A purification process for 4,4'-hexafluoroisopropylidene diphthalic anhydride

Abstract

In order to overcome the problem that the recrystallization using acetic acid as a solvent for preparing 4,4'-(hexafluoroisopropylidene)diphthalic anhydride in the prior art directly purifies the product by drying, which easily causes the 6-FDA solid to turn yellow, the high yellowness and B value, the application provides a purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, which comprises the following steps: obtaining 4,4'-(hexafluoroisopropylidene)diphthalic anhydride crude product, adding fluorinated ether solvent to obtain a mixture, and then sequentially performing heating and washing, filtering and drying to obtain 4,4'-(hexafluoroisopropylidene)diphthalic anhydride finished product. The application provides a purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, which is purified by the way of washing, azeotropy and direct drying to obtain 6-FDA crystal with a purity of more than 99.8%, no acetic acid is detected, and the B value of yellowness is less than 1.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of purification, and particularly relates to a purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride. BACKGROUND

[0002] Compared with traditional polyimides, fluorine-containing polyimides have advantages of low dielectric constant, low refractive index, low moisture absorption, high transparency and the like, and have become a type of high-performance materials with great development prospects in many high-tech fields. Especially, fluorine-containing polyimides can greatly reduce optical loss in the optical communication wavelength region due to the obvious reduction of C-H bond vibration absorption caused by the replacement of part of hydrogen atoms by fluorine atoms, and thus have wide application in the optical field such as light guide, waveguide and liquid crystal. Among them, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (hereinafter referred to as 6-FDA) is the most important monomer of fluorine-containing polyimides. 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) is a new type of polyimide monomer material. The polyimide using hexafluoro dianhydride as a monomer has the following advantages in performance: 1) low dielectric constant; the dielectric constant of ordinary polyimide is about 3.4, and after adding 6-FDA, the dielectric constant can be reduced to 2.5; the low dielectric constant brings about the reduction of signal delay and loss, which has great value in electrical applications. 2) transparency and controllable refractive index; because the polyimide is slightly yellow or brown, after adding 6-FDA, it can become transparent, and according to the amount of 6-FDA added, the refractive index can be controlled, which has great effect in optical element applications. 3) chemical and thermal stability; after introducing fluorine atoms, the chemical and thermal stability of the polyimide will be improved due to the strong negative property of fluorine atoms, so that the product can work under special chemical or temperature conditions. 4) lubricity; because of the low polarity of fluorine atoms, the fluorine-containing polyimide has very low surface free energy, smooth surface and small friction. 5) the fluorine-containing polyimide synthesized by using 6-FDA has very good thermal oxidation resistance, high temperature hot melting property and radiation resistance, and is the preferred structural material in the aerospace industry.

[0003] The existing purification of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is generally recrystallization using acetic acid as a solvent to precipitate crystalline 6-FDA crude product. The obtained 6-FDA crude product contains residual acetic acid, and the 6-FDA solid is prone to yellowing, high yellowness and high B value after drying. The residual acetic acid leads to low purity of 6-FDA, and in the subsequent preparation of polyimide polymerization reaction, the polymerization degree is low; at the same time, the polyimide prepared therefrom is yellow in color, which affects the transparency index of the polyimide. SUMMARY

[0004] The present application provides a purification process of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride.

[0005] To solve the above technical problems, the present application provides a purification process of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, comprising the following steps:

[0006] The crude 4,4'-(hexafluoroisopropylidene) diphthalic anhydride is obtained, and a fluorinated ether solvent is added to obtain a mixture, and then heating and washing, filtering and drying are sequentially performed to obtain the finished 4,4'-(hexafluoroisopropylidene) diphthalic anhydride.

[0007] Preferably, the drying step comprises a first-stage drying, and the first-stage drying comprises the following steps: under the condition of a pressure of-0.09 to-0.08 MPa, the temperature is raised to 50 to 80℃, and the first-stage drying is performed for 4 to 8 hours.

[0008] Preferably, the drying step further comprises a second-stage drying, and the second-stage drying comprises the following steps: after the first-stage drying is completed, the temperature is continuously raised to 110 to 120℃, and the second-stage drying is performed for 6 to 12 hours.

[0009] Preferably, the heating and washing, filtering step is: the mixture is washed at a temperature of 50 to 80℃ for 0.5 to 2 hours, and then the temperature is lowered to 20 to 30℃, and then filtering is performed to obtain 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid; the fluorinated ether solvent is repeatedly added to the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid, and then the heating, washing and filtering steps are performed, and the number of repetitions is greater than or equal to 3 times.

[0010] The mass ratio of the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid to the fluorinated ether solvent is 1:(2 to 4).

[0011] Preferably, the fluoroether solvent includes one or more of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, 1,1,1,2,3,3-hexafluoro-2-(trifluoromethyl)-3-methoxypropane, 1,1,1,2,3,4,4,4-octafluoro-2-methoxy-3-(trifluoromethyl)butane, 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-trifluoromethylpentane, 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, 1-(difluoro(trifluoromethoxy)methoxy)-1,1,2,2-tetrafluoro-2-methoxyethane, 1,1,2,2-tetrafluoro-1-methoxy-2-trifluoromethoxyethane.

[0012] Preferably, the mass ratio of the fluoroether solvent to the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is (2-4):1.

[0013] Advantages:

[0014] Compared with the prior art, the purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride provided by the application uses a fluoroether solvent as a washing solvent, does not dissolve 6-FDA, does not react with acetic acid or 6-FDA, does not destroy the crystal structure, and does not introduce new impurities; the first heating washing and filtering steps can remove part of the acetic acid, and then the 6-FDA wet solid is dried by using azeotropy to remove acetic acid, fluoroether solvent and trace amounts of acetic acid residues, and the 6-FDA crystal obtained by the purification process of washing, azeotropy and direct drying has a purity of more than 99.8%, no acetic acid is detected, and the B value of yellowness is less than 1, which has a good effect of removing impurities and reducing yellowness. The fluoroether solvent used in the purification process has the characteristics of convenient recovery, less loss, non-flammable and non-explosive, environmental protection and safety, so that the entire purification process is green and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the liquid chromatogram of the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride in Example 1;

[0016] Figure 2 is the yellowness test data graph of the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride in Example 1;

[0017] Figure 3 is the liquid chromatogram of the purified 6-FDA in Example 1;

[0018] Figure 4 is the yellowness test data graph of the purified 6-FDA in Example 1;

[0019] Figure 5is the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride in Example 2 - the liquid chromatogram;

[0020] Figure 6 is the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride in Example 2 - the yellowness test data graph;

[0021] Figure 7 is the 6-FDA after purification in Example 2 - the liquid chromatogram;

[0022] Figure 8 is the 6-FDA after purification in Example 2 - the yellowness test data graph. DETAILED DESCRIPTION

[0023] In order to make the technical problems solved by the present application, technical solutions and beneficial effects more clearly understood, the present application will be further described in detail below in conjunction with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0024] For the convenience of distinguishing and understanding, the crude 6-FDA or crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride described herein is called the pre-washing stage, and the 6-FDA wet solid or 4,4'-(hexafluoroisopropylidene)diphthalic anhydride wet solid is called the 6-FDA containing impurities after being washed by hydrofluoroether.

[0025] The present application provides a purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, which comprises the following steps:

[0026] The crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is obtained, and a fluorinated ether solvent is added to obtain a mixture, and then heating washing, filtering and drying are sequentially performed to obtain the finished 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0027] The obtained crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride is the 6-FDA (4,4'-(hexafluoroisopropylidene)diphthalic anhydride) crude product obtained by recrystallization using acetic acid as a solvent. The step of obtaining the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride includes but is not limited to the following steps: preparing 4,4'-(hexafluoroisopropylidene)diphthalic anhydride by existing technical methods, mixing and stirring with acetic acid, heating to 90-120℃, dissolving and then lowering to room temperature (20-35℃), precipitating 6-FDA crystals, and then filtering to obtain the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0028] The 6-FDA solid obtained by recrystallization using acetic acid as a solvent still contains acetic acid, and the 6-FDA wet solid is prone to yellowing and has high yellowness and B value after drying. To solve this problem, the inventors have found that fluoroether solvent is not soluble in 6-FDA, and acetic acid is soluble in both 6-FDA and fluoroether solvent. By adding a large amount of fluoroether solvent to the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, and then sequentially performing heating and washing and filtering, part of the acetic acid dissolved in the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride can be removed. The wet solid of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride containing a small amount of acetic acid and fluoroether solvent is obtained by filtering. Then, the wet solid of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride containing a small amount of acetic acid and fluoroether solvent is dried by using acetic acid and fluoroether solvent azeotropy, so as to remove the small amount of acetic acid and fluoroether solvent and the acetic acid remaining in the wet solid of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0029] Compared with the prior art, the purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride provided by the application uses fluoroether solvent as a washing solvent, which does not dissolve 6-FDA, does not react with acetic acid and 6-FDA, does not destroy the crystal structure, and does not introduce new impurities. The heating and washing and filtering steps performed for the first time can remove part of the acetic acid. Then, the 6-FDA wet solid is dried by using azeotropy to remove acetic acid and fluoroether solvent and trace amounts of acetic acid. The 6-FDA crystal obtained by purification through washing, azeotropy and direct drying has a purity of more than 99.8%, no acetic acid is detected, the yellowness B value is less than 1, and has a good effect of removing impurities and reducing yellowness. The fluoroether solvent used in the purification process has the characteristics of convenient recovery, low loss, non-flammable and non-explosive, environmental protection and safety, so that the entire purification process is green and environmentally friendly.

[0030] In some embodiments, the drying step includes a first-stage drying, and the first-stage drying includes the following steps: under the condition of a pressure of -0.09 to -0.08 MPa, heating to a temperature in the range of 50 to 80℃, and performing first-stage drying for 4 to 8 hours.

[0031] Specifically, the first-stage drying mainly utilizes the azeotropic characteristics of acetic acid and fluoroether to remove acetic acid and fluoroether solvent in the 6-FDA wet solid. The drying temperature in the first-stage drying is 50-80°C. At this temperature range, the azeotropic boiling point of acetic acid and fluoroether solvent is reached, and the acetic acid and fluoroether solvent is distilled, so that the acetic acid and fluoroether solvent in the 6-FDA wet solid can be removed. If the drying temperature is lower than 50°C, the azeotropic boiling point of acetic acid and fluoroether solvent is not reached, and the acetic acid and fluoroether solvent in the 6-FDA wet solid cannot be effectively removed. If the drying temperature is higher than 80°C, the purification process cost is increased. Similarly, the drying time in the first-stage drying step is in the range of 4-8h. Within this drying time range, it is beneficial to remove the acetic acid and fluoroether solvent in the 6-FDA wet solid. If the drying time is too short, there will be residual acetic acid and fluoroether solvent, which reduces the purity of the 6-FDA solid. If the drying time is too long, i.e., the heating time is too long, the purification process cost is increased, and the yellowness of the product is increased, which increases the yellowness of the product and reduces the purity.

[0032] In the first-stage drying step, the drying temperature can be 50°C, 53°C, 55°C, 58°C, 60°C, 63°C, 65°C, 70°C, 72°C, 75°C, 78°C, 80°C, etc., as long as the drying temperature is in the range of 50-80°C.

[0033] It should be noted that in order to improve the heating rate, the present application limits the temperature in the first-stage drying step to be raised to the range of 50-80°C, and the temperature rising time is controlled to be within 2h.

[0034] In some embodiments, the drying step further comprises a second-stage drying, which comprises the following steps: after the first-stage drying, the temperature is continuously raised to the range of 110-120°C, and the second-stage drying is performed, and the second-stage drying time is 6-12h.

[0035] Specifically, after the 6-FDA wet solid is subjected to the first-stage drying step, the second-stage drying step is performed, which is mainly used to remove the trace amount of acetic acid residue in the 6-FDA solid, and reduce the yellowness and B value of the 6-FDA solid. In the second-stage drying step, the drying temperature is 110-120°C, which can make the acetic acid evaporate and achieve the purpose of removing the trace amount of acetic acid. Controlling the drying time in the range of 6-12h is beneficial to remove the acetic acid as much as possible and reduce the content of acetic acid in the 6-FDA solid. If the drying temperature is lower than 110°C or the drying time is lower than 6h, the acetic acid cannot be effectively removed, and the obtained 6-FDA solid contains acetic acid. If the drying temperature is higher than 120°C or the drying time is higher than 12h, the purification process cost is increased.

[0036] In the second-stage drying step, the drying temperature can be 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, etc., as long as the drying temperature is in the range of 110°C to 120°C.

[0037] It should be noted that, in order to improve the heating rate, the application limits the temperature in the second-stage drying step to be in the range of 110°C to 120°C, and the temperature rising time is controlled to be less than 2 hours.

[0038] In some embodiments, the heating and washing step is heating the mixture to a temperature in the range of 50°C to 80°C.

[0039] Heating the mixture to a temperature in the range of 50°C to 80°C also takes advantage of the azeotropic characteristics of acetic acid and fluoroether solvent to remove part of the acetic acid in the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid.

[0040] Specifically, the heating temperature can be 50°C, 55°C, 58°C, 60°C, 65°C, 67°C, 70°C, 74°C, 75°C, 78°C, 80°C, etc., as long as the heating temperature is in the range of 50°C to 80°C. It should be noted that in the heating and washing step, the temperature is raised while stirring, and the mixture is stirred at a certain temperature for a period of time. Stirring makes the mixture more uniform, so that the acetic acid that can be taken away by the fluoroether solvent is stripped out of the solid as much as possible, and the purpose of cleaning is achieved to the greatest extent. If there is no heating step, only by washing and filtering, although repeated several times, the acetic acid removed is less, and the acetic acid residue is more after direct drying, so the 6-FDA crystal still has high yellowness. Combining heating and washing with filtering can remove most of the acetic acid.

[0041] In some embodiments, the heating and washing, filtering step is washing the mixture at a temperature in the range of 50°C to 80°C, the washing time is 0.5 to 2 hours, after washing, the temperature is lowered to 20 to 30°C, and then filtering; repeating adding the fluoroether solvent to the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid, and then performing the heating, washing and filtering steps, the number of repetitions is greater than or equal to 3 times.

[0042] After washing, the temperature is lowered to the range of 20 to 30°C, and then filtering, which also takes advantage of the fact that acetic acid is also soluble in fluoroether solvent, and filtering can also remove part of the acetic acid dissolved in fluoroether solvent, thereby achieving the purpose of removing part of the acetic acid in the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride crude product. Repeating adding the fluoroether solvent to the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid, and then performing the heating, washing and filtering steps, the number of repetitions is greater than or equal to 3 times, mainly to remove as much acetic acid as possible in the 4,4'-(hexafluoroisopropylidene) diphthalic anhydride crude product.

[0043] Specifically, the mixture is washed at a temperature in the range of 50-80 °C, which can be 50 °C, 55 °C, 58 °C, 60 °C, 65 °C, 67 °C, 70 °C, 74 °C, 75 °C, 78 °C, 80 °C, etc., as long as the mixture is heated to a temperature in the range of 50-80 °C.

[0044] In some preferred embodiments, the number of repetitions is 3-6.

[0045] Specifically, the number of repetitions can be 3, 4, 5, 6, etc., as long as the number of repetitions is in the range of 3-6.

[0046] In some embodiments, the mass ratio of the 4,4'-(hexafluoroisopropylidene)dithioic anhydride wet solid to the fluoroether solvent is 1:(2-4).

[0047] In subsequent repeated heating, washing, and filtering operations, the mass ratio of the 4,4'-(hexafluoroisopropylidene)dithioic anhydride wet solid to the fluoroether solvent is (2-4):1, which is the same as the original mass ratio of the 4,4'-(hexafluoroisopropylidene)dithioic anhydride crude product to the fluoroether solvent.

[0048] In some embodiments, the 4,4'-(hexafluoroisopropylidene)dithioic anhydride wet solid is added to the fluoroether solvent, followed by the heating, washing, and filtering steps, and the number of repetitions is greater than or equal to 3, which can remove most of the acetic acid in the crude product.

[0049] In some embodiments, the fluoroether solvent includes one or more of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, 1,1,1,2,3,3-hexafluoro-2-(trifluoromethyl)-3-methoxypropane, 1,1,1,2,3,4,4,4-octafluoro-2-methoxy-3-(trifluoromethyl)butane, 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2-trifluoromethylpentane, 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, 1-(difluoro(trifluoromethoxy)methoxy)-1,1,2,2-tetrafluoro-2-methoxyethane, 1,1,2,2-tetrafluoro-1-methoxy-2-trifluoromethoxyethane.

[0050] It can be understood that the above-mentioned fluoroether solvents include types that are not soluble with 6-FDA, do not react with acetic acid, and are soluble with acetic acid.

[0051] In some embodiments, the mass ratio of the fluoroether solvent to the 4,4'-(hexafluoroisopropylidene)dithioic anhydride crude product is (2-4):1.

[0052] The application limits the mass ratio of fluorine ether solvent to the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to be in the range of (2-4):1, the mass of the fluorine ether solvent is much greater than that of the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, and the content of the fluorine ether solvent is relatively high, which is beneficial to remove acetic acid in the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0053] The specific embodiment modes of the application will be further explained by examples below, but the protection scope of the application is not limited in the range described in the examples.

[0054] Example 1

[0055] This example is used to illustrate the purification process of the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride disclosed in the application.

[0056] Step one, obtain the crude 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA):

[0057] Stir 1 kg of 6-FDA and 2 kg of acetic acid, heat to 100°C to dissolve and then cool to 30°C to completely precipitate 6-FDA crystals, filter to obtain 2 kg of 6-FDA crude product; test the sample of the 6-FDA crude product and the residual amount of acetic acid is 40.23%, after drying, test the content, which is 99.35% (such as Figure 1 ), the yellowness is 2.27, and the B value is 1.37 (such as Figure 2 ).

[0058] Step two: take 2 kg of 6-FDA crude product obtained in step one and 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, stir to obtain a mixture, heat the mixture to 70°C, and perform cleaning at 70°C, clean for 2 hours, after cleaning, cool to 30°C, remove the filtrate by filtration, and obtain 2 kg of 6-FDA wet solid.

[0059] Step three: repeat the addition of 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride wet solid, followed by the heating, washing and filtration steps, for a total of two repetitions of the above steps, for a total of three washes with 12 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added in 4 kg portions each, with each portion being 4 kg in mass. After three repetitions, 1.98 kg of 6-FDA wet solid is obtained by filtration, which is then transferred to a double cone oven and subjected to a staged temperature increase under negative pressure, with the pressure being in the range of -0.090 to -0.080 MPa. The first stage of the drying step is a slow temperature increase to 60 °C over 2 h, with the drying being performed for 6 h. The second stage of the drying step is a temperature increase to 110 °C over 2 h, with the drying being performed for an additional 6 h. The 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane and acetic acid are removed to obtain 0.96 kg of 6-FDA crystals, with the washing yield being 96%.

[0060] The sample testing shows that the content of 6-FDA is 99.81% (as Figure 3 ), the yellowness is 1.08, and the B value is 0.6 (as Figure 4 ), and acetic acid is not detected.

[0061] The above recovery: the 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane filtrate is combined and washed with water, and the lower solvent is separated and dehydrated to obtain 10.6 kg of the lower solvent, which is dried and condensed to recover 1 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, for a total of 11.6 kg, with the loss of the washing solvent being 3.3%.

[0062] Example 2:

[0063] Step one: obtain 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) crude product:

[0064] 0.5 kg of 6-FDA and 1 kg of acetic acid are mixed and stirred, heated to 100 °C to dissolve, and then cooled to 30 °C to completely precipitate the 6-FDA crystals, and 1 kg of 6-FDA crude product is obtained by filtration. The sample testing of the 6-FDA crude product shows that the residual amount of acetic acid is 38.21%, and after drying, the purity content is 99.26% (as Figure 5 ), the yellowness is 1.91, and the B value is 1.15 (as Figure 6 ).

[0065] Step two: take 1 kg of 6-FDA crude product from step one and 2 kg of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, mix and stir, heat to 70°C, and wash at 70°C for 2 hours. After washing, cool to 30°C, filter to remove the filtrate, and obtain 1 kg of 6-FDA wet solid.

[0066] Step three: repeat the addition of 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride wet solid, followed by the heating and filtering steps, three times in total. The total amount of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added is 8 kg, with 2 kg added each time. After filtering, obtain 0.89 kg of 6-FDA wet solid, and transfer it to a double-cone drying oven. Under a negative pressure of -0.090 to -0.080 MPa, perform a staged temperature increase. The first stage is a slow increase to 60°C over 2 hours, and the second stage is an increase to 110°C over 2 hours. After drying for 6 hours at 110°C, remove the 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane and acetic acid to obtain 0.46 kg of 6-FDA crystals, with a washing yield of 92%.

[0067] Sample testing shows that the purity of the 6-FDA is 99.93% (as shown in Table 1 Figure 7 ), the yellowness is 0.95, the B value is 0.44 (as shown in Table 2 Figure 8 ), and acetic acid is not detected.

[0068] The above recovery: the 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane filtrate is combined and washed with water, and the lower layer solvent is obtained by removing the water, which is 6.8 kg. After drying and condensation, 0.6 kg of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane is recovered, for a total of 7.4 kg, with a loss of 7.5% of the washing solvent.

[0069] Example 3

[0070] Example 3 differs from Example 1 in that the amount of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added in step two of Example 3 is 8 kg, and the amount of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added in each washing in step three is 8 kg. The rest is the same as in Example 1.

[0071] Example 4

[0072] Example 4 differs from Example 1 in that in Example 4 step two the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4- (trifluoromethoxy)butane added is 2 kg and in step three the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4- (trifluoromethoxy)butane added per wash is 2 kg, otherwise it is the same as Example 1.

[0073] Example 5

[0074] Example 5 differs from Example 1 in that in Example 5 step two the mixture is warmed to 50°C, otherwise it is the same as Example 1.

[0075] Example 6

[0076] Example 6 differs from Example 1 in that in Example 6 step two the mixture is warmed to 40°C, otherwise it is the same as Example 1.

[0077] Example 7

[0078] Example 7 differs from Example 1 in that in Example 7 step three the first stage drying step is a slow ramp to 80°C over 2h and the drying is for 6h, otherwise it is the same as Example 1.

[0079] Example 8

[0080] Example 8 differs from Example 1 in that in Example 8 step three the first stage drying step is a slow ramp to 40°C over 2h and the drying is for 6h, otherwise it is the same as Example 1.

[0081] Example 9

[0082] Example 9 differs from Example 1 in that in Example 9 step three the first stage drying step is a slow ramp to 60°C over 2h and the drying is for 5h, otherwise it is the same as Example 1.

[0083] Example 10

[0084] Example 10 differs from Example 1 in that in Example 9 step three the second stage drying step is a ramp to 120°C over 2h and the drying is for 6h, otherwise it is the same as Example 1.

[0085] Example 11

[0086] Example 11 differs from Example 1 in that in Example 9 step three the second stage drying step is a ramp to 100°C over 2h and the drying is for 6h, otherwise it is the same as Example 1.

[0087] Example 12

[0088] Example 12 is the same as Example 1 except that in Example 9 Step 3, the second stage drying step is to heat to 110°C over 2h and then dry for 5h. The rest is the same as Example 1.

[0089] Example 13

[0090] Example 13 is the same as Example 1 except that in Example 13 Step 3, the drying procedure is different and is as follows:

[0091] Step 3: Repeat the addition of 4kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride wet solid, followed by the heating, washing and filtration steps, for two more times. A total of 12kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane is added over the three washings, with 4kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane being added each time. After the three repetitions, 1.98kg of 6-FDA wet solid is obtained and is then transferred to a double cone drying kettle and is subjected to a negative pressure. The pressure is maintained at -0.090 to -0.080 MPa and the temperature is increased slowly to 110°C over 4h. The 6-FDA is then dried for 10h to obtain 0.95kg of 6-FDA crystals, with a washing yield of 95%.

[0092] Example 14

[0093] Example 14 is the same as Example 1 except that in Example 13 Step 3, the drying procedure is different and is as follows:

[0094] Step 3: Repeat the addition of 4kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the 4,4'-(hexafluoroisopropylidene)diphthalic anhydride wet solid, followed by the heating, washing and filtration steps, for two more times. A total of 12kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane is added over the three washings, with 4kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane being added each time. After the three repetitions, 1.98kg of 6-FDA wet solid is obtained and is then transferred to a double cone drying kettle and is subjected to a negative pressure. The pressure is maintained at -0.090 to -0.080 MPa and the temperature is increased slowly to 60°C over 2h (not completely dried). The 6-FDA is then dried for 10h to obtain 0.96kg of 6-FDA crystals, with a washing yield of 96%.

[0095] Comparative Example 1

[0096] Comparative Example 1 is different from Example 13 in that Comparative Example 1 is not heated before washing, and is washed at room temperature, and the rest is the same as Example 13.

[0097] The 6-FDA purified in the above Examples 3-12 is tested for purity, yellowness, and B value, and the loss rate of fluorine ether solvent used in the purification process is also tested, and the test results are shown in Table 1.

[0098] Use The yellowness and B value of the product are tested by a VIS colorimeter.

[0099] The test method for acetic acid in the 6-FDA wet solid prepared in the above Examples 1-12 is as follows: The acetic acid content is determined by using an internal standard method. Acetone standard solutions with different acetic acid concentrations are sampled and tested on an Agilent liquid chromatograph to obtain the peak area data of the corresponding standard concentration of acetic acid; and a curve is drawn according to the obtained points to obtain a curve formula.

[0100] Table 1 Data table of 6-FDA obtained in each example and comparative example

[0101]

[0102]

[0103] From Table 1 and Figures 1-8 It can be seen that, in comparison between Example 13 and Comparative Example 1, the acetic acid residual amount of the wet solid 6-FDA after purification in Comparative Example 1 is much higher than that in Example 13, which shows that heating and washing is beneficial to the fluorine ether solvent to take away part of the acetic acid in the solid, and to reduce the acetic acid content of the final product. In comparison between Examples 13-14 and Example 1, the products obtained by directly drying at 110-120°C in the drying step have higher yellowness and B value, or the products obtained by only performing the first stage drying have high acetic acid content and low yellowness and B value after purification, which shows that, by performing the first stage drying and the second stage drying in the drying step, more acetic acid is removed, and the purity of the product after purification is higher.

[0104] Compared with Example 1, 5 and Example 6, in the heating and washing step, the temperature is lower than 50℃, the content of acetic acid after purification is high, and the yellowness of the product is high, which indicates that the temperature in the heating and washing step is controlled in the range of 50-80℃, the azeotropic boiling point of acetic acid and fluoroether solvent can be reached, and the acetic acid and fluoroether solvent can be distilled to remove part of the acetic acid. Compared with Example 1, 7, 9 and Example 8, in the first stage drying step, the drying temperature is lower than 50℃, the azeotropic boiling point of acetic acid and fluoroether solvent is not reached, and more acetic acid remains, the 6-FDA obtained by the second stage drying has low purity and higher yellowness. Compared with Example 1, 10 and Example 11, the second drying temperature is lower than 110-120℃, the 6-FDA solid after purification has acetic acid residue, and the purity is reduced, which indicates that the second stage drying temperature in the range of 110-120℃ is more conducive to the removal of acetic acid and the improvement of the purity of 6-FDA product. Compared with Example 1 and Example 12, the second stage drying time is too short, the 6-FDA solid after purification has acetic acid residue, and the purity is reduced, which indicates that the second stage drying time in the range of 6-12h is more conducive to the removal of acetic acid and the improvement of the purity of 6-FDA product.

[0105] Compared with Example 1 and Example 2, the mass ratio of fluoroether solvent to 4,4'-(hexafluoroisopropylidene) diphthalic anhydride wet solid is in the range of (2-4):1, increasing the washing times can reduce the content of acetic acid in the 6-FDA solid after purification, wherein the test data of Example 1 is shown in Table 1, Figures 1-4 , and the test data of Example 2 is shown in Table 2, Figures 5-8 Compared with Example 1 and Example 3-4, increasing the mass ratio of fluoroether solvent to 4,4'-(hexafluoroisopropylidene) diphthalic anhydride crude product is conducive to reducing the content of acetic acid in the 6-FDA solid after purification, improving the purity of 6-FDA product, reducing the yellowness value and B value.

[0106] The above only describes the preferred embodiments of the present application and is not used to limit the present application, any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, characterized by, The method comprises the following steps: obtaining a 4,4'- (hexafluoroisopropylidene) diphthalic anhydride crude product, adding a fluorinated ether solvent to obtain a mixture, and then sequentially performing heating washing, filtering, and drying to obtain a 4,4'- (hexafluoroisopropylidene) diphthalic anhydride finished product; The drying step comprises a first-stage drying, and the first-stage drying comprises the following steps: under a pressure of -0.09 to -0.08 MPa, heating to a temperature in a range of 50 to 80 DEG C, and performing the first-stage drying for 4 to 8 hours. The drying step further comprises a second-stage drying, and the second-stage drying comprises the following steps: After the first-stage drying is completed, the temperature is continuously increased to a range of 110 to 120 DEG C, and the second-stage drying is performed for 6 to 12 hours. The heating washing and filtering step is as follows: the mixture is washed at a temperature in a range of 50 to 80 DEG C for 0.5 to 2 hours, the temperature is then decreased to 20 to 30 DEG C after the washing is completed, and then filtering is performed to obtain a 4,4'- (hexafluoroisopropylidene) diphthalic anhydride wet solid; the fluorinated ether solvent is repeatedly added to the 4,4'- (hexafluoroisopropylidene) diphthalic anhydride wet solid, and then the heating washing and filtering steps are repeatedly performed for more than or equal to 3 times. The fluorinated ether solvent comprises one or more of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, 1,1,1,2,3,3-hexafluoro-2- (trifluoromethyl) -3-methoxypropane, 1,1,1,2,3,4,4,4-octafluoro-2-methoxy-3- (trifluoromethyl) butane, 1,1,1,2,3,4,4,5,5,5-decafluoro-3-methoxy-2- (trifluoromethyl) pentane, 1,1,1,2,3,4,4-heptafluoro-2- (trifluoromethyl) -3-methoxy-4- (trifluoromethoxy) butane, 1- (difluoro (trifluoromethoxy) methoxy) -1,1,2,2-tetrafluoro-2-methoxyethane, and 1,1,2,2-tetrafluoro-1-methoxy-2- (trifluoromethoxy) ethane.

2. The purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride according to claim 1, characterized in that, The mass ratio of the 4,4'- (hexafluoroisopropylidene) diphthalic anhydride wet solid to the fluorinated ether solvent is 1: (2 to 4).

3. The purification process of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride according to claim 1, characterized by, The mass ratio of the fluorinated ether solvent to the 4,4'- (hexafluoroisopropylidene) diphthalic anhydride crude product is (2 to 4) : 1.

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