Method for preparing hexafluorobutadiene through two-step gas-phase continuous reaction

Abstract

The invention provides a method for preparing hexafluorobutadiene through two-step gas-phase continuous reaction, which comprises the following steps: gas-phase telomerization reaction: taking chlorotrifluoroethylene as a raw material, and carrying out gas-phase telomerization chain-forming reaction in the presence of a telomerization catalyst to obtain 3, 4-dichlorohexafluoro-1-butene; the reaction conditions are as follows: the reaction pressure is 0.1-1.5 MPa, the reaction temperature is 300-600 DEG C, and the contact time is 0.5-100 seconds; the method comprises the following steps: carrying out gas-phase dichlorination reaction, namely carrying out dichlorination reaction on 3, 4-dichlorohexafluoro-1-butene serving as a raw material in the presence of a dechlorination catalyst and hydrogen; the reaction conditions are as follows: the molar ratio of the hydrogen to the 3, 4-dichlorohexafluoro-1-butene is (1-3): 1, the reaction pressure is 0.1-1.5 MPa, the reaction temperature is 200-400 DEG C, and the contact time is 0.5-100 seconds. The method for synthesizing hexafluorobutadiene has the advantages of high one-way yield, high selectivity, short reaction time, easy realization of gas phase independent circulation continuous reaction, and high synthesis efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical synthesis, and particularly relates to a method for preparing hexafluorobutadiene by two-step gas-phase continuous reactions of trichloroethylene through telomerization and de-dichlorination. BACKGROUND

[0002] Hexafluorobutadiene is used as a key material for etching gas for chips with a size of 3 nm and below, and its stable supply for mass production is mainly controlled by international companies such as Japan Kanto Denka Co., Ltd. and Daikin Co., Ltd., and the domestic production rate is less than 5%.

[0003] At present, among the many synthetic routes of hexafluorobutadiene, the synthetic route of trichloroethylene as a starting material through telomerization and de-dichlorination has the advantages of low raw material price and low product comprehensive cost, and is concerned. At present, the environmental impact information reported by Shandong Feiyuan and Fujian Jianyang Jinshi uses this route for industrialization, and the total yield of hexafluorobutadiene of the route is 42.8% and 44%, respectively. The reaction equation is as follows:

[0004]

[0005] Up to now, the research on the above-mentioned synthetic route is mainly as follows:

[0006] (1) Research on the first step of telomerization reaction

[0007] CN116768695A reports a catalyst of molecular sieve loaded with titanium dioxide, which catalyzes the telomerization reaction of trichloroethylene at 410℃, and 3,4-dichlorohexafluoro-1-butene and 1,2-dichlorohexafluorocyclobutane are obtained at the same time, wherein the content of 3,4-dichlorohexafluoro-1-butene in the crude product is only 28.1%.

[0008] US2668182A reports that trichloroethylene undergoes telomerization reaction in a tubular reactor under the conditions of “reaction temperature 550℃, contact time several seconds, normal pressure”, and the conversion rate of trichloroethylene is 36.2%, and the yield of 3,4-dichlorohexafluoro-1-butene and 1,2-dichlorohexafluorocyclobutane is 14.4% and 7.4%, respectively.

[0009] US2733277A reports that trichloroethylene with a flow rate of 30-40 g / h undergoes telomerization reaction at 550-600℃, and the yield of 3,4-dichlorohexafluoro-1-butene and 1,2-dichlorohexafluorocyclobutane is 35% and 30%, respectively.

[0010] (2) Research on the second step of de-dichlorination reaction

[0011] CN116768695A reported that 3,4-dichlorohexafluoro-1-butene reacted with zinc powder in ethanol at 50℃, and the yield of hexafluorobutadiene was 19.3%.

[0012] CN113061074A reported that 3,4-dichlorohexafluoro-1-butene reacted with zinc powder in ethanol at 40℃, and the conversion rate of 3,4-dichlorohexafluoro-1-butene was 91%, the selectivity of hexafluorobutadiene was 92.9%, and the yield of hexafluorobutadiene was 84.4%.

[0013] The route has the following disadvantages: (1) In the telomerization reaction, the yield of the key intermediate 3,4-dichlorohexafluoro-1-butene is low; (2) A large amount of solvent and reducing agent zinc powder is used in the de-bis-chlorination reaction, generating a large amount of liquid waste and solid waste, causing serious environmental pollution; (3) The de-bis-chlorination reaction is a batch process, which is difficult to realize continuous production, and has the disadvantage of low efficiency. SUMMARY

[0014] The present application provides a method for the directional conversion of trifluorochloroethylene telomerization to 3,4-dichlorohexafluoro-1-butene, which has a high one-way yield of hexafluorobutadiene, a shorter reaction time, a high synthesis efficiency, and is easy to realize the two-step gas-phase continuous reaction for preparing hexafluorobutadiene. The present application is mainly used for the gas-phase continuous cyclic production of hexafluorobutadiene with high conversion rate and high selectivity.

[0015] The technical solution of the present application is as follows:

[0016] A method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction, comprising the following steps:

[0017] (1) Gas-phase telomerization reaction: using trifluorochloroethylene as raw material, a gas-phase telomerization chain reaction occurs in the presence of a telomerization catalyst to obtain 3,4-dichlorohexafluoro-1-butene;

[0018] The reaction conditions are as follows: the reaction pressure is 0.1-1.5 MPa, the reaction temperature is 300-600℃, and the contact time is 0.5-100 s;

[0019] (3) Gas-phase de-bis-chlorination reaction: using 3,4-dichlorohexafluoro-1-butene as raw material, a de-bis-chlorination reaction occurs in the presence of a de-chlorination catalyst and hydrogen;

[0020] The reaction conditions are as follows: the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene is 1-3:1, the reaction pressure is 0.1-1.5 MPa, the reaction temperature is 200-400℃, and the contact time is 0.5-100 s.

[0021] There is an equation relationship between the contact time, the total flow rate of the reactants, and the catalyst volume, and the contact time is equal to the ratio of the catalyst volume to the total flow rate.

[0022] Preferably, the telomerization catalyst in step (1) is a mixture of alkali metal fluoride and carrier A in a mass percentage of (1% to 20%):(80% to 99%), the sum of the mass percentages being 100%;

[0023] The alkali metal fluoride is any one or several of sodium fluoride, potassium fluoride, rubidium fluoride, and cesium fluoride.

[0024] The carrier A is any one or several of porous polytetrafluoroethylene (PTFE), porous tetrafluoroethylene-ethylene copolymer (ETFE), porous soluble polytetrafluoroethylene (PFA), porous polyperfluoroalkyl-ethylene (FEP), porous polyvinylidene fluoride (PVDF), and porous polytrifluorochloroethylene (PCTFE).

[0025] Preferably, the mass ratio of alkali metal fluoride to carrier A is (5% to 15%):(85% to 95%).

[0026] Preferably, the reaction pressure in step (1) is 0.1 to 0.5 MPa, the reaction temperature is 400 to 500℃, and the contact time is 5 to 50 s.

[0027] Preferably, the product of the gas-phase telomerization reaction in step (1) includes trifluorochloroethylene, 1,2-dichlorohexafluorocyclobutane, 3,4-dichlorohexafluoro-1-butene, and trifluorochloroethylene polymer, the degree of polymerization of the trifluorochloroethylene polymer is greater than or equal to 3, and the mass percentage content of 3,4-dichlorohexafluoro-1-butene is more than 80%, pure 3,4-dichlorohexafluoro-1-butene is obtained by rectification in a rectification column, and the purity is greater than 99%.

[0028] Preferably, the dechlorination catalyst in step (2) is a mixture of metal element A and carrier B in a mass percentage of (1% to 10%):(90% to 99%), the sum of the mass percentages being 100%.

[0029] The metal element A is any one or several of zinc, iron, copper, cadmium, ruthenium, and silver.

[0030] The carrier B is any one or several of aluminum fluoride, iron fluoride, magnesium fluoride, calcium fluoride, and chromium fluoride.

[0031] Preferably, the mass ratio of metal element to carrier B is (3% to 8%):(82% to 97%).

[0032] Preferably, the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene in step (2) is 1.5 to 2.5:1.

[0033] The reaction pressure is 0.1-0.5 MPa, the reaction temperature is 250-350 DEG C, and the contact time is 5-50 s.

[0034] Preferably, the product of the gas-phase debichlorination reaction in step (2) comprises 3,4-dichlorohexafluoro-1-butene, hexafluorobutadiene, hydrogen and hydrogen chloride, the hexafluorobutadiene accounts for more than 80% of the mass percentage of the organic product, and the pure product hexafluorobutadiene is obtained by rectification in a rectification tower, with a purity of more than 99.99%.

[0035] Compared with the prior art, the application has the following beneficial effects:

[0036] (1) In the application, the telomerization reaction of chlorotrifluoroethylene can realize directional conversion to linear structure 3,4-dichlorohexafluoro-1-butene, and the content of cyclic structure 1,2-dichlorohexafluorocyclobutane is very low or even zero;

[0037] (2) Compared with the prior art, the preparation method of hexafluorobutadiene in the application has higher single-pass yield, higher selectivity, shorter reaction time, and is easy to realize gas-phase independent circulation continuous reaction, and has the characteristics of high efficiency;

[0038] (3) The application adopts a gas-phase method to prepare hexafluorobutadiene, and through a gas-phase independent circulation process, the incomplete reaction materials are independently circulated, so that the initial raw materials can be almost completely converted into target products, and the target products can be finally collected from the process system, so that liquid waste and waste gas are not produced, and green production is realized. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The reaction equation diagram of the application.

[0040] Figure 2 The preparation process flow diagram of hexafluorobutadiene prepared by gas-phase telomerization and gas-phase debichlorination reaction of chlorotrifluoroethylene as a starting raw material is shown.

[0041] Fig. 1 is a schematic diagram of the preparation process of hexafluorobutadiene according to the application.

[0042] 8-First pipeline; 9-Second pipeline: 10-Third pipeline; 11-Fourth pipeline: 12-Fifth pipeline; 13-Sixth pipeline: 14-Seventh pipeline; 15-Eighth pipeline: 16-Ninth pipeline; 17-Tenth pipeline: 18-Eleventh pipeline; 19-Twelfth pipeline: 20-Thirteenth pipeline; 21-Fourteenth pipeline: 22-Fifteenth pipeline; 23-Sixteenth pipeline; 24-Seventeenth pipeline. DETAILED DESCRIPTION

[0043] The application will be further described in conjunction with experimental examples. It should be appreciated that the experimental examples are only used for further illustrating and explaining the application, and are not intended to limit the application.

[0044] Unless otherwise defined, all technical and scientific terms used in the present disclosure have the same meaning as commonly understood by one of ordinary skill in the art. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, illustrative methods and materials are described below. However, if there is a conflict between the definitions in the specification including that of the priority document, the instant specification will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. The present application is further described in conjunction with the following experimental examples, which are not intended to limit the scope of the application.

[0045] The present application provides a method for preparing hexafluorobutadiene in gas phase continuously, which includes three steps of gas phase telomerization, gas phase de-dichlorination and gas phase isomerization. Specifically as follows:

[0046] (1) The first step: gas phase telomerization

[0047] The 3,4-dichlorohexafluoro-1-butene is obtained by the gas phase telomerization chain reaction of trichloroethylene as raw material in the presence of telomerization catalyst.

[0048] The telomerization catalyst is composed of alkali metal fluoride and carrier A according to the mass percentage (1%~20%):(80%~99%), and the sum of the mass percentages of the two is 100%.

[0049] The alkali metal fluoride is any one or several of sodium fluoride, potassium fluoride, rubidium fluoride and cesium fluoride.

[0050] The carrier A is any one or several of porous polytetrafluoroethylene (PTFE), porous tetrafluoroethylene-ethylene copolymer (ETFE), porous soluble polytetrafluoroethylene (PFA), porous polyperfluoroalkylpropene (FEP), porous polyvinylidene fluoride (PVDF) and porous polytrifluorochloroethylene (PCTFE).

[0051] The telomerization catalyst is prepared by the following method: according to the mass percentage composition of alkali metal fluoride and carrier A, the alkali metal fluoride is impregnated on the carrier A, filtered, dried and calcined to obtain the telomerization catalyst.

[0052] The traditional telomerization reaction of chlorotrifluoroethylene generally does not use a catalyst, resulting in that the telomerization product of chlorotrifluoroethylene is 1,2-dichlorohexafluorocyclobutane and 3,4-dichlorohexafluoro-1-butene, and the content of the two is not much different, resulting in poor selectivity of 3,4-dichlorohexafluoro-1-butene. The specific catalyst is used in the application, and the telomerization reaction of chlorotrifluoroethylene is realized to directional conversion of 3,4-dichlorohexafluoro-1-butene, not only the conversion rate of chlorotrifluoroethylene is high, but also the selectivity of 3,4-dichlorohexafluoro-1-butene is high, realizing the continuous process of gas phase synthesis of 3,4-dichlorohexafluoro-1-butene, and greatly improving the synthesis efficiency.

[0053] In some embodiments of the application, the mass ratio of the alkali metal fluoride to the carrier A is (5% to 15%): (85% to 95%).

[0054] In some embodiments of the application, the mass ratio of the alkali metal fluoride to the carrier A can be 5%:95%, 6%:94%, 7%:93%, 8%:92%, 9%:91%, 10%:90%, 11%:89%, 12%:88%, 13%:87%, 14%:86%, 15%:85% or any range therebetween. If the content of the alkali metal fluoride is less than 5%, the concentration of the active component is too low to be sufficient for the rapid and efficient progress of the reaction; if the content of the alkali metal fluoride is higher than 30%, the active component can seriously block the pore volume of the carrier, thereby being not conducive to the efficient progress of the reaction catalyzed by the catalyst.

[0055] In some embodiments of the application, in the preparation of the telomerization catalyst, the drying condition is that the drying temperature is 120℃ to 200℃, and the drying time is 6 to 15 hours, wherein the drying temperature can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or any range therebetween, and the drying time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or any range therebetween.

[0056] In some embodiments of the present application, in the preparation of the telomerization catalyst, the calcination conditions are as follows: the calcination temperature is 250-500°C, and the calcination time is 6-15 hours, wherein the calcination temperature can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, or any range between any two of them, and the calcination time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any range between any two of them.

[0057] The gas-phase telomerization reaction conditions are as follows: using trifluorochloroethylene as the raw material in the presence of the telomerization catalyst, the reaction pressure is 0.1-0.5 MPa, the reaction temperature is 300-600°C, and the contact time is 0.5-100 s.

[0058] In some embodiments of the present application, the gas-phase telomerization reaction conditions are as follows: using trifluorochloroethylene as the raw material in the presence of the telomerization catalyst, the reaction pressure is 0.1-0.5 MPa, the reaction temperature is 400-500°C, and the contact time is 5-50 s.

[0059] In some embodiments of the present application, the reaction pressure can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, or any range between any two of them, the reaction temperature can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, or any range between any two of them, and the contact time can be 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, or any range between any two of them.

[0060] In the present application, the material flow of the gas-phase telomerization reaction is composed of trifluorochloroethylene, 1,2-dichlorohexafluorocyclobutane, 3,4-dichlorohexafluoro-1-butene, and trifluorochloroethylene polymer (polymerization degree greater than or equal to 3), wherein the mass percentage of 3,4-dichlorohexafluoro-1-butene is more than 80%, and the pure 3,4-dichlorohexafluoro-1-butene is obtained by purification in a rectifying column.

[0061] In the present application, the contact time refers to the time for the reaction material to pass through the catalyst bed, i.e., the time for a single pass reaction in a fixed bed.

[0062] (2) Second step reaction: gas-phase debichlorination reaction

[0063] In the presence of a dechlorination catalyst and an appropriate amount of hydrogen, 3,4-dichlorohexafluoro-1-butene is subjected to a de-bis-chlorination reaction.

[0064] The dechlorination catalyst is a combination of a metal element A and a carrier B in a mass ratio of (1-10)%: (90-99)%.

[0065] The metal element A is any one or several of zinc, iron, copper, cadmium, ruthenium, and silver.

[0066] The carrier B is any one or several of aluminum fluoride, iron fluoride, magnesium fluoride, calcium fluoride, and chromium fluoride.

[0067] The dechlorination catalyst is prepared by impregnating a soluble salt of the metal element A on the carrier B according to the mass ratio of the metal element A and the carrier B, filtering, drying, calcining, and activating to obtain the dechlorination catalyst.

[0068] The traditional de-bis-chlorination reaction of 3,4-dichlorohexafluoro-1-butene generally does not use a catalyst, but uses a reducing agent of zinc powder in an organic solvent to dechlorinate 3,4-dichlorohexafluoro-1-butene. The existing de-bis-chlorination reaction of 3,4-dichlorohexafluoro-1-butene uses a large amount of reducing agent of zinc powder and flammable solvent of ethanol or methanol, which not only increases the risk level of the reaction device, but also produces a large amount of waste liquid and waste solid, causing serious environmental pollution.

[0069] In the present application, the dechlorination catalyst is used to de-bis-chlorinate 3,4-dichlorohexafluoro-1-butene in a hydrogen atmosphere. The principle is that the metal element A (A = zinc, iron, copper, cadmium, ruthenium, or silver) in the catalyst first removes the bis-chlorine atoms in 1,2-dichlorohexafluorocyclobutane to obtain hexafluorocyclobutene and metal chloride ACl n (the valence of element A in the metal chloride is n+); then hydrogen activates the metal chloride ACl n in the catalyst to obtain the metal element A and hydrogen chloride. The de-bis-chlorination process of the present application has the advantages of high conversion rate, high selectivity, green and high efficiency, and is easy to realize gas-phase continuous large-scale production.

[0070] In some embodiments of the present application, the mass ratio of the metal element A to the carrier B is (3-8)%: (92-97)%.

[0071] In some embodiments of the present application, the mass ratio of the metal element A to the carrier B can be 3%:97%, 4%:96%, 5%:95%, 6%:94%, 7%:93%, 8%:92%, or any range therebetween. If the content of the metal element is less than 3%, the concentration of the active component is too low to catalyze the reaction to proceed rapidly and efficiently; if the content of the metal element is higher than 8%, the active component can seriously block the pore volume of the carrier, thereby adversely affecting the efficient catalysis of the catalyst.

[0072] In some embodiments of the present application, in the preparation of the dechlorination catalyst, the drying conditions are: the drying temperature is 120-200℃, and the drying time is 6-15 hours, wherein the drying temperature can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, or any range therebetween, and the drying time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any range therebetween.

[0073] In some embodiments of the present application, in the preparation of the dechlorination catalyst, the calcination conditions are: the calcination temperature is 300-500℃, and the calcination time is 6-15 hours, wherein the calcination temperature can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, or any range therebetween, and the calcination time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any range therebetween.

[0074] In some embodiments of the present application, in the preparation of the dechlorination catalyst, the activation conditions are: the activation treatment is carried out in a mixed gas of nitrogen and hydrogen, the molar ratio of nitrogen to hydrogen is (1-10):1, the activation temperature is 250-450℃, and the activation time is 8-20 hours, wherein the activation temperature can be 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, or any range therebetween, and the activation time can be 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any range therebetween.

[0075] The gas phase debichlorination reaction conditions are as follows: in the presence of a debchlorination catalyst, using 3,4-dichlorohexafluoro-1-butene and hydrogen as raw materials, the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene is 1-3:1, the reaction pressure is 0.1-0.5 MPa, the reaction temperature is 200-400 ℃, and the contact time is 0.5-100 s

[0076] In some embodiments of the present application, the gas phase debichlorination reaction conditions are as follows: in the presence of a debchlorination catalyst, using 3,4-dichlorohexafluoro-1-butene as a raw material, the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene is 1.5-2.5:1, the reaction pressure is 0.1-0.5 MPa, the reaction temperature is 250-350 ℃, and the contact time is 5-50 s.

[0077] In some embodiments of the present application, the reaction pressure can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, or any range therebetween, the reaction temperature can be 250 ℃, 260 ℃, 270 ℃, 280 ℃, 290 ℃, 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃, 350 ℃, or any range therebetween, and the contact time can be 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, or any range therebetween.

[0078] In the present application, the material flow of the gas phase debichlorination reaction is composed of 3,4-dichlorohexafluoro-1-butene, hexafluorobutadiene, hydrogen, and hydrogen chloride, wherein the percentage of hexafluorocyclobutene in the organic product is more than 80%, and pure hexafluorocyclobutene is obtained after purification by a rectifying column.

[0079] The present application provides a method for continuously producing hexafluorobutadiene in gas phase with high conversion rate and high selectivity.

[0080] To achieve the purpose of the present application, the present application provides a method for producing hexafluorobutadiene by gas phase regulation polymerization and gas phase debichlorination reaction using trifluorochloroethylene as a starting material, and the intermediate is 3,4-dichlorohexafluoro-1-butene. The reaction equation is as shown in Figure 1 .

[0081] The present application provides a method for continuously producing hexafluorobutadiene in gas phase as follows: in the presence of a debchlorination catalyst, 3,4-dichlorohexafluoro-1-butene and hydrogen undergo a gas phase debichlorination reaction in a tubular reactor to obtain hexafluorobutadiene.

[0082] The raw material 3,4-dichlorohexafluoro-1-butene can be obtained by directional regulation polymerization and chain reaction of trifluorochloroethylene in the presence of a regulation polymerization catalyst.

[0083] The gas phase telomerization reaction and the gas phase de-dichlorination reaction can realize a gas phase independent cycle continuous process method. Due to the great difference in boiling points of the raw materials and reaction products, the raw materials, intermediates and products can be effectively separated by phase separators, distillation columns and other means, and the unreacted raw materials and incompletely reacted intermediates are continuously circulated to the reactor to continue to participate in the reaction, while the product hexafluorobutadiene and the byproduct HCl are extracted from the system. The boiling point of hexafluorobutadiene is 7-8℃ (760mmHg); the boiling point of 1,2-dichlorohexafluorocyclobutane is 59.9℃ (760mmHg); the boiling point of 3,4-dichlorohexafluoro-1-butene is 65-66℃ (760mmHg); the boiling point of trifluorochloroethylene is -28.4℃ (760mmHg); the boiling point of H2 is -252.77℃ (760mmHg); the boiling point of HCl is -85.1℃ (760mmHg); and so on.

[0084] The present application uses a fixed bed reactor. When the catalyst is placed in the constant temperature zone of the fixed bed reactor to obtain a catalyst bed, when the gas or liquid raw material flows through the fixed bed at a small speed, the upward resistance of the flowing raw material does not change the movement state of the initiator or the catalyst, and the bed height remains unchanged; the bed pressure drop increases with the logarithmic increase of the flow rate.

[0085] The type of reactor used for the reaction is not critical, and a tubular reactor, a fluidized bed reactor, etc. can be used. In addition, an adiabatic reactor or an isothermal reactor can also be used.

[0086] Reference Figure 2, fresh trifluorochloroethylene via the fourth line 11, together with trifluorochloroethylene recycled via the sixth line 13, enters the first reactor 1 filled with telomerization catalyst to react, the product flows into the first distillation column 2 via the seventh line 14 to separate, the overhead component is trifluorochloroethylene, the bottom component is 1,2-dichlorohexafluorocyclobutane and 3,4-dichlorohexafluoro-1-butene, the overhead component is recycled to the first reactor 1 via the sixth line 13 and the fifth line 12 to continue to react, the bottom component enters the second distillation column 3 via the eighth line 15 to continue to separate, the overhead component is 1,2-dichlorohexafluorocyclobutane, the bottom component is 3,4-dichlorohexafluoro-1-butene, the overhead component is withdrawn from the system via the ninth line 16, the bottom component 3,4-dichlorohexafluoro-1-butene enters the second reactor 4 via the tenth line 17, together with fresh hydrogen gas punched in via the eleventh line 18, together with hydrogen gas recycled via the fifteenth line 22, together with 3,4-dichlorohexafluoro-1-butene recycled via the line, to undergo de-bis-chlorination reaction via the thirteenth line 20, the product flows into the third distillation column 5 via the fourteenth line 21 to separate; the overhead component of the third distillation column 5 is hydrogen gas, which enters the second reactor 4 via the fifteenth line 22 to continue to be recycled, the bottom component is hydrogen chloride, hexafluorobutadiene and 3,4-dichlorohexafluoro-1-butene, the bottom component enters the fourth distillation column 6 via the sixteenth line 23 to continue to separate; the overhead component of the fourth distillation column 6 is hydrogen chloride, which is withdrawn to be sold as hydrogen chloride or formulated into hydrochloric acid, the bottom component is hexafluorobutadiene and 3,4-dichlorohexafluoro-1-butene, the bottom component enters the fifth distillation column 7 via the seventeenth line 24 to continue to separate; the bottom component of the fifth distillation column 7 is 3,4-dichlorohexafluoro-1-butene, the bottom component enters the second reactor 4 via the twelfth line 19 and the thirteenth line 20 to continue to react, the overhead component is hexafluorobutadiene, the overhead component is subjected to subsequent drying, rectification and other steps to obtain high-purity hexafluorobutadiene with a purity of greater than 99.99%.

[0087] Analytical instrument: Agilent 8860 gas chromatograph, chromatographic column type: J&W GS-GasPro (i.d. 0.32mm; length 60m).

[0088] Gas chromatography analysis method: high-purity helium and hydrogen are used as carrier gas. Detector temperature 240℃, vaporization chamber temperature 150℃, column initial temperature 40℃, hold for 10 minutes, increase to 240℃ at 20℃ / min, hold for 10 minutes.

[0089] The following experimental examples further illustrate the present application, but do not limit the scope of the present application.

[0090] Preparation of carrier B: A water solution of a metal soluble salt is prepared. Ammonia water with a concentration of 10% is added dropwise to the water solution until the pH reaches 9.0. The solution is filtered and washed until the pH of the filtrate reaches 7.0. The solid is dried at 80-200°C under nitrogen atmosphere for 10-20 hours, and then calcined at 250-500°C under nitrogen atmosphere for 10-20 hours. The catalyst particles with a particle size of 3-5 mm are prepared and packed in a fixed bed. The metal fluoride is prepared by activating the catalyst particles in an atmosphere of HF or NF3for 10-20 hours. The metal soluble salt is any one of a chloride, a nitrate, and an acetate. The final product is any one of aluminum fluoride, iron fluoride, magnesium fluoride, calcium fluoride, and chromium fluoride.

[0091] Example

[0092] Example 1

[0093] Preparation of telomerization catalyst: cesium fluoride is impregnated on the carrier according to the mass ratio of potassium fluoride to porous soluble polytetrafluoroethylene of 10:90. The catalyst precursor is obtained by filtration. The telomerization catalyst is prepared by drying the catalyst precursor at 150°C under nitrogen atmosphere for 10 hours and calcining at 400°C for 10 hours.

[0094] Example 2

[0095] Example 2 is different from Example 1 only in that the mass ratio of potassium fluoride to porous soluble polytetrafluoroethylene is 5:95, and the rest of the conditions are the same.

[0096] Example 3

[0097] Example 3 is different from Example 1 only in that the mass ratio of potassium fluoride to porous soluble polytetrafluoroethylene is 15:85, and the rest of the conditions are the same.

[0098] Example 4

[0099] Example 4 is different from Example 1 only in that the mass ratio of potassium fluoride to porous soluble polytetrafluoroethylene is 1:99, and the rest of the conditions are the same.

[0100] Example 5

[0101] Example 5 is different from Example 1 only in that the mass ratio of potassium fluoride to porous soluble polytetrafluoroethylene is 20:80, and the rest of the conditions are the same.

[0102] Example 6

[0103] Example 6 is different from Example 1 only in that the mass ratio of potassium fluoride to porous polytetrafluoroethylene is 10:90, and the rest of the conditions are the same.

[0104] Example 7

[0105] Example 7 differs from Example 1 only in that the mass ratio composition of potassium fluoride and porous tetrafluoroethylene-ethylene copolymer is 10:90, and the remaining conditions are the same.

[0106] Example 8

[0107] Example 8 differs from Example 1 only in that the mass ratio composition of potassium fluoride and porous polyfluoroethylene-propylene is 10:90, and the remaining conditions are the same.

[0108] Example 9

[0109] Example 9 differs from Example 1 only in that the mass ratio composition of potassium fluoride and porous polyvinylidene fluoride is 10:90, and the remaining conditions are the same.

[0110] Example 10

[0111] Example 10 differs from Example 1 only in that the mass ratio composition of potassium fluoride and porous polytrifluorochloroethylene is 10:90, and the remaining conditions are the same.

[0112] Example 11

[0113] Example 11 differs from Example 1 only in that the mass ratio composition of sodium fluoride and porous soluble polytetrafluoroethylene is 10:90, and the remaining conditions are the same.

[0114] Example 12

[0115] Example 12 differs from Example 1 only in that the mass ratio composition of rubidium fluoride and porous soluble polytetrafluoroethylene is 10:90, and the remaining conditions are the same.

[0116] Example 13

[0117] Example 13 differs from Example 1 only in that the mass ratio composition of cesium fluoride and porous soluble polytetrafluoroethylene is 10:90, and the remaining conditions are the same.

[0118] Table 1 Preparation of telomerization catalysts

[0119]

[0120]

[0121] Example 14

[0122] Preparation of the dechlorination catalyst: Zn soluble salt was impregnated on chromium fluoride according to the mass ratio of Zn to chromium fluoride of 5:95, and a catalyst precursor was obtained by filtration. The precursor was dried at 150°C for 10 hours, calcined at 400°C for 10 hours, and activated at 300°C for 10 hours using a mixed gas of nitrogen and hydrogen at a molar ratio of 2:1 to prepare the dechlorination catalyst.

[0123] Example 15

[0124] Example 15 differs from Example 14 only in that the mass ratio of Zn to chromium fluoride is 3:97, and the remaining conditions are the same.

[0125] Example 16

[0126] Example 16 differs from Example 14 only in that the mass ratio of Zn to chromium fluoride is 8:92, and the remaining conditions are the same.

[0127] Example 17

[0128] Example 17 differs from Example 14 only in that the mass ratio of Zn to chromium fluoride is 1:99, and the remaining conditions are the same.

[0129] Example 18

[0130] Example 18 differs from Example 14 only in that the mass ratio of Zn to chromium fluoride is 10:90, and the remaining conditions are the same.

[0131] Example 19

[0132] Example 19 differs from Example 14 only in that the mass ratio of Zn to aluminum fluoride is 5:95, and the remaining conditions are the same.

[0133] Example 20

[0134] Example 20 differs from Example 14 only in that the mass ratio of Zn to iron fluoride is 5:95, and the remaining conditions are the same.

[0135] Example 21

[0136] Example 21 differs from Example 14 only in that the mass ratio of Zn to magnesium fluoride is 5:95, and the remaining conditions are the same.

[0137] Example 22

[0138] Example 22 differs from Example 14 only in that the mass ratio of Zn to calcium fluoride is 2:98, and the remaining conditions are the same.

[0139] Example 23

[0140] Example 23 differs from Example 14 only in that the mass ratio composition of Fe and chromium fluoride is 2:98, and the rest of the conditions are the same.

[0141] Example 24

[0142] Example 24 differs from Example 14 only in that the mass ratio composition of Cu and chromium fluoride is 2:98, and the rest of the conditions are the same.

[0143] Example 25

[0144] Example 25 differs from Example 14 only in that the mass ratio composition of Cd and chromium fluoride is 2:98, and the rest of the conditions are the same.

[0145] Example 26

[0146] Example 26 differs from Example 14 only in that the mass ratio composition of Ru and chromium fluoride is 2:98, and the rest of the conditions are the same.

[0147] Example 27

[0148] Example 27 differs from Example 14 only in that the mass ratio composition of Ag and chromium fluoride is 2:98, and the rest of the conditions are the same.

[0149] Table 2 Preparation of dechlorination catalysts

[0150] Metallic element A Support B Mass ratio of metallic element A and support B Example 14 Zn Chromium fluoride 5∶95 Example 15 Zn Chromium fluoride 3∶97 Example 16 Zn Chromium fluoride 8∶92 Example 17 Zn Chromium fluoride 1∶99 Example 18 Zn Chromium fluoride 10∶90 Example 19 Zn Aluminium fluoride 5∶95 Example 20 Zn Iron fluoride 5∶95 Example 21 Zn Magnesium fluoride 5∶95 Example 22 Zn Calcium fluoride 5∶95 Example 23 Fe Chromium fluoride 5∶95 Example 24 Cu Chromium fluoride 5∶95 Example 25 Cd Chromium fluoride 5∶95 Example 26 Ru Chromium fluoride 5∶95 Example 27 Ag Chromium fluoride 5∶95

[0151] Experimental Example

[0152] Experimental Example 1

[0153] A tube reactor made of inconel with an inner diameter of 1 / 2 inch and a length of 30 cm was filled with 10 milliliters of the catalyst prepared in Example 1. The reactor was heated to 300°C, and trifluorochloroethylene was introduced to perform the telomerization reaction, the contact time was 10 seconds, the reaction pressure was 0.1 MPa, and after 10 hours of reaction, the reaction crude product was collected and analyzed by gas chromatography for its composition, and the results are shown in Table 3.

[0154] Experimental Example 2

[0155] The same operation as in Experimental Example 1 was performed, except that the reaction temperature was changed to 400°C, and the results are shown in Table 3.

[0156] Experimental Example 3

[0157] The same operation as in Experimental Example 1 was performed, except that the reaction temperature was changed to 450°C, and the results are shown in Table 3.

[0158] Experimental Example 4

[0159] The same operation as in Experimental Example 1 was performed, except that the reaction temperature was changed to 500°C, and the results are shown in Table 3.

[0160] Experimental Example 5

[0161] The same operation as Experimental Example 1 was performed except that the reaction temperature was changed to 600°C, and the results are shown in Table 3.

[0162] Experimental Example 6

[0163] The same operation as Experimental Example 3 was performed except that the contact time was changed to 0.5 seconds, and the results are shown in Table 3.

[0164] Experimental Example 7

[0165] The same operation as Experimental Example 3 was performed except that the contact time was changed to 5 seconds, and the results are shown in Table 3.

[0166] Experimental Example 8

[0167] The same operation as Experimental Example 3 was performed except that the contact time was changed to 50 seconds, and the results are shown in Table 3.

[0168] Experimental Example 9

[0169] The same operation as Experimental Example 3 was performed except that the contact time was changed to 100 seconds, and the results are shown in Table 3.

[0170] Experimental Example 10

[0171] The same operation as Experimental Example 3 was performed except that the reaction pressure was changed to 0.5 MPa, and the results are shown in Table 3.

[0172] Experimental Example 11

[0173] The same operation as Experimental Example 3 was performed except that the reaction pressure was changed to 1 MPa, and the results are shown in Table 3.

[0174] Experimental Example 12

[0175] The same operation as Experimental Example 3 was performed except that the reaction pressure was changed to 1.5 MPa, and the results are shown in Table 3.

[0176] Experimental Example 13

[0177] Experimental Example 13 used the catalyst from Example 2, and the rest was the same as Experimental Example 3, and the results are shown in Table 3.

[0178] Experimental Example 14

[0179] Experimental Example 14 used the catalyst from Example 3, and the rest was the same as Experimental Example 3, and the results are shown in Table 3.

[0180] Experimental Example 15

[0181] Experimental Example 15 used the catalyst from Example 4, and the rest was the same as Experimental Example 3, and the results are shown in Table 3.

[0182] Experimental Example 16

[0183] The catalyst used in Experimental Example 16 was derived from Example 5, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0184] Experimental Example 17

[0185] The catalyst used in Experimental Example 17 was derived from Example 6, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0186] Experimental Example 18

[0187] The catalyst used in Experimental Example 18 was derived from Example 7, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0188] Experimental Example 19

[0189] The catalyst used in Experimental Example 19 was derived from Example 8, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0190] Experimental Example 20

[0191] The catalyst used in Experimental Example 20 was derived from Example 9, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0192] Experimental Example 21

[0193] The catalyst used in Experimental Example 21 was derived from Example 10, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0194] Experimental Example 22

[0195] The catalyst used in Experimental Example 22 was derived from Example 11, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0196] Experimental Example 23

[0197] The catalyst used in Experimental Example 23 was derived from Example 12, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0198] Experimental Example 24

[0199] The catalyst used in Experimental Example 24 was derived from Example 13, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0200] Comparative Example 1

[0201] Comparative Example 1 did not use a catalyst, and the rest was the same as Experimental Example 3. The results are shown in Table 3.

[0202] Table 3

[0203]

[0204]

[0205] Note: (1) No catalyst in Comparative Example 1, the contact time here is strictly speaking the residence time of the reactants in the reactor, the reaction temperature, reaction pressure and the flow rate of trifluorochloroethylene are the same as in Example 3, except that no catalyst is used.

[0206] As can be seen from Table 3, Examples 1-24, the catalyst prepared in the present application, when used to prepare 3,4-dichlorohexafluoro-l-butene by trifluorochloroethylene telomerization, has a high conversion rate, up to 100%, and a high selectivity of 3,4-dichlorohexafluoro-l-butene, up to over 99%, and is suitable for the process of continuous synthesis of 3,4-dichlorohexafluoro-l-butene in gas phase, greatly improving the synthesis efficiency. In the process of gas phase telomerization, the reaction temperature, reaction pressure and contact time have certain influence on the reaction efficiency. Among them, in the reaction temperature range of 400-500°C, the conversion rate of trifluorochloroethylene and the selectivity of 3,4-dichlorohexafluoro-l-butene are high; when the contact time is 5-50 seconds, the conversion rate of trifluorochloroethylene and the selectivity of 3,4-dichlorohexafluoro-l-butene are high, and the reaction efficiency is high.

[0207] Experimental Example 25

[0208] A tubular reactor made of inconel with an inner diameter of 1 / 2 inch and a length of 30 cm was loaded with 10 milliliters of the catalyst prepared in Example 13. The reactor was heated to 200°C, and 3,4-dichlorohexafluoro-l-butene and hydrogen were introduced for debichlorination reaction, wherein the molar ratio of hydrogen to 3,4-dichlorohexafluoro-l-butene was 2:1, the contact time was 20 seconds, and the reaction pressure was 0.1 MPa. After 10 hours of reaction, the reaction product was washed with water, washed with alkali and dried, and the organic crude product was collected. The composition of the organic crude product was analyzed by gas chromatography, and the results are shown in Table 4.

[0209] Experimental Example 26

[0210] The same operation as in Experimental Example 25, except that the reaction temperature was changed to 250°C, and the results are shown in Table 4.

[0211] Experimental Example 27

[0212] The same operation as in Experimental Example 25, except that the reaction temperature was changed to 300°C, and the results are shown in Table 4.

[0213] Experimental Example 28

[0214] The same operation as in Experimental Example 25, except that the reaction temperature was changed to 350°C, and the results are shown in Table 4.

[0215] Experimental Example 29

[0216] The same operation as in Experimental Example 25, except that the reaction temperature was changed to 400°C, and the results are shown in Table 4.

[0217] Experimental Example 30

[0218] The same operation as Experimental Example 27 was conducted except that the ratio of the amount of substance of hydrogen gas to 3,4-dichlorohexafluoro-l-butene was changed to 1:1, and the results are shown in Table 4.

[0219] Experimental Example 31

[0220] The same operation as Experimental Example 27 was conducted except that the ratio of the amount of substance of hydrogen gas to 3,4-dichlorohexafluoro-l-butene was changed to 1.5:1, and the results are shown in Table 4.

[0221] Experimental Example 32

[0222] The same operation as Experimental Example 27 was conducted except that the ratio of the amount of substance of hydrogen gas to 3,4-dichlorohexafluoro-l-butene was changed to 2.5:1, and the results are shown in Table 4.

[0223] Experimental Example 33

[0224] The same operation as Experimental Example 27 was conducted except that the ratio of the amount of substance of hydrogen gas to 3,4-dichlorohexafluoro-l-butene was changed to 3:1, and the results are shown in Table 4.

[0225] Experimental Example 34

[0226] The same operation as Experimental Example 27 was conducted except that the contact time was changed to 0.5 seconds, and the results are shown in Table 4.

[0227] Experimental Example 35

[0228] The same operation as Experimental Example 27 was conducted except that the contact time was changed to 5 seconds, and the results are shown in Table 4.

[0229] Experimental Example 36

[0230] The same operation as Experimental Example 27 was conducted except that the contact time was changed to 50 seconds, and the results are shown in Table 4.

[0231] Experimental Example 37

[0232] The same operation as Experimental Example 27 was conducted except that the contact time was changed to 100 seconds, and the results are shown in Table 4.

[0233] Experimental Example 38

[0234] The same operation as Experimental Example 27 was conducted except that the reaction pressure was changed to 0.5 MPa, and the results are shown in Table 4.

[0235] Experimental Example 39

[0236] The same operation as Experimental Example 27 was conducted except that the reaction pressure was changed to 1 MPa, and the results are shown in Table 4.

[0237] Experimental Example 40

[0238] The same operation as Experimental Example 27 was conducted except that the reaction pressure was changed to 1.5 MPa, and the results are shown in Table 4.

[0239] Experimental Example 41

[0240] The catalyst used in Experimental Example 41 was derived from Example 15, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0241] Experimental Example 42

[0242] The catalyst used in Experimental Example 42 was derived from Example 16, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0243] Experimental Example 43

[0244] The catalyst used in Experimental Example 43 was derived from Example 17, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0245] Experimental Example 44

[0246] The catalyst used in Experimental Example 44 was derived from Example 18, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0247] Experimental Example 45

[0248] The catalyst used in Experimental Example 45 was derived from Example 19, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0249] Experimental Example 46

[0250] The catalyst used in Experimental Example 46 was derived from Example 20, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0251] Experimental Example 47

[0252] The catalyst used in Experimental Example 47 was derived from Example 21, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0253] Experimental Example 48

[0254] The catalyst used in Experimental Example 48 was derived from Example 22, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0255] Experimental Example 49

[0256] The catalyst used in Experimental Example 49 was derived from Example 23, and the rest was the same as Experimental Example 27, and the results are shown in Table 4.

[0257] Experimental Example 50

[0258] The catalyst used in Experimental Example 50 was derived from Example 24, and the rest was the same as Experimental Example 27. The results are shown in Table 4.

[0259] Experimental Example 51

[0260] The catalyst used in Experimental Example 51 was derived from Example 25, and the rest was the same as Experimental Example 27. The results are shown in Table 4.

[0261] Experimental Example 52

[0262] The catalyst used in Experimental Example 52 was derived from Example 26, and the rest was the same as Experimental Example 27. The results are shown in Table 4.

[0263] Experimental Example 53

[0264] The catalyst used in Experimental Example 53 was derived from Example 27, and the rest was the same as Experimental Example 27. The results are shown in Table 4.

[0265] Comparative Example 2

[0266] Comparative Example 2 did not use a catalyst, and the rest was the same as Experimental Example 27. The results are shown in Table 4.

[0267] Table 4

[0268]

[0269]

[0270] Note: (1) In Comparative Example 2, there was no catalyst, so the contact time here is strictly the residence time of the reactants in the reactor. Compared with Example 26, the reaction temperature, reaction pressure, hydrogen flow rate, and 1,2-dichlorohexafluorocyclobutane flow rate were all the same, except that no catalyst was used.

[0271] As can be seen from Table 4, Examples 25-53, the catalyst prepared in this application, when used to prepare hexafluorocyclobutene by gas-phase double-dechlorination of 1,2-dichlorohexafluorocyclobutane and hydrogen, has a high conversion rate, up to 100%, and a high selectivity for hexafluorocyclobutene, up to more than 99%, and is suitable for the process of continuous gas-phase synthesis of hexafluorocyclobutene, greatly improving the synthesis efficiency. In the process of gas-phase double-dechlorination, the reaction temperature, reaction pressure, and contact time have a certain effect on the reaction efficiency. Among them, within the reaction temperature range of 250-350°C, the conversion rate of 1,2-dichlorohexafluorocyclobutane and the selectivity of hexafluorocyclobutene are high; when the contact time is 5-50 seconds, the conversion rate of 1,2-dichlorohexafluorocyclobutane and the selectivity of hexafluorocyclobutene are high, and the reaction efficiency is high.

[0272] Although the present application has been disclosed with reference to experimental examples, it is not intended to limit the present application, and any person skilled in the art can make some changes and modifications without departing from the spirit and scope of the present application. The scope of protection of the present application is defined by the appended patent claims.

Claims

1. A method for preparing hexafluorobutadiene by a two-step gas-phase continuous reaction, characterized in that: The following steps are involved: (1) Gas phase telomerization reaction: Using chlorotrifluoroethylene as the raw material, a gas phase telomerization chain reaction occurs in the presence of a telomerization catalyst to produce 3,4-dichlorohexafluoro-1-butene; The reaction conditions are as follows: reaction pressure of 0.1-1.5 MPa, reaction temperature of 300-600° C., and contact time of 0.5-100 s; (2) Gas-phase dechlorination reaction: 3,4-dichlorohexafluoro-1-butene is used as the raw material, and dechlorination reaction occurs in the presence of a dechlorination catalyst and hydrogen; The reaction conditions are: the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene is 1-3:1, the reaction pressure is 0.1-1.5 MPa, the reaction temperature is 200-400° C., and the contact time is 0.5-100 seconds.

2. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 1, characterized in that: The telomerization catalyst in step (1) is a mixture of alkali metal fluoride and carrier A in a mass percentage ratio of (1% to 20%): (80% to 99%), and the sum of the mass percentages of the two is 100%; The alkali metal fluoride is any one or more of sodium fluoride, potassium fluoride, rubidium fluoride and cesium fluoride; Carrier A is any one or more of porous polytetrafluoroethylene (PTFE), porous tetrafluoroethylene-ethylene copolymer (ETFE), porous soluble polytetrafluoroethylene (PFA), porous polyperfluoroethylene propylene (FEP), porous polyvinylidene fluoride (PVDF), and porous polychlorotrifluoroethylene (PCTFE).

3. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 2, characterized in that: The mass ratio of the alkali metal fluoride to the carrier A is (5% to 15%): (85% to 95%).

4. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 1, characterized in that: In step (1), the reaction pressure is 0.1-0.5 MPa, the reaction temperature is 400-500° C., and the contact time is 5-50 s.

5. The method for preparing hexafluorobutadiene by a two-step gas-phase continuous reaction according to claim 1 to claim 3, characterized in that: The product of the gas phase telomerization reaction in step (1) includes chlorotrifluoroethylene, 1,2-dichlorohexafluorocyclobutane, 3,4-dichlorohexafluoro-1-butene and chlorotrifluoroethylene polymer, the polymerization degree of the chlorotrifluoroethylene polymer is greater than or equal to 3, wherein the amount percentage of 3,4-dichlorohexafluoro-1-butene is greater than 80%, and pure 3,4-dichlorohexafluoro-1-butene is obtained by distillation and purification in a distillation tower.

6. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 1, characterized in that: The dechlorination catalyst in step (2) is a mixture of metal element A and carrier B in a mass percentage of (1% to 10%): (90% to 99%), and the sum of the mass percentages of the two is 100%; The metal element A is any one or more of zinc, iron, copper, cadmium, ruthenium, and silver; The carrier B is any one or more of aluminum fluoride, iron fluoride, magnesium fluoride, calcium fluoride, and chromium fluoride.

7. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 6, characterized in that: The mass ratio of the metal element to the carrier B is (3% to 8%): (82% to 97%).

8. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 1, characterized in that: In step (2), the molar ratio of hydrogen to 3,4-dichlorohexafluoro-1-butene is 1.5 to 2.5:1; The reaction pressure is 0.1-0.5 MPa, the reaction temperature is 250-350° C., and the contact time is 5-50 seconds.

9. The method for preparing hexafluorobutadiene by two-step gas-phase continuous reaction according to claim 1, characterized in that: The products of the gas-phase dechlorination reaction in step (2) include 3,4-dichlorohexafluoro-1-butene, hexafluorobutadiene, hydrogen and hydrogen chloride, and the amount of hexafluorobutadiene in the organic product accounts for more than 80%. Pure hexafluorobutadiene is obtained by distillation and purification in a distillation tower.

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