Thermal decomposition reactor and system for preparing fluoroaromatic hydrocarbons, and continuous preparation process

Abstract

The present invention provides a thermal decomposition reactor and a system and a continuous preparation process for preparing fluoroaromatic hydrocarbons. The thermal decomposition reactor includes at least two spiral tubular reactors connected in series; the reaction temperatures of the two spiral tubular reactors are different; the application of the thermal decomposition spiral tubular reactor for the thermal decomposition reaction of hydrogen fluoride diazonium salt of aromatic amine has significant comprehensive advantages compared with the existing intermittent production process and straight tube reactor. The reaction yield can be significantly improved, the operation process is easy to control, the production capacity is increased, the investment cost, energy consumption and labor cost are saved, and it is safe and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the technical field of fluoroaromatic preparation, and in particular to a thermal decomposition reactor and a system and a continuous preparation process for preparing fluoroaromatic. Background Art

[0002] Fluorinated aromatics are important organic chemical raw materials, widely used in the preparation of medicines, pesticides, liquid crystals, dyes, new materials and other fields. Due to their special functions, wide range of uses and broad market prospects, they are multi-purpose and irreplaceable organic intermediates.

[0003] For fluoroaromatic hydrocarbons with high charge content and low steric hindrance, they are generally prepared by diazotization reaction of aromatic amine hydrogen fluoride salt at corresponding position with sodium nitrite, followed by thermal decomposition at elevated temperature. The selectivity of fluoroaromatic hydrocarbons is relatively high:

[0004]

[0005] However, in today's world, existing manufacturers of fluoroaromatics can only produce them in an intermittent manner and on a small scale. Li Cailin et al., Research Progress in Fluorobenzene Synthesis, Shanxi Chemical Industry, 2006 (2): 19-21 reported that the intermittent fluoroaromatic preparation process includes the following three stages:

[0006] Stage 1: Preparation of diazonium hydrogen fluoride salts of aromatic hydrocarbons.

[0007] Under stirring and low temperature, add aromatic amine to several times excess frozen hydrogen fluoride, and cool to below 5° C. Keep the temperature below 5° C., add solid sodium nitrite in batches, continue stirring for 1 hour, and the preparation of aromatic diazonium salt is completed.

[0008] The second stage: thermal decomposition reaction of diazonium salt.

[0009] The low-temperature diazonium salt hydrogen fluoride solution prepared as above is heated to above 5°C for thermal decomposition reaction to prepare fluoroaromatic hydrocarbons. The temperature is slowly and gradually raised to 40°C over about 20-30 hours. The fluoroaromatic hydrocarbons and hydrogen fluoride volatilized with nitrogen are recovered through freezing at the vent until the reaction is complete.

[0010] The third stage: separation of products.

[0011] The reaction solution was allowed to stand for stratification, and the organic phase was neutralized with alkali and steam distilled to obtain fluoroaromatic hydrocarbons with a yield of about 80%.

[0012] In the above process, the key, difficulty and crux is the thermal decomposition reaction. The intermittent thermal decomposition reaction has obvious disadvantages:

[0013] First, the reaction control is difficult. Since the thermal decomposition reaction needs to be preheated to the reaction temperature, and the reaction is a highly exothermic process, it is difficult to control the reaction temperature. Once the reaction temperature is out of control, the large amount of nitrogen generated instantly will inevitably cause excessive pressure in the reactor, which is prone to explosion accidents.

[0014] Second, the environmental protection risk is relatively high. Since hydrogen fluoride is a highly corrosive material, if the reaction gets out of control in an instant, the large amount of hydrogen fluoride gas that escapes with the nitrogen will not be absorbed and reused, which has a very serious and unacceptable impact on the environment.

[0015] Third, the reaction conversion rate is low. In fact, the reaction is still incomplete when the reaction is continued for 4 hours at 40°C, and 3-5% of the diazonium salt is still not decomposed. This part of the diazonium salt will only slowly decompose in the subsequent post-treatment steps. This has a significant impact on the reaction selectivity of the unconverted diazonium salt and also increases the complexity of the process.

[0016] Fourth, the reaction selectivity is low. Since the diazotization reaction generates 2 moles of water, and water easily reacts with diazonium salts to generate phenols, this leads to the generation of more phenols and their azo compounds, thus reducing the yield.

[0017] There is also a Chinese invention patent application ZL200610049757.5, a production device and a production method for aromatic fluorine compounds, which is not feasible for implementation:

[0018] First, the reactor is in the form of a straight tube without built-in filler. The mass transfer of this reactor is extremely poor, and it is difficult to meet the mass transfer requirements required by the thermal decomposition reaction.

[0019] Second, the heating form of the reactor is electric heating tiles or heating jackets. Due to the extremely small reaction heat exchange surface, it cannot meet the heat exchange effect required by the reaction process.

[0020] Third, the straight tube form of the reactor determines an extremely large flow rate, which results in an extremely short residence time and fails to meet the high conversion rate requirements.

[0021] In view of the above reasons, the reactor described in the above patent document is not practical, which is the fundamental reason why the reactor cannot be applied to industrialization so far. Summary of the invention

[0022] In view of the above drawbacks of the intermittent and literature-based diazonium salt thermal decomposition processes, the present invention has discovered a continuous thermal decomposition process and equipment for aromatic hydrogen fluoride diazonium salts, and the technical solution is as follows:

[0023] A thermal decomposition reactor for preparing fluoroaromatic hydrocarbons, wherein the thermal decomposition reactor comprises at least two spiral tubular reactors connected in series; the reaction temperatures of the two spiral tubular reactors are different.

[0024] As a preferred technical solution, the spiral tubular reactor is equipped with fillers resistant to acid corrosion; and the reaction pressure of the spiral tubular reactor is ≥0.5 MPa.

[0025] As a preferred technical solution, each spiral tubular reactor is provided with an independent temperature control device;

[0026] As a preferred technical solution, the two spiral tubular reactors connected in series are R1 and R2 respectively along the flow direction of the feed, and the reaction temperature of R2 is greater than that of R1.

[0027] As a preferred technical solution, the thermal decomposition reactor includes at least three spiral tubular reactors R1, R2 and R3 connected in series; at least two of R1, R2 and R3 have different reaction temperatures; preferably, R1, R2 and R3 are connected in series in sequence along the flow direction of the feed, the temperature of R2 and R3 is greater than the temperature of R1, and the temperature of R2 and R3 is the same.

[0028] The present invention also provides a system for preparing fluoroaromatic hydrocarbons, comprising any of the above-mentioned thermal decomposition reactors.

[0029] The system equipment for preparing fluoroaromatic hydrocarbons comprises a reactor for diazotization reaction, characterized in that the discharge end of the reactor is connected to the feed end of the thermal decomposition reactor via a high-pressure metering pump.

[0030] The present invention also provides a method for preparing fluoroaromatic hydrocarbons by using the thermal decomposition reactor described above, wherein the temperature of the spiral tube reactor is controlled at 35-65°C.

[0031] As a preferred technical solution, the reaction temperature of R1 is controlled at 35-45°C; the reaction temperatures of R2 and R3 are controlled at 55-65°C; and the reaction selectivity of the raw materials is ≥95%.

[0032] As a preferred technical solution, the method includes the step of thermal decomposition of the diazonium salt; when the diazonium salt is thermally decomposed in the method, the ratio of the diazonium salt to hydrogen fluoride is 1:12 to 30 in terms of molar ratio.

[0033] As a preferred technical solution, the flow rate of each spiral tubular reactor is controlled at 30-40 ml / s.

[0034] The preferred reaction material ratio is that when the diazonium salt is thermally decomposed, the ratio (molar ratio) of the diazonium salt to hydrogen fluoride is 1:12-30 (i.e., the molar number of hydrogen fluoride is 12-30 times that of the diazonium salt) to improve the reaction selectivity.

[0035] Preferably, the reaction temperatures of the two spiral tubular reactors connected in series are different by providing an independent temperature control device.

[0036] Preferably, an independent temperature control device is provided to achieve different reaction temperatures of at least two spiral tubular reactors among R1, R2 and R3.

[0037] More preferably, among R1, R2 and R3, the temperature of R2 is the same as that of R3.

[0038] The temperature control device is preferably a constant temperature water bath. When R1, R2, and R3 are placed in a constant temperature hot water bath to achieve heat exchange, the temperature of the water bath is regulated by switching between cold and hot water.

[0039] Preferably, the discharge end of the last spiral tubular reactor is connected to a condenser, a stratifier and a cryogenic collector in sequence.

[0040] The experimental results show that the continuous thermal decomposition preparation process of fluorinated aromatic diazonium salt hydrogen fluoride solution completely overcomes the drawbacks of the intermittent method and invention patent ZL200610049757.5.

[0041] The present invention has a series of advantages in terms of practicality, such as high yield, short cycle, easy control, low energy consumption, greater safety and environmental protection, and low labor cost:

[0042] (1) The device provided by the present invention is easy to control. The low-temperature diazonium salt hydrogen fluoride solution is quantitatively and continuously pumped into the series-connected thermal decomposition spiral tube reactor by a high-pressure metering pump, and the reaction temperature is directly reached without preheating. During the thermal decomposition reaction, since the material flow rate at any moment is equal, a certain amount of nitrogen is generated per unit time. The discharge of nitrogen is easy to control through the freezing and hydrogen fluoride recovery process and the gas absorption process, which ensures that the gas is discharged in compliance with the standard.

[0043] (2) By comparing different reaction temperatures with different flow rates (i.e. different residence times), we found that higher temperatures (40-60°C) are conducive to the reaction between fluoride anions and diazonium salts. In this temperature range, the parallel side reaction of water and diazonium salts to form phenols is effectively suppressed.

[0044] (3) The use of a thermal decomposition spiral tube reactor with built-in fillers greatly enhances the mass transfer process, increases the back mixing of materials, and increases the ratio of hydrogen fluoride to diazonium salt, thereby inhibiting side reactions and improving reaction selectivity.

[0045] (4) By connecting three or more groups of thermal decomposition spiral tubular reactors in series and carrying out the reaction process under pressure conditions, the reaction residence time can be increased and the reaction time can be extended.

[0046] (5) By adopting the method of quantitative continuous feeding of diazonium salt hydrogen fluoride solution, the equipment volume is minimized and the heat exchange area of ​​the reactor is maximized, which makes the temperature control of the reaction materials very easy and accurate, and fundamentally eliminates the occurrence of over-temperature, over-pressure and other reaction runaway phenomena; the reaction temperature is increased, the heat exchange area of ​​the same mass of materials is increased, and the reaction conversion rate is increased by more than 99%.

[0047] (6) Continuous operation saves energy and labor costs.

[0048] (7) The reaction temperature of the thermal decomposition is controlled by adjusting and controlling the temperature of the heat transfer medium of the three-stage thermal decomposition spiral tubular reactor. R1, R2 and R3 can respectively adjust the temperature of their respective heat exchange materials to achieve the purpose of controlling the reaction rate; at the same time, the continuous operation process significantly reduces the material inventory in the thermal decomposition spiral tubular reactor and is not prone to over-temperature and over-pressure, thereby improving the safety of the reaction control process and ensuring the safety of on-site personnel.

[0049] (8) In the continuous spiral tube reactor, the flow rate of the inlet and outlet materials is equal at any moment, making it easy to recover fluorobenzene and hydrogen fluoride in the exhaust nitrogen, which is beneficial to environmental protection. DETAILED DESCRIPTION BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Process flow chart

[0051] Example

[0052] The continuous thermal decomposition process and its reaction results are explained below with reference to the accompanying drawings by way of example.

[0053] Process and equipment

[0054] Depend on Figure 1It can be seen that: in this process, the hydrogen fluoride solution of the diazonium salt enters the pyrolysis reactor (R1, R2 and R3) through the bottom valve of the diazotization kettle and is quantitatively input into the pyrolysis reactor (R1, R2 and R3). The reacted material enters the condenser, and the condensed material enters the separator. The non-condensable gas (nitrogen) enters the (organic gas) adsorber through the deep cold collector, and then goes to the fourth stage of absorption before being discharged. The thermal decomposition spiral tubular reactor is filled with polytetrafluoroethylene as a filler resistant to acid corrosion (the nominal diameter and length of a single group of thermal decomposition spiral tubular reactors are DN20 and L=6000mm, respectively, and are made into a spiral coil type - as shown in Figures R1, R2 and R3, and are placed in a bath tank). The organic layer and the inorganic layer are separated in the separator, and the organic layer is treated as a product, and the inorganic layer is treated as a by-product. A pressure gauge (P1) is set on the outlet pipeline of the high-pressure metering pump, and a pressure gauge P2 is set on the pipeline between reactors R2 and R3. A thermometer (T1) is provided in the heating medium of reactor R1, and a thermometer (T2) is provided in the heating medium of reactors R2 and R3. A pressure regulating valve is provided on the outlet pipeline of reactor R3.

[0055] Process conditions

[0056] A. According to the set reaction device, the flow rate and residence time show opposite trends. We choose flow rate as the first variable. According to the internal volume of the thermal decomposition spiral tube reactor in this experiment is 1884ml, we set the maximum flow rate of the reaction liquid to 60ml / s. And reduce the flow rate to 50ml / s, 40ml / s, 30ml / s and 20ml / s in turn, aiming to increase the residence time.

[0057] B. The reaction device that has been set up is composed of 3 groups of thermal decomposition spiral tubular reactors connected in series with heat exchangers (condensers), collection devices, etc., and each group of reactors can select heating media of different temperatures. We set the first group of reactors as the first heating temperature zone T1, and the second and third groups of reactors as the second heating temperature zone T2.

[0058] C. Due to the set reaction device, the actual temperature in the reactor is difficult to measure. We use the actual temperature of the heat exchange medium to represent the temperature in the reactor. This has a smaller error for the thermal decomposition spiral tube reactor with a very high heat transfer rate.

[0059] D. Set pressure gauge P1 before the reactor inlet, and set pressure gauge P2 between R2 and R3 for the experiment.

[0060] Measured value.

[0061] Experimental results and discussion

[0062] Since the temperature of the thermal decomposition spiral tubular reactor is relatively easy to control, we prefer the ratio of diazonium salt to hydrogen fluoride to be 1:18, and examine the favorable process conditions by comparing the yields under different temperatures and different flow rates (i.e., different residence times).

[0063] In the following table, flow rate is measured in ml / s, temperature is measured in °C, and pressure is measured in MPa. The experimental results are shown in Table 3-1:

[0064] Table 3-1 is the device test results

[0065]

[0066] According to the above experimental results, the following conclusions can be drawn:

[0067] The use of a thermal decomposition spiral tubular reactor to replace the currently used batch reactor and straight tube reactor has significant comprehensive advantages, and the yield is increased from 80-81% of the batch reaction to more than 90% of the continuous reaction.

[0068] The optimized process conditions for achieving a yield of more than 90% are: the optimal flow rate is controlled at 30-40 ml / s. As the flow rate increases, the yield decreases, and as the flow rate decreases, the production capacity is affected.

[0069] The reaction temperature is related to the flow rate. Under the condition of a flow rate of 30-40 ml / s, the optimal reaction temperature is 40-60°C. The yield is lower at low temperatures, while the pressure increases at high temperatures.

[0070] The uniqueness of this experimental result is that the application of the thermal decomposition spiral tubular reactor for the thermal decomposition reaction of the hydrogen fluoride diazonium salt of aromatic amine has significant comprehensive advantages compared with the existing intermittent production process and the straight tube reactor. It can significantly improve the reaction yield, the operation process is easy to control, the production capacity is increased, the investment cost, energy consumption and labor cost are saved, and it is safe and environmentally friendly.

[0071] The thermal decomposition spiral tubular reactor is used for the thermal decomposition reaction of hydrogen fluoride diazonium salt of aromatic amine. When more than three groups of thermal decomposition spiral tubular reactors are connected in series, T1 is 40±5°C, T2 is 60±5°C, and the flow rate is controlled between 30 and 40 ml / s, the reaction yield can reach more than 90%.

Claims

1. A method for preparing fluoroaromatic hydrocarbons, wherein the system equipment for preparing fluoroaromatic hydrocarbons includes a reactor for diazotization reaction, characterized in that: The method utilizes a system device for preparing fluoroaromatic hydrocarbons, and the system device includes a thermal decomposition reactor; The discharge end of the reaction kettle is connected to the feed end of the thermal decomposition reactor via a high-pressure metering pump; The thermal decomposition reactor comprises three spiral tubular reactors R1, R2 and R3 connected in series; R1, R2 and R3 are connected in series in sequence along the flow direction of the feed, the temperature of R2 and R3 is greater than the temperature of R1, and the temperature of R2 and R3 is the same; the spiral tubular reactor is equipped with a filler resistant to acid corrosion; The reaction temperature of R1 is controlled at 35-45°C; the reaction temperatures of R2 and R3 are controlled at 55-65°C; The flow rate of each spiral tubular reactor is controlled at 20~40ml / s, and the reaction selectivity of the raw materials is >91%; The discharge end of the spiral tubular reactor at the end is connected to a condenser, a stratifier and a cryogenic collector in sequence.

2. The method according to claim 1, characterized in that The reaction pressure of the spiral tubular reactor is ≥0.5 MPa.

3. The method according to claim 1, characterized in that Each spiral tubular reactor is provided with an independent temperature control device.

4. The method according to claim 1, comprising the step of thermally decomposing a diazonium salt; characterized in that: When the diazonium salt is thermally decomposed, the ratio of the diazonium salt to hydrogen fluoride is 1:12-30 in terms of molar ratio.

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