Preparation method for hexafluorobutadiene

Abstract

Provided in the present application is a preparation method for hexafluorobutadiene. The preparation method comprises the following steps: (1) putting a trifluorovinylzinc bromide solution, a catalyst and a first organic solvent into a pressure-resistant reactor, purging the reactor with an inert gas, then adding trifluorobromoethylene thereto, and reacting same, so as to obtain hexafluorobutadiene, wherein the first organic solvent is a polar aprotic organic solvent; and step (2), after the reaction is completed, enabling a gas-phase material to pass through a circulating spraying system loaded with a second organic solvent so as to absorb an excess of trifluorobromoethylene and fluoroolefin impurities, and rectifying and purifying an unabsorbed crude hexafluorobutadiene product, wherein the second organic solvent is selected from a polar aprotic organic solvent or an ionic liquid. In the present invention, the method for preparing hexafluorobutadiene by means of the cross-coupling of trifluorobromoethylene with trifluorovinylzinc bromide is implemented, and the method has the advantages of a low raw material cost, a small amount of discharged industrial waste (waste gas, wastewater, solid waste), etc. In the present application, a spraying circulation absorption device is used, thereby relieving the pressure of subsequent rectification and purification of the product.

Description

A method for preparing hexafluorobutadiene

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 1, 2023, with application number 202311639961.2. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present invention relates to fluorine-containing electronic gas, and in particular to a method for preparing hexafluorobutadiene. Background Art

[0003] Hexafluorobutadiene (C4F6) is a colorless, liquefiable fluorine-containing gas with a boiling point of 5.5°C at atmospheric pressure and a liquid density of 1.44 g / mL at 15°C. Currently, hexafluorobutadiene is primarily used as a dry etching gas for precision etching of critical dimensions (up to 100nm) for the production of rectifier circuit boards containing Cu and a low-K dielectric constant. It boasts better selectivity and aspect ratios than other etching gases. For example, compared to octafluorocyclobutane (c-C4F8), C4F6 has an etching aspect ratio of up to 10, while c-C4F8 has a ratio of only 3, making C4F6 suitable for extremely narrow linewidth processes. C4F6 only etches silicon oxide films, leaving photoresist, silicon films, and nitride films unaffected, resulting in excellent etching selectivity. Hexafluorobutadiene also has good environmental performance, with an ODP of 0, a GWP (100) of 290, and a lifetime in the atmosphere of only 1.9 days, making it a very low greenhouse effect, environmentally friendly etching gas. Therefore, with the development of the integrated circuit industry and the focus on greenhouse gases, hexafluorobutadiene, with its optimal etching performance and environmentally friendly properties, is bound to become a leading product and be widely used in the laser etching agent market.

[0004] The preparation and purification process of hexafluorobutadiene has been one of the research hotspots in recent years. The following reports are mainly available on the preparation of hexafluorobutadiene in the prior art:

[0005] WO 2006 / 026400 discloses a method of preparing trifluoroethylene bromide (CF2=CFBr) from trifluorochloroethylene (CF2=CFCl) through hydrodechlorination, bromination, and dehydrobromination, and then reacting with zinc powder to prepare trifluoroethylene zinc bromide (CF2=CFZnBr). 3+ or Cu 2+ Hexafluorobutadiene is obtained through a self-coupling reaction in the presence of ions. Although this method uses relatively cheap materials, it involves multiple hazardous production processes, a long process, and the intermediate trifluoroethylene has the risk of self-polymerization, making it unsuitable for industrial scale-up production.

[0006] CN 104829415 discloses a process for preparing hexafluorobutadiene using tetrafluoroethane (HFC-134a) as a raw material. First, tetrafluoroethane reacts with bromine at high temperature to obtain 1,1-dibromotetrafluoroethane; then, it reacts with zinc powder in a polar aprotic solvent to prepare trifluorovinyl zinc bromide; and finally, the reaction is carried out in Fe 3+ Hexafluorobutadiene is obtained by self-coupling in the presence of an oxidizing agent, with an overall yield of 47%. This reaction uses the inexpensive refrigerant HFC-134a as a raw material, and the process route is relatively short. However, the low activity of 1,1-dibromotetrafluoroethane leads to a low yield when reacting it with zinc powder to prepare trifluorovinyl zinc bromide. This results in high unit costs, large amounts of three wastes, and low prospects for industrialization.

[0007] US304630 discloses a method for preparing perfluorobutadiene using chlorotrifluoroethylene as a raw material. Chlorotrifluoroethylene first reacts with iodine chloride (ICl) in a sealed system at 35-40°C to produce 1,2-dichloro-1,2,2-trifluoroiodoethane. This is then coupled with an equivalent amount of mercury under ultraviolet light to produce 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane. Finally, 1,2,3,4-tetrachloro-1,1,2,3,4,4-hexafluorobutane is dechlorinated in an alcohol solvent under the action of zinc powder to produce hexafluorobutadiene. This method requires the use of chemically equivalent amounts of iodine chloride and mercury in the reaction, resulting in mercuric iodide as one of the products, which is highly toxic and requires expensive reagents.

[0008] US2894043 discloses the dimerization of 1,2-dichlorodifluoroethylene (CFCl=CFCl) in the presence of fluorine gas to produce the intermediate product 1,2,3,4-tetrachlorohexafluorobutane, which is then dechlorinated with zinc powder to obtain the target product, perfluorobutadiene. This method requires low temperatures (-70°C) and the use of the highly hazardous gas F2 during the fluorination and dimerization stages. US2676193 improved this method, but the reaction still required high temperatures (300°C) and high pressures (12 MPa). The reaction yield was low, at only 30-40%, and numerous byproducts were produced, making product separation difficult.

[0009] WO 2018235883 discloses a self-coupling reaction using trifluorochloroethylene as a raw material in the presence of a palladium catalyst, a phosphorus ligand, and zinc powder to produce hexafluorobutadiene, with a maximum yield of 86.1%. Patent CN 116693365 discloses a cross-coupling reaction using trifluorochloroethylene and trifluoroethylene as raw materials in the presence of an active palladium catalyst and a basic compound to produce hexafluorobutadiene, with a maximum yield of 83%. Although this method is simple, it uses expensive palladium as a catalyst, which does not offer advantages in terms of raw material costs.

[0010] The purification of hexafluorobutadiene in the prior art is mainly reported by the following:

[0011] US Pat. No. 6,544,319 discloses a method for purifying hexafluorobutadiene by adsorption. This method is low-cost, operates under mild conditions, and effectively adsorbs azeotropic fluorinated olefins and alcohol impurities. However, this method is exothermic during adsorption of alcohol impurities, and hexafluorobutadiene is susceptible to rearrangement and isomerization upon heating, generating impurities such as hexafluoro-2-butyne, which are difficult to remove.

[0012] CN 111247120 discloses the use of oxygen-containing hydrocarbons such as alcohols, ketones, and ethers, halogenated saturated hydrocarbons, halogenated unsaturated hydrocarbons, and the like as extraction solvents to carry out rectification and purification of a crude hexafluorobutadiene product containing octafluoro-1-butene, octafluoro-2-butene, heptafluoro-1-butene, and heptafluoro-2-butene, with 14 theoretical plates to obtain a hexafluorobutadiene product with a purity of 99.99%.

[0013] CN 111138240 discloses a method for removing moisture from hexafluorobutadiene using dioctyl phthalate, ethylene glycol, dimethyldiamide, and glycerol as extractants. The moisture content of the purified product is 10-12 ppm. However, the method only discloses the use of the extractant to remove moisture from the product, and the separation of the crude hexafluorobutadiene product without heptafluorobutene-like impurities. The purity of the hexafluorobutadiene product is also not disclosed.

[0014] CN 116903438 discloses the purification of hexafluorobutene using a combination of extraction, rectification, and adsorption. Furfural, methyl ethyl ketone, and cyclopentanone are used as extractants, and organic bases and copper salt-doped modified graphene oxide are used as adsorbents. The maximum product purity can reach over 5N, but the raw material purity is not given.

[0015] In view of the shortcomings of the existing technology, it is necessary to provide a method for preparing hexafluorobutadiene with simple process and low cost. Summary of the Invention

[0016] In order to improve the problems of high cost, multiple steps, poor yield and potential safety hazards in the preparation method of hexafluorobutadiene in the related art, the present application provides a preparation method of hexafluorobutadiene to make up for the shortcomings of the existing preparation method of hexafluorobutadiene. The technical route of the present invention is as follows:

[0017] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0018] A method for preparing hexafluorobutadiene comprises the following steps:

[0019] Step (1), placing a trifluoroethylene zinc bromide solution, a catalyst and a first organic solvent in a pressure-resistant reactor, replacing with an inert gas, and then adding trifluoroethylene bromide to react to obtain hexafluorobutadiene;

[0020] The catalyst comprises a monovalent copper salt or a monovalent copper oxide and an organic phosphine ligand;

[0021] Preferably, the monovalent copper salt is selected from any one or more of cuprous iodide, cuprous bromide, cuprous chloride and cuprous acetate, and the monovalent copper oxide is cuprous oxide;

[0022] The organophosphine ligand is selected from any one or more of 1,10-phenanthroline, PPh3, PR1R2R3, PPhR1R2, PPh2R1, 1,2-bis(diphenylphosphino)ethane and 2,2'-bis(diphenylphosphino)biphenyl, wherein R1, R2, and R3 are each independently selected from any one of n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; preferably, the organophosphine ligand is selected from one of 1,10-phenanthroline, PPh3, 1,2-bis(diphenylphosphino)ethane and 2,2'-bis(diphenylphosphino)biphenyl;

[0023] The first organic solvent is a polar aprotic organic solvent;

[0024] The first organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, sulfolane and N-methylpyrrolidone, and the water content of the polar aprotic organic solvent used in the first organic solvent is ≤500ppm.

[0025] Preferably, the organic solvent in step (1) is selected from one of N,N-dimethylformamide and N,N-dimethylacetamide, and has a water content of ≤200 ppm.

[0026] Step (2), after the reaction is completed, the gaseous material is passed through a circulating spray system filled with a second organic solvent to absorb excess trifluorobromoethylene and fluoroolefin impurities produced by the reaction, and the unabsorbed crude hexafluorobutadiene is purified by distillation.

[0027] The second organic solvent is selected from polar aprotic organic solvents or ionic liquids.

[0028] The polar aprotic organic solvent used for the second organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, and cyclopentane; the ionic liquid is selected from any one or more of 1-butyl-3-methylimidazolium phosphate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoroacetate, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium L-lactate, and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0029] Preferably, the second organic solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide, 1-butyl-3-methylimidazolium trifluoroacetate, 1-butyl-3-methylimidazolium nitrate and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0030] The molar ratio of trifluorovinyl zinc bromide to monovalent copper salt or monovalent copper oxide in the trifluorovinyl zinc bromide solution is 1:(0.01-0.3); the molar ratio of monovalent copper salt or monovalent copper oxide to organic phosphine ligand is 1:(1.0-10).

[0031] Preferably, the molar ratio of trifluorovinyl zinc bromide to monovalent copper salt or monovalent copper oxide in the trifluorovinyl zinc bromide solution is 1:(0.01-0.20); the molar ratio of monovalent copper salt or monovalent copper oxide to organic phosphine ligand is 1:(1.0-5.0).

[0032] More preferably, the molar ratio of trifluorovinyl zinc bromide to monovalent copper salt or monovalent copper oxide in the trifluorovinyl zinc bromide solution is 1:(0.05-0.10); the molar ratio of monovalent copper salt or monovalent copper oxide to organic phosphine ligand is 1:(1.0-3.0).

[0033] In the step (1), the molar ratio of trifluorovinyl zinc bromide to trifluoroethylene bromide in the trifluorovinyl zinc bromide solution is 1: (1.0-10.0).

[0034] Preferably, the molar ratio of trifluorovinylzinc bromide to trifluoroethylene bromide in the trifluorovinylzinc bromide solution in step (1) is 1:(1.0-5.0).

[0035] The reaction temperature in step (1) is 60-140° C., the reaction pressure is 0.05-2.0 MPa, and the reaction time is 3-24 hours.

[0036] Preferably, the reaction temperature in step (1) is 80-120° C., the reaction pressure is 0.3-1.0 MPa, and the reaction time is 6-12 h.

[0037] The circulating spray system in step (2) is a secondary circulating spray absorption system with a temperature of -10 to 20° C. and a pressure of 0 to 0.5 MPa.

[0038] Preferably, the circulating spray system in step (2) is a secondary circulating spray absorption system with a temperature of -5 to 10°C and a pressure of 0 to 0.2 MPa.

[0039] In the method for preparing hexafluorobutadiene, the organic solution absorbed in the circulating spraying system in step (2) is subjected to distillation treatment to recover trifluoroethylene bromide and directly circulate for reuse.

[0040] The content of bromotrifluoroethylene in the crude hexafluorobutadiene treated by the circulating spraying system is less than or equal to 0.3%, and the content of heptafluorobutene is less than or equal to 0.02%. After distillation, a hexafluorobutadiene product with a purity of ≥99.99% can be obtained.

[0041] Beneficial effects of the present invention:

[0042] (1) The present invention uses cheap monovalent copper salts or oxides as catalysts and organophosphorus as ligands to achieve a method for preparing hexafluorobutadiene by cross-coupling trifluoroethylene bromide with trifluorovinyl zinc bromide. Compared with the oxidative self-coupling process, this method has the advantages of low raw material cost and less discharge of three wastes.

[0043] (2) The reaction product is passed through a spray circulation absorption device filled with a special solvent, and the excess trifluoroethylene bromide and the difficult-to-separate impurity heptafluorobutene are dissolved in the solvent. The content of trifluoroethylene bromide in the obtained hexafluorobutadiene crude product is ≤0.3%, and the content of heptafluorobutene is ≤0.02%, which reduces the pressure on the distillation and purification of subsequent products. Through conventional distillation, a product with a purity of ≥99.99% can be obtained.

[0044] (3) The present invention realizes the recycling of trifluoroethylene bromothioate through simple distillation treatment, thereby improving the utilization rate of trifluoroethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a device for preparing hexafluorobutadiene in an embodiment of the present invention, comprising: a device for continuously preparing trifluoroethylene zinc bromide solution in a continuous method for preparing hexafluorobutadiene, comprising: 1. a trifluoroethylene bromide cylinder; 2. a trifluoroethylene zinc bromide solution cylinder; 3. a pressure-resistant reactor; 4. a condenser; 5. a buffer tank; 6. a first spray circulation absorption tower; 7. a first spray circulation absorption tower; and 8. a crude product tank.

[0046] FIG2 is a chromatogram of the product after distillation in Example 10. DETAILED DESCRIPTION

[0047] 1 , the preparation system used in the present invention will be described first, including a pressure-resistant reactor 3 , a condenser 4 , a buffer tank 5 , a first spray circulation absorption tower 6 , a second spray circulation absorption tower 7 , and a crude product tank 8 .

[0048] The trifluoroethylene bromide cylinder 1 and the trifluoroethylene zinc bromide solution cylinder 2 are connected to the feed port of the pressure-resistant reactor 3, the top discharge port of the pressure-resistant reactor 3 is connected to the feed port of the condenser 4, the discharge port of the condenser 4 is connected to the feed port of the buffer tank 5, the discharge port of the buffer tank 5 is connected to the feed port of the first spray circulation absorption tower 6, the discharge port of the first spray circulation absorption tower 6 is connected to the feed port of the second spray circulation absorption tower 7, the discharge port of the second spray circulation absorption tower 7 is connected to the feed port of the crude product tank 8, and the discharge port of the crude product tank 8 is connected to the distillation equipment.

[0049] The above system was tested for the following reasons.

[0050] Example 1

[0051] (1) A 5L 316L pressure-resistant reactor equipped with a condensation reflux device was added with 1810g of trifluorovinyl zinc bromide in N,N-dimethylacetamide (mass fraction 25%, 2.0mol), 1000g of N,N-dimethylacetamide (water content 150ppm), 38.2g of cuprous iodide (0.2mol) and 72.2g of 1,10-phenanthroline (0.4mol). The reactor was replaced with high-purity nitrogen and evacuated to a vacuum of ≥0.1MPa. 644g of trifluoroethylene bromide (4.0mol) was added to the pressure-resistant reactor, stirring was started, the reactor temperature was raised to 100℃, the condenser jacket medium temperature was 20℃, and the reactor pressure was 0.8MPa. After 6h of reaction, a sample was taken from the liquid phase tube of the pressure-resistant reactor and analyzed by nuclear magnetic resonance fluorine internal standard method (trifluorotoluene as internal standard). The trifluorovinyl zinc bromide had been completely converted.

[0052] (2) Add 1 L of 1-butyl-3-methylimidazolium hexafluorophosphate to each of the 1 L secondary circulation spray devices. Control the internal temperature to 4-6 ° C. Turn on the internal circulation pump at a flow rate of 100 mL / min. Open the gas phase outlet regulating valve of the pressure-resistant reactor, raise the reactor temperature to 130 ° C, and allow the gaseous product to enter the secondary circulation spray device. The unabsorbed tail gas is collected in a cold trap absorption device with liquid nitrogen as the coolant. The results are as follows: 244.8 g of crude hexafluorobutene was collected in cold trap 1, with a purity of 97.82%, a conversion of 239.4 g, a theoretical yield of 324.0 g, and a yield of 73.9%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0053] (3) The 1-butyl-3-methylimidazolium hexafluorophosphate solution in the secondary circulation spray device was added to a pressure-resistant autoclave for distillation. The temperature was raised to 120°C, and the dissolved fluoroolefins were evaporated and collected in a cold trap absorption device with liquid nitrogen as the coolant. The results were as follows: a total of 341.9 g was collected in cold trap 2, with a chromatographic content of 89.50% for trifluoroethylene bromide and 9.75% for hexafluorobutadiene. The contents of other components are shown in Table 2.

[0054] Example 2

[0055] The operation of this example is the same as that of Example 1, except that 19.1 g of cuprous iodide (0.1 mol) is added to a 5 L 316 L pressure reactor instead of 38.2 g of cuprous iodide (0.2 mol). Other conditions remain unchanged. The results are:

[0056] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the conversion rate of trifluorovinyl zinc bromide was 94.5%.

[0057] In step (2), the cold trap 1 collected 234.2 g of crude hexafluorobutene with a purity of 96.60%, a conversion of 226.2 g, a theoretical yield of 324.0 g, and a yield of 69.8%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0058] In step (3), a total of 358.7 g was collected in the cold trap 2, with a chromatographic content of bromotrifluoroethylene of 90.80% and a chromatographic content of hexafluorobutadiene of 8.55%. The contents of other components are shown in Table 2.

[0059] Example 3

[0060] The operation of this embodiment is the same as that of Example 1, except that 19.8 g of cuprous chloride (0.2 mol) is added to a 5 L pressure reactor made of 316 L material instead of 38.2 g of cuprous iodide (0.2 mol), and other conditions remain unchanged.

[0061] The result is:

[0062] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the trifluorovinyl zinc bromide was completely converted.

[0063] In step (2), the cold trap 1 collected 244.0 g of crude hexafluorobutene with a purity of 96.32%, equivalent to 235 g, a theoretical yield of 324.0 g, and a yield of 72.5%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0064] In step (3), a total of 339.3 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 89.25% and a chromatographic content of hexafluorobutadiene of 10.10%. The contents of other components are shown in Table 2.

[0065] Example 4

[0066] The operation of this example is the same as that of Example 1, except that 104.9 g of triphenylphosphine (0.4 mol) is added to a 5 L pressure reactor made of 316 L material instead of 72.2 g of 1,10-phenanthroline (0.4 mol), and other conditions remain unchanged. The results are:

[0067] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the conversion rate of trifluorovinyl zinc bromide was 97.9%.

[0068] In step (2), the cold trap 1 collected 254.0 g of crude hexafluorobutene with a purity of 95.83%, a conversion of 243.4 g, a theoretical yield of 324.0 g, and a yield of 75.1%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0069] In step (3), a total of 340.6 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 91.40% and a chromatographic content of hexafluorobutadiene of 8.29%. The contents of other components are shown in Table 2.

[0070] Example 5

[0071] The operation of this example is the same as that of Example 1, except that 1810 g of a 25% by mass, 2.0 mol solution of trifluorovinylzinc bromide in N,N-dimethylacetamide was added to a 5 L 316 L pressure reactor, replaced by 1810 g of a 25% by mass, 2.0 mol solution of trifluorovinylzinc bromide in N,N-dimethylformamide, and 1000 g of N,N-dimethylacetamide (150 ppm water) was replaced by 1000 g of N,N-dimethylformamide (150 ppm water). Other conditions remained unchanged. The results are:

[0072] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the trifluorovinyl zinc bromide was completely converted.

[0073] In step (2), the cold trap 1 collected 251.0 g of crude hexafluorobutene with a purity of 96.59%, a conversion of 242.4 g, a theoretical yield of 324.0 g, and a yield of 74.8%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0074] In step (3), a total of 338.7 g of the product was collected in the cold trap 2. The chromatographic content of trifluorobromoethylene was 89.85%, the chromatographic content of hexafluorobutadiene was 9.31%, and the contents of other components were shown in Table 2.

[0075] Example 6

[0076] The operation of this example is the same as that of Example 1, except that the temperature inside the reactor is raised to 80°C instead of 100°C, and other conditions remain unchanged. The results are:

[0077] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard substance). The conversion rate of trifluorovinyl zinc bromide was 80.5%.

[0078] In step (2), the cold trap 1 collected 205.6 g of crude hexafluorobutene with a purity of 95.50%, a conversion of 196.4 g, a theoretical yield of 324.0 g, and a yield of 60.6%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0079] In step (3), a total of 391.28 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 93.31% and a chromatographic content of hexafluorobutadiene of 5.75%. The contents of other components are shown in Table 2.

[0080] Example 7

[0081] The operation of this example is the same as that of Example 1, except that the second organic solvent 1-butyl-3-methylimidazolium hexafluorophosphate in step (2) is replaced with 1-butyl-3-methylimidazolium trifluoroacetate, and other conditions remain unchanged. The results are:

[0082] In step (2), the cold trap 1 collected 253.0 g of crude hexafluorobutene with a purity of 96.20%, a conversion of 247.2 g, a theoretical yield of 324.0 g, and a yield of 76.3%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0083] In step (3), a total of 337.85 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 89.61% and a chromatographic content of hexafluorobutadiene of 9.20%. The contents of other components are shown in Table 2.

[0084] Example 8

[0085] The operation of this embodiment is the same as that of embodiment 1, except that the internal temperature of the secondary circulation spraying device in step (2) is changed from 4 to 6°C to 2 to 4°C, and other conditions remain unchanged. The results are:

[0086] In step (2), the cold trap 1 collected 233.8 g of crude hexafluorobutene with a purity of 97.85%, a conversion of 228.8 g, a theoretical yield of 324.0 g, and a yield of 70.6%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0087] In step (3), a total of 356.4 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 88.02% and a chromatographic content of hexafluorobutadiene of 11.46%. The contents of other components are shown in Table 2.

[0088] Example 9

[0089] The operation of this embodiment is the same as that of embodiment 1, except that: in step (1), recovered bromotrifluoroethylene is used as raw material, and the purity of the recovered bromotrifluoroethylene is 93.20%, and the purity of hexafluorobutadiene is 6.25%.

[0090] The feed amount is: 691g (bromotrifluoroethylene equivalent to 644g). Other conditions remain unchanged. The results are:

[0091] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the trifluorovinyl zinc bromide was completely converted.

[0092] In step (2), the cold trap 1 collected 330.6 g of crude hexafluorobutene with a purity of 96.33%, a % reduction of 318.4 g, a theoretical yield of 324.0 g, and a yield of 98.30%. The contents of various impurities in the crude hexafluorobutadiene are shown in Table 1.

[0093] In step (3), a total of 341.9 g of cold trap 2 was collected, with a chromatographic content of bromotrifluoroethylene of 88.90% and a chromatographic content of hexafluorobutadiene of 10.52%. The contents of other components are shown in Table 2.

[0094] Table 1 Component contents of crude hexafluorobutadiene in each batch

[0095] Table 2 Component content of each batch of absorption liquid

[0096] Note: Excluding the second organic solvent

[0097] Example 10

[0098] The crude hexafluorobutadiene prepared in Examples 1 to 7 was used as a raw material to conduct a distillation experiment. The distillation tower parameters and distillation parameters are shown in Tables 3 and 4 below:

[0099] Table 3 Distillation column parameters

[0100] Table 4 Distillation process parameters

[0101] 800g of feed was distilled, yielding 57.5g of the fore-fraction, 608g of the product, and 118.5g of the still residue. The product purity was 99.990%, the single-batch distillation yield was 76.0%, and the material balance was 98.0%. The chromatogram of the product after distillation is shown in Figure 2, and the results are as follows:

[0102] Comparative Example 1

[0103] The operation of this embodiment is the same as that of embodiment 1, except that the monovalent copper salt catalyst is not added in step (1). Other conditions remain unchanged. The results are:

[0104] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard substance), and the conversion rate of trifluorovinyl zinc bromide was 0.5%.

[0105] In step (2), the cold trap 1 does not collect the hexafluorobutadiene product.

[0106] Comparative Example 2

[0107] The operation of this example is the same as that of Example 1, except that no organic phosphine ligand is added in step (1). Other conditions remain unchanged. The results are:

[0108] After 6 hours of reaction in step (1), a sample was taken from the liquid phase tube of the autoclave and analyzed by nuclear magnetic resonance fluorine spectrum internal standard method (trifluorotoluene was used as the internal standard), and the conversion rate of trifluorovinyl zinc bromide was 62.2%.

[0109] In step (2), the cold trap 1 collected 65.3 g of crude hexafluorobutene with a purity of 95.47%, a conversion of 62.3 g, a theoretical yield of 162.0 g, and a yield of 38.5%.

[0110] In step (3), a total of 444.4 g of the product was collected in the cold trap 2, with a chromatographic content of bromotrifluoroethylene of 92.81% and a chromatographic content of hexafluorobutadiene of 6.55%.

[0111] Comparative Example 3

[0112] The operation of this example was the same as that of Example 1, except that the product prepared in step (1) was not treated in step (2) but was directly collected in a cold trap absorption device using liquid nitrogen as the coolant. The results were: 607.3 g of crude hexafluorobutene was collected in cold trap 1, with a purity of 41.7%, a conversion of 253.4 g, a theoretical yield of 324.0 g, and a yield of 78.2%.

Claims

1. A method for preparing hexafluorobutadiene, characterized in that: The following steps are involved: Step (1), placing a trifluoroethylene zinc bromide solution, a catalyst and a first organic solvent in a pressure-resistant reactor, replacing with an inert gas, and then adding trifluoroethylene bromide to react to obtain hexafluorobutadiene; The catalyst comprises a monovalent copper salt or a monovalent copper oxide and an organic phosphine ligand; The organophosphine ligand is selected from any one or more of 1,10-phenanthroline, PPh3, PR1R2R3, PPhR1R2, PPh2R1, 1,2-bis(diphenylphosphino)ethane and 2,2'-bis(diphenylphosphino)biphenyl, wherein R1, R2 and R3 are each independently selected from any one of n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; The first organic solvent is a polar aprotic organic solvent; Step (2), after the reaction is completed, passing the gaseous material through a circulating spray system filled with a second organic solvent to absorb excess trifluoroethylene bromide and fluoroolefin impurities generated by the reaction, and purifying the unabsorbed crude hexafluorobutadiene by distillation; The second organic solvent is selected from polar aprotic organic solvents or ionic liquids.

2. The method for preparing hexafluorobutadiene according to claim 1, characterized in that: The monovalent copper salt is selected from any one or more of cuprous iodide, cuprous bromide, cuprous chloride and cuprous acetate, and / or the monovalent copper oxide is cuprous oxide.

3. The method for preparing hexafluorobutadiene according to claim 1 or 2, characterized in that: The first organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, sulfolane and N-methylpyrrolidone, and the water content of the polar aprotic organic solvent used in the first organic solvent is ≤500ppm; The polar aprotic organic solvent used for the second organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide and cyclopentane sulfone; the ionic liquid is selected from any one or more of 1-butyl-3-methylimidazolium phosphate, 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoroacetate, 1-butyl-3-methylimidazolium nitrate, 1-butyl-3-methylimidazolium L-lactate and 1-butyl-3-methylimidazolium hexafluorophosphate.

4. The method for preparing hexafluorobutadiene according to any one of claims 1 to 3, characterized in that: In the step (1), the first organic solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide and sulfolane.

5. The method for preparing hexafluorobutadiene according to any one of claims 1 to 4, characterized in that: The molar ratio of trifluorovinyl zinc bromide to the monovalent copper salt or monovalent copper oxide in the trifluorovinyl zinc bromide solution is 1:(0.01-0.3); the molar ratio of the monovalent copper salt or monovalent copper oxide to the organic phosphine ligand is 1:(1.0-10).

6. The method for preparing hexafluorobutadiene according to claim 5, characterized in that: The molar ratio of trifluorovinyl zinc bromide to the monovalent copper salt or monovalent copper oxide in the trifluorovinyl zinc bromide solution is 1:(0.01-0.20), preferably 1:(0.05-0.10); the molar ratio of the monovalent copper salt or monovalent copper oxide to the organic phosphine ligand is 1:(1.0-5.0), preferably 1:(1.0-3.0).

7. The method for preparing hexafluorobutadiene according to any one of claims 1 to 6, characterized in that: The molar ratio of trifluorovinyl zinc bromide to trifluoroethylene bromide in the trifluorovinyl zinc bromide solution is 1:(1-10), preferably 1:(1.0-5.0).

8. The method for preparing hexafluorobutadiene according to any one of claims 1 to 7, characterized in that: The reaction temperature in step (1) is 60-140° C., the reaction pressure is 0.05-2.0 MPa, and the reaction time is 3-24 h; preferably, the reaction temperature in step (1) is 80-120° C., the reaction pressure is 0.3-1.0 MPa, and the reaction time is 6-12 h.

9. The method for preparing hexafluorobutadiene according to any one of claims 1 to 8, characterized in that: In the step (2), the second organic solvent is selected from any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, cyclopentane, 1-butyl-3-methylimidazole phosphate, 1-butyl-3-methylimidazole acetate, 1-butyl-3-methylimidazole trifluoroacetate and 1-butyl-3-methylimidazole hexafluorophosphate.

10. The method for preparing hexafluorobutadiene according to any one of claims 1 to 9, characterized in that: The circulating spray system in step (2) is a secondary circulating spray absorption, the temperature in the circulating spray system is -10 to 20°C, and the pressure is 0 to 0.5 MPa; preferably, the temperature in the circulating spray system is -5 to 10°C, and the pressure is 0 to 0.2 MPa.

11. The method for preparing hexafluorobutadiene according to any one of claims 1 to 10, characterized in that: The organic solution absorbed in the circulating spray system in the step (2) is treated by distillation to recover bromotrifluoroethylene and directly circulate it for reuse.

12. The method for preparing hexafluorobutadiene according to any one of claims 1 to 11, characterized in that: The content of bromotrifluoroethylene in the crude hexafluorobutadiene treated by the circulating spraying system is ≤0.3%, and the content of heptafluorobutene is ≤0.02%. After distillation, a hexafluorobutadiene product with a purity of ≥99.99% can be obtained.

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