Process for the preparation of pyromellitic dianhydride

Abstract

The present application relates to the technical field of organic compound purification, and particularly relates to a preparation method of pyromellitic dianhydride, which comprises the following steps: adding anhydride into crude pyromellitic acid prepared by a liquid-phase oxidation method to perform a contact reaction, adding an anti-solvent into a reaction product after cooling, and performing at least one operation of heating sublimation-cooling condensation alternately on crude pyromellitic dianhydride solid which is separated out. The pyromellitic dianhydride prepared by the method has high purity, up to 99%, can meet the requirements of industrial polymerization grade, and is easy to be purified in batches.

Description

Technical Field

[0001] This invention relates to the field of organic compound purification technology, specifically to a method for preparing pyromellitic dianhydride. Background Technology

[0002] Polyimide (PI) is a new type of high-performance engineering material with excellent properties such as lightweight, resistance to high and low temperatures, high strength and high modulus, and fire resistance. It is widely used in military, aerospace, liquid crystal, and electronics industries. Pyromellitic dianhydride (PMDA) is an important monomer for the preparation of PI and can be obtained by dehydrating pyromellitic acid (PMA).

[0003] Currently, there are two main industrial methods for producing pyromellitic dianhydride (PMDA): One is using pseudotrimethylbenzene as a raw material, including alkylation with propylene or carbonylation with CO. However, this process is overly complex and unsuitable for large-scale industrial production, and has been gradually phased out. The second is the mainstream PMDA production process used by most companies, which involves the gas-phase oxidation of pyromellitic dianhydride (DR) with air in a fixed-bed reactor. With the development of the petrochemical industry, the production of C10 aromatics has increased dramatically, and the cost of DR has decreased significantly, making the DR gas-phase oxidation method increasingly competitive. In addition, some companies also use the DR liquid-phase oxidation method to produce PMDA.

[0004] Regardless of the process described above, numerous intermediate reactions and excessive oxidation side reactions occur. Therefore, the purification of crude pyromellitic dianhydride becomes crucial. Currently, commonly used methods for purifying crude pyromellitic dianhydride include solvent extraction and distillation. Solvent extraction uses specific solvents to separate and purify components based on their solubility differences, but this leads to a decrease in product yield. Distillation collects components based on their boiling points, with lower-boiling-point components collected at the top and bottom of the distillation column; however, this method is extremely demanding in terms of raw material purity and boiling point, and is difficult to operate. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of complex preparation methods and low product purity in existing technologies for pyromellitic dianhydride, and to provide a preparation method for pyromellitic dianhydride that is simple in process and produces high product purity.

[0006] To achieve the above objectives, the present invention provides a method for preparing pyromellitic dianhydride, the method comprising: adding an anhydride to crude pyromellitic acid prepared by liquid-phase oxidation for contact reaction; adding an antisolvent after cooling the reaction product; and subjecting the precipitated crude pyromellitic dianhydride solid to at least one alternating heating-sublimation-cooling-deposition operation.

[0007] Through the above technical solution, the present invention has the following advantages:

[0008] The method of the present invention prepares pyromellitic dianhydride with high purity, up to 99%, which can meet the requirements of industrial polymerization grade and is easy to purify in batches. Attached Figure Description

[0009] Figure 1 This is an operating device for heating sublimation-cooling deposition according to a preferred embodiment of the present invention.

[0010] Explanation of reference numerals in the attached figures

[0011] 1-Sublimation unit; 5-Cooling medium inlet;

[0012] 2-Insulation components; 6-Cooling medium outlet;

[0013] 3-Sublimation unit; 7-Vacuum regulating valve;

[0014] 31-Cooling component; 8-Vacuum interface.

[0015] 4-Enriched components; Detailed Implementation

[0016] 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.

[0017] This invention provides a method for preparing pyromellitic dianhydride, the method comprising: adding an anhydride to crude pyromellitic acid prepared by liquid-phase oxidation for contact reaction; adding an antisolvent after cooling the reaction product; and subjecting the precipitated crude pyromellitic dianhydride solid to at least one alternating heating-sublimation-cooling-deposition operation.

[0018] The method of the present invention prepares pyromellitic dianhydride with high purity, up to 99%, which can meet the requirements of industrial polymerization grade and is easy to purify in batches.

[0019] According to a preferred embodiment of the present invention, the precipitated crude pyromellitic dianhydride solid is subjected to 2-5 alternating heating-sublimation-cooling-deposition operations. Preferably, the temperature of each subsequent heating-sublimation operation is 10-20°C lower than the previous one. By adopting the aforementioned preferred scheme, the purity of the product can be further improved.

[0020] According to a preferred embodiment of the present invention, the temperature for heating and sublimation is 120-250°C; the sublimation time is 1-24 h; and the vacuum degree is 0.01-0.10 kPa.

[0021] According to a preferred embodiment of the present invention, the cooling sublimation is carried out by cooling sublimation through a cooling medium with a temperature of -20 to 25°C.

[0022] In this invention, the conditions for the contact reaction 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 contact reaction conditions include: a mass ratio of crude pyromellitic acid (based on pyromellitic acid) to acid anhydride of 1:(3-15), preferably 1:(5-10). According to a preferred embodiment of the invention, the contact reaction conditions include: a contact temperature of 120-200℃, preferably 140-180℃. At this temperature, boiling and reflux are beneficial for further improving the purity of the pyromellitic dianhydride. According to a preferred embodiment of the invention, the contact reaction conditions include: a contact time of 1-10 hours, preferably 3-5 hours.

[0023] According to a preferred embodiment of the present invention, the temperature of the reaction product after cooling is 0-30°C.

[0024] According to a preferred embodiment of the present invention, the mass of the antisolvent added is 1-10 times the mass of the acid anhydride added.

[0025] According to a preferred embodiment of the present invention, the reaction product is cooled and then an antisolvent is added, followed by filtration and drying to obtain crude pyromellitic dianhydride.

[0026] In this invention, the filtration method can be a conventional method in the art, such as filtration, vacuum filtration, etc.

[0027] According to a preferred embodiment of the present invention, the drying conditions include: a drying temperature of 70-100°C and a vacuum degree of 0.01-0.10 kPa.

[0028] According to a preferred embodiment of the present invention, the method for preparing crude pyromellitic acid by liquid-phase oxidation includes: oxidizing an oxidant with mesitylene and a catalyst under solvent conditions to obtain pyromellitic acid; wherein the solvent is an acetic acid-water mixed solvent, and the acetic acid content is 70-85 wt% based on the total weight of the mixed solvent.

[0029] According to a preferred embodiment of the present invention, the catalyst contains Co, Mn and Br.

[0030] According to a preferred embodiment of the present invention, the oxidant comprises 25-40% O2 by volume percentage.

[0031] According to a preferred embodiment of the present invention, the conditions for contact oxidation include: a reaction temperature of 150-300°C; preferably 200-250°C.

[0032] According to a preferred embodiment of the present invention, the acid anhydride is selected from at least one of acetic anhydride, BOC anhydride, and propionic anhydride.

[0033] According to a preferred embodiment of the present invention, the antisolvent is selected from at least one of diethyl ether, petroleum ether, ethyl acetate, isopropyl ether, and methyl tert-butyl ether.

[0034] According to a preferred embodiment of the present invention, the heating sublimation-cooling deposition operation is carried out in an apparatus comprising: a sublimation unit 1 for heating pyromellitic dianhydride solid to sublimate it; a deposition unit 3 including an internal cooling component 31 and a bottom enrichment component 4 for receiving the gaseous stream from the sublimation unit and condensing and enriching it; an inclined tube connecting the sublimation unit and the deposition unit, and an external heat insulation component 2 for conveying the gaseous stream obtained from the sublimation unit to the deposition unit.

[0035] According to a preferred embodiment of the present invention, the cooling component includes at least one cooling medium inlet 5 and at least one cooling medium outlet 6.

[0036] According to a preferred embodiment of the present invention, the condensation unit is connected to a vacuum adjustment component via a vacuum regulating valve 7 and a vacuum interface 8 in sequence.

[0037] The present invention will be described in detail below through embodiments.

[0038] Unless otherwise specified, the raw materials used in the following examples are all commercially available products.

[0039] The structural formula of pyromellitic dianhydride is:

[0040] The structural formula of pyromellitic acid (PMA) is:

[0041] Preparation Example 1

[0042] Mesitylene, acetic acid, water, cobalt acetate, manganese acetate, and hydrobromic acid were mixed thoroughly and then pumped into an oxidation reactor. The solvent content (HAc / H2O) was 92% by weight; the solvent-to-mesitylene weight ratio was 49:1; and the ion concentrations were 200 ppm for Co ions, 400 ppm for Mn ions, and 600 ppm for Br ions. A gaseous mixture of O2, air, and N2 (O2 content 21.0 vol%) was introduced into the reactor to initiate the oxidation reaction. The oxidation reaction conditions were: a stirrer speed of 800 rpm, a temperature of 215℃, a reaction pressure of 3.0 MPa, a reaction time of 90 min (based on the average residence time in the solvent), and an oxygen partial pressure of 3.6% in the tail gas. The product yield results from liquid chromatography analysis are shown in Table 1.

[0043] Preparation Example 2

[0044] The preparation method was the same as in Example 1, except that the acetic acid content in the solvent was 70 wt%, and the other conditions were the same as in Example 1. The product yield results of liquid chromatography analysis are shown in Table 1.

[0045] Example 1

[0046] Acetic anhydride (the mass ratio of crude pyromellitic acid to anhydride was 1:7, calculated as pyromellitic acid) was added to the product obtained in Preparation Example 2. The mixture was heated to boiling at 150°C and refluxed for 5 hours to obtain a solution. The solution was cooled to room temperature (20°C), and methyl tert-butyl ether (twice the amount of anhydride added) was added to precipitate pyromellitic dianhydride solid. The solid was then filtered, and dried in a vacuum oven at 70°C to obtain crude pyromellitic dianhydride. The crude pyromellitic dianhydride was then used... Figure 1 The apparatus shown is used for processing. In sublimation unit 1, the sublimation temperature is 215℃ and the sublimation time is 5h. During the sublimation process, a vacuum is continuously evacuated and maintained at a vacuum degree of 0.05kPa. The sublimation gas flow is introduced into the deposition unit 3 through an inclined tube insulated by the heat preservation component. The temperature of the coolant in deposition unit 3 is 20℃. The resulting pyromellitic dianhydride is enriched at the enrichment component. After the sublimation operation is completed, the crystals in deposition unit 3 are collected and placed into the sublimation unit for secondary and tertiary sublimation. The secondary sublimation temperature is 195℃ and the sublimation time is 5h. The tertiary sublimation temperature is 175℃ and the sublimation time is 5h. During each sublimation process, a vacuum is continuously evacuated and maintained at a vacuum degree of 0.05kPa. The temperature of the coolant is maintained at 20℃.

[0047] Liquid chromatography analysis showed that the purity of pyromellitic dianhydride after the third sublimation was 99.2%.

[0048] Example 2

[0049] Same as Example 1, except that:

[0050] The mass ratio of crude pyromellitic acid to acid anhydride, calculated as pyromellitic acid, is 1:9.

[0051] The mass of methyl tert-butyl ether added is 4 times the mass of the acid anhydride added;

[0052] Only two sublimations are performed:

[0053] The first sublimation occurred at a temperature of 200℃ for 10 hours.

[0054] The second sublimation occurred at 190℃ for 10 hours.

[0055] Maintain the temperature of the coolant supplied at -20℃.

[0056] The purity of pyromellitic dianhydride after the second sublimation was 99%.

[0057] Example 3

[0058] Same as Example 1, except that:

[0059] The mass ratio of crude pyromellitic acid to acid anhydride, calculated as pyromellitic acid, is 1:5; the mass of methyl tert-butyl ether added is 8 times the mass of acid anhydride added.

[0060] Four sublimations:

[0061] The first sublimation occurred at a temperature of 240℃ for 2 hours.

[0062] The second sublimation occurred at 225℃ for 2 hours.

[0063] The third sublimation occurred at 210℃ for 2 hours.

[0064] The fourth sublimation occurred at a temperature of 195℃ for 2 hours.

[0065] Maintain the temperature of the coolant flowing into the system at 0°C.

[0066] The purity of pyromellitic dianhydride after the fourth sublimation was 99.5%.

[0067] Example 4

[0068] Same as Example 1, except that the temperature for all three sublimations was 190°C. The purity of pyromellitic dianhydride after the third sublimation was 98%.

[0069] Example 5

[0070] Same as Example 1, except that the product obtained in Preparation Example 1 was treated. The purity of the pyromellitic dianhydride after the third sublimation was 97.5%.

[0071] Example 6

[0072] Same as Example 1, except that: only one sublimation at 190°C is performed.

[0073] The purity of the sublimated pyromellitic dianhydride is 90%.

[0074] Example 7

[0075] Similar to Example 1, but with the difference that: no sublimation unit is set up, and the "sublimation-deposition" step is directly performed in the deposition unit. That is, crude pyromellitic dianhydride is directly introduced into the enrichment component, and the enrichment component is heated to 215°C for 5 hours. After the end, the crystals on the cooling component 31 are removed and placed into the enrichment component 4 for the second and third sublimation-deposition.

[0076] The purity of pyromellitic dianhydride after the third sublimation and deposition was 98%.

[0077] Table 1

[0078]

[0079] 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 preparing pyromellitic dianhydride, characterized in that, The method includes: adding an acid anhydride to crude pyromellitic acid prepared by liquid-phase oxidation for contact reaction; adding an antisolvent after cooling the reaction product; and subjecting the precipitated crude pyromellitic acid dianhydride solid to at least one alternating heating-cooling-deposition operation.

2. The preparation method according to claim 1, wherein, The precipitated crude pyromellitic dianhydride solid is subjected to 2-5 alternating heating-sublimation-cooling-deposition operations. Preferably, the temperature of each subsequent heating-sublimation operation is 10-20°C lower than the previous one.

3. The preparation method according to claim 1 or 2, wherein, The heating and sublimation temperature is 120-250℃; the sublimation time is 1-24h; the vacuum degree is 0.01-0.10kPa; and / or The cooling and sublimation method is to use a cooling medium with a temperature of -20 to 25°C for cooling and sublimation.

4. The preparation method according to any one of claims 1-3, wherein, The conditions for the contact reaction include: The mass ratio of crude pyromellitic acid (calculated as pyromellitic acid) to acid anhydride is 1:(3-15); and / or Contact temperature is 120-200℃; and / or The contact time is 1-10 hours.

5. The preparation method according to any one of claims 1-4, wherein, The reaction product is cooled to a temperature of 0-30°C; and / or The mass of the antisolvent added is 1-10 times the mass of the acid anhydride added.

6. The preparation method according to any one of claims 1-5, wherein, The method for preparing crude pyromellitic acid by liquid-phase oxidation includes: under solvent conditions, an oxidant is contacted with mesitylene and a catalyst for oxidation to obtain pyromellitic acid; The solvent is an acetic acid-water mixture, with an acetic acid content of 70-85 wt% based on the total weight of the mixture.

7. The preparation method according to any one of claims 1-6, wherein, The anhydride is selected from at least one of acetic anhydride, BOC anhydride, and propionic anhydride.

8. The preparation method according to any one of claims 1-7, wherein, The antisolvent is selected from at least one of diethyl ether, petroleum ether, ethyl acetate, isopropyl ether, and methyl tert-butyl ether.

9. The preparation method according to any one of claims 1-8, wherein, The heating sublimation-cooling deposition operation is performed in an apparatus comprising: The sublimation unit is used to heat the solid pyromellitic dianhydride to sublimate it. The sublimation unit includes an internal cooling component and a bottom enrichment component, used to receive the gaseous stream from the sublimation unit and condense and enrich it. An inclined tube connecting the sublimation unit and the condensation unit is equipped with an external heat-insulating component for conveying the gaseous stream obtained from the sublimation unit to the condensation unit.

10. The preparation method according to claim 9, wherein, The cooling component includes at least one cooling medium inlet and at least one cooling medium outlet; and / or The condensation unit is externally connected to a vacuum adjustment component.

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