A method for the synthesis of 2,2'-dithiodibenzothiazole under negative pressure

Abstract

The application provides a method for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure, wherein the absolute pressure of a reaction system is controlled to be 20-45 kpaA, the reaction temperature in a reaction kettle is kept at 30-60 DEG C under the pressure, 2-mercaptobenzothiazole slurry and an oxidizing agent are reacted, 2,2'-dithiobisbenzothiazole is synthesized by a one-step method, and solvent vapor is returned to a solvent recovery tank after being condensed. The method can control the reaction temperature by controlling the vacuum degree of the reaction system, the reaction kettle body does not need to be provided with heat exchange pipes, the problem of poor heat transfer effect caused by fouling can be effectively avoided, the production can be continuously and stably carried out, the cost of starting and stopping and the safety risk can be effectively reduced, the reaction heat can be effectively utilized to recover the solvent, the energy consumption cost of 200 yuan per ton of product can be directly reduced, the temperature in the reaction system kettle is more uniform, the side reaction is less, the product content is high, and the yield is high.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and to a method for synthesizing 2,2′-dibenzothiazole disulfide under negative pressure. Background Technology

[0002] Accelerator 2,2′-dibenzothiazole disulfide, abbreviated as DM, chemical formula C 14 H8N2S4 is a pale yellow crystal, slightly toxic, odorless, and slightly bitter. It is a general-purpose accelerator for natural rubber, synthetic rubber, and reclaimed rubber, and can be used to manufacture tires, hoses, belts, rubber sheets, and general industrial rubber products. It is also a very important intermediate in pharmaceutical synthesis.

[0003] At present, the synthesis of accelerator DM is generally carried out by reacting an oxidant with 2-mercaptobenzothiazole slurry (abbreviated as M slurry). The main synthesis methods are as follows: (1) Sodium hypochlorite oxidation method: Sodium hypochlorite is used as an oxidant to oxidize M, and water is used as a solvent to prepare DM. The process is mature, but the disadvantage is that 10 to 15 tons of high-salt wastewater will be generated for every ton of product produced; (2) Ammonia water synthesis method: M is dissolved in ammonia water, filtered to obtain M ammonium salt solution, and a catalyst is added. Under certain temperature and pressure, oxygen or air is introduced to react and obtain DM product. The disadvantages of this reaction are that it needs to be carried out under high temperature and high pressure conditions, oxygen is used to make the reaction system heterogeneous, an additional catalyst needs to be added during the reaction process, the ammonium salt solution needs to be filtered, the process operation is complicated, the process flow is long, and 5 to 10 tons of high ammonia nitrogen production wastewater will be generated for every ton of product produced, and the product purity and yield are low; (3) Organic solvent synthesis method: ethanol, methanol, isopropanol, benzene or toluene are used as solvents to dissolve the M promoter, a mixture of NO and NO2 is used as a catalyst, and oxygen is used as an oxidant, and the synthesis is carried out under normal pressure and 40 to 60°C. The disadvantages of this reaction are that the gas phase space of the reaction vessel will contain a mixture of solvent, oxygen and catalyst, which is explosive, the inherent safety of the reaction is reduced, and the reaction system becomes a heterogeneous reaction when oxygen is used, resulting in local oxidation, low product purity and yield, and the solvent also needs to be distilled. Summary of the Invention

[0004] This invention addresses the aforementioned problems by innovatively providing a method for synthesizing DM under negative pressure. By controlling the vacuum level of the reaction system, the reaction temperature is controlled, thus avoiding the use of oxygen and catalysts, and also avoiding the series of problems caused by traditional methods of controlling reaction temperature using circulating water or chilled water heat exchange. To achieve this objective, the technical solution adopted by this invention is as follows:

[0005] In a first aspect, the present invention provides a method for synthesizing 2,2′-dibenzothiazole disulfide under negative pressure, comprising the following steps: using M slurry and oxidant as reaction raw materials, controlling the absolute pressure of the reaction system at 20-45 kPaA, maintaining the reaction temperature in the reactor at 30-60°C under this pressure, synthesizing 2,2′-dibenzothiazole disulfide in one step, and returning the solvent vapor to the solvent recovery tank after condensation.

[0006] Preferably, in the negative pressure synthesis method for DM provided by the present invention, a reactor without a heat exchanger is used for the synthesis reaction, and a magnetic stirrer is installed inside the reactor. The reactor body has no heat exchange tubes, which effectively avoids the problem of poor heat transfer caused by scaling, enabling continuous and stable production; the reactor is stirred using a magnetic stirrer, ensuring that the system is sealed and leak-free.

[0007] This invention uses reaction pressure to control reaction temperature, with different reaction pressures corresponding to different reaction temperatures. Based on the results of specific embodiments, the preferred reaction pressure in this invention is 30–40 kPaA.

[0008] Preferably, in the method for negative pressure synthesis of 2,2′-dibenzothiazole disulfide provided by the present invention, the slurry M is a suspension formed by uniformly dispersing the accelerator M (2-mercaptobenzothiazole) in an organic volatile solvent, wherein the mass ratio of the organic volatile solvent to the accelerator M is 2.0 to 6.0:1.0.

[0009] More preferably, in the method for synthesizing 2,2′-dibenzothiazole disulfide under negative pressure provided by the present invention, the organic volatile solvent is selected from any one of ethanol, methanol, and isopropanol.

[0010] Preferably, in the method for synthesizing 2,2′-dibenzothiazole disulfide under negative pressure provided by the present invention, the oxidant is hydrogen peroxide with a mass concentration of 10-40%.

[0011] More preferably, in the method for negative pressure synthesis of 2,2′-dibenzothiazole disulfide provided by the present invention, the molar ratio between the accelerator M and hydrogen peroxide is 2.0:(1.1 to 1.4).

[0012] Preferably, in the negative pressure synthesis method of 2,2′-dibenzothiazole disulfide provided by the present invention, nitrogen is used to control the pressure of the reaction system. The use of nitrogen to regulate the system pressure in this invention is not only more stable than simply using a vacuum unit to control the system pressure, but also allows for nitrogen passivation of the reaction system, improving system safety.

[0013] Preferably, in the negative pressure synthesis method of 2,2′-dibenzothiazole disulfide provided by the present invention, the solvent vapor is condensed and cooled to 20-30°C before being returned to the solvent recovery tank. This utilizes the heat of reaction to recover part of the solvent, reducing steam consumption during solvent recovery and lowering product energy consumption.

[0014] A second aspect of the present invention provides an apparatus for the negative pressure synthesis of 2,2′-dibenzothiazole disulfide, comprising a reaction vessel, a condenser connected to the top of the reaction vessel, a gas-liquid separator connected to the bottom of the condenser, and a solvent recovery tank connected to the bottom of the gas-liquid separator. The reaction vessel has no heat exchanger, is equipped with a magnetic stirrer, and has a pressure control valve connected to its top and a product storage tank connected to its bottom; the top of the gas-liquid separator is connected to a vacuum spray system.

[0015] Preferably, in the apparatus for negative pressure synthesis of 2,2′-dibenzothiazole disulfide provided by the present invention, the vacuum spraying system uses a water jet vacuum pump with a spraying tower, and the vacuum pump is designed to have an ultimate vacuum of 18 kPaA.

[0016] A third aspect of the present invention provides an accelerator, 2,2′-dibenzothiazole disulfide, synthesized using the above method.

[0017] The beneficial protections and effects of this invention are as follows:

[0018] 1. Raw material input

[0019] The organic volatile solvent used in this invention has a certain solubility for the promoter M, and the oxidant hydrogen peroxide is completely dissolved in the solvent. The reaction process is basically a homogeneous reaction with a large contact area of ​​reactants, a fast reaction rate, and few side reactions. No additional catalyst is required, which saves on raw material costs.

[0020] 2. Advantages in production stability and safety

[0021] The negative pressure synthesis method for DM provided by this invention controls the reaction temperature by controlling the vacuum degree of the reaction system. The reaction vessel body does not need to be equipped with heat exchange tubes, which can effectively avoid the problem of poor heat transfer caused by scaling, and help to enable continuous and stable production.

[0022] This invention uses hydrogen peroxide as the oxidant, which is completely dissolved in the solvent, avoiding the explosive situation of solvent gas and oxidant gas mixing in the gas phase space of the reaction vessel in existing technologies, thus improving reaction safety. Furthermore, this invention uses nitrogen to regulate the system pressure, which is not only more stable than simply using a vacuum unit to control the system pressure, but also allows for nitrogen passivation of the reaction system, improving system safety.

[0023] 3. Production cost advantage

[0024] ① Compared to using heat exchangers for temperature control, reactors are prone to fouling, leading to reduced heat exchange efficiency and requiring frequent shutdowns for cleaning. The synthesis method of this invention can effectively reduce start-up and shutdown costs and safety risks;

[0025] ② The solvent recovery method of this invention adopts reactive distillation + conventional distillation. Part of the solvent can be recovered by utilizing the heat of reaction: the heat of reaction of DM is 1100-1200kJ / kg, and the heat of solvent vaporization is about 900-1200kJ / kg. During the reaction, 1.0-1.5 parts of solvent can be recovered directly by utilizing the heat of reaction, and the energy consumption cost can be directly reduced by 200 yuan per ton of finished product.

[0026] 4. Advantages in product quality and yield

[0027] Compared to synthesis methods that use indirect heat exchangers for temperature control, these methods suffer from localized overheating leading to localized peroxidation during the reaction, resulting in more impurities in the product, a purity of approximately 95.5%, and a lower yield of 95%. The synthesis method of this invention, by controlling the temperature within the reaction vessel through vacuum control, achieves more uniform temperature distribution, reduces side reactions, and increases the product content to 95% and the yield to 97%.

[0028] 5. Waste liquid treatment

[0029] Compared with the synthesis method that uses indirect heat exchange to achieve temperature control, the present invention generates no waste and the wastewater COD is also lower, only about 15,000 PPM, while the wastewater COD of the indirect heat exchange method is 30,000 PPM, thus reducing the wastewater treatment cost. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the production device for synthesizing DM using a negative pressure method in this invention;

[0031] Figure 2 This is a schematic diagram of the production unit that synthesizes DM using a heat exchange method in the comparative example;

[0032] Figure 3 This is a schematic diagram of the solvent recovery system. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0034] All reagents and raw materials used in this invention are commercially available or can be prepared according to literature methods. Experimental methods in the following examples, unless otherwise specified, are generally performed under standard conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight.

[0035] Figure 1This diagram illustrates the structure of a production apparatus for synthesizing DM using a negative pressure method, as described in this invention. The apparatus includes a reactor 1, a condenser 2 connected to the top of the reactor 1, a gas-liquid separator 3 connected to the bottom of the condenser 2, and a solvent recovery tank 4 connected to the bottom of the gas-liquid separator 3. The reactor 1 does not contain any heat exchange elements but is equipped with a magnetic stirrer. A pressure control valve 7 is connected to the top of the reactor and is linked to a nitrogen valve 5. Nitrogen is used to regulate the vacuum level of the entire system. When the system pressure is low, the nitrogen valve 5 is opened to increase the system pressure; when the system pressure is high, the nitrogen valve 5 is closed to decrease the system pressure. The system is automatically controlled by a DCS or PLC system. The pressure signal is output to the nitrogen valve 5 via a PID controller to achieve precise control. The vacuum spray system 6 is connected to the gas-liquid separator 3. It uses a water jet vacuum pump to match the spray tower. The vacuum pump is designed with an ultimate vacuum of 18 kPaA to avoid the reaction liquid from boiling over due to excessively low vacuum. The spray tower can absorb the solvent, and the absorbent liquid can be recovered by a distillation tower to avoid solvent loss and environmental hazards caused by solvent emissions into the atmosphere.

[0036] During the synthesis reaction, M slurry and hydrogen peroxide with a mass concentration of 10-40% are used as the main reaction raw materials. The absolute pressure of the reaction system is controlled at 20-45 kPaA. Under this pressure, the reaction temperature in reactor 1 is maintained at 30-60℃, and DM is synthesized in one step.

[0037] The product solution flows out from the bottom of reactor 1 and enters the reaction liquid storage tank for storage. The vaporized solvent vapor distills out from the top of reactor 1, is condensed by condenser 2, and then enters gas-liquid separator 3 for gas-liquid separation. After being separated from the uncondensed solvent vapor and the nitrogen gas that comes with reactor 1, it enters solvent recovery tank 4 for storage.

[0038] Specific implementations under different conditions are described in Examples 1 to 9 below:

[0039] Example 1

[0040] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 45 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 60℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 3.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0041] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, the heat of reaction can recover 1 part isopropanol (mass of M), with a conversion rate of 99.1% for M, a yield of 97.2%, and a purity of 95.3% for DM.

[0042] Example 2

[0043] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 35 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 45℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 3.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0044] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, 1.1 parts of isopropanol (mass of M) can be recovered from the heat of reaction, with a conversion rate of 99.4% for M, a yield of 97.3%, and a purity of 95.5% for DM.

[0045] Example 3

[0046] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 20 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 30℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 3.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0047] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, 1.3 parts of isopropanol (M mass) can be recovered from the heat of reaction, with a M conversion rate of 99.1%, a yield of 97.2%, and a DM purity of 96.4%.

[0048] Example 4

[0049] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 20 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 30℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 3.0:1.0 to the reactor, and simultaneously add 40% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0050] After the reaction is qualified, the solution is continuously drawn into the reaction liquid storage tank through the liquid level control valve. Under this condition, 1.3 parts of isopropanol (M mass) can be recovered from the heat of reaction, the conversion rate of M is 99.3%, the yield is 97.4%, and the purity of DM is 96.3%.

[0051] Example 5

[0052] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 20 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 30℃; continuously add ethanol and accelerator M slurry with a mass ratio of 3.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0053] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, 1.4 parts of ethanol (M mass) can be recovered from the heat of reaction, with a M conversion rate of 99.1%, a yield of 97.3%, and a DM purity of 96.3%.

[0054] Example 6

[0055] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 45 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 60℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 6.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.4, and turn on the agitator and pump for circulation.

[0056] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, the heat of reaction can recover 1 part isopropanol (mass of M), with a conversion rate of 99.2% for M, a yield of 97.4%, and a purity of 95.5% for DM.

[0057] Example 7

[0058] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 45 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 60℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 6.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.1, and turn on the agitator and pump for circulation.

[0059] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, the heat of reaction can recover 1 part isopropanol (mass of M), with a conversion rate of 99.0%, a yield of 97.0%, and a purity of 95.0% for DM.

[0060] Example 8

[0061] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 30 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 40℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 6.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.1, and turn on the agitator and pump for circulation.

[0062] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, 1.2 parts of isopropanol (mass of M) can be recovered from the heat of reaction, with a conversion rate of 99.1% for M, a yield of 97.3%, and a purity of 96.5% for DM.

[0063] Example 9

[0064] Turn on the reaction vacuum spray system and control the pressure inside the reactor to 40 kPaA through the nitrogen pressure control valve, and maintain the reaction temperature at 50℃; continuously add isopropanol and accelerator M slurry with a mass ratio of 6.0:1.0 to the reactor, and simultaneously add 10% hydrogen peroxide with a molar ratio of accelerator M and hydrogen peroxide of 2.0:1.1, and turn on the agitator and pump for circulation.

[0065] After the reaction is successful, the solution is continuously pumped into the reaction tank via a level control valve. Under these conditions, 1.3 parts of isopropanol (mass of M) can be recovered from the heat of reaction, with a conversion rate of 99.2% for M, a yield of 97.4%, and a purity of 96.6% for DM.

[0066] Comparative Example

[0067] In this comparative example, M is also used as the raw material, isopropanol, ethanol, methanol, benzene, etc. are used as solvents, hydrogen peroxide is used as the oxidant, and the reaction temperature is also 30–60℃. The difference is that the reaction is carried out under normal pressure, the reactor is cooled by cooling water through a jacket, and the solvent is recovered and recycled through a distillation column. See the apparatus structure below. Figure 2 and Figure 3 .

[0068] Because the reaction temperature is controlled by circulating water or chilled water through the reactor, existing heat transfer methods, whether using built-in or external coolers, tend to cause DM crystals generated during the reaction to form scale on the inner wall of the reactor or on the heat exchange tubes, resulting in poor heat transfer efficiency and necessitating shutdown for flushing and replacement. Furthermore, the use of indirect heat exchangers can lead to localized overheating, causing localized peroxidation during the reaction, resulting in numerous side reactions and high COD in the wastewater, reaching as high as 30,000 PPM.

[0069] At the same time, according to Figure 3 When the solvent is recovered through the distillation column 8, steam is required. The solvent vapor distilled from the top of the column is condensed by the condenser 9 and the subcooler 10 and then enters the reflux tank 11. The reflux tank 11 and the solvent tank 13 are connected by the reflux pump 12.

[0070] Based on the comparative examples and comparative embodiments, the results are as follows:

[0071] In terms of yield: the synthesis method of this invention can increase the product content to over 95%, the yield to over 97%, and the M conversion rate to over 99.0%, with extremely high raw material utilization and almost no waste generation. This is higher than the 95.5% product purity and 95% product yield achieved by the comparative example using a partitioned heat exchange synthesis method. The product purity of this invention is comparable to or even better than that of the comparative example, and it further improves the product yield, while also offering stable production and lower costs.

[0072] Regarding production stability: The synthesis reaction is carried out in a reactor without heat exchangers. The reactor body has no heat exchange tubes, effectively avoiding the problem of reduced heat transfer due to scaling, thus enabling continuous and stable production.

[0073] In terms of cost: The solvent vapor in this invention is condensed and cooled to 20-30°C before returning to the solvent recovery tank. This step effectively utilizes the heat of reaction to recover the solvent: the heat of reaction for DM is 1100-1200 kJ / kg, and the heat of solvent vaporization is approximately 900-1200 kJ / kg. During the reaction, 1.0-1.5 parts of solvent can be directly recovered using the heat of reaction, directly reducing energy costs by 200 yuan per ton of finished product. Utilizing the heat of reaction to recover part of the solvent reduces steam consumption during solvent recovery, thus lowering product energy consumption.

[0074] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method of synthesis of 2,2'-dithiobisbenzothiazole under negative pressure, characterized in that, It comprises the following steps: The reaction system is controlled at an absolute pressure of 20-45 kPa A, and the reaction temperature in the reactor is maintained at 30-60℃ under this pressure. 2-mercaptobenzothiazole slurry and oxidizing agent are reacted to synthesize 2,2'-dithiobisbenzothiazole by one-step method. The solvent vapor is condensed and returned to the solvent recovery tank, The reaction is carried out in a reaction kettle without heat exchanger; The oxidizing agent is hydrogen peroxide with a mass concentration of 10-40%, and the molar ratio between 2-mercaptobenzothiazole slurry and hydrogen peroxide is 2.0: (1.1-1.4); The 2-mercaptobenzothiazole slurry is a suspension formed by uniformly dispersing accelerator 2-mercaptobenzothiazole in an organic volatile solvent, and the mass ratio of the organic volatile solvent to the accelerator 2-mercaptobenzothiazole slurry is 2.0-6.0:1.0, The organic volatile solvent is selected from any one of ethanol, methanol, and isopropanol.

2. The method for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure according to claim 1, characterized in that: wherein The reaction kettle is provided with a magnetic stirrer.

3. The method for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure according to claim 1, characterized in that: wherein The absolute pressure of the reaction system is 30-40 kPa A.

4. The method for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure according to claim 1, characterized in that: wherein, N2 is used to control the pressure of the reaction system during the reaction.

5. The method for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure according to claim 1, characterized in that: wherein The solvent vapor is condensed and cooled to 20-30℃ before being returned to the solvent recovery tank.

6. An apparatus for carrying out the process for the synthesis of 2,2'-dithiobisbenzothiazole under negative pressure according to any one of claims 1 to 5, characterized in that: It comprises a reaction kettle, a condenser connected to the top of the reaction kettle, a gas-liquid separator connected to the bottom of the condenser, and a solvent recovery tank connected to the bottom of the gas-liquid separator; The reaction kettle is provided with a magnetic stirrer, a pressure control valve is arranged on the top, and a product storage tank is arranged on the bottom; the pressure control valve is connected to a nitrogen valve, and nitrogen is used to adjust the vacuum degree of the entire system; The top of the gas-liquid separator is connected to a vacuum spraying system.

7. The device for synthesizing 2,2'-dithiobisbenzothiazole under negative pressure according to claim 6, characterized in that: wherein The vacuum spraying system is a spraying tower matched with a water jet vacuum pump, and the limit vacuum degree of the vacuum pump is 18 kPa A.

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