Method for producing hexafluorobutadiene, continuous production system and application thereof

Abstract

The invention relates to the technical field of organic chemical synthesis, and particularly discloses a method for producing hexafluorobutadiene, a continuous production system and application thereof. The method for producing hexafluorobutadiene comprises the following steps: (1) bromination reaction: reacting tetrafluoroethylene with liquid bromine to generate dibromotetrafluoroethane; (2) telomerization reaction: reacting the dibromo tetrafluoroethane with tetrafluoroethylene under the action of a catalyst to generate dibromo octafluorobutane; the catalyst is cuprous bromide; and (3) elimination reaction: reacting the dibromo octafluorobutane under the action of a Grignard reagent to generate hexafluorobutadiene. The method provided by the invention has the advantages of simple process, easily available raw materials, high production efficiency, continuous production, low production cost and industrial mass production value.

Description

Technical Field

[0001] The invention relates to the technical field of organic chemical synthesis, in particular to a method for producing hexafluorobutadiene, a continuous production system and application thereof. Background Art

[0002] Hexafluoro-1,3-butadiene (C4F6) is an important high-performance chemical widely used in coatings, materials, medicine and electronics. Compared with traditional plasma etching gases CF4, C2F6, C3F8 and NF3, C4F6 has faster etching speed, higher etching selectivity and high aspect ratio. As a highly efficient dry etching gas with extremely low greenhouse effect GWP and green environmental protection, it is considered to be an ideal product to replace traditional electronic etching gases.

[0003] The preparation process routes of hexafluorobutadiene can be divided into trifluorovinyl zinc bromide route, 3,4-dichlorohexafluoro-1-butene route, 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane route, and dihalooctafluorobutane route. The trifluorovinyl zinc bromide route uses trifluoroethylene bromide or dibromotetrafluoroethane as raw materials to prepare trifluorovinyl zinc bromide. Trifluorovinyl zinc bromide is polymerized by coupling in a non-protonic polar solvent containing copper or iron ion catalyst to generate hexafluorobutadiene. This route has a simple process, but the raw materials are not mature industrial products and need to be synthesized separately, which has some limitations on large-scale production. 3,4-Dichlorohexafluoro-1-butene can be directly dechlorinated to obtain hexafluorobutadiene. The reaction is relatively simple and has a high yield. However, 3,4-dichlorohexafluoro-1-butene is mainly obtained by thermal cracking of chlorotrifluoroethylene. The product selectivity of the thermal cracking reaction is poor. The yield of the target product 3,4-dichlorohexafluoro-1-butene is less than 30%, and the by-product 1,2-dichlorohexafluorocyclobutane has a similar boiling point to the target product. The subsequent dechlorination products hexafluorocyclobutene and hexafluoro-2-butyne are also difficult to separate from hexafluorobutadiene, which makes it difficult to prepare high-purity hexafluorobutadiene. 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane undergoes dechlorination reaction in the environment of zinc powder and organic solvent to generate hexafluorobutadiene. The reaction conditions are relatively mild, and the yield of the target product hexafluorobutadiene is as high as 93%~98%. However, there are many problems in the preparation of the intermediate 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane. It is usually prepared from 1,2-dichloroethylene, trifluorochloroethylene, 1,2,3,4-tetrachlorobutane, etc. The preparation process is complicated and reagents such as F2 and iodine chloride are used, which is troublesome to handle. The dihalooctafluorobutane route uses diiodooctafluorobutane and dibromooctafluorobutane as raw materials to generate hexafluorobutadiene under the action of Grignard reagents and organic solvents. The yield of the target product is close to 98%. The reaction of this route is simple, and the selectivity and conversion rate of each step can be controlled above 90%. However, dihalooctafluorobutane is difficult to obtain, and it is difficult to obtain a good dihalooctafluorobutane yield by reacting tetrafluoroethylene with halogen in one step. Specific currently known methods include: Chinese patent CN112645794 discloses a method of preparing TFE by cracking R22 as a raw material, TFE reacts with Br2 to generate dibromotetrafluoroethane, and dibromotetrafluoroethane reacts with TFE at a certain temperature under the conditions of zinc powder and DMF and toluene combined solvent to prepare hexafluorobutadiene, but the process is a liquid phase intermittent reaction, which is not conducive to industrial continuous production. Chinese patent CN116410055 discloses a continuous production method of hexafluorobutadiene and a modified catalyst for its production, which uses tetrafluoroethylene as a raw material and reacts with bromine in a fixed bed, and the fixed bed is filled with a modified catalyst for continuous production of hexafluorobutadiene, but because bromine has strong corrosiveness and oxidizing properties, it will cause corrosion of the fixed bed reactor and catalyst collapse, so this method does not have practical application value.

[0004] In summary, the prior art still has inconveniences and defects in actual production and cannot well realize industrial continuous production. Summary of the invention

[0005] One of the purposes of the present invention is to provide a continuous production method of hexafluorobutadiene with simple process and high preparation efficiency.

[0006] The present invention provides a method for producing hexafluorobutadiene, comprising: (1) Bromination reaction: Tetrafluoroethylene reacts with liquid bromine to produce dibromotetrafluoroethane; (2) Telomerization reaction: dibromotetrafluoroethane and tetrafluoroethylene react in the presence of a catalyst to produce dibromooctafluorobutane; the catalyst is cuprous bromide; (3) Elimination reaction: Dibromooctafluorobutane reacts with the Grignard reagent to generate hexafluorobutadiene.

[0007] The invention improves the yield of the telomerization reaction by selecting a specific catalyst, thereby successfully applying a new production route to obtain a new method for efficiently preparing hexafluorobutadiene. The production route can achieve continuous production of hexafluorobutadiene with the assistance of a vaporization device and a fixed bed, which is conducive to industrial application.

[0008] In the present invention, tetrafluoroethylene and liquid bromine are firstly reacted in a bromination reaction system to generate dibromotetrafluoroethane BrCF2CF2Br, and then dibromotetrafluoroethane and tetrafluoroethylene are polymerized in a polymerization reaction system under the action of a catalyst to obtain Br(CF2CF2)2Br, and then Br(CF2CF2)2Br is reacted in an elimination reaction system under the action of a Grignard reagent to generate hexafluorobutadiene.

[0009] In the method for producing hexafluorobutadiene of the present invention, in the bromination reaction, the molar ratio of tetrafluoroethylene to liquid bromine is (1.2-1.5):1, and the reaction temperature is 20-50°C.

[0010] In the method for producing hexafluorobutadiene of the present invention, the temperature of the polyurethane reaction is 180-350° C., the molar ratio of tetrafluoroethylene to dibromotetrafluoroethane is (1.3-3.2):1, the reaction pressure is 0.5-1.0 MPa, and the residence time is 8s-30s.

[0011] In the present invention, when performing the telomerization reaction, it is preferred to control the molar ratio of the reactants. If too much tetrafluoroethylene is added, dibromododecafluorohexane and higher carbon number perfluoroalkyl dibromide byproducts with no application value are easily generated.

[0012] In the method for producing hexafluorobutadiene of the present invention, the reaction temperature of the elimination reaction is 50-80° C., the solvent is tetrahydrofuran, dimethyl ether, ethyl ether or 1,4-dioxane; the Grignard reagent is methylmagnesium chloride, ethylmagnesium bromide or phenylmagnesium bromide, and the molar ratio of the Grignard reagent to dibromooctafluorobutane is (1.2-1.8):1.

[0013] In the method for producing hexafluorobutadiene of the present invention, the catalyst is a supported catalyst, which is prepared by loading cuprous bromide onto a porous material, wherein the porous material is selected from one or more of activated carbon, carbon nanotubes, and silicon dioxide, and the loading amount of the supported catalyst is 5wt% to 30wt%.

[0014] The present invention preferably uses a supported catalyst to facilitate the full reaction and the recycling of the catalyst. The specific preparation method of the supported catalyst is common knowledge in the art, such as the preparation method using an impregnation method, which specifically includes: weighing a certain amount of the carrier into a reaction kettle, adding deionized water, adding a certain amount of CuBr under a nitrogen atmosphere, stirring at room temperature, stopping the reaction after the system turns light blue, filtering, washing with ethanol, and vacuum drying to obtain the supported catalyst.

[0015] The method for producing hexafluorobutadiene of the present invention further comprises the steps of separating, purifying and condensing the product of the elimination reaction.

[0016] The method of the present invention preferably includes a purification step, and the purity of the hexafluorobutadiene product obtained after separation and purification can reach more than 99.8%.

[0017] The present invention also provides a continuous production system of hexafluorobutadiene, which comprises: a bromination reaction system, a telomerization reaction system, and an elimination reaction system; The bromination reaction system comprises a liquid bromine storage tank, a tetrafluoroethylene storage tank, a tetrafluoroethylene vaporization tank, a bromination reactor, a metering pump and a dibromotetrafluoroethane collecting tank; a bottom pipe is provided in the bromination reactor to the bottom of the reactor, the liquid bromine storage tank is connected to the feed port of the bromination reactor through the metering pump, the tetrafluoroethylene vaporization tank is connected to the bottom pipe in the bromination reactor through a pipeline, the discharge port of the bromination reactor is arranged in the middle and upper part of the bromination reactor, and the dibromotetrafluoroethane collecting tank is connected to the discharge port of the bromination reactor; liquid bromine is added to the bromination reactor through the metering pump, the tetrafluoroethylene in the tetrafluoroethylene vaporization tank enters the bottom of the bromination reactor through the bottom pipe of the bromination reactor to react with the liquid bromine, and the generated dibromotetrafluoroethane is collected in the dibromotetrafluoroethane collecting tank; The telomerization reaction system comprises a vaporizer and a fixed bed reactor; the inlet of the vaporizer is connected to a dibromotetrafluoroethane collection tank, and the outlet of the vaporizer is connected to a fixed bed reactor; the dibromotetrafluoroethane produced in the bromination reaction system is vaporized and enters the fixed bed reactor, and continuously contacts with the vaporized tetrafluoroethylene under the action of a catalyst to cause a telomerization reaction, and the telomerization reaction product directly enters an elimination reaction system; The elimination reaction system comprises a solvent storage tank, a Grignard reagent storage tank, an elimination reactor, and a metering pump; the solvent storage tank and the Grignard reagent storage tank are respectively connected to the elimination reactor through metering pumps, and the outlet of the elimination reactor is connected to a distillation purification system; the polycondensation reaction product reacts with the Grignard reagent in the elimination reactor to generate a crude hexafluorobutadiene product.

[0018] The present invention arranges the discharge port of the bromination reactor at the middle and upper part of the bromination reactor. The density of dibromotetrafluoroethane, a product of the bromination reaction, is smaller than that of liquid bromine. By controlling the feeding speed of tetrafluoroethylene and liquid bromine, most of the liquid bromine reacts with tetrafluoroethylene to generate dibromotetrafluoroethane, and a small amount of unreacted liquid bromine sinks to the bottom of the bromination reactor to continue to react. The generated dibromotetrafluoroethane can automatically flow into a dibromotetrafluoroethane storage tank through the discharge port.

[0019] The reaction system of the invention can realize the continuous production of hexafluorobutadiene and is suitable for industrial application.

[0020] The continuous production system of hexafluorobutadiene of the present invention also includes a distillation and purification system; the distillation and purification system includes a distillation tower and a condensation collector; the crude hexafluorobutadiene is condensed and stored in the condensation collector after distillation.

[0021] In the continuous production system of hexafluorobutadiene of the present invention, a plurality of exhaust holes are provided at the end of the bottom guide pipe; And / or, the catalyst in the fixed bed reactor is a supported catalyst, which is prepared by loading cuprous bromide onto a porous material, wherein the porous material is selected from one or more of activated carbon, carbon nanotubes, and silicon dioxide, and the loading amount of the supported catalyst is 5wt% to 30wt%.

[0022] The bromination reactor is made of high boron glass or enamel.

[0023] The present invention also provides application of the above method or the continuous production system of hexafluorobutadiene in improving the production efficiency of hexafluorobutadiene and / or reducing the production cost.

[0024] The beneficial effects of the present invention are at least: The present invention provides a continuous production method of hexafluorobutadiene, which significantly improves the yield of telomerization reaction, thereby improving the production efficiency of hexafluorobutadiene. The overall process is simple, the raw materials are easily available, the production efficiency is high, the production can be continuous, the production cost is low, and it has the value of industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of continuous production process. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention will be described in detail below in conjunction with examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0027] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available or prepared according to conventional methods in the art unless otherwise specified.

[0028] The present invention provides a continuous production system of hexafluorobutadiene (schematic diagram shown in Figure 1 ), with tetrafluoroethylene and liquid bromine as raw materials, the production system includes: a bromination reaction system, a telomerization reaction system, an elimination reaction system and a distillation purification system. The embodiment of the present invention adopts this production system to produce hexafluorobutadiene.

[0029] In the continuous production system of hexafluorobutadiene, the bromination reaction system includes a liquid bromine storage tank, a tetrafluoroethylene storage tank, a tetrafluoroethylene vaporization tank, a bromination reactor, a metering pump and a dibromotetrafluoroethane collection tank. A bottom guide pipe is provided in the bromination reactor to the bottom of the reactor, the liquid bromine storage tank is connected to the feed port of the bromination reactor through a metering pump, the tetrafluoroethylene vaporization tank is connected to the bottom guide pipe in the bromination reactor through a pipeline, the end of the bottom guide pipe contains a plurality of exhaust holes, the discharge port of the bromination reactor is arranged in the middle and upward position of the bromination reactor, and the dibromotetrafluoroethane collection tank is connected to the discharge port of the bromination reactor. Liquid bromine is added to the bromination reactor through a metering pump, and the tetrafluoroethylene in the tetrafluoroethylene vaporization tank enters the bottom of the bromination reactor through the bottom guide pipe of the bromination reactor to react with the liquid bromine, and the generated dibromotetrafluoroethane automatically flows into the dibromotetrafluoroethane collection tank.

[0030] The telomerization reaction system is composed of a vaporizer and a fixed bed reactor. The inlet of the vaporizer is connected to a dibromotetrafluoroethane collection tank, and the outlet of the vaporizer is connected to a fixed bed reactor. After dibromotetrafluoroethane is vaporized, it enters the fixed bed reactor and continuously contacts with the vaporized tetrafluoroethylene under the action of a catalyst to cause a telomerization reaction. The telomerization reaction products include dibromooctafluorobutane, a small amount of Br(CF2CF2)3Br and a very small amount of unreacted dibromotetrafluoroethane. The telomerization reaction mixed product directly enters the elimination reaction system.

[0031] The elimination reaction system consists of a solvent storage tank, a Grignard reagent storage tank, an elimination reactor, and a metering pump. The solvent storage tank and the Grignard reagent storage tank are respectively connected to the elimination reactor through metering pumps, and the outlet of the elimination reactor is connected to the distillation purification system. The telomerization reaction product reacts with the Grignard reagent in the elimination reactor to generate crude hexafluorobutadiene.

[0032] The distillation and purification system consists of a product distillation tower and a condensation collector. The crude hexafluorobutadiene is condensed and stored in the collector after distillation.

[0033] Specifically, in the bromination reaction, the molar ratio of tetrafluoroethylene to liquid bromine is (1.2~1.5):1, and the reaction temperature is 20~50°C.

[0034] The temperature of the telomerization reaction is 180-350°C, the molar ratio of tetrafluoroethylene to dibromotetrafluoroethane is 1.3-3.2:1, the reaction pressure is 0.5-1.0 MPa, and the residence time is 8-30 seconds. The catalyst used in the telomerization reaction is a supported catalyst, with cuprous bromide as the active center, and the carrier is selected from one or more of activated carbon, carbon nanotubes, and silica, with a loading amount of 5wt%-30wt%.

[0035] The temperature of the elimination reaction is 50-80° C., the molar ratio of the Grignard reagent to dibromooctafluorobutane is 1.2-1.8:1, the Grignard reagent is one or more of methylmagnesium chloride, ethylmagnesium bromide or phenylmagnesium bromide, the solvent is one or more of tetrahydrofuran, dimethyl ether, ethyl ether or 1,4-dioxane, and the added amount is equivalent to the volume of dibromooctafluorobutane.

[0036] Example 1 This embodiment provides a continuous production method of hexafluorobutadiene, which specifically includes: Weigh a certain amount of activated carbon (2000 g) into a two-necked flask, add deionized water (800 mL), add CuBr (200 g) under a nitrogen atmosphere, stir at room temperature until the system turns light blue, then filter, wash with ethanol several times, and vacuum dry to obtain the catalyst C-CuBr-0.1 (loading amount 10 wt%), which is then filled into a fixed bed reactor.

[0037] Liquid bromine and vaporized tetrafluoroethylene were added to the bromination reactor, the feeding rate was controlled so that the molar ratio of tetrafluoroethylene to liquid bromine was 1.2:1, the reaction temperature was controlled at 30°C, tetrafluoroethylene and liquid bromine were completely reacted to generate dibromotetrafluoroethane, the vaporized dibromotetrafluoroethane and tetrafluoroethylene were introduced into the fixed bed reactor in a molar ratio of 1:1.3, the temperature of the fixed bed reactor was controlled at 220°C, the reaction pressure was 0.5 MPa, the residence time was 10s, and the content of dibromooctafluorobutane in the polyurethane reaction product was 73.4%. The telomerization product is directly introduced into an elimination reactor, methylmagnesium chloride is selected as a Grignard reagent, tetrahydrofuran is selected as a solvent (the amount added is equivalent to the volume of dibromooctafluorobutane), the molar ratio of methylmagnesium chloride to dibromooctafluorobutane is 1.2:1, the reaction temperature is 50°C, the content of hexafluorobutadiene in the elimination reaction product is 86%, and the elimination reaction product is directly introduced into a distillation tower, the tower bottom temperature is set at 95°C, the tower top temperature is set at 15°C, and the pressure is 60Kpa. After pressurized distillation separation and purification, hexafluorobutadiene with a purity of 99.86% is obtained by condensation.

[0038] Example 2 This embodiment provides a continuous production method of hexafluorobutadiene, which specifically includes: Weigh a certain amount of carbon nanotubes (2000 g) into a two-necked flask, add deionized water (800 mL), add CuBr (100 g) under a nitrogen atmosphere, and stir at room temperature until the system turns light blue. Then filter, wash with ethanol several times, and vacuum dry to obtain the catalyst CNTs-CuBr-0.05 (loading amount 5 wt%), which is then filled into a fixed bed reactor.

[0039] Liquid bromine and vaporized tetrafluoroethylene were added to the bromination reactor, the feeding rate was controlled so that the molar ratio of tetrafluoroethylene to liquid bromine was 1.3:1, the reaction temperature was controlled at 40°C, tetrafluoroethylene and liquid bromine were completely reacted to generate dibromotetrafluoroethane, the vaporized dibromotetrafluoroethane and tetrafluoroethylene were introduced into the fixed bed reactor in a molar ratio of 1:3.2, the temperature of the fixed bed reactor was controlled at 350°C, the reaction pressure was 0.8 MPa, the residence time was 15 s, and the content of dibromooctafluorobutane in the polyurethane reaction product was 92.6%. The telomerization product is directly introduced into an elimination reactor, ethylmagnesium bromide is selected as a Grignard reagent, dimethyl ether is selected as a solvent (the amount added is equivalent to the volume of dibromooctafluorobutane), the molar ratio of ethylmagnesium bromide to dibromooctafluorobutane is 1.5:1, the reaction temperature is 60°C, the content of hexafluorobutadiene in the elimination reaction product is 91%, and the elimination reaction product is directly introduced into a distillation tower, the bottom temperature of the tower is set at 95°C, the top temperature of the tower is set at 15°C, and the pressure is 60Kpa, and after pressure distillation, condensation and purification, hexafluorobutadiene with a purity of 99.89% is obtained.

[0040] Example 3 This embodiment provides a continuous production method of hexafluorobutadiene, which specifically includes: Weigh a certain amount of silica (2000 g) into a two-necked flask, add deionized water (800 mL), add CuBr (400 g) under a nitrogen atmosphere, and stir at room temperature until the system turns light blue. Then filter, wash with ethanol several times, and vacuum dry to obtain the catalyst SiO2-CuBr-0.2 (loading amount 20 wt%), which is then filled into a fixed bed reactor.

[0041] Liquid bromine and vaporized tetrafluoroethylene were added to the bromination reactor, the feeding rate was controlled so that the molar ratio of tetrafluoroethylene to liquid bromine was 1.5:1, the reaction temperature was controlled at 20°C, tetrafluoroethylene and liquid bromine were completely reacted to generate dibromotetrafluoroethane, the vaporized dibromotetrafluoroethane and tetrafluoroethylene were introduced into the fixed bed reactor in a molar ratio of 1:2.0, the temperature of the fixed bed reactor was controlled at 180°C, the reaction pressure was 0.5 MPa, the residence time was 30s, and the content of dibromooctafluorobutane in the polyurethane reaction product was 78.3%. The telomerization product is directly introduced into an elimination reactor, methylmagnesium chloride is selected as a Grignard reagent, ether is selected as a solvent (the amount added is equivalent to the volume of dibromooctafluorobutane), the molar ratio of methylmagnesium chloride to dibromooctafluorobutane is 1.8:1, the reaction temperature is 80°C, the content of hexafluorobutadiene in the elimination reaction product is 92%, and the elimination reaction product is directly introduced into a distillation tower, the bottom temperature of the tower is set at 95°C, the top temperature of the tower is set at 15°C, and the pressure is 60Kpa. After pressure distillation and purification, hexafluorobutadiene with a purity of 99.92% is obtained by condensation.

[0042] Example 4 This embodiment provides a continuous production method of hexafluorobutadiene, which specifically includes: Weigh a certain amount of silica (2000 g) into a two-necked flask, add deionized water (800 mL), add CuBr (200 g) under a nitrogen atmosphere, stir at room temperature until the system turns light blue, then filter, wash with ethanol several times, and vacuum dry to obtain the catalyst SiO2-CuBr-0.1 (loading amount 10 wt%), which is then filled into a fixed bed reactor.

[0043] Liquid bromine and vaporized tetrafluoroethylene were added to the bromination reactor, the feeding rate was controlled so that the molar ratio of tetrafluoroethylene to liquid bromine was 1.4:1, the reaction temperature was controlled at 50°C, tetrafluoroethylene and liquid bromine were completely reacted to generate dibromotetrafluoroethane, the vaporized dibromotetrafluoroethane and tetrafluoroethylene were introduced into the fixed bed reactor in a molar ratio of 1:2.5, the temperature of the fixed bed reactor was controlled at 220°C, the reaction pressure was 1.0 MPa, the residence time was 20s, and the content of dibromooctafluorobutane in the polyurethane reaction product was 87.6%. The telomerization product is directly introduced into an elimination reactor, phenylmagnesium bromide is selected as a Grignard reagent, 1,4-dioxane is selected as a solvent (the amount added is equivalent to the volume of dibromooctafluorobutane), the molar ratio of phenylmagnesium bromide to dibromooctafluorobutane is 1.4:1, the reaction temperature is 70°C, the content of hexafluorobutadiene in the elimination reaction product is 87%, and the elimination reaction product is directly introduced into a distillation tower, the bottom temperature of the tower is set at 95°C, the top temperature of the tower is set at 15°C, and the pressure is 60Kpa. After pressure distillation and purification, hexafluorobutadiene with a purity of 99.85% is obtained by condensation.

[0044] Example 5 This embodiment provides a continuous production method of hexafluorobutadiene, which specifically includes: Weigh a certain amount of carbon nanotubes (2000 g) into a two-necked flask, add deionized water (800 mL), add CuBr (600 g) under a nitrogen atmosphere, and stir at room temperature until the system turns light blue. Then filter, wash with ethanol several times, and vacuum dry to obtain the catalyst CNTs-CuBr-0.3 (loading amount 30 wt%), which is then filled into a fixed bed reactor.

[0045] Liquid bromine and vaporized tetrafluoroethylene were added to the bromination reactor, the feeding rate was controlled so that the molar ratio of tetrafluoroethylene to liquid bromine was 1.3:1, the reaction temperature was controlled at 30°C, tetrafluoroethylene and liquid bromine were completely reacted to generate dibromotetrafluoroethane, the vaporized dibromotetrafluoroethane and tetrafluoroethylene were introduced into the fixed bed reactor in a molar ratio of 1:1.8, the temperature of the fixed bed reactor was controlled at 250°C, the reaction pressure was 0.6 MPa, the residence time was 20s, and the content of dibromooctafluorobutane in the polyurethane reaction product was 89.1%. The telomerization product is directly introduced into an elimination reactor, methylmagnesium chloride is selected as a Grignard reagent, tetrahydrofuran is selected as a solvent (the amount added is equivalent to the volume of dibromooctafluorobutane), the molar ratio of methylmagnesium chloride to dibromooctafluorobutane is 1.6:1, the reaction temperature is 60°C, the content of hexafluorobutadiene in the elimination reaction product is 88%, and the elimination reaction product is directly introduced into a distillation tower, the tower bottom temperature is set at 95°C, the tower top temperature is set at 15°C, and the pressure is set at 60Kpa. After pressure distillation and purification, hexafluorobutadiene with a purity of 99.93% is obtained by condensation.

[0046] Comparative Example 1 This comparative example provides a continuous production method of hexafluorobutadiene, which is basically the same as the method in Example 1, except that the catalyst is changed to supported cuprous iodide. The preparation method is to weigh a certain amount of carbon nanotubes (2000 g) in a two-necked flask, add deionized water (800 mL), add CuI (100 g) under a nitrogen atmosphere, stir at room temperature until the system turns light blue, then filter, wash with ethanol several times, and vacuum dry to obtain a catalyst CNTs-CuI-0.05 (loading amount 5 wt%). The content of dibromooctafluorobutane in the telomerization product is 62.5%.

[0047] Comparative Example 2 This comparative example provides a continuous production method of hexafluorobutadiene, which is basically the same as the method in Example 1, except that the molar ratio of tetrafluoroethylene to dibromotetrafluoroethane during the reaction is 3.5:1. The content of dibromooctafluorobutane in the telomerization product is 58.4%.

[0048] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for producing hexafluorobutadiene, characterized in that: include: (1) Bromination reaction: Tetrafluoroethylene reacts with liquid bromine to produce dibromotetrafluoroethane; (2) Telomerization reaction: dibromotetrafluoroethane and tetrafluoroethylene react in the presence of a catalyst to produce dibromooctafluorobutane; the catalyst is cuprous bromide; (3) Elimination reaction: Dibromooctafluorobutane reacts with a Grignard reagent to generate hexafluorobutadiene.

2. The method according to claim 1, characterized in that In the bromination reaction, the molar ratio of tetrafluoroethylene to liquid bromine is (1.2-1.5):1, and the reaction temperature is 20-50°C.

3. The method according to claim 1 or 2, characterized in that: The temperature of the telomerization reaction is 180-350° C., the molar ratio of tetrafluoroethylene to dibromotetrafluoroethane is (1.3-3.2):1, the reaction pressure is 0.5-1.0 MPa, and the residence time is 8s-30s.

4. The method according to any one of claims 1 to 3, characterized in that: The reaction temperature of the elimination reaction is 50-80° C., the solvent is tetrahydrofuran, dimethyl ether, ethyl ether or 1,4-dioxane; the Grignard reagent is methylmagnesium chloride, ethylmagnesium bromide or phenylmagnesium bromide, and the molar ratio of the Grignard reagent to dibromooctafluorobutane is (1.2-1.8):

1.

5. The method according to any one of claims 1 to 4, characterized in that: The catalyst is a supported catalyst, which is prepared by loading cuprous bromide onto a porous material, wherein the porous material is selected from one or more of activated carbon, carbon nanotubes, and silicon dioxide, and the loading amount of the supported catalyst is 5wt% to 30wt%.

6. The method according to any one of claims 1 to 5, characterized in that: The method also includes the steps of separating, purifying and condensing the product of the elimination reaction.

7. A continuous production system of hexafluorobutadiene, characterized in that: The continuous production system comprises: a bromination reaction system, a telomerization reaction system, and an elimination reaction system; The bromination reaction system comprises a liquid bromine storage tank, a tetrafluoroethylene storage tank, a tetrafluoroethylene vaporization tank, a bromination reactor, a metering pump and a dibromotetrafluoroethane collecting tank; a bottom pipe is provided in the bromination reactor to the bottom of the reactor, the liquid bromine storage tank is connected to the feed port of the bromination reactor through the metering pump, the tetrafluoroethylene vaporization tank is connected to the bottom pipe in the bromination reactor through a pipeline, the discharge port of the bromination reactor is arranged in the middle and upper part of the bromination reactor, and the dibromotetrafluoroethane collecting tank is connected to the discharge port of the bromination reactor; liquid bromine is added to the bromination reactor through the metering pump, the tetrafluoroethylene in the tetrafluoroethylene vaporization tank enters the bottom of the bromination reactor through the bottom pipe of the bromination reactor to react with the liquid bromine, and the generated dibromotetrafluoroethane is collected in the dibromotetrafluoroethane collecting tank; The telomerization reaction system comprises a vaporizer and a fixed bed reactor; the inlet of the vaporizer is connected to a dibromotetrafluoroethane collection tank, and the outlet of the vaporizer is connected to a fixed bed reactor; the dibromotetrafluoroethane produced in the bromination reaction system is vaporized and enters the fixed bed reactor, and continuously contacts with the vaporized tetrafluoroethylene under the action of a catalyst to cause a telomerization reaction, and the telomerization reaction product directly enters an elimination reaction system; The elimination reaction system comprises a solvent storage tank, a Grignard reagent storage tank, an elimination reactor, and a metering pump; the solvent storage tank and the Grignard reagent storage tank are respectively connected to the elimination reactor through metering pumps, and the outlet of the elimination reactor is connected to a distillation purification system; the polycondensation reaction product reacts with the Grignard reagent in the elimination reactor to generate a crude hexafluorobutadiene product.

8. The continuous production system of hexafluorobutadiene according to claim 7, characterized in that: It also includes a distillation and purification system; the distillation and purification system includes a distillation tower and a condensation collector; the crude hexafluorobutadiene is condensed and stored in the condensation collector after distillation.

9. The continuous production system of hexafluorobutadiene according to claim 7, characterized in that: The end of the bottom guide pipe is provided with a plurality of exhaust holes; And / or, the catalyst in the fixed bed reactor is a supported catalyst, which is prepared by loading cuprous bromide onto a porous material, wherein the porous material is selected from one or more of activated carbon, carbon nanotubes, and silicon dioxide, and the loading amount of the supported catalyst is 5wt% to 30wt%.

10. Use of the method according to any one of claims 1 to 6 or the continuous production system of hexafluorobutadiene according to any one of claims 7 to 9 in improving the production efficiency of hexafluorobutadiene and / or reducing the production cost.

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