Preparation method of fluoro aromatic compounds

Abstract

The invention discloses a preparation method of a fluoro aromatic compound, which comprises the following steps: (1) preparing arylamine hydrofluoride from hydrogen fluoride and arylamine in a ring reactor, and (2) enabling the arylamine hydrofluoride to flow into a diazotization ring reactor, and adding solid sodium nitrite into the diazotization ring reactor in proportion by a continuous feeder to carry out diazotization reaction; (3) transferring the diazotization product to carry out solid-liquid separation, and enabling the liquid to flow into a multi-stage pyrolysis annular reactor; (4) the multi-stage annular pyrolysis reactor comprises at least three stages of annular pyrolysis reactors, the pyrolysis temperature is gradually increased according to the inflow direction, and the temperature difference between the adjacent annular pyrolysis reactors is 3-10 DEG C; and (5) carrying out post-treatment to obtain the fluoro aromatic hydrocarbon compound. According to the method disclosed by the invention, the byproduct sodium bifluoride is recovered by solid-liquid separation of the diazonium liquid, and the tandem ring-shaped reactors can realize full-process automation, so that the reaction is accurately controlled, reliable, continuous and stable, few organic byproducts are generated, the yield is as high as 92% or above, and the purity is as high as 99.97%.

Description

Technical Field

[0001] The present invention relates to the technical field of pharmaceuticals, and particularly to a preparation method of fluoroaromatic compounds. Background Art

[0002] Fluoroaromatic compounds are an important type of basic raw materials. They can not only be used to synthesize pharmaceuticals (such as the main raw materials for preparing antipsychotic drugs trifluperidol, trifluperidol benzene, penfluridol, quinolone drugs - ciprofloxacin, etc.), pesticides (such as the fungicide fluxapyroxad), and dyes, but also can be further synthesized into fluoroaromatic derivatives through reactions such as nitration, chlorination, acylation, and reduction and applied to the above fields.

[0003] Fluorobenzene (abbreviated as fluorobenzene), as the simplest and most basic one in fluoroaromatic compounds, has also been developed in recent years for the identification of resin polymers, special engineering plastics, etc. In recent years, studies have shown that adding fluorobenzene to the electrolyte can improve battery performance such as the low-temperature characteristics, cycle characteristics, and storage characteristics of lithium-ion secondary batteries; driven by products such as smart phones, mobile power supplies, and tablet computers, the output value of the domestic lithium battery industry has continued to grow, making China a major and powerful global lithium battery producer; at the same time, the application of lithium-ion batteries is no longer limited to consumer electronics products, and the two new application directions of power and energy storage have brought unlimited market space for lithium batteries, which also makes the market demand for fluorobenzene increase rapidly. Conservatively estimated in the industry, the domestic and foreign market demand for fluorobenzene reaches 40,000 tons / year. The market demand for o-fluorotoluene, m-fluorotoluene, and p-fluorotoluene is about 20,000 tons / year, and the market demand for other small varieties of fluoroaromatic compounds such as 1-fluoronaphthalene is about 10,000 tons / year.

[0004] There are mainly three industrial production methods for fluoroaromatic compounds: the Balz-Schiemann method, the halogen exchange method, and the hydrogen fluoride method. The Balz-Schiemann method is a commonly used method in the production of fluoroaromatic compounds at present. However, it requires a large amount of tetrafluoroboric acid. During the thermal decomposition process, not only nitrogen gas is generated, but also strongly corrosive and toxic boron trifluoride gas is released. The environmental pollution is serious, and there are great potential safety hazards in the production process. At present, it is facing great pressure to be phased out. Compared with the Balz-Schiemann method, the halogen exchange method has simpler production operations and lower safety risks. However, it is only applicable to halogenated aromatic hydrocarbons containing strong electron-withdrawing groups on the benzene ring, and its application scope is narrow. The hydrogen fluoride method is an improvement of the Balz-Schiemann method. It avoids the use of tetrafluoroboric acid. Therefore, strong corrosive and toxic boron trifluoride gas is not generated during the thermal decomposition process, which improves the safety of the reaction and the environmental friendliness to a certain extent. The disadvantage is that an excessive amount of hydrogen fluoride is used in the reaction process. Due to the low boiling point, high volatility, high corrosivity, and high toxicity of hydrogen fluoride, there are still relatively large potential safety hazards and high depreciation costs of production equipment in the production process. Therefore, how to reduce the liquid holdup and unorganized volatilization amount of hydrogen fluoride in the production process, improve the safety of the production process, and reduce the depreciation cost of production equipment directly determines the application prospect and scope of the hydrogen fluoride method.

[0005] At present, the hydrogen fluoride method has been applied in the production of fluorobenzene. The process of producing fluorobenzene by the traditional hydrogen fluoride method is as follows: Aniline first forms a salt in hydrogen fluoride, and then undergoes a diazotization reaction with dry sodium nitrite. The reaction temperature is controlled at 0-5°C. After the reaction is completed, the diazonium salt solution is thermally decomposed below 40°C. After the thermal decomposition is completed, it is allowed to stand and layer. The separated organic layer is washed with water, washed with alkali, steam distilled, and rectified to obtain crude fluorobenzene. Finally, it is dehydrated with anhydrous calcium chloride to obtain the finished product of fluorobenzene, and the yield is about 83%. All processes are carried out in batch autoclave operation.

[0006] Compared with the fluorobenzene production method using fluoro boric acid, the traditional hydrogen fluoride method has the following advantages: less raw material consumption per unit product, short production process, less equipment investment, short return period, high reaction yield, good product quality (purity > 99%), etc. It has strong competitiveness and is the main method for industrial production of fluorobenzene at home and abroad at present.

[0007] However, due to the use of batch autoclave production mode, the traditional hydrogen fluoride method still has the following disadvantages:

[0008] 1) Poor production safety. First, during the production process, the holding amount of hydrogen fluoride is extremely large, up to 14 molar equivalents of the aniline raw material used. Hydrogen fluoride has characteristics such as low boiling point, high volatility, high corrosiveness, and high toxicity, resulting in significant potential safety hazards during the production process. Second, diazonium salts are very sensitive to heat, and nitrogen is generated during the thermal decomposition process. Coupled with the low boiling point and fast volatilization of hydrogen fluoride, if the temperature rises too quickly, the diazonium salts in the reaction kettle will decompose rapidly, generating a large amount of volatile gases, causing the system pressure to rise sharply, resulting in serious safety problems and even explosions.

[0009] 2) Low reaction yield. In the thermal decomposition stage, in order to control the thermal decomposition rate and ensure the orderly release of nitrogen, a step-by-step heating method is adopted. The entire thermal decomposition process of diazonium salts takes more than 30 hours. Under the long-term unstable heating conditions, about 7% of the diazonium salts hydrolyze to form by-products such as phenol, and about 10% undergo azo-coupling side reactions to synthesize toxic by-products such as aminobenzene azo compounds that are explosive and irritating to the eyes, skin, and respiratory system, resulting in a reaction yield of only about 83%.

[0010] 3) Large amount of three wastes and difficult to treat. During the long-term thermal decomposition process of diazonium salts, some diazonium salts undergo side reactions such as hydrolysis and polymerization, generating more tarry by-products. These tarry by-products will in turn affect the separation and recovery of fluorobenzene, hydrogen fluoride, etc., further increasing the generation of three wastes and ultimately forming a large amount of fluorine-containing hazardous solid waste, which is extremely difficult to treat.

[0011] 4) Poor production environment, not meeting the requirements of EHS. Due to the use of an intermittent kettle production method, it is impossible to achieve good sealing during the production process, and it is impossible to avoid the volatilization of hydrogen fluoride, which causes great harm to the health of operating workers and the surrounding environment and ecological safety. Long-term inhalation of low-concentration hydrogen fluoride by humans can cause chronic poisoning, vomiting, dizziness and other symptoms. When the HF concentration is greater than 30 μg / m 3 it can cause acute poisoning, and hydrogen fluoride in the atmosphere can also cause a reduction in the yield of fruit trees and crops such as ginkgo, apples, barley, corn, and rice.

[0012] In order to overcome the deficiencies existing in the production of fluorobenzene by the traditional batch kettle hydrogen fluoride method, CN110283039A discloses the use of a tubular reactor for the thermal decomposition reaction of diazonium salts to replace the traditional kettle thermal decomposition reaction. However, due to the poor heat exchange effect of the tubular reactor, in order to avoid the accumulation of reaction heat, only a small amount of slow feeding can be used to overcome it, resulting in an annual output of less than 300 tons per single set of equipment (calculated according to the continuous operation of the production equipment for 365 days per year), which is difficult to meet the market demand for 40,000 tons / year of fluorobenzene; carrying out the thermal decomposition at a high temperature controlled at 75-85°C is extremely likely to cause the reaction to get out of control, resulting in equipment explosion, casualties, and serious environmental and ecological pollution caused by material leakage, and it is also unable to well overcome the occurrence of side reactions such as hydrolysis and polymerization, and the reaction stability is also poor; in addition, the salt-forming reaction of aniline and hydrogen fluoride and the diazotization reaction still use the batch kettle process, so the improvement of the process for producing fluorobenzene by the hydrogen fluoride method is limited. CN111116303A discloses that on the basis of the above technology, using nitrosyl sulfuric acid as the diazotizing reagent and a microchannel reactor made of silicon carbide, a continuous diazotization reaction of the hydrofluoric acid solution of aniline hydrogen fluoride salt and nitrosyl sulfuric acid is realized. The diazotization reaction solution then enters the pyrolyzer, and finally a series of post-treatments are carried out to obtain fluorobenzene. This technology uses a silicon carbide microchannel reactor in the diazotization reaction stage to solve the continuous problem of the diazotization reaction, and has a relatively large improvement compared with the traditional batch kettle hydrogen fluoride method production process. However, calculated according to the diazotization of feeding the prepared aniline hydrogen fluoride solution into the microchannel reactor at a speed of 0.7 kg / min for diazotization, the annual output of fluorobenzene per single set of equipment is less than 80 tons (calculated according to the continuous operation of the production equipment for 300 days per year), and there is a huge gap with the annual market demand for 40,000 tons of fluorobenzene; moreover, the thermal decomposition reaction of benzene diazonium salt still uses a tubular reactor, and there are still similar defects to those of using a tubular reactor for the thermal decomposition of diazonium salts in CN110283039A, and the post-treatment still uses the traditional batch method, only realizing partial improvement of the production process of the batch kettle hydrogen fluoride method, and not fundamentally solving the drawbacks existing in the preparation of fluorobenzene by the hydrogen fluoride method.

[0013] CN112608212A discloses a fully continuous flow synthesis process for fluorinated aromatic compounds. Since the three main reactions involved in the entire production process are carried out in a microchannel reactor, namely: 1) the salt formation reaction of arylamine and hydrogen fluoride, in which the preheated arylamine and hydrogen fluoride are introduced into the microchannel reactor C for salt formation reaction to form a hydrofluoric acid solution of arylamine hydrogen fluoride salt; 2) the diazotization reaction of arylamine hydrogen fluoride salt, the hydrofluoric acid solution of arylamine hydrogen fluoride salt flows out from the outlet of the microchannel reactor C and enters the microchannel reactor E for diazotization reaction to obtain a hydrofluoric acid solution of the corresponding aryl diazonium salt; 3) the hydrofluoric acid solution of aryl diazonium salt flows out from the outlet of the microchannel reactor E and enters the microchannel reactor F. In the microchannel reactor F, the aryl diazonium salt undergoes thermal decomposition reaction to generate a mixture composed of the corresponding fluorinated aromatic hydrocarbon, hydrofluoric acid, sulfuric acid, nitrogen, etc. This makes the production of fluorinated aromatic compounds using the process disclosed in CN112608212A have good production safety, and can achieve full-process continuous production and automatic control. On the one hand, the thermal decomposition of aryl diazonium salt in the microchannel is carried out at high temperature, resulting in a sulfonation ratio of aniline or the generated fluorobenzene as high as 10-14%, and the hydrolysis of aryl diazonium salt produces aryl phenol by-products accounting for up to 18-20%; on the other hand, due to the objective characteristic of the small feed rate per unit time of the microchannel reactor, even if calculated according to the maximum flow rate of arylamine of 100 g / min, the corresponding fluorinated aromatic hydrocarbon prepared by a single set of equipment is only 60 tons / year (calculated according to the continuous operation of the production equipment for 365 days per year), which far cannot meet the market demand for important products such as fluorobenzene of 40,000 tons / year. Moreover, the diazotization reactions disclosed in CN111116303A and CN112608212A both use a sulfuric acid solution of nitrosylsulfuric acid as the diazotization raw material. Since the content of commercially available nitrosylsulfuric acid is only 40%, a large amount of sulfuric acid will inevitably be brought in. According to the weight ratio, the amount of nitrosylsulfuric acid used is 4.6 times that of sodium nitrite, which will inevitably occupy more than 40% of the production equipment space capacity, seriously reduce the equipment utilization rate, and increase a large amount of energy consumption. After the reaction, the concentration of sulfuric acid is greatly increased (above 90%). Although the obtained diazo solution does not contain sodium ions and there is no problem of blocking the pipeline due to the precipitation of by-product sodium fluoride as a solid, it is convenient for downstream application in the thermal decomposition reaction to prepare the corresponding fluorinated aromatic hydrocarbon. However, the applicant has tried this diazotization method many times and found that more than 20% of fluorobenzene undergoes sulfonation reaction to obtain by-products of o-fluorobenzenesulfonic acid or p-fluorobenzenesulfonic acid with sulfonation at the ortho or para position during diazotization. The formation of sulfonation by-products also conforms to the organic chemistry electrophilic reaction mechanism from the reaction conditions: as diazotization proceeds, nitrosylsulfuric acid will be consumed and more and more sulfuric acid will be generated, and it is sulfuric acid with a relatively high concentration (no additional water is added in this diazotization reaction). It is easy to obtain sulfonation by-products from the higher concentration of sulfuric acid generated in the diazotization reaction and fluorinated aromatic hydrocarbons. The formation of sulfonation by-products will greatly reduce the preparation yield of the target fluorinated aromatic hydrocarbon, increase the generation and treatment cost of organic solid waste.

[0014] Based on the current preparation methods or processes of fluorinated aromatic compounds, it is not difficult to find that a preparation method that can achieve continuous full-process production and automated control, whose production capacity can meet market demand, has few side reactions, and can prepare the target fluorinated aromatic compounds with high yield, is still expected in this field. Summary of the Invention

[0015] Objective of the Invention

[0016] To overcome the above deficiencies, the purpose of the present invention is to provide a method for preparing fluorinated aromatic compounds. The method of the present invention for preparing fluorinated aromatic compounds using a circular reactor. After preparing the diazonium salt, the reaction system contains approximately 20% by weight of solid sodium bifluoride, and it is difficult to achieve continuous gas-liquid-solid (sodium bifluoride is solid in the reaction, nitrogen gas is generated during pyrolysis, and the reaction solution is liquid) three-phase synthesis of fluorinated aromatic compounds. We adopted an innovative approach of first filtering sodium bifluoride; using a circular reactor can greatly increase the heat exchange area and enhance the production capacity of the equipment. Compared with an intermittent tank reactor, the production capacity of the same volume of reaction equipment is increased by 4-5 times. Multiple circular reactors are connected in series to achieve continuous flow operation. An operation of one process section is realized on each fixed piece of equipment, strengthening the function allocation, and through multi-stage pyrolysis reactions, the pyrolysis effect is better and it is easier to achieve precise automated control.

[0017] Solution

[0018] To achieve the purpose of the present invention, the technical solution adopted by the present invention is as follows:

[0019] On the one hand, the present invention provides a method for preparing fluorinated aromatic compounds, which includes:

[0020] (1) Hydrogen fluoride and aromatic amine form an aromatic amine hydrogen fluoride salt in a circular reactor, wherein the structural formula of the aromatic amine is as shown in Formula I

[0021]

[0022] R1 to R5 are each independently selected from H, halogen, a straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms, or a straight-chain or branched-chain alkoxy group having 1 to 5 carbon atoms;

[0023] (2) The aromatic amine hydrogen fluoride salt obtained in step (1) flows into a diazotization circular reactor, and solid sodium nitrite is added in proportion by a continuous feeder for diazotization reaction;

[0024] (3) The diazotization product obtained in step (2) is separated into solid and liquid, and the liquid flows into a multi-stage pyrolysis circular reactor;

[0025] (4) The multi-stage pyrolysis annular reactor includes at least three-stage pyrolysis annular reactors. In the inflow direction, the pyrolysis temperature increases step by step, and the temperature difference between adjacent pyrolysis annular reactors is 3 - 10 °C, and the temperature of the pyrolysis annular reactor is not higher than 60 °C;

[0026] (5) After the pyrolysis reaction, the temperature is lowered, and post-treatment is carried out to obtain fluoroaromatic compounds.

[0027] Further, in step (1), R1 - R5 are each independently selected from H, halogen, a straight-chain or branched-chain alkyl group having 1 - 3 carbon atoms, or a straight-chain or branched-chain alkoxy group having 1 - 3 carbon atoms. Optionally, R1 - R5 are each independently selected from a hydrogen group, chlorine, methyl, ethyl, methoxy, and ethoxy;

[0028] Further, the aromatic amine is selected from one of aniline, o-methylaniline, m-methylaniline, p-methylaniline, o-ethylaniline, m-ethylaniline, p-ethylaniline, 3-chloro-2-methylaniline, 5-chloro-2-methylaniline, 2,3-dimethylaniline, 2,4-dimethylaniline, 2,5-dimethylaniline, 2,6-dimethylaniline, 3,4-dimethylaniline, 3,5-dimethylaniline, 2,3,4-trimethylaniline, 2,3,5-trimethylaniline, 2,3,6-trimethylaniline, 2,4,5-trimethylaniline, 2,4,6-trimethylaniline, 3,4,5-trimethylaniline, 2,3,4,5-tetramethylaniline, 2,3,5,6-tetramethylaniline, 2,3,4,6-tetramethylaniline, pentamethylaniline, and p-methoxyaniline; Correspondingly, the fluoroaromatic compounds include one of fluorobenzene, o-methylfluorobenzene, m-methylfluorobenzene, p-methylfluorobenzene, o-ethylfluorobenzene, m-ethylfluorobenzene, p-ethylfluorobenzene, 3-chloro-2-methylfluorobenzene, 5-chloro-2-methylfluorobenzene, 2,3-dimethylfluorobenzene, 2,4-dimethylfluorobenzene, 2,5-dimethylfluorobenzene, 2,6-dimethylfluorobenzene, 3,4-dimethylfluorobenzene, 3,5-dimethylfluorobenzene, 2,3,4-trimethylfluorobenzene, 2,3,5-trimethylfluorobenzene, 2,3,6-trimethylfluorobenzene, 2,4,5-trimethylfluorobenzene, 2,4,6-trimethylfluorobenzene, 3,4,5-trimethylfluorobenzene, 2,3,4,5-tetramethylfluorobenzene, 2,3,5,6-tetramethylfluorobenzene, 2,3,4,6-tetramethylfluorobenzene, pentamethylfluorobenzene, and p-methoxyfluorobenzene.

[0029] Further, the flow rate ratio of hydrogen fluoride to aromatic amine is (2 - 5):1, optionally (2 - 3):1;

[0030] Further, the salt-forming temperature is -5 - 5 °C, optionally 2 - 5 °C.

[0031] Further, in step (2), the flow rate ratio of the aromatic amine hydrogen fluoride salt to solid sodium nitrite is (2 - 5):1, optionally (2 - 3):1;

[0032] And / or, in step (2), the diazotization reaction is that the arylamine hydrogen fluoride salt and solid sodium nitrite enter the diazotization annular reactor simultaneously in proportion for mixing and reaction, and the diazotization reaction solution flows out from the overflow port of the diazotization annular reactor and then enters the solid-liquid separation device; optionally, the position of the overflow port is 65% - 90% of the reactor height, and optionally 70 - 80%.

[0033] And / or, the diazotization reaction temperature is -5 to 5°C, and preferably 2 - 5°C.

[0034] Furthermore, in step (3), the separated solid includes sodium hydrogen fluoride, and sodium bifluoride can be sold externally or made into other fluorine-containing inorganic salts for sale.

[0035] Furthermore, the liquid diazo solution enters the intermediate tank of the diazo solution.

[0036] Furthermore, in step (4), the temperature of the first-stage pyrolysis annular reactor in the pyrolysis annular reactor is not lower than 8°C; optionally, the temperature of the pyrolysis annular reactor is not higher than 50°C.

[0037] Furthermore, the pyrolysis annular reactor includes: at least four, at least five, at least six, at least seven, at least eight or at least nine pyrolysis annular reactors;

[0038] Furthermore, the temperature difference in each stage of the pyrolysis annular reactor is controlled within ±3°C or ±2°C;

[0039] Furthermore, the temperature difference between adjacent pyrolysis annular reactors is 5 - 10°C;

[0040] Furthermore, the flow rate of the diazo solution entering the first-stage pyrolysis annular reactor is 0.015 - 25 kg / min, which can be adjusted according to the specifications of the annular reactor.

[0041] Furthermore, in step (5), the material enters the receiving kettle from the pyrolysis annular reactor for cooling, and the temperature is cooled to -5 to 5°C;

[0042] Furthermore, the post-treatment includes: extraction, alkali washing and distillation.

[0043] Furthermore, anti-corrosion linings are used inside all reactors;

[0044] Furthermore, each reactor is connected by a connecting pipe, and optionally, the connecting pipe is made of polytetrafluoroethylene material pipe;

[0045] Furthermore, a silicon carbide heat exchanger resistant to hydrogen fluoride corrosion is used for low-temperature maintenance or cooling.

[0046] Furthermore, the annular reactors in steps (1), (2) and / or (3) are each provided with an overflow port for material overflow. Optionally, the position of the overflow port is 65% - 80% of the reactor height, optionally 70 - 80%.

[0047] Since the reaction kettle in the old process for producing fluorobenzene was made of Q235 material, the reaction kettle was severely corroded by hydrogen fluoride. The coil inside the kettle needed to be replaced every 3 - 5 months, and the reaction kettle had to be replaced once a year. At the same time, during the production process, it was easy for the reaction kettle or the coil to be corroded and penetrated, resulting in the cooling water in the jacket or the coil entering the reaction system and causing serious accidents. Using an annular reactor can achieve complete anti-corrosion of the equipment. The reaction kettle body is lined with anti-corrosion material, the connecting pipes are made of polytetrafluoroethylene pipes, and the cooling is achieved by using a silicon carbide heat exchanger resistant to hydrogen fluoride corrosion, thus ensuring the safe, stable and continuous operation of the overall production equipment.

[0048] A specific implementation method of the present invention can be (taking the preparation of fluorobenzene as an example): 1. Hydrogen fluoride and aniline are continuously pumped into the salt-forming annular reactor from the storage tank through metering pumps at the same time in proportion, and the reaction temperature is maintained at -5 - 5°C. 2. The hydrogen fluoride solution of aniline hydrogen fluoride salt flowing out from the overflow port of the salt-forming annular reactor enters the feed port of the diazotization annular reactor, and at the same time, solid sodium nitrite is continuously added in proportion by the feeder for diazotization, and the reaction temperature is maintained at -5 - 5°C. 3. When the liquid level of the diazotization annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the material overflows into the three-in-one filtration device, and after filtration and solid-liquid separation, the solid-free diazonium solution flows into the intermediate storage tank. 4. The sodium hydrogen fluoride after solid-liquid separation in step 3 is rinsed, neutralized, filtered, and reacts with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity. 5. The diazonium salt solution in the intermediate storage tank of the diazonium salt is pumped into the first-stage thermal decomposition annular reactor by a metering pump, and the temperature is controlled at 10 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the second-stage thermal decomposition annular reactor. 6. Control the temperature in the second-stage thermal decomposition annular reactor at 15 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the third-stage thermal decomposition annular reactor. 7. Control the temperature in the third-stage thermal decomposition annular reactor at 20 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the fourth-stage thermal decomposition annular reactor. 8. Control the temperature in the fourth-stage thermal decomposition annular reactor at 25 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the fifth-stage thermal decomposition annular reactor. 9. Control the temperature in the fifth-stage thermal decomposition annular reactor at 30 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the sixth-stage thermal decomposition annular reactor. 10. Control the temperature in the sixth-stage thermal decomposition annular reactor at 35 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the seventh-stage thermal decomposition annular reactor. 11. Control the temperature in the seventh-stage thermal decomposition annular reactor at 40 ± 2°C. When the material in the reactor is higher than the specified liquid level, the material is transferred to the eighth-stage thermal decomposition annular reactor. 12. Control the temperature in the eighth-stage thermal decomposition annular reactor at -5 - 5°C. At this time, the thermal decomposition is completed. 13. When the material in the eighth-stage thermal decomposition annular reactor is higher than the specified liquid level, the material is transferred to the centrifugal extractor for separation; the separated organic phase is crude fluorobenzene, which is continuously washed and extracted with alkali. The alkali solution is recycled to the circulation tank, and the fluorobenzene is sent to the distillation device for distillation to obtain pure fluorobenzene with a content of 99.97% and a yield as high as 95 - 98%; the inorganic phase enters the hydrogen fluoride recovery storage tank, and after being sent for distillation and purification, anhydrous hydrogen fluoride (content 99.87%) is obtained for reuse, and the hydrofluoric acid with a content of 55% is cooled and packaged for external sale. As described above, through the continuous flow stepwise thermal decomposition process realized by using the annular reactor provided by the present invention, it is possible to achieve safe, precise control, reliable, continuous, stable production of fluorobenzene with few organic by-products, high yield, high purity, and large scale.

[0049] In the existing process, hydrogen fluoride containing sodium bifluoride reacts with sulfuric acid to recover hydrogen fluoride, while generating solid waste sodium bisulfate and waste sulfuric acid solution containing a large amount of azo compounds. The harmless treatment is difficult and costly, and it is easy to cause great damage to the environment. The preparation method provided by the present invention avoids generating solid waste sodium bisulfate and waste sulfuric acid solution containing a large amount of azo compounds. At the same time, the fluorinated salt produced after treatment can reach the 98% content standard and be sold as a product, achieving better economic and environmental benefits. The preparation method provided by the present invention feeds the hydrogen fluoride solution of aniline hydrogen fluoride salt and sodium nitrite simultaneously, ensuring that the diazotization reaction always proceeds in an environment maintaining nitrous acid, and avoiding a large number of coupling side reactions caused by the lack of nitrous acid environment when sodium nitrite is added at a high concentration of aniline hydrogen fluoride salt in the batch reaction. The preparation method provided by the present invention uses a 7-stage series connection for the pyrolysis of diazonium salts, controlling the corresponding temperature at each stage, precisely strengthening the function distribution, thereby realizing precise automatic control, reliable, continuous, stable production of fluorobenzene with few organic by-products, high yield, high purity, and on a large scale. The annular reactor adopted in the preparation method of the present invention has a strong double-mixing function, which can achieve a large proportion of pyrolysis at low temperature, not only greatly reducing the proportion of phenol by-products formed by hydroxyl groups occupying fluorine positions during high-temperature pyrolysis; at the same time, feeding in proportion simultaneously results in very few coupling side reactions of diazonium compounds, and the yield is greatly improved.

[0050] Advantageous Effects

[0051] The method for preparing fluorinated aromatic compounds by using an annular reactor according to the present invention has the following positive effects: It can achieve safe, precise control, reliable, continuous, stable production with few organic by-products, a yield of more than 92%, a purity of up to 99.97%, and large-scale production of fluoroaromatics (calculated based on 300 days, the annual output of fluorobenzene per single set of equipment can reach 2,500 tons); the by-product sodium bifluoride can be comprehensively utilized after treatment and sold as industrial-grade fluorinated salts with a large market demand. The hydrofluoric acid solution separated from the reaction solution can be recycled to obtain anhydrous hydrogen fluoride with a purity of up to 99.87% for reuse, and hydrofluoric acid with a content of 55% can be sold externally. The amount of three wastes is only 0.15 tons per ton of product (taking fluorobenzene as an example), and the economic and environmental benefits are remarkable. Description of the Drawings

[0052] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. The special word "exemplary" here means "serving as an example, embodiment, or illustration". Any embodiment illustrated as "exemplary" here does not have to be interpreted as superior to or better than other embodiments.

[0053] Figure 1It is the GC chromatogram of the crude fluorobenzene in Example 1 of the present invention; among them, the peak at 3.218 min is fluorobenzene, the peak at 6.734 min is phenol, and the peak at 10.700 is p-aminoazobenzene.

[0054] Figure 2 It is the GC chromatogram of the fluorobenzene product obtained after rectification in Example 1 of the present invention; among them, the peak at 3.212 min is fluorobenzene.

[0055] Figure 3 It is the GC chromatogram of the analysis sample in Comparative Example 1, where the peak at 0.602 min represents the sulfonation by-product fluorobenzenesulfonic acid by-product.

[0056] Figure 4 It is the mass spectrum of the analysis sample in Comparative Example 1. Detailed implementation manners

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0058] In addition, for better illustration of the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can also be implemented without some specific details. In some embodiments, raw materials, components, methods, means, etc. well-known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0059] Unless otherwise clearly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "having" etc. will be understood to include the stated elements or components, without excluding other elements or other components.

[0060] In the following embodiments, the annular reactor, intermediate tank, etc. can be obtained commercially or from the public literature. The annular reactor can achieve directional and regular circulating flow, mixing, mass transfer, heat transfer and chemical reactions during the flow, and has good heat transfer performance. The annular reactors of different levels have similar structures, and the names are used to distinguish them in order to achieve the corresponding reactions. For example, the diazotization annular reactor is for the diazotization reaction, and any annular reactor that can achieve this function can achieve the invention purpose of the present invention.

[0061] In the following examples, raw materials such as hydrogen fluoride, aniline, p-toluidine, and solid sodium nitrite are all commercially available products. The purity of hydrogen fluoride is 99.8%, the purity of aniline is 99%, the purity of p-toluidine and m-toluidine is 99.5%, the purity of o-toluidine and 3,5-dimethylaniline is 99%, the purity of 3-chloro-2-methylaniline is 98%, and the purity of solid sodium nitrite is 98%.

[0062] The following detection methods (GC, mass spectrometry, etc.) are conventional detection methods.

[0063] Example 1

[0064] This example is for the fully continuous flow synthesis of fluorobenzene, and the specific steps are as follows:

[0065] (1) After being metered by metering pumps respectively, hydrogen fluoride and aniline are simultaneously pumped into a salt-forming annular reactor (specification 5m 3 ); the flow rate of hydrogen fluoride is controlled at 13.75 kg / min; the flow rate of aniline is controlled at 5.5 kg / min; the temperature of the salt-forming annular reactor is controlled at -5 - 5°C, and a hydrogen fluoride solution of aniline hydrogen fluoride salt is obtained through the salt-forming reaction.

[0066] (2) When the liquid level of the salt-forming annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the hydrogen fluoride solution of aniline hydrogen fluoride salt overflows into a diazotization annular reactor (specification 5m 3 ), and at the same time, solid sodium nitrite is added by a continuous feeder at 4.125 kg / min. The temperature of the diazotization annular reactor is controlled at -5 - 5°C.

[0067] (3) When the liquid level of the diazotization annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the material overflows into a three-in-one filtration device. After filtration and solid-liquid separation, the solid-free diazonium solution is pumped into a primary pyrolysis annular reactor by a metering pump at 19.25 kg / min.

[0068] (4) The sodium hydrogen fluoride after solid-liquid separation in step (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0069] (5) After the primary pyrolysis annular reactor, it overflows into the second to seventh pyrolysis annular reactors in sequence to complete the pyrolysis reaction through sequential temperature increase. The temperature control of each pyrolysis annular reactor is as follows: the primary pyrolysis annular reactor is controlled at 10°C ± 2, the secondary pyrolysis annular reactor is controlled at 15°C ± 2, the tertiary pyrolysis annular reactor is controlled at 20°C ± 2, the quaternary pyrolysis annular reactor is controlled at 25°C ± 2, the quinary pyrolysis annular reactor is controlled at 30°C ± 2, the senary pyrolysis annular reactor is controlled at 35°C ± 2, and the septenary pyrolysis annular reactor is controlled at 40°C ± 2. The reaction mixture flowing out of the seventh pyrolysis annular reactor enters the receiving kettle, and the temperature of the receiving kettle is controlled at -5 - 5°C.

[0070] (6) After the pyrolysis is completed, the organic-inorganic mixture enters a high-speed centrifugal extractor directly due to the specific gravity difference of 0.2 g / mL to separate the organic phase from the inorganic phase. The inorganic phase is 85% hydrofluoric acid and enters the intermediate storage tank of hydrogen fluoride (10 m 3 ). After concentration and rectification treatment, hydrogen fluoride with a content of 99.87% is recovered and reused in product production. The rectification residue is 55% hydrofluoric acid, which can be sold externally or used to produce other inorganic fluorine salts. For every ton of 85% recovered hydrofluoric acid, 666 kg of 99.87% hydrogen fluoride and 334 kg of 55% hydrofluoric acid can be recovered; the organic phase is crude fluorobenzene. The phenol in the crude product is extracted with an alkali solution (30% sodium hydroxide solution) and the entrained hydrofluoric acid is neutralized. The fluorobenzene after alkali washing treatment is collected in the intermediate storage tank (10 m 3 ). Then it enters the rectification system, and the fraction with a boiling point of 84 - 85 °C is collected at atmospheric pressure to obtain the rectified product of fluorobenzene. The purity is 99.9% by GC detection (see Figure 2 ), which is a qualified product. When the concentration of the extraction alkali solution is lower than the limit (sodium hydroxide content 3%), it is replaced. The discharged waste alkali solution is neutralized with sulfuric acid to separate the organic phase of phenol, and phenol with a purity of 99% is obtained by distillation for product sales; the inorganic phase is a mixture of sodium sulfate and NaF. First, NaF crystals are separated by water recrystallization, and the mother liquor is concentrated, crystallized, and recrystallized three times to obtain sodium sulfate with a purity of 99.2% for product sales.

[0071] After the above steps, continuous salification, diazotization, and seven-stage pyrolysis are carried out. Sampling the crude fluorobenzene from the receiving kettle for GC detection shows that the aniline conversion rate reaches 97.879%, p-aminophenylazobenzene is 0.884%, and the phenol content is 1.186% (see details in Figure 1 ). The fraction at 84 - 85 °C can be preliminarily verified as fluorobenzene according to the boiling point, and the purity is 99.97% by GC detection (see Figure 2 ), which is consistent with the peak position of the GC spectrum of commercially available fluorobenzene (fluorobenzene peaks at about 3.2 min).

[0072] For the continuous flow synthesis process of fluorobenzene using a ring reactor in this example, from the start of feeding to the commissioning and stabilization, it takes 33 hours. Starting from the completion of commissioning, it runs stably for 150 hours, and the results are summarized as follows: A total of 49.5 tons of aniline, 123.75 tons of hydrogen fluoride, and 37.125 tons of sodium nitrite are consumed, and 47.21 tons of fluorobenzene finished products are obtained, with a yield of 92.39% and a purity of 99.97%. From this, it is calculated that a single set of equipment can produce 2757 tons of fluorobenzene annually (calculated based on 365 days of production in a year).

[0073] Example 2:

[0074] This example is the full continuous flow synthesis of fluorobenzene, and the specific steps are as follows:

[0075] (1) Hydrogen fluoride and aniline are respectively metered by metering pumps and then simultaneously pumped into a salt-forming annular reactor (specification: 20 L); the flow rate of hydrogen fluoride is controlled at 100 g / min; the flow rate of aniline is controlled at 40 g / min; the temperature of the salt-forming annular reactor is controlled at -5 - 5 °C, and a hydrogen fluoride solution of aniline hydrogen fluoride salt is obtained through a salt-forming reaction.

[0076] (2) When the liquid level of the salt-forming annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the hydrogen fluoride solution of aniline hydrogen fluoride salt overflows into the diazotization annular reactor, and at the same time, solid sodium nitrite (purity 98%) is added at 30 g / min by a continuous feeder, and the temperature of the diazotization annular reactor is controlled at -5 - 5 °C.

[0077] (3) When the liquid level of the diazotization annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the material overflows into the filtering device, and after solid-liquid separation by filtration, the solid-free diazonium solution is pumped into a primary pyrolysis annular reactor (specification: 20 L) at 140 g / min by a metering pump.

[0078] (4) The sodium hydrogen fluoride after the solid-liquid separation in (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0079] (5) After the primary pyrolysis annular reactor, it then enters the secondary to quaternary pyrolysis annular reactors in sequence to complete the pyrolysis reaction through sequential temperature increase. The temperature control of each pyrolysis annular reactor is as follows: the primary pyrolysis annular reactor is controlled at 10 ± 2 °C, the secondary pyrolysis annular reactor (specification: 20 L) is controlled at 20 ± 2 °C, the tertiary pyrolysis annular reactor (specification: 20 L) is controlled at 30 ± 2 °C, the quaternary pyrolysis annular reactor (specification: 20 L) is controlled at 40 ± 2 °C. The reaction mixture flowing out of the quaternary pyrolysis annular reactor enters the receiving kettle, and the temperature of the receiving kettle is controlled at -5 - 5 °C. Among them, the diazonium solution is pumped into the primary pyrolysis annular reactor at 104 g / min for reaction. After the liquid level reaches 70% of the reactor height, it overflows into the sequentially temperature-increasing pyrolysis annular reactors at all levels in sequence to complete the pyrolysis reaction and is collected into the receiving kettle.

[0080] After the above steps, continuous salt formation, diazotization, and quaternary pyrolysis are carried out. The crude fluorobenzene after pyrolysis is sampled from the receiving kettle for GC detection. The aniline conversion rate reaches 96.33%, the content of p-aminophenyl azobenzene is 0.987%, and the phenol content is 2.52%. Refer to step (6) of Example 1 for post-treatment. The fraction at 84 - 85 °C can be preliminarily verified as fluorobenzene according to the boiling point, and the GC detection purity is 99.92%, which is consistent with the peak positions of the GC spectrum of commercially available fluorobenzene.

[0081] In the continuous flow synthesis process of the fluorobenzene annular reactor in this example, it took 30 hours from the start of feeding to the stable commissioning. Starting from the completion of the commissioning, it ran stably for 300 hours, and the results are summarized as follows: A total of 576 kg of aniline, 1440 kg of hydrofluoric acid, and 482 kg of sodium nitrite were consumed, and 558 kg of fluorobenzene finished products were obtained, with a yield of 94.23% and a purity of 99.92%. From this, it is calculated that a single set of this 20L small annular reactor can produce 16.29 tons of fluorobenzene (purity 99.92%, calculated based on 365 days of production per year).

[0082] Example 3:

[0083] This example is the full continuous flow synthesis of fluorobenzene. The difference from Example 2 is that steps (1), (2), and (3) are the same, the treatment method in step (6) is similar, and steps (4) and (5) are different:

[0084] The flow rate of the pump into the primary pyrolysis annular reactor in step (4) is 83.2 g / min;

[0085] In step (5), after the primary annular reactor, it enters the secondary pyrolysis annular reactor to complete the pyrolysis reaction through sequential temperature increase. The temperature control of each pyrolysis annular reactor is as follows: the temperature control of the primary pyrolysis annular reactor is 10 ± 2 °C, the temperature control of the secondary pyrolysis annular reactor is 40 ± 2 °C, and the temperature control of the tertiary receiving kettle is -5 - 5 °C. The diazonium solution is pumped into the primary annular reactor at 100 g / min and then sequentially enters to complete the pyrolysis reaction through sequential temperature increase.

[0086] After the above steps, continuous salification, diazotization, and secondary pyrolysis are carried out. The crude fluorobenzene after pyrolysis is sampled for GC detection. The conversion rate reaches 90.95%, the content of p-aminophenyl azobenzene is 1.06%, and the content of phenol is 7.06%. Refer to step (6) of Example 1 for post-treatment. The fraction at 84 - 85 °C can be preliminarily verified as fluorobenzene according to the boiling point, and the GC purity is 99.95%, which is consistent with the peak position of the GC spectrum of commercially available fluorobenzene.

[0087] In the continuous flow synthesis process of the fluorobenzene annular reactor in this example, it took 24 hours from the start of feeding to the stable commissioning. Starting from the completion of the commissioning, it ran stably for 300 hours, and the results are summarized as follows: A total of 461 kg of aniline, 1152 kg of hydrofluoric acid, and 346 kg of sodium nitrite were consumed, and 418 kg of fluorobenzene finished products were obtained, with a yield of 87.84% and a GC purity of 99.95%.

[0088] It can be seen from this that the temperature gradient amplitude during pyrolysis has a great influence on the conversion rate. A slower increase rate has a significant effect on improving the conversion rate of the product and reducing side reactions. When the heating rate is faster, side reactions increase significantly. The impurities generated by side reactions cause losses in neutralization distillation during the post-treatment process of the product purification, resulting in a significant reduction in the yield. Considering the equipment investment and the impact of too many cascades on the equipment operation efficiency, the number of cascades of the pyrolysis annular reactor is preferably 5-10 levels.

[0089] Example 4:

[0090] This example is for the fully continuous flow synthesis of p-fluorotoluene. The specifications of the following annular reactor are 20L, and the limit position is 70% of the height of the reactor. The specific steps are as follows:

[0091] (1) Hydrogen fluoride and p-methylaniline are respectively metered by metering pumps and then simultaneously pumped into the salt-forming annular reactor. The flow rate of hydrogen fluoride is controlled at 100 g / min; the flow rate of p-methylaniline pumped into the salt-forming annular reactor after being metered by the metering pump is controlled at 46 g / min; the temperature of the salt-forming annular reactor is controlled at -5 - 5°C, and the hydrogen fluoride solution of p-methylaniline hydrogen fluoride salt is obtained through the salt-forming reaction.

[0092] (2) When the liquid level of the salt-forming annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the hydrogen fluoride solution of p-methylaniline hydrogen fluoride salt overflows into the diazotization annular reactor, and at the same time, solid sodium nitrite is added at a rate of 30 g / min by a continuous feeder. The temperature of the diazotization annular reactor is controlled at -5 - 5°C.

[0093] (3) When the liquid level of the diazotization annular reactor reaches the overflow port limit (for example, 70% of the height of the reactor), the material overflows into the filtration device. After solid-liquid separation by filtration, the solid-free diazonium solution is pumped into the first-stage pyrolysis annular reactor (specification 20L) by a metering pump at a rate of 136 g / min.

[0094] (4) The sodium fluoride after the solid-liquid separation in (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0095] (5) After the first-stage pyrolysis annular reactor, it enters the second to seventh-stage pyrolysis annular reactors to complete the pyrolysis reaction by stepwise heating. The temperature control of each stage of the pyrolysis annular reactor is as follows: the first-stage pyrolysis annular reactor is controlled at 20 ± 2°C, the second-stage pyrolysis annular reactor is controlled at 25 ± 2°C, the third-stage pyrolysis annular reactor is controlled at 30 ± 2°C, the fourth-stage pyrolysis annular reactor is controlled at 35 ± 2°C, the fifth-stage pyrolysis annular reactor is controlled at 40 ± 2°C, the sixth-stage pyrolysis annular reactor is controlled at 45 ± 2°C, and the seventh-stage pyrolysis annular reactor is controlled at 50 ± 2°C. The reaction mixture flowing out of the seventh-stage pyrolysis annular reactor enters the receiving kettle, and the temperature of the receiving kettle is controlled at -5 - 5°C.

[0096] (6) After the pyrolysis is completed, the organic and inorganic mixture enters a high-speed centrifugal extractor for separation due to a specific gravity difference of 0.2 g / mL. The inorganic phase, which is 85% hydrofluoric acid, enters the intermediate storage tank for hydrogen fluoride, and after concentration and rectification, hydrogen fluoride with a content of ≥99% is recovered and reused in product production. The rectification residue, which is 55% hydrofluoric acid, can be sold externally or used to produce other inorganic fluorine-containing salts. The crude organic phase of p-methylfluorobenzene is extracted with an alkali solution to remove p-methylphenol in the crude product and neutralize the entrained hydrofluoric acid. The p-methylfluorobenzene after alkali washing enters the intermediate storage tank and then enters the rectification system. The fraction with a boiling point of 115 - 116 °C is collected at atmospheric pressure to obtain the rectified product of p-methylfluorobenzene, and the GC detection purity of 99% is considered a qualified product. When the concentration of the extraction alkali solution is lower than the limit (sodium hydroxide content of 3%), it is replaced. The discharged waste alkali solution is neutralized with sulfuric acid to separate the organic phase of p-methylphenol, and after distillation, the purity of 99% is sold as a product. The inorganic phase is a mixture of sodium sulfate and NaF. First, NaF crystals are separated by water recrystallization, and the mother liquor is concentrated, crystallized, and recrystallized three times to obtain sodium sulfate with a purity of 99.2% for sale as a product.

[0097] After the above steps, continuous salification, diazotization, and seven-stage pyrolysis are carried out. Sampling from the receiving kettle for GC detection shows that the conversion rate of p-methylaniline reaches 97.07%, the by-product of azobenzene is 0.63%, and the content of p-methylphenol is 1.82%. The fraction at 115 - 116 °C can be preliminarily verified as p-methylfluorobenzene based on the boiling point, and the GC detection purity is 99.66%. It is consistent with the peak position of the GC spectrum of commercially available p-methylfluorobenzene.

[0098] For the continuous flow synthesis process of the annular reactor in this example, from the start of feeding to the commissioning and stabilization, it takes 33 hours. Starting from the completion of commissioning, it runs stably for 300 hours, and the results are summarized as follows: A total of 828 kg of p-methylaniline, 1800 kg of hydrofluoric acid, and 540 kg of sodium nitrite are consumed, and 806.2 kg of p-methylfluorobenzene finished product is obtained, with a yield of 94.71% and a purity of 99.66%.

[0099] Example 5:

[0100] This example is the full continuous flow synthesis of o-fluorotoluene. The following specifications of the annular reactor are 20 L, and the limiting position is 70% of the height of the reactor. The specific steps are as follows:

[0101] (1) Hydrogen fluoride and o-methylaniline are respectively metered by metering pumps and then pumped into the salification annular reactor simultaneously. The flow rate of hydrogen fluoride is controlled at 100 g / min; the flow rate of o-methylaniline is controlled at 46 g / min; the temperature of the salification annular reactor is controlled at -5 - 5 °C, and the hydrogen fluoride solution of o-methylaniline hydrogen fluoride salt is obtained through the salification reaction.

[0102] (2) When the liquid level of the salt ring reactor reaches the overflow port limit, the hydrogen fluoride solution of o-toluidine hydrogen fluoride salt overflows into the diazotization ring reactor, and at the same time, solid sodium nitrite is added by a continuous feeder at a rate of 30 g / min. The temperature of the diazotization ring reactor is controlled at -5 - 5°C.

[0103] (3) When the liquid level of the diazotization ring reactor reaches the upper overflow port limit (e.g., 70% of the height of the reactor), the material overflows into the filtration device. After filtration for solid-liquid separation, the solid-free diazonium solution is pumped into the first-stage pyrolysis ring reactor (specification 20L) by a metering pump at a rate of 136 g / min.

[0104] (4) The sodium hydrogen fluoride after the solid-liquid separation in (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0105] (5) After the first-stage pyrolysis ring reactor, it then enters the second to seventh-stage pyrolysis ring reactors in sequence to complete the pyrolysis reaction by gradually increasing the temperature. The temperature control of each stage of the pyrolysis ring reactor is as follows: the first-stage pyrolysis ring reactor is controlled at 20 ± 2°C, the second-stage pyrolysis ring reactor is controlled at 25 ± 2°C, the third-stage pyrolysis ring reactor is controlled at 30 ± 2°C, the fourth-stage pyrolysis ring reactor is controlled at 35 ± 2°C, the fifth-stage pyrolysis ring reactor is controlled at 40 ± 2°C, the sixth-stage pyrolysis ring reactor is controlled at 45 ± 2°C, and the seventh-stage pyrolysis ring reactor is controlled at 50 ± 2°C. The reaction mixture flowing out of the seventh-stage pyrolysis ring reactor enters the receiving kettle, and the temperature of the receiving kettle is controlled at -5 - 5°C.

[0106] (6) The mixture of organic and inorganic phases after pyrolysis has a specific gravity difference of 0.2 g / mL and directly enters a high-speed centrifugal extractor to separate the organic and inorganic phases. The inorganic phase is 85% hydrofluoric acid, which enters the intermediate storage tank of hydrofluoric acid. After concentration and rectification treatment, hydrogen fluoride with a content of ≥99% is recovered and reused for product production. The rectification residue is 55% hydrofluoric acid, which can be sold externally or used to produce other inorganic fluorine salts. The organic phase includes crude o-fluorotoluene. After extraction with lye, o-methylphenol in the crude o-fluorotoluene is extracted and the entrained hydrofluoric acid is neutralized. The o-fluorotoluene after alkali washing treatment enters the intermediate storage tank and then enters the rectification system. The fraction with a boiling point of 113 - 114°C is collected under normal pressure to obtain the rectified product of o-fluorotoluene. The product is qualified with a purity of more than 99% detected by GC. The extraction lye is replaced when its concentration is lower than the limit. The discharged waste lye is neutralized with sulfuric acid to separate out the organic phase of o-methylphenol, which is qualified by distillation and sold as a product. The inorganic phase is sodium sulfate, which is qualified by three-effect concentration crystallization and then recrystallization and sold as a product.

[0107] After the above steps, continuous salification, diazotization, and seven-stage pyrolysis were carried out. Sampling from the receiving kettle for GC detection showed that the conversion rate of o-toluidine reached 95.22%, the content of azobenzene was 0.73%, and the content of o-cresol was 3.66%. The fraction at 113 - 114 °C could be preliminarily verified as o-methylfluorobenzene based on the boiling point, and the GC detection purity was 99.93%. It was consistent with the peak positions of the GC spectrum of commercially available o-methylfluorobenzene.

[0108] For the continuous flow synthesis process of the annular reactor in this example, from the start of feeding to the commissioning and stabilization, it took 33 hours. Starting from the completion of commissioning, it ran stably for 300 hours, and the results were summarized as follows: A total of 828 kg of o-toluidine, 1800 kg of hydrofluoric acid, and 540 kg of sodium nitrite were consumed, and 800.5 kg of o-methylfluorobenzene finished product was obtained, with a yield of 94.71% and a purity of 99.93%.

[0109] Example 6:

[0110] This example is the full continuous flow synthesis of m-fluorotoluene. The specifications of the following annular reactor are 20L, and the limiting position is 70% of the height of the reactor. The specific steps are as follows:

[0111] (1) Hydrogen fluoride and m-toluidine were respectively metered by metering pumps and then simultaneously pumped into the salification annular reactor. The flow rate of hydrogen fluoride was controlled at 100 g / min; the flow rate of m-toluidine was controlled at 46 g / min; the temperature of the salification annular reactor was controlled at -5 - 5 °C, and the hydrogen fluoride solution of m-toluidine hydrogen fluoride salt was obtained through the salification reaction.

[0112] (2) When the liquid level of the salification annular reactor reached the overflow port limit, the hydrogen fluoride solution of m-toluidine hydrogen fluoride salt overflowed into the diazotization annular reactor, and at the same time, solid sodium nitrite was added by a continuous feeder at 30 g / min. The temperature of the diazotization annular reactor was controlled at -5 - 5 °C.

[0113] (3) When the liquid level of the diazotization annular reactor reached the overflow port limit (for example, 70% of the height of the reactor), the material overflowed into the filtration device. After solid-liquid separation by filtration, the solid-free diazonium solution was pumped into the first-stage pyrolysis annular reactor (specification 20L) by a metering pump at 136 g / min.

[0114] (4) The sodium fluoride after the solid-liquid separation in (3) was rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0115] (5) After passing through the first-stage pyrolysis annular reactor, it then enters the second to seventh-stage pyrolysis annular reactors in sequence, and the pyrolysis reaction is completed by gradually increasing the temperature. The temperature control of each stage of the pyrolysis annular reactor is as follows: the first-stage pyrolysis annular reactor is controlled at 20 ± 2 °C, the second-stage pyrolysis annular reactor is controlled at 25 ± 2 °C, the third-stage pyrolysis annular reactor is controlled at 30 ± 2 °C, the fourth-stage pyrolysis annular reactor is controlled at 35 ± 2 °C, the fifth-stage pyrolysis annular reactor is controlled at 40 ± 2 °C, the sixth-stage pyrolysis annular reactor is controlled at 45 ± 2 °C, and the seventh-stage pyrolysis annular reactor is controlled at 50 ± 2 °C. The reaction mixture flowing out of the seventh-stage pyrolysis annular reactor enters the receiving kettle, and the receiving kettle is controlled at -5 - 5 °C.

[0116] (6) The organic and inorganic phase mixture after pyrolysis has a specific gravity difference of 0.2 g / mL and directly enters a high-speed centrifugal extractor to achieve the separation of the organic and inorganic phases. The inorganic phase is 85% hydrofluoric acid and enters the intermediate storage tank for hydrogen fluoride. After concentration and rectification treatment, hydrogen fluoride with a content of ≥99% is recovered and reused in product production. The rectification residue is 55% hydrofluoric acid and can be sold externally or used to produce other inorganic fluorine salts. The organic phase includes crude p-methylfluorobenzene. After extraction with lye, m-methylphenol in the crude m-methylfluorobenzene is extracted and the entrained hydrofluoric acid is neutralized. The m-methylfluorobenzene after alkali washing enters the intermediate storage tank and then enters the rectification system. The fraction with a boiling point of 114 - 116 °C is collected under normal pressure to obtain the rectified product of m-methylfluorobenzene, and the purity detected by GC is 99% as a qualified product. The extraction lye is replaced when its concentration is lower than the limit. The discharged waste lye is neutralized with sulfuric acid to separate the organic phase m-methylphenol, which is distilled to be qualified and sold as a product. The inorganic phase is sodium sulfate, which is concentrated and crystallized in three-effect and then recrystallized to be qualified and sold as a product.

[0117] After the above steps, continuous salification, diazotization, and seven-stage pyrolysis are carried out. Sampling from the receiving kettle for GC detection shows that the conversion rate of m-methylaniline reaches 96.32%, azobenzenes is 0.87%, and the content of m-methylphenol is 2.38%. The fraction with a boiling point of 114 - 116 °C can be preliminarily verified as m-methylfluorobenzene according to the boiling point, and the purity detected by GC is 99.86%. It is consistent with the peak position of the GC spectrum of commercially available m-methylfluorobenzene.

[0118] For the continuous flow synthesis process of the annular reactor in this example, from the start of feeding to the commissioning and stabilization, it takes 33 hours. Starting from the completion of commissioning, it runs stably for 300 hours, and the results are summarized as follows: A total of 828 kg of m-methylaniline, 1800 kg of hydrofluoric acid, and 540 kg of sodium nitrite are consumed, and 798 kg of m-methylfluorobenzene finished product is obtained, with a yield of 93.75% and a purity of 99.86%.

[0119] Example 7:

[0120] This example is the full continuous flow synthesis of 3,5-dimethylfluorobenzene. The specifications of the following annular reactor are 20 L, and the limiting position is 70% of the height of the reactor. The specific steps are as follows:

[0121] (1) Hydrogen fluoride and 3,5-dimethylaniline are respectively metered by metering pumps and then pumped into a salt-forming annular reactor simultaneously. The flow rate of hydrogen fluoride is controlled at 100 g / min; the flow rate of 3,5-dimethylaniline is controlled at 52 g / min; the temperature of the salt-forming annular reactor is controlled at -5 - 5°C, and a hydrogen fluoride solution of 3,5-dimethylaniline hydrogen fluoride salt is obtained through a salt-forming reaction.

[0122] (2) When the liquid level of the salt-forming annular reactor reaches the overflow port limit, the hydrogen fluoride solution of 3,5-dimethylaniline hydrogen fluoride salt overflows into the diazotization annular reactor, and at the same time, solid sodium nitrite is added at 30 g / min by a continuous feeder. The temperature of the diazotization annular reactor is controlled at -5 - 5°C.

[0123] (3) When the liquid level of the diazotization annular reactor reaches the upper overflow port limit (for example, 70% of the height of the reactor), the material overflows through a filtering device, and after solid-liquid separation by filtration, the solid-free diazonium solution is pumped into a first-stage pyrolysis annular reactor (specification 20 L) by a metering pump at 142 g / min.

[0124] (4) The sodium hydrogen fluoride after the solid-liquid separation in (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0125] (5) After the first-stage pyrolysis annular reactor, it then enters the second to fifth-stage pyrolysis annular reactors in sequence to complete the pyrolysis reaction by successive temperature increases. The temperature control of each stage of the pyrolysis annular reactor is as follows: the first-stage pyrolysis annular reactor is controlled at 10 ± 2°C, the second-stage pyrolysis annular reactor is controlled at 20°C ± 2, the third-stage pyrolysis annular reactor is controlled at 30 ± 2°C, the fourth-stage pyrolysis annular reactor is controlled at 40 ± 2°C, and the fifth-stage pyrolysis annular reactor is controlled at 50 ± 2°C. The reaction mixture flowing out of the fifth-stage pyrolysis annular reactor enters a receiving kettle, and the temperature of the receiving kettle is controlled at 0 - 5 - 5°C.

[0126] (6) After the pyrolysis is completed, the organic-inorganic mixture enters a high-speed centrifugal extractor for separation of the organic and inorganic phases due to a specific gravity difference of 0.2 g / mL. The inorganic phase, which is 85% hydrofluoric acid, enters the intermediate storage tank for hydrogen fluoride, and after concentration and rectification treatment, hydrogen fluoride with a content of ≥99% is recovered and reused in product production. The rectification residue, which is 55% hydrofluoric acid, can be sold externally or used to produce other inorganic fluorine-containing salts. The organic phase is crude 3,5-dimethylfluorobenzene. After extraction with alkali solution, 3,5-dimethylphenol in the crude 3,5-dimethylfluorobenzene is extracted and the entrained hydrofluoric acid is neutralized. The 3,5-dimethylfluorobenzene after alkali washing enters the intermediate storage tank and then enters the rectification system. The fraction with a boiling point of 145 - 147°C is collected under normal pressure to obtain the rectified product of 3,5-dimethylfluorobenzene. The purity is 99% by GC detection, which is a qualified product. When the concentration of the extraction alkali solution is lower than the limit (replaced when the sodium hydroxide content is 3%), the discharged waste alkali solution is neutralized with sulfuric acid to separate the organic phase of 3,5-dimethylphenol. After distillation and being qualified, it is sold as a product. The inorganic phase includes sodium sulfate, which is concentrated, crystallized in three-effect and then recrystallized to be qualified and sold as a product.

[0127] After the above steps, continuous salification, diazotization, and five-stage pyrolysis are carried out. Sampling from the receiving kettle for GC detection shows that the conversion rate of 3,5-dimethylaniline reaches 94.62%, azobenzene is 0.93%, and the content of 3,5-dimethylphenol is 2.77%. The fraction with a boiling point of 145 - 147°C can be preliminarily verified as 3,5-dimethylfluorobenzene according to the boiling point, and the purity is 99.94% by GC detection. It is consistent with the peak positions of the GC spectrum of commercially available 3,5-dimethylfluorobenzene.

[0128] For the continuous flow synthesis process of the annular reactor in this example, from the start of feeding to the debugging and stabilization, it takes 33 hours. Starting from the completion of debugging, it runs stably for 300 hours. The results are summarized as follows: A total of 936 kg of 3,5-dimethylaniline, 1800 kg of hydrofluoric acid, and 540 kg of sodium nitrite are consumed, and 886 kg of the finished product of 3,5-dimethylfluorobenzene is obtained, with a yield of 92.37% and a purity of 99.94%.

[0129] Example 8:

[0130] This example is the full continuous flow synthesis of 3-chloro-2-methylfluorobenzene. The following specifications of the annular reactor are 20L, and the limiting position is 70% of the height of the reactor. The specific steps are as follows:

[0131] (1) Hydrogen fluoride and 3-chloro-2-methylaniline are respectively metered by metering pumps and then pumped into the salification annular reactor simultaneously. The flow rate of hydrogen fluoride is controlled at 120 g / min; the flow rate of 3-chloro-2-methylaniline is controlled at 61.5 g / min; the temperature of the salification annular reactor is controlled at -5 - 5°C, and the hydrogen fluoride solution of 3-chloro-2-methylaniline hydrogen fluoride salt is obtained through the salification reaction.

[0132] (2) When the liquid level of the salt ring reactor reaches the overflow port limit, the hydrogen fluoride solution of 3,5-dimethylaniline hydrogen fluoride salt overflows into the diazotization ring reactor. At the same time, solid sodium nitrite is added by a continuous feeder at a rate of 30 g / min. The temperature of the diazotization ring reactor is controlled at -5 - 5°C.

[0133] (3) When the liquid level of the diazotization ring reactor reaches the upper overflow port limit (for example, 70% of the height of the reactor), the material overflows into the filtration device. After filtration for solid-liquid separation, the solid-free diazonium solution is pumped into the first-stage pyrolysis ring reactor (specification 20L) by a metering pump at a rate of 180 g / min.

[0134] (4) The sodium hydrogen fluoride after the solid-liquid separation in (3) is rinsed, neutralized, filtered, and reacted with other inorganic salts to be converted into other fluorine-containing inorganic salts with market capacity.

[0135] (5) After the first-stage pyrolysis ring reactor, it then enters the second to fifth-stage pyrolysis ring reactors in sequence to complete the pyrolysis reaction through sequential temperature increase. The temperature control of each stage of the pyrolysis ring reactor is as follows: the first-stage pyrolysis ring reactor is controlled at 10 ± 2°C, the second-stage pyrolysis ring reactor is controlled at 20°C ± 2, the third-stage pyrolysis ring reactor is controlled at 30 ± 2°C, the fourth-stage pyrolysis ring reactor is controlled at 40 ± 2°C, and the fifth-stage pyrolysis ring reactor is controlled at 50 ± 2°C. The reaction mixture flowing out of the fifth-stage pyrolysis ring reactor enters the receiving kettle, and the temperature of the receiving kettle is controlled at -5 - 5°C.

[0136] (6) Due to the specific gravity difference of 0.2 g / mL between the organic and inorganic phase mixture after pyrolysis, it directly enters a high-speed rotating centrifugal extractor to separate the organic and inorganic phases. The inorganic phase is 85% hydrofluoric acid, which enters the intermediate storage tank of hydrogen fluoride. After concentration and rectification treatment, hydrogen fluoride with a content of ≥99% is recovered and reused for product production. The rectification residue is 55% hydrofluoric acid, which can be sold externally or used to produce other inorganic fluorine-containing salts. The organic phase is crude 3-chloro-2-methylfluorobenzene. After extraction with alkali solution, 3-chloro-2-methylphenol in the crude 3-chloro-2-methylfluorobenzene is extracted and the entrained hydrofluoric acid is neutralized. The 3-chloro-2-methylfluorobenzene after alkali washing enters the intermediate storage tank and then enters the rectification system. The fraction with a boiling point of 92 - 94°C is collected under normal pressure to obtain the rectified product of 3-chloro-2-methylfluorobenzene. The purity detected by GC is greater than 99% to be a qualified product. When the concentration of the extraction alkali solution is lower than the limit (sodium hydroxide content 3%), it is replaced. The discharged waste alkali solution is neutralized with sulfuric acid to separate the organic phase of 3-chloro-2-methylphenol. After distillation, it is sold as a product. The inorganic phase is a mixture of sodium sulfate and NaF. After three-effect concentration crystallization and then recrystallization, sodium sulfate with a purity of 99% is obtained and sold as a product.

[0137] After the above steps, continuous salification, diazotization, and five-stage pyrolysis were carried out. Sampling from the receiving kettle for HPLC detection showed that the conversion rate of 3-chloro-2-methylaniline reached 95.60%, azobenzene was 0.73%, and the content of 3-chloro-2-methylphenol was 2.87%. The fraction at 92-94 °C was preliminarily verified to be 3-chloro-2-methylfluorobenzene according to the boiling point, and the GC detection purity was 99.27%. It was consistent with the peak positions of the GC spectrum of commercially available 3-chloro-2-methylfluorobenzene.

[0138] For the continuous flow synthesis process of the annular reactor used to prepare 3-chloro-2-methylfluorobenzene in this example, from the start of feeding to the commissioning and stabilization, it took 33 hours. Starting from the completion of commissioning, it was stably operated for 300 hours, and the results were summarized as follows: A total of 1107 kg of 3-chloro-2-methylaniline, 2160 kg of hydrofluoric acid, and 540 kg of sodium nitrite were consumed, and 1058 kg of 3-chloro-2-methylfluorobenzene finished product was obtained, with a yield of 93.58% and a purity of 99.27%.

[0139] For the fixed fully continuous flow reaction device, since its equipment size has been determined and its internal structure and liquid holdup have been fixed, when the material flow rate changes, it will inevitably cause changes in the movement state and residence time of the material in the reactor. The material flow rate is an important parameter for the operation of the fully continuous flow reaction device. It forms a set of complex parameters related to each other with the reactor structure, operating temperature, material ratio, etc., and determines the success or failure of the fully continuous flow synthesis process. When the reactor structure, operating temperature, and material ratio are fixed, there must be an optimal flow rate that matches the above fixed parameters. The optimal flow rate needs to be finally obtained through a long time of equipment operation and debugging. At the optimal flow rate, it can ensure the most appropriate residence time and the best movement state of the material in the reactor, enable the reaction to proceed in the best state, and thus obtain the optimal reaction result.

[0140] The test example corresponding to Example 1 of Comparative Example 1 and CN112608212A is specifically as follows:

[0141] (1) Aniline was metered by a metering pump and then pumped into a thermostat, with the flow rate controlled at 50 g / min and the outlet temperature controlled at 5 ± 0.5 °C;

[0142] (2) Hydrogen fluoride was metered by a metering pump and then pumped into another thermostat, with the flow rate controlled at 215 g / min and the outlet temperature controlled at -10 ± 0.5 °C;

[0143] (3) The aniline and hydrogen fluoride flowing out of the thermostat immediately flowed into the salification microchannel reactor at the same time, and the hydrofluoric acid solution of aniline hydrogen fluoride salt was obtained through the salification reaction, with the outlet temperature controlled at 0 ± 0.5 °C;

[0144] (4) The sulfuric acid solution of 40% nitrosylsulfuric acid is metered by a metering pump and then pumped into another thermostat, with the flow rate controlled at 181 g / min and the outlet temperature controlled at 0 ± 0.5 °C;

[0145] (5) The hydrofluoric acid solution of aniline hydrogen fluoride salt flowing out of the microchannel reactor in step (3) and the sulfuric acid solution of nitrosylsulfuric acid flowing out of the thermostat in step (4) flow into the second microchannel reactor together for diazotization reaction. The diazotization reaction temperature is controlled at 5 - 10 °C, and the outlet material temperature is controlled at 10 ± 0.5 °C to obtain a phenyl diazonium salt solution;

[0146] (6) The phenyl diazonium salt solution flowing out of the second microchannel reactor in step (5) flows into a pyrolysis microchannel reactor for pyrolysis reaction. The pyrolysis temperature is controlled at 70 ± 2 °C, and a mixture composed of fluorobenzene, hydrofluoric acid, sulfuric acid, and nitrogen is obtained at the outlet;

[0147] (7) The mixture composed of fluorobenzene, hydrofluoric acid, sulfuric acid, and nitrogen flowing out of the pyrolysis microchannel reactor in step (6) flows into a cooler for cooling, and the outlet temperature of the cooler is controlled at 5 - 10 °C;

[0148] (8) The mixture composed of fluorobenzene, hydrofluoric acid, sulfuric acid, and nitrogen flowing out of the cooler enters a three-phase separator for continuous separation. Nitrogen is discharged from the top gas outlet of the three-phase separator H, the crude fluorobenzene flows out from the upper light liquid phase outlet of the three-phase separator H, and the mixture of hydrofluoric acid and sulfuric acid flows out from the bottom heavy liquid phase outlet of the three-phase separator. The material temperature in the three-phase separator is controlled at 5 - 10 °C;

[0149] (9) The crude fluorobenzene flowing out from the upper light liquid phase outlet of the three-phase separator is first washed with alkali in a continuous alkali washing tower to remove acid, then dehydrated in a continuous drying tower and rectified in a continuous rectification tower to obtain the finished product of fluorobenzene.

[0150] The spectral data and mass spectrometry data of the fluorobenzene finished product in Comparative Example 1 are as Figure 3 、 4 shown, Figure 3 The results show that only one product is eluted, Figure 4 The results show that the mass-to-charge ratios include 175.0 and 177.0, indicating that only the sulfonation by-product - fluorobenzenesulfonic acid by-product is obtained in Comparative Example 1, indicating that the target product cannot be obtained according to the method of CN112608212A. The formation of the sulfonation by-product also conforms to the mechanism of organic chemical electrophilic reaction from the reaction conditions: as the diazotization proceeds, nitrosylsulfuric acid will be consumed and more and more sulfuric acid will be generated, and it is concentrated sulfuric acid (no additional water is added in this diazotization reaction). It is easy to obtain the sulfonation by-product by the sulfonation reaction of the relatively high-concentration sulfuric acid generated in the diazotization reaction with the electron-rich unreacted aniline.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a fluoroaromatic compound, which comprises: (1) Hydrogen fluoride and an aromatic amine form an aromatic amine hydrogen fluoride salt in a ring reactor, wherein the structural formula of the aromatic amine is as shown in Formula I R1 to R5 are each independently selected from H, halogen, a straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms, or a straight-chain or branched-chain alkoxy group having 1 to 5 carbon atoms; (2) The aromatic amine hydrogen fluoride salt obtained in step (1) flows into a diazotization ring reactor, and solid sodium nitrite is added proportionally by a continuous feeder for diazotization reaction; (3) The diazotization product obtained in step (2) is subjected to solid-liquid separation, and the liquid flows into a multi-stage pyrolysis ring reactor; (4) The multi-stage pyrolysis ring reactor includes at least three-stage pyrolysis ring reactors. In the flowing direction, the pyrolysis temperature increases step by step, and the temperature difference between adjacent pyrolysis ring reactors is 3 to 10 °C, and the temperature of the pyrolysis ring reactor is not higher than 60 °C; (5) After the pyrolysis reaction, the temperature is lowered, and post-treatment is carried out to obtain a fluoroaromatic compound.

2. The preparation method according to claim 1, wherein In step (1), R1 to R5 are each independently selected from H, halogen, a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms, or a straight-chain or branched-chain alkoxy group having 1 to 3 carbon atoms. Optionally, R1 to R5 are each independently selected from a hydrogen group, chlorine, methyl, ethyl, methoxy, or ethoxy; Optionally, the aromatic amine is selected from one of aniline, o-methylaniline, m-methylaniline, p-methylaniline, o-ethylaniline, m-ethylaniline, p-ethylaniline, 3-chloro-2-methylaniline, 5-chloro-2-methylaniline, 2,3-dimethylaniline, 2,4-dimethylaniline, 2,5-dimethylaniline, 2,6-dimethylaniline, 3,4-dimethylaniline, 3,5-dimethylaniline, 2,3,4-trimethylaniline, 2,3,5-trimethylaniline, 2,3,6-trimethylaniline, 2,4,5-trimethylaniline, 2,4,6-trimethylaniline, 3,4,5-trimethylaniline, 2,3,4,5-tetramethylaniline, 2,3,5,6-tetramethylaniline, 2,3,4,6-tetramethylaniline, pentamethylaniline, p-methoxyaniline; correspondingly, the fluoroaromatic compound includes one of fluorobenzene, o-methylfluorobenzene, m-methylfluorobenzene, p-methylfluorobenzene, o-ethylfluorobenzene, m-ethylfluorobenzene, p-ethylfluorobenzene, 3-chloro-2-methylfluorobenzene, 5-chloro-2-methylfluorobenzene, 2,3-dimethylfluorobenzene, 2,4-dimethylfluorobenzene, 2,5-dimethylfluorobenzene, 2,6-dimethylfluorobenzene, 3,4-dimethylfluorobenzene, 3,5-dimethylfluorobenzene, 2,3,4-trimethylfluorobenzene, 2,3,5-trimethylfluorobenzene, 2,3,6-trimethylfluorobenzene, 2,4,5-trimethylfluorobenzene, 2,4,6-trimethylfluorobenzene, 3,4,5-trimethylfluorobenzene, 2,3,4,5-tetramethylfluorobenzene, 2,3,5,6-tetramethylfluorobenzene, 2,3,4,6-tetramethylfluorobenzene, pentamethylfluorobenzene, p-methoxyfluorobenzene; And / or, the flow rate ratio of hydrogen fluoride to the aromatic amine is (2 to 5):1, preferably (2 to 3):1; And / or, the salt-forming temperature is -5 to 5 °C, preferably 2 to 5 °C.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the flow rate ratio of the arylamine hydrogen fluoride salt to solid sodium nitrite is (2 - 5):1, preferably (2 - 3):1; And / or, in step (2), the diazotization reaction is that the arylamine hydrogen fluoride salt and solid sodium nitrite enter the diazotization annular reactor simultaneously in proportion for mixing and reaction, and the diazotization reaction solution flows out from the overflow port of the diazotization annular reactor and then transfers to the solid-liquid separation device; optionally, the position of the overflow port is 65% - 90% of the reactor height, optionally 70 - 80%; And / or, the diazotization reaction temperature is -5 to 5°C, preferably 2 - 5°C.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (3), the separated solid includes sodium hydrogen fluoride.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step (4), the temperature of the first-stage pyrolysis annular reactor in the pyrolysis annular reactor is not lower than 8°C; Optionally, the temperature of the pyrolysis annular reactor is not higher than 50°C; And / or, the pyrolysis annular reactor includes: at least four-stage, at least five-stage, at least six-stage, at least seven-stage, at least eight-stage or at least nine-stage pyrolysis annular reactors.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The temperature difference in each stage of the pyrolysis annular reactor is controlled within ±3°C or ±2°C; And / or, the temperature difference between adjacent pyrolysis annular reactors is 5 - 10°C; And / or, the flow rate of the diazo solution entering the first-stage pyrolysis annular reactor is 0.015 - 25 kg / min.

7. According to the preparation method described in any one of claims 1 to 6, characterized in that, In the said step (5), the material enters the receiving kettle from the pyrolysis annular reactor for cooling, and the temperature is cooled to -5 to 5°C; And / or, the post-treatment includes: extraction, alkali washing and distillation.

8. The preparation method according to any one of claims 1 to 6, characterized in that, An anti-corrosion lining is adopted inside all reactors; And / or, each reactor is connected by a connecting pipe, optionally, the connecting pipe is made of polytetrafluoroethylene material pipe; And / or, a silicon carbide heat exchanger resistant to hydrogen fluoride corrosion is used for low-temperature maintenance or cooling.

9. The preparation method according to any one of claims 1 to 8, characterized in that, The annular reactors in step (1), (2) and / or (3) are all provided with overflow ports for material overflow, optionally, the position of the overflow port is 65% - 80% of the reactor height, optionally 70 - 80%.

10. A fluoroaromatic compound prepared by the preparation method according to any one of claims 1 to 9.

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