CN115650844A - Method and apparatus for purifying 2, 6-naphthalenedicarboxylic acid - Google Patents

Abstract

The invention discloses a method and a device for refining 2, 6-naphthalene dicarboxylic acid, and the method for refining the 2, 6-naphthalene dicarboxylic acid comprises the following steps: adding crude 2, 6-naphthalene dicarboxylic acid, anhydrous methanol and a catalyst into an esterification reactor for esterification reaction to obtain crude dimethyl 2, 6-naphthalene dicarboxylic acid; melting the crude dimethyl 2, 6-naphthalene dicarboxylate, feeding the melted crude dimethyl 2, 6-naphthalene dicarboxylate into a rectifying tower for continuous rectification to obtain rectified dimethyl 2, 6-naphthalene dicarboxylate; adding the rectified dimethyl 2, 6-naphthalenedicarboxylate and anhydrous methanol into a reaction kettle to obtain recrystallized dimethyl 2, 6-naphthalenedicarboxylate in the reaction kettle; adding water and a hydrolysis catalyst into a reaction kettle, and performing hydrolysis reaction on the water and the recrystallized dimethyl 2, 6-naphthalene dicarboxylate to obtain hydrolyzed 2, 6-naphthalene dicarboxylate in the reaction kettle; adding anhydrous methanol into a reaction kettle to dissolve the hydrolyzed 2, 6-naphthalenedicarboxylic acid, and obtaining refined 2, 6-naphthalenedicarboxylic acid in the reaction kettle. The method for refining the 2, 6-naphthalenedicarboxylic acid provided by the embodiment of the invention has the advantages of high preparation efficiency, high yield and the like.

Description

Method and apparatus for purifying 2, 6-naphthalenedicarboxylic acid

Technical Field

The invention relates to the technical field of coal chemical industry, in particular to a method and a device for refining 2, 6-naphthalene dicarboxylic acid.

Background

2, 6-naphthalenedicarboxylic acid (2, 6 NDA) is a key intermediate for high-end specialty polyesters, and is used primarily for the production of polyethylene 2, 6-naphthalate (PEN) and Liquid Crystal Polymer (LCP) films. At present, the 2,6-NDA purification method mainly adopts an alkali dissolution-acid precipitation method and an esterification-hydrolysis method, but the purification method is operated in an intermittent mode, and multiple material transfer is needed, so that the operation efficiency is low, the material transfer process causes material waste, and the yield of the high-purity 2,6-NDA is low.

Disclosure of Invention

The present invention is directed to solving, at least in part, one of the technical problems in the related art.

Therefore, the examples of the present invention propose a method for purifying 2, 6-naphthalenedicarboxylic acid to improve the purification efficiency and yield of 2, 6-naphthalenedicarboxylic acid.

The method for refining 2, 6-naphthalenedicarboxylic acid according to the embodiment of the invention comprises the steps of:

adding crude 2, 6-naphthalene dicarboxylic acid, anhydrous methanol and a catalyst into an esterification reactor for esterification reaction to obtain crude dimethyl 2, 6-naphthalene dicarboxylic acid;

step two, melting the crude dimethyl 2, 6-naphthalene dicarboxylate, and then entering a rectifying tower for continuous rectification to obtain rectified dimethyl 2, 6-naphthalene dicarboxylate;

adding the rectified dimethyl 2, 6-naphthalene dicarboxylate and anhydrous methanol into a reaction kettle, and obtaining recrystallized dimethyl 2, 6-naphthalene dicarboxylate in the reaction kettle;

adding water and p-toluenesulfonic acid into the reaction kettle, and carrying out hydrolysis reaction on the water and the recrystallized dimethyl 2, 6-naphthalenedicarboxylate to obtain hydrolyzed 2, 6-naphthalenedicarboxylic acid in the reaction kettle;

and step five, adding anhydrous methanol into the reaction kettle to dissolve the hydrolyzed 2, 6-naphthalenedicarboxylic acid, and obtaining refined 2, 6-naphthalenedicarboxylic acid in the reaction kettle.

In some embodiments, in step three, the mass ratio of the anhydrous methanol to the crude dimethyl 2, 6-naphthalenedicarboxylate is from 5 to 7, and the mixture is first stirred and heated to 140 ℃ to 160 ℃ for from 1.5h to 2.5h; then cooling to 60-80 ℃, wherein the pressure value in the reaction kettle is 1.5-2.5 MPa; and then opening a discharge port of the reaction kettle, and realizing solid-liquid separation through a filtering device arranged at the discharge port of the reaction kettle.

In some embodiments, in step three, after the rectified dimethyl 2, 6-naphthalene dicarboxylate is added to the reaction kettle, a filter cloth wrapped activated carbon bag is added to the reaction kettle, followed by stirring and heating to 140 ℃ to 160 ℃.

In some embodiments, in step three, the mass ratio of the activated carbon in the activated carbon pack to the crude dimethyl 2, 6-naphthalate is from 2 to 4.

In some embodiments, in the fourth step, the cover of the reaction kettle is firstly opened, and the activated carbon bag is taken out of the reaction kettle; then adding water and p-toluenesulfonic acid into the reaction kettle, wherein the mass ratio of the water to the crude dimethyl 2, 6-naphthalenedicarboxylate is 300-350, the mass ratio of the p-toluenesulfonic acid to the crude dimethyl 2, 6-naphthalenedicarboxylate is 0.5-0.8, stirring and heating to 210-230 ℃, and the stirring and heating time is 7-9 h; and then cooling to 80-100 ℃, wherein the pressure value in the reaction kettle is 2.0-3.0 MPa, opening a discharge hole of the reaction kettle, and realizing solid-liquid separation through the filtering device.

In some embodiments, in the fourth step, after the discharge port of the reaction kettle is opened, the liquid in the reaction kettle is firstly pumped out by a vacuum pump; then opening a steam valve of the reaction kettle, heating to 100-120 ℃, and evaporating the residual liquid in the reaction kettle to the outside of the reaction kettle.

In some embodiments, in the fifth step, the mass ratio of the anhydrous methanol to the crude dimethyl 2, 6-naphthalenedicarboxylate is 2.5-3.5, the mixture is first stirred and heated to 100-120 ℃, the stirring and heating time is 0.5-1.2 h, and the pressure value in the reaction kettle is 0.3-0.4 MPa; then cooling to 70-80 ℃, opening a discharge port of the reaction kettle, and realizing solid-liquid separation through the filtering device.

In some embodiments, in the fifth step, after the discharge port of the reaction kettle is opened, the liquid in the reaction kettle is firstly pumped out by a vacuum pump; then opening a steam valve of the reaction kettle, heating to 100-120 ℃, and evaporating the residual liquid in the reaction kettle to the outside of the reaction kettle.

The embodiment of the invention provides a device for refining 2, 6-naphthalene dicarboxylic acid, which is used for improving the refining efficiency and yield of the 2, 6-naphthalene dicarboxylic acid.

The apparatus for purifying 2, 6-naphthalenedicarboxylic acid according to an embodiment of the present invention is used for carrying out the method for purifying 2, 6-naphthalenedicarboxylic acid according to any one of the above embodiments, and the apparatus for purifying 2, 6-naphthalenedicarboxylic acid comprises:

the reaction kettle comprises a kettle body and a kettle cover, wherein the kettle cover is separably connected with the kettle body, the top of the kettle body is provided with an opening, the kettle cover is used for plugging the opening so as to define a reaction chamber between the kettle body and the kettle cover, the bottom of the kettle body is provided with a discharge hole, and the kettle cover is provided with a solid feed inlet, a liquid feed inlet, an exhaust port and a steam outlet;

the filtering device is arranged in the reaction chamber, and at least one part of the filtering device is positioned at the discharge port;

the condenser is arranged outside the reaction cavity, and the condenser and the reaction cavity can be communicated through the steam outlet.

In some embodiments, the apparatus for refining 2, 6-naphthalenedicarboxylic acid further comprises a support, the kettle body is fixedly connected to the support, the support is provided with a slide rail extending along the height direction of the kettle body, the kettle cover is provided with a slide block, and the slide block is slidably engaged with the slide rail along the height direction of the kettle body.

In the method for refining 2, 6-naphthalenedicarboxylic acid according to the embodiment of the invention, only the crude dimethyl 2, 6-naphthalenedicarboxylate obtained by esterification, the crude dimethyl 2, 6-naphthalenedicarboxylate obtained by rectification, the rectified dimethyl 2, 6-naphthalenedicarboxylate are transferred to the reaction vessel, and then the recrystallization of the crude dimethyl 2, 6-naphthalenedicarboxylate, the hydrolysis of the recrystallized dimethyl 2, 6-naphthalenedicarboxylate and the recrystallization of the 2, 6-naphthalenedicarboxylic acid are all carried out in the same reaction vessel, so that the number of times of transfer of the materials in the refining process of the 2, 6-naphthalenedicarboxylic acid can be reduced, thereby not only improving the refining efficiency of the 2, 6-naphthalenedicarboxylic acid, but also improving the problem of low yield of the 2, 6-naphthalenedicarboxylic acid caused by material transfer.

Drawings

FIG. 1 is a flow chart of a process for producing 2, 6-naphthalenedicarboxylic acid according to one embodiment of the invention.

FIG. 2 is a schematic view showing the construction of an apparatus for producing 2, 6-naphthalenedicarboxylic acid according to an embodiment of the invention.

Fig. 3 is a perspective view of the bracket of fig. 2 with the bracket removed.

Fig. 4 is a front view of fig. 3.

Reference numerals are as follows:

an apparatus 100 for purifying 2, 6-naphthalenedicarboxylic acid;

a reaction kettle 1; a kettle body 101; a kettle cover 102; a reaction chamber 103; a solids feed inlet 104; a liquid feed port 105; an exhaust port 106; a discharge port 107; a steam outlet 108; an exhaust valve 109; a steam valve 110; a discharge valve 111; a filter device 112; an activated carbon pack 113; a heat exchange chamber 114; a media inlet 115; a media outlet 116;

a condenser 2;

a material storage tank 3;

a vacuum pump 4;

a first motor 5; a stirrer 501; a cooling coil 502;

a second motor 6;

a feed tube 7;

a discharge pipe 8;

a vacuum-pumping tube 9;

a support 10; a slide rail 1001; a slider 1002.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are illustrative and intended to explain the present invention and should not be construed as limiting the present invention.

As shown in FIG. 1, the method for purifying 2, 6-naphthalenedicarboxylic acid according to the embodiment of the invention comprises the steps of:

s1, adding crude 2, 6-naphthalene dicarboxylic acid (2, 6-NDA), anhydrous methanol and a catalyst into an esterification reactor for esterification reaction to obtain crude dimethyl 2, 6-naphthalene dicarboxylate (2, 6-NDC);

s2, melting the crude dimethyl 2, 6-naphthalene dicarboxylate, and then, continuously rectifying in a rectifying tower to obtain the rectified dimethyl 2, 6-naphthalene dicarboxylate;

s3, adding the rectified dimethyl 2, 6-naphthalenedicarboxylate and anhydrous methanol into a reaction kettle, heating and dissolving, and obtaining recrystallized dimethyl 2, 6-naphthalenedicarboxylate in the reaction kettle through solid-liquid separation;

s4, adding water and p-toluenesulfonic acid into a reaction kettle, carrying out hydrolysis reaction on the p-toluenesulfonic acid and the recrystallized dimethyl 2, 6-naphthalene dicarboxylate, and carrying out solid-liquid separation to obtain hydrolyzed 2, 6-naphthalene dicarboxylate in the reaction kettle;

s5, adding absolute methanol into the reaction kettle to dissolve the hydrolyzed 2, 6-naphthalenedicarboxylic acid, and obtaining refined 2, 6-naphthalenedicarboxylic acid in the reaction kettle through solid-liquid separation.

Wherein, in the first step, the catalyst is concentrated sulfuric acid (9% w). The purity of the hydrolyzed 2, 6-naphthalenedicarboxylic acid obtained through the fourth step is higher than that of the crude 2, 6-naphthalenedicarboxylic acid obtained through the first step and lower than that of the purified 2, 6-naphthalenedicarboxylic acid obtained through the fifth step.

In the method for refining the 2, 6-naphthalenedicarboxylic acid, crude 2, 6-naphthalenedicarboxylic acid is subjected to esterification reaction in an esterification reactor to obtain crude dimethyl 2, 6-naphthalenedicarboxylate; continuously rectifying the crude dimethyl 2, 6-naphthalene dicarboxylate by a rectifying tower to obtain rectified dimethyl 2, 6-naphthalene dicarboxylate; recrystallizing the rectified dimethyl 2, 6-naphthalenedicarboxylate in a reaction kettle to obtain recrystallized dimethyl 2, 6-naphthalenedicarboxylate; the recrystallized 2, 6-naphthalene dicarboxylic acid dimethyl ester is subjected to hydrolysis reaction in a reaction kettle to obtain hydrolyzed 2, 6-naphthalene dicarboxylic acid; the hydrolyzed 2, 6-naphthalenedicarboxylic acid is recrystallized in a reaction vessel to obtain refined 2, 6-naphthalenedicarboxylic acid.

In the refining process of the 2, 6-naphthalenedicarboxylic acid, only the crude dimethyl 2, 6-naphthalenedicarboxylate obtained by the esterification reaction, the rectified dimethyl 2, 6-naphthalenedicarboxylate obtained by rectifying the crude dimethyl 2, 6-naphthalenedicarboxylate, and the rectified dimethyl 2, 6-naphthalenedicarboxylate are transferred to the reaction vessel, and then the recrystallization process of the crude dimethyl 2, 6-naphthalenedicarboxylate, the hydrolysis process of the recrystallized dimethyl 2, 6-naphthalenedicarboxylate, and the recrystallization process of the 2, 6-naphthalenedicarboxylic acid are all performed in the same reaction vessel, so that the number of times of transferring the materials in the refining process of the 2, 6-naphthalenedicarboxylic acid can be reduced, thereby not only improving the refining efficiency of the 2, 6-naphthalenedicarboxylic acid, but also improving the problem of low yield of the 2, 6-naphthalenedicarboxylic acid caused by the transfer of the materials.

Therefore, the method for purifying 2, 6-naphthalenedicarboxylic acid according to the embodiment of the invention has advantages such as high efficiency of producing 2, 6-naphthalenedicarboxylic acid and high yield of 2, 6-naphthalenedicarboxylic acid.

The esterification reactor can be an esterification reactor in the prior art, and the details are not repeated. The reaction kettle can adopt a reaction kettle in the prior art, and can also adopt a device for refining the 2, 6-naphthalene dicarboxylic acid in the embodiment of the invention. An apparatus for purifying 2, 6-naphthalenedicarboxylic acid according to an embodiment of the invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 2 to 4, an apparatus 100 for purifying 2, 6-naphthalenedicarboxylic acid according to an embodiment of the invention comprises a reaction vessel 1. The reaction kettle 1 comprises a kettle body 101 and a kettle cover 102, wherein the kettle cover 102 is detachably connected with the kettle body 101. The kettle body 101 has an opening at the top, and the kettle cover 102 is used for sealing the opening, so that a reaction chamber 103 is defined between the kettle body 101 and the kettle cover 102. The bottom of the kettle body 101 is provided with a discharge port 107, and the kettle cover 102 is provided with a solid feed port 104, a liquid feed port 105, an exhaust port 106 and a steam outlet 108. Wherein, the liquid feed opening 105 can be used for adding anhydrous methanol, water and the like into the reaction chamber 103; a solids feed port 104 may be used to add p-toluenesulfonic acid to reaction chamber 103; the drain 107 may be used to drain the reaction chamber 103.

The rectifying tower can adopt a rectifying tower in the prior art, and the details are not repeated.

The melted crude dimethyl 2, 6-naphthalenedicarboxylate is rectified by a rectifying tower, so that the purity and the chromaticity of the crude dimethyl 2, 6-naphthalenedicarboxylate can be effectively improved, and the purity and the chromaticity of the crude dimethyl 2, 6-naphthalenedicarboxylate can be effectively improved.

Alternatively, the crude dimethyl 2, 6-naphthalenedicarboxylate is melted in a feed storage tank, and the heating temperature of the crude dimethyl 2, 6-naphthalenedicarboxylate is 195 ℃ to 200 ℃.

The crude 2, 6-naphthalenedicarboxylic acid dimethyl ester melted in the feed storage tank continuously enters a rectifying tower through a pump for rectification. Light components (mainly water, anhydrous methanol, methyl 2-naphthoate and trimethyl trimellitate) with lower boiling points are removed from the top of the rectifying tower, dimethyl 2, 6-naphthalenedicarboxylate is continuously extracted from the lateral line, and monomethyl 2, 6-naphthalenedicarboxylate, various colored impurities and a small amount of metal catalyst are removed from the bottom of the rectifying tower.

Optionally, the operating pressure of the rectifying tower is 0.1mbar-20mbar, the tower bottom temperature is 210-270 ℃, and the theoretical plate number of the rectifying tower is 5-7.

Optionally, dioctyl terephthalate is added to the bottom of the rectification column. Wherein the mass of the dioctyl terephthalate is 20 to 30 percent of the mass of the recrystallized dimethyl 2, 6-naphthalene dicarboxylate in the step three. By adding dioctyl terephthalate to the bottom of the rectifying tower, local overheat decomposition or color deterioration of dimethyl 2, 6-naphthalene dicarboxylate can be effectively prevented, and the yield and chromaticity of 2, 6-naphthalene dicarboxylate can be further improved.

Optionally, a heat tracing heat preservation device is additionally arranged at the part of the rectifying tower exposed in the air, and the heat tracing temperature is 190-205 ℃.

The apparatus 100 for purifying 2, 6-naphthalenedicarboxylic acid further comprises a filter 112, wherein the filter 112 is provided in the reaction chamber 103 and at least a part of the filter 112 is located at the discharge port 107.

At least a portion of the filtering means 112 is located at the discharge opening 107, which can be understood as: one part of the filtering device 112 is positioned at the discharge port 107, and the other part of the filtering device 112 is arranged far away from the discharge port 107; alternatively, the filtering device 112 is located entirely at the discharge port 107.

For example, as shown in fig. 4, the filtering device 112 is a filtering barrel with an open top, the bottom of the filtering barrel is located at the discharge port 107, and the side wall of the filtering barrel is located inside the side wall of the kettle body 101, at this time, the materials in the reaction chamber 103 are all located in the filtering barrel. Of course, the filtering device can also be a filtering plate, and the filtering plate is integrally positioned at the discharge opening.

Optionally, the filtering device 112 is detachably connected with the kettle body 101.

For example, an annular connecting plate is arranged in the kettle body 101, an annular flange is arranged at the top of the filtering device 112, a connecting hole is arranged on the connecting plate, a fixing hole is arranged on the flange, and the flange and the connecting plate are connected through a fastener penetrating through the fixing hole and the connecting hole. Wherein the fastener may be a bolt, a screw, or the like.

In some embodiments, the mass ratio of anhydrous methanol to crude dimethyl 2, 6-naphthalenedicarboxylate in step three is 5 to 7. Firstly, the stirrer 501 arranged on the reaction kettle 1 is used for stirring the materials in the reaction chamber 103, the heat source arranged on the reaction kettle 1 is used for heating the materials in the reaction chamber 103 to 140-160 ℃, the stirring and heating time is 1.5-2.5 h, and the pressure in the reaction kettle 1 is kept at 1.5-2.5 MPa. The contents of reaction chamber 103 are then cooled to 60-80 c to recrystallize the crude dimethyl 2, 6-naphthalenedicarboxylate to form the recrystallized dimethyl 2, 6-naphthalenedicarboxylate. Then, the discharge port 107 of the reaction vessel 1 is opened, the liquid material flows out of the reaction chamber 103 through the discharge port 107 under the pressure action in the reaction vessel 1, the fixed material is blocked by the filtering device 112 at the discharge port 107 and remains in the reaction chamber 103, and the solid-liquid separation (the recrystallized dimethyl 2, 6-naphthalate and the liquid components such as anhydrous methanol) is realized.

Wherein, the drain 107 of the kettle body 101 is provided with a drain valve 111, and the opening and closing of the drain 107 is controlled by controlling the drain valve 111. As shown in fig. 2 to 4, the agitator 501 is driven by the first motor 5.

The quality ratio of the anhydrous methanol to the crude dimethyl 2, 6-naphthalene dicarboxylate and the reaction temperature, time and pressure in the reaction kettle 1 are set, so that the yield and the chromaticity of the 2, 6-naphthalene dicarboxylic acid are further improved, and the operation is simple.

As shown in fig. 4, the stirrer 501 includes a stirring shaft and a stirring paddle, and the stirring shaft is provided with a cooling coil 502. From this, can lead to the coolant liquid in to cooling coil 502 to cooling off the (mixing) shaft, avoid the too much transmission of heat of stirring rake to first motor 5, lead to first motor 5 to damage.

Alternatively, as shown in fig. 4, the kettle body 101 has a heat exchange chamber 114, the heat exchange chamber 114 is disposed around the reaction chamber 103, and the kettle body 101 has a medium inlet 115 and a medium outlet 116 which are communicated with the heat exchange chamber 114.

Therefore, a heating medium (for example, 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, and the heated heating medium in the reaction chamber 103 flows out through the medium outlet 116. The 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, and the cooled cooling medium flows out of the reaction chamber 103 through the medium outlet 116.

Alternatively, in step three, after adding the rectified dimethyl 2, 6-naphthalene dicarboxylate to reaction tank 1, activated carbon pack 113 wrapped with filter cloth was added to reaction tank 1, followed by stirring and heating to 140 ℃ to 160 ℃.

Wherein, the activated carbon bag 113 wrapped by the filter cloth is as follows: the activated carbon pack 113 is formed by the filter cloth including activated carbon. The active carbon is wrapped by the filter cloth and then added into the reaction kettle 1, on one hand, the filter cloth can be used for preventing active carbon particles from entering the reaction chamber 103 and mixing with the recrystallized dimethyl 2, 6-naphthalene dicarboxylate to influence the purity of the recrystallized dimethyl 2, 6-naphthalene dicarboxylate; on the other hand, the filter cloth does not influence the contact of the activated carbon with other materials in the reaction chamber 103, so that the activated carbon can adsorb colored impurities in other materials in the reaction chamber 103.

In the purification method of the prior art, the chromaticity of the 2, 6-naphthalenedicarboxylic acid is controlled to be uneven, and the synthesized and purified 2, 6-naphthalenedicarboxylic acid has yellow color and cannot meet the requirements of polymerization products.

By adding the activated carbon bag 113 wrapped by the filter cloth into the reaction kettle 1, the activated carbon in the activated carbon bag 113 can be used for adsorbing colored impurities in the dimethyl 2, 6-naphthalenedicarboxylate, and the chroma of the recrystallized dimethyl 2, 6-naphthalenedicarboxylate is improved, so that the chroma of the 2, 6-naphthalenedicarboxylate can be improved, and the improvement of the quality of the 2, 6-naphthalenedicarboxylate is facilitated.

Alternatively, in step three, the mass ratio of the activated carbon in the activated carbon pack 113 to the crude dimethyl 2, 6-naphthalenedicarboxylate is 2 to 4.

For example, the mass ratio of the activated carbon in the activated carbon pack 113 to the crude dimethyl 2, 6-naphthalenedicarboxylate was 3.

By setting the mass ratio of the activated carbon to the crude dimethyl 2, 6-naphthalenedicarboxylate to 2-4, the usage amount of the activated carbon can be reduced and the waste of the activated carbon can be avoided while the adsorption effect of the activated carbon on colored impurities in the dimethyl 2, 6-naphthalenedicarboxylate is ensured.

In some embodiments, in step four, first, kettle lid 102 of reaction kettle 1 is opened and activated carbon bag 113 is removed from reaction kettle 1. Then, adding water and p-toluenesulfonic acid into the reaction kettle 1, wherein the mass ratio of the water to the crude dimethyl 2, 6-naphthalenedicarboxylate is 300-350, the mass ratio of the p-toluenesulfonic acid to the crude dimethyl 2, 6-naphthalenedicarboxylate is 0.5-0.8, stirring by using a stirrer 501, and heating to 210-230 ℃ by using a heat source arranged on the reaction kettle 1, so that the water, the p-toluenesulfonic acid and the recrystallized dimethyl 2, 6-naphthalenedicarboxylate are subjected to hydrolysis reaction. Wherein the stirring and heating time is 7-9 h, and the pressure value in the reaction kettle 1 is 2.0-3.0 MPa. The contents of the reaction chamber 103 are then cooled to 80-100 c to crystallize the 2, 6-naphthalenedicarboxylic acid, forming hydrolyzed 2, 6-naphthalenedicarboxylic acid. The drain port 107 of the reaction vessel 1 was opened, and solid-liquid separation (liquid components such as water and p-toluenesulfonic acid from the hydrolyzed 2, 6-naphthalenedicarboxylic acid) was effected by the filtration device 112.

The setting of the mass ratio of the water to the p-toluenesulfonic acid to the crude dimethyl 2, 6-naphthalenedicarboxylate and the setting of the reaction temperature, the reaction time and the reaction pressure in the reaction kettle 1 are beneficial to further improving the yield and the chromaticity of the 2, 6-naphthalenedicarboxylate, and the operation is simple.

Alternatively, as shown in fig. 2 to 4, the apparatus 100 for refining 2, 6-naphthalenedicarboxylic acid further comprises a vacuum pump 4 and a storage tank 3, wherein the storage tank 3 is communicated with the discharge port 107 through a discharge pipe 8, and the vacuum pump 4 is communicated with the storage tank 3 through an evacuation pipe 9. Wherein, the storage tank 3 is used for storing the material flowing out from the discharge port 107. The vacuum pump 4 is used for performing a vacuum operation on the material storage tank 3, so that a negative pressure is formed in the material storage tank 3, and the liquid material in the reaction chamber 103 flows into the material storage tank 3.

Alternatively, in the fourth step, after the discharge port 107 of the reaction vessel 1 is opened, the liquid in the reaction vessel 1 is first pumped out by the vacuum pump 4. Then, a steam valve 110 of the reaction kettle 1 is opened, the material in the reaction chamber 103 is heated to 100-120 ℃ by using a heat source arranged on the reaction kettle 1, and the residual liquid (such as water and p-toluenesulfonic acid) in the reaction kettle 1 is evaporated to the outside of the reaction kettle 1.

By evaporating the residual liquid in the reaction vessel 1 to the outside of the reaction vessel 1, the purity of the hydrolyzed 2, 6-naphthalenedicarboxylic acid can be improved, which is advantageous for further improving the purity of the 2, 6-naphthalenedicarboxylic acid.

Alternatively, as shown in FIGS. 2 to 4, the apparatus 100 for purifying 2, 6-naphthalenedicarboxylic acid further comprises a condenser 2, wherein the condenser 2 is provided outside the reaction chamber 103, and the condenser 2 and the reaction chamber 103 can be connected through a vapor outlet 108.

For example, as shown in fig. 3 and 4, the steam outlet 108 is provided with a steam valve 110, and the opening and closing of the condenser 2 and the reaction chamber 103 can be controlled by controlling the steam valve 110.

The water and the paratoluenesulfonic acid steam flowing out through the steam outlet 108 enter the condenser 2 and are condensed in the condenser 2, so that the water and the paratoluenesulfonic acid are recovered, the recovered water and the paratoluenesulfonic acid can be reused, the material utilization rate is favorably improved, and the refining cost of the 2, 6-naphthalenedicarboxylic acid is favorably reduced.

In some embodiments, in step five, the mass ratio of anhydrous methanol to crude dimethyl 2, 6-naphthalenedicarboxylate is from 2.5 to 3.5. Firstly, the stirrer 501 arranged on the reaction kettle 1 is used for stirring the materials in the reaction chamber 103, the heat source arranged on the reaction kettle 1 is used for heating the materials in the reaction chamber 103 to 100-120 ℃, the stirring and heating time is 0.5-1.2 h, and the pressure value in the reaction kettle 1 is 0.3-0.4 MPa. The contents of the reaction chamber 103 are then cooled to 70-80 c to recrystallize the 2, 6-naphthalenedicarboxylic acid to form purified 2, 6-naphthalenedicarboxylic acid. Then, the discharge port 107 of the reaction vessel 1 is opened, the liquid material flows out of the reaction chamber 103 through the discharge port 107 under the pressure action in the reaction vessel 1, and the solid material is blocked by the filtering device 112 at the discharge port 107 and remains in the reaction chamber 103, thereby realizing the separation of solid and liquid (liquid components such as refined 2, 6-naphthalenedicarboxylic acid and anhydrous methanol).

The quality ratio of the anhydrous methanol to the crude dimethyl 2, 6-naphthalene dicarboxylate and the reaction temperature, time and pressure in the reaction kettle 1 are set, so that the yield and the chromaticity of the 2, 6-naphthalene dicarboxylic acid are further improved, and the operation is simple.

Alternatively, in step five, after the discharge port 107 of the reaction vessel 1 is opened, first, the liquid in the reaction vessel 1 is pumped out by the vacuum pump 4. Then, a steam valve 110 of the reaction kettle 1 is opened, the material in the reaction chamber 103 is heated to 100 ℃ to 120 ℃ by using a heat source arranged on the reaction kettle 1, and the residual liquid (such as anhydrous methanol) in the reaction kettle 1 is evaporated to the outside of the reaction kettle 1.

The purity of 2, 6-naphthalenedicarboxylic acid can be further improved by evaporating the residual liquid in reaction vessel 1 to the outside of reaction vessel 1.

Optionally, the anhydrous methanol and the monoester solution of 2, 6-dimethyl naphthalene dicarboxylate discharged after recrystallization are returned to the esterification reactor in the first step to continue the esterification reaction. The water obtained by the condenser 2 and p-toluenesulfonic acid were returned to the fourth step to continue the hydrolysis reaction.

Optionally, the exhaust port 106 is provided with an exhaust valve 109, so that the opening and closing of the exhaust port 106 are controlled by the exhaust valve 109.

In some embodiments, the apparatus 100 for purifying 2, 6-naphthalenedicarboxylic acid further comprises a frame 10, and the vessel 101 is fixedly connected to the frame 10. The support 10 is provided with a slide rail 1001 extending along the height direction of the kettle body 101, the kettle cover 102 is provided with a slide block 1002, and the slide block 1002 is slidably matched with the slide rail 1001 along the slide rail 1001.

For example, as shown in fig. 2, the height direction of the kettle body 101 coincides with the up-down direction, the slide rails 1001 extend in the up-down direction, and the slide blocks 1002 slidably engage with the slide rails 1001 in the up-down direction, so that the kettle cover 102 moves in the up-down direction.

The slide rails 1001 are arranged on the bracket 10 connected with the kettle body 101, and the slide blocks 1002 are arranged on the kettle cover 102, so that the kettle cover 102 can move along a preset path when opening or closing the opening of the kettle body 101, the kettle cover 102 is conveniently covered on the opening of the kettle body 101, and the refining efficiency of the 2, 6-naphthalenedicarboxylic acid is improved.

Optionally, the kettle 101 is detachably connected to the support 10. For example, the kettle 101 is connected to the support 10 by bolts or screws.

Optionally, the kettle cover 102 is connected to the kettle body 101 through bolts or screws.

Optionally, the apparatus 100 for refining 2, 6-naphthalenedicarboxylic acid further comprises a second motor 6, wherein the second motor 6 is a linear motor, the second motor 6 is fixed to the frame 10, and the second motor 6 is connected to the slide block 1002 so that the kettle cover 102 is driven by the second motor 6 to slide along the slide rails 1001.

By arranging the second motor 6, the kettle cover 102 is driven by the second motor 6 to slide along the slide rail 1001, so that the kettle cover 102 can be conveniently opened or the opening of the kettle body 101 can be conveniently plugged, and the refining efficiency of the 2, 6-naphthalenedicarboxylic acid can be further improved.

Alternatively, as shown in fig. 2 to 4, a feeding pipe 7 is provided on the liquid feeding port 105, and the liquid material may be fed into the reaction chamber 103 through the feeding pipe 7.

For example, the feed tube 7 is connected to a peristaltic pump, and liquid materials are pumped into the reaction chamber 103 by the peristaltic pump.

The device for refining the 2, 6-naphthalenedicarboxylic acid provided by the embodiment of the invention can realize recrystallization-hydrolysis-hot washing operation in the same reaction kettle 1, and reduces the transfer times of materials in the refining process of the 2, 6-naphthalenedicarboxylic acid, thereby being beneficial to improving the refining efficiency of the 2, 6-naphthalenedicarboxylic acid and solving the problem of low yield of the 2, 6-naphthalenedicarboxylic acid caused by material transfer.

The process for purifying 2, 6-naphthalenedicarboxylic acid according to the examples of the present invention will be further described below by way of specific examples.

Example 1

Adding the prepared crude 2, 6-naphthalene dicarboxylic acid (with the purity of 94.0%) and anhydrous methanol into an esterification reactor, wherein the mass ratio of the crude 2, 6-naphthalene dicarboxylic acid to the anhydrous methanol is 1:7.5, the esterification reaction was carried out at 160 ℃ under 2.2MPa (gauge pressure) for 7 hours. After the reaction is finished, the temperature is reduced, deionized water is used for washing and suction filtration, and the obtained yellow flaky crystal is crude dimethyl 2, 6-naphthalene dicarboxylate, the yield is 97.0 percent, the purity is 95.0 percent, and the chroma is 120.

Melting crude dimethyl 2, 6-naphthalene dicarboxylate in a feed storage tank at 195-200 ℃, continuously introducing the rectified dimethyl 2, 6-naphthalene dicarboxylate into a rectifying tower for continuous rectification, wherein the heat tracing temperature is 190-205 ℃, the operating pressure is 0.1-20 mbar, the tower bottom temperature is 210-270 ℃, and the theoretical plate number of the rectifying tower is 7. Removing light components (mainly comprising water, anhydrous methanol, methyl 2-naphthoate and trimethyl trimellitate) with lower boiling point from the top of the rectifying tower, and continuously extracting rectified dimethyl 2, 6-naphthalenedicarboxylate from a lateral line; meanwhile, the 2, 6-naphthalene dicarboxylic acid monomethyl ester, various colored impurities and a small amount of metal catalyst are removed from the bottom of the rectifying tower. In order to prevent local overheating decomposition or color deterioration of dimethyl 2, 6-naphthalenedicarboxylate, 20% w-30% w of dioctyl terephthalate was added to the bottom of the rectifying column.

The rectified dimethyl-2, 6-naphthalenedicarboxylate taken off at the side is fed into a reaction vessel 1, and a discharge port 107 of the reaction vessel 1 is provided with a filtration device 112 (e.g., a sand core filter plate having a pressure resistance). Then adding an activated carbon bag 113 wrapped by filter cloth, wherein the mass of the activated carbon in the activated carbon bag 113 is 3 percent of the mass of the crude dimethyl 2, 6-naphthalene dicarboxylate. Then, anhydrous methanol was added thereto, and the mass ratio of the anhydrous methanol to the crude 2, 6-naphthalenedicarboxylic acid was 7. The mixture was heated with stirring at 150 ℃ under 2.0MPa for 2 hours, and the mixture was cooled to 70 ℃. The discharge valve 111 is opened to separate solid from liquid by the pressure of the reaction vessel 1. The steam valve 110 at the top of the cover 102 is opened, and the anhydrous methanol in the reaction vessel 1 is distilled and recovered by heating.

The kettle cover 102 is opened, the activated carbon bag 113 in the kettle body 101 is taken out and then covered on the kettle cover 102, water is added through the liquid feed opening 105, paratoluenesulfonic acid is introduced through the solid feed opening 104, the mass of the water is 320 percent of the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate, and the mass of the paratoluenesulfonic acid is 0.74 percent of the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate. Stirring and hydrolyzing for 8 hours at 220 ℃ and 2.5MPa. After the reaction is finished, the reaction kettle is cooled to 100 ℃, and solid and liquid are separated by utilizing the pressure of the reaction kettle 1. A certain amount of distilled water was added through the liquid feed port 105 to wash the solids in the vessel body 101, and the vacuum pump 4 was turned on to pump out the water. The steam valve 110 at the top of the vessel cover 102 is opened, and the residual liquid in the reaction vessel 1 is distilled and recovered by heating.

Through the liquid feed port 105, 3 times of anhydrous methanol equivalent to the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate was added, and the mixture was dissolved under stirring at 100 ℃ for 1 hour, and the discharge valve 111 was opened to separate the solid from the liquid under the pressure of the reaction vessel 1. The steam valve 110 at the top of the vessel cover 102 is opened, and the anhydrous methanol in the reaction vessel 1 is distilled and recovered by heating. The kettle cover 102 is opened, and the high-purity 2, 6-naphthalene dicarboxylic acid is taken out, wherein the purity is more than 99.95 percent, and the chroma is less than 5.

Comparative example 1

Adding the prepared crude 2, 6-naphthalene dicarboxylic acid (with the purity of 94.0%) and anhydrous methanol into an esterification reactor, wherein the mass ratio of the crude 2, 6-naphthalene dicarboxylic acid to the anhydrous methanol is 1:7.5, esterification reaction is carried out at 160 ℃ and 2.2MPa (gauge pressure) for 7 hours. After the reaction is finished, the temperature is reduced, deionized water is used for washing and suction filtration, and the obtained yellow flaky crystal is crude dimethyl 2, 6-naphthalene dicarboxylate, the yield is 97.0 percent, the purity is 95.0 percent, and the chroma is 120.

Melting crude dimethyl 2, 6-naphthalenedicarboxylate in a feeding storage tank at 195-200 ℃, continuously introducing rectified dimethyl 2, 6-naphthalenedicarboxylate into a rectifying tower for continuous rectification, wherein the parts of the rectifying tower exposed to air need heat tracing, the heat tracing temperature is 190-205 ℃, the operating pressure is 0.1-20 mbar, the tower bottom temperature is 210-270 ℃, and the theoretical plate number of the rectifying tower is 7. Removing light components (mainly comprising water, anhydrous methanol, methyl 2-naphthoate and trimethyl trimellitate) with lower boiling point from the top of the rectifying tower, and continuously extracting rectified dimethyl 2, 6-naphthalenedicarboxylate from a lateral line; meanwhile, the bottom of the rectifying tower removes 2, 6-naphthalene dicarboxylic acid monomethyl ester, various colored impurities and a small amount of metal catalyst. In order to prevent local overheating decomposition or color deterioration of dimethyl 2, 6-naphthalenedicarboxylate, 20% w-30% w of dioctyl terephthalate was added to the bottom of the rectifying column.

The rectified dimethyl-2, 6-naphthalenedicarboxylate taken off at the side is introduced into a reaction vessel 1, and a discharge port 107 of the reaction vessel 1 is provided with a filter device 112 (e.g., a sand core filter plate having pressure resistance). Then, absolute methanol was added, and the mass ratio of the absolute methanol to the crude 2, 6-naphthalenedicarboxylic acid was 77. The mixture was heated with stirring at 150 ℃ under 2.0MPa for 2 hours, and the mixture was cooled to 70 ℃. The discharge valve 111 is opened to separate solid from liquid by the pressure of the reaction vessel 1. The steam valve 110 at the top of the cover 102 is opened, and the anhydrous methanol in the reaction vessel 1 is distilled and recovered by heating.

Water was added through a liquid feed port 105, and p-toluenesulfonic acid was introduced through a solid feed port 104, the mass of water was 320% of the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate, and the mass of p-toluenesulfonic acid was 0.74% of the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate. Stirring and hydrolyzing for 8 hours at 220 ℃ and 2.5MPa. After the reaction is finished, the reaction kettle is cooled to 100 ℃, and solid and liquid are separated by utilizing the pressure of the reaction kettle 1. A certain amount of distilled water was added through the liquid feed port 105 to wash the solids in the vessel body 101, and the vacuum pump 4 was turned on to pump out the water. The steam valve 110 at the top of the vessel cover 102 is opened, and the distilled water in the reaction vessel 1 is distilled and recovered by heating.

Through the liquid feed port 105, 3 times of anhydrous methanol equivalent to the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate was added, and the mixture was dissolved under stirring at 100 ℃ for 1 hour, and the discharge valve 111 was opened to separate the solid from the liquid under the pressure of the reaction vessel 1. The steam valve 110 at the top of the cover 102 is opened, and the anhydrous methanol in the reaction vessel 1 is distilled and recovered by heating. The kettle cover 102 is opened, and the high-purity 2, 6-naphthalene dicarboxylic acid is taken out, wherein the purity is more than 99.95 percent, and the chroma is less than 60.

Comparative example 1 differs from example 1 in that: in comparative example 1, no activated carbon packet 113 was added during recrystallization of the rectified dimethyl 2, 6-naphthalenedicarboxylate. The activated carbon pack 113 can adsorb colored impurities in the dimethyl-2, 6-naphthalenedicarboxylate to reduce the color of the dimethyl-2, 6-naphthalenedicarboxylate, thereby reducing the color of the purified 2, 6-naphthalenedicarboxylic acid, and when the activated carbon pack 113 is added, the color of the purified 2, 6-naphthalenedicarboxylic acid is reduced.

Comparative example 2

Adding the prepared crude 2, 6-naphthalene dicarboxylic acid (with the purity of 94.0%) and anhydrous methanol into an esterification reactor, wherein the mass ratio of the crude 2, 6-naphthalene dicarboxylic acid to the anhydrous methanol is 1:7.5, the esterification reaction was carried out at 160 ℃ under 2.2MPa (gauge pressure) for 7 hours. After the reaction is finished, the temperature is reduced, deionized water is used for washing and suction filtration, and the obtained yellow flaky crystal is crude dimethyl 2, 6-naphthalene dicarboxylate, the yield is 97.0 percent, the purity is 95.0 percent, and the chroma is 120.

Adding the crude dimethyl 2, 6-naphthalenedicarboxylate into a reaction kettle 1, and then adding an activated carbon bag 113 wrapped by filter cloth, wherein the mass of activated carbon in the activated carbon bag 113 is 3% of that of the crude dimethyl 2, 6-naphthalenedicarboxylate. Then, anhydrous methanol was added thereto in a mass ratio of 7 with respect to the crude 2, 6-naphthalenedicarboxylic acid. The mixture was heated with stirring at 150 ℃ under 2.0MPa for 2 hours, and cooled to 70 ℃. The discharge valve 111 is opened to separate solid from liquid by the pressure of the reaction vessel 1. The steam valve 110 at the top of the vessel cover 102 is opened, and the residual liquid in the reaction vessel 1 is distilled and recovered by heating.

The kettle cover 102 is opened, the activated carbon bag 113 in the kettle body 101 is taken out and then covered on the kettle cover 102, water is added through the liquid feed opening 105, and p-toluenesulfonic acid is fed through the solid feed opening 104, the mass of the water is 320% of the mass of the crude dimethyl 2, 6-naphthalene dicarboxylate, and the mass of the p-toluenesulfonic acid is 0.74% of the mass of the crude dimethyl 2, 6-naphthalene dicarboxylate. Stirring and hydrolyzing for 8 hours at 220 ℃ and 2.5MPa. After the reaction is finished, the reaction kettle is cooled to 100 ℃, and solid and liquid are separated by utilizing the pressure of the reaction kettle 1. Through the liquid feed port 105, a certain amount of distilled water is added to wash the solids in the kettle body 101, and the vacuum pump 4 is turned on to pump out the water. The steam valve 110 at the top of the vessel cover 102 is opened, and the distilled water in the reaction vessel 1 is distilled and recovered by heating.

Through the liquid feed port 105, 3 times of anhydrous methanol equivalent to the mass of the crude dimethyl 2, 6-naphthalenedicarboxylate was added, and the mixture was dissolved under stirring at 100 ℃ for 1 hour, and the discharge valve 111 was opened to separate the solid from the liquid under the pressure of the reaction vessel 1. The steam valve 110 at the top of the vessel cover 102 is opened, and the residual liquid in the reaction vessel 1 is distilled and recovered by heating. The kettle cover 102 is opened, and the high-purity 2, 6-naphthalene dicarboxylic acid is taken out, wherein the purity is less than 98.50 percent, and the chroma is less than 100.

Comparative example 2 differs from example 1 in that: in comparative example 2, the crude dimethyl 2, 6-naphthalenedicarboxylate obtained by recrystallization was directly charged into the reaction vessel 1 without being rectified by a rectifying column to conduct hydrolysis reaction. After the crude dimethyl 2, 6-naphthalenedicarboxylate is rectified, the impurities in the crude dimethyl 2, 6-naphthalenedicarboxylate are less, and the purity of the obtained refined 2, 6-naphthalenedicarboxylic acid is increased and the chroma is reduced.

The method for refining the 2, 6-naphthalenedicarboxylic acid of the embodiment of the invention has the following advantages:

a plurality of reaction processes are carried out in the same reaction kettle 1, so that the problems of yield reduction and solvent waste caused by material transfer in intermittent operation are avoided, and the yield of the obtained high-purity 2, 6-naphthalenedicarboxylic acid is higher;

the purity of 2, 6-naphthalene dicarboxylic acid obtained in the prior art is mostly more than 99 percent, and the invention purifies and hydrolyzes the obtained 2, 6-naphthalene dicarboxylic acid by washing with hot methanol, thereby removing trace M, M-NDC and D, and the purity of M-NDC and 2, 6-naphthalene dicarboxylic acid reaches more than 99.95 percent.

In the process of purifying the 2, 6-naphthalene dicarboxylic acid, the activated carbon bag 113 is added as a decoloring agent, so that the product can be decolored and cannot be contaminated by impurities.

The reaction kettle 1 is internally provided with a filtering device 112 for filter pressing and rapid solid-liquid separation; the discharge port 107 can be connected with a vacuum pump 4 for suction filtration; the reaction vessel 1 has a condenser 2 at the top thereof, and the solvent in the reaction vessel 1 can be recovered by distillation.

The rectification and the recrystallization are continuous, so that the energy consumption for reheating and melting the 2, 6-naphthalenedicarboxylic acid is avoided, and the purification and synthesis efficiency of the 2, 6-naphthalenedicarboxylic acid is improved.

In the description of the present invention, it is to 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", "circumferential", and the like, indicate orientations or positional relationships based on those shown in the drawings, merely for the purpose of facilitating description and simplifying description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore, should not be considered as limiting the invention.

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

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; either mechanically or electrically or in communication with each other; either directly or indirectly through intervening media, either internally or in any combination, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "above," and "over" a second feature may be directly on or obliquely above the second feature, or simply mean that the first feature is at a higher level than the second feature. A first feature "under," "below," and "beneath" a second feature may be directly or obliquely under the first feature or may simply mean that the first feature is at a lesser elevation than the second feature.

In the present disclosure, the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" and the like mean that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Moreover, various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described, it is understood that the above embodiments are illustrative and not to be construed as limiting the present invention and that many changes, modifications, substitutions and alterations can be made in the above embodiments by one of ordinary skill in the art without departing from the scope of the present invention.

Claims (10)

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

adding crude 2, 6-naphthalene dicarboxylic acid, anhydrous methanol and a catalyst into an esterification reactor for esterification reaction to obtain crude dimethyl 2, 6-naphthalene dicarboxylate;

step two, melting the crude dimethyl 2, 6-naphthalene dicarboxylate, and then entering a rectifying tower for continuous rectification to obtain rectified dimethyl 2, 6-naphthalene dicarboxylate;

step three: adding the rectified dimethyl 2, 6-naphthalene dicarboxylate and anhydrous methanol into a reaction kettle, and obtaining recrystallized dimethyl 2, 6-naphthalene dicarboxylate in the reaction kettle;

adding water and p-toluenesulfonic acid into the reaction kettle, and carrying out hydrolysis reaction on the water and the recrystallized dimethyl 2, 6-naphthalenedicarboxylate to obtain hydrolyzed 2, 6-naphthalenedicarboxylic acid in the reaction kettle;

and step five, adding anhydrous methanol into the reaction kettle to dissolve the hydrolyzed 2, 6-naphthalenedicarboxylic acid, and obtaining refined 2, 6-naphthalenedicarboxylic acid in the reaction kettle.

2. The method for refining 2, 6-naphthalenedicarboxylic acid according to claim 1, wherein in said third step, said anhydrous methanol and said crude dimethyl 2, 6-naphthalenedicarboxylate are mixed and heated at a mass ratio of 5 to 7 under stirring and heating to 140 ℃ to 160 ℃ for 1.5 to 2.5 hours; then cooling to 60-80 ℃, wherein the pressure value in the reaction kettle is 1.5-2.5 MPa; and then opening a discharge port of the reaction kettle, and realizing solid-liquid separation through a filtering device arranged at the discharge port of the reaction kettle.

3. The method of purifying 2, 6-naphthalenedicarboxylic acid according to claim 2, wherein in the third step, after said rectified dimethyl 2, 6-naphthalenedicarboxylate is added to said reaction vessel, an activated carbon pack wrapped with a filter cloth is added to said reaction vessel, followed by stirring and heating to 140 ℃ to 160 ℃.

4. The method of purifying 2, 6-naphthalenedicarboxylic acid according to claim 3, wherein the mass ratio of the activated carbon in said activated carbon pack to the crude dimethyl 2, 6-naphthalenedicarboxylate in the third step is 2 to 4.

5. The method of purifying 2, 6-naphthalenedicarboxylic acid according to claim 3, wherein in said fourth step, a vessel lid of said reaction vessel is first opened, and said activated carbon pack is taken out from said reaction vessel; then adding water and p-toluenesulfonic acid into the reaction kettle, wherein the mass ratio of the water to the crude dimethyl 2, 6-naphthalene dicarboxylate is 300-350, the mass ratio of the p-toluenesulfonic acid to the crude dimethyl 2, 6-naphthalene dicarboxylate is 0.5-0.8, stirring and heating to 210-230 ℃, and the stirring and heating time is 7-9 h; and then cooling to 80-100 ℃, wherein the pressure value in the reaction kettle is 2.0-3.0 MPa, opening a discharge hole of the reaction kettle, and realizing solid-liquid separation through the filtering device.

6. A process for purifying 2, 6-naphthalenedicarboxylic acid as claimed in claim 5, wherein in said fourth step, after opening a discharge port of said reaction vessel, the liquid in said reaction vessel is first withdrawn by a vacuum pump; then opening a steam valve of the reaction kettle, heating to 100-120 ℃, and evaporating the residual liquid in the reaction kettle to the outside of the reaction kettle.

7. The method of purifying 2, 6-naphthalenedicarboxylic acid as set forth in claim 2, wherein in said step five, said anhydrous methanol and said crude dimethyl 2, 6-naphthalenedicarboxylate are stirred and heated at 100 ℃ to 120 ℃ for 0.5h to 1.2h in a mass ratio of 2.5 to 3.5, and the pressure in said reaction vessel is set to 0.3MPa to 0.4MPa; then cooling to 70-80 ℃, opening a discharge port of the reaction kettle, and realizing solid-liquid separation through the filtering device.

8. A method for purifying 2, 6-naphthalenedicarboxylic acid as claimed in claim 7, wherein in said fifth step, after opening a drain port of said reaction vessel, the liquid in said reaction vessel is first pumped out by a vacuum pump; then opening a steam valve of the reaction kettle, heating to 100-120 ℃, and evaporating the residual liquid in the reaction kettle to the outside of the reaction kettle.

9. An apparatus for purifying 2, 6-naphthalenedicarboxylic acid, which apparatus is used for carrying out the method for purifying 2, 6-naphthalenedicarboxylic acid according to any one of claims 1 to 8, and which apparatus for purifying 2, 6-naphthalenedicarboxylic acid comprises:

the reaction kettle comprises a kettle body and a kettle cover, wherein the kettle cover is separably connected with the kettle body, the top of the kettle body is provided with an opening, the kettle cover is used for plugging the opening so as to define a reaction chamber between the kettle body and the kettle cover, the bottom of the kettle body is provided with a discharge port, and the kettle cover is provided with a solid feed inlet, a liquid feed inlet, an exhaust port and a steam outlet;

the filtering device is arranged in the reaction chamber, and at least one part of the filtering device is positioned at the discharge port; and

the condenser is arranged outside the reaction cavity, and the condenser and the reaction cavity can be communicated through the steam outlet.

10. The apparatus for refining 2, 6-naphthalenedicarboxylic acid according to claim 9, further comprising a support, wherein said kettle body is fixedly connected to said support, said support is provided with a slide rail extending in the height direction of said kettle body, said kettle cover is provided with a slide block, and said slide block is slidably engaged with said slide rail in the height direction of said kettle body.

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