Refining method of 1, 4-naphthalic acid

Abstract

The invention relates to a refining method of 1, 4-naphthalic acid, and belongs to the technical field of synthesis of drug intermediates. In order to solve the problems of low reaction yield and large solid waste in the prior art, the invention provides a method for refining 1, 4-naphthalic acid, which is characterized by comprising the following steps: adding a 1, 4-naphthalic acid crude product into an acetic acid solvent system, with the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the 1, 4-naphthalic acid crude product being within 10% and the content of 1, 4-naphthalic acid being more than 90%, and the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the 1, 4-naphthalic acid crude product being less than 10%. Heating and controlling the temperature to be 40 DEG C to the reflux temperature for heat preservation, and then cooling until a solid product is separated out, so as to obtain the refined 1, 4-naphthalic acid. According to the method, the purity of the 1, 4-naphthalic acid can be improved, the purity reaches 99.5% or above, and the yield reaches 82% or above.

Description

Technical Field

[0001] The invention relates to a method for refining 1,4-naphthalenedicarboxylic acid, and belongs to the technical field of pharmaceutical intermediate synthesis. Background Art

[0002] 1,4-Naphthalene dicarboxylic acid is used to manufacture high-performance polyester fibers and insulating materials. It is an important monomer for polyethylene naphthalate (PEN), liquid crystal polymers and polyurethane resins. The main synthesis methods of this intermediate include oxidation of 1-methyl-4-acetylnaphthalene with potassium dichromate at a high temperature of 200-300°C and under a pressure of about 4MPa for more than 18 hours. It can also be obtained by liquid phase oxidation of 1,4-dimethylnaphthalene with cobalt-manganese-bromine as a catalyst at a high temperature of about 120°C and under a condition of about 3kPa. Both of the above two synthetic routes are difficult to operate under high temperature, high pressure and high catalyst, and are also prone to produce impurity products at high temperatures, affecting the purity, quality and yield of the products.

[0003] Another synthetic route is to use potassium permanganate as an oxidant and water as a solvent to oxidize and synthesize 1,4-naphthalenedicarboxylic acid at room temperature. Potassium permanganate oxidant is added in batches during the oxidation reaction. The synthetic route is as follows:

[0004]

[0005] The process conditions are mild, but the main problem of this synthetic route is that potassium permanganate has strong oxidizing properties and is used in large amounts, which can cause the naphthalene ring to open during the oxidation process. The reason for the naphthalene ring opening is mainly due to the fact that during the oxidation reaction, as the amount of potassium permanganate added increases, the 4-methyl-1-naphthalenecarboxylic acid raw material gradually decreases, while the product 1,4-naphthalenedicarboxylic acid gradually increases, showing a slow upward trend. When potassium permanganate is first added, the oxidation mainly occurs at the -1 position methyl of 4-methyl-1-naphthalenecarboxylic acid. As the oxidation reaction proceeds, the raw material 4-methyl-1-naphthalenecarboxylic acid in the reaction system gradually decreases. In the existing synthesis reaction, the conversion of the substrate 4-methyl-1-naphthalenecarboxylic acid is usually controlled, and the reaction is terminated when the content of 4-methyl-1-naphthalenecarboxylic acid is lower than 0.5%. During the reaction process, as the content of 4-methyl-1-naphthalenecarboxylic acid decreases, the probability of contact with the added potassium permanganate becomes lower and lower, while the probability of the product 1,4-naphthalenedicarboxylic acid contacting with potassium permanganate becomes higher and higher, so that the main oxidation site of potassium permanganate is gradually transferred from the -1 site methyl of 4-methyl-1-naphthalenecarboxylic acid to the naphthalene ring of 1,4-naphthalenedicarboxylic acid. As the reaction proceeds, the probability of 1,4-naphthalene dicarboxylic acid opening becomes larger and larger. In the actual research and development of the synthetic route, it is found that when the content of 1,4-naphthalene dicarboxylic acid in the reaction system reaches more than 90%, it is quite difficult to completely oxidize the remaining substrate when further oxidizing the substrate 4-methyl-1-naphthalene carboxylic acid to a product. It is necessary to further add a large amount of potassium permanganate for oxidation, which will lead to the opening of the naphthalene ring in the product and reduce the yield. The molar yield of the crude product is only about 50%, and the amount of oxidant such as potassium permanganate is greatly increased, which is equivalent to about 3 times the amount of substrate, which not only causes a waste of raw materials, but also a large amount of solid waste generated will cause environmental pollution. Summary of the invention

[0006] The present invention aims at the defects existing in the above prior art and provides a method for refining 1,4-naphthalenedicarboxylic acid, which solves the problem of how to improve the yield and purity quality of the product.

[0007] The object of the present invention is achieved by the following technical scheme: a method for refining 1,4-naphthalenedicarboxylic acid, characterized in that the method comprises adding a crude 1,4-naphthalenedicarboxylic acid product into an acetic acid solvent system, wherein the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid product is within 10%, the content of 1,4-naphthalenedicarboxylic acid is above 90%, heating and heating the temperature under the condition of controlling the temperature between 40°C and the reflux temperature, and then cooling the temperature to precipitate a solid product to obtain refined 1,4-naphthalenedicarboxylic acid.

[0008] By adopting an acetic acid solvent system, it is found that the solubility difference between 4-methyl-1-naphthalenecarboxylic acid and 1,4-naphthalenecarboxylic acid contained in a crude 1,4-naphthalenecarboxylic acid product in the acetic acid solvent system is found. When a large amount of 4-methyl-1-naphthalenecarboxylic acid is contained, 4-methyl-1-naphthalenecarboxylic acid can be well dissolved in the acetic acid solvent, while 1,4-naphthalenecarboxylic acid has poor solubility, thereby improving the purity of 1,4-naphthalenecarboxylic acid to more than 99.5%. Therefore, by utilizing the refining treatment method of the present invention, the problem of subsequent naphthalene ring opening in the process of synthesizing 1,4-naphthalenedicarboxylic acid by using 4-methyl-1-naphthalenecarboxylic acid as a substrate through oxidation with a strong oxidant can be effectively solved. By utilizing the refining method, the substrate 4-methyl-1-naphthalenecarboxylic acid does not need to be completely oxidized to 1,4-naphthalenedicarboxylic acid during the synthesis of the crude 1,4-naphthalenedicarboxylic acid product. It is only necessary to make the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the obtained crude 1,4-naphthalenedicarboxylic acid product within 10% and the content of 1,4-naphthalenedicarboxylic acid above 90%, and the reaction can be directly terminated. The crude product utilizes the refining method of the present invention, and only needs one refining treatment to effectively remove the residual 4-methyl-1-naphthalenecarboxylic acid and other impurities, thereby obtaining high-purity 1,4-naphthalenedicarboxylic acid, the purity of which reaches above 99.5%, and the yield can also reach above 82%.

[0009] Simultaneously, because the purification method of the present invention is applicable to the residual quantity of 4-methyl-1-naphthalenecarboxylic acid, still can keep the purity quality of the refined product under the situation of within 10%, thereby make without the need for 1, the residual quantity of substrate 4-methyl-1-naphthalenecarboxylic acid in the 4-naphthalene dicarboxylic acid crude product is controlled at low content (within 0.5%), like this in the crude product building-up process, follow-up 1, when the content of 4-naphthalene dicarboxylic acid reaches more than 90%, effectively reduce and avoid the strong oxidant to act on 1, the probability on the naphthalene ring of 4-naphthalene dicarboxylic acid causes the problem of open loop and yield decline, make improve the synthetic yield of crude product and the advantage of low impurity content on the whole.In addition, the mother liquor after the refining is recyclable, further the substrate 4-methyl-1-naphthalenecarboxylic acid in the mother liquor is recycled and reused as raw material, greatly improve the atomic utilization of raw material, even in the crude product synthesis, substrate content still has high content within 10%, also can not cause waste.

[0010] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, as a preference, an alcohol solvent is also added to the acetic acid solvent system. By adding an alcohol solvent to the main solvent acetic acid system, the presence of a small amount of alcohol solvent can better promote the dissolution of the substrate 4-methyl-1-naphthalenecarboxylic acid and remove it during the refining process, and the purity quality of the product can be better guaranteed, so that the purity reaches more than 99.8%. The above-mentioned alcohol solvent can be a low-grade alcohol solvent of C1 to C4. As a further preference, the alcohol solvent is selected from one or more of methanol, ethanol and propanol.

[0011] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, the acetic acid solvent system can be made of acetic acid as the reaction solvent, or the acetic acid solvent system can contain a mixed solvent of acetic acid and an organic solvent (such as an alcohol solvent). It is best to make the acetic acid content in the acetic acid solvent system account for more than 90%. It can effectively ensure that the residual raw materials are removed during the refining process, and can effectively ensure that 1,4-naphthalenedicarboxylic acid is fully separated. Preferably, the mass ratio of acetic acid to alcohol solvent is 10:1.0-3.0.

[0012] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, preferably, the mass ratio of the crude 1,4-naphthalenedicarboxylic acid to acetic acid is 1:10 to 15. This can more effectively dissolve the substrate but not the product, and is more conducive to ensuring the purity and quality of the refined product.

[0013] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, preferably, the temperature of the insulation is controlled at 75°C to the reflux temperature, which can better dissolve the residual raw materials, facilitate better removal of the residues in the subsequent cooling and crystallization process, and improve the purity and quality of the refined product.

[0014] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, it is preferred that the temperature of the cooling is reduced to 15° C. to 30° C. This can make the product 1,4-naphthalenedicarboxylic acid precipitate more effectively, and can effectively remove the residual raw materials and other impurities, so as to have the effect of high product purity quality, and the product purity reaches more than 99.5%.

[0015] In the above-mentioned method for refining 1,4-naphthalenedicarboxylic acid, preferably, the crude 1,4-naphthalenedicarboxylic acid is prepared by the following method:

[0016] Potassium permanganate is used as an oxidant, and a substrate 4-methyl-1-naphthalenecarboxylic acid is subjected to an oxidation reaction under an alkaline condition in the presence of an alkali metal hydroxide. During the oxidation reaction, the reaction is stopped when the content of the product 1,4-naphthalene dicarboxylic acid reaches more than 90%, thereby obtaining a crude 1,4-naphthalene dicarboxylic acid product. Since the crude 1,4-naphthalene dicarboxylic acid product with a high residual amount of the substrate 4-methyl-1-naphthalene carboxylic acid can be effectively removed by adopting the above-mentioned refining method, the reaction can be stopped when the content of the 1,4-naphthalene dicarboxylic acid reaches 90% (or more) during the synthesis process using a strong oxidant method, and the substrate does not need to be completely reacted, thereby effectively avoiding the phenomenon that the naphthalene ring of the product is opened in the subsequent oxidation process, ensuring the product yield of the crude product synthesis, and the purity quality reaches more than 90%. Preferably, in the synthetic process, when the content of 1,4-naphthalenedicarboxylic acid in the reaction solution reaches 90% (or more), the residual amount of 4-methyl-1-naphthalenecarboxylic acid is within 10%, and more preferably the residual amount of 4-methyl-1-naphthalenecarboxylic acid is 9.0% to 10%. This can more effectively avoid the oxidation ring-opening of naphthalene rings in the oxidation process product, which is conducive to improving product yield and purity quality. As further preferred, the added mass of the potassium permanganate is 1.5 to 2.0 times the added mass of the 4-methyl-1-naphthalenecarboxylic acid, and the potassium permanganate is added in batches during the reaction, and the mass of the potassium permanganate added every 5min to 10min is 0.5% to 1.5% of the added mass of the 4-methyl-1-naphthalenecarboxylic acid. The problem of excessive oxidizing property of potassium permanganate oxidant added at one time can be avoided. The method adopts batch addition and adds once every 5-10 minutes. The amount added each time is controlled within the above-mentioned smaller range, which can better ensure the effective progress of the reaction and the purity quality of the product, and can better monitor and detect the content of the product in the oxidation reaction process, which is more conducive to operation. Since the reaction can be stopped only when the product content reaches more than 90%, the amount of potassium permanganate oxidant can be effectively reduced. The total amount of potassium permanganate only needs to be 1.5-2.0 times of the amount of 4-methyl-1-naphthalenecarboxylic acid added to complete the reaction, which reduces the amount of solid waste and the pollution to the environment, and is conducive to industrial production.

[0017] In summary, compared with the prior art, the present invention has the following advantages:

[0018] 1. The purification method of the present invention can effectively dissolve 4-methyl-1-naphthalenecarboxylic acid in a solvent, and 1,4-naphthalenedicarboxylic acid has good solubility, thereby improving the purity of 1,4-naphthalenedicarboxylic acid to more than 99.5%, and the yield reaches more than 82%.

[0019] 2. The present invention does not need to control the residual amount of the substrate 4-methyl-1-naphthalenecarboxylic acid in the crude 1,4-naphthalene dicarboxylic acid to a low content, and effectively avoids the problem that when the content of subsequent 1,4-naphthalene dicarboxylic acid reaches more than 90% during the crude product synthesis process, the strong oxidant potassium permanganate has a higher probability of acting on the naphthalene ring of 1,4-naphthalene dicarboxylic acid, resulting in ring opening and reduced yield, thereby improving the yield of the crude product synthesis and the advantages of low impurity content as a whole. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further specifically described below through specific embodiments, but the present invention is not limited to these embodiments.

[0021] Example 1

[0022] 218g of water and 17.5g of caustic soda flakes are added into a three-necked flask, stirred to dissolve, 30g of 4-methyl-1-naphthalenecarboxylic acid raw material after drying is added at one time, stirred to dissolve, and then the temperature of the system is heated to 35°C, and potassium permanganate as an oxidant is added to react. During the reaction, 0.2g of potassium permanganate is added every 5 minutes while stirring. During the reaction, when the content of 1,4-naphthalene dicarboxylic acid reaches more than 90% (the reaction progress is monitored by HPLC control, when the content of 1,4-naphthalene dicarboxylic acid is ≧90%), the reaction is stopped, filtered, and the filter cake is rinsed with an appropriate amount of water. The filtrate obtained is slowly adjusted to a pH value of the system with 30% hydrochloric acid until a large amount of solid is precipitated, filtered, and a wet solid 1,4-naphthalene dicarboxylic acid crude product is obtained, which is 28.1g in dry form. The residual amount of 4-methyl-1-naphthalenecarboxylic acid in the crude 1,4-naphthalene dicarboxylic acid is within 10%, and the content of 1,4-naphthalene dicarboxylic acid is 91.2%.

[0023] Example 2

[0024] Take 25 g of the crude 1,4-naphthalene dicarboxylic acid obtained by the method of Example 1 and add it into a single-mouth bottle. Stir it magnetically, add 250 g of acetic acid, control the temperature and stir it under micro-reflux for 1 hour, then slowly cool it to room temperature for full crystallization and filter it with suction; rinse the filter cake with an appropriate amount of water, dry the filter cake, and obtain 21.3 g of the refined product 1,4-naphthalene dicarboxylic acid with a yield of 85.2% and a purity of 99.6%.

[0025] The collected filtrate can be further recycled, specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate solids, and the solids are collected by suction filtration; and the 4-methyl-1-naphthalenecarboxylic acid raw material is used as the reaction material for the next batch reaction and then put into the reaction system for further oxidation.

[0026] Example 3

[0027] 218g of water and 20g of caustic soda flakes are added into a three-necked flask, stirred to dissolve, 30g of 4-methyl-1-naphthalenecarboxylic acid raw material is added at one time, stirred to dissolve, and then heated to raise the temperature of the system to 40°C, and potassium permanganate as an oxidant is added to react. During the reaction, 0.18g of potassium permanganate is added every 5 minutes while stirring. During the reaction, when the content of 1,4-naphthalene dicarboxylic acid reaches more than 90% (the reaction progress is monitored by HPLC central control, and the reaction can be stopped when the content of 1,4-naphthalene dicarboxylic acid is ≧90%), the reaction is stopped. After the reaction is completed, the filter cake is washed with an appropriate amount of water, and the filtrate obtained is slowly adjusted to a pH value of the system with 30% hydrochloric acid until a large amount of solids are precipitated, and filtered to obtain a wet solid 1,4-naphthalene dicarboxylic acid crude product; 28.6g of the wet solid 1,4-naphthalene dicarboxylic acid crude product is dried, and the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the 1,4-naphthalene dicarboxylic acid crude product is less than 10%, and the content of 1,4-naphthalene dicarboxylic acid is 91.3%.

[0028] Example 4

[0029] Take 25 g of the crude 1,4-naphthalene dicarboxylic acid obtained by the method of Example 3 and add it into a single-mouth bottle. Stir it magnetically, add 230 g of acetic acid solvent, control the temperature and keep it warm and stir it under micro-reflux for 1.5 hours, then slowly cool it to room temperature for full crystallization, filter it with suction, rinse the filter cake with an appropriate amount of water, and dry the filter cake to obtain 21.5 g of the refined product 1,4-naphthalene dicarboxylic acid, with a yield of 86% and a purity of 99.7%.

[0030] The collected filtrate can be further recycled, specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate solids, and the solids are collected by suction filtration; and the 4-methyl-1-naphthalenecarboxylic acid raw material is used as the reaction material for the next batch reaction and then put into the reaction system for further oxidation.

[0031] Example 5

[0032] 230g of water and 18.5g of caustic soda flakes are added into a three-necked flask, stirred to dissolve, 30g of 4-methyl-1-naphthalenecarboxylic acid raw material after drying is added at one time, stirred to dissolve, and then the temperature of the system is heated to 40°C, and potassium permanganate as an oxidant is added to react. During the reaction, 0.2g of potassium permanganate is added every 5 minutes while stirring. During the reaction, when the content of 1,4-naphthalene dicarboxylic acid reaches more than 90% (the reaction progress is monitored by HPLC, when the content of 1,4-naphthalene dicarboxylic acid is ≧90%), the reaction is stopped. After the reaction is completed, suction filtration is performed, and the filter cake is rinsed with an appropriate amount of water. The filtrate obtained is slowly adjusted to a pH value of the system with 30% hydrochloric acid until a large amount of solids are precipitated, and suction filtration is performed to obtain a wet solid 1,4-naphthalene dicarboxylic acid crude product, 28.4g of which is dried; the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the 1,4-naphthalene dicarboxylic acid crude product is within 10%, and the content of 1,4-naphthalene dicarboxylic acid is 90.8%.

[0033] Example 6

[0034] Take 25 g of the crude 1,4-naphthalene dicarboxylic acid obtained by the method of Example 5, add it into a single-mouth bottle, stir it magnetically, add acetic acid-ethanol system (250 g of acetic acid, 25 g of ethanol), control the temperature at about 80°C, keep it warm and stir it for 1 hour, then slowly cool it to room temperature for full crystallization, and filter it with suction; rinse the filter cake with an appropriate amount of water, and dry the filter cake to obtain 21.4 g of the refined product 1,4-naphthalene dicarboxylic acid, with a yield of 85.6% and a purity of 99.7%.

[0035] The collected filtrate can be further recycled, specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate solids, and the solids are collected by suction filtration; and the 4-methyl-1-naphthalenecarboxylic acid raw material is used as the reaction material for the next batch reaction and then put into the reaction system for further oxidation.

[0036] Example 7

[0037] 230g of water and 18.5g of caustic soda flakes are added into a three-necked flask, stirred to dissolve, 30g of 4-methyl-1-naphthalenecarboxylic acid raw material after drying is added at one time, stirred to dissolve, and then the temperature of the system is heated to 40°C, and potassium permanganate as an oxidant is added to react. During the reaction, 0.2g of potassium permanganate is added every 5 minutes while stirring. During the reaction, when the content of 1,4-naphthalene dicarboxylic acid reaches more than 90% (the reaction progress is monitored by HPLC, when the content of 1,4-naphthalene dicarboxylic acid is ≧90%), the reaction is stopped. After the reaction is completed, suction filtration is performed, and the filter cake is rinsed with an appropriate amount of water. The filtrate obtained is slowly adjusted to a pH value of the system with 30% hydrochloric acid until a large amount of solids are precipitated, and suction filtration is performed to obtain a wet solid 1,4-naphthalene dicarboxylic acid crude product, 28.7g of which is dried; the residual amount of 4-methyl-1-naphthalene carboxylic acid in the 1,4-naphthalene dicarboxylic acid crude product is within 10%, and the content of 1,4-naphthalene dicarboxylic acid is 91.5%.

[0038] Example 8

[0039] Take 25 g of the crude 1,4-naphthalene dicarboxylic acid obtained by the method of Example 7 and add it into a single-mouth bottle. Stir it magnetically, add acetic acid-ethanol system (250 g of acetic acid, 40 g of ethanol), control the temperature at 78°C-80°C, keep stirring for 1 hour, then slowly cool to room temperature for full crystallization and filter by suction; rinse the filter cake with an appropriate amount of water, dry the filter cake, and obtain 21.3 g of the refined product 1,4-naphthalene dicarboxylic acid, with a yield of 85.2% and a purity of 99.5%.

[0040] The collected filtrate can be further recycled, specifically, the filtrate is concentrated to dryness, an appropriate amount of water is added to the residue to precipitate solids, and the solids are collected by suction filtration; and the 4-methyl-1-naphthalenecarboxylic acid raw material is used as the reaction material for the next batch reaction and then put into the reaction system for further oxidation.

[0041] The specific embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

[0042] Although the present invention has been described in detail and some specific embodiments have been cited, it is obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

Claims

1. A method for refining 1,4-naphthalenedicarboxylic acid, characterized in that: The method comprises adding a crude 1,4-naphthalenedicarboxylic acid product into an acetic acid solvent system, wherein the residual amount of 4-methyl-1-naphthalenecarboxylic acid in the crude 1,4-naphthalenedicarboxylic acid product is less than 10%, and the content of 1,4-naphthalenedicarboxylic acid is more than 90%, heating and heating the product under the condition of controlling the temperature between 40 DEG C and reflux temperature, and then cooling the product until a solid product precipitates, thereby obtaining refined 1,4-naphthalenedicarboxylic acid.

2. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 1, characterized in that: An alcohol solvent is also added to the acetic acid solvent system.

3. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 2, characterized in that: The alcohol solvent is selected from one or more of methanol, ethanol and propanol.

4. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 2 or 3, characterized in that: The mass ratio of acetic acid to alcohol solvent in the acetic acid solvent system is 10:1.0-3.

0.

5. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 1, 2 or 3, characterized in that: The mass ratio of the crude 1,4-naphthalene dicarboxylic acid to acetic acid is 1:10-15.

6. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 1, 2 or 3, characterized in that: The insulation temperature is controlled at 75° C. to reflux temperature.

7. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 1, 2 or 3, characterized in that: The cooling temperature is reduced to 20°C to 30°C.

8. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 1, 2 or 3, characterized in that: The crude 1,4-naphthalene dicarboxylic acid is prepared by the following method: Potassium permanganate is used as an oxidant to carry out an oxidation reaction on a substrate 4-methyl-1-naphthalenecarboxylic acid in the presence of an alkali metal hydroxide. During the oxidation reaction, when the content of the product 1,4-naphthalenedicarboxylic acid reaches more than 90%, the reaction is stopped to obtain a crude 1,4-naphthalenedicarboxylic acid product.

9. The method for refining 1,4-naphthalenedicarboxylic acid according to claim 8, characterized in that: The added mass of the potassium permanganate is 1.5 to 2.0 times the added mass of the 4-methyl-1-naphthalenecarboxylic acid, and the potassium permanganate is added in batches during the reaction, and the mass of the potassium permanganate added every 5 to 10 minutes is 0.5% to 1.5% of the added mass of the 4-methyl-1-naphthalenecarboxylic acid.

Images