Process and apparatus for refining 2,6-naphthalene dicarboxylic acid

Abstract

The application discloses a method and device for refining 2,6-naphthalene dicarboxylic acid. The method comprises the following steps: adding crude 2,6-naphthalene dicarboxylic acid, anhydrous methanol and a catalyst into an esterification reactor to perform an esterification reaction, so as to obtain crude 2,6-naphthalene dicarboxylic acid dimethyl ester; melting the crude 2,6-naphthalene dicarboxylic acid dimethyl ester into a continuous rectification tower to perform continuous rectification, so as to obtain rectified 2,6-naphthalene dicarboxylic acid dimethyl ester; adding the rectified 2,6-naphthalene dicarboxylic acid dimethyl ester and anhydrous methanol into a reaction kettle, so as to obtain 2,6-naphthalene dicarboxylic acid dimethyl ester after recrystallization in the reaction kettle; adding water and a hydrolysis catalyst into the reaction kettle to perform a hydrolysis reaction with the 2,6-naphthalene dicarboxylic acid dimethyl ester after recrystallization, so as to obtain hydrolyzed 2,6-naphthalene dicarboxylic acid in the reaction kettle; adding anhydrous methanol into the reaction kettle to dissolve the hydrolyzed 2,6-naphthalene dicarboxylic acid, so as to obtain refined 2,6-naphthalene dicarboxylic acid in the reaction kettle. The method for refining 2,6-naphthalene dicarboxylic acid has the advantages of high preparation efficiency and high yield.

Description

Technical Field

[0001] This invention relates to the field of coal chemical technology, specifically to a method and apparatus for refining 2,6-naphthalenedicarboxylic acid. Background Technology

[0002] 2,6-Naphthalenedicarboxylic acid (2,6NDA) is a key intermediate in high-end specialty polyesters, primarily used in the production of polyethylene 2,6-naphthalenedicarboxylic acid (PEN) and liquid crystal polymer (LCP) films. Currently, the main purification methods for 2,6-NDA are alkali dissolution-acid precipitation and esterification-hydrolysis, but both are intermittent operations requiring multiple material transfers. This not only results in low operational efficiency but also material waste during the transfer process, leading to low yields of high-purity 2,6-NDA. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, embodiments of the present invention provide a method for purifying 2,6-naphthalenedicarboxylic acid to improve the purification efficiency and yield of 2,6-naphthalenedicarboxylic acid.

[0005] The method for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention includes the following steps:

[0006] Step 1: Crude 2,6-naphthalenedicarboxylic acid, anhydrous methanol and catalyst are added to the esterification reactor to carry out the esterification reaction to obtain crude dimethyl 2,6-naphthalenedicarboxylic acid.

[0007] Step 2: The crude dimethyl 2,6-naphthalenedicarboxylate is melted and then continuously distilled in a distillation column to obtain distilled dimethyl 2,6-naphthalenedicarboxylate.

[0008] Step 3: Add the distilled 2,6-naphthalenedicarboxylate and anhydrous methanol to a reaction vessel to obtain recrystallized 2,6-naphthalenedicarboxylate in the reaction vessel;

[0009] Step four: Water and p-toluenesulfonic acid are added to the reaction vessel and hydrolyzed with the recrystallized dimethyl 2,6-naphthalenedicarboxylate to obtain hydrolyzed 2,6-naphthalenedicarboxylate in the reaction vessel;

[0010] Step 5: Add anhydrous methanol to the reaction vessel to dissolve the hydrolyzed 2,6-naphthalenedicarboxylic acid, and obtain purified 2,6-naphthalenedicarboxylic acid in the reaction vessel.

[0011] In some embodiments, in step three, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 5-7. The mixture is first stirred and heated to 140°C-160°C for 1.5-2.5 hours; then cooled to 60°C-80°C, with a pressure of 1.5 MPa-2.5 MPa inside the reactor. Afterward, the discharge port of the reactor is opened, and solid-liquid separation is achieved through a filter device located at the discharge port.

[0012] In some embodiments, in step three, after adding the distilled dimethyl 2,6-naphthalenedicarboxylate to the reaction vessel, an activated carbon bag wrapped with filter cloth is added to the reaction vessel, and then the mixture is stirred and heated to 140°C-160°C.

[0013] In some embodiments, in step three, the mass ratio of activated carbon in the activated carbon bag to crude dimethyl 2,6-naphthalenedicarboxylate is 2-4.

[0014] In some embodiments, in step four, firstly, the lid of the reactor is opened, and the activated carbon pack is removed from the reactor; then, water and p-toluenesulfonic acid are added to the reactor, the mass ratio of water to crude dimethyl 2,6-naphthalenedicarboxylate is 300-350, and the mass ratio of p-toluenesulfonic acid to crude dimethyl 2,6-naphthalenedicarboxylate is 0.5-0.8. The mixture is stirred and heated to 210℃-230℃ for 7-9 hours; then, it is cooled to 80℃-100℃, the pressure inside the reactor is 2.0MPa-3.0MPa, the discharge port of the reactor is opened, and solid-liquid separation is achieved through the filtration device.

[0015] In some embodiments, in step four, after opening the discharge port of the reactor, the liquid inside the reactor is first extracted by a vacuum pump; then the steam valve of the reactor is opened and heated to 100°C-120°C to evaporate the remaining liquid inside the reactor to the outside of the reactor.

[0016] In some embodiments, in step five, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 2.5-3.5. The mixture is first stirred and heated to 100°C-120°C for 0.5-1.2 hours, with a pressure of 0.3-0.4 MPa inside the reactor. Then, it is cooled to 70-80°C, the discharge port of the reactor is opened, and solid-liquid separation is achieved through the filtration device.

[0017] In some embodiments, in step five, after opening the discharge port of the reactor, the liquid inside the reactor is first extracted by a vacuum pump; then the steam valve of the reactor is opened and heated to 100°C-120°C to evaporate the remaining liquid inside the reactor to the outside of the reactor.

[0018] Embodiments of the present invention provide an apparatus for purifying 2,6-naphthalenedicarboxylic acid, thereby improving the purification efficiency and yield of 2,6-naphthalenedicarboxylic acid.

[0019] The apparatus for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention is used to implement the method for purifying 2,6-naphthalenedicarboxylic acid described in any of the above embodiments. The apparatus for purifying 2,6-naphthalenedicarboxylic acid includes:

[0020] A reaction vessel, comprising a vessel body and a vessel lid, the vessel lid being detachably connected to the vessel body, the top of the vessel body having an opening, the vessel lid being used to seal the opening so as to define a reaction chamber between the vessel body and the vessel lid, the bottom of the vessel body having a discharge port, and the vessel lid having a solid feed port, a liquid feed port, an exhaust port and a steam outlet;

[0021] A filtration device is disposed within the reaction chamber, with at least a portion of the filtration device located at the discharge port.

[0022] A condenser is provided outside the reaction chamber, and the condenser and the reaction chamber are connected through the steam outlet.

[0023] In some embodiments, the apparatus for refining 2,6-naphthalenedicarboxylic acid further includes a support, the vessel body is fixedly connected to the support, the support is provided with a slide rail extending along the height direction of the vessel body, and the vessel cover is provided with a slider, the slider being slidably engaged with the slide rail along the height direction of the vessel body.

[0024] The method for refining 2,6-naphthalenedicarboxylic acid in this embodiment of the invention only requires that crude dimethyl 2,6-naphthalenedicarboxylic acid obtained through esterification be distilled to obtain refined dimethyl 2,6-naphthalenedicarboxylic acid. The refined dimethyl 2,6-naphthalenedicarboxylic acid is then transferred to a reaction vessel. Subsequently, the recrystallization process of the crude dimethyl 2,6-naphthalenedicarboxylic acid, the hydrolysis process of the recrystallized dimethyl 2,6-naphthalenedicarboxylic acid, and the recrystallization process of 2,6-naphthalenedicarboxylic acid are all carried out in the same reaction vessel. This reduces the number of material transfers during the refining process of 2,6-naphthalenedicarboxylic acid, thereby not only improving the refining efficiency of 2,6-naphthalenedicarboxylic acid but also addressing the problem of low yield of 2,6-naphthalenedicarboxylic acid caused by material transfer. Attached Figure Description

[0025] Figure 1This is a flowchart of a method for preparing 2,6-naphthalenedicarboxylic acid according to an embodiment of the present invention.

[0026] Figure 2 A schematic diagram of the apparatus for preparing 2,6-naphthalenedicarboxylic acid according to an embodiment of the present invention.

[0027] Figure 3 yes Figure 2 A 3D view with the support structure removed.

[0028] Figure 4 yes Figure 3 The main view.

[0029] Figure label:

[0030] Apparatus 100 for refining 2,6-naphthalenedicarboxylic acid;

[0031] Reactor 1; Reactor body 101; Reactor cover 102; Reaction chamber 103; Solid feed port 104; Liquid feed port 105; Exhaust port 106; Discharge port 107; Steam outlet 108; Exhaust valve 109; Steam valve 110; Discharge valve 111; Filter device 112; Activated carbon bag 113; Heat exchange chamber 114; Medium inlet 115; Medium outlet 116;

[0032] Condenser 2;

[0033] Storage tank 3;

[0034] Vacuum pump 4;

[0035] First motor 5; stirrer 501; cooling coil 502;

[0036] Second motor 6;

[0037] Feed pipe 7;

[0038] Feed pipe 8;

[0039] Vacuum tube 9;

[0040] Bracket 10; slide rail 1001; slider 1002. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] like Figure 1 As shown, the method for purifying 2,6-naphthalenedicarboxylic acid according to an embodiment of the present invention includes the following steps:

[0043] S1, crude 2,6-naphthalenedicarboxylic acid (2,6-NDA), anhydrous methanol and catalyst are added to an esterification reactor to carry out an esterification reaction to obtain crude dimethyl 2,6-naphthalenedicarboxylic acid (2,6-NDC);

[0044] S2, crude dimethyl 2,6-naphthalenedicarboxylate is melted and then fed into a distillation column for continuous distillation to obtain distilled dimethyl 2,6-naphthalenedicarboxylate;

[0045] S3, Dimethyl 2,6-naphthalenedicarboxylate and anhydrous methanol are added to a reaction vessel, heated to dissolve, and then recrystallized dimethyl 2,6-naphthalenedicarboxylate is obtained in the reaction vessel through solid-liquid separation;

[0046] S4, water and p-toluenesulfonic acid are added to the reactor and hydrolyzed with the recrystallized dimethyl 2,6-naphthalenedicarboxylate. Hydrolyzed 2,6-naphthalenedicarboxylate is obtained in the reactor by solid-liquid separation.

[0047] S5. Anhydrous methanol is added to the reaction vessel to dissolve the hydrolyzed 2,6-naphthalenedicarboxylic acid. Purified 2,6-naphthalenedicarboxylic acid is obtained in the reaction vessel through solid-liquid separation.

[0048] In step one, the catalyst is concentrated sulfuric acid (9% w). The purity of the hydrolyzed 2,6-naphthalenedicarboxylic acid obtained in step four is greater than that of the crude 2,6-naphthalenedicarboxylic acid in step one, but less than that of the purified 2,6-naphthalenedicarboxylic acid obtained in step five.

[0049] The method for refining 2,6-naphthalenedicarboxylic acid according to an embodiment of the present invention involves: crude 2,6-naphthalenedicarboxylic acid undergoing esterification in an esterification reactor to obtain crude dimethyl 2,6-naphthalenedicarboxylic acid; the crude dimethyl 2,6-naphthalenedicarboxylic acid is continuously distilled through a distillation column to obtain distilled dimethyl 2,6-naphthalenedicarboxylic acid; the distilled dimethyl 2,6-naphthalenedicarboxylic acid is recrystallized in a reaction vessel to obtain recrystallized dimethyl 2,6-naphthalenedicarboxylic acid; the recrystallized dimethyl 2,6-naphthalenedicarboxylic acid undergoes hydrolysis in a reaction vessel to obtain hydrolyzed 2,6-naphthalenedicarboxylic acid; and the hydrolyzed 2,6-naphthalenedicarboxylic acid is recrystallized in a reaction vessel to obtain refined 2,6-naphthalenedicarboxylic acid.

[0050] The above-described purification process for 2,6-naphthalenedicarboxylic acid only requires the following steps: crude dimethyl 2,6-naphthalenedicarboxylic acid is obtained through esterification; the crude dimethyl 2,6-naphthalenedicarboxylic acid is then distilled to obtain refined dimethyl 2,6-naphthalenedicarboxylic acid; the refined dimethyl 2,6-naphthalenedicarboxylic acid is transferred to a reaction vessel; and the recrystallization processes of the crude dimethyl 2,6-naphthalenedicarboxylic acid, the hydrolysis of the recrystallized dimethyl 2,6-naphthalenedicarboxylic acid, and the recrystallization of 2,6-naphthalenedicarboxylic acid are all carried out in the same reaction vessel. This reduces the number of material transfers during the purification process, thereby not only improving the purification efficiency of 2,6-naphthalenedicarboxylic acid but also mitigating the problem of low yield caused by material transfers.

[0051] Therefore, the method for purifying 2,6-naphthalenedicarboxylic acid according to the embodiments of the present invention has the advantages of high efficiency in the preparation of 2,6-naphthalenedicarboxylic acid and high yield of 2,6-naphthalenedicarboxylic acid.

[0052] The esterification reactor described above can be any existing esterification reactor, which will not be elaborated further here. The reaction vessel described above can be any existing reaction vessel, or it can be the apparatus for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention. The apparatus for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0053] like Figures 2 to 4 As shown, the apparatus 100 for refining 2,6-naphthalenedicarboxylic acid according to an embodiment of the present invention includes a reaction vessel 1. The reaction vessel 1 includes a vessel body 101 and a vessel cover 102, the vessel cover 102 being detachably connected to the vessel body 101. The top of the vessel body 101 has an opening, and the vessel cover 102 is used to seal the opening so that a reaction chamber 103 is defined between the vessel body 101 and the vessel cover 102. The bottom of the vessel body 101 has a discharge port 107, and the vessel cover 102 has a solid feed port 104, a liquid feed port 105, an exhaust port 106, and a steam outlet 108. The liquid feed port 105 can be used to add anhydrous methanol, water, etc., into the reaction chamber 103; the solid feed port 104 can be used to add p-toluenesulfonic acid into the reaction chamber 103; and the discharge port 107 can be used to discharge the material from the reaction chamber 103.

[0054] The distillation column described above can be any existing distillation column, which will not be elaborated here.

[0055] The molten crude dimethyl 2,6-naphthalenedicarboxylate is purified by distillation in a distillation column, which can effectively improve the purity and color of crude dimethyl 2,6-naphthalenedicarboxylate, thereby effectively improving the purity and color of purified dimethyl 2,6-naphthalenedicarboxylate.

[0056] Optionally, crude dimethyl 2,6-naphthalenedicarboxylate is melted in a feed storage tank, and the heating temperature of crude dimethyl 2,6-naphthalenedicarboxylate is 195℃-200℃.

[0057] The crude dimethyl 2,6-naphthalenedicarboxylate melted in the feed storage tank is continuously pumped into the distillation column for distillation. At the top of the distillation column, lower-boiling-point light components (mainly water, anhydrous methanol, methyl 2-naphthaleneate, and trimethyl trimellitic acid) are removed, while dimethyl 2,6-naphthalenedicarboxylate is continuously collected via a side stream. Simultaneously, at the bottom of the distillation column, monomethyl 2,6-naphthalenedicarboxylate, various colored impurities, and a small amount of metal catalyst are removed.

[0058] Optionally, the operating pressure of the distillation column is 0.1 mbar-20 mbar, the bottom temperature is 210-270℃, and the number of theoretical plates is 5-7.

[0059] Optionally, dioctyl terephthalate is added to the bottom of the distillation column. The mass of dioctyl terephthalate added is 20%-30% of the mass of dimethyl 2,6-naphthalenedicarboxylate after recrystallization in step three. Adding dioctyl terephthalate to the bottom of the distillation column effectively prevents localized overheating and decomposition or color deterioration of dimethyl 2,6-naphthalenedicarboxylate, thus further improving the yield and color of 2,6-naphthalenedicarboxylic acid.

[0060] Optionally, the parts of the distillation column exposed to air may be equipped with heat tracing and insulation devices, with a heat tracing temperature of 190℃-205℃.

[0061] The apparatus 100 for refining 2,6-naphthalenedicarboxylic acid also includes a filter device 112, which is located in the reaction chamber 103, with at least a portion of the filter device 112 located at the discharge port 107.

[0062] At least a portion of the filter device 112 is located at the discharge port 107. This can be understood as: a portion of the filter device 112 is located at the discharge port 107, and another portion of the filter device 112 is located away from the discharge port 107; or, the entire filter device 112 is located at the discharge port 107.

[0063] For example, such as Figure 4 As shown, the filter device 112 is a filter barrel with an open top. The bottom of the filter barrel is located at the discharge port 107, and the side wall of the filter barrel is located inside the side wall of the vessel body 101. At this time, the material in the reaction chamber 103 is all located inside the filter barrel. Of course, the filter device can also be a filter plate, with the entire filter plate located at the discharge port.

[0064] Optionally, the filter device 112 is detachably connected to the vessel body 101.

[0065] For example, the vessel body 101 has an annular connecting plate, the top of the filter device 112 has an annular folded edge, the connecting plate has a connecting hole, and the folded edge has a fixing hole. The folded edge and the connecting plate are connected by fasteners passing through the fixing hole and the connecting hole. The fasteners can be bolts, screws, etc.

[0066] In some embodiments, in step three, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 5-7. First, the material in the reaction chamber 103 is stirred using a stirrer 501 mounted on the reactor 1, and heated to 140°C-160°C using a heat source mounted on the reactor 1. The stirring and heating time is 1.5-2.5 hours, and the pressure inside the reactor 1 is maintained at 1.5 MPa-2.5 MPa. Then, the material in the reaction chamber 103 is cooled to 60°C-80°C, causing the crude dimethyl 2,6-naphthalenedicarboxylate to recrystallize, forming recrystallized dimethyl 2,6-naphthalenedicarboxylate. Then, the discharge port 107 of the reactor 1 is opened. Under the pressure inside the reactor 1, the liquid material flows out of the reaction chamber 103 through the discharge port 107, while the solid material is blocked by the filter device 112 at the discharge port 107 and remains in the reaction chamber 103, thus achieving solid-liquid separation (liquid components such as dimethyl 2,6-naphthalenedicarboxylate and anhydrous methanol after recrystallization).

[0067] The discharge port 107 of the vessel body 101 is equipped with a discharge valve 111, and the opening and closing of the discharge port 107 is controlled by controlling the discharge valve 111. Figures 2 to 4 As shown, the stirrer 501 is driven by the first motor 5.

[0068] By setting the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate, as well as the reaction temperature, time, and pressure in reactor 1, it is beneficial to further improve the yield and color of 2,6-naphthalenedicarboxylate, and the operation is simple.

[0069] like Figure 4 As shown, the agitator 501 includes an agitator shaft and an agitator blade, and a cooling coil 502 is provided on the agitator shaft. Coolant can be circulated into the cooling coil 502 to cool the agitator shaft, preventing excessive heat transfer from the agitator blade to the first motor 5, which could damage the first motor 5.

[0070] Optionally, such as Figure 4 As shown, the vessel body 101 has a heat exchange chamber 114, which surrounds the reaction chamber 103. The vessel body 101 has a medium inlet 115 and a medium outlet 116 that communicate with the heat exchange chamber 114.

[0071] Therefore, a heating medium (such as heating oil) can be introduced into the heat exchange chamber 114 through the medium inlet 115 to heat the material in the reaction chamber 103. The heating medium, after heating the reaction chamber 103, flows out through the medium outlet 116. Alternatively, a cooling medium (such as cooling oil or cooling water) can be introduced into the heat exchange chamber 114 through the medium inlet 115 to cool the material in the reaction chamber 103. The cooling medium, after cooling the reaction chamber 103, flows out through the medium outlet 116.

[0072] Optionally, in step three, after adding the distilled dimethyl 2,6-naphthalenedicarboxylate to reactor 1, an activated carbon bag 113 wrapped with filter cloth is added to reactor 1, and then the mixture is stirred and heated to 140℃-160℃.

[0073] The activated carbon package 113 wrapped in filter cloth refers to the activated carbon package formed by using filter cloth to contain activated carbon. The activated carbon is wrapped in filter cloth before being added to the reaction vessel 1. On the one hand, the filter cloth prevents activated carbon particles from entering the reaction chamber 103 and mixing with the recrystallized dimethyl 2,6-naphthalenedicarboxylate, thus affecting the purity of the recrystallized dimethyl 2,6-naphthalenedicarboxylate. On the other hand, the filter cloth does not affect the contact between the activated carbon and other materials in the reaction chamber 103, allowing the activated carbon to adsorb colored impurities from other materials in the reaction chamber 103.

[0074] The color control of 2,6-naphthalenedicarboxylic acid in existing purification methods is inconsistent, and the synthesized and purified 2,6-naphthalenedicarboxylic acid has a yellowish color, which does not meet the requirements of the polymer product.

[0075] By adding activated carbon pack 113 wrapped with filter cloth to reaction vessel 1, the activated carbon in the activated carbon pack 113 can adsorb colored impurities in dimethyl 2,6-naphthalenedicarboxylate, thereby improving the color of the recrystallized dimethyl 2,6-naphthalenedicarboxylate and thus improving the color of refined 2,6-naphthalenedicarboxylate, which is beneficial to improving the quality of 2,6-naphthalenedicarboxylate.

[0076] Optionally, in step three, the mass ratio of activated carbon in activated carbon package 113 to crude dimethyl 2,6-naphthalenedicarboxylate is 2-4.

[0077] For example, the mass ratio of activated carbon to crude dimethyl 2,6-naphthalenedicarboxylate in activated carbon package 113 is 3.

[0078] By setting the mass ratio of activated carbon to crude dimethyl 2,6-naphthalenedicarboxylate to 2-4, the amount of activated carbon used can be reduced while ensuring the adsorption effect of activated carbon on colored impurities in dimethyl 2,6-naphthalenedicarboxylate, thus avoiding waste.

[0079] In some embodiments, in step four, firstly, the lid 102 of the reactor 1 is opened, and the activated carbon bag 113 is removed from the reactor 1. Then, water and p-toluenesulfonic acid are added to the reactor 1. The mass ratio of water to crude dimethyl 2,6-naphthalenedicarboxylate is 300-350, and the mass ratio of p-toluenesulfonic acid to crude dimethyl 2,6-naphthalenedicarboxylate is 0.5-0.8. The mixture is stirred using a stirrer 501 and heated to 210°C-230°C using a heat source set on the reactor 1, causing a hydrolysis reaction in the water, p-toluenesulfonic acid, and recrystallized dimethyl 2,6-naphthalenedicarboxylate. The stirring and heating time is 7-9 hours, and the pressure inside the reactor 1 is 2.0 MPa-3.0 MPa. Afterward, the material in the reaction chamber 103 is cooled to 80°C-100°C, causing 2,6-naphthalenedicarboxylate to crystallize, forming hydrolyzed 2,6-naphthalenedicarboxylate. Open the discharge port 107 of the reaction vessel 1, and achieve solid-liquid separation (hydrolyzed 2,6-naphthalenedicarboxylic acid and liquid components such as water and p-toluenesulfonic acid) through the filtration device 112.

[0080] By setting the mass ratio of water, p-toluenesulfonic acid, and crude dimethyl 2,6-naphthalenedicarboxylate, as well as the reaction temperature, time, and pressure in reactor 1, it is beneficial to further improve the yield and color of 2,6-naphthalenedicarboxylate, and the operation is simple.

[0081] Optionally, such as Figures 2 to 4 As shown, the apparatus 100 for refining 2,6-naphthalenedicarboxylic acid also includes a vacuum pump 4 and a storage tank 3. The storage tank 3 is connected to the discharge port 107 via a discharge pipe 8, and the vacuum pump 4 is connected to the storage tank 3 via a vacuum extraction pipe 9. The storage tank 3 is used to store the material flowing out of the discharge port 107. The vacuum pump 4 is used to perform a vacuum operation on the storage tank 3, creating a negative pressure inside the storage tank 3 so that the liquid material in the reaction chamber 103 can flow into the storage tank 3.

[0082] Optionally, in step four, after opening the discharge port 107 of the reactor 1, the liquid inside the reactor 1 is first extracted using the vacuum pump 4. Then, the steam valve 110 of the reactor 1 is opened, and the material in the reaction chamber 103 is heated to 100°C-120°C using the heat source provided on the reactor 1, thereby evaporating the residual liquid (e.g., water and p-toluenesulfonic acid) inside the reactor 1 to the outside of the reactor 1.

[0083] By evaporating the residual liquid inside reactor 1 to the outside of reactor 1, the purity of hydrolyzed 2,6-naphthalenedicarboxylic acid can be improved, which is beneficial to further improve the purity of purified 2,6-naphthalenedicarboxylic acid.

[0084] Optionally, such as Figures 2 to 4As shown, the apparatus 100 for refining 2,6-naphthalenedicarboxylic acid also includes a condenser 2, which is located outside the reaction chamber 103 and can be connected to the reaction chamber 103 via a steam outlet 108.

[0085] For example, such as Figure 3 and Figure 4 As shown, the steam outlet 108 is equipped with a steam valve 110, which can control the opening and closing of the condenser 2 and the reaction chamber 103 by controlling the steam valve 110.

[0086] Water and p-toluenesulfonic acid vapor flowing out through steam outlet 108 enter condenser 2, where condensation occurs, allowing the water and p-toluenesulfonic acid to be recovered. The recovered water and p-toluenesulfonic acid can be reused, which helps to improve material utilization and thus reduce the refining cost of 2,6-naphthalenedicarboxylic acid.

[0087] In some embodiments, in step five, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 2.5-3.5. First, the material in the reaction chamber 103 is stirred using a stirrer 501 mounted on the reactor 1, and heated to 100°C-120°C using a heat source mounted on the reactor 1. The stirring and heating time is 0.5-1.2 hours, and the pressure inside the reactor 1 is 0.3-0.4 MPa. Then, the material in the reaction chamber 103 is cooled to 70°C-80°C to recrystallize 2,6-naphthalenedicarboxylate, forming purified 2,6-naphthalenedicarboxylate. Then, the discharge port 107 of the reactor 1 is opened. Under the pressure inside the reactor 1, the liquid material flows out of the reaction chamber 103 through the discharge port 107, while the solid material is blocked by the filter device 112 at the discharge port 107 and remains in the reaction chamber 103, thus achieving solid-liquid (liquid components such as purified 2,6-naphthalenedicarboxylic acid and anhydrous methanol) separation.

[0088] By setting the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate, as well as the reaction temperature, time, and pressure in reactor 1, it is beneficial to further improve the yield and color of 2,6-naphthalenedicarboxylate, and the operation is simple.

[0089] Optionally, in step five, after opening the discharge port 107 of the reactor 1, the liquid inside the reactor 1 is first extracted by the vacuum pump 4. Then, the steam valve 110 of the reactor 1 is opened, and the material in the reaction chamber 103 is heated to 100°C-120°C using the heat source provided on the reactor 1, so that the residual liquid (e.g., anhydrous methanol) inside the reactor 1 is evaporated to the outside of the reactor 1.

[0090] The purity of purified 2,6-naphthalenedicarboxylic acid can be further improved by evaporating the residual liquid inside reactor 1 to the outside of reactor 1.

[0091] Optionally, the anhydrous methanol and dimethyl 2,6-naphthalenedicarboxylate solution discharged after recrystallization are returned to the esterification reactor in step one to continue the esterification reaction. The water and p-toluenesulfonic acid obtained through condenser 2 are returned to step four to continue the hydrolysis reaction.

[0092] Optionally, the exhaust port 106 is provided with an exhaust valve 109 so as to control the opening and closing of the exhaust port 106.

[0093] In some embodiments, the apparatus 100 for refining 2,6-naphthalenedicarboxylic acid further includes a support 10, and the vessel body 101 is fixedly connected to the support 10. The support 10 is provided with a slide rail 1001 extending along the height direction of the vessel body 101, and the vessel cover 102 is provided with a slider 1002, which slidably engages with the slide rail 1001 along the slide rail 1001.

[0094] For example, such as Figure 2 As shown, the height direction of the vessel body 101 is consistent with the vertical direction, the slide rail 1001 extends in the vertical direction, and the slider 1002 slidably cooperates with the slide rail 1001 in the vertical direction, thereby causing the vessel lid 102 to move in the vertical direction.

[0095] By setting a slide rail 1001 on the bracket 10 connected to the vessel body 101 and a slider 1002 on the vessel lid 102, the vessel lid 102 can move along a preset path when opening or closing the opening of the vessel body 101, which makes it convenient for the vessel lid 102 to be installed at the opening of the vessel body 101, and is beneficial to improving the purification efficiency of 2,6-naphthalenedicarboxylic acid.

[0096] Optionally, the vessel body 101 is detachably connected to the support 10. For example, the vessel body 101 and the support 10 are connected by bolts or screws.

[0097] Optionally, the lid 102 is connected to the body 101 by bolts or screws.

[0098] Optionally, the apparatus 100 for refining 2,6-naphthalenedicarboxylic acid also includes a second motor 6, which is a linear motor. The second motor 6 is fixed on the bracket 10 and connected to the slider 1002 so as to drive the vessel lid 102 to slide along the slide rail 1001.

[0099] By setting a second motor 6, the kettle cover 102 is driven to slide along the slide rail 1001, which facilitates the opening of the kettle cover 102 or the sealing of the opening of the kettle body 101, and helps to further improve the purification efficiency of 2,6-naphthalenedicarboxylic acid.

[0100] Optionally, such as Figures 2 to 4 As shown, a feeding pipe 7 is provided on the liquid feeding port 105, and liquid materials can be added into the reaction chamber 103 through the feeding pipe 7.

[0101] For example, the feed pipe 7 is connected to a peristaltic pump, which pumps liquid materials into the reaction chamber 103.

[0102] The apparatus for refining 2,6-naphthalenedicarboxylic acid in this embodiment of the invention can realize recrystallization-hydrolysis-hot washing operations in the same reactor 1, reducing the number of material transfers during the refining process of 2,6-naphthalenedicarboxylic acid. This not only helps to improve the refining efficiency of 2,6-naphthalenedicarboxylic acid, but also improves the problem of low yield of 2,6-naphthalenedicarboxylic acid caused by material transfer.

[0103] The method for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention is further described below through specific examples.

[0104] Example 1

[0105] Crude 2,6-naphthalenedicarboxylic acid (purity 94.0%) and anhydrous methanol were added to an esterification reactor at a mass ratio of 1:7.5. The esterification reaction was carried out at 160℃ and 2.2 MPa (gauge pressure) for 7 hours. After the reaction, the mixture was cooled, washed with deionized water, and filtered. The resulting yellow flaky crystals were crude dimethyl 2,6-naphthalenedicarboxylic acid, with a yield of 97.0%, a purity of 95.0%, and a color of 120.

[0106] Crude dimethyl 2,6-naphthalenedicarboxylate in the feed storage tank is melted at 195℃-200℃. The refined dimethyl 2,6-naphthalenedicarboxylate is continuously fed into a distillation column for continuous distillation. All air-exposed parts of the distillation column require heating at 190℃-205℃ and an operating pressure of 0.1mbar-20mbar. The bottom temperature is 210℃-270℃, and the theoretical number of plates in the distillation column is 7. At the top of the distillation column, lower-boiling-point light components (mainly water, anhydrous methanol, methyl 2-naphthaleneate, and trimethyl trimellitic acid) are removed, while the refined dimethyl 2,6-naphthalenedicarboxylate is continuously collected via a side stream. Simultaneously, at the bottom of the distillation column, monomethyl 2,6-naphthalenedicarboxylate, various colored impurities, and a small amount of metal catalyst are removed. To prevent localized overheating and decomposition or color deterioration of dimethyl 2,6-naphthalenedicarboxylate, 20%w-30%w of dioctyl terephthalate is added to the bottom of the distillation column.

[0107] Dimethyl 2,6-naphthalenedicarboxylate, obtained from the side stream distillation, is added to reactor 1, whose discharge port 107 is equipped with a filter device 112 (e.g., a pressure-resistant sand core filter plate). Then, an activated carbon bag 113 wrapped in filter cloth is added, the activated carbon in the bag being 3% of the mass of the crude dimethyl 2,6-naphthalenedicarboxylate. Anhydrous methanol is then added, with a mass ratio of anhydrous methanol to crude 2,6-naphthalenedicarboxylate of 7. The mixture is stirred and heated at 150°C and 2.0 MPa for 2 hours, and then cooled to 70°C. The discharge valve 111 is opened, and the solid and liquid are separated using the pressure of reactor 1. The steam valve 110 on the top of reactor lid 102 is opened, and the anhydrous methanol in reactor 1 is distilled and recovered by heating.

[0108] Open the reactor lid 102, remove the activated carbon pack 113 from the reactor body 101, and then replace the lid 102. Add water through the liquid feed port 105 and p-toluenesulfonic acid through the solid feed port 104. The mass of water is 320% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate, and the mass of p-toluenesulfonic acid is 0.74% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate. Hydrolyze the mixture at 220℃ and 2.5MPa for 8 hours with stirring. After the reaction, cool to 100℃ and use the pressure of the reactor 1 to separate the solid and liquid. Add a certain amount of distilled water through the liquid feed port 105 to wash the solid in the reactor body 101, and then turn on the vacuum pump 4 to extract the water. Open the steam valve 110 at the top of the reactor lid 102 and distill and recover the remaining liquid in the reactor 1 by heating.

[0109] Add anhydrous methanol, equivalent to three times the mass of crude dimethyl 2,6-naphthalenedicarboxylate, through the liquid feed port 105. Stir and dissolve at 100°C for 1 hour. Open the discharge valve 111 and use the pressure of the reactor 1 to separate the solid and liquid phases. Open the steam valve 110 at the top of the reactor lid 102 and distill and recover the anhydrous methanol in the reactor 1 by heating. Open the reactor lid 102 and remove high-purity 2,6-naphthalenedicarboxylic acid, with a purity >99.95% and a color <5.

[0110] Comparative Example 1

[0111] Crude 2,6-naphthalenedicarboxylic acid (purity 94.0%) and anhydrous methanol were added to an esterification reactor at a mass ratio of 1:7.5. The esterification reaction was carried out at 160℃ and 2.2 MPa (gauge pressure) for 7 hours. After the reaction, the mixture was cooled, washed with deionized water, and filtered. The resulting yellow flaky crystals were crude dimethyl 2,6-naphthalenedicarboxylic acid, with a yield of 97.0%, a purity of 95.0%, and a color of 120.

[0112] Crude dimethyl 2,6-naphthalenedicarboxylate in the feed storage tank is melted at 195℃-200℃. The refined dimethyl 2,6-naphthalenedicarboxylate is continuously fed into a distillation column for continuous distillation. All air-exposed parts of the distillation column require heating at 190℃-205℃ and an operating pressure of 0.1mbar-20mbar. The bottom temperature is 210℃-270℃, and the theoretical number of plates in the distillation column is 7. At the top of the distillation column, lower-boiling-point light components (mainly water, anhydrous methanol, methyl 2-naphthaleneate, and trimethyl trimellitic acid) are removed, while the refined dimethyl 2,6-naphthalenedicarboxylate is continuously collected via a side stream. Simultaneously, at the bottom of the distillation column, monomethyl 2,6-naphthalenedicarboxylate, various colored impurities, and a small amount of metal catalyst are removed. To prevent localized overheating and decomposition or color deterioration of dimethyl 2,6-naphthalenedicarboxylate, 20%w-30%w of dioctyl terephthalate is added to the bottom of the distillation column.

[0113] Dimethyl 2,6-naphthalenedicarboxylate, obtained from a side stream distillation, is added to reactor 1, which has a filter device 112 (e.g., a pressure-resistant sand core filter plate) at its discharge port 107. Anhydrous methanol is then added, with a mass ratio of anhydrous methanol to crude 2,6-naphthalenedicarboxylate of 77. The mixture is stirred and heated at 150°C and 2.0 MPa for 2 hours, then cooled to 70°C. The discharge valve 111 is opened, and the solid and liquid are separated using the pressure of reactor 1. The steam valve 110 at the top of reactor lid 102 is opened, and the anhydrous methanol in reactor 1 is distilled and recovered by heating.

[0114] Water is added through the liquid feed port 105, and p-toluenesulfonic acid is added through the solid feed port 104. The mass of water is 320% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate, and the mass of p-toluenesulfonic acid is 0.74% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate. Hydrolysis is carried out under stirring at 220℃ and 2.5MPa for 8 hours. After the reaction, the mixture is cooled to 100℃, and the solid and liquid are separated using the pressure of the reactor 1. A certain amount of distilled water is added through the liquid feed port 105 to wash the solid inside the reactor body 101, and the water is extracted by turning on the vacuum pump 4. The steam valve 110 on the top of the reactor lid 102 is opened, and the distilled water inside the reactor 1 is distilled and recovered by heating.

[0115] Add anhydrous methanol, equivalent to three times the mass of crude dimethyl 2,6-naphthalenedicarboxylate, through the liquid feed port 105. Stir and dissolve at 100°C for 1 hour. Open the discharge valve 111 and use the pressure of the reactor 1 to separate the solid and liquid phases. Open the steam valve 110 at the top of the reactor lid 102 and distill and recover the anhydrous methanol in the reactor 1 by heating. Open the reactor lid 102 and remove high-purity 2,6-naphthalenedicarboxylate, with a purity >99.95% and a color <60.

[0116] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, activated carbon packet 113 was not added during the recrystallization of dimethyl 2,6-naphthalenedicarboxylate. Activated carbon packet 113 can adsorb colored impurities in dimethyl 2,6-naphthalenedicarboxylate to reduce its color, thereby reducing the color of the purified 2,6-naphthalenedicarboxylate. When activated carbon packet 113 is added, the color of the purified 2,6-naphthalenedicarboxylate will be reduced.

[0117] Comparative Example 2

[0118] Crude 2,6-naphthalenedicarboxylic acid (purity 94.0%) and anhydrous methanol were added to an esterification reactor at a mass ratio of 1:7.5. The esterification reaction was carried out at 160℃ and 2.2 MPa (gauge pressure) for 7 hours. After the reaction, the mixture was cooled, washed with deionized water, and filtered. The resulting yellow flaky crystals were crude dimethyl 2,6-naphthalenedicarboxylic acid, with a yield of 97.0%, a purity of 95.0%, and a color of 120.

[0119] Crude dimethyl 2,6-naphthalenedicarboxylate was added to reactor 1, followed by an activated carbon bag 113 wrapped in filter cloth, the activated carbon in the bag being 3% of the mass of the crude dimethyl 2,6-naphthalenedicarboxylate. Anhydrous methanol was then added, with a mass ratio of anhydrous methanol to crude 2,6-naphthalenedicarboxylate of 7. The mixture was stirred and heated at 150°C and 2.0 MPa for 2 hours, then cooled to 70°C. The discharge valve 111 was opened, and the solid and liquid were separated using the pressure of reactor 1. The steam valve 110 on the top of reactor lid 102 was opened, and the remaining liquid in reactor 1 was distilled and recovered by heating.

[0120] Open the reactor lid 102, remove the activated carbon pack 113 from the reactor body 101, and then replace the lid 102. Add water through the liquid feed port 105 and p-toluenesulfonic acid through the solid feed port 104. The mass of water is 320% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate, and the mass of p-toluenesulfonic acid is 0.74% of the mass of crude dimethyl 2,6-naphthalenedicarboxylate. Hydrolyze the mixture at 220℃ and 2.5MPa for 8 hours with stirring. After the reaction, cool to 100℃ and use the pressure of the reactor 1 to separate the solid and liquid. Add a certain amount of distilled water through the liquid feed port 105 to wash the solid in the reactor body 101, and then turn on the vacuum pump 4 to extract the water. Open the steam valve 110 at the top of the reactor lid 102 and distill and recover the distilled water in the reactor 1 by heating.

[0121] Add anhydrous methanol, equivalent to three times the mass of crude dimethyl 2,6-naphthalenedicarboxylate, through the liquid feed port 105. Stir and dissolve at 100°C for 1 hour. Open the discharge valve 111 and use the pressure of the reactor 1 to separate the solid and liquid. Open the steam valve 110 at the top of the reactor lid 102 and distill and recover the remaining liquid in the reactor 1 by heating. Open the reactor lid 102 and remove high-purity 2,6-naphthalenedicarboxylate, with a purity <98.50% and a color <100.

[0122] The difference between Comparative Example 2 and Example 1 is that the crude dimethyl 2,6-naphthalenedicarboxylate obtained by recrystallization in Comparative Example 2 was not distilled in a distillation column but was directly added to reactor 1 for hydrolysis. After distillation, the crude dimethyl 2,6-naphthalenedicarboxylate contains fewer impurities, resulting in increased purity and decreased color of the purified 2,6-naphthalenedicarboxylate.

[0123] The method for purifying 2,6-naphthalenedicarboxylic acid according to embodiments of the present invention has the following advantages:

[0124] Multiple reaction processes are carried out in the same reactor 1, which avoids the problems of reduced yield and solvent waste caused by material transfer during batch operation, and the yield of high-purity 2,6-naphthalenedicarboxylic acid is high.

[0125] The purity of 2,6-naphthalenedicarboxylic acid obtained in the prior art is mostly above 99%. The 2,6-naphthalenedicarboxylic acid obtained by the present invention through hot methanol washing and hydrolysis removes trace amounts of M,M-NDC and D,M-NDC, and the purity of 2,6-naphthalenedicarboxylic acid reaches above 99.95%.

[0126] In the process of purifying 2,6-naphthalenedicarboxylic acid, this invention adds activated carbon packet 113 as a decolorizing agent, which can decolorize the product without contaminating it.

[0127] The reactor 1 is equipped with a filter device 112 for pressure filtration and rapid solid-liquid separation; the discharge port 107 can be connected to a vacuum pump 4 for suction filtration; the top of the reactor 1 is equipped with a condenser 2, which can distill and recover the solvent in the reactor 1.

[0128] By connecting distillation and recrystallization continuously, the energy consumption of reheating and melting 2,6-naphthalenedicarboxylic acid is avoided, thereby improving the purification and synthesis efficiency of 2,6-naphthalenedicarboxylic acid.

[0129] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0130] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0131] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0132] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0133] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0134] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for purifying 2,6-naphthalenedicarboxylic acid, characterized in that, Includes the following steps: Step 1: Crude 2,6-naphthalenedicarboxylic acid, anhydrous methanol and catalyst are added to the esterification reactor to carry out the esterification reaction to obtain crude dimethyl 2,6-naphthalenedicarboxylic acid. Step 2: The crude dimethyl 2,6-naphthalenedicarboxylate is melted and then continuously distilled in a distillation column to obtain distilled dimethyl 2,6-naphthalenedicarboxylate. Step 3: Add the distilled 2,6-naphthalenedicarboxylate and anhydrous methanol to the reaction vessel to obtain recrystallized 2,6-naphthalenedicarboxylate; then open the discharge port of the reaction vessel and achieve solid-liquid separation through the filter device installed at the discharge port of the reaction vessel. Step four: Add water and p-toluenesulfonic acid to the reaction vessel, stir and heat to 210℃-230℃ to hydrolyze the recrystallized dimethyl 2,6-naphthalenedicarboxylate, and obtain hydrolyzed 2,6-naphthalenedicarboxylic acid in the reaction vessel; then cool to 80℃-100℃, with the pressure inside the reaction vessel being 2.0MPa-3.0 MPa, open the discharge port of the reaction vessel, and achieve solid-liquid separation through the filtration device; Step 5: Add anhydrous methanol to the reaction vessel to dissolve the hydrolyzed 2,6-naphthalenedicarboxylic acid, obtaining purified 2,6-naphthalenedicarboxylic acid in the reaction vessel; first, stir and heat to 100℃-120℃ for 0.5h-1.2h, with a pressure of 0.3MPa-0.4MPa inside the reaction vessel; then cool to 70℃-80℃ to recrystallize the 2,6-naphthalenedicarboxylic acid, forming purified 2,6-naphthalenedicarboxylic acid; open the discharge port of the reaction vessel and achieve solid-liquid separation through the filtration device.

2. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 1, characterized in that, In step three, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 5-7. First, the mixture is stirred and heated to 140℃-160℃ for 1.5h-2.5h. Then, it is cooled to 60℃-80℃, and the pressure inside the reactor is 1.5MPa-2.5MPa.

3. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 2, characterized in that, In step three, after adding the distilled 2,6-naphthalenedicarboxylate to the reaction vessel, an activated carbon bag wrapped in filter cloth is added to the reaction vessel, and then the mixture is stirred and heated to 140°C-160°C.

4. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 3, characterized in that, In step three, the mass ratio of activated carbon in the activated carbon package to crude dimethyl 2,6-naphthalenedicarboxylate is 2-4.

5. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 3, characterized in that, In step four, firstly, the lid of the reactor is opened, and the activated carbon pack is removed from the reactor. Then, water and p-toluenesulfonic acid are added to the reactor. The mass ratio of water to crude dimethyl 2,6-naphthalenedicarboxylate is 300-350, and the mass ratio of p-toluenesulfonic acid to crude dimethyl 2,6-naphthalenedicarboxylate is 0.5-0.

8. The stirring and heating time is 7-9 hours.

6. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 5, characterized in that, In step four, after opening the discharge port of the reactor, the liquid inside the reactor is first extracted by a vacuum pump; then the steam valve of the reactor is opened and heated to 100℃-120℃ to evaporate the remaining liquid inside the reactor to the outside of the reactor.

7. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 2, characterized in that, In step five, the mass ratio of anhydrous methanol to crude dimethyl 2,6-naphthalenedicarboxylate is 2.5-3.

5.

8. The method for purifying 2,6-naphthalenedicarboxylic acid according to claim 7, characterized in that, In step five, after opening the discharge port of the reactor, the liquid inside the reactor is first extracted by a vacuum pump; then the steam valve of the reactor is opened and heated to 100℃-120℃ to evaporate the remaining liquid inside the reactor to the outside of the reactor.

Images