阅读说明：本技术 合成2,6-萘二甲酸的方法 (Method for synthesizing 2,6-naphthalene dicarboxylic acid ) 是由 朱庆才 张海涛 畅延青 于 2019-09-04 设计创作，主要内容包括：本发明合成2,6-萘二甲酸的方法,主要解决现有技术中2,6-二异丙基萘空气氧化生成的粗2,6-萘二甲酸中杂质2-甲酰基-6-萘甲酸和2-乙酰基-6-萘甲酸含量较高的问题。本发明通过采用合成2,6-萘二甲酸的方法,包括如下步骤：(1)以醋酸为溶剂,在催化剂存在下,2,6-二异丙基萘与含自由氧的氧化剂反应,以2,6-二异丙基萘投料总重为100计,中间产物6-异丙基-2-萘甲酸与2,6-二异丙基萘投料总重的重量比0.05以下；(2)添加K和Br,继续反应0.5-2h；其中步骤(1)中所述催化剂包括Co化合物、Mn化合物、Br化合物和K化合物的技术方案,较好的解决了该问题,可用于2,6-萘二甲酸的生产中。(The invention discloses a method for synthesizing 2,6-naphthalene dicarboxylic acid, which mainly solves the problem that the content of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, in crude 2,6-naphthalene dicarboxylic acid generated by air oxidation of 2, 6-diisopropylnaphthalene in the prior art is high. The invention adopts a method for synthesizing 2,6-naphthalene dicarboxylic acid, which comprises the following steps: (1) acetic acid is taken as a solvent, 2, 6-diisopropyl naphthalene reacts with an oxidant containing free oxygen in the presence of a catalyst, and the weight ratio of the total weight of the intermediate product 6-isopropyl-2-naphthoic acid and the total weight of the 2, 6-diisopropyl naphthalene is less than 0.05, calculated by the total weight of the 2, 6-diisopropyl naphthalene as 100; (2) adding K and Br, and continuing to react for 0.5-2 h; the catalyst in the step (1) comprises a Co compound, a Mn compound, a Br compound and a K compound, so that the problem is solved well, and the catalyst can be used for producing 2,6-naphthalene dicarboxylic acid.)

1. A method for synthesizing 2, 6-naphthalenedicarboxylic acid comprising the steps of:

(1) acetic acid is taken as a solvent, 2, 6-diisopropyl naphthalene reacts with an oxidant containing free oxygen in the presence of a catalyst, and the weight ratio of the total weight of the intermediate product 6-isopropyl-2-naphthoic acid and the total weight of the 2, 6-diisopropyl naphthalene is less than 0.05, calculated by the total weight of the 2, 6-diisopropyl naphthalene as 100;

(2) adding K and Br, and continuing to react for 0.5-2 h;

wherein the catalyst in the step (1) comprises a Co compound, a Mn compound, a Br compound and a K compound.

2. The method according to claim 1, wherein the mass ratio of K added in the step (2) to K in the step (1) is 0.1 to 1.

3. The method according to claim 1, wherein the mass ratio of the Br added in the step (2) to the Br in the step (1) is 0.1 to 1.

4. The method according to claim 1, wherein the molar ratio of the amount of K added to the amount of Br added in step (2) is 0.2 to 5.

5. The method according to claim 1, wherein the reaction temperature in step (1) and step (2) is independently selected from 160 to 220 ℃.

6. The synthesis process according to claim 1, wherein the reaction pressure in step (1) and step (2) is independently 2 to 3 MPa.

7. The synthesis method according to claim 1, wherein the space velocity of the 2, 6-diisopropylnaphthalene fed in the step (1) is 0.001-0.003 min relative to the mass of the solvent in the reaction kettle in the step (1)^-1。

8. The method according to claim 1, wherein the molar ratio of Mn to Co in the catalyst in the step (1) is 0.5 to 2 based on 1 mol of Co.

9. The method according to claim 1, wherein the catalyst in the step (1) has a molar ratio of Br to (Co + Mn) of 1 to 4 based on 1 mole of Co.

10. The method according to claim 1, wherein the molar ratio of K to (Co + Mn) in the catalyst in the step (1) is 2 to 5 based on 1 mol of Co.

Technical Field

The present invention relates to a method for synthesizing 2, 6-naphthalenedicarboxylic acid.

Background

2,6-naphthalene dicarboxylic acid (2,6-NDA) and derivatives thereof are important monomers for preparing various polyesters, polyurethane materials, Liquid Crystal Polymers (LCP) and the like, and particularly polyethylene naphthalate (PEN) prepared by polycondensation of 2,6-NDA and ethylene glycol has wide application prospects in films, packaging containers (especially beer bottles) and industrial fibers. Due to the high degree of symmetry in the 2,6-NDA structure. The PEN has the characteristics of a straight-chain polymer, and is a high-performance material with good rigidity, high strength and excellent hot workability. Compared with polyethylene terephthalate (PET), PEN has better heat resistance, barrier property, mechanical property, chemical resistance, ultraviolet resistance and the like.

At present, dialkyl naphthalene is synthesized into 2,6-NDA through air liquid phase oxidation of dialkyl naphthalene under Co-Mn-Br catalyst in industry, 2,6-NDA is prepared through 2, 6-dialkyl naphthalene oxidation method, wherein the oxidation reaction is liquid phase exothermic reaction, a Co-Mn-Br catalyst system is adopted, acetic acid is used as solvent, the reaction temperature is about 200 ℃, and the reaction pressure is about 3 MPa. The reaction condition is mild, and the reaction is easy to control, so that the method becomes the only method for industrially producing the 2,6-NDA at present. The 2, 6-dialkylnaphthalene oxidation method includes a 2, 6-dimethylnaphthalene oxidation method, a 2, 6-diisopropylnaphthalene oxidation method, a 2, 6-alkylacylnaphthalene oxidation method and a 2, 6-diethylnaphthalene oxidation method. For example, U.S. Pat. No. 5, 5183933 (titled: Process for preparing 2,6-naphthalene-dicarboxylic acid) produced 93% yield of 2,6-NDA using 2, 6-dimethylnaphthalene (2, 6-DMN). In various liquid-phase oxidation methods of 2, 6-dialkylnaphthalene, because the physical properties of 2, 6-dimethylnaphthalene are similar to the physical and chemical properties of 2, 7-dimethylnaphthalene, separation is difficult and operation cost is high; and 2, 6-diisopropyl naphthalene (2,6-DIPN) is easy to separate and purify from raw materials (isomer mixture), and the operation cost is lower. Therefore, the process route for preparing 2,6-NDA by the 2,6-DIPN oxidation method has more development prospect in view of industrial production and economic cost. 2, 6-diisopropyl naphthalene is catalyzed and oxidized in solvent to prepare 2,6-N DCA. However, similar reaction conditions were used to oxidize 2, 6-diisopropylnaphthalene, as in the case of 2, 6-dimethylnaphthalene oxidation, and the yield of 2,6-NDA product was less than 50%. Hirose lsao et al (European patent EP031510019 titled Process for producing,2,6-naphthalene dicarboxylic acid form 2, 6-Dipropropylnaphthalene) have found that the activity of a naphthalene ring containing an isopropyl group is high, hydrogen peroxide is easily formed from the isopropyl group on the naphthalene ring at the initial stage of oxidation, and the hydrogen radical of hydrogen peroxide is unstable and rapidly decomposed into a naphthol compound. The naphthol compound is not easy to oxidize, and finally naphthalene ring cracking is caused to generate trimellitic acid. In order to improve the yield of the oxidized product 2,6-NDA and to suppress the occurrence of side reactions, many researchers have conducted studies. It is found that in the oxidation reaction of 2, 6-diisopropyl naphthalene, the concentration of raw materials in a reactor is not high enough, otherwise, the reaction is too fast in the initial stage, so that the side reaction is accelerated, the yield of 2,6-NDA is reduced, and the trimellitic acid as a byproduct is increased. The continuous feeding of 2, 6-diisopropylnaphthalene or the small-amount multiple feeding can be adopted to control the raw materials in the reactor to be kept in a low concentration state. For example, in the patent US4709088 (titled: Process for preparing 2,6-naphthalene-dicarboxylic acid), a semi-continuous method is adopted, 2,6-DIPN as a raw material is continuously added into a mixed solution of a catalyst and a solvent for reaction at a certain rate, and after the feeding is finished, deep oxidation is carried out for 2 hours, so that the yield of 2,6-DNA is 91.7 mol%, but the dosage of the catalyst is very large.

The crude 2,6-NDCA contains a plurality of impurities, different reaction raw materials and different reaction processes, the types and the contents of the impurities in the crude product are completely different, the main impurities comprise trimellitic acid (TMA), bromo-2, 6-NDA, aldehyde derivatives (2-formyl-6-naphthoic acid), 2-naphthoic acid, colored substances, Co, Mn, Br residues and the like, and if the impurities are not removed, the quality of the polyester is seriously influenced. For example, TMA causes branching in the polymer, affects the linearity thereof, and decreases the mechanical strength of the polymer; bromo-2, 6-NDA lowers the softening point of the polymer; aldehyde derivatives can disrupt the polymer chain, affect polymerization rate and molecular weight, and also darken the color of the polymer, affecting its appearance quality (pyronin et al. 2, 6-naphthalenedicarboxylic acid synthesis and purification technology advances [ J ]. petrochemical technology and applications 2002, 20 (6): 410-. Therefore, the crude 2, 6-naphthalenedicarboxylic acid must be purified. However, the content of the impurities mainly comprises 2-formyl-6-naphthoic acid (2,6-FNA) and 2-acetyl-6-naphthoic acid (2,6-ANA), and the content of the two impurities has a great influence on the performance and color of the polymer, which is similar to that of p-carboxybenzaldehyde (4-CBA) in Terephthalic Acid (TA) prepared by oxidizing p-xylene (PX), while in the PTA industry, the content of the 4-CBA is strictly limited before hydrofining, and is usually 0.25-0.35 wt%.

Disclosure of Invention

The invention aims to solve the technical problem that the content of impurities 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid in crude 2, 6-naphthalenedicarboxylic acid generated by air oxidation of 2, 6-diisopropylnaphthalene in the prior art is high, and provides a method for synthesizing 2, 6-naphthalenedicarboxylic acid, which can obviously reduce the content of impurities 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid in the crude 2, 6-naphthalenedicarboxylic acid.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a method for synthesizing 2, 6-naphthalenedicarboxylic acid comprising the steps of:

(1) acetic acid is taken as a solvent, 2, 6-diisopropyl naphthalene reacts with an oxidant containing free oxygen in the presence of a catalyst, and the weight ratio of the total weight of the intermediate product 6-isopropyl-2-naphthoic acid and the total weight of the 2, 6-diisopropyl naphthalene is less than 0.05, calculated by the total weight of the 2, 6-diisopropyl naphthalene as 100;

(2) adding K and Br, and continuing to react for 0.5-2 h;

wherein the catalyst in the step (1) comprises a Co compound, a Mn compound, a Br compound and a K compound.

The addition of K and Br in step (2) can reduce the contents of 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid in naphthalenedicarboxylic acid, while the addition of K and Br in step (1) is much earlier than in the present invention.

In the above technical solution, the mass ratio of K added in step (2) to K in step (1) is preferably 0.1 to 1, for example, but not limited to, the mass ratio of K added in step (2) to K in step (1) is 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and the like, and more preferably 0.3 to 0.5.

In the above technical solutions, the mass ratio of the added Br in the step (2) to the Br in the step (1) is preferably 0.1 to 1, and for example, but not limited to, the mass ratio of the added Br in the step (2) to the Br in the step (1) is 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and the like, and more preferably 0.3 to 0.5.

In the above technical solution, the molar ratio of the amount of K added in step (2) to the amount of Br added is preferably 0.2 to 5, for example, but not limited to, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 2.5, 3.0, 3.5, 4.0, 4.5, and the like, and more preferably 0.5 to 2. For convenience, K and Br in step (2) can be supplemented by using KBr as raw material, and the molar ratio of the amount of K added simultaneously to the amount of Br added simultaneously in step (2) is 1.0. .

In the technical scheme, the reaction temperature of the step (1) and the step (2) is preferably 160-220 ℃.

In the technical scheme, the reaction pressure of the step (1) and the step (2) is independently preferably 2-3 MPa.

In the above technical scheme, the feeding airspeed of 2, 6-diisopropyl naphthalene in step (1) is preferably 0.001-0.003 min relative to the mass of the solvent in the reaction kettle in step (1)^-1。

In the technical scheme, the feeding speed of the free oxygen-containing gas in the step (1) and the step (2) is independently and preferably 10-30 in terms of air relative to the feeding speed of the 2, 6-diisopropyl naphthalene in the step (1), and the feeding speed is, for example, but not limited to, independently 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and the like.

In the above technical solution, in the catalyst in the step (1), the molar ratio of Mn to Co is preferably 0.5 to 2, for example, but not limited to, 0.52, 0.55, 1, 1.12, 1.52, 1.82, and 1.98, based on 1 mol of Co.

In the above technical solution, in the catalyst in the step (1), the molar ratio of Br to (Co + Mn) is preferably 1 to 4, for example, but not limited to 2.2, 2.5, 3, 3.2, 3.52, and 3.98, based on 1 mole of Co.

In the above technical solution, in the catalyst in step (1), the molar ratio of K to (Co + Mn) is preferably 2 to 5, for example, but not limited to, 2.2, 2.5, 3, 3.2, 3.52, 3.98, 4.51, and 4.99, based on 1 mol of Co.

In the above solution, Co is preferably used in the form of cobalt acetate, and/or Mn is preferably used in the form of manganese acetate, and/or K is preferably used in the form of potassium bromide or potassium acetate, and/or Br is preferably used in the form of an alkali metal bromide, more preferably potassium bromide.

In the above technical scheme, cobalt acetate is Co (OAc)₂·4H₂Calculated as O, manganese acetate Mn (OAc)₂·4H₂O, Br in KBr, K in KBr and CH₃COOK, the mass of the solvent acetic acid and the catalyst in the step (1) is preferably 4-20, for example, but not limited to, the mass of the solvent acetic acid and the catalyst in the step (1) is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and the like.

In the above-mentioned embodiment, the step (2) is preferably followed by a step of separating a solid from a liquid and/or washing a solid phase with acetic acid and/or washing a solid phase with water, and more preferably by a step of drying. The acetic acid wash temperature is preferably greater than 60 ℃ to below the acetic acid boiling point, and/or the water wash temperature is preferably greater than 60 ℃ to below the water boiling point. With respect to boiling point, one skilled in the art will recognize that this can vary with operating pressure.

The invention adopts the following components: mn: br: the catalyst proportion of K ═ 1:1:2:5 (molar ratio), acetic acid is used as solvent, the reaction temperature is 200 ℃, the reaction pressure is 2.75MPa, the mass ratio of 2, 6-diisopropyl naphthalene to solvent acetic acid is 0.0013min^-1The reaction is carried out for 1h, after the reaction is finished, the obtained reaction product is filtered, washed and dried, and then the content of impurities 2-formyl-6-naphthoic acid is only 0.15 wt%, and the content of 2-acetyl-6-naphthoic acid is only 0.16 wt%, so that the difficulty of subsequent separation and purification is greatly reduced, and a better technical effect is obtained.

Detailed Description

[ example 1 ]

(1) 311.25gCo (OAc)₂·4H₂O、306.25gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) 496g of acetic acid solution containing 99.2g of KBr is added into a reaction kettle, the reaction is continued for 1 hour under the condition of keeping the reaction condition unchanged, after the reaction is finished, reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid is filtered, and is respectively washed by acetic acid at 60 ℃ and water at 80 ℃, the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, are analyzed after sampling and drying.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 2 ]

(1) 415.13gCo (OAc)₂·4H₂O、204.24gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) 496g of acetic acid solution containing 99.2g of KBr is added into a reaction kettle, the reaction is continued for 1 hour under the condition of keeping the reaction condition unchanged, after the reaction is finished, reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid is filtered, and is respectively washed by acetic acid at 60 ℃ and water at 80 ℃, the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, are analyzed after sampling and drying.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 3 ]

(1) 207.56gCo (OAc)₂·4H₂O、408.48gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) 496g of acetic acid solution containing 99.2g of KBr is added into a reaction kettle, the reaction is continued for 1 hour under the condition of keeping the reaction condition unchanged, after the reaction is finished, reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid is filtered, and is respectively washed by acetic acid at 60 ℃ and water at 80 ℃, the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, are analyzed after sampling and drying.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 4 ]

(1) 311.25gCo (OAc)₂·4H₂O、306.25gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) 148.9g of acetic acid solution containing 29.75g of KBr is added into a reaction kettle, the reaction is continued for 1 hour under the condition of keeping the reaction condition unchanged, after the reaction is finished, reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid is filtered, and is respectively washed by 60 ℃ acetic acid and 80 ℃ water, the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, are analyzed after sampling and drying.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 5 ]

(1) 311.25gCo (OAc)₂·4H₂O、306.25gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) Adding 743.75g of acetic acid solution containing 148.75g of KBr into a reaction kettle, continuously reacting for 1h under the condition of keeping the reaction condition unchanged, filtering reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid after the reaction is finished, respectively washing by adopting 60 ℃ acetic acid and 80 ℃ water, wherein the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and sampling and drying are carried out to analyze the contents of impurities 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 6 ]

(1) 311.25gCo (OAc)₂·4H₂O、306.25gMn(OAc)₂·4H₂O、892.5gKBr、245.35gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) Adding 992g of acetic acid solution containing 297.5g of KBr into a reaction kettle, continuously reacting for 1h under the condition of keeping the reaction condition unchanged, filtering reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid after the reaction is finished, respectively washing by adopting 60 ℃ acetic acid and 80 ℃ water, wherein the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and sampling and drying are carried out to analyze the contents of impurities 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ example 7 ]

(1) 311.25gCo (OAc)₂·4H₂O、306.25gMn(OAc)₂·4H₂O、297.5gKBr、1256.2gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 20g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) 496g of acetic acid solution containing 99.2g of KBr is added into a reaction kettle, the reaction is continued for 1 hour under the condition of keeping the reaction condition unchanged, after the reaction is finished, reaction product mixed liquor containing crude 2, 6-naphthalenedicarboxylic acid is filtered, and is respectively washed by acetic acid at 60 ℃ and water at 80 ℃, the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid, are analyzed after sampling and drying.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ COMPARATIVE EXAMPLE 1 ]

(1) 311.25gCo (OAc)₂·4H2O、306.25gMn(OAc)₂·4H₂O、297.5gKBr、367.5gCH₃COOK and 7700g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, sufficient air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) And (3) continuing the reaction for 1h, after the reaction is finished, filtering the reaction product mixed liquor containing the crude 2, 6-naphthalenedicarboxylic acid, washing by using acetic acid at 60 ℃ and water at 80 ℃, wherein the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and sampling and drying to analyze the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid.

For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

[ COMPARATIVE EXAMPLE 2 ]

The only difference from example 1 is that 496g of 99.2g kbr in acetic acid was also added in step (1), specifically:

(1) 311.25gCo (OAc)₂·4H2O、306.25gMn(OAc)₂·4H₂O、396.7gKBr、367.5gCH₃COOK and 8196g acetic acid are mixed and added into a reaction kettle, then stirring is started, the temperature is raised to 200 ℃, the pressure of the reaction kettle is controlled to be 2.75MPa, 1000g2, 6-diisopropyl naphthalene is heated to be molten, then the mixture enters the reaction kettle at the speed of 10g/min, simultaneously 80L/min of air is introduced for reaction, and after the feeding is finished, the reaction is continued until the content of the intermediate product 6-isopropyl-2-naphthoic acid is less than 5 g.

(2) And (3) continuing the reaction for 1h, after the reaction is finished, filtering the reaction product mixed liquor containing the crude 2, 6-naphthalenedicarboxylic acid, washing by using acetic acid at 60 ℃ and water at 80 ℃, wherein the dosage of the washing acetic acid is 1000g, the dosage of the washing water is 1000g, and sampling and drying to analyze the contents of impurities, namely 2-formyl-6-naphthoic acid and 2-acetyl-6-naphthoic acid. For convenience of comparison, the main experimental conditions and experimental results are listed in table 1.

TABLE 1