2,6-dichlorobenzonitrile with a purity of 99.8% is obtained and continuously transported to raw material liquid preparation tank 7.

[0031] Material preparation and online deep dehydration: Sulfolane is added to the raw material preparation tank 7, and the first stirrer 21 and the first constant temperature jacket 19 are turned on to maintain the temperature inside the tank at 50°C. The raw material is stirred to prepare a homogeneous raw material solution. Anhydrous potassium fluoride and tetrabutylammonium bromide are added to the fluorinated suspension preparation tank 8. The amount of tetrabutylammonium bromide added is 2% of the mass of 2,6-dichlorobenzonitrile, and the molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride is 1:2.5. The second stirrer 22 and the second constant temperature jacket 20 are turned on to maintain the temperature inside the tank at 50°C. The fluorinated suspension is stirred to prepare a homogeneous fluorinated suspension. The fluorinated suspension is continuously transported to the dehydration vessel 9 through the corrosion-resistant pipe 17. The vacuum system 10 is turned on to control the pressure inside the dehydration vessel 9 at -0.08MPa, and the fluorinated suspension is continuously dehydrated online.

[0032] Continuous fluorination reaction: The first metering pump 12 and the second metering pump 13 are turned on to synchronously and continuously transport the raw material liquid in the raw material preparation tank 7 and the dehydrated fluorinated suspension in the dehydration kettle 9 to the continuous reactor 14 in proportion. The reaction temperature of the continuous reactor 14 is adjusted to 120℃, the reaction pressure to 0.5MPa, and the material residence time to 60min by the control system 23 to complete the continuous fluorination reaction.

[0033] Continuous post-treatment and solvent recycling: The reaction effluent from the continuous reactor 14 is continuously fed to a cooler to cool to room temperature, and then enters a phase separator for solid-liquid separation. The separated liquid phase is continuously fed to a vacuum desolventizing tower to remove sulfolane under operating pressure of -0.09 MPa and operating temperature of 100°C. The removed sulfolane is condensed and recovered and then recycled to the feed liquid preparation tank 7 for reuse, with a solvent recovery rate of 97%. The desolventized material is continuously fed to a precision distillation tower, and after distillation and purification, 2,6-difluorobenzonitrile is obtained as a finished product with a purity of 99.9% and a molar yield of 98.2%.

[0034] Example 2 The device structure and function of this embodiment are the same as those of Embodiment 1, with only some process parameters and equipment selections adjusted. The continuous reactor 14 is a microchannel reactor. The specific process implementation is as follows: Continuous preparation and purification of 2,6-dichlorobenzonitrile: o-dichlorobenzene, cuprous cyanide, and nickel chloride were added to continuous reaction vessel 1. The molar ratio of o-dichlorobenzene to cuprous cyanide was 1:1.05, and the amount of nickel chloride added was 0.8% of the mass of o-dichlorobenzene. The stirring speed was 60 r / min, the temperature control device 4 controlled the temperature inside the vessel at 70℃ and the pressure at 0.1 MPa, and the nitrogen gas introduction rate was 0.5 L / min. The reaction was carried out continuously for 3 h. The product was purified by distillation purification column 2 to obtain 2,6-dichlorobenzonitrile with a purity of 99.7%, and then transported to raw material liquid preparation tank 7.

[0035] Material preparation and online deep dehydration: γ-Butyrolactone is added to the raw material preparation tank 7 to prepare the raw material solution, and the temperature inside the tank is maintained at 25°C; anhydrous potassium fluoride and 18-crown-6 are added to the fluorinated suspension preparation tank 8, with the amount of 18-crown-6 added being 0.5% of the mass of 2,6-dichlorobenzonitrile, and the molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride being 1:2.0. The temperature inside the tank is maintained at 25°C. After the fluorinated suspension is prepared, it is transported to the dehydration kettle 9 for online dehydration under a negative pressure of -0.06MPa.

[0036] Continuous fluorination reaction: The first metering pump 12 and the second metering pump 13 simultaneously transport the raw material liquid and the dehydrated fluorinated suspension to the microchannel continuous reactor 14, control the reaction temperature at 80℃, the pressure at 0.1MPa, and the material residence time at 10min to complete the continuous fluorination reaction.

[0037] Continuous post-treatment and solvent recycling: After cooling and solid-liquid separation, the reaction effluent is sent to a vacuum desolventizing tower to remove γ-butyrolactone under operating conditions of -0.08 MPa and 80°C, with a solvent recovery rate of 95%. The desolventized material is purified by a precision distillation tower to obtain 2,6-difluorobenzonitrile as the final product, with a purity of 99.8% and a molar yield of 97.5%.

[0038] Example 3 The device structure, connection, and function of this embodiment are the same as those of Embodiment 1, with only some process parameters adjusted. The specific process implementation is as follows: Continuous preparation and purification of 2,6-dichlorobenzonitrile: o-dichlorobenzene, potassium cyanide, and palladium chloride were added to continuous reaction vessel 1. The molar ratio of o-dichlorobenzene to potassium cyanide was 1:1.15, and the amount of palladium chloride added was 1.5% of the mass of o-dichlorobenzene. The stirring speed was 120 r / min, the temperature control device 4 controlled the temperature inside the vessel at 90℃ and the pressure at 0.3 MPa, and the nitrogen gas introduction rate was 1.5 L / min. The reaction was carried out continuously for 5 h. The product was purified by distillation purification column 2 to obtain 2,6-dichlorobenzonitrile with a purity of 99.9%, and then transferred to raw material liquid preparation tank 7.

[0039] Material preparation and online deep dehydration: An equal mass mixture of sulfolane and γ-butyrolactone is added to the raw material preparation tank 7 to prepare the raw material solution, and the temperature inside the tank is maintained at 60℃; anhydrous potassium fluoride and tetraphenylphosphonium bromide are added to the fluorinated suspension preparation tank 8, with the amount of tetraphenylphosphonium bromide added being 5% of the mass of 2,6-dichlorobenzonitrile, and the molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride being 1:3.0, and the temperature inside the tank is maintained at 60℃. After the fluorinated suspension is prepared, it is transported to the dehydration kettle 9 for online dehydration under a negative pressure of -0.095MPa.

[0040] Continuous fluorination reaction: The first metering pump 12 and the second metering pump 13 simultaneously transport the raw material liquid and the dehydrated fluorinated suspension to the tubular continuous reactor 14, control the reaction temperature at 150℃, the pressure at 1.0MPa, and the material residence time at 120min to complete the continuous fluorination reaction.

[0041] Continuous post-treatment and solvent recycling: After cooling and solid-liquid separation, the reaction effluent is sent to a vacuum desolventizing tower to remove the mixed solvent under operating conditions of -0.095 MPa and 120°C, with a solvent recovery rate of 98%. The desolventized material is purified by a precision distillation tower to obtain 2,6-difluorobenzonitrile product with a purity of 99.9% and a molar yield of 98.5%.

[0042] Example 4 The device structure, functionality, and equipment selection in this embodiment are completely identical to those in Embodiment 1. A tubular reactor is used for the continuous reactor 14. The process is implemented with the lower limit of phase transfer catalyst addition (0.1%) and the median residence time of the fluorination reaction (30 min) to further verify the stability and feasibility of the process within a wide parameter range. The specific process implementation is as follows: Continuous preparation and purification of 2,6-dichlorobenzonitrile o-Dichlorobenzene, potassium cyanide, and nickel chloride are added to the continuous reaction vessel 1 through their respective feed inlets. The molar ratio of o-dichlorobenzene to potassium cyanide is 1:1.12, and the amount of nickel chloride added is 1.2% of the mass of o-dichlorobenzene. The stirring device 3 is turned on, and the stirring speed is adjusted to 90 r / min. The temperature inside the vessel is controlled at 85℃ and the pressure is controlled at 0.25MPa by the temperature control device 4. At the same time, nitrogen gas is introduced into the vessel for protection at a rate of 1.2 L / min. The reaction is carried out continuously for 4.5 h. The reaction product is continuously transported to the distillation purification tower 2 through the corrosion-resistant pipeline 17. After the light components are recovered by the distillation purification and condensation recovery device 6, 2,6-dichlorobenzonitrile with a purity of 99.85% is obtained and continuously transported to the raw material liquid preparation tank 7.

[0043] Material preparation and online deep dehydration Sulfolane is added to the raw material preparation tank 7 as an aprotic polar solvent. The first stirrer 21 and the first thermostatic jacket 19 are turned on to maintain the temperature inside the tank at 40°C, and a homogeneous raw material solution is prepared by stirring. Anhydrous potassium fluoride and tetrabutylammonium chloride (quaternary ammonium salt phase transfer catalyst) are added to the fluorinated suspension preparation tank 8. The amount of tetrabutylammonium chloride added is 0.1% of the mass of 2,6-dichlorobenzonitrile, and the molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride is 1:2.2. The second stirrer 22 and the second thermostatic jacket 20 are turned on to maintain the temperature inside the tank at 40°C, and a homogeneous fluorinated suspension is prepared by stirring. The fluorinated suspension is continuously transported to the dehydration tank 9 through the corrosion-resistant pipe 17. The vacuum system 10 is turned on to control the pressure inside the dehydration tank 9 at -0.07MPa, and the fluorinated suspension is continuously and deeply dehydrated online.

[0044] Continuous fluorination reaction: The first metering pump 12 and the second metering pump 13 are turned on to synchronously and continuously transport the raw material liquid in the raw material preparation tank 7 and the dehydrated fluorinated suspension in the dehydration kettle 9 to the tubular continuous reactor 14 in proportion. The reaction temperature of the continuous reactor 14 is adjusted to 100℃, the reaction pressure is adjusted to 0.3MPa, and the material residence time is controlled to 30min through the control system 23 to complete the continuous fluorination halogen exchange reaction.

[0045] Continuous post-treatment and solvent recycling The effluent from the continuous reactor 14 is continuously fed to a cooler to cool to room temperature, and then enters a phase separator for efficient solid-liquid separation. The separated liquid phase is continuously fed to a vacuum desolventizing tower to remove sulfolane under operating conditions of -0.085 MPa and 90°C. The removed sulfolane is condensed and recovered and then recycled to the feed liquid preparation tank 7 for reuse, with a solvent recovery rate of 96.5%. The desolventized material is continuously fed to a precision distillation column (30 theoretical plates, reflux ratio 3:1) and purified by high-precision distillation to obtain 2,6-difluorobenzonitrile product with a purity of 99.85% and a molar yield of 97.8%.

[0046] Example 4 Verification Conclusion This embodiment, under the conditions of adding 0.1% of the phase transfer catalyst (the lower limit of the claim) and a fluorination reaction residence time of 30 min, still achieves the technical effect of ≥99.8% purity of 2,6-difluorobenzonitrile and ≥95% solvent recovery rate. This proves that the process parameter range of the present invention has good adaptability, and that a low dose of phase transfer catalyst can achieve a highly efficient fluorination reaction, further reducing the catalyst usage cost and improving the greenness and economy of the process. At the same time, it verifies the adjustability and stability of the material residence time within the range of 10~120 min.

[0047] In the above embodiments, the corrosion-resistant pipes 17 and control valves 18 of each unit of the device can flexibly adjust the material conveying path and flow rate according to the production capacity. The control system 23 can realize the linkage control of various process parameters, ensuring the stability of continuous production throughout the entire process and the uniformity of product quality. The device of the present invention has a reasonable structural design, with each unit functioning synergistically. The process conditions are mild, requiring no additional highly toxic and costly catalysts. The solvent recovery rate is high, enabling large-scale, green, and continuous production of 2,6-difluorobenzonitrile with a finished product purity ≥99.8%, meeting the application requirements of high-end pesticides, pharmaceuticals, and liquid crystal materials.

[0048] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process and apparatus for the continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions, characterized in that, It sequentially includes an interconnected 2,6-dichlorobenzonitrile preparation unit, a raw material preparation unit, an online dehydration unit, a continuous metering feed unit, a continuous reaction unit, and a post-processing unit; the 2,6-dichlorobenzonitrile preparation temperature is 70–90℃ and the pressure is 0.1–0.3MPa, and the fluorination reaction temperature is 80–150℃ and the pressure is 0.1–1.0MPa; The 2,6-dichlorobenzonitrile preparation unit includes a continuous reactor (1) and a distillation purification tower (2); the continuous reactor (1) is equipped with a stirring device (3), a temperature control device (4) and a catalyst feeding port (5), with a temperature control accuracy of ±1℃; the distillation purification tower (2) is a packed tower, with a condensation recovery device (6) on one side of the top of the tower, and 2,6-dichlorobenzonitrile with a purity ≥99.5% is obtained after purification; The raw material preparation unit includes a raw material liquid preparation tank (7) and a fluorinated suspension preparation tank (8); the raw material liquid preparation tank (7) is connected to the distillation and purification tower (2); the fluorinated suspension preparation tank (8) is used to prepare a fluorinated suspension of anhydrous potassium fluoride and a phase transfer catalyst. The online dehydration unit is a dehydration kettle (9) connected to the fluorinated suspension preparation tank (8), equipped with a vacuum system (10) and a condensation recovery system (11), with a dehydration pressure of -0.06 to -0.095 MPa; The continuous metering feeding unit includes a first metering pump (12) and a second metering pump (13), which are respectively connected to the raw material liquid preparation tank (7) and the dehydration kettle (9); The continuous reaction unit is a temperature-controlled continuous reactor (14), selected from microchannel reactors or tubular reactors, with internal heat exchange channels (15) and temperature sensors (16), and temperature control accuracy ±1℃. The post-processing unit includes a cooler, a phase separator, a depressurization desolvation tower, and a precision distillation tower connected in sequence; the discharge end of the continuous reactor (14) and the feed end of the cooler of the post-processing unit are connected to the control valve (18) through a corrosion-resistant pipe (17).

2. The apparatus for continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions according to claim 1, characterized in that, The continuous reaction vessel (1) has a volume of 500–5000L, the stirring speed of the stirring device (3) is 60–120r / min, and the temperature control device (4) can achieve precise temperature control of 70–90℃; the theoretical number of plates of the distillation purification column (2) is 15–30, and the reflux ratio is 1:1–3:

1.

3. The apparatus for continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions according to claim 1, characterized in that, The continuous reactor (14) has an inner diameter of 1–10 mm in the reaction channel, an effective reaction volume of 10–100 L, and can be adjusted to reaction conditions of 80–150 °C and 0.1–1.0 MPa. The material residence time can be adjusted within the range of 10–120 min.

4. The apparatus for continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions according to claim 1, characterized in that, The raw material preparation tank (7) includes a first thermostatic jacket (19) and a first stirrer (21), and the fluorinated suspension preparation tank (8) includes a second thermostatic jacket (20) and a second stirrer (22); the first thermostatic jacket (19) and the second thermostatic jacket (20) maintain a constant temperature environment of 25–60℃, and the stirring speed of the first stirrer (21) and the second stirrer (22) is 40–80 r / min; the operating pressure of the vacuum desolvation tower is -0.08 to -0.095 MPa, and the operating temperature is 80–120℃; the theoretical number of theoretical plates of the precision distillation tower is 20–40, and the reflux ratio is 2:1–4:

1.

5. The apparatus for continuous fluorination preparation of 2,6-difluorobenzonitrile under mild conditions according to claim 1, characterized in that, It also includes a control system (23), which is electrically connected to the temperature control device (4), the first metering pump (12), the second metering pump (13), the control valve (18), and the temperature sensor (16) of each unit.

6. A process for the continuous preparation of 2,6-difluorobenzonitrile using the apparatus of claim 1, characterized in that, Includes the following steps: 1) Preparation of 2,6-dichlorobenzonitrile: o-dichlorobenzene, cyaniding reagent, and catalyst are added to a continuous reaction vessel (1) and reacted at 70–90℃ and 0.1–0.3MPa for 3–5h. The product is purified by a distillation purification column (2) to obtain 2,6-dichlorobenzonitrile with a purity ≥99.5%. The cyaniding reagent is one of cuprous cyanide and potassium cyanide, the molar ratio of o-dichlorobenzene to cyaniding reagent is 1:(1.05–1.15), and the catalyst is one of palladium chloride and nickel chloride, with an addition amount of 0.8%–1.5% of the mass of o-dichlorobenzene. 2) Material preparation and dehydration: The purified 2,6-dichlorobenzonitrile is prepared into a raw material solution with an aprotic polar solvent, and anhydrous potassium fluoride is prepared into a fluorinated suspension with a phase transfer catalyst. The fluorinated suspension is dehydrated in a dehydration kettle (9). The aprotic polar solvent is selected from one or more of sulfolane and γ-butyrolactone, and the phase transfer catalyst is one of quaternary ammonium salt, quaternary phosphorus salt, and crown ether. The amount added is 0.1%–5% of the mass of 2,6-dichlorobenzonitrile, and the molar ratio of 2,6-dichlorobenzonitrile to potassium fluoride is 1:(2.0–3.0). 3) Continuous fluorination reaction: The raw material liquid and the dehydrated fluorinated suspension are fed into the continuous reactor (14) in proportion by the first metering pump (12) and the second metering pump (13), and reacted for 10–120 min at 80–150℃ and 0.1–1.0MPa. 4) Post-processing: The reaction effluent is cooled by a cooler, separated by a phase separator, desolventized by a solvent removal tower, and purified by a distillation tower to obtain 2,6-difluorobenzonitrile product with a purity ≥99.8%.

7. The process according to claim 6, characterized in that, In the preparation step of 2,6-dichlorobenzonitrile, the reaction process is protected by nitrogen, and the nitrogen introduction rate is 0.5–1.5 L / min. After purification, the purity of 2,6-dichlorobenzonitrile is ≥99.7%.

8. The process according to claim 6, characterized in that, In the post-processing step, the solvent removed by the solvent removal tower is condensed and recovered, and can be recycled for the preparation of raw material liquid, with a solvent recovery rate of ≥95%.

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