A process for the preparation of 2,6-naphthalene dicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as catalyst

Abstract

The application discloses a 2,6-naphthalene dicarboxylic acid and a preparation method thereof, which is catalyzed by cobalt bromide-manganese bromide-cobalt acetate-manganese acetate, and belongs to the fine chemical field. 2,6-naphthalene dicarboxylic acid is obtained through a carboxylation reaction of 2,6-dimethylnaphthalene with air under the action of a catalyst containing bromine, cobalt and manganese, and through cooling crystallization, centrifugal filtration and drying. The application provides a catalyst containing bromine, cobalt and manganese and free of alkali metal cations, which can solve the corrosion problem of the catalyst on stainless steel equipment in the prior art under the premise of ensuring production efficiency, greatly reduces the energy consumption in production, and is beneficial to the industrialized production of 2,6-naphthalene dicarboxylic acid monomer.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst. Background Technology

[0002] Polyethylene naphthalene glycol (PEN), polybutylene naphthalene glycol (PBN), and high-performance liquid crystal polymers (LCPs) are crucial raw materials for photovoltaic backsheets, liquid crystal displays, high-performance fibers, and electrical insulation encapsulation processes. Their industrial production directly impacts the modernization and technological development of high-end electronic information materials in my country. These high-performance polymers are all prepared by polycondensation reactions of 2,6-naphthalenedicarboxylic acid (2,6-NDA) with ethylene glycol, butanediol, and aromatic polyols, respectively. However, the high cost of raw materials, demanding reaction conditions, and low production efficiency result in persistently high production costs. Therefore, optimizing reaction conditions to achieve efficient synthesis of 2,6-NDA and reduce costs is a significant concern for scholars and the chemical industry both domestically and internationally.

[0003] Methods for preparing 2,6-naphthalenedicarboxylic acid (NDA) include the Heinkel process and the oxidation of 2,6-dimethylnaphthalene. The Heinkel process, however, is no longer used industrially due to its use of highly toxic cadmium salts as catalysts, high temperatures and pressures, and large acid and alkali consumption. Amoco has established a 2,6-NDA production facility using the oxidation of 2,6-dimethylnaphthalene as a catalyst. The catalysts are cobalt acetate, manganese acetate, and bromides (hydrogen bromide, sodium bromide, and potassium bromide, etc.), and production is carried out at 180-2220℃ and 2-5 MPa. This method is widely used due to its high production efficiency; however, the alkali metal cations introduced by the bromides under high temperature and pressure conditions severely corrode stainless steel equipment, requiring frequent shutdowns for maintenance, which is detrimental to continuous industrial production. Therefore, industrial production often uses equipment made of precious metal alloys such as titanium and zirconium, which undoubtedly increases the cost of 2,6-NDA and hinders the promotion of high-performance polymer materials for electronic information applications. Summary of the Invention

[0004] To address the issue of catalyst corrosion of reaction equipment during industrial applications in existing 2,6-NDA preparation methods, which result in high costs due to the use of precious metals, this invention aims to provide a method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst. This method significantly reduces reaction temperature and pressure while ensuring yield, achieving efficient synthesis of 2,6-NDA under relatively mild conditions. It effectively solves the problem of catalyst corrosion of equipment, significantly reduces the production cost of 2,6-NDA, and facilitates the promotion and application of subsequent high-performance polymers, demonstrating significant industrial application value.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst includes the following steps:

[0007] Using 2,6-dimethylnaphthalene as a reactant, a carboxylation reaction was carried out with air under the action of a catalyst containing bromine, cobalt and manganese. After cooling and crystallization, centrifugation and filtration, and drying, 2,6-naphthalenedicarboxylic acid was obtained.

[0008] Furthermore, the catalyst containing bromine, cobalt, and manganese is a mixture of cobalt acetate, manganese acetate, cobalt bromide, and manganese bromide.

[0009] Furthermore, the mass ratio of cobalt bromide:manganese bromide:cobalt acetate:manganese acetate = 0.04-0.08:0.09-0.15:0.028-0.056:0.058-0.12.

[0010] Furthermore, the mass ratio of 2,6-dimethylnaphthalene to the catalyst containing bromine, cobalt, and manganese is 50-150:0.01-0.5.

[0011] Furthermore, the solvent used in the carboxylation reaction is acetic acid, and the mass ratio of 2,6-dimethylnaphthalene to acetic acid is 50-150:200-700.

[0012] Furthermore, the reaction temperature is 80-120℃, and the reaction time is 1-3 hours.

[0013] Furthermore, the air flow rate is 10-16 L / min.

[0014] Furthermore, the reaction pressure is 1-2 MPa.

[0015] A 2,6-naphthalenedicarboxylic acid prepared according to the preparation method, wherein the purity of 2,6-naphthalenedicarboxylic acid is 90.8-93.5%, the mass content of 2-formyl-6-naphthalenedicarboxylic acid is 3.2-4.8%, and the mass content of trimellitic acid is 2.2-3.6%.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] In the catalyst of this invention, bromide ions can initiate the extraction of hydrogen from the naphthalene ring and generate bromide. Cobalt and manganese ions can play a synergistic reducing role, decomposing the peroxide group generated during the oxidation process into an aldehyde group, which is then oxidized to Co. 3+ and Mn 3 + Co 3+ and Mn 3+It activates bromides, allowing bromide ions in the bromide to continue extracting hydrogen. The specific advantages of this invention are as follows:

[0018] 1. Mild catalytic reaction conditions. This invention provides a quaternary catalyst free of alkali metal cations, enabling the synthesis of 2,6-NDA in conventional metal reactors at 80-120℃ and 1-2 MPa. This reduces production costs and overcomes the problem of industrial production of 2,6-NDA using cobalt acetate, manganese acetate, or bromides as catalysts under high temperature and pressure. Under these conditions, the alkali metal cations introduced by bromides severely corrode stainless steel equipment, typically requiring titanium or zirconium reactors, which significantly increases production costs.

[0019] 2. High catalytic efficiency. The reaction temperature of this invention is 80-120℃, and the pressure is 1-2MPa. The reaction conditions are mild, which greatly reduces the catalyst deactivation rate and effectively improves the catalytic efficiency. This overcomes the problem that the industrial synthesis of 2,6-NDA requires a reaction temperature of 180-220℃ and a pressure of 2-5MPa, which accelerates catalyst deactivation and results in a short lifespan.

[0020] 3. Low energy consumption in production. The catalyst disclosed in this invention can produce 2,6-NDA under mild conditions, which can significantly reduce energy consumption compared to current industrial production processes.

[0021] Furthermore, an excess of bromide ions will generate more bromides. Cobalt acetate and manganese acetate are used to adjust the atomic ratio of bromide ions to cobalt ions.

[0022] Furthermore, the present invention provides an efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst. This method can synthesize 2,6-naphthalenedicarboxylic acid at 80-120℃ and 1-2MPa, which can avoid the impact of alkali metal cations introduced by bromides on equipment corrosion while ensuring production efficiency, reducing energy consumption in the production process, and greatly reducing the production cost of 2,6-NDA. It has great economic benefits and commercial value.

[0023] Furthermore, in this invention, 2,6-naphthalenedicarboxylic acid is synthesized using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst under conditions of 100-120℃ and 1-2MPa. After filtration, washing, and vacuum drying, 2,6-naphthalenedicarboxylic acid crystals with an impurity content of 7-10% are obtained. This method can solve the problem of catalyst corrosion on stainless steel equipment in existing processes while ensuring production efficiency, and significantly reduce production costs.

[0024] The 2,6-naphthalenedicarboxylic acid prepared by this invention has a purity of 90.8-93.5%, a mass content of 3.2-4.8% for 2-formyl-6-naphthalenedicarboxylic acid, and a mass content of 2.2-3.6% for trimellitic acid, indicating high purity. Detailed Implementation

[0025] The present invention will now be described more fully with reference to embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0026] The alkali metal cations introduced by the catalyst during the synthesis of 2,6-NDA are highly corrosive to stainless steel equipment under high temperature and pressure conditions. Therefore, titanium reactors are typically used, which significantly increases production costs. By changing the type and ratio of catalyst, the corrosive effects of alkali metal cations introduced by bromides can be avoided while ensuring production efficiency, thus greatly reducing production costs.

[0027] The present invention discloses a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, the steps of which are as follows:

[0028] (1) The synthesis method of 2,6-naphthalenedicarboxylic acid is as follows: 2,6-dimethylnaphthalene is used as the raw material and undergoes carboxylation reaction with air under the action of a catalyst. The resulting mixture is cooled and crystallized, centrifuged and filtered, and vacuum dried to obtain 2,6-NDA crystals.

[0029] Specifically, by mass fraction, the air inside the reactor is replaced with nitrogen at room temperature. After complete air replacement, 50-150 parts of 2,6-dimethylnaphthalene, 0.01-0.5 parts of the quaternary catalyst, and 200-700 parts of acetic acid are added to the reactor. The temperature is gradually increased to 80-120℃, and air is introduced at a flow rate of 10-16 L / min. The stirrer speed is set to 100-300 r / min, and the reactor pressure is controlled at 1-2 MPa. Under these conditions, the reaction is carried out for 1-3 hours to obtain a mixture containing 2,6-naphthalenedicarboxylic acid crystals. The mixture containing 2,6-naphthalenedicarboxylic acid crystals is cooled and crystallized at 10-30℃. After centrifugation and filtration, it is washed 2-3 times with a solvent at 50-65℃, and then dried in a vacuum oven at 80-120℃ for 1-3 hours to obtain 2,6-naphthalenedicarboxylic acid crystals.

[0030] The quaternary catalyst is a mixture of cobalt bromide, manganese bromide, cobalt acetate, and manganese acetate in a mass ratio of 0.04-0.08:0.09-0.15:0.028-0.056:0.058-0.12, with a cobalt ion concentration of 300-1000 ppm, a manganese ion concentration of 500-1500 ppm, and a bromide ion concentration of 500-2500 ppm, while maintaining an atomic ratio of bromine to cobalt of 2-4.

[0031] The 2,6-naphthalenedicarboxylic acid crystals contain 2,6-naphthalenedicarboxylic acid with a purity of 90.8-93.5%, 2-formyl-6-naphthalenedicarboxylic acid with a content of 3.2-4.8%, and trimellitic acid with a content of 2.2-3.6%.

[0032] The technical solution of the present invention will be described in detail below through specific embodiments:

[0033] Example 1

[0034] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0035] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0036] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0037] The purity of the sample was determined by weighing and liquid chromatography analysis, and the results are shown in the table below:

[0038] Table 1. 2,6-NDA crystals obtained in Example 1 and their impurity content.

[0039]

[0040] Example 2

[0041] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0042] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 120℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0043] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0044] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0045] Table 2. 2,6-NDA crystals obtained in Example 2 and their impurity content.

[0046]

[0047] Example 3

[0048] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0049] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 80℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0050] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0051] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0052] Table 3. 2,6-NDA crystals obtained in Example 3 and their impurity content.

[0053]

[0054] Example 4

[0055] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0056] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve and heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 10L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0057] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0058] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0059] Table 4. 2,6-NDA crystals obtained in Example 4 and their impurity content.

[0060]

[0061] Example 5

[0062] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0063] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.028g of cobalt acetate, and 0.058g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0064] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0065] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0066] Table 5. 2,6-NDA crystals obtained in Example 5 and their impurity content.

[0067]

[0068] Example 6

[0069] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0070] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve and heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.0MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0071] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0072] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0073] Table 6. 2,6-NDA crystals obtained in Example 6 and their impurity content.

[0074]

[0075] Example 7

[0076] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0077] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 90℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 16L / min, control the reactor pressure to 1MPa, and stop the reaction after 3 hours. Cool down to obtain the mixture.

[0078] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 50°C. Place it in a vacuum oven and dry it at 80°C for 3 hours to obtain 2,6-NDA crystals.

[0079] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0080] Table 7. 2,6-NDA crystals obtained in Example 7 and their impurity content.

[0081]

[0082]

[0083] Example 8

[0084] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0085] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 110℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 12L / min, control the reactor pressure to 2MPa, and stop the reaction after 3 hours. Cool down to obtain the mixture.

[0086] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 20°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 55°C. Place it in a vacuum oven and dry it at 120°C for 3 hours to obtain 2,6-NDA crystals.

[0087] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0088] Table 8. 2,6-NDA crystals obtained in Example 8 and their impurity content.

[0089]

[0090] Example 9

[0091] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0092] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 90℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 14L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 3 hours. Cool down to obtain the mixture.

[0093] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 20°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 65°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0094] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0095] Table 9. 2,6-NDA crystals obtained in Example 9 and their impurity content.

[0096]

[0097] Example 10

[0098] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0099] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 90℃. Take 50g of 2,6-dimethylnaphthalene, 200g of acetic acid, 0.04g of cobalt bromide, 0.09g of manganese bromide, 0.03g of cobalt acetate, and 0.07g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 16L / min, control the reactor pressure to 1MPa, and stop the reaction after 1 hour. Cool down to obtain the mixture.

[0100] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 50°C. Place it in a vacuum oven and dry it at 80°C for 3 hours to obtain 2,6-NDA crystals.

[0101] Example 11

[0102] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0103] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 110℃. Take 150g of 2,6-dimethylnaphthalene, 700g of acetic acid, 0.08g of cobalt bromide, 0.12g of manganese bromide, 0.04g of cobalt acetate, and 0.1g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 12L / min, control the reactor pressure to 2MPa, and stop the reaction after 3 hours. Cool down to obtain the mixture.

[0104] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 20°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 55°C. Place it in a vacuum oven and dry it at 120°C for 1 hour to obtain 2,6-NDA crystals.

[0105] Example 12

[0106] This embodiment provides a highly efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0107] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 90℃. Take 80g of 2,6-dimethylnaphthalene, 400g of acetic acid, 0.05g of cobalt bromide, 0.15g of manganese bromide, 0.05g of cobalt acetate, and 0.08g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 14L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 1.5 hours. Cool down to obtain the mixture.

[0108] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 30°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 65°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0109] Comparative Example 1

[0110] This comparative example provides an efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0111] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 200℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0112] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0113] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0114] Table 10 shows the 2,6-NDA crystals obtained in Comparative Example 1 and their impurity content.

[0115]

[0116] Comparative Example 2

[0117] This comparative example provides an efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0118] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve. Heat to 100℃, and mix 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, and 0.11g of manganese bromide. Pump the mixture into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, and control the reactor pressure to 1.5MPa. After reacting for 2 hours, stop the reaction, cool down, and obtain the mixture.

[0119] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0120] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0121] Table 11 shows the 2,6-NDA crystals obtained in Comparative Example 2 and their impurity content.

[0122]

[0123] Comparative Example 3

[0124] This comparative example provides an efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0125] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve and heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 8L / min, control the reactor pressure to 1.5MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0126] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0127] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0128] Table 12 shows the 2,6-NDA crystals obtained in Comparative Example 3 and their impurity content.

[0129]

[0130] Comparative Example 4

[0131] This comparative example provides an efficient method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, comprising the following steps:

[0132] (1) Open the nitrogen valve of the reactor to replace the air in the reactor with nitrogen, then close the nitrogen valve and heat to 100℃. Take 100g of 2,6-dimethylnaphthalene, 580g of acetic acid, 0.06g of cobalt bromide, 0.11g of manganese bromide, 0.056g of cobalt acetate, and 0.12g of manganese acetate, mix them, and pump them into a 1L titanium reactor using a constant flow pump. Open the air valve, adjust the air flow rate to 15L / min, control the reactor pressure to 0.8MPa, and stop the reaction after 2 hours. Cool down to obtain the mixture.

[0133] (2) Pass low-temperature heat transfer oil into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, open the reactor and take out the mixture. Wash it twice with hot acetic acid at 60°C. Place it in a vacuum oven and dry it at 100°C for 2 hours to obtain 2,6-NDA crystals.

[0134] The content of 2,6-NDA and its impurities was determined using the method shown in Example 1, and the results are shown in the table below:

[0135] Table 13 shows the 2,6-NDA crystals obtained in Comparative Example 4 and their impurity content.

[0136]

[0137] As can be seen from Examples 1-6 and Comparative Examples 1-4 above, the oxidation of 2,6-DMN using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as catalyst can yield 2,6-NDA crystals with good product quality under conditions of 80-120℃ and 1-2MPa. The catalyst ratio, air flow rate, reaction pressure, and reaction temperature all affect the purity of 2,6-NDA.

[0138] Table 11: Reactions of Examples and Comparative Examples

[0139]

[0140]

[0141] This invention utilizes cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as catalysts to efficiently prepare 2,6-naphthalenedicarboxylic acid under conditions of 80-120℃ and 1-2 MPa. This method can address the corrosion problem of stainless steel equipment caused by alkali metal cations introduced by bromides under high temperature and high pressure conditions in traditional oxidation methods. Furthermore, this method can obtain high-quality 2,6-naphthalenedicarboxylic acid while ensuring production efficiency, demonstrating broad industrial application prospects and commercial value.

[0142] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0143] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst, characterized in that, Includes the following steps: Using 2,6-dimethylnaphthalene as a reactant, a carboxylation reaction was carried out with air in the presence of a catalyst containing bromine, cobalt and manganese. After cooling and crystallization, centrifugation and filtration, and drying, 2,6-naphthalenedicarboxylic acid was obtained. The mass ratio of cobalt bromide:manganese bromide:cobalt acetate:manganese acetate is 0.04-0.08:0.09-0.15:0.028-0.056:0.058-0.

12. The atomic ratio of bromine to cobalt is 2-4; The reaction temperature is 80-120℃, and the reaction time is 1-3 hours; The concentration of cobalt ions is 300-1000 ppm, the concentration of manganese ions is 500-1500 ppm, and the concentration of bromide ions is 500-2500 ppm. The air flow rate is 10⁻¹⁶ L / min; The reaction pressure is 1-2 MPa.

2. The method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst according to claim 1, characterized in that, The catalyst containing bromine, cobalt, and manganese is a mixture of cobalt acetate, manganese acetate, cobalt bromide, and manganese bromide.

3. The method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst according to claim 1, characterized in that, The mass ratio of 2,6-dimethylnaphthalene to a catalyst containing bromine, cobalt, and manganese is 50-150:0.01-0.

5.

4. The method for preparing 2,6-naphthalenedicarboxylic acid using cobalt bromide-manganese bromide-cobalt acetate-manganese acetate as a catalyst according to claim 1, characterized in that, The solvent used in the carboxylation reaction is acetic acid, and the mass ratio of 2,6-dimethylnaphthalene to acetic acid is 50-150:200-700.

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