A process for the preparation of hexafluoropropylene oligomers

Abstract

The application discloses a preparation method of hexafluoropropylene oligomer and relates to the technical field of fluorine chemical synthesis. Specifically, the hexafluoropropylene oligomer is prepared by using a deep eutectic solvent (ChCl+XZnCl2). The deep eutectic solvent (ChCl+XZnCl2), hexafluoropropylene (HFP) and a polar bio-based solvent are sequentially added into a pressure-resistant reaction kettle in proportion, and constant-temperature stirring is carried out. After the reaction is stopped, the reaction is cooled to room temperature, and liquid separation is carried out, so that the lower layer of the crude product is obtained. After the crude product is further rectified, the hexafluoropropylene oligomer is obtained. The preparation method of the hexafluoropropylene oligomer provided by the application is not only green, environmentally friendly, low in cost, simple in synthesis route and high in production efficiency, but also has high selectivity for the oligomer.

Description

Technical Field

[0001] This application relates to the field of fluorochemical synthesis technology, and in particular to a method for preparing hexafluoropropylene oligomers. Background Technology

[0002] Hexafluoropropylene oligomers possess excellent thermodynamic and chemical stability, making them important intermediates for the synthesis of fluorinated surfactants and derivatives, pharmaceutical active substances, pesticides, and fire extinguishing products. Hexafluoropropylene oligomers are typically obtained through the oligomerization of hexafluoropropylene, including hexafluoropropylene dimers and trimers. The hexafluoropropylene dimer contains two isomers, being a compound with six carbon atoms and one double bond (perfluorinated), exhibiting a cis-trans isomer D1 and a branched dimer D2. Synthetic methods include gas-phase and liquid-phase methods. The gas-phase method involves a continuous reaction of hexafluoropropylene gas through a catalyst layer, requiring no solvent and typically carried out in a tubular reactor, but requiring high temperatures. The liquid-phase method usually involves adding a catalyst, co-solvent, and aprotic polar solvent to a closed, pressure-resistant reactor, followed by the introduction of hexafluoropropylene gas for batch or continuous reaction. This method does not require high temperatures and is more commonly used.

[0003] US Patent 4377717 discloses a gas-phase method for synthesizing hexafluoropropylene dimers, using metal fluorides adsorbed on activated carbon as catalysts to synthesize hexafluoropropylene oligomers at relatively high temperatures. However, this reaction has low selectivity and conversion rates and requires high temperatures. Patent CN93121609 uses hexafluoropropylene as a raw material in a polar dipolar aprotic inert solvent, with quaternary ammonium, quaternary phosphorus, alkali metal cyanides, cyanates, and thiocyanates as catalysts, achieving high yields of hexafluoropropylene dimers. Chinese Patent CN200610059035 discloses a method using hexafluoropropylene as a raw material, acetonitrile as a solvent, and potassium thiocyanate as a catalyst, to prepare hexafluoropropylene dimers by stirring the reaction at an appropriate temperature.

[0004] However, the aforementioned patents all use cyanide or cyanate as catalysts, which are highly toxic. Furthermore, they employ highly environmentally unfriendly and non-renewable polar dipolar petroleum-based solvents. The products are immiscible with the solvents after the reaction, allowing for direct separation, but leaving small amounts of solvent and catalyst residues that require further distillation and washing, making subsequent purification relatively complex. Chinese patent CN201710616035 discloses the synthesis of hexafluoropropylene oligomers using solvents such as acetonitrile and N,N-dimethylformamide, with CsF, NaF, KF, and RbF as catalysts, and using crown ethers as co-catalysts. However, crown ethers are relatively expensive, and the solvents acetonitrile and N,N-dimethylformamide are both highly environmentally unfriendly and difficult to recycle, resulting in high costs. Chinese patent CN112745191 discloses the preparation of hexafluoropropylene oligomers using ionic liquids as catalysts and acetonitrile as solvents under stirring at appropriate temperatures. Although environmentally friendly ionic liquids are used as catalysts, the toxicity of the environmentally unfriendly petroleum-based solvent acetonitrile is unavoidable. Summary of the Invention

[0005] In order to provide a green, environmentally friendly, low-cost, simple synthetic route and high production efficiency method for preparing hexafluoropropylene oligomers, this application provides a method for preparing hexafluoropropylene oligomers.

[0006] This application provides a method for preparing hexafluoropropylene oligomers, which adopts the following technical solution:

[0007] A method for preparing hexafluoropropylene oligomers includes the following steps:

[0008] S1. Preparation of deep eutectic solvent: Add choline chloride (ChCl) and zinc chloride (ZnCl2) to the reaction vessel in a molar ratio of 1:X, stir at a constant temperature under mechanical stirring, stop the reaction, and wait for the reaction to cool to room temperature to obtain the deep eutectic solvent (ChCl+XZnCl2).

[0009] S2. Preparation of hexafluoropropylene oligomer (HFPD): The deep eutectic solvent (ChCl+XZnCl2), hexafluoropropylene (HFP) and polar bio-based solvent prepared in step (1) are added to a pressure-resistant reactor in proportion. The reaction mixture is stirred at a constant temperature under mechanical stirring. After the reaction is stopped, the mixture is separated after cooling to room temperature to obtain the lower crude product. The crude product is further distilled to obtain hexafluoropropylene oligomer.

[0010] By adopting the above technical solution, using choline chloride (ChCl) and zinc chloride (ZnCl2) synthesized into a deep eutectic solvent in a molar ratio as a catalyst, it is not only green, environmentally friendly, low in toxicity, and biodegradable, but also allows for the acquisition of the target product in a relatively short time and at a high yield. Furthermore, by using a renewable, environmentally friendly polar bio-based solvent instead of a non-renewable polar dipolar petroleum-based solvent as the reaction solvent, no additional expensive catalysts and auxiliaries are required. This results in a relatively high conversion rate of raw materials and high selectivity of the target product during the preparation of hexafluoropropylene oligomers, effectively improving the yield of hexafluoropropylene oligomers. Moreover, the post-processing is simple, and both the catalyst and solvent can be recycled and reused.

[0011] Preferably, the value of X in S1 is 1-5; further, the value of X is 4.

[0012] By adopting the above technical solution, the deep eutectic solvent prepared by choline chloride and zinc chloride has the advantages of being inexpensive, readily available, low in toxicity, non-flammable, biodegradable, and designable. By controlling the molar ratio of choline chloride (ChCl) and zinc chloride (ZnCl2), it is beneficial to obtain a deep eutectic solvent with high catalytic activity, which can effectively improve the relatively high conversion rate of raw materials and the high selectivity of target products in the preparation of hexafluoropropylene oligomers, thereby improving the yield of hexafluoropropylene oligomers.

[0013] Preferably, the temperature of the isothermal reaction in S1 is 50-100°C; further, the temperature of the isothermal reaction is 85°C.

[0014] By adopting the above technical solution and controlling the reaction temperature for producing deep eutectic solvents, it is beneficial to obtain deep eutectic solvents with high catalytic activity. Preferably, the reaction temperature for deep eutectic solvents is 50-100℃, and further, the reaction temperature is 85℃, which can obtain deep eutectic solvents with high catalytic activity.

[0015] Preferably, the isothermal reaction time in S1 is 8-12 hours; further, the isothermal reaction time is 10 hours.

[0016] By adopting the above technical solution and controlling the reaction time for producing deep eutectic solvent, it is beneficial to obtain deep eutectic solvent with high catalytic activity. Preferably, the reaction time for deep eutectic solvent is 8-12 hours, and further, a reaction time of 10 hours can be selected to obtain deep eutectic solvent with high catalytic activity.

[0017] Preferably, the hexafluoropropylene oligomer in S2 is a mixture of one or more of hexafluoropropylene dimer D1, hexafluoropropylene dimer D2, and hexafluoropropylene trimer. Preferably, the mass ratio of the deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent in S2 is 1:50:50-1:200:200; further, the mass ratio for preparing dimer D1 is 1:60:60, the mass ratio for preparing dimer D2 is 1:100:100, and the mass ratio for preparing trimer is 1:150:150.

[0018] By adopting the above technical solution, hexafluoropropylene is reacted to generate hexafluoropropylene oligomers under the catalysis of a deep eutectic solvent and a polar bio-based solvent. By controlling the mass ratio of the deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent, it is beneficial to obtain a deep eutectic solvent with high catalytic activity. Preferably, the mass ratio of the deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent is 1:50:50-1:200:200. Furthermore, the mass ratio for preparing dimer D1 is 1:60:60, the mass ratio for preparing dimer D2 is 1:100:100, and the mass ratio for preparing trimer is 1:150:150, which can obtain hexafluoropropylene oligomers with high yields.

[0019] Preferably, the polar bio-based solvent is one or a mixture of γ-valerol, 2-methyltetrahydrofuran, and sorbitol dimethyl ether; preferably, it is 2-methyltetrahydrofuran.

[0020] By adopting the above technical solution, γ-valerolactone, 2-methyltetrahydrofuran, and sorbitol dimethyl ether are used as polar bio-based solvents because of their important properties, especially their unique polarity compared to the above petroleum-based dipolar aprotic solvents. They are ideal renewable bio-based solvents to replace non-renewable petroleum-based dipolar aprotic polar solvents. Traditional petroleum-based dipolar aprotic solvents such as dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile are widely used in the chemical industry. However, these solvents are not green or economical because they have various toxic effects on humans, cause environmental damage, and generate large amounts of wastewater during post-treatment. The green and environmentally friendly bio-based solvent used in this application is low in toxicity, non-toxic, recyclable, biodegradable, and renewable. It can effectively replace petroleum-based solvents and improve the production efficiency of hexafluoropropylene oligomers.

[0021] Preferably, the temperature of the isothermal reaction in S2 is 60-100°C; further, the temperature of the isothermal reaction is 70°C.

[0022] By adopting the above technical solution and controlling the reaction temperature for producing hexafluoropropylene oligomers, it is beneficial to improve the production efficiency of hexafluoropropylene oligomers. Preferably, the reaction temperature for producing hexafluoropropylene oligomers is 60-100℃, and further, the reaction temperature is 70℃, which can yield hexafluoropropylene oligomers with a higher yield.

[0023] Preferably, the isothermal reaction time in S2 is 2-5 hours; further, the isothermal reaction time is 3 hours.

[0024] By adopting the above technical solution and controlling the reaction time for producing hexafluoropropylene oligomers, it is beneficial to improve the production efficiency of hexafluoropropylene oligomers. Preferably, the reaction time for hexafluoropropylene oligomers is 2-5 hours, and further, a reaction time of 3 hours can be selected to obtain hexafluoropropylene oligomers with a higher yield.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. By adopting the above technical solution, using choline chloride (ChCl) and zinc chloride (ZnCl2) synthesized into a deep eutectic solvent in a molar ratio as a catalyst, it is not only green, environmentally friendly, low in toxicity, and biodegradable, but also allows for the acquisition of the target product in a relatively short time with a high yield. Furthermore, by using a renewable, environmentally friendly polar bio-based solvent instead of a non-renewable polar dipolar petroleum-based solvent as the reaction solvent, no additional expensive catalysts and additives are required. This results in a relatively high conversion rate of raw materials and high selectivity of the target product during the preparation of hexafluoropropylene oligomers, effectively improving the yield of hexafluoropropylene oligomers. Moreover, the post-processing is simple, and both the catalyst and solvent can be recycled.

[0027] 2. By adopting the above technical solution, γ-valerolactone, 2-methyltetrahydrofuran, and sorbitol dimethyl ether are used as polar bio-based solvents because of their important properties, especially their unique polarity compared to the above petroleum-based dipolar aprotic solvents. They are ideal renewable bio-based solvents to replace non-renewable petroleum-based dipolar aprotic polar solvents. Traditional petroleum-based dipolar aprotic solvents such as dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile are widely used in the chemical industry. However, these solvents are not green or economical because they have various toxic effects on humans, cause environmental damage, and generate large amounts of wastewater during post-treatment. The green and environmentally friendly bio-based solvent used in this application is low in toxicity, non-toxic, recyclable, biodegradable, and renewable. It can effectively replace petroleum-based solvents and improve the production efficiency of hexafluoropropylene oligomers.

[0028] 3. By adopting the above technical solution, hexafluoropropylene is reacted to generate hexafluoropropylene oligomers under the catalysis of a deep eutectic solvent and a polar bio-based solvent. By controlling the mass ratio of the deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent, it is beneficial to obtain a deep eutectic solvent with high catalytic activity. Preferably, the mass ratio of the deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent is 1:50:50-1:200:200; furthermore, a mass ratio of 1:100:100 can obtain a deep eutectic solvent with high catalytic activity. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the embodiments.

[0030] Preparation Example

[0031] Preparation Examples 1-4 provide methods for preparing deep eutectic solvents ChCl+ZnCl2, ChCl+4ZnCl2, ChCl+5ZnCl2, and ChCl+6ZnCl2, respectively, as follows:

[0032] Preparation Example 1: Preparation of the deep eutectic solvent ChCl + ZnCl2

[0033] 0.035 mol of choline chloride and 0.035 mol of zinc chloride were added to a reaction vessel and stirred at 50°C for 8 hours under mechanical stirring. The reaction was then stopped and allowed to cool to room temperature to obtain the deep eutectic solvent ChCl + ZnCl2.

[0034] Preparation Example 2: Preparation of the deep eutectic solvent ChCl + 4ZnCl2

[0035] 0.035 mol of choline chloride and 0.14 mol of zinc chloride were added to a reaction vessel and stirred at 85°C for 10 h under mechanical stirring. The reaction was then stopped and allowed to cool to room temperature to obtain the deep eutectic solvent ChCl + 4ZnCl2.

[0036] Preparation Example 3: Preparation of the deep eutectic solvent ChCl + 5ZnCl2

[0037] 0.035 mol of choline chloride and 0.175 mol of zinc chloride were added to a reaction vessel and stirred at 100°C for 12 h under mechanical stirring. The reaction was then stopped and allowed to cool to room temperature to obtain the deep eutectic solvent ChCl + 5ZnCl2.

[0038] Preparation Example 4: Preparation of the deep eutectic solvent ChCl + 6ZnCl2

[0039] 0.035 mol of choline chloride and 0.21 mol of zinc chloride were added to a reaction vessel and stirred at 100°C for 12 h with mechanical stirring. The reaction was then stopped and allowed to cool to room temperature to obtain the deep eutectic solvent ChCl + 6ZnCl2.

[0040] Example

[0041] Example 1

[0042] 1.0 g of the deep eutectic solvent (ChCl+ZnCl2) obtained in Preparation Example 1, 50 g of the polar bio-based solvent γ-valerolactone, and 50 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 60°C for 2 h under mechanical stirring. The reaction was then stopped, and after the reaction cooled to room temperature, it was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0043] Example 2

[0044] 1.0 g of the deep eutectic solvent (ChCl+4ZnCl2) obtained in Preparation Example 2, 100 g of the polar bio-based solvent 2-methyltetrahydrofuran, and 100 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at a constant temperature of 70°C for 3 h under mechanical stirring. The reaction was then stopped, and after the reaction cooled to room temperature, it was allowed to stand and separate to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0045] Example 3

[0046] 1.0 g of the deep eutectic solvent (ChCl+5ZnCl2) obtained in Preparation Example 3, 200 g of the polar bio-based solvent sorbitol dimethyl ether, and 200 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 100°C for 5 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, it was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0047] Example 4

[0048] 1.0 g of the deep eutectic solvent (ChCl+4ZnCl2) obtained in Preparation Example 2, 100 g of the polar bio-based solvent 2-methyltetrahydrofuran, and 100 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 100°C for 3 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, it was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0049] Example 5

[0050] 1.0 g of the deep eutectic solvent (ChCl+4ZnCl2) obtained in Preparation Example 2, 150 g of the polar bio-based solvent 2-methyltetrahydrofuran, and 150 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 150°C for 4 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, the mixture was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0051] Comparative Example

[0052] Comparative Example 1

[0053] 1.0 g of the deep eutectic solvent (ChCl+ZnCl2) obtained in Preparation Example 1, 300 g of solvent γ-valerolactone, and 300 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 60°C for 3 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, the mixture was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0054] Comparative Example 2

[0055] 1.0 g of the deep eutectic solvent (ChCl+4ZnCl2) obtained in Preparation Example 2, 100 g of the polar bio-based solvent 2-methyltetrahydrofuran, and 100 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 120°C for 3 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, the mixture was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0056] Comparative Example 3

[0057] 1.0 g of the deep eutectic solvent (ChCl+5ZnCl2) obtained in Preparation Example 3, 200 g of the polar bio-based solvent sorbitol dimethyl ether, and 200 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 100°C for 7 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, it was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0058] Comparative Example 4

[0059] 1.0 g of the deep eutectic solvent (ChCl+6ZnCl2) obtained in Preparation Example 4, 100 g of the polar bio-based solvent 2-methyltetrahydrofuran, and 100 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 100°C for 3 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, the mixture was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0060] Comparative Example 5

[0061] 1.0 g of the deep eutectic solvent (ChCl+4ZnCl2) obtained in Preparation Example 2, 150 g of the polar bio-based solvent acetonitrile, and 150 g of hexafluoropropylene were added sequentially to a pressure-resistant reactor. The reaction mixture was stirred at 150°C for 4 h under mechanical stirring. The reaction was then stopped. After the reaction cooled to room temperature, it was allowed to stand and separated to obtain the lower crude product. The crude product was further distilled to obtain hexafluoropropylene oligomers.

[0062] Performance testing

[0063] The yields of hexafluoropropylene oligomers prepared in Examples 1-5 and Comparative Examples 1-5 were weighed and their yields were calculated. The results are shown in Table 1.

[0064] The specific test results are as follows:

[0065] Table 1 Performance Test Results

[0066]

[0067]

[0068] As can be seen from the test results of Examples 1-5 and Comparisons 1-5, the method for preparing hexafluoropropylene oligomers provided in this application yields hexafluoropropylene oligomers with a yield of 84-93%, which is significantly higher. This indicates that the deep eutectic solvent preparation method and the hexafluoropropylene oligomer preparation process provided in this application are both beneficial to improving the production efficiency of hexafluoropropylene oligomers.

[0069] As can be seen from the results of Example 1 and Comparative Example 1, when the mass ratio of deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent exceeds the range of 1:50:50-1:200:200, the yield of hexafluoropropylene oligomers decreases significantly and the yield becomes significantly lower. Therefore, in order to improve production efficiency, the mass ratio of deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent should be controlled. The preferred mass ratio of deep eutectic solvent, hexafluoropropylene, and polar bio-based solvent is 1:50:50-1:200:200.

[0070] As can be seen from the results of Example 2 and Comparative Example 2, when the reaction temperature for preparing hexafluoropropylene oligomers exceeds 60-100°C, the yield of hexafluoropropylene oligomers decreases significantly and the yield becomes significantly lower. Therefore, in order to improve production efficiency, the reaction temperature of hexafluoropropylene oligomers should be controlled, and the preferred reaction temperature for hexafluoropropylene oligomers is 60-100°C.

[0071] As can be seen from the results of Example 3 and Comparative Example 3, when the reaction time for preparing hexafluoropropylene oligomers exceeds 2-5 hours, the yield of hexafluoropropylene oligomers decreases significantly and the yield becomes significantly lower. Therefore, in order to improve production efficiency, the reaction time of hexafluoropropylene oligomers should be controlled, and the preferred reaction time is 2-5 hours.

[0072] The results of Example 4 and Comparative Example 4 show that when the deep eutectic solvent (ChCl+XZnCl2) used in the reaction to prepare hexafluoropropylene oligomers is 1-5, it is beneficial to obtain a higher yield of hexafluoropropylene oligomers. However, when the value of X exceeds 5, the yield of hexafluoropropylene oligomers is lower when the deep eutectic solvent is used. Therefore, in order to improve production efficiency, the value of X in the deep eutectic solvent (ChCl+XZnCl2) should be controlled to be 1-5.

[0073] The results of Example 5 and Comparative Example 5 show that when the polar bio-based solvent used in the reaction to prepare hexafluoropropylene oligomers is one or more of γ-valerolactone, 2-methyltetrahydrofuran, and sorbitol dimethyl ether, it is beneficial to improve the yield of hexafluoropropylene oligomers. However, when other types of solvents, such as acetonitrile, are used, the yield of hexafluoropropylene oligomers is significantly lower. Therefore, in order to improve production efficiency, the polar bio-based solvent can be one or more of γ-valerolactone, 2-methyltetrahydrofuran, and sorbitol dimethyl ether.

[0074] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for the preparation of hexafluoropropylene oligomers, characterized by: The method comprises the following steps: S1. Preparation of deep eutectic solvent: choline chloride (ChCl) and zinc chloride (ZnCl2) are added into a reaction kettle at a molar ratio of 1:X, and constant temperature stirring is carried out under mechanical stirring. After the reaction is stopped, the reaction is cooled to room temperature to obtain a deep eutectic solvent (ChCl+XZnCl2); S2. Preparation of hexafluoropropylene oligomer (HFPD): the deep eutectic solvent (ChCl+XZnCl2), hexafluoropropylene (HFP) and polar bio-based solvent prepared in step (1) are sequentially added into a pressure-resistant reaction kettle, and the reaction mixture is constant temperature stirred under mechanical stirring. After the reaction is stopped, the reaction is cooled to room temperature, and then separated to obtain a lower layer of crude product. After further rectification of the crude product, a hexafluoropropylene oligomer is obtained; The value of X in S1 is 1-5; The temperature of the constant temperature reaction in S1 is 50-100℃; The time of the constant temperature reaction in S1 is 8-12h; The hexafluoropropylene oligomer in S2 is a mixture of one or more of hexafluoropropylene dimer D1, hexafluoropropylene dimer D2 and hexafluoropropylene trimer; The mass ratio of the deep eutectic solvent, hexafluoropropylene and polar bio-based solvent in S2 is 1:50:50-1:200:200; The polar bio-based solvent is one or more of a mixture of γ-valerolactone, 2-methyltetrahydrofuran and sorbitol dimethyl ether; The temperature of the constant temperature reaction in S2 is 60-100℃; The time of the constant temperature reaction in S2 is 2-5h.

2. The method of claim 1, wherein the method is characterized by: The value of X in S1 is 4.

3. The method of claim 1, wherein the method is characterized by: The temperature of the constant temperature reaction in S1 is 85℃.

4. The method of claim 1, wherein the method is characterized by: The time of the constant temperature reaction in S1 is 10h.

5. The method of claim 1, wherein the method is characterized by: The mass ratio of the deep eutectic solvent, hexafluoropropylene and polar bio-based solvent when preparing dimer D1 in S2 is 1:60:60; the mass ratio of the deep eutectic solvent, hexafluoropropylene and polar bio-based solvent when preparing dimer D2 is 1:100:100; and the mass ratio of the deep eutectic solvent, hexafluoropropylene and polar bio-based solvent when preparing trimer is 1:150:

150.

6. The method of claim 1, wherein the hexafluoropropene oligomer is prepared by the process comprising: reacting a hexafluoropropene monomer with a catalyst to form the hexafluoropropene oligomer. The polar bio-based solvent is 2-methyltetrahydrofuran.

7. The method of claim 1, wherein the method is characterized by: The temperature of the constant temperature reaction in S2 is 70℃.

8. The method of claim 1, wherein the hexafluoropropene oligomer is prepared by the process comprising: reacting a hexafluoropropene monomer with a catalyst to form the hexafluoropropene oligomer. The time of the constant temperature reaction in S2 is 3h.

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