Purification process of 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride

Abstract

In order to overcome the problems that in the prior art, during preparation of 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride, acetic acid is used as a solvent for recrystallization, direct purification is performed, and drying is performed, so that a 6-FDA solid is prone to yellowing and high in yellowness and B value, the invention provides a purification process of 4, 4'-(hexafluoroisopropenyl) diphthalic anhydride, and the purification process comprises the following steps: obtaining 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride; and adding a fluoroether solvent into the 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride crude product to obtain a mixture, and sequentially heating, washing, filtering and drying to obtain a 4, 4'-(hexafluoroisopropenyl) diphthalic anhydride finished product. According to the purification process of 4, 4 '-(hexafluoroisopropenyl) diphthalic anhydride provided by the invention, 6-FDA crystals with the purity of 99.8% or above, no acetic acid being detected and the yellowness B value being 1 or below are obtained through purification in manners of washing, azeotropy and direct drying.

Description

Technical Field

[0001] The invention belongs to the technical field of purification, and in particular relates to a purification process of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride. Background Art

[0002] Compared with traditional polyimide, fluorinated polyimide has advantages such as low dielectric constant, low refractive index, low moisture absorption, and high transparency, and has become a class of high-performance materials with great development prospects in many high-tech fields. In particular, since some hydrogen atoms of fluorinated polyimide are replaced by fluorine atoms, the vibration absorption of the CH bond is significantly reduced, which can greatly reduce the optical loss in the wavelength region of optical communication. Therefore, fluorinated polyimide is widely used in the optical field such as light guides, waveguides and liquid crystals. Among them, 4,4'-(hexafluoroisopropenyl) diphthalic anhydride (hereinafter referred to as 6-FDA) is the most important monomer of fluorinated polyimide. 4,4'-(Hexafluoroisopropylene) diphthalic anhydride (6-FDA) is a new type of polyimide monomer material. The polyimide using hexafluorodianhydride as a monomer has the following advantages in performance: 1) Low dielectric constant; the dielectric constant of ordinary polyimide is about 3.4, but after adding 6-FDA, its dielectric constant can be reduced to 2.5; the low dielectric constant brings about the reduction of signal delay and loss, which is of great value in electrical applications. 2) Transparency and controllable refractive index; because polyimide is slightly yellowish or brown, after adding 6-FDA, it can become transparent, and according to the amount of 6-FDA added, its refractive index can be controlled. These properties play a great role in the application of optical components. 3) Chemical and thermal stability; after the introduction of fluorine atoms, due to the strong negative charge of fluorine atoms, the chemical and thermal stability of polyimide will be improved, so that the product can work under special chemical or temperature conditions. 4) Lubricity: Due to the low polarity of fluorine atoms, fluorinated polyimide has very low surface free energy, smooth surface and low friction. 5) Fluorinated polyimide materials synthesized with 6-FDA have very good resistance to thermal oxidation, high temperature hot melting and radiation resistance, and are the preferred structural materials in the aerospace industry.

[0003] The existing purification of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride generally uses acetic acid as a solvent for recrystallization to precipitate a crystalline 6-FDA crude product. The obtained 6-FDA crude product contains residual acetic acid. After drying, the 6-FDA crude product is easy to cause the 6-FDA solid to turn yellow, with high yellowness and B value. The residual acetic acid leads to low purity of 6-FDA. In the subsequent polymerization reaction of making polyimide, it will lead to low polymerization degree; at the same time, the polyimide prepared in this way is yellow in color, which affects the transparency index of the polyimide. Summary of the invention

[0004] The present invention aims to solve the problem that the existing preparation of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride uses acetic acid as a solvent for recrystallization, and direct purification and drying easily lead to yellowing of 6-FDA solid, high yellowness and B value. The present application provides a purification process of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride.

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

[0006] A crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product is obtained, a fluoroether solvent is added to obtain a mixture, and then heating, washing, filtering and drying are performed in sequence to obtain a finished 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product.

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

[0008] Preferably, the drying step also includes a second stage of drying, and the second stage of drying includes the following steps: after the first stage of drying is completed, continue to heat up to a range of 110 to 120° C., and perform a second stage of drying, and the second stage of drying time is 6 to 12 hours.

[0009] Preferably, the heating, washing and filtering steps are: washing the mixture at a temperature range of 50°C to 80°C for 0.5 to 2h, cooling the mixture to 20 to 30°C after washing, and then filtering to obtain a wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride; repeatedly adding the fluoroether solvent to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, and then performing the heating, washing and filtering steps, and the number of repetitions is greater than or equal to 3 times.

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

[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, and 1,1,2,2-tetrafluoro-1-methoxy-2-trifluoromethoxyethane.

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

[0013] Beneficial effects:

[0014] Compared with the prior art, the present application provides a purification process for 4,4'-(hexafluoroisopropenyl) diphthalic anhydride, which uses a fluoroether solvent as a washing solvent, 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 first heating washing and filtering step can remove part of the acetic acid, and then the 6-FDA wet solid is dried by azeotropy to remove acetic acid and fluoroether solvent and trace acetic acid residues, and the 6-FDA crystals with a purity of more than 99.8% and no acetic acid detected are obtained by washing, azeotropy and direct drying, and the B value of yellowness reaches 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 easy recovery, low loss, non-flammable and non-explosive, and environmentally safe, making the entire purification process green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0016] Figure 2 This is a yellowness test data diagram of crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride in Example 1;

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

[0018] Figure 4 It is the 6-FDA-yellowness test data graph after purification in Example 1;

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

[0020] Figure 6 This is a yellowness test data diagram of crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride in Example 2;

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

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

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

[0024] Supplementary explanation: For the convenience of distinction and understanding, the crude 6-FDA or 4,4'-(hexafluoroisopropenyl) diphthalic anhydride crude product mentioned in this article is called the crude product before washing, and the wet solid 6-FDA or 4,4'-(hexafluoroisopropenyl) diphthalic anhydride wet solid is called the 6-FDA still containing impurities after washing with hydrofluoroether.

[0025] The present application provides a purification process for 4,4'-(hexafluoroisopropenyl) diphthalic anhydride, comprising the following steps:

[0026] A crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product is obtained, a fluoroether solvent is added to obtain a mixture, and then heating, washing, filtering and drying are performed in sequence to obtain a finished 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product.

[0027] The obtained crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride is recrystallized using acetic acid as a solvent to precipitate crystals to obtain a crude 6-FDA (4,4'-(hexafluoroisopropenyl) diphthalic anhydride). The steps for obtaining the crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride include but are not limited to the following steps: preparing 4,4'-(hexafluoroisopropenyl) diphthalic anhydride by an existing technical method, mixing and stirring with acetic acid, heating to 90-120°C, cooling to room temperature (20°C-35°C) after dissolution, precipitating 6-FDA crystals, and then filtering to obtain the crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride.

[0028] Acetic acid remains in the 6-FDA solid obtained by recrystallization using acetic acid as a solvent. After drying the wet 6-FDA solid, the 6-FDA solid is likely to turn yellow, with a high yellowness and B value. To address this problem, the inventors have found through extensive research that fluoroether solvents are incompatible with 6-FDA, and acetic acid is soluble in both 6-FDA and fluoroether solvents. A large amount of fluoroether solvent is added to the crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride, and the solvents are heated, washed, and filtered in sequence to remove the dissolved 6-FDA solid. Part of the acetic acid in the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride is filtered to obtain a wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride containing a small amount of acetic acid and a fluoroether solvent. The wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride containing a small amount of acetic acid and a fluoroether solvent is then dried using acetic acid and a fluoroether solvent to azeotropically remove the remaining small amount of acetic acid and the fluoroether solvent as well as the remaining acetic acid in the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride.

[0029] Compared with the prior art, the present application provides a purification process for 4,4'-(hexafluoroisopropenyl) diphthalic anhydride, which uses a fluoroether solvent as a washing solvent, 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 first heating washing and filtering step can remove part of the acetic acid, and then the 6-FDA wet solid is dried by azeotropy to remove acetic acid and fluoroether solvent and trace acetic acid residues, and the 6-FDA crystals with a purity of more than 99.8% and no acetic acid detected are obtained by washing, azeotropy and direct drying, and the B value of yellowness reaches 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 easy recovery, low loss, non-flammable and non-explosive, and environmentally safe, making the entire purification process green and environmentally friendly.

[0030] In some embodiments, the drying step includes first stage drying, and the first stage drying includes the following steps: under a pressure of -0.09 to -0.08 MPa, the temperature is raised to 50 to 80°C, and the first stage drying time is 4 to 8 hours.

[0031] Specifically, the first stage of drying is mainly to remove the acetic acid and fluoroether solvents in the 6-FDA wet solid by utilizing the azeotropic characteristics of acetic acid and fluoroether. The drying temperature in the first stage of drying is 50-80°C. Within this temperature range, the azeotropic boiling point of acetic acid and fluoroether solvent is reached, and the acetic acid and fluoroether solvent are distilled to remove the acetic acid and fluoroether solvents in the 6-FDA wet solid. 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 solvents 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 of drying step is within the range of 4-8h. Within this drying time range, it is beneficial to remove the acetic acid and fluoroether solvents in the 6-FDA wet solid; if the drying time is too short, there will be residues of acetic acid and fluoroether solvent, reducing the purity of the 6-FDA solid; if the drying time is too long, that is, the heating time is too long, the purification process cost is increased, and the yellowness of the product will increase, the yellowness of the product will increase, and the purity will decrease.

[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 within the range of 50°C to 80°C.

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

[0034] In some embodiments, the drying step also includes a second stage of drying, and the second stage of drying includes the following steps: after the first stage of drying is completed, the temperature continues to rise to a range of 110 to 120°C, and the second stage of drying is performed, and the second stage of drying time is 6 to 12 hours.

[0035] Specifically, after the 6-FDA wet solid undergoes the first stage drying step, the second stage drying step is mainly used to remove trace amounts of acetic acid residues 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, within which the acetic acid can be evaporated to achieve the purpose of removing trace amounts of acetic acid; controlling the drying time within the range of 6-12h is conducive to removing acetic acid as much as possible and reducing 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, acetic acid cannot be effectively removed, and the obtained 6-FDA solid containing acetic acid is obtained; if the drying temperature is higher than 120°C, or the drying time is higher than 12h, the purification process cost increases.

[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 within the range of 110°C to 120°C.

[0037] It should be noted that, in order to increase the heating rate, the present application limits the temperature in the second stage drying step to a range of 110 to 120° C., and the heating time is controlled within 2 hours.

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

[0039] The mixture is heated to a temperature range of 50°C to 80°C, and the azeotropic properties of acetic acid and fluoroether solvent are also utilized to remove part of the acetic acid in the wet solid of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride.

[0040] Specifically, the heating temperature can be 50 ℃, 55 ℃, 58 ℃, 60 ℃, 65 ℃, 67 ℃, 70 ℃, 74 ℃, 75 ℃, 78 ℃, 80 ℃, etc., as long as it is heated to 50 ℃ ~ 80 ℃ temperature range. It should be noted that in the heating and washing step, it is stirred while heating, and a certain temperature is maintained for a period of time, and the stirring is more uniform, so that the acetic acid that can be taken away by the fluoroether solvent can be stripped from 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 the operation is repeated several times, the acetic acid removed is also less, and the subsequent direct drying has a large amount of acetic acid residue, and the 6-FDA crystal is still high in yellowness. Combining heating, washing and filtering can remove most of the acetic acid.

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

[0042] After washing, the temperature is lowered to 20-30°C and filtered. Acetic acid is also soluble in the fluoroether solvent. Filtration can also remove part of the acetic acid dissolved in the fluoroether solvent, thereby achieving the purpose of removing part of the acetic acid in the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride. Repeatedly add the fluoroether solvent to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, and then perform 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 crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride.

[0043] Specifically, the mixture is cleaned within a temperature range of 50°C to 80°C. The 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 mixture is heated to a temperature range of 50°C to 80°C.

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

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

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

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

[0048] In some embodiments, a fluoroether solvent is added to the wet solid of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride, followed by heating, washing and filtering steps, which are repeated 3 times or more to 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, and 1,1,2,2-tetrafluoro-1-methoxy-2-trifluoromethoxyethane.

[0050] It is understandable that the above-mentioned fluoroether solvents include types that are not compatible with 6-FDA, do not react with acetic acid, and are compatible with acetic acid.

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

[0052] The present application limits the mass ratio of the fluoroether solvent to the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride to within the range of (2 to 4):1. The mass of the fluoroether solvent is much greater than the mass of the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride. The high content of the fluoroether solvent is beneficial for removing acetic acid from the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride.

[0053] The specific embodiments of the present invention will be further explained below through examples, but it does not mean that the protection scope of the present invention is limited to the scope described in the examples.

[0054] Example 1

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

[0056] Step 1, obtain the crude product of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride (6-FDA):

[0057] 1 kg 6-FDA and 2 kg acetic acid were mixed and stirred, heated to 100 ° C to dissolve, and then cooled to 30 ° C to completely precipitate 6-FDA crystals, and filtered to obtain 2 kg 6-FDA crude product; the 6-FDA crude product was sampled and tested for acetic acid residue of 40.23%, and the content was tested after drying, and the content was 99.35% (such as Figure 1 ), yellowness is 2.27, B value is 1.37 (such as Figure 2 ).

[0058] Step 2: Take 2 kg of the crude 6-FDA obtained in step 1 and 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, mix and stir to obtain a mixture, heat the mixture to 70°C, and wash it at 70°C for 2 hours. After washing, cool it to 30°C, filter and remove the filtrate to obtain 2 kg of 6-FDA wet solid.

[0059] Step 3: Repeat each time adding 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, then perform heating, washing and filtering steps, repeat the above steps twice, and add a total of 12 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane for three washings, and the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added each time is 4 kg. After repeating three times, 1.98 kg of 6-FDA wet solid was obtained by filtration, and then transferred to a double-cone drying kettle and negative pressure was drawn. The pressure was -0.090 to -0.080 MPa, and the temperature was increased in stages. The first stage drying step was to slowly increase the temperature to 60 ° C within 2 hours and dry for 6 hours; the second stage drying step was to increase the temperature to 110 ° C within 2 hours and then dry for 6 hours to remove 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane and acetic acid to obtain 0.96 kg of 6-FDA crystals with a washing yield of 96%.

[0060] Sampling test, 6-FDA content 99.81% (such as Figure 3 ), yellowness is 1.08, B value is 0.6 (such as Figure 4 ) and acetic acid were not detected.

[0061] The above recovery: 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane filtrate, combined water washing, separation and dewatering to obtain 10.6 kg of lower layer solvent, drying and condensation recovery to obtain 1 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane, a total of 11.6 kg, washing solvent loss of 3.3%.

[0062] Embodiment 2:

[0063] Step 1, obtain the crude product of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride (6-FDA):

[0064] 0.5 kg 6-FDA and 1 kg acetic acid were mixed and stirred, heated to 100 ° C to dissolve, then cooled to 30 ° C to completely precipitate 6-FDA crystals, and filtered to obtain 1 kg 6-FDA crude product. The acetic acid residue of the crude 6-FDA sample was 38.21%, and the purity was tested after drying, and the content was 99.26% (such as Figure 5 ), yellowness is 1.91, B value is 1.15 (such as Figure 6 ).

[0065] Step 2: Take 1 kg of the crude 6-FDA obtained in step 1 and 2 kg of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, mix and stir to obtain a mixture, heat the mixture to 70°C, and wash it at 70°C for 2 hours. After washing, cool it to 30°C, filter and remove the filtrate to obtain 1 kg of 6-FDA wet solid.

[0066] Step 3: Repeat each time adding 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, and then perform heating, washing and filtering steps. Repeat the above steps three times. A total of 8 kg of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane is added for four washings. The mass of 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane added each time is 2 kg. After filtration, 0.89 kg of 6-FDA wet solid was obtained, which was transferred to a double-cone drying kettle and negative pressure was drawn. The pressure was -0.090 to -0.080 MPa, and the temperature was increased in stages. The first stage drying step was to slowly increase the temperature to 60°C within 2 hours and dry for 6 hours. The second stage drying step was to increase the temperature to 110°C within 2 hours and then dry for 6 hours. 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane and acetic acid were removed by drying to obtain 0.46 kg of 6-FDA crystals with a washing yield of 92%.

[0067] Sampling test, 6-FDA purity content 99.93% (such as Figure 7 ), yellowness is 0.95, B value is 0.44 (such as Figure 8 ) and acetic acid were not detected.

[0068] The above recovery: 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane filtrate, combined water washing, separation and dehydration to obtain 6.8 kg of lower layer solvent, drying and condensation recovery to obtain 1,1,1,2,2,3,3-heptafluoro-3-methoxypropane, 0.6 kg, a total of 7.4 kg, washing solvent loss 7.5%.

[0069] Example 3

[0070] Compared with Example 1, Example 3 differs in that the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added in Step 2 of Example 3 is different, which is 8 kg, and the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added for each washing in Step 3 is 8 kg, and the rest is the same as Example 1.

[0071] Example 4

[0072] Compared with Example 1, Example 4 differs in that the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added in step 2 of Example 4 is different, which is 2 kg, and the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added for each washing in step 3 is 2 kg, and the rest is the same as Example 1.

[0073] Example 5

[0074] Compared with Example 1, Example 5 is different in that in step 2 of Example 5, the mixture is heated to 50° C., and the rest is the same as Example 1.

[0075] Example 6

[0076] Compared with Example 1, Example 6 differs in that in step 2 of Example 6, the mixture is heated to 40° C., and the rest is the same as Example 1.

[0077] Example 7

[0078] Compared with Example 1, Example 7 differs in that in step 3 of Example 7, the first stage drying step is to slowly heat up to 80° C. within 2 hours and dry for 6 hours, and the rest is the same as Example 1.

[0079] Example 8

[0080] Compared with Example 1, Example 8 differs in that in step 3 of Example 8, the first stage drying step is to slowly heat up to 40° C. within 2 hours and dry for 6 hours, and the rest is the same as Example 1.

[0081] Example 9

[0082] Compared with Example 1, Example 9 differs in that in step 3 of Example 9, the first stage drying step is to slowly heat up to 60° C. within 2 hours and dry for 5 hours, and the rest is the same as Example 1.

[0083] Example 10

[0084] Compared with Example 1, Example 10 differs in that in step 3 of Example 9, the second stage drying step is to heat up to 120° C. within 2 hours and then dry for 6 hours, and the rest is the same as Example 1.

[0085] Embodiment 11

[0086] Compared with Example 1, Example 11 differs in that in step 3 of Example 9, the second stage drying step is to heat up to 100° C. within 2 hours and then dry for 6 hours, and the rest is the same as Example 1.

[0087] Example 12

[0088] Compared with Example 1, Example 12 differs in that in step 3 of Example 9, the second stage drying step is to heat up to 110° C. within 2 hours and then dry for 5 hours, and the rest is the same as Example 1.

[0089] Example 13

[0090] The difference between Example 13 and Example 1 is that in step 3 of Example 13, the drying operation is different, and the specific operation is as follows:

[0091] Step 3: Repeat each time adding 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, then perform heating, washing and filtering steps, repeat the above steps twice, and add a total of 12 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane for three washings, and the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added each time is 4 kg. After repeating three times, 1.98 kg of 6-FDA wet solid was filtered and then transferred to a double-cone drying kettle under negative pressure. The temperature was increased at -0.090 to -0.080 MPa and slowly increased to 110°C within 4 hours. The solid was dried for 10 hours to obtain 0.95 kg of 6-FDA crystals with a washing yield of 95%.

[0092] Embodiment 14

[0093] The difference between Example 14 and Example 1 is that in step 3 of Example 13, the drying operation is different, and the specific operation is as follows:

[0094] Step 3: Repeat each time adding 4 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, then perform heating, washing and filtering steps, repeat the above steps twice, and add a total of 12 kg of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane for three washings, and the mass of 1,1,1,2,3,4,4-heptafluoro-2-(trifluoromethyl)-3-methoxy-4-(trifluoromethoxy)butane added each time is 4 kg. After repeating the process three times, 1.98 kg of 6-FDA wet solid was obtained by filtration, which was then transferred to a double-cone drying kettle and subjected to negative pressure. The temperature was raised at a pressure of -0.090 to -0.080 MPa and the temperature was slowly raised to 60°C within 2 h (not completely dried). The solid was dried for 10 h to obtain 0.96 kg of 6-FDA crystals with a washing yield of 96%.

[0095] Comparative Example 1

[0096] The difference between Comparative Example 1 and Example 13 is 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 was tested for purity, yellowness and B value, and the washing loss rate of the fluoroether solvent used in the purification process was also tested. The test results are shown in Table 1.

[0098] use VIS colorimeter tests the yellowness and B value of the product.

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

[0100] Table 1 Data table of 6-FDA obtained in various embodiments and comparative examples

[0101]

[0102]

[0103] Through Table 1 and Figure 1-8 It can be seen that, compared with Example 13, Comparative Example 1 was not heated during washing, and the residual amount of wet solid 6-FDA acetic acid after purification was much higher than that of Example 13, indicating that heating and washing are conducive to the fluoroether solvent taking away part of the acetic acid in the solid, thereby reducing the acetic acid content of the final product. Compared with Example 1, Examples 13-14 were directly dried at 110-120°C in the drying step, and the yellowness and B value of the obtained product were higher, or only the first stage of drying was performed, and the acetic acid content of the purified product was high, and the yellowness and B value were low, indicating that the first stage of drying and the second stage of drying in the drying step removed more acetic acid, and the purity of the purified product was higher.

[0104] In contrast to Example 6, in the heating and washing step, the temperature is lower than 50°C, the content of acetic acid after purification is high, and the yellowness of the product is high, indicating that the temperature of the heating and washing step is controlled within the range of 50 to 80°C, and the azeotropic boiling point of acetic acid and the fluoroether solvent can be reached. The acetic acid and the fluoroether solvent are distilled to remove part of the acetic acid. In contrast to Example 8, in the first stage drying step, the drying temperature is lower than 50°C, and the azeotropic boiling point of acetic acid and the fluoroether solvent is not reached. There will be more acetic acid remaining, and the 6-FDA obtained by continuing the second stage drying will have low purity and higher yellowness. In contrast to Example 1 and Example 10, the second drying temperature is lower than the range of 110 to 120°C, and there is acetic acid remaining in the 6-FDA solid after purification, and the purity is reduced, indicating that the second stage drying temperature is within the range of 110 to 120°C, which is more conducive to the removal of acetic acid and improves the purity of the 6-FDA product. Compared with Example 1 and Example 12, the drying time of the second stage drying is too short, acetic acid remains in the 6-FDA solid after purification, and the purity is reduced, indicating that the drying time of the second stage drying is within the range of 6 to 12 hours, which is more conducive to the removal of acetic acid and improves the purity of the 6-FDA product.

[0105] Comparing Example 1 with Example 2, the mass ratio of the fluoroether solvent to the wet solid of 4,4'-(hexafluoroisopropenyl) diphthalic anhydride is in the range of (2 to 4):1. Increasing the number of washings can reduce the acetic acid content in the purified 6-FDA solid. The test data of Example 1 is shown in Figure 1-4 , the test data of Example 2 is shown in Figure 5-8 Compared with Examples 3-4, increasing the mass ratio of the fluoroether solvent to the crude 4,4'-(hexafluoroisopropenyl) diphthalic anhydride is beneficial to reducing the acetic acid content in the purified 6-FDA solid, improving the purity of the 6-FDA product, and reducing the yellowness value and B value.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A purification process for 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, characterized in that: The following steps are involved: A crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product is obtained, a fluoroether solvent is added to obtain a mixture, and then heating, washing, filtering and drying are performed in sequence to obtain a finished 4,4'-(hexafluoroisopropenyl)diphthalic anhydride product.

2. The purification process of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride according to claim 1, characterized in that: The drying step includes first-stage drying, which includes the following steps: under a pressure of -0.09 to -0.08 MPa, the temperature is raised to 50 to 80° C., and the first-stage drying is performed for 4 to 8 hours.

3. The purification process of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride according to claim 2, characterized in that: The drying step further includes a second stage of drying, and the second stage of drying includes the following steps: After the first stage of drying is completed, the temperature continues to rise to 110-120°C for the second stage of drying. The second stage of drying time is 6-12 hours.

4. The purification process of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride according to claim 1, characterized in that: The heating, washing and filtering steps are as follows: washing the mixture at a temperature range of 50° C. to 80° C. for 0.5 to 2 hours, cooling the mixture to 20 to 30° C. after washing, and filtering to obtain a wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride; repeatedly adding the fluoroether solvent to the wet solid of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride, and then performing the heating, washing and filtering steps, the number of repetitions being greater than or equal to 3 times.

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

6. The purification process of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride according to claim 1, characterized in that: 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, and 1,1,2,2-tetrafluoro-1-methoxy-2-trifluoromethoxyethane.

7. The purification process of 4,4'-(hexafluoroisopropenyl)diphthalic anhydride according to claim 1, characterized in that: The mass ratio of the fluoroether solvent to the crude 4,4'-(hexafluoroisopropenyl)diphthalic anhydride is (2-4):1.

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