Process for the production of pyromellitic anhydride from a pyromellitic acid dehydration process

Abstract

The application provides a method for producing pyromellitic anhydride by a pyromellitic acid dehydration process and belongs to the technical field of organic compound synthesis. The method comprises the following steps: (1) dissolving pyromellitic acid in an organic solvent and heating and dehydrating; and (2) cooling and crystallizing and separating to obtain pyromellitic dianhydride. The organic solvent comprises diphenyl ether and hydrogenated terphenyl. The mixture of diphenyl ether and hydrogenated terphenyl is used in the application, the low-temperature operation window is expanded, and better PMDA yield and PMDA purity are obtained compared with the case of using diphenyl ether or hydrogenated terphenyl as the solvent, and the problems of easy formation of a viscous system, narrow temperature operation window and inconvenient operation during low-temperature crystallization in the prior art are solved.

Description

Technical Field

[0001] This invention relates to a method for dehydrating and purifying pyromellitic tetracarboxylic acid to obtain pyromellitic tetracarboxylic anhydride, belonging to the field of organic compound synthesis technology. Background Technology

[0002] Pyromellitic anhydride (PMDA) is an important organic chemical raw material, mainly used in the production of polyimide, epoxy resin, polyester resin, plasticizer, etc. It can also be used as an adhesive, surfactant, metal corrosion inhibitor, leather tanning agent, high-temperature lubricant, fuel, etc.

[0003] Currently, the production processes for pyromellitic dianhydride are mainly divided into two categories: gas-phase oxidation and liquid-phase oxidation. Gas-phase oxidation primarily uses mesitylene as a raw material and V₂O₅ as a catalyst, directly producing pyromellitic dianhydride at high temperatures. Although the gas-phase method can generate pyromellitic dianhydride in one step, it suffers from low conversion rates, high product impurities, and requires hydrolysis and purification before it can be used as an intermediate. Furthermore, the reaction temperature is too high, resulting in significant energy consumption. The liquid-phase method mainly uses a Co-Mn-Br catalyst system to oxidize mesitylene in acetic acid solvent to produce pyromellitic acid, followed by dehydration and purification to obtain pyromellitic dianhydride. This process also involves high reaction temperatures.

[0004] In the existing technology, when pyromellitic anhydride is purified by dehydration of pyromellitic acid, diphenyl ether is used as the solvent alone. This can easily cause the system to become viscous or even crystallize diphenyl ether at low temperatures. In addition, the temperature operating window for low-temperature crystallization is narrow and the operation is inconvenient. Alternatively, acetic anhydride and pyromellitic acid can be mixed and heated for dehydration, but the consumption of acetic anhydride is too large and the acetic anhydride is difficult to recover, resulting in high costs. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention proposes a method for dehydrating and purifying pyromellitic tetracarboxylic acid to obtain pyromellitic tetracarboxylic anhydride, which yields good PMDA yield and PMDA purity.

[0006] According to one aspect of the present invention, a method for producing pyromellitic anhydride by dehydration of pyromellitic tetracarboxylic acid is provided, the method comprising:

[0007] (1) A mixture containing pyromellitic acid and organic solvent is heated and dehydrated to obtain a mixture;

[0008] (2) The mixture is cooled and crystallized, and then separated to obtain a crystalline substance containing pyromellitic anhydride;

[0009] The organic solvents include diphenyl ether and hydrogenated terphenyl.

[0010] Optionally, the mass ratio of hydrogenated terphenyl to diphenyl ether in the organic solvent is 4 to 15.

[0011] In the above technical solution, as a non-limiting example, the mass ratio of hydrogenated terphenyl to diphenyl ether in the organic solvent is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or any value between any two of the above points.

[0012] Optionally, the mass ratio of pyromellitic acid to organic solvent in the mixed solution is 0.1 to 0.4.

[0013] In the above technical solution, as a non-limiting example, the mass ratio of pyromellitic acid to organic solvent is 0.15, 0.2, 0.25, 0.3, 0.35, or any value between any two of the above points.

[0014] Optionally, the temperature for heating and dehydration is 150–270°C.

[0015] In the above technical solution, as a non-limiting example, the heating and dehydration temperature is 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, or any value between any two of the above points.

[0016] Optionally, the heating and dehydration time is 1 to 6 hours.

[0017] In the above technical solution, as a non-limiting example, the heating and dehydration time is 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or any value between any two of the above points.

[0018] Optionally, the heating and dehydration is divided into a first stage of heating and dehydration and a second stage of heating and dehydration.

[0019] Optionally, the temperature of the first stage of heating and dehydration is 150–210°C, and the time is 1–3 hours.

[0020] Optionally, the temperature of the second stage of heating and dehydration is 220–270°C, and the time is 1–3 hours.

[0021] In the above technical solution, as a non-limiting example, the heating and dehydration time of the first stage is 1.5h, 2h, 2.5h, 3h, or any value between any two of the above points; the heating and dehydration temperature of the first stage is 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, or any value between any two of the above points.

[0022] The second stage of heating and dehydration time is 1.5h, 2h, 2.5h, 3h, or any value between any two of the above; the second stage of heating and dehydration temperature is 220℃, 230℃, 240℃, 250℃, 260℃, 265℃, or any value between any two of the above.

[0023] Optionally, the cooling crystallization temperature is 5–35°C.

[0024] In the above technical solution, as a non-limiting example, the cooling crystallization temperature is 10℃, 12℃, 15℃, 18℃, 20℃, 22℃, 25℃, 30℃, or any value between any two of the above points.

[0025] Optionally, the cooling crystallization time is 2 to 10 hours.

[0026] In the above technical solution, as a non-limiting example, the cooling crystallization time is 3h, 4h, 5h, 6h, 7h, 8h, 9h, or any value between any two of the above points.

[0027] Optionally, the purity of the pyromellitic acid is 80 wt.% to 100 wt.%.

[0028] The yield of pyromellitic anhydride described in this application is greater than 90.0 mol.%, preferably greater than 95.0 mol.%; the purity of pyromellitic anhydride in the crystals is greater than 91.0%, preferably 99.8%.

[0029] The present invention has the following beneficial effects:

[0030] Existing technologies use diphenyl ether as a solvent, but when diphenyl ether is used alone, it easily causes the system to become viscous or even crystallizes during low-temperature crystallization. The operating temperature window for low-temperature crystallization is narrow, making operation inconvenient. This invention uses a mixture of diphenyl ether and hydrogenated terphenyl, which expands the low-temperature operating window and achieves better PMDA yield and purity than when using diphenyl ether or hydrogenated terphenyl alone as a solvent. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0032] In this application,

[0033] Y (yield, mol%) = (C 均苯四甲酸二酐(末) -C 均苯四甲酸二酐(初) ) / C 均苯四甲酸(初)

[0034] C 均苯四甲酸二酐(末) : Content of pyromellitic dianhydride at the end of the reaction, in mol;

[0035] C 均苯四甲酸二酐(初) : Initial average content of phenyl dianhydride in the reaction, in mol;

[0036] C 均苯四甲酸(初) : Initial average content of phenyltetracarboxylic acid, in mol.

[0037] The purity parameter of pyromellitic dianhydride was measured by liquid chromatography (GC 780) and the integral area S of the pyromellitic dianhydride standard (99.9 wt%, Sinopharm).

[0038] Purity % = S (测试样) / S (均苯四甲酸二酐标样) .

[0039] Example 1

[0040] 100 g of pyromellitic acid (90 wt.%) and 50 g of diphenyl ether were stirred until homogeneous. Then, 400 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and standing for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 96.6 mol.%, and the purity was 99.8%.

[0041] For ease of comparison, the experimental results are listed in Table 1.

[0042] Example 2

[0043] 100 g of pyromellitic acid (90 wt.%) and 50 g of diphenyl ether were stirred until homogeneous. Then, 400 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 20 °C and standing for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 90.5 mol.%, and the purity was 91.2%. For comparison, the experimental results are listed in Table 1.

[0044] Example 3

[0045] 100 g of pyromellitic acid (90 wt.%) and 40 g of diphenyl ether were stirred until homogeneous. Then, 410 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and allowing it to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 94.4 mol.%, and the purity was 95.7%.

[0046] For ease of comparison, the experimental results are listed in Table 1.

[0047] Example 4

[0048] 100 g of pyromellitic acid (90 wt.%) and 70 g of diphenyl ether were stirred until homogeneous. Then, 380 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and allowing it to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 92.5 mol.%, and the purity was 91.9%.

[0049] For ease of comparison, the experimental results are listed in Table 1.

[0050] Example 5

[0051] 100 g of pyromellitic acid (90 wt.%) and 50 g of diphenyl ether were stirred until homogeneous. Then, 400 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. After maintaining the temperature at 2 hours, the mixture was cooled to 30 °C and allowed to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 82.3 mol.%, and the purity was 90.6%.

[0052] For ease of comparison, the experimental results are listed in Table 1.

[0053] Example 6

[0054] 100 g of pyromellitic acid (90 wt.%) and 50 g of diphenyl ether were stirred until homogeneous. Then, 400 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 260 °C and maintained for 2 hours, followed by cooling to 30 °C and allowing it to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 95.2 mol.%, and the purity was 98.9%.

[0055] Example 7

[0056] 100 g of pyromellitic acid (90 wt.%) and 70 g of diphenyl ether were stirred until homogeneous. Then, 560 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and allowing it to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 95.0 mol.%, and the purity was 97.7%.

[0057] For ease of comparison, the experimental results are listed in Table 1.

[0058] Example 8

[0059] 100 g of pyromellitic acid (90 wt.%) and 30 g of diphenyl ether were stirred until homogeneous. Then, 240 g of hydrogenated terphenyl was added to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and standing for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 90.3 mol.%, and the purity was 94.1%.

[0060] For ease of comparison, the experimental results are listed in Table 1.

[0061] Comparative Example 1

[0062] 100 g of pyromellitic acid (90 wt.%) was added to 450 g of hydrogenated terphenyl to obtain a mixed solution. The solution was then heated to 200 °C with continuous stirring at a rate of 10 °C / min at 30 °C, and maintained for 2 h to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 h, followed by cooling to 30 °C and standing for 6 h to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 h to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 40.1 mol.%, and the purity was 64.3%.

[0063] For ease of comparison, the experimental results are listed in Table 1.

[0064] Comparative Example 2

[0065] 100 g of pyromellitic dianhydride (90 wt.%) was stirred thoroughly with 450 g of diphenyl ether to obtain a mixed solution. The solution was then heated to 200 °C at a rate of 10 °C / min with continuous stirring at 30 °C, and maintained for 2 hours to obtain a final mixture. Insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 30 °C and allowing it to stand for 6 hours to form solid crystals. The solid crystals were filtered off, washed twice with acetic anhydride, and dried under vacuum at 60 °C for 3 hours to obtain the pyromellitic dianhydride (PMDA) product. The yield of the pyromellitic dianhydride (PMDA) product was 80.4 mol.%, and the purity was 83.9%.

[0066] For ease of comparison, the experimental results are listed in Table 1.

[0067] Comparative Example 3

[0068] 100 g of pyromellitic acid (90 wt.%) and 450 g of diphenyl ether were stirred until homogeneous to obtain a mixed solution. The solution was then heated to 200 °C with continuous stirring at a heating rate of 10 °C / min at 30 °C, and maintained for 2 hours to obtain a final mixture. The insoluble matter in the mixture was then filtered off while hot, and the filtrate was retained. The filtrate was then heated to 240 °C and maintained for 2 hours, followed by cooling to 20 °C. The liquid mixture gradually thickened until it solidified, making crystallization impossible.

[0069] For ease of comparison, the experimental results are listed in Table 1.

[0070] Table 1.

[0071]

[0072]

[0073] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0074] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for producing pyromellitic anhydride by dehydrating pyromellitic tetracarboxylic acid, characterized in that, The method includes: (1) A mixture containing pyromellitic acid and an organic solvent is heated and dehydrated to obtain a mixture; (2) The mixture is cooled and crystallized, and separated to obtain a crystalline substance containing pyromellitic anhydride; The organic solvents include diphenyl ether and hydrogenated terphenyl; The mass ratio of hydrogenated terphenyl to diphenyl ether in the organic solvent is 4-15; The cooling crystallization temperature is 5~35℃.

2. The method according to claim 1, characterized in that, The mass ratio of hydrogenated terphenyl to diphenyl ether in the organic solvent is 5-12.

3. The method according to claim 1, characterized in that, The mass ratio of hydrogenated terphenyl to diphenyl ether in the organic solvent is 8-12.

4. The method according to claim 1, characterized in that, The mass ratio of pyromellitic acid to organic solvent in the mixed solution is 0.1~0.

4.

5. The method according to claim 1, characterized in that, The temperature for heating and dehydration is 150~270℃; And / or, the heating and dehydration time is 1 to 6 hours.

6. The method according to claim 1, characterized in that, The heating and dehydration process is divided into a first stage of heating and dehydration and a second stage of heating and dehydration.

7. The method according to claim 6, characterized in that, The temperature of the first stage of heating and dehydration is 150~210℃, and the time is 1~3h; And / or, the temperature of the second stage of heating and dehydration is 220~270℃, and the time is 1~3h.

8. The method according to claim 1, characterized in that, The cooling crystallization temperature is 20~35℃.

9. The method according to claim 1, characterized in that, The cooling crystallization temperature is 25~35℃.

10. The method according to claim 1, characterized in that, The cooling and crystallization time is 2 to 10 hours.

11. The method according to any one of claims 1-10, characterized in that, The purity of the pyromellitic acid is 80 wt.%~100 wt.%.

12. The method according to any one of claims 1-10, characterized in that, The yield of the pyromellitic anhydride is greater than 90.0 mol.%; the purity of the pyromellitic anhydride in the crystals is greater than 91.0 wt%.

13. The method according to claim 12, characterized in that, The yield of the pyromellitic anhydride is greater than 95.0 mol.%; and / or the purity of the pyromellitic anhydride in the crystals is greater than 99.8% by weight.

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