A kind of preparation method of hexafluorobutadiene

Abstract

The invention discloses a method for preparing hexafluorobutadiene, and the preparation process includes passing chlorotrifluoroethylene gas through a tubular reactor filled with molecular sieve-loaded titanium dioxide, chlorotrifluoroethylene is catalytically pyrolyzed on the surface of the molecular sieve by titanium dioxide to generate a pyrolysis product containing 3,4-dichlorohexafluoro-1-butene, and then 3,4-dichlorohexafluoro-1-butene separated from the pyrolysis product is dechlorinated with zinc powder in a polar solvent to generate hexafluorobutadiene. Compared with the prior art, the present invention uses molecular sieve-loaded titanium dioxide as a catalyst, catalytically pyrolyzes chlorotrifluoroethylene at high temperature to generate 3,4-dichlorohexafluoro-1-butene, and prepares hexafluorobutadiene after dechlorination, improves the selectivity and yield of hexafluorobutadiene, reduces the pyrolysis temperature, and through the selection of reactants and the control of reaction conditions, the production of high-purity hexafluorobutadiene can be achieved, and the method is simple in process and improves the preparation effect of hexafluorobutadiene.

Description

Technical Field

[0001] The invention relates to the field of new energy technology, and in particular to a method for preparing hexafluorobutadiene. Background Art

[0002] As an electronic gas, hexafluorobutadiene is mainly used in semiconductor products, such as plasma medium etching processing of ultra-large-scale integrated circuits, and can be used as an important monomer for synthesizing fluorine-containing resins. Hexafluorobutadiene (also known as perfluorobutadiene, abbreviated as C4F6 or HFBD) is a perfluorodiolefin compound with a structural formula of CF2=CF-CF=CF2, a boiling point of 5.8℃, and a density of 1.4g / mL at 15℃. In the early days, hexafluorobutadiene was used to synthesize fluorine-containing resins, and now it is more used in plasma etching of silicon wafers. Compared with carbon tetrafluoride, hexafluoroethane, octafluoropropane, and octafluorocyclobutane, hexafluorobutadiene has the advantages of higher etching selectivity, accuracy, and aspect ratio. It can etch electronic circuits less than 100nm or even narrower. In addition, the global warming potential (GWP) of C4F6 is 290, and its life in the atmosphere is less than 2 days. C4F6 is an excellent etching gas that can provide the required etching conditions and reduce greenhouse gas emissions.

[0003] There are many synthetic routes for the preparation of hexafluorobutadiene disclosed at home and abroad, but there are not many methods that can be applied to industrial production. They are mainly obtained by dechlorinating 1,2,3,4-tetrachlorohexafluorobutane and 3,4-dichlorohexafluoro-1-butene as intermediates, or by coupling reaction with fluorovinyl zinc halide as intermediates to prepare hexafluorobutadiene.

[0004] In the prior art, patent number CN201910774511.1 discloses a method for preparing hexafluorobutadiene: trifluorochloroethylene is used as a raw material and hydrogenated under the action of a first catalyst to obtain trifluoroethylene, trifluoroethylene is passed into a bromination reactor and bromine is reacted to obtain 1,2-dibromo-1,1,2-trifluoroethane, and dehydrobromination is performed to obtain trifluorobromoethylene. Trifluorobromoethylene reacts in a reactor containing a solvent, an initiator and zinc powder to generate a zinc reagent trifluorovinyl zinc bromide, and the zinc reagent trifluorovinyl zinc bromide undergoes a coupling reaction under the action of a second catalyst to obtain hexafluorobutadiene. This preparation method has the advantage of high yield, but the bromide residues and residues generated during the reaction process are relatively large and difficult to handle.

[0005] The existing patent number CN201410856791.8 discloses a method for preparing 3,4-dichlorohexafluoro-1-butene: preheating chlorotrifluoroethylene to 160-250°C; then cracking the preheated material at a temperature of 350-500°C to generate pyrolysis products of 3,4-dichlorohexafluoro-1-butene and dichlorohexafluorocyclobutane; and recycling the separated dichlorohexafluorocyclobutane to the chlorotrifluoroethylene preheating step. The high reaction temperature of this process will cause carbonization of the material and reduce the service life of the equipment.

[0006] The existing patent number CN202110224766.8 discloses a method for preparing hexafluorobutadiene: 3,4-dichlorohexafluoro-1-butene raw material and organic solvent are dehydrated separately, and then added to a dechlorination reactor together with zinc powder, and a dechlorination product is obtained after dechlorination reaction, and then the dechlorination product is distilled and catalytically converted to obtain hexafluorobutadiene. This process has high requirements for the purity of 3,4-dichlorohexafluoro-1-butene, and the dechlorination process requires continuous replenishment of solvent and zinc powder, which increases the difficulty of process operation.

[0007] The existing patent number CN202210845020.3 discloses a method for preparing hexafluorobutadiene: liquid chlorotrifluoroethylene raw material is introduced into the reactor from the bottom of the reactor for pyrolysis reaction, condensed and recovered after pyrolysis, and fractionated in a high-pressure water bath. The fraction is reacted with elemental zinc in ethanol as a catalyst, and the gas product is collected and pyrolyzed with hydrogen iodide gas, and then reacted with chlorine water under photocatalysis, and added to butyl carbitol. Zinc is used as a catalyst to heat the reaction to remove impurities, and the gas product passes through a porous solid catalyst to obtain hexafluorobutadiene. This method has many reaction steps and many intermittent operation steps, and the industrial production process is complicated.

[0008] The existing patent number CN202011061917.4 discloses a method for preparing hexafluorobutadiene: by preparing a polar base liquid, activated zinc and 1,2-dichloro-2-iodo-1,1,2-trifluoroethane, further preparing 1,2,3,4-tetrachlorohexafluorobutane, and finally dechlorinating 1,2,3,4-tetrachlorohexafluorobutane with zinc in a polar solvent to prepare hexafluorobutadiene. This method has many reaction steps, a complicated process, and a large amount of three wastes are generated in the industrial production process. Summary of the invention

[0009] (1) Technical issues to be solved

[0010] The purpose of the present invention is to provide a method for preparing hexafluorobutadiene. Aiming at the defects of the existing disclosed hexafluorobutadiene preparation technology, the present invention uses molecular sieve loaded titanium dioxide as a catalyst, catalytically pyrolyzes chlorotrifluoroethylene at high temperature to generate 3,4-dichlorohexafluoro-1-butene, and prepares hexafluorobutadiene after dechlorination, thereby improving the selectivity and yield of hexafluorobutadiene, reducing the pyrolysis temperature, solving the problems of low industrial production yield and complicated production process of the process, and reducing waste discharge.

[0011] (2) Technical solution

[0012] In order to solve the above technical problems, the present invention discloses a method for preparing hexafluorobutadiene, comprising the following steps:

[0013] Soak 5A molecular sieve with a particle size of 3 to 3.3 mm in a titanium tetrachloride solution for 2 to 4 hours, preferably 3 hours, and then spray deionized water on the surface of the molecular sieve to hydrolyze the titanium tetrachloride loaded on the surface and pores of the molecular sieve to obtain titanium dioxide.

[0014] The molecular sieve loaded with the catalyst titanium dioxide was placed in an oven at 300°C for 4 hours to remove all the moisture inside the molecular sieve and activate the molecular sieve to obtain the titanium dioxide catalyst loaded on the molecular sieve;

[0015] The molecular sieve-loaded titanium dioxide catalyst is filled in a double-layer mesh metal tube sandwich with an inner tube nominal diameter of 20 mm, an outer tube nominal diameter of 32 mm, and a length of 3.0 m-5.5 m, preferably a double-layer mesh metal tube sandwich with a length of 4.8 m; wherein the mesh diameter of the mesh of the mesh metal tube matching it is 2 mm, and the mesh metal tube containing the catalyst is fixed in a tubular reactor with a diameter of 45 mm and a length of 3.1 m-5.6 m, preferably a tubular reactor with a length of 4.9 m for the best reaction effect;

[0016] The tubular reactor is heated after nitrogen substitution, and the temperature is controlled to 380-430°C, wherein the preferred temperature is 380-410°C, and the optimal temperature control point is 410°C. The flow meter is used to adjust the gas flow rate of chlorotrifluoroethylene to pass through the tubular reactor at 4-8L / min. Generally, a gas flow rate of 4L / min is selected for easy control, and the pressure difference before and after chlorotrifluoroethylene passes through the tubular reactor is 600-1000Pa;

[0017] In a tubular reactor, catalytic pyrolysis is performed on chlorotrifluoroethylene to undergo free radical heterolysis and double bond cleavage addition reactions to generate pyrolysis products containing 3,4-dichlorohexafluoro-1-butene. The pyrolysis products after the reaction are condensed and collected in a condenser at -5 to -10°C, and 3,4-dichlorohexafluoro-1-butene in the pyrolysis products is separated. Anhydrous ethanol and zinc powder with a particle size of 200 mesh and a purity of more than 98% are added to a reactor, and the temperature is raised to 50°C. The separated 3,4-dichlorohexafluoro-1-butene is added dropwise to the reactor for dechlorination reaction to obtain hexafluorobutadiene.

[0018] (3) Beneficial effects

[0019] Compared with the prior art, the present invention uses molecular sieve-loaded titanium dioxide as a catalyst, catalytically pyrolyzes trifluorochloroethylene at high temperature to generate 3,4-dichlorohexafluoro-1-butene, and prepares hexafluorobutadiene after dechlorination, thereby improving the selectivity and yield of hexafluorobutadiene and reducing the pyrolysis temperature. The production of high-purity hexafluorobutadiene can be achieved through the selection of reactants and the control of reaction conditions. The method of the present invention has a simple process, uses low-cost raw material trifluorochloroethylene for production and preparation, and improves the yield of hexafluorobutadiene, thereby improving the preparation effect of hexafluorobutadiene. The problem of low industrial production yield and complex production process of the process is solved, the discharge and treatment of waste are reduced, and the economic benefits of preparing hexafluorobutadiene are improved. The scheme is suitable for industrial large-scale production. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with different processing techniques. The enumerated embodiments can enable those skilled in the art to better understand the present invention, but do not limit the present invention in any form.

[0021] The embodiments of the present invention are as follows:

[0022] Implementation case 1 (comparative example):

[0023] A 3.1 m long tubular reactor was replaced with nitrogen, and then the tubular reactor was heated to 380°C. A flow meter was used to adjust the gas flow rate of trifluorochloroethylene to 4 L / min through the tubular reactor. The gas after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography, and the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 6.3%.

[0024] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%. Take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 4.3%.

[0025] In addition, it is necessary to explain that: since the purity of 3,4-dichlorohexafluoro-1-butene used in the dechlorination process is above 98%, and the conversion rate of the dechlorination process is stable at 99%, the data of the product hexafluorobutadiene is expressed by the yield to illustrate the improvement effect of this process.

[0026] Implementation Case 2:

[0027] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg of titanium tetrachloride solution for 1h, filter out the soaked molecular sieve, and 9.0kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve, soak it for 30 minutes, filter out the molecular sieve, put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is filled in the interlayer of a double-layer mesh metal tube with an inner tube diameter of 20mm, an outer tube diameter of 32mm, and a length of 3.0m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 3.1m. The tubular reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is used to adjust the gas flow rate of trifluorochloroethylene through the tubular reactor at 4L / min. The gas after the reaction was condensed and collected in a condenser at a temperature of -5°C. The collected material was analyzed by gas chromatography, and the content of 3,4-dichlorohexafluoro-1-butene in the collected material was 15.8%.

[0028] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 10.9%.

[0029] From the comparison between the above-mentioned implementation case 2 and the implementation case 1, it can be seen that, under the condition that other conditions remain unchanged, the addition of the molecular sieve-supported titanium dioxide catalyst can increase the 3,4-dichlorohexafluoro-1-butene content in the collected material from 6.3% to 15.8%, and the hexafluorobutadiene yield from 4.3% to 10.9%. This shows that the present invention is effective in increasing the 3,4-dichlorohexafluoro-1-butene content in the pyrolysis product of trifluorochloroethylene, and correspondingly also increases the hexafluorobutadiene yield.

[0030] Implementation Case 3:

[0031] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg of titanium tetrachloride solution for 2h, filter out the soaked molecular sieve, and 8.7kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve, soak it for 30 minutes, take it out and put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is filled in the interlayer of a double-layer mesh metal tube with an inner tube diameter of 20mm, an outer tube diameter of 32mm, and a length of 3.0m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 3.1m. The reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is used to adjust the gas flow rate of trifluorochloroethylene through the tubular reactor at 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 18.3%.

[0032] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 12.6%.

[0033] From the comparison between Implementation Case 3 and Implementation Case 2, it can be seen that the soaking time of the molecular sieve in titanium tetrachloride will affect the saturation of the molecular sieve's adsorption of titanium tetrachloride, thereby affecting the loading of the catalyst titanium dioxide, and also affecting the selectivity of the product 3,4-dichlorohexafluoro-1-butene and the yield of hexafluorobutadiene.

[0034] Implementation Case 4:

[0035] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg of titanium tetrachloride solution for 3h, filter out the soaked molecular sieve, and 8.6kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve. After soaking for 30 minutes, take out the molecular sieve and put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is loaded into the interlayer of a double-layer mesh metal tube with an inner tube diameter of 20㎜, an outer tube diameter of 32㎜, and a length of 3.0m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45㎜ and a length of 3.1m. The tubular reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is adjusted to allow trifluorochloroethylene to pass through the tubular reactor at a gas flow rate of 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 18.5%.

[0036] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 12.7%.

[0037] Implementation Case 5:

[0038] Weigh 20.0kg 5A molecular sieve, soak it in 10.0kg titanium tetrachloride solution for 4h, filter out the soaked molecular sieve, and 8.6kg titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve. After soaking for 30 minutes, filter out the molecular sieve and put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is loaded into the interlayer of a double-layer mesh metal tube with an inner tube nominal diameter of 20mm, an outer tube nominal diameter of 32mm, and a length of 3.0m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 3.1m. The tubular reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is adjusted to allow trifluorochloroethylene to pass through the tubular reactor at a gas flow rate of 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 18.4%.

[0039] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%. Take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 12.6%.

[0040] From the above implementation cases, it can be concluded that: when other conditions remain unchanged, the addition of molecular sieve-loaded titanium dioxide catalyst can significantly increase the content of 3,4-dichlorohexafluoro-1-butene in the high-temperature pyrolysis product of chlorotrifluoroethylene, and the amount of catalyst used will also affect the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product.

[0041] When other conditions remain unchanged, the effects of catalyst and dosage on the content of 3,4-dichlorohexafluoro-1-butene in the high-temperature pyrolysis product of trifluorochloroethylene and the yield of hexafluorobutadiene, the dechlorination product, are shown in Table 1.1:

[0042]

[0043] Table 1.1

[0044] Implementation Case 6:

[0045] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg of titanium tetrachloride solution for 3h, filter out the soaked molecular sieve, and 8.6kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve. After soaking for 30 minutes, filter out the molecular sieve and put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is loaded into the interlayer of a double-layer mesh metal tube with an inner tube nominal diameter of 20㎜, an outer tube diameter of 32㎜, and a length of 4.8m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45㎜ and a length of 4.9m. The tubular reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is adjusted to allow trifluorochloroethylene to pass through the tubular reactor at a gas flow rate of 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 23.4%.

[0046] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 16.1%.

[0047] From the comparison between Case 6 and Case 4, it can be seen that when the length of the tubular reactor is extended from 3.1m to 4.8m under the condition that other conditions remain unchanged, the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product increases from 18.5% to 23.4%, and the yield of hexafluorobutadiene increases from 12.7% to 16.1%.

[0048] Implementation Case 7:

[0049] Weigh 20.0kg 5A molecular sieve, soak it in 10.0kg titanium tetrachloride solution for 3h, filter out the soaked molecular sieve, and 8.6kg titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve. After soaking for 30 minutes, take out the molecular sieve and put it in an oven, and bake it at 300℃ for 4 hours. The molecular sieve is loaded into the interlayer of a double-layer mesh metal tube with an inner tube nominal diameter of 20mm, an outer tube nominal diameter of 32mm, and a length of 5.5m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 5.6m. The tubular reactor is replaced with nitrogen and heated to 380℃ after nitrogen replacement. The flowmeter is adjusted to allow trifluorochloroethylene to pass through the tubular reactor at a gas flow rate of 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 21.2%.

[0050] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 14.6%.

[0051] By comparing Implementation Case 7 with Implementation Case 6, when other conditions remain unchanged and the length of the tubular reactor is changed from 4.9 m to 5.6 m, the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product decreases from 23.2% to 21.2%, and the yield of hexafluorobutadiene decreases from 16.1% to 14.6%.

[0052] When other conditions remain unchanged, the effect of tubular reactor length on the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product and the yield of hexafluorobutadiene as the dechlorination product is shown in Table 1.2:

[0053]

[0054] Table 1.2

[0055] Implementation Case 8:

[0056] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg titanium tetrachloride solution for 3h, filter out the soaked molecular sieve, and 8.6kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve, soak it for 30 minutes, filter it out, and bake it in an oven at 300℃ for 4 hours. The molecular sieve is filled in the interlayer of a double-layer mesh metal tube with an inner tube nominal diameter of 20mm, an outer tube diameter of 32mm, and a length of 4.8m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 4.9m. The tubular reactor is replaced with nitrogen and heated to 410℃ after nitrogen replacement. The flowmeter is used to adjust the gas flow rate of trifluorochloroethylene through the tubular reactor at 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 28.1%.

[0057] Take an amount of anhydrous ethanol that matches the ratio in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 19.3%.

[0058] By comparing Implementation Case 8 with Implementation Case 6, when other conditions remain unchanged, the temperature of the reactor is increased from 380°C to 410°C, the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product is increased from 23.4% to 28.1%, and the yield of hexafluorobutadiene is increased from 16.1% to 19.3%.

[0059] Implementation Case 9:

[0060] Weigh 20.0kg of 5A molecular sieve, soak it in 10.0kg of titanium tetrachloride solution for 3h, filter out the soaked molecular sieve, and 8.6kg of titanium tetrachloride remains. Spray the molecular sieve with deionized water until the water level is above the molecular sieve, soak it for 30 minutes, filter it out, and bake it in an oven at 300℃ for 4 hours. The molecular sieve is filled in the interlayer of a double-layer mesh metal tube with an inner tube nominal diameter of 20mm, an outer tube diameter of 32mm, and a length of 4.8m. The mesh metal tube containing the molecular sieve is fixed in a tubular reactor with a diameter of 45mm and a length of 4.9m. The tubular reactor is replaced with nitrogen and heated to 430℃ after nitrogen replacement. The flowmeter is used to adjust the gas flow rate of trifluorochloroethylene through the tubular reactor at 4L / min. The pyrolysis product after the reaction was condensed and collected in a condenser at a temperature of -5°C. After collection, it was analyzed by gas chromatography. The content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product was 26.5%.

[0061] Take anhydrous ethanol in the same proportion as in the case and add it to a 20L reactor. After stirring, add 2.7kg of zinc powder with a particle size of 200 mesh and a purity of more than 98%, and take the separated 3,4-dichlorohexafluoro-1-butene and add it to the dropping tank. After nitrogen replacement of the reaction system, heat the reactor to 50°C, slowly drop 3,4-dichlorohexafluoro-1-butene into the reactor, and collect the dechlorinated product hexafluorobutadiene in a collection system at a temperature of -10°C. The yield of hexafluorobutadiene is 18.2%.

[0062] By comparing Implementation Case 9 with Implementation Case 8, when the temperature of the reactor was increased from 410°C to 430°C, the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product decreased from 28.1% to 26.5%, and the yield of hexafluorobutadiene decreased from 19.3% to 18.2%.

[0063] When other conditions remain unchanged, the effect of the temperature of the tubular reactor on the content of 3,4-dichlorohexafluoro-1-butene in the pyrolysis product and the yield of hexafluorobutadiene, the dechlorination product, is shown in Table 1.3:

[0064]

[0065] Table 1.3

[0066] From the above case data, it can be seen that the present invention uses molecular sieve-supported titanium dioxide catalyst to catalyze the cracking reaction of chlorotrifluoroethylene at high temperature to generate 3,4-dichlorohexafluoro-1-butene, and significantly improves the selectivity and yield of 3,4-dichlorohexafluoro-1-butene, and correspondingly also improves the yield of hexafluorobutadiene. The present invention can meet the conditions for the industrial production of hexafluorobutadiene.

[0067] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention. The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected.

Claims

1. A method for preparing hexafluorobutadiene, characterized in that: The process includes the following steps: Step 1: passing chlorotrifluoroethylene gas through a tubular reactor filled with molecular sieve loaded with titanium dioxide, and chlorotrifluoroethylene is thermally decomposed on the surface of the molecular sieve by the catalysis of titanium dioxide to generate a thermal decomposition product containing 3,4-dichlorohexafluoro-1-butene; Step 2: Dechlorination reaction of 3,4-dichlorohexafluoro-1-butene separated from the pyrolysis product with zinc powder in a polar solvent to generate hexafluorobutadiene.

2. The method for preparing hexafluorobutadiene according to claim 1, characterized in that: The polar solvent is anhydrous ethanol.

3. The method for preparing hexafluorobutadiene according to claim 1, characterized in that: The purity of the zinc powder exceeds 98%, and the particle size is 200 meshes.

4. A method for preparing hexafluorobutadiene according to any one of claims 1 to 3, characterized in that: The preparation operation of the molecular sieve-loaded titanium dioxide catalyst in step 1 includes the following steps: ① soaking the molecular sieve in titanium tetrachloride for 2-4 hours, taking it out and spraying it with deionized water to hydrolyze the titanium tetrachloride in the molecular sieve to generate titanium dioxide; ② drying the molecular sieve loaded with titanium dioxide and placing it in a mesh metal tube; ③ inserting the mesh metal tube into a tubular reactor and heating the tubular reactor; after completing the above operations, passing chlorotrifluoroethylene gas into the tubular reactor for catalytic pyrolysis reaction.

5. The method for preparing hexafluorobutadiene according to claim 4, characterized in that: The molecular sieve is 5A molecular sieve with a particle size of 3.0-3.3 mm.

6. The method for preparing hexafluorobutadiene according to claim 5, characterized in that: The molecular sieve-supported titanium dioxide catalyst is prepared by hydrolyzing titanium tetrachloride adsorbed in the molecular sieve pores and on the surface, and then drying at 300°C.

7. The method for preparing hexafluorobutadiene according to claim 6, characterized in that: The mesh metal tube is double-layered, with an inner tube nominal diameter of 20 mm, an outer tube nominal diameter of 32 mm, a mesh diameter of 2 mm, and a length of 4.8 m. The molecular sieve-loaded titanium dioxide catalyst used is installed in the interlayer of the mesh metal tube. The mesh metal tube containing the catalyst is fixed in a tubular reactor with a diameter of 45 mm and a length of 4.9 m.

8. The method for preparing hexafluorobutadiene according to claim 7, characterized in that: The heating temperature of the tubular reactor is set to 380-410°C.

9. The method for preparing hexafluorobutadiene according to claim 8, characterized in that: In the step 1, the gas flow rate of chlorotrifluoroethylene gas passing through the tubular reactor filled with molecular sieve-loaded titanium dioxide is set to 4-8 L / min.

10. The method for preparing hexafluorobutadiene according to claim 9, characterized in that: In the step 1, the pressure difference before and after the trifluorochloroethylene gas passes through the tubular reactor is 600-1000 Pa.

Images