Purification method of pyromellitic dianhydride and pyromellitic dianhydride

Abstract

The invention discloses a purification method of pyromellitic dianhydride and pyromellitic dianhydride, the purity of the pyromellitic dianhydride is greater than or equal to 99.99%, the free acid value is lower than 1wt%, preferably lower than 0.5 wt%, more preferably 0.01-0.2%, the particle size D10 of the pyromellitic dianhydride is 100-140 [mu] m, the particle size D90 of the pyromellitic dianhydride is 140-150 [mu] m, and the particle size D90 of the pyromellitic dianhydride is 0.1-0.2%. The method comprises the following steps: (1) filtering and concentrating a mixed material containing a crude pyromellitic dianhydride product to obtain a crude pyromellitic dianhydride concentrated solution; the solvent in the mixed material comprises dioxane and acetone; (2) carrying out first cooling crystallization treatment and second cooling crystallization treatment on the coarse pyromellitic dianhydride concentrated solution to obtain pyromellitic dianhydride crystals; washing the crystal in an inert gas atmosphere, and finally drying; the cooling rate of the first cooling crystallization treatment is higher than that of the second cooling crystallization treatment. The pyromellitic dianhydride product obtained by the invention has the characteristics of high purity (as high as 99.99 wt%), low free acid value (as low as 0.04 wt%), small and uniform particle size of pyromellitic dianhydride crystals and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to a method for purifying pyromellitic dianhydride and pyromellitic dianhydride itself. Background Technology

[0002] Pyromellitic dianhydride (C10H2O6, PMDA) is a high-value-added chemical intermediate. Its two symmetrical anhydride groups can undergo condensation polymerization with diamine compounds, making it an important monomer for the synthesis of polyimides. Polyimides possess excellent mechanical and dielectric properties and are widely used in high-tech industries such as aerospace and electronics. With the increasing development of downstream industrial chains, the demand for dianhydride as a major raw material is shifting from electrical-grade products to high-purity electronic-grade products.

[0003] Currently, the main method for producing homohydric anhydride is the gas-phase oxidation process of mesitylene. This reaction process is a complex multiphase selective oxidation process, resulting in the presence of anhydrides (trimethylammonium trimellitic anhydride, phthalic anhydride), aldehydes, and acids (pyromellitic acid) as byproducts in the crude product, which is difficult to meet the requirements of subsequent polymerization-grade products. Therefore, it is necessary to develop an effective method for purifying the crude homohydric anhydride.

[0004] Existing research (Modern Chemical Industry, 1994(01):31-32 Zhang Wei et al., Petrochemical Industry (07):505-510 [2024-01-10] Wang Yushan et al.) shows that the main purification methods for crude anhydride products include sublimation condensation method, generated gas capture method and solvent method.

[0005] Sublimation condensation is an early industrial refining method, including vacuum sublimation and hot gas flow sublimation. Vacuum sublimation involves condensing all the reaction products and then sublimating them under vacuum at 300°C. The sublimated gas is then condensed and crystallized to obtain the refined homogeneous anhydride. The disadvantages of this method are the complex condensation-sublimation-condensation process, high equipment costs, and the ease with which the product decomposes during sublimation.

[0006] The hot gas entrainment method involves directly and continuously adding the crude product into a hot, inert gas stream to cause it to sublimate, followed by deposition and collection to obtain high-purity homogeneous anhydride. CN211635279U argues that this method requires the use of a large amount of gas for entrainment, and the heat exchange efficiency of the gas heating and cooling equipment must be strictly controlled, especially the cooling efficiency of the cooling equipment. If the cooling efficiency is too low, the fine particles of the product that have been deposited cannot be captured quickly, ultimately reducing the purity of the homogeneous anhydride after deposition.

[0007] The generated gas trapping method utilizes the difference in vapor pressure between homogenate and other byproducts. By controlling the temperature gradient of a multi-stage trap and using traps with special structures, selective trapping can be achieved. The drawback of this method is that it requires the selection of a high-performance catalyst; otherwise, it is difficult to obtain high-yield and high-purity products.

[0008] Solvent-based methods include washing, recrystallization, and complexation separation. Washing removes impurities and byproducts using solvents. CN113583016A proposes a purification method using methyl tert-butyl ether (MTBE) as a solvent, utilizing the principle that homohydric anhydride has extremely low solubility in MTBE while other impurities (homogeneous acid, meta-acid, and meta-anhydride) have higher solubility. The disadvantages of this method are that the solvent is difficult to recover after washing, energy consumption is high, product quality is lost, and the purified product is prone to solvent residue.

[0009] Recrystallization is a purification method that involves dissolving crude anhydride in a solvent and then recrystallizing it. CN100475820C proposes a solvent recrystallization purification method. The main steps include mixing and reacting crude anhydride, a dehydrating agent, and a decolorizing agent, followed by filtration. The filtrate is then crystallized in a crystallization vessel, filtered, and dried to obtain the purified product. The advantages of this method are its simple process flow, low energy consumption, high yield of purified product, and the ability to recycle the mother liquor, making it economically viable. Solvent recrystallization is currently a widely used purification method in industry, but it still faces technical challenges such as low purity of the purified product, high free acid value, and uneven particle size, which urgently need to be addressed.

[0010] As can be seen, solvent recrystallization has many advantages. Therefore, developing a method for purifying homogenate with high product purity, low free acid value, and uniform particle size is of great significance. Summary of the Invention

[0011] To address the shortcomings of existing technologies, one of the technical problems this invention aims to solve is to provide a purification method for pyromellitic dianhydride. The dianhydride purified by this method has the characteristics of high purity, low free acid value, and small and uniform crystal particle size.

[0012] To achieve the above objectives, the present invention provides a method for purifying pyromellitic dianhydride, the method comprising:

[0013] (1) The mixture containing crude pyromellitic dianhydride was filtered and concentrated to obtain a crude pyromellitic dianhydride concentrated solution;

[0014] The solvents in the mixture include dioxane and acetone;

[0015] (2) The crude homogeneous anhydride solution is subjected to a first cooling crystallization treatment and a second cooling crystallization treatment to obtain homogeneous anhydride crystals; then the crystals are washed in an inert gas atmosphere and then dried.

[0016] The cooling rate of the first cooling crystallization process is higher than that of the second cooling crystallization process;

[0017] The second cooling crystallization process is carried out in the presence of homogeneous anhydride seed crystals.

[0018] The second aspect of the present invention provides a pyromellitic dianhydride, wherein the pyromellitic dianhydride has a purity ≥99.99%, a free acid value of less than 1 wt%, preferably less than 0.5 wt%, more preferably 0.01-0.2%, and a particle size D10 of 100-140 μm and a particle size D90 of 140-150 μm.

[0019] The crude anhydride is purified using the above-mentioned technical solution. The resulting homogeneous anhydride product has the characteristics of high purity (up to 99.99 wt%), low free acid value (down to 0.04 wt%), and small and uniform crystal size, and has good application prospects. Attached Figure Description

[0020] Figure 1 This is the liquid chromatogram of crude pyromellitic dianhydride;

[0021] Figure 2 This is the liquid chromatogram of the homogenate prepared in Example 1-1. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0024] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0025] When this specification uses the prefixes "known to those skilled in the art," "prior art," or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those conventionally used in the art at the time the invention was proposed, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0026] It should be noted that the two or more aspects (or embodiments) disclosed in the context of this specification can be arbitrarily combined with each other, and the resulting technical solutions (such as methods or systems) are part of the original disclosure of this specification and also fall within the protection scope of this invention.

[0027] This invention provides a method for purifying pyromellitic dianhydride, the method comprising:

[0028] (1) The mixture containing crude pyromellitic dianhydride was filtered and concentrated to obtain a crude pyromellitic dianhydride concentrated solution;

[0029] The solvents in the mixture include dioxane and acetone;

[0030] (2) The crude homogeneous anhydride solution is subjected to a first cooling crystallization treatment and a second cooling crystallization treatment to obtain homogeneous anhydride crystals; then the crystals are washed in an inert gas atmosphere and finally dried.

[0031] The cooling rate of the first cooling crystallization process is higher than that of the second cooling crystallization process;

[0032] The second cooling crystallization process is carried out in the presence of homogeneous anhydride seed crystals.

[0033] In this invention, the mixture containing crude pyromellitic dianhydride is mainly obtained by dissolving crude pyromellitic dianhydride in a solvent. To ensure uniform mixing, appropriate heating and stirring are generally used to achieve thorough mixing.

[0034] In this invention, by using a mixed solvent of dioxane and acetone to dissolve the homogenizing anhydride and adopting a two-step crystallization method during the crystallization process, it is possible to obtain high-purity homogenizing anhydride with low free acid value while controlling the resulting crystal particle size to be small and uniform, which has good application prospects.

[0035] In this invention, the mixture containing crude pyromellitic dianhydride is a mixed solution of crude anhydride and solvent. Using the aforementioned embodiments, the resulting pyromellitic anhydride product exhibits high purity, low free acid value, and small, uniform crystal particle size, demonstrating promising application prospects.

[0036] In this invention, the filtration operation is not specifically defined. The following is an illustrative description, but it does not limit the scope of the invention. In some embodiments of the invention, the filtration method is, for example, to remove insoluble impurities by fully dissolving the crude anhydride in the solvent and then using a hot filtration funnel under constant temperature conditions.

[0037] In this invention, the concentration operation is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. The concentration operation is, for example, by heating and concentrating the mixture containing crude pyromellitic dianhydride in an evaporating kettle.

[0038] In this invention, the crude homogeneous anhydride concentrate solution is a solution obtained by filtering and concentrating a mixture containing crude pyromellitic dianhydride.

[0039] In this invention, the solvent for the mixture includes dioxane and acetone. In some preferred embodiments of this invention, the solvent for the mixture is dioxane and acetone. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0040] In this invention, the specific operation method of the first cooling crystallization treatment is not particularly limited. The following is an illustrative description, but it does not limit the scope of this invention. The specific operation method of the first cooling crystallization treatment is to rapidly cool the concentrated crude homogeneous anhydride solution obtained by concentration to carry out preliminary crystallization. Using the aforementioned embodiments, the homogeneous anhydride product obtained has the characteristics of high purity, low free acid value, and small and uniform homogeneous anhydride crystal particle size, and has good application prospects.

[0041] In this invention, the specific operation method of the second cooling crystallization treatment is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. The specific operation method of the second cooling crystallization treatment is to continue temperature-controlled crystallization of the liquid obtained after the first cooling crystallization. Using the aforementioned embodiments, the obtained homohydric anhydride product has the characteristics of high purity, low free acid value, and small and uniform homohydric anhydride crystal particle size, and has good application prospects.

[0042] In this invention, the washing liquid can be selected from a wide range of options. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the washing liquid can be one or a mixture of dioxane, acetone and anhydrous ethanol. In the embodiments of the invention, acetone is used for washing.

[0043] In this invention, the cooling rate of the first cooling crystallization treatment is higher than that of the second cooling crystallization treatment. Using the aforementioned embodiments, the resulting homogeneous anhydride product exhibits high purity, low free acid value, and small, uniform crystal particle size, demonstrating promising application prospects.

[0044] In this invention, the seed crystals are not specifically limited. Any suitable seed crystal can be used as a raw material as long as it can achieve the purpose of this invention. According to a preferred embodiment of this invention, the seed crystal is a pyromellitic dianhydride seed crystal with a purity of 99%. Using the aforementioned embodiments, the resulting pyromellitic dianhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0045] In this invention, the mass ratio of dioxane to acetone can be selected within a wide range. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of dioxane to acetone is 0.05-0.9, preferably 0.05-0.5, and more preferably 0.2-0.3. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0046] In this invention, the mass ratio of solvent to crude anhydride in the mixture can be selected within a wide range. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of solvent to crude anhydride in the mixture is 12-18, for example, 13, 14, 15, 16, 17, etc. Using the aforementioned embodiments, the resulting homogenized anhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0047] In this invention, the difference between the cooling rate of the first cooling crystallization treatment and the cooling rate of the second cooling crystallization treatment can be selected within a wide range. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the difference between the cooling rate of the first cooling crystallization treatment and the cooling rate of the second cooling crystallization treatment is 1.5-19 °C / min, preferably 3.5-17 °C / min, and more preferably 6.5-9 °C / min. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0048] In this invention, the cooling rate of the first cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first cooling crystallization treatment include: a first cooling rate of 3-20°C / min, preferably 5-18°C / min, and more preferably 8-10°C / min. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0049] In this invention, the cooling rate of the second cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second cooling crystallization treatment include: a cooling rate of 1-1.5℃ / min, for example, 1.1℃ / min, 1.2℃ / min, 1.3℃ / min, 1.4℃ / min, 1.5℃ / min, etc. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0050] In this invention, the starting temperature of the first cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the starting temperature of the first cooling crystallization treatment is 55-60°C. Using the aforementioned embodiment, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform homogenate crystal particle size, and has good application prospects.

[0051] In this invention, the starting temperature of the second cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the starting temperature of the second cooling crystallization treatment is 45-50°C. Using the aforementioned embodiment, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform homogenate crystal particle size, and has good application prospects.

[0052] In this invention, the filtration temperature can be selected over a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the filtration temperature is 40-50°C. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0053] In this invention, the concentration temperature can be selected over a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the reflux temperature is set to 55-60°C during the concentration operation. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0054] In this invention, the mass ratio of solvent to crude pyromellitic dianhydride in the crude homogeneous anhydride concentrated solution can be selected within a wide range. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of solvent to crude homogeneous anhydride in the crude homogeneous anhydride concentrated solution is 5-7, for example, 5.2, 5.5, 5.8, 6.0, 6.2, 6.5, 6.8, etc. Using the aforementioned embodiments, the homogeneous anhydride product obtained has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0055] In this invention, the endpoint temperature of the first cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first cooling crystallization treatment include: the endpoint temperature of the first cooling crystallization is 45-50°C. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0056] In this invention, the crystallization time of the first cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the first cooling crystallization treatment include: the crystallization time of the first cooling crystallization treatment is 1-1.5 min. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0057] In this invention, the endpoint temperature of the second cooling crystallization treatment has a wide selectable range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second cooling crystallization treatment include: the endpoint temperature of the second cooling crystallization treatment is 0-5℃. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0058] In this invention, the crystallization time of the second cooling crystallization treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the second cooling crystallization treatment include: the crystallization time of the second cooling crystallization treatment is 1-3 hours. Using the aforementioned embodiments, the resulting homogeneous anhydride product has the characteristics of high purity, low free acid value, and small and uniform anhydride crystal particle size, and has good application prospects.

[0059] In this invention, the amount of seed crystals added is not particularly limited. As long as the purpose of this invention is achieved, the amount of seed crystals added can be freely selected. According to a preferred embodiment of this invention, the amount of seed crystals is 0.01-5 wt% of the mass of crude pyromellitic dianhydride, preferably 0.05-2 wt%, and more preferably 0.1-1 wt%. Using the aforementioned embodiments, the resulting pyromellitic dianhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0060] In this invention, the particle size of the seed crystals is not particularly limited. As long as the objective of this invention is achieved, the particle size of the seed crystals can be freely selected. According to a preferred embodiment of this invention, the particle size of the seed crystals is 50-250 μm, preferably 80-150 μm, and more preferably 80-100 μm. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0061] In this invention, the seed crystals are not specifically limited; any suitable seed crystal can be used as a raw material as long as it achieves the purpose of this invention. According to a preferred embodiment of this invention, the seed crystal is a pyromellitic dianhydride seed crystal with a purity of 99-99.99%. Using the aforementioned embodiments, the resulting pyromellitic dianhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0062] In this invention, the source of the crude anhydride (crude pyromellitic dianhydride) can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the crude anhydride is crude pyromellitic dianhydride obtained by gas-phase oxidation of pyromellitic dianhydride. Using the aforementioned embodiments, the obtained pyromellitic anhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0063] In this invention, the content of homogeneous anhydride in the crude anhydride can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the content of pyromellitic dianhydride in the crude anhydride is 90-99 wt%. Using the aforementioned embodiments, the homogeneous anhydride product obtained has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0064] In this invention, the range of inert gases that can be selected is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the inert gas is selected from nitrogen and / or argon. Using the aforementioned embodiments, the resulting homogenate product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0065] In this invention, there are no special limitations on the drying process. Any drying method in the prior art can be selected as long as it achieves the purpose of this invention. According to one embodiment of this invention, the drying process is carried out in a vacuum oven.

[0066] In this invention, the vacuum degree of the drying process can be selected within a wide range, and commonly used drying environments are applicable to this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the vacuum degree of the drying conditions is 0.8-1 bar, for example, 0.82 bar, 0.85 bar, 0.88 bar, 9.2 bar, 9.5 bar, or 9.8 bar.

[0067] In this invention, the drying temperature range for the drying process is relatively wide, and commonly used drying temperatures are applicable to this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the drying temperature for the drying conditions is 55-60°C.

[0068] In this invention, the drying time for the drying process can be selected within a wide range, and commonly used drying times are applicable to this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the drying time is 2-3 hours. Using the aforementioned embodiments, the resulting homohydric anhydride product has the characteristics of high purity, low free acid value, and small and uniform crystal particle size, and has good application prospects.

[0069] The second aspect of the present invention provides a pyromellitic dianhydride, wherein the pyromellitic dianhydride has a purity ≥99.99%, a free acid value of less than 1 wt%, preferably less than 0.5 wt%, more preferably 0.01-0.2%, and a particle size D10 of 100-140 μm and a particle size D90 of 140-150 μm.

[0070] The present invention will be described in detail below through embodiments. In the following embodiments,

[0071] The purity of pyromellitic dianhydride was determined using a Waters Alliance series high-performance liquid chromatography system equipped with a Waters e2695 separation module and a 2998 PDA detector. The mobile phase consisted of a gradient of aqueous formic acid (0.2% formic acid) and acetonitrile.

[0072] The free acid value of pyromellitic acid was determined by chemical titration using acetone as the solvent, triethylamine / acetone as the standard solution, and bromophenol blue as the indicator. The free acid content ω was calculated using the following formula:

[0073]

[0074] In the formula, the concentration of the C-triethylamine standard solution is mol / L.

[0075] v1 — Volume of triethylamine solution consumed in the titration of pyromellitic dianhydride

[0076] v2—Volume of triethylamine solution consumed in the titration of blank acetone

[0077] M-pyromellitic dianhydride mass

[0078] The particle size of pyromellitic dianhydride crystals was determined using a NKT6100-H laser particle size analyzer from NKT Instruments Co., Ltd.

[0079] In this embodiment of the invention, the crude pyromellitic dianhydride is a commercially available product from Puyang Shenghuade Chemical Co., Ltd., with a purity of 95%, a free acid value of 2.5%, and a crystal particle size of 710-840 μm; the pyromellitic dianhydride seed crystals are commercially available products from Innochem, with a purity of 99%.

[0080] In this embodiment of the invention, acetone is a commercially available product from Sinopharm Chemical Reagent Co., Ltd., specification AR (Shanghai Test), ≥99.5%. Dioxane (1,4-dioxane) is a commercially available product from Sinopharm Chemical Reagent Co., Ltd., specification AR (Shanghai Test), ≥99.5%.

[0081] The purification method for pyromellitic dianhydride described in this invention yields a dianhydride product with high purity (up to 99.99 wt%), low free acid value (down to 0.04 wt%), and small and uniform crystal particle size, thus showing promising application prospects.

[0082] The present invention will be described in detail below through embodiments.

[0083] Example 1-1

[0084] Weigh 1020g of acetone and 240g of dioxane into a dissolving vessel and stir until homogeneous to prepare a solvent. Add 100g of crude pyromellitic dianhydride, and slowly heat to 40℃ while stirring thoroughly. Perform hot filtration at 40℃ to remove insoluble impurities, then transfer the filtrate to an evaporating vessel. Control the reflux temperature at 60℃ and evaporate and concentrate the filtrate to obtain a concentrated crude pyromellitic dianhydride solution. The solvent to crude dianhydride mass ratio in the concentrated crude pyromellitic dianhydride solution is 5.5.

[0085] The crude homogeneous anhydride solution was transferred to a crystallization vessel. The cooling rate for the first cooling crystallization treatment was controlled at 8℃ / min, with a final cooling temperature of 50℃. After adding 0.5g of 80μm homogeneous anhydride seed crystals, the cooling rate for the second cooling crystallization treatment was controlled at 1.5℃ / min, with a final cooling temperature of 0℃ and a crystallization time of 2 hours, yielding crystalline material. The crystalline material was filtered and dried in a glove box filled with nitrogen at a vacuum of 1 bar, a drying temperature of 60℃, and a drying time of 3 hours. The purity of the sample was determined by liquid chromatography, the free acid value was determined by chemical titration, and the particle size was determined by a particle size analyzer. The results are shown in Table 1.

[0086] Examples 1-2

[0087] Unlike Example 1-1, 1200g of acetone and 60g of dioxane were weighed and stirred evenly in a dissolving vessel to prepare a mixed solvent.

[0088] Examples 1-3

[0089] Unlike Example 1-1, 860g of acetone and 400g of dioxane were weighed and stirred evenly in a dissolving vessel to prepare a mixed solvent.

[0090] Examples 1-4

[0091] Unlike Example 1-1, 630g of acetone and 630g of dioxane were weighed and stirred evenly in a dissolving vessel to prepare a mixed solvent.

[0092] Example 2-1

[0093] Unlike Example 1-1, the filtrate was evaporated and concentrated to a crude homogeneous anhydride solution with a solvent-to-crude anhydride mass ratio of 6.5.

[0094] Example 2-2

[0095] Unlike Example 1-1, the filtrate was evaporated and concentrated to a crude homogeneous anhydride solution with a solvent-to-crude anhydride mass ratio of 7.0.

[0096] Example 2-3

[0097] Unlike Example 1-1, the filtrate was evaporated and concentrated to a crude homogeneous anhydride solution with a solvent-to-crude anhydride mass ratio of 7.5.

[0098] Examples 2-4

[0099] Unlike Example 1-1, the filtrate was evaporated and concentrated to a crude homogeneous anhydride solution with a solvent-to-crude anhydride mass ratio of 4.5.

[0100] Example 3-1

[0101] Unlike Example 1-1, the cooling rate of the first cooling crystallization process was controlled at 10°C / min.

[0102] Example 3-2

[0103] Unlike Example 1-1, the cooling rate of the first cooling crystallization process was controlled at 3°C / min.

[0104] Example 3-3

[0105] Unlike Example 1-1, the cooling rate of the first cooling crystallization process was controlled at 20°C / min.

[0106] Example 4-1

[0107] Unlike Example 1-1, the particle size of the added anhydride seed crystals is 100 μm.

[0108] Example 4-2

[0109] Unlike Example 1-1, the particle size of the added anhydride seed crystals was 90 μm.

[0110] Example 4-3

[0111] Unlike Example 1-1, the particle size of the anhydride seed crystals added was 40 μm.

[0112] Example 4-4

[0113] Unlike Example 1-1, the particle size of the anhydride seed crystals added was 200 μm.

[0114] Example 5-1

[0115] Unlike Example 1-1, 1g of homogenate seed crystals were added.

[0116] Example 5-2

[0117] Unlike Example 1-1, 2g of homogenate seed crystals were added.

[0118] Comparative Example 1-1

[0119] Unlike Example 1-1, the solvent in the mixture was only 1260g of dioxane.

[0120] Comparative Examples 1-2

[0121] Unlike Example 1-1, the solvent in the mixture is only 1260g of acetone.

[0122] Comparative Example 2

[0123] Unlike Example 1-1, 1020g of acetone and 240g of acetonitrile were weighed and stirred evenly in a dissolving vessel to prepare a solvent.

[0124] Comparative Example 3

[0125] Unlike Example 1-1, the cooling rate of the first cooling crystallization process was controlled at 1.5°C / min.

[0126] Comparative Example 4

[0127] Unlike Example 1-1, the crystalline material was filtered and dried in an air atmosphere.

[0128] Comparative Example 5

[0129] Unlike Example 1-1, the second cooling crystallization process was carried out under conditions where no homogeneous anhydride seed crystals were present.

[0130] Table 1:

[0131]

[0132]

[0133] As can be seen from the above results, the homogenate prepared by the preferred embodiment of the present invention has excellent characteristics such as high purity, low free acid concentration, and uniform particle size.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for purifying pyromellitic dianhydride, characterized in that, The method includes: (1) The mixture containing crude pyromellitic dianhydride was filtered and concentrated to obtain a crude pyromellitic dianhydride concentrated solution; The solvents in the mixture include dioxane and acetone; (2) The crude homogeneous anhydride solution is subjected to a first cooling crystallization treatment and a second cooling crystallization treatment to obtain homogeneous anhydride crystals; then the crystals are washed in an inert gas atmosphere and then dried. The cooling rate of the first cooling crystallization process is higher than that of the second cooling crystallization process; The second cooling crystallization process is carried out in the presence of homogeneous anhydride seed crystals.

2. The purification method according to claim 1, characterized in that, In step (1), The mass ratio of dioxane to acetone is 0.05-0.90, preferably 0.05-0.50, more preferably 0.20-0.30; and / or The mass ratio of solvent to crude anhydride in the mixture is 12-18; and / or, In step (2), The cooling rate of the first cooling crystallization treatment is 1.5-19℃ / min higher than that of the second cooling crystallization treatment, preferably 3.5-17℃ / min, and more preferably 6.5-9℃ / min; More preferably, The first cooling rate is 3-20°C / min, preferably 5-18°C / min, more preferably 8-10°C / min; and / or The cooling rate of the second cooling crystallization treatment is 1.0-1.5℃ / min; More preferably, the starting temperature of the first cooling crystallization treatment is 55-60°C, and the starting temperature of the second cooling crystallization treatment is 45-50°C.

3. The purification method according to claim 1 or 2, characterized in that, The filtration temperature is 40-50℃; and / or The concentration temperature is 55-60°C; and / or The mass ratio of solvent to crude pyromellitic dianhydride in the crude homogeneous anhydride concentrated solution is 5-7.

4. The purification method according to any one of claims 1-3, characterized in that, The conditions for the first cooling crystallization treatment include: The final temperature for cooling is 45-50℃.

5. The purification method according to any one of claims 1-4, characterized in that, The conditions for the second cooling crystallization treatment include: The final temperature for cooling is 0-5℃; The final temperature holding time is 1-3 hours.

6. The purification method according to any one of claims 1-5, characterized in that, The seed crystals comprise 0.01-5 wt% of the crude pyromellitic dianhydride, preferably 0.05-2 wt%; more preferably 0.1-1 wt%; and / or The seed crystals have a particle size of 50-250 μm; preferably 80-150 μm; more preferably 80-100 μm; and / or The seed crystal is pyromellitic dianhydride with a purity of 99.00-99.99%.

7. The purification method according to any one of claims 1-6, characterized in that, The crude pyromellitic dianhydride is crude pyromellitic dianhydride obtained by gas-phase oxidation of pyromellitic tetramethylbenzene; and / or The crude pyromellitic dianhydride contains 90-99 wt% pyromellitic dianhydride.

8. The purification method according to any one of claims 1-7, characterized in that, The inert gas is selected from nitrogen and / or argon.

9. The purification method according to any one of claims 1-8, characterized in that, The drying conditions include: The vacuum level is 0.8-1 bar; and / or The temperature is 55-60℃; and / or The time is 2-3 hours.

10. A pyromellitic dianhydride, characterized in that, The purity of pyromellitic dianhydride is ≥99.99%, the free acid value is less than 1 wt%, preferably less than 0.5 wt%, more preferably 0.01-0.2%, and the particle size D10 of pyromellitic dianhydride is 100-140 μm, and the particle size D90 is 140-150 μm.

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