A device and process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt

Abstract

The application relates to a device and a process for continuously preparing 3,3-dichlorobenzidine diazonium salt, which comprises an aniline batching kettle, a sodium nitrite batching kettle, a reactor, a time-delay pipe and a product receiving kettle, wherein the reactor is provided with an aniline hydrochloric acid slurry inlet, a sodium nitrite solution inlet and a material outlet; the aniline batching kettle is connected with the aniline hydrochloric acid slurry inlet through a first pipeline, and the first pipeline is provided with a first input pump and a first flowmeter; the sodium nitrite batching kettle is connected with the sodium nitrite solution inlet through a second pipeline, and the second pipeline is provided with a second input pump and a second flowmeter; the material outlet is connected with the product receiving kettle through a third pipeline, and the third pipeline is provided with a third flowmeter, a time-delay pipe and a sampling pipe. The application can obtain a high diazonium salt conversion rate in a short reaction time at a reaction temperature close to room temperature, and the reaction process is safe.

Description

Technical Field

[0001] This invention relates to the field of diazotization technology of aniline compounds, specifically to an apparatus and process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt. Background Technology

[0002] Diazotization products, specifically diazonium salts, have significant applications in organic synthesis, including biomedicine, indicators, chemical testing, and the modification of composite materials. However, diazonium salts are extremely unstable. Traditional batch diazotization reactions require temperatures between 0 and 5°C, necessitating low-temperature operation and excessive energy consumption. Furthermore, poor mass transfer in the reactor leads to slow feeding rates, which can easily cause localized hot spots and deactivate the diazonium salt at high temperatures. The reaction is also exothermic, increasing the risk of runaway reactions and accidents, potentially even explosions. Slow feeding increases reaction time, energy consumption, and production efficiency, resulting in variations in diazonium salt quality between batches. Additionally, the diazonium salt solution often has a reddish appearance and produces numerous byproducts, negatively impacting subsequent reactions. Summary of the Invention

[0003] The purpose of this invention is to provide an apparatus and process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt, which can achieve a high diazonium salt conversion rate at a reaction temperature close to room temperature and in a shorter reaction time, and the reaction process is safe.

[0004] The objective of this invention is achieved through the following technical solution: An apparatus for the continuous preparation of 3,3-dichlorobenzidine diazonium salt includes an aniline mixing tank, a sodium nitrite mixing tank, a reactor, a delay tube, and a product receiving tank. The reactor is equipped with an aniline hydrochloric acid slurry inlet, a sodium nitrite solution inlet, and a material outlet. The aniline mixing tank is connected to the aniline hydrochloric acid slurry inlet via a first pipeline, which is equipped with a first input pump and a first flow meter. The sodium nitrite mixing tank is connected to the sodium nitrite solution inlet via a second pipeline, which is equipped with a second input pump and a second flow meter. Two flow meters are used. The material outlet is connected to the product receiving vessel through a third pipeline, which is equipped with a third flow meter, a delay tube, and a sampling tube. The reactor has a reactor flow channel inside, which includes a primary mixing section on the input side and a strong mixing section on the output side. The aniline hydrochloric acid slurry inlet is connected to the end of the primary mixing section away from the strong mixing section. The sodium nitrite solution inlet is located on the upper side of the primary mixing section, and a dispersion spray plate is provided between the primary mixing section and the sodium nitrite solution inlet. The dispersion spray plate is evenly distributed with micropores.

[0005] The strong mixing section includes multiple heart-shaped strong mixing module cavities connected in series, wherein the strong mixing module cavity at the input end is connected to the primary mixing section, and the strong mixing module cavity at the output end is connected to the material outlet.

[0006] The dispersing spray plate is removably and replaceably mounted on the reactor, wherein the sodium nitrite solution inlet is connected to the primary mixing section through a connecting channel, the reactor is provided with a slot, and the dispersing spray plate is inserted into the connecting channel through the slot.

[0007] The rear end of the dispersion spray plate is provided with a sealing flange, and the sealing flange is fixed to the reactor by bolts. The sealing flange is provided with a handle.

[0008] The aniline mixing vessel is equipped with a first heat exchanger, the sodium nitrite mixing vessel is equipped with a second heat exchanger, and the delay tube is equipped with a third heat exchanger.

[0009] Pressure sensors and temperature sensors are provided on the first pipeline between the first flow meter and the reactor, and on the second pipeline between the second flow meter and the reactor. Pressure sensors, temperature sensors, and check valves are provided on the third pipeline between the third flow meter and the delay tube. Temperature sensors are provided on the third pipeline between the delay tube and the product receiving vessel.

[0010] The aniline mixing tank, sodium nitrite mixing tank, and product receiving tank are all equipped with stirring blades driven by a motor.

[0011] A process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt by the aforementioned apparatus includes the following steps: Step 1: Prepare a slurry of aniline hydrochloric acid that meets the requirements in an aniline mixing tank, and prepare a sodium nitrite solution that meets the requirements in a sodium nitrite mixing tank; Step 2: Run water through the pipes to check for leaks; Step 3: Adjust the appropriate pump flow rates of the first and second input pumps to control the material's time in the reactor and delay tube to meet the requirements; Step 4: Control the reaction temperature in the reactor and delay tube to 15-20℃, and open the sampling tube to observe the state of the generated product. After the product state meets the requirements, open the product receiving vessel to receive the product. Step 5: After the reaction is complete, replace the reactants in the aniline mixing tank and the sodium nitrite mixing tank with clean water and rinse until the liquid flowing out of the sampling tube outlet is colorless; Step 6: Perform a conversion rate test on the generated diazonium salt.

[0012] In step two, if the room temperature is higher than the set reaction temperature, the pipeline is circulated with ice water; if the room temperature is lower than the set reaction temperature, the pipeline is circulated with clean water.

[0013] In step four, the initial product containing byproducts is discharged through a sampling tube. After the product clarifies, starch-potassium iodide test paper is used to verify whether the product contains excessive sodium nitrite. Only after it meets the requirements is the product receiving vessel opened.

[0014] The advantages and positive effects of this invention are as follows: 1. The present invention can achieve a high conversion rate of diazonium salts at a reaction temperature close to room temperature and in a shorter reaction time. Compared with the existing batch preparation of diazonium salts with a conversion rate of 95% to 96%, the conversion rate of the present invention can reach 99.5%. Moreover, compared with the existing batch preparation of diazonium salts with a reaction time of about 30 minutes, the reaction time of the present invention can be shortened to 0.5 to 2 minutes, and the reaction process is safe.

[0015] 2. This invention employs a dispersing spray plate for initial mixing, thereby accelerating the sodium nitrite solution with a certain initial velocity through small holes on the dispersing plate. This allows the slurry raw materials and sodium nitrite solution to be rapidly initially mixed, completing a low-degree diazotization reaction. To prevent the low-degree diazotization reaction liquid from directly entering the delay tube and causing system pressure increase and instability, the initially mixed reaction liquid is then passed through a heart-shaped strong mixing module cavity inside the reactor for thorough mixing. The merging and splitting of the reaction liquid streams ensures that some small particles in the slurry are fully mixed with the sodium nitrite solution. This is highly effective for treating reaction liquids with a certain viscosity. The final solution leaving the reactor is almost homogeneous. After passing through a section of tubular reactor, the final reaction slurry can be rapidly converted into diazonium salts.

[0016] 3. Due to the rapid reaction and absence of backmixing, the diazonium salt product prepared by this invention has a clearer appearance than that prepared by batch reaction, and no tar byproducts are generated. The diazonium salt yield is higher and the reaction time is shorter. The product can directly participate in the next reaction without further purification. Moreover, the internal structure of the microreactor of this invention is easy to implement, and the microreactor of this invention can be scaled up as needed according to the reaction flux, so as to quickly realize industrialization. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention. Figure 2 for Figure 1 A schematic diagram of the reactor structure in the diagram. Figure 3 for Figure 2 A schematic diagram of the installation of the dispersion spray plate.

[0018] Wherein, 1 is the aniline mixing vessel, 2 is the first input pump, 3 is the first flow meter, 4 is the reactor, 5 is the sodium nitrite mixing vessel, 6 is the second input pump, 7 is the second flow meter, 8 is the third flow meter, 9 is the delay tube, and 10 is the product receiving vessel; 101 is the aniline hydrochloric acid slurry inlet, 401 is the reactor flow channel, 4011 is the initial mixing section, 4012 is the strong mixing module cavity, 402 is the material outlet, 403 is the connecting flow channel, 501 is the sodium nitrite solution inlet, 502 is the dispersion spray plate, 5021 is the sealing flange, and 5022 is the handle. Detailed Implementation

[0019] The invention will now be described in further detail with reference to the accompanying drawings.

[0020] like Figure 1 As shown, the apparatus of the present invention includes an aniline mixing tank 1, a sodium nitrite mixing tank 5, a reactor 4, a delay tube 9, and a product receiving tank 10, wherein... Figure 2 As shown, the reactor 4 is provided with an aniline hydrochloric acid slurry inlet 101, a sodium nitrite solution inlet 501, and a material outlet 402. The aniline mixing vessel 1 is connected to the aniline hydrochloric acid slurry inlet 101 through a first pipeline, and a first input pump 2 and a first flow meter 3 are sequentially provided on the first pipeline along the material conveying direction. The sodium nitrite mixing vessel 5 is connected to the sodium nitrite solution inlet 501 through a second pipeline, and a second input pump 6 and a second flow meter 7 are sequentially provided on the second pipeline along the material conveying direction. In this embodiment, the first input pump 2 is a peristaltic pump, and the second input pump 6 is a horizontal flow pump. The material outlet 402 is connected to the product receiving vessel 10 through a third pipeline, and a third flow meter 8, a delay tube 9, and a sampling tube are sequentially provided on the third pipeline along the material conveying direction.

[0021] like Figure 2 As shown, in this embodiment, the reactor 4 is provided with a reactor flow channel 401, which includes a primary mixing section 4011 on the input side and a strong mixing section on the output side. The aniline hydrochloric acid slurry inlet 101 is connected to the end of the primary mixing section 4011 away from the strong mixing section. The sodium nitrite solution inlet 501 is provided on the upper side of the primary mixing section 4011, and a dispersion spray plate 502 is provided between the primary mixing section 4011 and the sodium nitrite solution inlet 501. In this embodiment, the dispersion spray plate 502 is evenly distributed with micropores of 1-2 mm. After the sodium nitrite solution flows in, it is dispersed and sprayed into the primary mixing section 4011 through the dispersion spray plate 502 and undergoes preliminary mixing with the aniline hydrochloric acid slurry that continuously flows in through the aniline hydrochloric acid slurry inlet 101. Then, it enters the strong mixing section to achieve forced and thorough mixing.

[0022] like Figure 2As shown, in this embodiment, the strong mixing section includes a plurality of heart-shaped strong mixing module cavities 4012 connected in series, wherein the strong mixing module cavity 4012 at the input end is connected to the primary mixing section 4011, and the strong mixing module cavity 4012 at the output end is connected to the material outlet 402.

[0023] like Figure 3 As shown, in this embodiment, the dispersing spray plate 502 is removably and replaceably mounted on the reactor 4. The sodium nitrite solution inlet 501 is connected to the initial mixing section 4011 via a connecting channel 403. The reactor 4 has a slot, and the dispersing spray plate 502 is inserted into the connecting channel 403 through the slot. The connecting channel 403 needs to have a sufficient diameter, and the micropores on the dispersing spray plate 502 need to have a certain density. This ensures that the material flowing in through the sodium nitrite solution inlet 501 can achieve a dispersing spray effect after passing through the dispersing spray plate 502. A sealing flange 5021 is provided at the rear end of the dispersing spray plate 502, and the sealing flange 5021 is fixed to the reactor 4 with bolts. Appropriate sealing elements can be provided between the sealing flange 5021 and the outer wall of the reactor 4 as needed to ensure the internal sealing of the reactor 4. A handle 5022 is provided on the sealing flange 5021 for easy removal and replacement of the dispersing spray plate 502. The present invention allows for the selection of a dispersing spray plate 502 with a suitable micropore diameter based on the actual reaction conditions. In addition, this invention uses a dispersion spray plate 502 for initial mixing and a heart-shaped strong mixing module cavity 4012 for thorough mixing. Its function is to accelerate the sodium nitrite solution with a certain initial velocity through the small holes on the dispersion plate, so that the slurry raw material and sodium nitrite solution are rapidly initially mixed, completing a low degree of diazotization reaction. At this time, the reaction liquid gradually changes from a slurry to a solution state, and the viscosity drops rapidly, and the system pressure decreases. This instantaneous reaction change means that the raw material is not enough to completely diazotize. In order to prevent the low degree of diazotization reaction liquid from directly entering the delay tube, which may cause the system pressure to rise and lead to system instability, the reaction liquid after initial mixing is specially designed to be mixed again through the heart-shaped structure inside the reactor. The merging and splitting of the reaction liquid streams allows some small particles in the reaction liquid slurry to be fully mixed with the sodium nitrite solution. This is very effective for treating reaction liquids with a certain viscosity. The final solution leaving the reactor is almost in a homogeneous state. After passing through a section of tubular reactor, the final reaction liquid slurry can be quickly converted into diazonium salt. Because of its rapid and backmixing-free process, the diazonium salt product prepared in this manner is clearer in appearance than that prepared by batch reactions, and no tar byproducts are generated. The diazonium salt yield is higher, the reaction time is shorter, and the product can directly participate in the next reaction without further purification. Furthermore, the internal structure of the microreactor of this invention is easy to implement, and the microreactor can be scaled up as needed according to the reaction flux, enabling rapid industrialization.

[0024] In this embodiment, the aniline mixing vessel 1 is equipped with a first heat exchanger, the sodium nitrite mixing vessel 5 is equipped with a second heat exchanger, and the delay tube 9 is equipped with a third heat exchanger. In this embodiment, the heat exchanger can adopt a structure in which heat exchange tubes are arranged on the inner wall of the vessel or the inner wall of the tube. Water or other heat exchange liquid is contained in the heat exchange tubes to achieve heat exchange and maintain the temperature inside the vessel or the tube. This is a well-known technology in the art.

[0025] A pressure sensor and a temperature sensor are provided on the first pipeline between the first flow meter 3 and the reactor 4. A pressure sensor and a temperature sensor are also provided on the second pipeline between the second flow meter 7 and the reactor 4. A pressure sensor, a temperature sensor and a check valve are provided on the third pipeline between the third flow meter 8 and the delay pipe 9. A temperature sensor is provided on the third pipeline between the delay pipe 9 and the product receiving vessel 10.

[0026] like Figure 1 As shown, the aniline mixing tank 1, the sodium nitrite mixing tank 5, and the product receiving tank 10 are all equipped with stirring blades that are driven to rotate by a motor.

[0027] The working principle of this invention is as follows: The process of this invention includes the following steps: Step 1: Prepare an aniline hydrochloric acid slurry with the required mass concentration in aniline mixing tank 1, and prepare a sodium nitrite solution in sodium nitrite mixing tank 5 according to the ratio.

[0028] Step 2: Run water through the pipeline first to check for leaks. If the room temperature is higher than the set reaction temperature (20°C), run ice water through the pipeline first. If the room temperature is lower than the set reaction temperature (20°C), run clean water through the pipeline first.

[0029] Step 3: Adjust the appropriate flow rates of the first input pump 2 and the second input pump 6. Specifically, first turn on the first input pump 2, then turn on the second input pump 6. After the material is mixed by collision in the reactor 4, the mixture passes through a delay tube 9 of a certain length and reaches the product receiving vessel 10. It is necessary to control the time the material spends in the reactor 4 and the delay tube 9 to meet the requirements. In addition, if the generated diazonium salt needs to continuously participate in the next reaction, this invention requires adding an aminosulfonic acid solution input pipeline to react with the diazonium salt that has passed through a delay tube in an auxiliary reactor to destroy excess sodium nitrite in the diazonium salt.

[0030] Step 4: Control the reaction temperature at 15-20℃ using each heat exchanger, and open the sampling tube to observe the state of the generated product.

[0031] The reaction temperature of the reactants is controlled at 15-20℃ to obtain a high diazonium salt conversion rate in a short time. In addition, due to the mismatch in concentration of the initial product, there are many by-products, which need to be discharged as waste liquid through the sampling tube. After the product becomes clear, it is immediately verified with starch-potassium iodide test paper whether there is an excess of sodium nitrite. After meeting the requirements, the product receiving vessel 10 is opened to allow the product to be loaded into the product receiving vessel 10.

[0032] Step 5: After the reaction is complete, replace the reactants in aniline mixing tank 1 and sodium nitrite mixing tank 5 with clean water for rinsing until the liquid flowing out of the sampling tube outlet is colorless.

[0033] Step Six: Diazonium Salt Conversion Rate Test. Specifically, select a coupling component and prepare a standard solution of a certain concentration. For each test, take an appropriate volume of the coupling component and prepare a coupling component with a buffer solution of acetic acid and sodium acetate. Then, take a certain amount of the diazonium salt to be tested, and prepare a standard solution by destroying excess sodium nitrite with sulfamic acid. Use an acid burette to add the diazonium salt to be tested to the coupling component until the H acid on the filter paper changes from colorless to slightly blue using the permeation method. Record the volume of diazonium salt consumed. Then, calculate the actual concentration of diazonium salt in the product using the formula and compare it with the theoretical concentration to calculate the diazonium salt conversion rate.

[0034] The following are some application examples to further illustrate this point.

[0035] Application Example 1 First, prepare a 5% (w / w) aniline hydrochloride slurry. Weigh 2542g of 3,3-dichlorobenzidine hydrochloride (74.67%, 7.5mol) and pour it into aniline mixing tank 1. Then weigh 19069g of tap water and dissolve 2837g of hydrochloric acid (32.8%, 25.5mol) in the water to prepare a hydrochloric acid solution. Pour the well-stirred hydrochloric acid solution into aniline mixing tank 1. Control the slurry temperature at 0-5℃ using the first heat exchanger and slurry for at least 0.5 hours. Set aside for later use. Weigh 1108g of sodium nitrite (99%, 15.9mol) and pour it into 2263... 9g of tap water was stirred evenly at 10-15℃ using the second heat exchanger. At the start of the reaction, the peristaltic pump flow rate was set to 350ml / min, and the horizontal flow pump flow rate was set to 315ml / min. The molar ratio of 3,3-dichlorobenzidine hydrochloride to sodium nitrite was manually controlled at 2.12:1 using a flow meter. The diazotization temperature in the delay tube 9 was controlled at 18℃ using the third heat exchanger, and the reaction residence time was controlled at 0.692min using the delay tube 9. After the system stabilized, samples were taken, and the diazonium salt conversion rate was calculated to be 99.55% under these process conditions.

[0036] Application Example 2 First, prepare a 5% (w / w) aniline hydrochloride slurry. Weigh 2542g of 3,3-dichlorobenzidine hydrochloride (74.67%, 7.5mol) and pour it into aniline mixing tank 1. Then weigh 19069g of tap water and dissolve 2837g of hydrochloric acid (32.8%, 25.5mol) in the water to prepare a hydrochloric acid solution. Pour the well-stirred hydrochloric acid solution into aniline mixing tank 1. Control the slurry temperature at 0-5℃ using the first heat exchanger and slurry for at least 0.5 hours. Set aside for later use. Weigh 1108g of sodium nitrite (99%, 15.9mol) and pour it into 226... 39g of tap water was stirred evenly at 10-15℃ using the second heat exchanger. At the start of the reaction, the peristaltic pump flow rate was set to 350ml / min, and the horizontal flow pump flow rate was set to 315ml / min. The molar ratio of 3,3-dichlorobenzidine hydrochloride to sodium nitrite was manually controlled at 2.12:1 using a flow meter. The diazotization temperature in the delay tube 9 was controlled at 18℃ using the third heat exchanger, and the reaction residence time was controlled at 1.1min using the delay tube 9. After the system stabilized, samples were taken, and the diazonium salt conversion rate was calculated to be 99.50% under these process conditions.

Claims

1. An apparatus for the continuous preparation of 3,3-dichlorobenzidine diazonium salt, characterized in that: The system includes an aniline mixing tank (1), a sodium nitrite mixing tank (5), a reactor (4), a delay tube (9), and a product receiving tank (10). The reactor (4) is equipped with an aniline hydrochloric acid slurry inlet (101), a sodium nitrite solution inlet (501), and a material outlet (402). The aniline mixing tank (1) is connected to the aniline hydrochloric acid slurry inlet (101) via a first pipeline, which is equipped with a first input pump (2) and a first flow meter (3). The sodium nitrite mixing tank (5) is connected to the sodium nitrite solution inlet (501) via a second pipeline, which is equipped with a second input pump (6) and a second flow meter (7). The material... The outlet (402) is connected to the product receiving vessel (10) through a third pipeline, and the third pipeline is equipped with a third flow meter (8), a delay tube (9) and a sampling tube. The reactor (4) is equipped with a reactor flow channel (401), and the reactor flow channel (401) includes a primary mixing section (4011) on the input side and a strong mixing section on the output side. The aniline hydrochloric acid slurry inlet (101) is connected to the end of the primary mixing section (4011) away from the strong mixing section. The sodium nitrite solution inlet (501) is provided on the upper side of the primary mixing section (4011), and a dispersion spray plate (502) is provided between the primary mixing section (4011) and the sodium nitrite solution inlet (501). The strong mixing section includes a plurality of heart-shaped strong mixing module cavities (4012) connected in series, wherein the strong mixing module cavity (4012) at the input end is connected to the primary mixing section (4011), and the strong mixing module cavity (4012) at the output end is connected to the material outlet (402). The dispersing spray plate (502) is removably and replaceably disposed on the reactor (4), wherein the sodium nitrite solution inlet (501) is connected to the primary mixing section (4011) through a connecting channel (403), the reactor (4) is provided with a slot, and the dispersing spray plate (502) is inserted into the connecting channel (403) through the slot; The rear end of the dispersion spray plate (502) is provided with a sealing flange (5021), and the sealing flange (5021) is fixed to the reactor (4) by bolts. The sealing flange (5021) is provided with a handle (5022). The dispersion spray plate (502) has micropores of 1-2 mm evenly distributed on it. After the sodium nitrite solution flows in, it is dispersed and sprayed into the initial mixing section (4011) through the dispersion spray plate (502).

2. The apparatus for the continuous preparation of 3,3-dichlorobenzidine diazonium salt according to claim 1, characterized in that: The aniline mixing vessel (1) is equipped with a first heat exchanger, the sodium nitrite mixing vessel (5) is equipped with a second heat exchanger, and the delay tube (9) is equipped with a third heat exchanger.

3. The apparatus for the continuous preparation of 3,3-dichlorobenzidine diazonium salt according to claim 1, characterized in that: Pressure sensors and temperature sensors are provided on the first pipeline between the first flow meter (3) and the reactor (4) and on the second pipeline between the second flow meter (7) and the reactor (4). Pressure sensors, temperature sensors and one-way valves are provided on the third pipeline between the third flow meter (8) and the delay pipe (9). Temperature sensors are provided on the third pipeline between the delay pipe (9) and the product receiving vessel (10).

4. The apparatus for the continuous preparation of 3,3-dichlorobenzidine diazonium salt according to claim 1, characterized in that: The aniline mixing tank (1), sodium nitrite mixing tank (5), and product receiving tank (10) are all equipped with stirring blades driven by a motor.

5. A process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt using the apparatus described in claim 1, characterized in that: Includes the following steps: Step 1: Prepare a slurry of aniline hydrochloric acid that meets the requirements in the aniline mixing tank (1), and prepare a sodium nitrite solution that meets the requirements in the sodium nitrite mixing tank (5); Step 2: Run water through the pipes to check for leaks; Step 3: Adjust the appropriate pump flow rates of the first input pump (2) and the second input pump (6) to control the time the material spends in the reactor (4) and the delay tube (9) to meet the requirements; Step 4: Control the reaction temperature in the reactor (4) and the delay tube (9) to 15-20℃, and open the sampling tube to observe the state of the generated product. After the product state meets the requirements, open the product receiving vessel (10) to receive the product. Step 5: After the reaction is complete, replace the reactants in the aniline mixing tank (1) and the sodium nitrite mixing tank (5) with clean water for cleaning until the liquid flowing out of the sampling tube outlet is colorless; Step 6: Perform a conversion rate test on the generated diazonium salt.

6. The process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt according to claim 5, characterized in that: In step two, if the room temperature is higher than the set reaction temperature, the pipeline is circulated with ice water; if the room temperature is lower than the set reaction temperature, the pipeline is circulated with clean water.

7. The process for the continuous preparation of 3,3-dichlorobenzidine diazonium salt according to claim 5, characterized in that: In step four, the initial product containing byproducts is discharged through a sampling tube. After the product is clarified, starch-potassium iodide test paper is used to verify whether the product contains excessive sodium nitrite. If it meets the requirements, the product receiving vessel (10) is opened.

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