A method for producing 2,6-naphthalenedicarboxylic acid

Abstract

This invention discloses a method for producing 2,6-naphthalenedicarboxylic acid. The method involves stopping the reaction when the yield of crude 2,6-naphthalenedicarboxylic acid reaches 40-65 wt%, yielding a reaction mixture. The reaction mixture is then filtered once at a temperature above 80°C to obtain an oxidation mother liquor (denoted as A) and the crude 2,6-naphthalenedicarboxylic acid product. The oxidation mother liquor A is then filtered a second time, and the resulting filtrate (denoted as B) is used as the mother liquor for further reaction. Using this method, the mother liquor can be recycled to a maximum extent while simultaneously reducing the impact on product purity.

Description

Technical Field

[0001] This invention relates to a method for producing 2,6-naphthalenedicarboxylic acid. Background Technology

[0002] Polyethylene naphthalate (PEN) is a new polyester variety commercialized in the 1990s, formed by the polycondensation of dimethyl 2,6-naphthalenedicarboxylate (NDC) or 2,6-naphthalenedicarboxylic acid (NDA) with ethylene glycol (EG). Like traditional polyester (PET), PEN can be processed into films, fibers, hollow containers, and sheets. However, PEN exhibits superior physical and mechanical properties, gas barrier properties, chemical stability, and resistance to heat, UV radiation, and other harmful substances compared to PET. Due to its excellent overall performance and broad potential market, it has attracted the attention of the global polyester industry. The key technology in PEN polyester production is the synthesis technology of its monomer, 2,6-naphthalenedicarboxylic acid.

[0003] Currently, the only industrial method for synthesizing 2,6-NDA is through air-liquid phase oxidation under a Co-Mn-Br catalyst, using 2,6-dimethylnaphthalene as a raw material. For example, US Patent 5183933 (invention title: Process for preparing 2,6-naphthalene-dicarboxylic acid) uses 2,6-dimethylnaphthalene (2,6-DMN) to produce 2,6-NDA with a yield of 93%. However, considering the cost of raw materials, 2,6-diisopropylnaphthalene (2,6-DIPN) has a more significant advantage. Therefore, the 2,6-DIPN oxidation method for preparing 2,6-NDA has greater development potential. For example, patent US4709088 (invention title: Process for preparing 2,6-naphthalene-dicarboxylic acid) uses a semi-continuous method, continuously adding the raw material 2,6-DIPN to a mixture of catalyst and solvent at a certain rate. After the feed is completed, it undergoes a 2-hour deep oxidation process, achieving a 2,6-DNA yield of 91.7 mol%, but requiring a very large amount of catalyst. Furthermore, impurities have a significant impact on subsequent polymerization reactions. Extensive experiments have revealed that the main impurities in the 2,6-DIPN oxidation products are 2-formyl-6-naphthoic acid (2,6-FNA) and 2-acetyl-6-naphthoic acid (2,6-ANA). The content of these two impurities greatly affects the polymer's properties and color; therefore, subsequent purification is necessary to remove these impurities. When preparing 2,6-naphthalene-dicarboxylic acid from 2,6-diisopropylnaphthalene, it typically contains a large number of impurities, especially 2-acetyl-6-naphthoic acid (2,6-ANA), which is difficult to remove through subsequent processes such as hydrogenation purification. In order to control the content of impurities, only a small amount of the mother liquor can be recycled in the existing reaction, otherwise the purity of the product will be affected. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing 2,6-naphthalenedicarboxylic acid. This method can improve the recycling rate of the reaction mother liquor, maximizing the utilization of the recycled mother liquor while reducing the impact on product purity.

[0005] To achieve the above-mentioned objective, the present invention provides a method for producing 2,6-naphthalenedicarboxylic acid, comprising the following steps:

[0006] (1) In the process of producing 2,6-naphthalenedicarboxylic acid using raw material 2,6-diisopropylnaphthalene, the reaction is stopped when the yield of crude 2,6-naphthalenedicarboxylic acid reaches 40-65 wt%, and a reaction mixture is obtained.

[0007] (2) The reaction mixture obtained in step (1) is filtered once at a temperature greater than 80°C to obtain the oxidation mother liquor, denoted as A, and the crude 2,6-naphthalenedicarboxylic acid product.

[0008] (3) The oxidation mother liquor A is filtered twice, and the resulting filtrate is recorded as B. Filtrate B is used as the reaction mother liquor to continue the reaction.

[0009] Furthermore, any existing suitable method can be used in the process of producing 2,6-naphthalenedicarboxylic acid from the raw material 2,6-diisopropylnaphthalene. For example, the raw material 2,6-diisopropylnaphthalene is introduced into a reactor containing a catalyst and an organic solvent; at the same time, a gas containing free oxygen is introduced into the reactor to cause the 2,6-diisopropylnaphthalene to undergo an oxidation reaction to produce crude 2,6-naphthalenedicarboxylic acid.

[0010] Furthermore, the catalyst is any one or a mixture of compounds containing Co, Mn, Br, and K.

[0011] Furthermore, the mass ratio of the catalyst to 2,6-diisopropylnaphthalene is 1:1 to 2:1.

[0012] Furthermore, the organic solvent is preferably acetic acid (i.e., acetic acid). The amount of organic solvent added is 3-10 times the mass of the catalyst, preferably 5-7 times.

[0013] Furthermore, the gas containing free oxygen is air.

[0014] Furthermore, the reaction conditions for the oxidation reaction are: temperature of 160-210℃, pressure of 1-3MPa, and the ratio of the rate of charging of free oxygen gas to the feed rate of raw material 2,6-diisopropylnaphthalene is (8-15):1 (L / g).

[0015] Furthermore, in step (2), the temperature of the reaction mixture during the first filtration is preferably 85-100°C.

[0016] Furthermore, in step (3), the temperature of the secondary filtration is 10-30℃.

[0017] Furthermore, in step (3), when filtrate B continues to react as the mother liquor, 2,6-diisopropylnaphthalene, catalyst and solvent are added to it.

[0018] Further, the amount of additional reactants is 0.5-2 times the weight of the reactants in step (1), the amount of additional catalyst is 5-10 wt% of the initial catalyst weight, and the amount of additional solvent is 5-10 wt% of the initial solvent weight. Maintaining the reaction temperature and pressure constant, a gas containing free oxygen is introduced into the reactor to oxidize 2,6-diisopropylnaphthalene to produce crude 2,6-naphthalenedicarboxylic acid. The reaction is stopped when the yield of crude 2,6-naphthalenedicarboxylic acid reaches 40-65 wt%.

[0019] The present invention has the following advantages:

[0020] This invention controls the production process of 2,6-naphthalenedicarboxylic acid, stopping the reaction when the yield of crude 2,6-naphthalenedicarboxylic acid reaches a certain proportion, rather than pursuing the yield of a single reaction. The operation method of this invention can improve the recycling rate of the reaction mother liquor, and reduce the impact on product purity while making the maximum use of the recycled mother liquor.

[0021] This invention employs a secondary filtration method for the reaction products, particularly controlling the temperature of the primary filtration to effectively remove impurities, further improving the recycling rate of the mother liquor, and minimizing the impact on product purity while maximizing the utilization of the recycled mother liquor.

[0022] Using the method of this invention, the mother liquor can be directly recycled, whereas conventional mother liquor recycling methods generally cannot directly recycle the mother liquor, otherwise the purity of the product will be less than 85 wt%. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but it should be understood that the specific embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection.

[0024] In this invention, the crude 2,6-naphthalenedicarboxylic acid yield (%) = the mass of the dried crude 2,6-naphthalenedicarboxylic acid obtained from the oxidation reaction / (the theoretical mass of 2,6-naphthalenedicarboxylic acid obtained from the oxidation of 2,6-diisopropylnaphthalene) * 100%.

[0025] The purity of the product 2,6-naphthalenedicarboxylic acid was analyzed by liquid chromatography using the external standard method with reference materials.

[0026]

Example 1

[0027] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 64.50wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed to be 656.72 g.

[0028] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 8015.68 g. 31.11 g Co(OAc)2·4H2O, 30.63 g Mn(OAc)2·4H2O, 29.75 g KBr, 36.75 g CH3COOK, and 770 g acetic acid were added to filtrate B, and the mixture was then added to a reaction vessel.

[0029] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0030] For ease of comparison, the analysis results are listed in Table 1.

[0031]

Example 2

[0032] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then fed into the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 20min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 55wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 592.88g.

[0033] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 8079.6g. 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g were added to filtrate B and then mixed and added to the reaction vessel.

[0034] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 20 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0035] For ease of comparison, the analysis results are listed in Table 1.

[0036]

Example 3

[0037] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then fed into the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 15min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 45wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 485.06g.

[0038] After cooling the mother liquor A to 20°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 8134.78 g. 31.11 g Co(OAc)2·4H2O, 30.63 g Mn(OAc)2·4H2O, 29.75 g KBr, 36.75 g CH3COOK and 770 g acetic acid were added to filtrate B and then mixed and added to the reaction vessel.

[0039] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 15 min. The following products were obtained: mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1.

[0040] For ease of comparison, the analysis results are listed in Table 1.

[0041]

Example 4

[0042] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 6500g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 160℃, with the reactor pressure controlled at 1.5MPa. 641g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 80L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 40.63wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 95°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 265.17g.

[0043] After cooling the mother liquor A to 30°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 7401.9 g. 31.11 g Co(OAc)2·4H2O, 30.63 g Mn(OAc)2·4H2O, 29.75 g KBr, 36.75 g CH3COOK, and 650 g acetic acid were added to filtrate B, and the mixture was then added to a reaction vessel.

[0044] Stirring was started and the temperature was raised to 160℃. The pressure in the reactor was controlled at 1.5 MPa. Then, 641 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 80 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0045] For ease of comparison, the analysis results are listed in Table 1.

[0046]

Example 5

[0047] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 3847.5g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 180℃, with the reactor pressure controlled at 2.5MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then fed into the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 120L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 58wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 100°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 590.44g.

[0048] After cooling the mother liquor A to 15°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 5001.83 g. 31.11 g Co(OAc)2·4H2O, 30.63 g Mn(OAc)2·4H2O, 29.75 g KBr, 36.75 g CH3COOK, and 384.75 g acetic acid were added to filtrate B, and the mixture was then added to the reaction vessel.

[0049] Stirring was started and the temperature was raised to 180℃. The pressure in the reactor was controlled at 2.5 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 120 L / min to carry out the reaction. The reaction temperature and pressure were maintained and the reaction was continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0050] For ease of comparison, the analysis results are listed in Table 1.

[0051]

Example 6

[0052] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 12000g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then fed into the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 150L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 63.03wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 85°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 641.72g.

[0053] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 12566.24 g. 24.89 g Co(OAc)2·4H2O, 24.50 g Mn(OAc)2·4H2O, 23.80 g KBr, 29.40 g CH3COOK, and 616 g acetic acid were added to filtrate B, and the mixture was then added to a reaction vessel.

[0054] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 150 L / min to carry out the reaction. The reaction temperature and pressure were maintained and the reaction was continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0055] For ease of comparison, the analysis results are listed in Table 1.

[0056]

Example 7

[0057] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 64.50wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed to be 656.72 g.

[0058] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 8015.68 g. 15.56 g Co(OAc)2·4H2O, 15.31 g Mn(OAc)2·4H2O, 14.88 g KBr, 18.37 g CH3COOK, and 385 g acetic acid were added to filtrate B, and the mixture was then added to a reaction vessel.

[0059] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. The reaction temperature and pressure were maintained and the reaction was continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

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

[0061]

Comparative Example 1

[0062] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 45min. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 77.18wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed 785.82g.

[0063] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 7825.75g. 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g acetic acid were added to filtrate B and then mixed and added to the reaction vessel.

[0064] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 45 min. The following products were obtained: mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1.

[0065] For ease of comparison, the analysis results are listed in Table 1.

[0066] [Comparative Example 2]

[0067] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then fed into the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 5 minutes. The calculated yield of crude 2,6-naphthalenedicarboxylic acid was 31.59wt%. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90°C to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. After drying, D weighed 321.64g.

[0068] After cooling the mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 8316.35 g. 31.11 g Co(OAc)2·4H2O, 30.63 g Mn(OAc)2·4H2O, 29.75 g KBr, 36.75 g CH3COOK, and 770 g of other chemicals were added to filtrate B and then mixed and added to the reaction vessel.

[0069] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 5 min. The following products were obtained: mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1.

[0070] For ease of comparison, the analysis results are listed in Table 1.

[0071] [Comparative Example 3]

[0072] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 30min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 70℃ to obtain mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D. D was dried and weighed to be 865.78g.

[0073] After cooling mother liquor A to 25°C, it was filtered to obtain filtrate B and filter cake C. The weight of filtrate B was 7675.85 g. 31.11 g Co(OAc)₂·4H₂O, 30.63 g Mn(OAc)₂·4H₂O, 29.75 g KBr, 36.75 g CH₃COOK, and 770 g acetic acid were added to filtrate B, and the mixture was then added to a reaction vessel.

[0074] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 30 min. Mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0075] For ease of comparison, the analysis results are listed in Table 1.

[0076] Table 1

[0077]

[0078] The specific 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 combining the 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 producing 2,6-naphthalenedicarboxylic acid, characterized in that, Includes the following steps: (1) In the process of producing 2,6-naphthalenedicarboxylic acid using raw material 2,6-diisopropylnaphthalene, the reaction is stopped when the yield of crude 2,6-naphthalenedicarboxylic acid reaches 40-65 wt%, and the reaction mixture is obtained; (2) The reaction mixture obtained in step (1) is filtered once to obtain the oxidation mother liquor, denoted as A, and the crude 2,6-naphthalenedicarboxylic acid product; (3) The mother liquor A of oxidation is filtered twice, and the resulting filtrate is recorded as B. Filtrate B is used as the mother liquor for further reaction. In step (1), the process of producing 2,6-naphthalenedicarboxylic acid from raw material 2,6-diisopropylnaphthalene is as follows: the raw material 2,6-diisopropylnaphthalene is introduced into a reaction vessel containing a catalyst and an organic solvent; at the same time, a gas containing free oxygen is introduced into the reaction vessel to cause 2,6-diisopropylnaphthalene to undergo an oxidation reaction to generate crude 2,6-naphthalenedicarboxylic acid. In step (2), the temperature for the first filtration is 85-100℃; In step (3), when filtrate B is used as the mother liquor for the reaction, 2,6-diisopropylnaphthalene, catalyst and solvent are added to it; wherein, the amount of added reaction raw material is 0.5-2 times the weight of the raw material in step (1), the amount of added catalyst is 5-10 wt% of the weight of the catalyst in step (1), and the amount of added solvent is 5-10 wt% of the weight of the solvent in step (1).

2. The method according to claim 1, characterized in that, The catalyst is any one or a mixture of compounds containing Co, Mn, Br, and K.

3. The method according to claim 1, characterized in that, The mass ratio of the catalyst to 2,6-diisopropylnaphthalene is 1:1 to 2:

1.

4. The method according to claim 1, characterized in that, The organic solvent is acetic acid.

5. The method according to claim 1, characterized in that, The amount of organic solvent added is 3-10 times the mass of the catalyst.

6. The method according to claim 5, characterized in that, The amount of organic solvent added is 5-7 times the mass of the catalyst.

7. The method according to claim 1, characterized in that, The gas containing free oxygen is air.

8. The method according to claim 1, characterized in that, The reaction conditions for the oxidation reaction are: temperature 160-210℃, pressure 1-3MPa, and the ratio of the rate of charging of free oxygen gas to the feed rate of raw material 2,6-diisopropylnaphthalene is (8-15):1, unit: L / g.

9. The method according to claim 1, characterized in that, In step (3), the temperature for secondary filtration is 10-30℃.

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