Synthesis method of dimethyl 2, 6-naphthalate

Abstract

The invention relates to the technical field of synthesis, and provides a synthesis method of dimethyl 2, 6-naphthalate, which comprises the following steps: S1, preheating 2, 6-naphthalic acid and methanol, feeding into a high-pressure kettle, adding a catalyst, reacting in the high-pressure kettle, and filtering to obtain a liquid material; s2, cooling and crystallizing the liquid material, recrystallizing, and rectifying to obtain 2, 6-dimethyl naphthalate; the catalyst is a supported catalyst. According to the technical scheme, the problem that the yield and the purity of the dimethyl 2, 6-naphthalate in the prior art need to be improved is solved.

Description

Technical Field

[0001] This invention relates to the field of synthetic technology, and specifically to a method for synthesizing dimethyl 2,6-naphthalenedicarboxylate. Background Technology

[0002] Dimethyl 2,6-naphthalenedicarboxylate is an important chemical intermediate widely used in the synthesis of high-performance polyesters, liquid crystal polymers, dyes, and pharmaceuticals. In particular, it is used in the preparation of the novel polyester material polyethylene naphthalate (PEN). Polyethylene naphthalate synthesized from it has advantages such as strong heat resistance, high mechanical strength, and excellent gas barrier properties, making it promising for applications in flexible printed circuit boards (FPCs), outdoor flexible screens, Class F motor insulation materials, tire cords, and fuel cell membrane electrode sealing materials.

[0003] Currently, the main industrial method for synthesizing dimethyl 2,6-naphthalenedicarboxylate (DIC) involves esterification of 2,6-naphthalenedicarboxylic acid and methanol under catalysis. This method has advantages such as readily available raw materials and a relatively simple reaction route, but it also presents some challenges in practical industrial application. Commonly used catalysts, such as sulfuric acid and molybdenum trioxide, have drawbacks. Sulfuric acid can cause equipment corrosion over long-term use, and corrosion-resistant equipment increases production costs. Furthermore, sulfuric acid leads to an increase in byproducts during production. Molybdenum trioxide exhibits problems such as easy aggregation, uneven dispersion, and poor catalytic stability during catalysis, resulting in low reaction selectivity and increased side reactions. This not only reduces the yield of the target product but also increases the difficulty of subsequent purification, making it difficult to meet the stringent purity requirements for the preparation of polyethylene naphthalate (PEG).

[0004] Therefore, proposing a synthetic method that can optimize the reaction process and improve the product yield and purity is of great significance for promoting the efficient preparation of dimethyl 2,6-naphthalenedicarboxylate and its application in downstream high-value-added products. Summary of the Invention

[0005] This invention proposes a method for synthesizing dimethyl 2,6-naphthalenedicarboxylate, which solves the problem that the yield and purity of dimethyl 2,6-naphthalenedicarboxylate need to be improved in related technologies.

[0006] The technical solution of the present invention is as follows: This invention proposes a method for synthesizing dimethyl 2,6-naphthalenedicarboxylate, comprising the following steps: S1. 2,6-Naphthalenedicarboxylic acid and methanol are preheated and then fed into a high-pressure reactor. A catalyst is added, and the mixture is reacted in the high-pressure reactor. After filtration, a liquid material is obtained. S2. Cool the liquid material to crystallize, recrystallize, and distill to obtain the dimethyl 2,6-naphthalenedicarboxylate; The catalyst is a supported catalyst.

[0007] As a further technical solution, the preheating treatment involves a pre-reaction in a tubular reactor at a temperature of 240-260°C and a residence time of 10-60 minutes. The reaction in the autoclave is carried out at a temperature of 120°C for 3 to 6 hours.

[0008] As a further technical solution, the crystallization solvent for recrystallization includes methanol; The amount of methanol added is 8 to 15 times the mass of the solid material after the liquid material is cooled and crystallized.

[0009] As a further technical solution, the recrystallization process specifically involves adding a crystallization solvent to the solid material after the liquid material has cooled and crystallized, heating it to 120°C in a high-pressure autoclave, cooling it to 25~50°C, separating it, and obtaining the recrystallized dimethyl 2,6-naphthalenedicarboxylate.

[0010] As a further technical solution, during the distillation process, the reflux ratio in the distillation column is 3~6, ​​and the pressure at the top of the column is 1~3 kPa.

[0011] In this invention, during the distillation process, the reflux ratio in the distillation column is controlled to be 3-6. When the reflux ratio is 3-6, the distillation effect is better. When the reflux ratio increases within the range of 3-6, the flow rate of the reflux liquid in the column increases, which enhances the mass transfer and separation of the gas and liquid phases in the column. Finally, the purity of the dimethyl 2,6-naphthalenedicarboxylate obtained by distillation will be improved.

[0012] During the distillation process, the pressure at the top of the column is 1~3 kPa. Under this vacuum, the distillation operating temperature is relatively low, which can reduce the occurrence of side reactions of the target product to a certain extent. When the pressure at the top of the column is in the range of 1~3 kPa, the lower the vacuum, the lower the temperature at the top of the column, and the more stable the melt color of the obtained dimethyl 2,6-naphthalenedicarboxylate.

[0013] As a further technical solution, the cooling and crystallization temperature is 25~30℃, for example, it can be 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃, preferably 25℃.

[0014] As a further technical solution, the mass ratio of 2,6-naphthalenedicarboxylic acid to methanol is 1:9.5~10.5, and the amount of catalyst added is 7%~10% of the mass of 2,6-naphthalenedicarboxylic acid, for example, it can be 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, preferably 9%.

[0015] As a further technical solution, the raw materials for the supported catalyst include a support and an active component precursor; The active component precursor includes ammonium molybdate.

[0016] In the supported catalyst of this invention, ammonium molybdate serves as the precursor of the active component. Through post-processing, a molybdenum-based active catalytic component with high catalytic activity can be obtained. By loading it onto a support, the uniform dispersion of the molybdenum-based active catalytic component in the reaction system can be improved, avoiding the aggregation of the active catalytic component. At the same time, the high specific surface area and porous structure of the support enrich the 2,6-naphthalenedicarboxylic acid reaction substrate, increasing the concentration of the substrate around the catalytic active sites and providing a more stable catalytic environment for the molybdenum-based active catalytic component. This lays the foundation for improving the catalytic effect of the molybdenum-based active catalytic component and ultimately helps to increase the yield of dimethyl 2,6-naphthalenedicarboxylic acid.

[0017] As a further technical solution, the mass ratio of the carrier to the active component precursor is 8~10:1.

[0018] As a further technical solution, the carrier includes one of molecular sieve, activated carbon, and alumina, preferably a molecular sieve.

[0019] As a further technical solution, the active component precursor also includes a water-soluble tungsten source; The mass ratio of the ammonium molybdate to the water-soluble tungsten source is 4~24:1.

[0020] As a further technical solution, the water-soluble tungsten source includes ammonium metatungstate.

[0021] In this invention, when the active component precursor also includes a water-soluble tungsten source, the yield of dimethyl 2,6-naphthalenedicarboxylate can be further improved by using the water-soluble tungsten source in combination with ammonium molybdate. The reason for this is speculated to be that the tungsten source supported on the support can further enhance the Lewis acidity of Mo in the molybdenum-based active catalytic component during the catalytic process. At the same time, the combination of the tungsten-based active catalytic component and the molybdenum-based active catalytic component can more effectively activate the C=O in the carboxyl group, improve the catalytic effect of the catalyst, promote the nucleophilic attack of methanol, and thus improve the yield of dimethyl 2,6-naphthalenedicarboxylate.

[0022] In this invention, by optimizing the mass ratio of ammonium molybdate to water-soluble tungsten source, the mass ratio of ammonium molybdate to water-soluble tungsten source is adjusted to be 4~24:1, preferably 17:3~9:1. When the mass ratio of ammonium molybdate to water-soluble tungsten source is 17:3~9:1, the yield of dimethyl 2,6-naphthalenedicarboxylate can be further improved.

[0023] As a further technical solution, the preparation method of the supported catalyst includes the following steps: dispersing the active component precursor in water, adding the support, mixing evenly to obtain a mixture, drying the mixture, and calcining it to obtain the supported catalyst.

[0024] As a further technical solution, the mixing is achieved by stirring at a speed of 400-600 rpm for a duration of 1.5-2.5 h.

[0025] As a further technical solution, the calcination temperature is 580~630℃ and the time is 5~6h.

[0026] The working principle and beneficial effects of this invention are as follows: 1. In this invention, 2,6-naphthalenedicarboxylic acid and methanol are used as reaction raw materials. After preheating, 2,6-naphthalenedicarboxylic acid and methanol undergo a preliminary reaction to obtain a mixture. The mixture is placed in a high-pressure reactor and, under the action of a catalyst, a liquid material containing dimethyl 2,6-naphthalenedicarboxylic acid product is obtained. After cooling, crystallization, recrystallization, and distillation, the liquid material is further processed to obtain dimethyl 2,6-naphthalenedicarboxylic acid with high yield and high product quality, which meets the polymerization requirements for the subsequent preparation of polyethylene naphthalate from dimethyl 2,6-naphthalenedicarboxylic acid.

[0027] 2. The catalyst of this invention is a supported catalyst. By using a support to load the active catalytic component, the concentration of the reaction substrate around the catalytic active site can be increased. At the same time, the catalytic environment of the supported catalyst is more stable, which can improve the yield of dimethyl 2,6-naphthalenedicarboxylate. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] In the following examples and comparative examples, the purity of 2,6-naphthalenedicarboxylic acid was 99.8 wt%; the molecular sieve was MCM-22 molecular sieve with a specific surface area ≥800 m². 2 / g, Na2O content ≤0.1%, grain size 1~10μm, pore size 0.55~1.2nm; ammonium molybdate effective component content 99wt%; ammonium metatungstate effective component content 99wt%.

[0030] Example 1 The preparation method of the supported catalyst includes the following steps: 30g of ammonium molybdate was dispersed in 500g of water, and 270g of molecular sieve was added. After stirring at 500rpm for 2h, a mixture was obtained. The mixture was dried and calcined in a muffle furnace at 600℃ for 6h to obtain a supported catalyst. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate includes the following steps: S1. 1000g of 2,6-naphthalenedicarboxylic acid and 9500g of methanol are pre-reacted in a tubular reactor at a temperature of 240℃. After staying in the tubular reactor for 60 minutes, the mixture is transferred to an autoclave and 70g of supported catalyst is added. The autoclave is heated to 120℃ and reacted for 3 hours. The mixture is then filtered to obtain liquid material. S2. After cooling the liquid material from 120°C to 25°C, filter to obtain a solid material. Add the solid material to methanol (the amount of methanol added is 8 times the mass of the solid material) for recrystallization. After heating to 120°C, cool to 25°C and centrifuge to obtain the recrystallized dimethyl 2,6-naphthalenedicarboxylate. Add the recrystallized dimethyl 2,6-naphthalenedicarboxylate to a distillation column for distillation. Under the conditions of reflux ratio of 3, column top pressure of 3 kPa, and column top temperature of 243°C, distillation is carried out to obtain dimethyl 2,6-naphthalenedicarboxylate.

[0031] Example 2 The preparation method of the supported catalyst includes the following steps: 30g of ammonium molybdate was dispersed in 500g of water, and 270g of molecular sieve was added. After stirring at 500rpm for 2h, a mixture was obtained. The mixture was dried and calcined in a muffle furnace at 600℃ for 6h to obtain a supported catalyst. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate includes the following steps: S1. 1000g of 2,6-naphthalenedicarboxylic acid and 10000g of methanol are pre-reacted in a tubular reactor at a temperature of 250℃. After staying in the tubular reactor for 30 minutes, the mixture is transferred to an autoclave and 90g of supported catalyst is added. The autoclave is heated to 120℃ and reacted for 4 hours. The mixture is then filtered to obtain liquid material. S2. After cooling the liquid material from 120°C to 25°C, filter to obtain a solid material. Add methanol (the amount of methanol added is 10 times the mass of the solid material) to recrystallize the solid material. After heating to 120°C, cool to 30°C and centrifuge to obtain the recrystallized dimethyl 2,6-naphthalenedicarboxylate. Add the recrystallized dimethyl 2,6-naphthalenedicarboxylate to a distillation column for distillation. Under the conditions of reflux ratio of 6, column top pressure of 2 kPa, and column top temperature of 232°C, distillation is carried out to obtain dimethyl 2,6-naphthalenedicarboxylate.

[0032] Example 3 The preparation method of the supported catalyst includes the following steps: 30g of ammonium molybdate was dispersed in 500g of water, and 270g of molecular sieve was added. After stirring at 500rpm for 2h, a mixture was obtained. The mixture was dried and calcined in a muffle furnace at 600℃ for 6h to obtain a supported catalyst. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate includes the following steps: S1. 1000g of 2,6-naphthalenedicarboxylic acid and 10500g of methanol are pre-reacted in a tubular reactor at a temperature of 260℃. After staying in the tubular reactor for 10 minutes, the mixture is transferred to an autoclave and 100g of supported catalyst is added. The autoclave is heated to 120℃ and reacted for 6 hours. The mixture is then filtered to obtain liquid material. S2. After cooling the liquid material from 120°C to 25°C, filter to obtain a solid material. Add methanol (the amount of methanol added is 15 times the mass of the solid material) to recrystallize the solid material. After heating to 120°C, cool to 50°C and centrifuge to obtain the recrystallized dimethyl 2,6-naphthalenedicarboxylate. Add the recrystallized dimethyl 2,6-naphthalenedicarboxylate to a distillation column for distillation. Under the conditions of reflux ratio of 5, column top pressure of 1 kPa, and column top temperature of 214°C, distillation is carried out to obtain dimethyl 2,6-naphthalenedicarboxylate.

[0033] Example 4 The only difference between this embodiment and Embodiment 2 is that the reflux ratio is 2 during the distillation process in this embodiment.

[0034] Example 5 The only difference between this embodiment and Embodiment 2 is that the reflux ratio is 7 during the distillation process in this embodiment.

[0035] Example 6 The only difference between this embodiment and Example 2 is that the preparation method of the supported catalyst is different in this embodiment, specifically: 24g ammonium molybdate and 6g ammonium metatungstate were dispersed in 500g water, and 270g molecular sieve was added. After stirring at 500rpm for 2h, the mixture was filtered to obtain a mixture. The mixture was dried and calcined in a muffle furnace at 600℃ for 6h to obtain a supported catalyst.

[0036] Example 7 The only difference between this embodiment and Example 6 is that in the preparation method of the supported catalyst in this embodiment, 28.8g of ammonium molybdate and 1.2g of ammonium metatungstate are added.

[0037] Example 8 The only difference between this embodiment and Example 6 is that in the preparation method of the catalyst in this embodiment, 25.5g of ammonium molybdate and 4.5g of ammonium metatungstate are added.

[0038] Example 9 The only difference between this embodiment and Example 6 is that in the preparation method of the catalyst in this embodiment, 27g of ammonium molybdate and 3g of ammonium metatungstate are added.

[0039] Example 10 The only difference between this embodiment and Example 9 is that the preparation method of the supported catalyst is different in this embodiment, specifically: 27g ammonium molybdate and 3g ammonium metatungstate were dispersed in 500g water, and 240g molecular sieve was added. After stirring at 400rpm for 2.5h, a mixture was obtained. The mixture was dried and calcined in a muffle furnace at 580℃ for 6h to obtain a supported catalyst.

[0040] Example 11 The only difference between this embodiment and Example 9 is that the preparation method of the supported catalyst is different in this embodiment, specifically: 27g ammonium molybdate and 3g ammonium metatungstate were dispersed in 500g water, and 300g molecular sieve was added. After stirring at 600rpm for 1.5h, a mixture was obtained. The mixture was dried and calcined in a muffle furnace at 630℃ for 5h to obtain a supported catalyst.

[0041] Comparative Example 1 The only difference between this comparative example and Example 2 is that in this comparative example, the supported catalyst is replaced with an equal amount of sulfuric acid with a mass fraction of 98%.

[0042] Comparative Example 2 The only difference between this comparative example and Example 2 is that the supported catalyst is replaced with an equal amount of molybdenum trioxide in this comparative example.

[0043] Experimental Example The dimethyl 2,6-naphthalenedicarboxylates synthesized in Examples 1-11 and Comparative Examples 1-2 were tested and evaluated. During the testing and evaluation process, the dimethyl ether content in the liquid material was detected by gas chromatography, and the purity of the dimethyl 2,6-naphthalenedicarboxylates was determined by liquid chromatography. The purity after esterification is the purity of dimethyl 2,6-naphthalenedicarboxylate in the solid material obtained after cooling and crystallization of the liquid material; the purity after distillation is the purity of the final dimethyl 2,6-naphthalenedicarboxylate obtained. The yield of dimethyl 2,6-naphthalenedicarboxylate was determined by cooling and drying the liquid material after esterification. The yield of the solid material was calculated as: yield = mass of solid material × purity after esterification / theoretical mass of dimethyl 2,6-naphthalenedicarboxylate × 100%. The molten color after distillation was tested according to the method in GB / T 6324.7-2014 "Test Methods for Organic Chemical Products Part 7: Determination of Melt Color"; the test results are shown in Table 1.

[0044] Table 1 Test results of Examples 1-11 and Comparative Examples 1-2

[0045] Compared with Comparative Examples 1-2, in Examples 1-11, the yield of dimethyl 2,6-naphthalenedicarboxylate was increased after the esterification reaction during the synthesis of dimethyl 2,6-naphthalenedicarboxylate. This indicates that using a supported catalyst as a catalyst in the synthesis of dimethyl 2,6-naphthalenedicarboxylate through esterification can effectively improve the yield of dimethyl 2,6-naphthalenedicarboxylate.

[0046] Compared with Example 4, the purity of dimethyl 2,6-naphthalenedicarboxylate after distillation in Examples 1-3 was improved, indicating that controlling the reflux ratio in the distillation column to 3-6 resulted in higher purity of the final dimethyl 2,6-naphthalenedicarboxylate. Among them, although the purity of dimethyl 2,6-naphthalenedicarboxylate after distillation in Example 7 was slightly improved compared with Example 2, the energy consumption was high and the production efficiency was relatively low when the reflux ratio was 7. Therefore, the best overall effect was achieved when the reflux ratio was 3-6.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing dimethyl 2,6-naphthalenedicarboxylate, characterized in that, Includes the following steps: S1. 2,6-Naphthalenedicarboxylic acid and methanol are preheated and then fed into a high-pressure reactor. A catalyst is added, and the mixture is reacted in the high-pressure reactor. After filtration, a liquid material is obtained. S2. Cool the liquid material to crystallize, recrystallize, and distill to obtain the dimethyl 2,6-naphthalenedicarboxylate; The catalyst is a supported catalyst.

2. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 1, characterized in that, During the preheating treatment, a pre-reaction is carried out in a tubular reactor at a temperature of 240~260℃, and the residence time in the tubular reactor is 10~60min. The reaction in the autoclave is carried out at a temperature of 120°C for 3 to 6 hours.

3. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 1, characterized in that, The crystallization solvent for recrystallization includes methanol; The amount of methanol added is 8 to 15 times the mass of the solid material after the liquid material is cooled and crystallized.

4. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 3, characterized in that, The recrystallization process is as follows: after the liquid material is cooled and crystallized, a crystallization solvent is added to the solid material, the temperature is raised to 120°C in an autoclave, then cooled to 25~50°C, and the material is separated to obtain recrystallized dimethyl 2,6-naphthalenedicarboxylate.

5. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 1, characterized in that, During the distillation process, the reflux ratio in the distillation column is 3-6, and the pressure at the top of the column is 1-3 kPa.

6. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 1, characterized in that, The raw materials for the supported catalyst include a support and an active component precursor. The active component precursor includes ammonium molybdate.

7. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 6, characterized in that, The mass ratio of the carrier to the active component precursor is 8~10:

1.

8. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 6, characterized in that, The active component precursor also includes a water-soluble tungsten source; The mass ratio of the ammonium molybdate to the water-soluble tungsten source is 4~24:

1.

9. The method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to claim 8, characterized in that, The water-soluble tungsten source includes ammonium metatungstate.

10. A method for synthesizing dimethyl 2,6-naphthalenedicarboxylate according to any one of claims 6 to 9, characterized in that, The preparation method of the supported catalyst includes the following steps: dispersing the active component precursor in water, adding the support, mixing evenly to obtain a mixture, drying the mixture, and calcining it to obtain the supported catalyst.

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