Preparation method of hexafluoropropylene tripolymer

Abstract

The invention relates to a preparation method of a hexafluoropropylene tripolymer, which specifically comprises the following steps: in a non-polar ester organic solvent, under the catalytic action of a fluorinating reagent, reacting hexafluoropropylene gas to generate the hexafluoropropylene tripolymer, the non-polar ester organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, trimethyl borate, triethyl borate, ethyl oleate, ethyl silicate or pentaerythritol tetraethyl hexanoate, and the T3 isomer of the hexafluoropropylene tripolymer accounts for more than 80%. The preparation method disclosed by the invention is high in reaction selectivity, short in reaction time, few in byproducts, environment-friendly and suitable for industrial production; and the obtained hexafluoropropylene tripolymer has higher T3 isomer proportion, and can be used in the fields of liquid cooling industry, cleaning industry and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of organofluorine chemistry, and particularly relates to a preparation method of hexafluoropropylene trimer. Background Art

[0002] Hexafluoropropylene trimer is an important fluorinated organic intermediate, which can be derived into many fluorinated surfactants and used in fields such as detergents, textiles, and leather, or can be directly used as a reaction solvent or heat transfer medium. In addition, with the increasing environmental protection requirements, hexafluoropropylene trimer with environmental protection advantages is directly used in fields such as the liquid cooling industry, cleaning industry, and anti-fingerprint diluents.

[0003] Hexafluoropropylene trimer has three structural forms: T1, T2, and T3. Among them, T2 and T3 have highly branched characteristics and negatively charged substituents, so they have special reaction activities, while the activity of T1 is relatively low. Therefore, when hexafluoropropylene trimer is used in fields requiring strong activity, the content of the T1 isomer should be as low as possible.

[0004]

[0005] Moreover, compared with the T2 isomer, the T3 isomer has a higher boiling point and better stability. For example, in the field of surface treatment of optical glass, it is required that the content of the T3 isomer in hexafluoropropylene trimer must be above 60%. In the liquid cooling field, due to the relatively high boiling point of the T3 isomer, the liquid cooling product can cool equipment at higher temperatures, while reducing volatilization, which can reduce the temperature control cost and raw material loss. Therefore, it is very necessary to prepare a hexafluoropropylene trimer product with a T3 isomer content greater than 60% or even higher.

[0006] In the prior art, there are many literatures reporting the oligomerization reaction of hexafluoropropene, mainly including two types of methods: one is the gas-phase oligomerization method of hexafluoropropene. The gas-phase oligomerization does not require a solvent and uses metal fluorides, activated carbon, and metal fluorides attached to activated carbon as catalysts; the other is the liquid-phase oligomerization method, which is more common. The oligomerization reaction occurs under the action of a polar solvent and a catalyst. The solvents include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, etc. The selectable catalysts include KF, KSCN, KOCN, KCN, crown ether, ammonium fluoride, etc. By selecting different polar solvents and catalysts, the ratio of the dimer to the trimer can be controlled. By adding crown ether, the solubility of the catalyst in the system can be increased, and the oligomerization rate can be improved. Each of the two methods has its own advantages. The gas-phase method has a high degree of automation and is suitable for large-scale production, but the single-pass conversion rate is relatively low, the equipment investment is large, and the polymerization reaction is difficult to control, and the selectivity of the reaction is slightly poor; the liquid-phase method has a higher one-time conversion rate and yield, has better selectivity by adjusting process parameters, and has lower requirements for reaction control than the gas-phase method, but has higher requirements for raw materials, catalysts, and solvents, and the post-treatment is relatively cumbersome.

[0007] Regarding the product selectivity of the hexafluoropropene oligomerization reaction, the discussion is generally limited to between the dimer and the trimer. For example, Chinese Patent CN112830863A discloses a method for continuously and controllably preparing hexafluoropropene dimer / trimer, using an alkali metal fluoride as a catalyst and a crown ether as a catalytic promoter to highly selectively prepare hexafluoropropene dimer or hexafluoropropene trimer in an aprotic polar solvent. However, this method has problems such as unclear proportions of various isomers, long pre-mixing time of the catalyst, and high equipment requirements.

[0008] In the prior art, there are few reports on the selective regulation between the isomers of the dimer or trimer. Only Chinese Patent CN113968770A introduces a method for synthesizing a hexafluoropropene trimer with a low proportion of T1 isomer. However, this method only controls the proportion of the T1 isomer, but does not control the proportions of the isomers T2 and T3. The proportion of the isomer T3 is about 50%, which cannot meet the requirements in fields such as surface treatment or liquid cooling. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention proposes a method for preparing a hexafluoropropene trimer with high reaction selectivity and a proportion of T3 isomer exceeding 80%.

[0010] The object of the present invention is achieved through the following technical solutions:

[0011] A preparation method of hexafluoropropylene trimer, specifically including: in a non-polar ester organic solvent, under the catalytic action of a fluorination reagent, hexafluoropropylene gas reacts to generate hexafluoropropylene trimer. The non-polar ester organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, trimethyl borate, triethyl borate, ethyl oleate, tetraethyl orthosilicate or pentaerythritol tetraethylhexanoate. The proportion of the T3 isomer of the hexafluoropropylene trimer exceeds 80%.

[0012] The polarity of the solvent can affect the stability of free radicals and intermolecular interactions in the polymerization reaction. Usually, polar solvents can weaken the interaction force between free radicals, making the free radicals easier to diffuse, thus promoting the progress of the polymerization reaction. Therefore, it has been reported that using polar solvents can optimize the conversion of hexafluoropropylene to hexafluoropropylene dimer and trimer. However, although polar solvents have excellent polymerization promotion effects and enable the high-selectivity conversion of hexafluoropropylene to hexafluoropropylene trimer, they will also cause the selectivity of hexafluoropropylene trimer to shift simultaneously to isomers T2 and T3.

[0013] The research of the present invention finds that this is related to the fact that the reaction temperatures required for the two isomers T2 and T3 of hexafluoropropylene trimer in the reaction process are similar. Therefore, the selectivities of the isomers hexafluoropropylene trimer T2 and T3 are similar, and the contents of the isomers hexafluoropropylene trimer T2 and T3 obtained are similar. Therefore, although polar solvents are beneficial to the oligomerization reaction of hexafluoropropylene to generate hexafluoropropylene trimer, the selectivity of isomer T3 is only 50 - 60%.

[0014] The present invention uses a non-polar ester solvent with a polar group as the reaction solvent. Since the electron density distribution of the molecule is uniform, and the uneven charge distribution in the polar group is not sufficient to affect the polarity of the whole molecule, the polarity is small and it is a non-polar molecule. It can weaken the interaction force between free radicals to a certain extent, promote the polymerization reaction of hexafluoropropylene, enable hexafluoropropylene to generate hexafluoropropylene trimer with high selectivity, and at the same time, by increasing the reaction temperature, the temperature difference required for generating isomer T2 and isomer T3 is increased. Therefore, it is easier to control the generation of isomer T3, making the selectivity of isomer T3 reach more than 80%.

[0015] Specifically, the reaction temperature is 50 - 110 °C, the reaction pressure is 0 - 1 MPa, and the reaction time is 15 - 60 min; preferably, the reaction temperature is 80 - 100 °C, the reaction pressure is 0.1 - 0.4 MPa, and the reaction time is 30 - 45 min.

[0016] The fluorination reagent is at least one of tetraalkylammonium fluoride or alkali metal fluoride. Preferably, the fluorination reagent is tetraalkylammonium fluoride.

[0017] Tetraalkylammonium fluoride has good nucleophilicity under anhydrous conditions and is an excellent nucleophilic fluorination reagent. However, in practical applications, especially in the industrial scale-up process, due to the water-absorbing property of this substance, and because water molecules have a great polarity, the excessive polarity is likely to quench free radicals, resulting in the termination of the free radical reaction. Therefore, it has not been widely used. However, the non-polar ester organic solvent described in the present invention has a large difference in compatibility with water. It can not only effectively control the water content in the reaction system of the present invention, but also improve the catalytic effect of tetraalkylammonium fluoride, further improve the selectivity of hexafluoropropylene trimer, and shorten the reaction time.

[0018] Preferably, the fluorination reagent is selected from at least one of tetramethylammonium fluoride, tetraethylammonium fluoride, tetrapropylammonium fluoride or tetrabutylammonium fluoride.

[0019] The molar ratio of the fluorination reagent to hexafluoropropylene gas is 1:(10 - 200), preferably 1:(20 - 50). The molar ratio of the non-polar ester organic solvent to hexafluoropropylene gas is (0.1 - 10):1, preferably (0.5 - 2):1.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The preparation method of the present invention has high reaction selectivity, short reaction time, less by-products, is environmentally friendly, and is suitable for industrial production;

[0022] 2. The T3 isomer of the hexafluoropropylene trimer obtained by the preparation method of the present invention has a high proportion and can be used in fields such as the liquid cooling industry and the cleaning industry. Specific Embodiments

[0023] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative, improved and equivalent solutions that may be included within the scope of the claims.

[0024] In the embodiments of the present invention, gas chromatography analysis is used, and the analysis instrument is Shimadzu GC-2014; chromatographic column: SH-1301 (60mX 0.25mm X 1um). GC analysis method: detector temperature 240°C, vaporization chamber temperature 200°C, column temperature: 30°C (10min) 15°C / min 200°C (15min); carrier gas (N) flow rate 30mL / min, air flow rate 100mL / min, hydrogen flow rate 40mL / min, split ratio 30:1, injection volume 0.2mL.

[0025] Example 1

[0026] Add 100 ml of dimethyl carbonate and 5 g of tetrabutylammonium fluoride to a 250-ml autoclave equipped with stirring and heating. After covering and sealing it, use a vacuum device to remove the air in the autoclave, then introduce nitrogen, and then evacuate again. After replacement, make the pressure in the autoclave zero. Raise the temperature to 85 °C, and the stirring speed is 500 revolutions per minute. After activation for 30 min, introduce 100 g of hexafluoropropene gas under a gauge pressure of 0.3 MPa. After continuously stirring at 85 °C for 30 min, stop stirring and cool down. Transfer the reaction product to a separatory funnel and let it stand to separate the lower layer of colorless and transparent hexafluoropropene oligomer.

[0027] By gas chromatography analysis, the mass content of hexafluoropropene dimer is 2.4%, and the content of hexafluoropropene trimer is 97.6%. Among them, the mass proportion of isomer T1 in hexafluoropropene trimer is 1.7%, the mass proportion of isomer T2 is 7.2%, and the mass proportion of isomer T3 is 91.1%.

[0028] Example 2

[0029] The operation of Example 2 is the same as that of Example 1, except that the catalyst is changed to tetraethylammonium fluoride and other operations remain unchanged.

[0030] By gas chromatography analysis, the mass content of hexafluoropropene dimer is 4.1%, and the content of hexafluoropropene trimer is 95.9%. Among them, the mass proportion of isomer T1 in hexafluoropropene trimer is 2.4%, the mass proportion of isomer T2 is 10.3%, and the mass proportion of isomer T3 is 87.3%

[0031] Example 3

[0032] The operation of Example 3 is the same as that of Example 1, except that the solvent is changed to diethyl carbonate and other operations remain unchanged.

[0033] By gas chromatography analysis, the mass content of hexafluoropropene dimer is 2.9%, and the content of hexafluoropropene trimer is 97.1%. Among them, the mass proportion of isomer T1 in hexafluoropropene trimer is 1.9%, the mass proportion of isomer T2 is 8.9%, and the mass proportion of isomer T3 is 89.2%.

[0034] Example 4

[0035] The operation of Example 4 is the same as that of Example 1, except that the solvent is changed to triethyl borate and the reaction temperature is changed to 110 °C, and other operations remain unchanged.

[0036] By gas chromatography analysis, the mass content of hexafluoropropene dimer is 5.5%, and the content of hexafluoropropene trimer is 94.5%. Among them, the mass proportion of isomer T1 in hexafluoropropene trimer is 2.7%, the mass proportion of isomer T2 is 15.2%, and the mass proportion of isomer T3 is 82.1%.

[0037] Example 5

[0038] The operation of Example 5 is the same as that of Example 1, except that the reaction temperature is changed to 50 °C and other operations remain unchanged.

[0039] By gas chromatography analysis, the mass content of hexafluoropropylene dimer is 4.3%, and the trimer content is 95.7%. Among them, the mass ratio of isomer T1 in hexafluoropropylene trimer is 2.5%, the mass ratio of isomer T2 is 11.6%, and the mass ratio of isomer T3 is 85.9%.

[0040] Example 6

[0041] The operation of Example 6 is the same as that of Example 1, except that the reaction pressure is changed to 1 MPa and other operations remain unchanged.

[0042] By gas chromatography analysis, the mass content of hexafluoropropylene dimer is 2.8%, and the trimer content is 97.2%. Among them, the mass ratio of isomer T1 in hexafluoropropylene trimer is 5.2%, the mass ratio of isomer T2 is 10.4%, and the mass ratio of isomer T3 is 84.4%.

[0043] Example 7

[0044] The operation of Example 7 is the same as that of Example 1, except that the reaction pressure is changed to 0.1 MPa and other operations remain unchanged.

[0045] By gas chromatography analysis, the mass content of hexafluoropropylene dimer is 8.5%, and the trimer content is 91.5%. Among them, the mass ratio of isomer T1 in hexafluoropropylene trimer is 3.2%, the mass ratio of isomer T2 is 16.6%, and the mass ratio of isomer T3 is 80.2%.

[0046] Example 8

[0047] The operation of Example 8 is the same as that of Example 1, except that the catalyst is changed to cesium fluoride and other operations remain unchanged.

[0048] By gas chromatography analysis, the mass content of hexafluoropropylene dimer is 3.4%, and the hexafluoropropylene trimer content is 96.6%. Among them, the mass ratio of isomer T1 in hexafluoropropylene trimer is 3.1%, the mass ratio of isomer T2 is 15.4%, and the mass ratio of isomer T3 is 81.5%.

[0049] Example 9

[0050] After premixing 100 ml of dimethyl carbonate and 5 g of tetrabutylammonium fluoride, they were simultaneously introduced into a microchannel reactor together with 100 g of hexafluoropropene gas. The reaction temperature was 60 °C, the reaction pressure was 0.5 MPa, and the residence time of the materials in the microchannel reactor was 30 s. The reaction product was transferred to a separatory funnel and allowed to stand to separate out the colorless and transparent hexafluoropropene oligomer in the lower layer.

[0051] By gas chromatography analysis, the mass content of hexafluoropropene dimer was 1.3%, and the content of hexafluoropropene trimer was 98.7%. Among them, the mass ratio of isomer T1 in the hexafluoropropene trimer was 4.9%, the mass ratio of isomer T2 was 9.9%, and the mass ratio of isomer T3 was 85.2%.

[0052] Comparative Example 1

[0053] 100 ml of acetonitrile, 5 g of 18-crown-6 and 2 g of potassium fluoride were added to a 250-ml stirred and heated autoclave. After covering and sealing, the air in the autoclave was removed with a vacuum device, then nitrogen was introduced, and then evacuated again. After replacement, the pressure in the autoclave was zero. The temperature was raised to 80 °C, the stirring speed was 500 revolutions per minute, and after activation for 30 min, 100 g of hexafluoropropene gas was introduced at a gauge pressure of 0.4 MPa. After continuous stirring at 80 °C for 2 h, the stirring was stopped and cooled. The reaction product was transferred to a separatory funnel and allowed to stand to separate out the colorless and transparent hexafluoropropene oligomer in the lower layer.

[0054] By gas chromatography analysis, the mass content of hexafluoropropene dimer was 12.1%, and the content of hexafluoropropene trimer was 87.9%. Among them, the mass ratio of isomer T1 in the hexafluoropropene trimer was 6.9%, the mass ratio of isomer T2 was 37.2%, and the mass ratio of isomer T3 was 55.9%.

[0055] Comparative Example 2

[0056] The operation of Comparative Example 2 was the same as that of Comparative Example 1, except that: after continuous stirring at 80 °C for 30 min, the stirring was stopped and cooled, and other operations remained unchanged.

[0057] By gas chromatography analysis, the mass content of hexafluoropropene dimer was 51.3%, and the content of hexafluoropropene trimer was 48.7%. Among them, the mass ratio of isomer T1 in the hexafluoropropene trimer was 45.1%, the mass ratio of isomer T2 was 17.7%, and the mass ratio of isomer T3 was 37.2%.

[0058] Comparative Example 3

[0059] Add 100 ml of acetonitrile and 5 g of tetrabutylammonium fluoride to a 250-ml autoclave with stirring and heating. After covering and sealing it, use a vacuum device to remove the air in the autoclave, then introduce nitrogen, and then evacuate again. After replacement, make the pressure in the autoclave zero. Heat the temperature to 75 °C, with a stirring speed of 500 revolutions per minute. After activation for 30 min, introduce 100 g of hexafluoropropene gas at a gauge pressure of 0.3 MPa. After continuously stirring at 75 °C for 30 min, stop stirring and cool. Transfer the reaction product to a separatory funnel and let it stand to separate the lower colorless and transparent hexafluoropropene oligomer.

[0060] By gas chromatography analysis, the mass content of hexafluoropropene dimer is 66.5%, and the content of hexafluoropropene trimer is 33.5%. Among them, the mass proportion of isomer T1 in the hexafluoropropene trimer is 6.0%, the mass proportion of isomer T2 is 38.8%, and the mass proportion of isomer T3 is 55.2%.

[0061] From the results of Examples 1 to 9 and Comparative Examples 1 to 3, it can be seen that the preparation method described in the present invention can effectively increase the proportion of isomer T3 in the hexafluoropropene trimer to more than 80%.

Claims

1. A preparation method of hexafluoropropylene trimer, characterized in that: In a non-polar ester organic solvent, in the presence of a fluorination reagent as a catalyst, hexafluoropropylene gas reacts to form hexafluoropropylene trimer. The non-polar ester organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, trimethyl borate, triethyl borate, ethyl oleate, tetraethyl orthosilicate or pentaerythritol tetraethylhexanoate. The proportion of the T3 isomer of the hexafluoropropylene trimer exceeds 80%.

2. The preparation method according to claim 1, characterized in that: The non-polar ester organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, trimethyl borate or triethyl borate.

3. The preparation method according to claim 1, wherein: The fluorination reagent is at least one of tetraalkylammonium fluoride or alkali metal fluoride salt.

4. The preparation method according to claim 3, wherein: The fluorination reagent is selected from at least one of tetramethylammonium fluoride, tetraethylammonium fluoride, tetrapropylammonium fluoride or tetrabutylammonium fluoride.

5. The preparation method according to claim 1, characterized in that: The reaction temperature is 50 - 110 °C, the reaction pressure is 0 - 1 MPa, and the reaction time is 15 - 60 min.

6. The preparation method according to claim 5, characterized in that: The reaction temperature is 80 - 100 °C, the reaction pressure is 0.1 - 0.4 MPa, and the reaction time is 30 - 45 min.

7. The preparation method according to claim 1, wherein: The molar ratio of the fluorination reagent to the hexafluoropropylene gas is 1:(10 - 200).

8. The preparation method according to claim 7, characterized in that: The molar ratio of the fluorination reagent to the hexafluoropropylene gas is 1:(20 - 50).

9. The preparation method according to claim 1, characterized in that: The molar ratio of the non-polar ester organic solvent to the hexafluoropropylene gas is (0.1 - 10):

1.

10. The preparation method according to claim 9, characterized in that: The molar ratio of the non-polar ester organic solvent to the hexafluoropropylene gas is (0.5 - 2):1.

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