A method for preparing 2-bromine heptafluoropropane

Abstract

The application belongs to the technical field of fluorine-containing fine chemical synthesis, and particularly relates to a preparation method of 2-bromoheptafluoropropane. Liquid heptafluoropropane and liquid bromine are heated and vaporized, sent into a static mixer, mixed, and then sent into a tubular reactor for bromination reaction. The reactor comprises a preheating section and four reaction sections connected in sequence. The temperature of the preheating section is controlled to be 300-350 DEG C. According to the material flow direction, the center temperatures of the four reaction sections are controlled to be 500-505 DEG C, 500-505 DEG C, 495-500 DEG C and 490-495 DEG C in sequence. The mixed gas after reaction is sent into a quenching device for cooling, and then subjected to defluorination, water washing, alkali washing, dehydration and condensation separation to obtain high-purity 2-bromoheptafluoropropane. The application integrates full-silicon material containers, multi-section intelligent partition heating and rapid quenching, significantly improves reaction conversion rate and operation stability, and finally improves product quality and reduces production cost.

Description

Technical Field

[0001] This invention belongs to the field of fluorine-containing fine chemical synthesis technology, specifically relating to a method for preparing 2-bromoheptafluoropropane. Background Technology

[0002] 2-Bromoheptafluoropropane is an important fluorinated organic intermediate widely used in the synthesis of pharmaceutical and pesticide intermediates, especially as a key raw material for the synthesis of highly effective insecticides such as fipronil, and market demand continues to grow. Currently, the mainstream industrial method for preparing 2-bromoheptafluoropropane is to react heptafluoropropane (HFC-227ea) with bromine at high temperature via a free radical substitution reaction. Existing technologies mostly employ stainless steel or glass-lined reactors / tubular reactors, combined with single-stage electric heating or heat transfer oil jacket heating.

[0003] However, this type of process has the following drawbacks: (1) Stainless steel is easily corroded by Br2 and by-product HF at temperatures above 400℃, releasing Fe 3+ Cr 3+ Ni 2+ The presence of metal ions not only interferes with subsequent reactions, but also causes the product to appear pale yellow or slightly red, affecting product quality indicators. (2) Although glass is corrosion resistant, it has poor thermal conductivity, low mechanical strength, and is easily corroded by HF, resulting in a short lifespan. (3) The conversion rate of heptafluoropropane in traditional processes is between 70-80%, and side reactions such as polybromination are prone to occur during the reaction stage, which is the main reason for the low conversion rate. Therefore, a novel reaction system is urgently needed to achieve efficient and continuous synthesis of 2-bromoheptafluoropropane, while improving conversion rate and effectively reducing production costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing 2-bromoheptafluoropropane, which significantly improves the reaction conversion rate and operational stability by using an all-silicon carbide container, multi-stage intelligent zone heating, and rapid quenching integration, ultimately improving product quality and reducing production costs.

[0005] To achieve the above objectives, the present invention provides a method for preparing 2-bromoheptafluoropropane, comprising the following steps: (1) Heptafluoropropane and liquid bromine are heated and vaporized, and then fed into a static mixer at a molar ratio of 1.02-1.05:1 to obtain a mixed gas; (2) The mixed gas is fed into a tubular reactor and heated for bromination reaction. The tubular reactor includes a preheating section and four reaction sections connected in sequence. The temperature of the preheating section is controlled at 300-350℃. The temperature of the reaction section is controlled at 505-490℃. The center temperature of the four reaction sections decreases sequentially according to the material direction. The total residence time of the reaction section is 20-25 seconds. (3) The mixed gas after the reaction is sent to a quench cooler to cool down to below 150°C within 3 seconds, and then defluorination, water washing, alkali washing, dehydration and condensation separation are carried out to obtain high-purity 2-bromoheptafluoropropane.

[0006] Preferably, the static mixer, tubular reactor, quench cooler, and the parts in contact with the material are all made of silicon carbide.

[0007] Preferably, the center temperatures of the four reaction sections decrease sequentially according to the material flow: the center temperatures of the four reaction sections are controlled sequentially at 500-505℃, 500-505℃, 495-500℃, and 490-495℃.

[0008] More preferably, the center temperatures of the four reaction sections are controlled sequentially at 502-505℃, 502-505℃, 495-498℃, and 490-493℃.

[0009] Preferably, the temperatures of the preheating section and the four reaction sections are all automatically controlled and adjusted using a PID controller.

[0010] Preferably, in the reaction section, the radial temperature difference between the inner surface of the tubular reactor wall and the center of the reactor is <5℃.

[0011] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The inventors discovered that, due to the strong corrosiveness of bromine and hydrofluoric acid, Fe can be released in a metal reactor. 3+ Cr 3+ Ni 2+ The presence of metal ions not only interferes with subsequent reactions, but also causes the product to appear pale yellow or slightly red, affecting product quality indicators. However, the static mixer, tubular reactor, and quench cooler used in this invention are all made of silicon carbide in contact with the reactants. Since the vaporization of the raw materials begins, metal-free silicon carbide is used, completely eliminating corrosion and its adverse effects, and improving product quality.

[0012] (2) The inventors discovered that materials with low thermal conductivity, such as stainless steel, can cause overheating of the reactor wall. Overheating of the wall increases the efficiency of homolytic cracking of bromine to generate free radicals (active intermediates containing unpaired electrons). The surge in free radical concentration leads to excessive bromine substitution, exacerbating side reactions and generating polybrominated compounds and isomerized products. Since polybrominated compounds have high boiling points, they are prone to depositing on the wall to form scale, further hindering heat transfer and reducing the reaction efficiency. The tubular reactor used in this invention is made of silicon carbide, which has a thermal conductivity of over 120 W / (m·K), more than 5 times that of stainless steel. This significantly reduces radial thermal resistance, allowing the temperature difference between the center of the reaction section tube and the inner wall surface to be less than 5°C. This solves the problem caused by overheating of the wall, improves product quality, and reduces operating costs.

[0013] (3) The inventors discovered that the essence of the bromination reaction is that bromine is heated at high temperature to generate free radicals, and the generated active free radicals then undergo a substitution reaction with heptafluoropropane. According to the test, at around 500℃, 2 bromines can easily replace 2 hydrogens to generate 2-bromoheptafluoropropane. If the temperature is too low, the concentration of free radicals generated by the homolytic cleavage reaction of bromine is low, and it is not easy for the substitution reaction to occur. If the temperature is too high, the concentration of free radicals generated by the homolytic cleavage reaction of bromine will increase, and it is easy to form a polybrominated substitution reaction, that is, a side reaction will occur. In order to reduce the occurrence of side reactions, it is necessary to precisely control the temperature so that the concentration of free radicals generated by the homolytic cleavage reaction of bromine is kept within the range required for the substitution reaction. However, the existing technology is affected by the shape and material of the reactor, and the reaction temperature control fluctuates greatly, resulting in an unsatisfactory product conversion rate and consequently an unsatisfactory product quality. Therefore, the uniform heating of the reactants in the reactor is a key factor affecting the reaction efficiency. This invention employs a five-segment tubular electric heating furnace as the reactor, with segmented heating and automatic temperature control of each segment using a PID controller. High thermal conductivity silicon carbide material is selected to reduce the temperature difference between the tube wall and the tube center. After passing through the preheating section, the reaction gas enters a highly uniform thermal environment with a radial temperature difference of <5℃ between the tube wall and the tube center, effectively suppressing polybromination and cracking side reactions caused by local overheating. The selectivity of 2-bromoheptafluoropropane is increased to >85%, further improving product quality.

[0014] (4) The inventors discovered that the temperature control should be different depending on the reaction progress throughout the entire reaction process, because the main reaction is completed in the first two stages, and the amount of reactant in the reactor decreases in the last two stages. Therefore, the reaction temperature needs to be slightly reduced to ensure the reaction proceeds, while also reducing the occurrence of side reactions such as the continued bromination of the completed reactants.

[0015] (5) The inventors found that in the prior art, the cooling stage uses a water bath method for cooling, and the cooling time is 10-15 seconds. The cooling time is relatively long, which also increases the time for side reactions to occur at high temperatures. The present invention uses a silicon carbide quencher, which can quickly cool down and get away from the reaction temperature within 3 seconds, thus avoiding the occurrence of side reactions.

[0016] (6) The inventors discovered that in the prior art, uneven reaction temperature can cause a lot of side reactions. In order to minimize the occurrence of side reactions, it is necessary to use an excess of heptafluoropropane to dilute the concentration of bromine free radicals and control the molar ratio at 1.18-2.0:1. This reduces the occurrence of side reactions by sacrificing the conversion rate, which increases the cost of subsequent separation. After adopting the above-mentioned solution of the present invention, the reaction temperature and reaction time of the materials can be precisely controlled, and the conditions for the occurrence of side reactions are avoided to the greatest extent. Therefore, it is no longer necessary to use an excess of heptafluoropropane and control the molar ratio at 1.02-1.05:1, which is close to the theoretical value of 1:1, thus reducing the cost of subsequent separation.

[0017] In summary, this invention resolves the long-standing contradiction of corrosion-heat transfer-selectivity in fluorinated bromination reactions, and provides a highly selective high-temperature tubular reaction technology with precise temperature control. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of a specific embodiment of the method for preparing 2-bromoheptafluoropropane according to the present invention. Detailed Implementation

[0019] 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 are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Figure 1 A process flow diagram of the method for preparing 2-bromoheptafluoropropane according to the present invention is shown, and the specific operation is as follows: (1) Pretreatment: Liquid heptafluoropropane and liquid bromine are fed into the vaporizer by metering pump, heated and vaporized at 120-150℃, and then fed into the silicon carbide static mixer at a molar ratio of 1.02-1.05:1 after vaporization. (2) Continuous reaction: The mixed gas is fed into a tubular reactor and heated for bromination. The reactor includes a preheating section and four reaction sections connected in sequence. The temperature of the preheating section is controlled at 300-350℃. The temperature of the four reaction sections is controlled by four PID controllers according to the material flow, and is successively controlled at 503-505℃, 500-502℃, 495-497℃, and 490-492℃. The total residence time of the reaction sections is 20-25 seconds. (3) Cooling: After the reaction, the material enters a quench cooler to cool down to below 150°C within 3 seconds, resulting in a mixed gas containing 2-bromoheptafluoropropane. (4) Refining: The mixed gas containing 2-bromoheptafluoropropane is further treated by conventional methods such as defluorination, water washing, alkali washing, dehydration, and condensation to separate high-purity 2-bromoheptafluoropropane.

[0021] The tubular reactor comprises a preheating section and four reaction sections connected in sequence. The tube walls are all made of silicon carbide, with a material channel on the inner side of the silicon carbide tube wall and an electric heater covering the outer side. The temperatures of the preheating section and the four reaction sections are automatically controlled and regulated in segments using a PID controller. The tubular reactor can be manufactured using existing technologies.

[0022] The static mixer and quencher made of silicon carbide can also be made using existing technologies and existing solutions, and no specific limitations are made here.

[0023] Examples and Comparative Examples The 2-bromoheptafluoropropane product was prepared using the specific operating steps of the above-mentioned 2-bromoheptafluoropropane preparation process. In Examples 1-3, the molar ratio of heptafluoropropane to bromine was 1.02-1.05:1, the preheating temperature was 300-350℃, the quenching time was 3 seconds, and the material temperature after quenching was 150℃. Other control parameters are shown in Table 1.

[0024] Comparative Example 1 The difference from Example 3 is that the radial temperature difference of the reaction section is <8°C, while the other parameters are the same as in Example 3, and the specific operation described above is followed.

[0025] Comparative Example 2 The difference from Example 3 is that the temperature of all four reaction sections is controlled at 502-505℃, while other parameters are the same as in Example 3, and the specific operations described above are followed.

[0026] Comparative Example 3 The difference from Example 3 is that the temperature of both the first and second reaction sections is controlled at 500-510℃, while other parameters are the same as in Example 3, and the specific operations described above are followed.

[0027] Comparative Example 4 The difference from Example 3 is that the residence time of the mixed gas in the reaction section is 15 seconds, while the other parameters are the same as in Example 3, and the specific operation described above is followed.

[0028] Comparative Example 5 The difference from Example 3 is that the material residence time in the reaction section is 30 seconds, while other parameters are the same as in Example 3, and the specific operation described above is followed.

[0029] Table 1: Control parameters and indicators for the examples and comparative examples

[0030] As can be seen from the table above, the conversion rate of heptafluoropropane in Examples 1-3 was all above 85%, which is more than 5% higher than the current conversion rate level of 70-80%, indicating a significant improvement in reaction efficiency. Comparative Example 1, with a radial temperature difference of <8℃ in the reaction section and other parameters the same as Example 3, showed a significant decrease in conversion rate, indicating that uneven temperature control in the reactor and excessive fluctuations can lead to increased side reactions, which is detrimental to improving the conversion rate. Comparative Example 2, with the temperature of all four reaction sections controlled at 502-505℃ and other parameters the same as Example 3, also showed a significant decrease in conversion rate, indicating that temperature control should vary depending on the reaction progress. Since the main reaction is completed in the first two sections, the amount of reactant in the latter two sections of the reactor decreases, requiring a slight reduction in reaction temperature to ensure the reaction continues while minimizing further bromination of the completed reactants. Side reactions occurred, so the temperature control of the four reactor stages could not be exactly the same. In Comparative Example 3, the temperatures of the first and second reaction stages were both controlled at 500-510℃, and other parameters were the same as in Example 3. The conversion rate decreased to 75.3%, indicating that after the reaction temperature of the first two stages increased, the concentration of free radicals generated by the homolytic cleavage reaction of bromine increased, making substitution reactions more likely and increasing the probability of side reactions, thus reducing the conversion rate. In Comparative Example 4, the material residence time in the reaction stage was 15 seconds, and other parameters were the same as in Example 3. The conversion rate decreased to 78.6%, indicating that the reaction was incomplete due to insufficient residence time, resulting in a decrease in the conversion rate. In Comparative Example 5, the material residence time in the reaction stage was 30 seconds, and other parameters were the same as in Example 3. Due to the excessive reaction time, the probability of side reactions increased, resulting in a decrease in the conversion rate.

Claims

1. A method for preparing 2-bromoheptafluoropropane, characterized in that, Includes the following steps: (1) Heptafluoropropane and liquid bromine are heated and vaporized, and then fed into a static mixer at a molar ratio of 1.02-1.05:1 to obtain a mixed gas; (2) The mixed gas is fed into a tubular reactor for heating to carry out a bromination reaction. The tubular reactor includes a preheating section and four reaction sections connected in sequence. The temperature of the preheating section is controlled at 300-350℃; the temperature of the reaction section is controlled at 505-490℃, and the center temperature of the four reaction sections decreases sequentially according to the material direction. The total residence time of the mixed gas in the reaction section is 20-25 seconds. The center temperatures of the four reaction sections decrease sequentially according to the material direction as follows: the center temperatures of the four reaction sections are controlled sequentially at 500-505℃, 500-505℃, 495-500℃, and 490-495℃. In the reaction section, the radial temperature difference between the inner surface of the tubular reactor wall and the center of the reactor is <5℃. (3) The mixed gas after the reaction is sent to a quencher to cool down to below 150°C, and then defluorinated, washed with water, washed with alkali, dehydrated and condensed to obtain high-purity 2-bromoheptafluoropropane.

2. The preparation method according to claim 1, characterized in that, The static mixer, tubular reactor, and quench cooler are all made of silicon carbide.

3. The preparation method according to claim 1, characterized in that, The center temperatures of the four reaction sections are controlled sequentially at 502-505℃, 495-498℃, and 490-493℃.

4. The preparation method according to claim 1, characterized in that, The temperatures of the preheating section and the four reaction sections are all automatically controlled and regulated using a PID controller.

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