KR101073068B1 - Process for refining of 2,6-naphthalene dicarboxylic acid - Google Patents

Abstract

The present invention relates to a method for purifying 2,6-naphthalene dicarboxylic acid, and more particularly, to recrystallize 2,6-naphthalene dicarboxylic acid, a) crude 2,6-naphthalene dicarboxylic acid and amine Mixing a compound and a solvent and a nonsolvent mixed solvent b) a dissolution step of dissolving the obtained mixture by heating c) crystallization of cooling the obtained mixed solution to precipitate a 2,6-naphthalene dicarboxylic acid amine salt in a crystalline state. And then filtration and d) deamination of the 2,6-naphthalene dicarboxylic acid amine salt in the crystalline state through heat treatment to recover 2,6-naphthalene dicarboxylic acid. Iii) repeating step c) by injecting and dissolving a mixed solvent in the crystals of 2,6-naphthalene dicarboxylic acid amine salt precipitated after step c), and ii) remaining residues after step c). Concentrate the filtrate A method for purifying 2,6-naphthalene dicarboxylic acid, which performs any one or more of the steps of further crystallizing the 2,6-naphthalene dicarboxylic acid amine salt, and then filtering and recovering it back to step a). will be.

Repeating the recrystallization step according to the present invention improves the purity and color of the 2,6-naphthalene dicarboxylic acid, as well as additionally the 2,6-naphthalene dicarboxylic acid amine salt dissolved in the filtrate remaining after crystal recovery. By recovering, 2, 6- dicarboxylic acid can be refine | purified in high yield.

2,6-naphthalene dicarboxylic acid, recrystallized, purified, distilled

Description

Purification method of 2,6-naphthalene dicarboxylic acid {PROCESS FOR REFINING OF 2,6-NAPHTHALENE DICARBOXYLIC ACID}

1 is a flow chart showing a purification step according to the first embodiment of the present invention.

2 is a flow chart showing a purification step according to a second embodiment of the present invention.

Figure 3 is a flow chart showing a purification step according to a third embodiment of the present invention.

4 is a diagram showing a purification system according to a first embodiment of the present invention.

5 is a schematic diagram of a purification system according to a second embodiment of the present invention;

6 is a schematic diagram of a purification system according to a third embodiment of the present invention;

The present invention relates to a method for purifying 2,6-naphthalene dicarboxylic acid capable of obtaining a high yield of 2,6-naphthalene dicarboxylic acid having excellent purity and color.

Polyesters made by the polymerization of 2,6-naphthalene dicarboxylic acid and diols are known for their excellent physical properties such as thermal stability, tensile strength and gas permeability. It is expected to be a good material for the back. In particular, polyethylene naphthalate (PEN) resins made by polymerization of 2,6-naphthalene dicarboxylic acid and ethylene glycol are expected to be widely used for high functional heat resistant resins in which polyethylene terephthalate (PET) cannot be used.

2,6-naphthalene dicarboxylic acid is mainly obtained by oxidizing 2,6-dimethyl naphthalene to a gas containing oxygen under a catalyst such as cobalt, manganese, bromine compound or the like. The so-called crude 2,6-naphthalene dicarboxylic acid thus obtained is an acid having one functional group such as formyl naphthoic acid and methyl naphthoic acid obtained by incomplete oxidation of 2,6-dimethylnaphthalene and trimellitic acid obtained by the collapse of the naphthalene ring, And many impurities such as brominated naphthalene, naphthoic acid, naphthalene tricarboxylic acid, colored organic impurities of unknown structure, or metal impurities such as cobalt and manganese complexes.

The polyester obtained by the polymerization of crude 2,6-naphthalene dicarboxylic acid and ethylene glycol containing many impurities as described above shows poor properties in physical properties, thermal stability, structural stability, and the like. Moreover, the polyester becomes colored and of low quality.

Among the impurities, impurities of mono carboxylic acids such as methyl naphthoic acid and naphthoic acid are particularly problematic. If the mono carboxylic acid exceeds a certain amount, there is a problem that the polymerization rate is lowered, and gelation and coloring in the polyester production process. Formyl naphthoic acid, in particular, has a devastating effect on the above problem. Therefore, it is important to reduce these impurities in order to obtain high quality polyester.

2,6-naphthalene dicarboxylic acid cannot be purified by distillation because it decomposes without vapor at high temperature, and is not easily dissolved in a general solvent, and purification using recrystallization is also not easy.

There are several methods for purifying 2,6-naphthalene dicarboxylic acid known to date. First, 2,6-naphthalene dicarboxylic acid is dissolved in a general solvent and crystallized after hydrogenation. Secondly, 2,6-naphthalene dicarboxylic acid is made into an alkali salt, and then dissolved and recrystallized. Thirdly, 2,6-naphthalene dicarboxylic acid is made into an amine salt, and then dissolved and recrystallized. Also, commercially, 2,6-dimethylnaphthalene dicarboxylate is prepared by reacting 2,6-naphthalene dicarboxylic acid with methanol, and purified by distillation to obtain pure 2,6-dimethylnaphthalene dicarboxylate. Produce and sell. However, as can be seen in the production of polyethylene terephthalate resin, since the acid form is more advantageous in terms of fairness and economy than the ester form as a raw material of polyester synthesis, it is convenient and economical to directly purify 2,6-naphthalene dicarboxylic acid. More research is needed.

U. S. Patent No. 5,256, 817 discloses a method for dissolving 2,6-naphthalene dicarboxylic acid in water or acetic acid, followed by hydrogenation, crystallization and purification. However, the above method requires heating to a high temperature in order to dissolve 2,6-naphthalene dicarboxylic acid, so that not only does the production of naphthoic acid increase, but also the hydrogenation process requires an expensive metal catalyst. have. In addition, there is a problem in that the initial investment cost increases because the reactor for high temperature and high pressure should be manufactured.

Japanese Patent Laid-Open No. 62-230747 discloses activated carbon after dissolving 2,6-naphthalene dicarboxylic acid in a polar solvent such as dimethylsulfoxide, dimethylformamide, dimethylacetamide, and the like. It discloses the method of adsorb | sorption, undergoing a hydrogenation reaction, and then crystallizing. However, the method has a problem that not only a large amount of solvent and activated carbon are used, but also the solvent can be hydrogenated, and formyl naphthoic acid is not removed, so that the yield of the product is low.

Japanese Patent Application Laid-Open No. 5-32586 discloses a method for purifying 2,6-naphthalene dicarboxylic acid by dissolving pyridine or a pyridine derivative as a solvent and then crystallizing the same. The solubility of, 6-naphthalene dicarboxylic acid is not sensitive to temperature, resulting in low yield.

Another way to purify 2,6-naphthalene dicarboxylic acid is to make it into a metal salt, and then dissolve and recrystallize. Japanese Patent Application Laid-Open No. 52-20993 and Japanese Patent Application Laid-open No. 48-68554 dissolve 2,6-naphthalene dicarboxylic acid in an aqueous solution of KOH or NaOH to make an alkali metal salt, and then adsorb with a solid adsorbent. Disclosed is a method for crystallization and purification. It is possible to obtain purified 2,6-naphthalene dicarboxylic acid by disproportionation by adding water to the resulting mono alkali salt. However, the above method has a problem in that a large amount of solid adsorbent and solvent are used, and since all mono alkali salts are crystallized, salts generated by impurities such as naphthoic acid and formyl naphthoic acid are also crystallized and it is difficult to separate them.

Japanese Patent Application Laid-Open No. 52-20994 and Japanese Patent Application Laid-open No. 48-68555 disclose a method for purifying with diacid salt. This method is to dissolve 2,6-naphthalene dicarboxylic acid in KOH or NaOH aqueous solution, and then adsorb to the adsorbent and crystallize the produced diacid salt. However, the above method also requires a large amount of adsorbent, is difficult to remove a small amount of alkali salt impurities, and has a problem of low yield. Japanese Patent Application Laid-Open No. 2-243652 discloses a method of dissolving 2,6-naphthalene dicarboxylic acid in an aqueous alkali solution, followed by adding a polar organic solvent mixed with water to precipitate an alkali salt, but having high purity. There is a problem in that the yield is low when obtaining 2,6-naphthalene dicarboxylic acid.

A method of purifying by dissolving 2,6-naphthalene dicarboxylic acid in the form of amine salts and then recrystallization has also been proposed. The resulting 2,6-naphthalene dicarboxylic acid in the form of the amine salt can be obtained as pure 2,6-naphthalene dicarboxylic acid by heating to a temperature above the break point of the amine. Japanese Patent Application Laid-open No. 50-142542 discloses a method of dissolving 2,6-naphthalene dicarboxylic acid in an amine aqueous solution, distilling and concentrating a solvent to precipitate it in the form of 2,6-naphthalene dicarboxylic acid amine salt. It is disclosed. Japanese Patent Application Laid-Open No. 50-135062 discloses a method of dissolving 2,6-naphthalene dicarboxylic acid in an amine aqueous solution and then cooling or condensing the solution to precipitate it. Japanese Unexamined Patent Application Publication No. Hei 5-294892 No. discloses a method in which 2,6-naphthalene dicarboxylic acid is dissolved in a mixed solution of alcohol and amine, precipitated with an amine salt and heated to obtain pure 2,6-naphthalene dicarboxylic acid. However, all of the above methods have a problem in that, when obtaining high purity 2,6-naphthalene dicarboxylic acid, the crystallization time is long and the yield of the product is low.                         

U.S. Pat.No. 5,859,294 discloses a 2,6-naphthalene dicarboxylic acid diamine salt by mixing 2,6-naphthalene dicarboxylic acid with an amine, then dissolving in a mixed solution of water, ketone, or acetonitrile. After precipitation, it discloses about the method of distilling this and obtaining pure 2, 6- naphthalene dicarboxylic acid. However, the method also takes a long time to recrystallize, there is a problem that the yield is low when obtaining a high purity 2,6-naphthalene dicarboxylic acid.

Thus, 2,6-naphthalene dicarboxylic acid not only can be obtained 2,6-naphthalene dicarboxylic acid excellent in purity and color, but also high purity 2,6-naphthalene dicarboxylic acid can be obtained in high yield. There is a need for further development of the purification process of leric acid.

An object of the present invention for solving the above problems is a method for purifying 2,6-naphthalene dicarboxylic acid which can obtain a high yield of 2,6-naphthalene dicarboxylic acid with excellent purity and color in a short time. To provide.

Another object of the present invention is to recycle the solvent used in the purification process and to use the by-product of the reaction process as a solvent, which is not only environmentally friendly and energy-saving, but also shorten the processing time, easy to process and economical It is to provide a purification method capable of purifying 2,6-naphthalene dicarboxylic acid.

In order to achieve the above object, the present invention is to re-determinate 2,6-naphthalene dicarboxylic acid,

a) mixing a crude 2,6-naphthalene dicarboxylic acid with an amine compound and a mixed solvent of a solvent and a nonsolvent

b) a dissolution step of dissolving the resulting mixture by heating

c) cooling the obtained mixed solution to crystallize to precipitate 2,6-naphthalene dicarboxylic acid amine salt in a crystalline state, and then filtering

d) deamination of a 2,6-naphthalene dicarboxylic acid amine salt in a crystalline state by heat treatment to recover 2,6-naphthalene dicarboxylic acid,

Iii) repeating step c) by injecting and dissolving a mixed solvent in the 2,6-naphthalene dicarboxylic acid amine salt crystal deposited after step c); and

Ii) concentrating the remaining filtrate remaining after step c) and further crystallizing the 2,6-naphthalene dicarboxylic acid amine salt followed by filtration and returning to step a) A method for purifying 2,6-naphthalene dicarboxylic acid is provided.

In this case, the steps a) and b) may be carried out step by step, or may occur simultaneously in one reactor, and further, the mixed solution of step c) may be used by concentration by removing the solvent in the mixed solution before cooling, or the step The mixture of c) is further cooled by further adding an alkyl acetate solvent.

Hereinafter, the present invention will be described in detail.                     

While the present inventors have been studying a purification method capable of obtaining high purity 2,6-naphthalene dicarboxylic acid in high yield, crude 2,6-naphthalene dicarboxylic acid in the form of an amine salt is used as water, alcohol and Crystallization using a soluble solvent selected from the group consisting of a mixture of and a non-soluble solvent such as alkyl acetate together confirmed that high purity 2,6-naphthalene dicarboxylic acid can be obtained in high yield. On the basis of this, the present invention has been completed.

In particular, the present invention increases the purity and color by repeating the crystallization of 2,6-naphthalene dicarboxylic acid two or more times, and reprocessing the remaining filtrate remaining after the crystallization process of 2,6-naphthalene dicarboxylic acid In addition to improving recovery, the solvent used during the treatment process can be reused.

1 is a flow chart showing a purification step of 2,6-naphthalene dicarboxylic acid according to the first embodiment of the present invention.

Referring to Figure 1, the purification method of 2,6-naphthalene dicarboxylic acid according to a first embodiment of the present invention

a) mixing a crude 2,6-naphthalene dicarboxylic acid with an amine compound and a mixed solvent of a solvent and a nonsolvent

b) a dissolution step of dissolving by heating the mixture obtained in step a)

c) crystallization of cooling the mixed solution obtained in step b) to precipitate 2,6-naphthalene dicarboxylic acid amine salt into a crystalline state, followed by filtration

d) adding a solvent to the 2,6-naphthalene dicarboxylic acid amine salt crystal precipitated in step c) and then dissolving, repeating step c)

e) deamination of the recrystallized 2,6-naphthalene dicarboxylic acid amine salt via heat treatment to recover 2,6-naphthalene dicarboxylic acid.

Each step will be described in more detail below.

Step a) Mixing Amine Compound

In step a), an amine compound and a solvent are mixed with the crude 2,6-naphthalene dicarboxylic acid to be purified to prepare a salt form.

The amine compound is converted to diamine form of crude 2,6-naphthalene dicarboxylic acid to increase the solubility in the solvent, can be recovered by cooling in the deamination process to heat the salt in a subsequent process.

The amine compound is required to have a certain amount of content relative to the 2,6-naphthalene dicarboxylic acid functional group, preferably used in 0.9 to 1.5, more preferably 1.0 to 1.3 equivalents, not limited in the present invention, but representative In consideration of price, specific heat and the like, it is preferable to use ammonia, trimethyl amine, triethyl amine, diethyl amine, dimethyl amine, methyl amine, ethyl amine, or the like.

At this time, the mixing process is not particularly limited and is performed at room temperature and atmospheric pressure.

Step b) dissolution step

In step b), a mixture of crude 2,6-naphthalene dicarboxylic acid in the form of the amine salt obtained in step a) and a mixed solvent of a soluble solvent and an insoluble solvent thereof is sufficiently dissolved at 25 to 150 ° C.                     

There are many methods for crystallization and purification of the compound, but in the present invention, after dissolving under certain conditions, the compound is precipitated in a crystalline state when released under the above conditions. The purity and yield of the compound in this crystallization purification method is the most important factor is the choice of the appropriate solvent and non-solvent and the mixing ratio between each solvent.

In the present invention, as a solvent capable of dissolving 2,6-naphthalene dicarboxylic acid amine salt, a proton polar polar solvent selected from the group consisting of alcohol, water and mixtures thereof is used, and alkyl acetate and acetone as nonsolvents and these An aprotic solvent selected from the group consisting of mixtures is used. This solvent / non-solvent mixed solvent has a high solubility at high temperature due to its high solubility constant in the 2,6-naphthalene dicarboxylic acid amine salt at high temperature, but is low in solubility at low temperature and is preferable for crystallization purification.

As mentioned, the solvent / non-solvent content ratio of the mixed solvent is also directly involved in the yield in the crystallization purification process. In the present invention, the solvent / non-solvent is mixed in a weight ratio of 1: 1 to 1:20. In this case, the solvent is alcohol and water or a mixed solvent of alcohol and water in a weight ratio of 1:10 to 100: 1. If the content of the solvent / non-solvent and the content ratio of alcohol / water is out of the range, 2,6-naphthalene recovered due to the low solubility difference according to the temperature of the crude 2,6-naphthalene dicarboxylic acid amine salt dissolved in the mixed solvent Since the yield of dicarboxylic acid is lowered, it is performed within the above range.

The alcohol is preferably a lower alcohol, and typically, at least one selected from the group consisting of methanol, ethanol, propanol and isopropanol is used.

The nonpolar solvent may be an alkyl acetate, acetone and mixtures thereof, and the alkyl acetate is not particularly limited in the present invention. For example, 1 may be selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, and isopropyl acetate. One or more species are selected and used, and methyl acetate is used preferably. The methyl acetate is produced as a by-product of the oxidation reaction process in the production of terephthalic acid, and from the viewpoint of using the by-product, it is not only environmentally friendly, but also has an effect of reducing production costs.

In this case, the step of filtering the obtained mixed solvent may be further performed to remove impurities in the crude 2,6-naphthalene dicarboxylic acid amine salt. This filtration is carried out by a conventional filtration apparatus and is carried out at the same temperature conditions as the above dissolution step in order to precipitate the 2,6-naphthalene dicarboxylic acid amine salt in high yield in the crystallization step of the subsequent process.

Step c) crystallization step

In this step, the mixed solution obtained in step b) is cooled to precipitate 2,6-naphthalene dicarboxylic acid amine salt in the mixed solution in a crystalline state, and then filtered to obtain a 2,6-naphthalene dicarboxylic acid in a crystalline state. Recover the amine salt.

The degree of precipitation of the 2,6-naphthalene dicarboxylic acid amine salt produced in the crystallization step is performed in consideration of the treatment temperature in step b), that is, the temperature of the mixed solution before cooling. Preferably, the larger the difference between the mixed solution temperature and the cooling temperature before cooling, the more the content of precipitated 2,6-naphthalene dicarboxylic acid amine salt is increased, and more preferably, it is carried out at -10 to 50 ℃.

At this time, in order to further increase the content of the precipitated 2,6-naphthalene dicarboxylic acid amine salt, the mixed solution obtained in step b) is concentrated before cooling and slowly stirred in the form of a concentrated solution, or the mixture obtained in step b) Step c) can be carried out by adding a non-solvent to the solution.

 The 2,6-naphthalene dicarboxylic acid amine salt precipitated in the crystallization step is separated by filtration by a conventional filter.

Step d) recrystallization step

In this step, in order to improve the purity and color of the 2,6-naphthalene dicarboxylic acid, the 2,6-naphthalene dicarboxylic acid amine salt crystal recovered in step c) is added to the mixed solvent presented in step b). After re-dissolution, the crystallization step of step c) is carried out.

Processing conditions of the recrystallization step are performed in the same manner as in steps b) and c).

By repeating the crystallization step in this way, the purity and color of the 2,6-naphthalene dicarboxylic acid finally obtained can be further improved.

Step e) deamination step

In this step, the 2,6-naphthalene dicarboxylic acid amine salt in the crystal state recovered in step d) is washed and then heat-treated at 50 to 120 ° C. to deamination to obtain 2,6-naphthalene dicarboxylic acid and amine compound. And the amine compound is purified and reused through a separate purification apparatus.                     

Thus, 2,6-naphthalene dicarboxylic acid purified through the steps a) to e) can be recovered in a yield of 90% or more, purity is 99.6% or more, color-b is 3.2 or less excellent. In particular, trace amounts of bromine are less than 3 ppm, cobalt and manganese are less than 10 ppm and 3 ppm, respectively.

Figure 2 is a flow chart showing the purification step of 2,6-naphthalene dicarboxylic acid according to a second embodiment of the present invention.

2, the purification method of 2,6-naphthalene dicarboxylic acid according to a second embodiment of the present invention

a) mixing a crude 2,6-naphthalene dicarboxylic acid with an amine compound and a mixed solvent of a solvent and a nonsolvent

b) a dissolution step of dissolving by heating the mixture obtained in step a)

c) crystallization of cooling the mixed solution obtained in step b) to precipitate 2,6-naphthalene dicarboxylic acid amine salt into a crystalline state, followed by filtration

d) concentrating the remaining filtrate remaining after filtration in step c) and cooling to further precipitate 2,6-naphthalene dicarboxylic acid amine salt,

e) sending the 2,6-naphthalene dicarboxylic acid amine salt further precipitated in step d) back to step a) and

f) recovering 2,6-naphthalene dicarboxylic acid by deamination of the 2,6-naphthalene dicarboxylic acid amine salt precipitated in step c) through heat treatment.

Steps a) to c) and f) are the same as those mentioned in the first embodiment, and the steps d) and e) are described below.

The 2,6-naphthalene dicarboxylic acid amine salt crystals precipitated through the crystallization step are separated by filtration, and the obtained crystals are immediately subjected to the deamination process of step f). At this time, even if the treatment conditions are best adjusted in the crystallization step, 100% of 2,6-naphthalene dicarboxylic acid amine salts are not precipitated. The salt does not precipitate into crystals and is contained in the remaining filtrate after filtration.

Therefore, in the present invention, to increase the yield of 2,6-naphthalene dicarboxylic acid, the residual filtrate after filtration is concentrated and then cooled to precipitate the 2,6-naphthalene dicarboxylic acid amine salt contained in the residual filtrate. In this case, the crystallization process is performed in the same manner as in step c) of the first embodiment.

The amount of 2,6-naphthalene dicarboxylic acid amine salt further recovered by step d) is determined by the degree of concentration of the remaining filtrate and the cooling temperature. However, recovering too much of the 2,6-naphthalene dicarboxylic acid amine salt will have a worse quality than the crude 2,6-naphthalene dicarboxylic acid first introduced and if sent to step a), Accumulation of impurities and gradual degradation of color can result. To prevent this, the amount should be adjusted to recover the 2,6-naphthalene dicarboxylic acid amine salt to a degree close to the quality of the crude 2,6-naphthalene dicarboxylic acid first introduced.

Due to the concentrated crystallization of the residual filtrate, the yield, which was only 60 to 80%, can be improved to 95% or more to recover high yield of 2,6-naphthalene dicarboxylic acid.

3 is a flowchart showing a purification step of 2,6-naphthalene dicarboxylic acid according to a third embodiment of the present invention.

Referring to Figure 3, the purification method of 2,6-naphthalene dicarboxylic acid according to a third embodiment of the present invention

a) mixing a crude 2,6-naphthalene dicarboxylic acid with an amine compound and a mixed solvent of a solvent and a nonsolvent

b) a dissolution step of dissolving by heating the mixture obtained in step a)

c) crystallization of cooling the mixed solution obtained in step b) to precipitate 2,6-naphthalene dicarboxylic acid amine salt into a crystalline state, followed by filtration

d) concentrating the remaining filtrate remaining after filtration in step c) and cooling to precipitate 2,6-naphthalene dicarboxylic acid amine salt

e) sending the 2,6-naphthalene dicarboxylic acid amine salt further precipitated in step d) back to step a)

f) repeating step c) by injecting and dissolving a mixed solvent in the 2,6-naphthalene dicarboxylic acid amine salt crystal precipitated in step c);

g) The recrystallized 2,6-naphthalene dicarboxylic acid amine salt is deaminated via heat treatment to recover 2,6-naphthalene dicarboxylic acid.

Steps a) to c), and g) are the same as those mentioned in the first embodiment, wherein the remaining filtrate of steps d) and e) and the recrystallization process of step f) are the second embodiment and the second embodiment, respectively. As mentioned in the first embodiment.

Purification of 2,6-naphthalene dicarboxylic acid according to the first to third embodiments as described above may be performed by various methods, for example, the first to third embodiments in FIGS. A system that can implement three implementations is illustrated. 4 to 6 is merely an example of the present invention and may be appropriately modified by those skilled in the art.

4 schematically illustrates a purification system of 2,6-naphthalene dicarboxylic acid according to the first embodiment of the present invention. The first embodiment of the present invention performs a process for recrystallizing the precipitated 2,6-naphthalene dicarboxylic acid amine salt after the crystallization step to improve the purity and color of the 2,6-naphthalene dicarboxylic acid.

Referring to FIG. 4, a compound of a storage tank (not shown) in which a crude 2,6-naphthalene dicarboxylic acid, an amine compound and a mixed solvent are stored is injected into the first melting tank 100, and uniformly heated and stirred. Prepare a mixed solution. The mixed solution injected into the first melting tank 100 is transferred to the first filter 120 to remove impurities, and then the obtained mixed solution is transferred to the first crystallization tank 140. The first crystallization tank 140 includes a cooling device, and cools the mixed solution transferred from the first filter 120 to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.

In order to recrystallize the crystal formed in the first crystallization tank 140, it is transferred to the second melting tank 102, wherein the 2,6-naphthalene dicarboxylic acid amine salt crystal in the second melting tank 102 for dissolving Inject a mixed solvent. The mixed solution obtained in the second dissolution tank 102 is a 2,6-naphthalene dikar recrystallized through the third filter 122, the second crystallizer 142 and the fourth filter 162 as described above. Acid amine salt crystals are recovered. The 2,6-naphthalene dicarboxylic acid amine salt crystal obtained through the fourth filter 162 is subjected to a deamination process through a dry dryer after washing, and then purified 2,6-naphthalene dicarboxylic acid In order to obtain the volatilized amine compound, the amine compound is recovered, purified through a separate purification apparatus, and reused.

In this case, an additional injection device (not shown) is added to the first crystallization tank 140 and the second crystallization tank 142 to increase the crystallization yield to inject an alkyl acetate solvent, or a mixed solution before performing the crystallization process. It is carried out by concentrating. Concentration of the mixed solution is performed by further inserting a solvent evaporator (not shown) between the first filter 120 and the first crystallization tank 140, the third filter 122 and the second crystallization tank 142. At this time, the evaporated solvent is recovered and reused through a separate refining apparatus, or returned to the first dissolution tank 100 or the second dissolution tank 102.

In addition, the residual filtrate remaining through the second filter 160 and the fourth filter 161 to recover the solvent using a separate purification device, and removes the remaining waste.

5 schematically illustrates a purification system of 2,6-naphthalene dicarboxylic acid according to a second embodiment of the present invention. The second embodiment of the present invention is subjected to a process of recovering the 2,6-naphthalene dicarboxylic acid amine salt in the remaining filtrate remaining after the crystallization step, thereby improving the purification yield of 2,6-naphthalene dicarboxylic acid Increase.

Referring to FIG. 5, a reservoir (not shown) in which a crude 2,6-naphthalene dicarboxylic acid, an amine compound, and a mixed solvent are stored, and the compound are injected to form a uniform mixed solution, and a heating and stirring device is mounted. The first dissolution tank 200, the first filter 220 connected to the dissolution tank 200 and filtering the mixed solution, and the first crystallization tank 240 connected to the first filter 220 and provided with a cooling device. ) Is connected to the first crystallization tank 240 and is connected to a second filter 260 for filtering 2,6-naphthalene dicarboxylic acid amine salt crystals and an outlet of one side of the second filter 160. And 2,6-naphthalene dicarboxylic acid is obtained through a dryer 280 for heat treatment of the crystal obtained in the second filter 260.

At this time, in order to recover the 2,6-naphthalene dicarboxylic acid amine salt in the residual filtrate remaining through the second filter 260, the remaining filtrate separated from the second filter 260, the first solvent evaporator 210 Transfer to to remove solvent and concentrate. At this time, the volatilized solvent is reused through a separate purification device.

The mixture concentrated in the first solvent evaporator 210 is transferred to the second crystallization tank 230 and cooled to precipitate 2,6-naphthalene dicarboxylic acid amine salt. The slurry obtained in the second crystallization tank 230 is solid-liquid separated in the third filter 250, and the 2,6-naphthalene dicarboxylic acid amine salt crystal is returned to the dissolution tank 200, and the remaining filtrate is the second solvent. The solvent is recovered by passing through an evaporator 270 and the remaining waste is discharged.

In this case, in order to increase the crystallization yield, an alkyl acetate solvent is further injected into the first and second crystallization tanks 240 and 230 as in the first embodiment, or the first filter 220 and the first crystallization tank 240 A solvent evaporator (not shown) is inserted between the layers to concentrate the mixed solution and then perform a crystallization process.                     

6 is a schematic of a purification system of 2,6-naphthalene dicarboxylic acid according to a third embodiment of the present invention. In a third embodiment of the present invention, the 2,6-naphthalene dicarboxylic acid amine salt recovered first through the second filter 360 is recrystallized, and the remaining filtrate is concentrated to remain in the remaining filtrate. A process of recovering 2,6-naphthalene dicarboxylic acid is carried out to increase the recovery of 2,6-naphthalene dicarboxylic acid and to improve purity and color.

Referring to FIG. 6, a storage tank (not shown) in which a crude 2,6-naphthalene dicarboxylic acid, an amine compound and a mixed solvent are stored, and the compound are injected to form a uniform mixed solution, and a heating and stirring device is mounted. A first melting tank 300, a first filter 320 connected to the first melting tank 300 and filtering the mixed solution, and a first cooling device connected to the first filter 320. 2,6-naphthalene dicarboxylic acid amine salt crystals are obtained through a crystallization tank 340 and a second filter 360 for filtering 2,6-naphthalene dicarboxylic acid amine salt crystals. The 2,6-naphthalene dicarboxylic acid amine salt crystal recovered from the second filter 360 is transferred to the second dissolution tank 302 in which the mixed solvent is injected, and the third filter ( 322), second crystallization tank 342 and fourth filter 362 to recrystallize the 2,6-naphthalene dicarboxylic acid amine salt. The 2,6-naphthalene dicarboxylic acid amine salt recrystallization obtained from the fourth filter 362 is subjected to deamination through a dryer 380 connected to an outlet of the fourth filter 362 to perform deamination. Recover the naphthalene dicarboxylic acid.

In this case, an additional injection device (not shown) is added to the first crystallization tank 340 and the second crystallization tank 342 in order to increase the recrystallization effect, or an alkyl acetate solvent is injected, or a mixed solution before performing the crystallization process. It is carried out by concentrating. The concentration of the mixed solution is carried out by further inserting a solvent evaporator (not shown) between the first filter 320 and the first crystallization tank 340, the third filter 322 and the second crystallization tank 342. In this case, the evaporated solvent is recovered and reused through a separate refining apparatus, or returned to the first dissolution tank 300 or the second dissolution tank 302.

On the other hand, the residual filtrate remaining from the second filter 360 and the residual filtrate recovered from the fourth filter 362 is the first solvent to recover the 2,6-naphthalene dicarboxylic acid amine salt contained in the residual filtrate After concentration in the evaporator 310 and crystallization in the third crystallization tank 330, and then liquid-liquid separation through the fifth filter 350, the obtained 2,6-naphthalene dicarboxylic acid amine salt again the first melting tank ( 300). At this time, the solvent distilled from the first solvent evaporator 310 is collected and recovered. In addition, the solvent remaining through the fifth filter 350 is transferred to the second solvent evaporator 370 to recover the solvent, and the remaining waste is discharged.

As described above, a specific solvent is selected for purifying 2,6-naphthalene dicarboxylic acid according to the present invention, and then a crystallization process is performed under appropriate conditions to give a high purity and color of 2,6-naphthalene dicarboxylic acid. Can be obtained. In particular, further treatment of the residual filtrate after the crystallization process not only greatly improves the recovery of the 2,6-naphthalene dicarboxylic acid, but also reuses the solvent used during the treatment process and is very economical.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

Example 1

At room temperature and atmospheric pressure, 50.0 g of crude 2,6-naphthalene dicarboxylic acid and 55.2 g of triethylamine were mixed in a 1-neck Erlenmeyer flask with a Pyrex cap.

A mixed solution of 2,6-naphthalene dicarboxylic acid amine salt was added thereto by adding 400 g of a mixed solvent mixed at a weight ratio of 17.5: 2.5: 80.0 of methanol: water: methyl acetate and then stirring at 60 ° C. for 30 minutes. Got.

The filtrate obtained by filtering the mixed solution with filter paper having a pore size of 7 μm at 60 ° C. was cooled to room temperature and stirred slowly for 1 hour to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals. .

Subsequently, in order to recrystallize the crystal, the crystal was recovered and dissolved in 400 g of a mixed solvent of 17.5: 2.5: 80.0 volume ratio of methanol: water: methyl acetate, and then recrystallized in the same manner as above to obtain 2,6-naphthalene dicarboxylic acid. Amine salt crystals were precipitated.

The mixed solution containing the crystals was filtered to separate the crystals, and the mixture was left at 90 ° C. for 1 hour to remove the solvent, thereby obtaining purified 2,6-naphthalene dicarboxylic acid.

Comparative Example 1

At room temperature and atmospheric pressure, 50.0 g of crude 2,6-naphthalene dicarboxylic acid and 55.2 g of triethylamine were mixed and mixed in a one-neck Erlenmeyer flask with a Pyrex cap.

To this was added 315 g of a mixed solvent mixed at a weight ratio of 17.5: 2.5: 80.0 in methanol: water: methyl acetate, and then stirred at 55 ° C. for 30 minutes to prepare a mixed solution of 2,6-naphthalene dicarboxylic acid amine salt. Got.

The mixed solution was filtered under reduced pressure with a filter having a pore size of 7 μm at 60 ° C., and the obtained filtrate was heated to 55 ° C. for 30 minutes. Thereafter, the temperature was lowered to room temperature, and left for 12 hours to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.

The mixed solution containing the crystals was filtered to separate the crystals, and the mixture was left at 90 ° C. for 1 hour to remove the solvent, thereby obtaining purified 2,6-naphthalene dicarboxylic acid.

The contents of the bromine compound, cobalt and manganese remaining in the 2,6-naphthalene dicarboxylic acid obtained in Example 1 and Comparative Example 1, and the yield, purity, and chromaticity of 2,6-naphthalene dicarboxylic acid were measured. It is shown in Table 1 below. Purity was measured by gas chromatography (G.C). In this case, the 2,6-naphthalene dicarboxylic acid was measured by dividing it into a case where the crystallization process was performed once and when it was recrystallized.

division Example 1 Comparative Example 1 Joe 2,6-NDA 1st decision 2nd decision 1st decision - Yield (%) 60.3 22.5 62.2 - Purity (%) 99.48 99.62 99.57 98.19 Chromaticity (Color-b) 6.18 3.17 3.60 11.23 T-Br (ppm) 108 2.5 84 574.1 Co (ppm) 24 6.4 21 26.8 Mn (ppm) 2 1.1 2 2.5

Referring to Table 1, it can be seen that when the recrystallization is performed twice in accordance with the present invention, the purity is improved and impurities such as bromine, cobalt and manganese are almost removed.

Example 2

At room temperature and atmospheric pressure, 50.0 g of crude 2,6-naphthalene dicarboxylic acid and 60.0 g of triethylamine were mixed and mixed in a one-neck Erlenmeyer flask with a Pyrex lid.

A mixed solution of 2,6-naphthalene dicarboxylic acid amine salt was added thereto by adding 400 g of a mixed solvent mixed at a weight ratio of 17.5: 2.5: 80.0 of methanol: water: methyl acetate and then stirring at 60 ° C. for 30 minutes. Got.

The filtrate obtained by filtering the mixed solution with a filter paper having a pore size of 7 μm at 60 ° C. was heated to remove a portion of the solvent in the filtrate. The resulting concentrate was cooled to room temperature and slowly stirred for 1 hour to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.

Subsequently, in order to recrystallize the crystal, the crystal was recovered and dissolved in 400 g of a mixed solvent of 17.5: 2.5: 80.0 volume ratio of methanol: water: methyl acetate, and then recrystallized in the same manner as above to obtain 2,6-naphthalene dicarboxylic acid. Amine salt crystals were precipitated.

The mixed solution containing the crystals was filtered to separate the crystals, and the mixture was left at 90 ° C. for 1 hour to remove the solvent, thereby obtaining purified 2,6-naphthalene dicarboxylic acid.

Example 3

Except for increasing the content of the solvent removed in the filtrate after the filtration, it was carried out in the same manner as in Example 2 to obtain a purified 2,6-naphthalene dicarboxylic acid.                     

The content of bromine compound, cobalt and manganese remaining in the 2,6-naphthalene dicarboxylic acid obtained in Examples 2 and 3, and the yield, purity, and chromaticity of 2,6-naphthalene dicarboxylic acid were measured. It is shown in Table 2 below. Purity was measured by gas chromatography (G.C). In this case, the 2,6-naphthalene dicarboxylic acid was measured by dividing it into a case where the crystallization process was performed once and when it was recrystallized.

division Example 2 Example 3 1st decision 2nd decision 2nd decision Amount of solvent removed by distillation 120 120 240 Yield (%) 61.27 32.2 34.5 Purity (%) 99.48 99.64 99.64 Chromaticity (Color-b) 5.47 2.97 3.89

Referring to Table 2, it can be seen that the purity and chromaticity characteristics are improved by performing recrystallization in purifying 2,6-naphthalene dicarboxylic acid. In addition, it can be seen that the yield in the secondary crystal increases by removing the solvent in the mixed solution and concentrating.

Example 4

At room temperature and atmospheric pressure, 50.0 g of crude 2,6-naphthalene dicarboxylic acid and 55.2 g of triethylamine were mixed in a 1-neck Erlenmeyer flask with a Pyrex cap.

A mixed solution of 2,6-naphthalene dicarboxylic acid amine salt was added thereto by adding 400 g of a mixed solvent mixed at a weight ratio of 17.5: 2.5: 80.0 of methanol: water: methyl acetate and then stirring at 60 ° C. for 30 minutes. Got.

The mixed solution was concentrated by removing the solvent from the filtrate obtained by filtering the filter paper with a filter paper of 7 ㎛ pore size at 60 ℃. Methyl acetate was added to the concentrate as much as the amount of solvent removed, and then cooled to room temperature and stirred slowly for 1 hour to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.

The crystals were then recovered to recrystallize the crystals, dissolved in 400 g of a mixed solvent of 17.5: 2.5: 80.0 volume ratio of methanol: water: methyl acetate and filtered. The solvent was removed by concentration in the filtrate obtained at this time. Methyl acetate was added to the concentrate as much as the amount of solvent removed, and then cooled to room temperature and stirred slowly for 1 hour to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.

The mixed solution containing the crystals was filtered to separate the crystals, and the mixture was left at 90 ° C. for 1 hour to remove the solvent, thereby obtaining purified 2,6-naphthalene dicarboxylic acid.

Example 5

Except for using ethyl acetate as a solvent to be injected after concentration, it was carried out in the same manner as in Example 4 to obtain a purified 2,6-naphthalene dicarboxylic acid.

When ethyl acetate was used as a non-solvent, the quality of the obtained 2,6-naphthalene dicarboxylic acid and the content of T-Br and metals were low, but the yield was relatively high. If no acid is required, it can be regarded as a suitable solvent in terms of economy.

 Example 6

Except for using acetone as a solvent to be injected after concentration, it was carried out in the same manner as in Example 4 to obtain a purified 2,6-naphthalene dicarboxylic acid.                     

Yield, purity, and chromaticity of the 2,6-naphthalene dicarboxylic acid obtained in Examples 4 to 6 are shown in Table 3, measured in the same manner as in Example 1.

division Example 4 Example 5 Example 6 Organic solvent Methyl acetate Ethyl acetate Acetone Amount of solvent removed by distillation (g) 200 200 200 Yield (%) 63.0 89.9 66.5 Purity (%) 99.64 99.21 99.36 Chromaticity (Color-b) 3.92 7.95 5.75 Co (ppm) 5.6 27.6 15.6 Mn (ppm) 1.1 2.2 1.3

Referring to Table 3, when methyl acetate is used as the non-solvent, it can be seen that the removal rate of bromine, cobalt and manganese is excellent.

Example 7

At room temperature and atmospheric pressure, 750 g of crude 2,6-naphthalene dicarboxylic acid and 900 g of triethyl amine were added to a 10-liter dissolution tank made of SUS-316 and mixed. 2885 g of a mixed solvent of 17.5: 2.5: 80.0 weight ratio of methanol: water: methyl acetate was added thereto, and the mixture was heated and heated at 70 ° C and 3 atm, and stirred for 30 minutes to give 2,6-naphthalene dicarboxylic acid. An amine salt mixed solution was obtained.

The resultant mixed solution was passed through a cartridge filter having a pore size of 5 μm while maintaining 70 ° C. to remove undissolved impurities, and the solution after filtration was transferred to a 20 liter crystallizer made of SUS-316 for crystallization. At this time, for more efficient crystallization, by cooling to room temperature while concentrating by flashing method to precipitate 2,6-naphthalene dicarboxylic acid amine salt crystals.                     

The mixed solution containing the crystals was filtered to separate the crystals. The 2,6-naphthalene dicarboxylic acid amine salt crystal obtained at this time was heat-processed at 90 degreeC, and 2,6-naphthalene dicarboxylic acid was obtained by removing an amine compound.

Further, the remaining filtrate obtained after the filtration was distilled off to remove the solvent, and the obtained concentrate was poured into the crystallizer to crystallize in the same manner as described above, followed by filtration and heat treatment to obtain 2,6-naphthalene dicarboxylic acid.

Example 8

A mixed solvent was purified in the same manner as in Example 7, except that methanol: water: methyl acetate was mixed in a weight ratio of 17.5: 4.5: 78.0 to obtain a purified 2,6-naphthalene dicarboxylic acid.

Example 9

The mixed solvent was purified in the same manner as in Example 7, except that methanol: water: methyl acetate was mixed in a weight ratio of 17.5: 8.0: 74.5 to obtain purified 2,6-naphthalene dicarboxylic acid.

Yield, purity, and chromaticity of the 2,6-naphthalene dicarboxylic acid obtained in Examples 7 to 9 were measured in the same manner as in Example 1, and are shown in Table 4 below. In this case, the 2,6-naphthalene dicarboxylic acid was measured by dividing into a case obtained through the crystal obtained after precipitation in the crystallization process, and a case obtained through the residual filtrate.

Example 7 Example 8 Example 9 decision Residual filtrate decision Residual filtrate decision Residual filtrate yield(%) 77.9 64.5 80.5 62.4 81 72.9 water(%) 99.92 98.9 99.91 98.7 99.86 97.3 Color-b 4.53 10.9 4.51 9.4 4.50 11.2 T-Br (ppm) 134 - 103 - 118 - Co (ppm) 27.5 - 33.6 - 98.1 - Mn (ppm) 2.6 - 2.6 - 6.4 - Distillation amount (%) - 66.1 - 79.4 - 85.2 Total yield (%) 92 91 94

Referring to Table 4 above, the yields were very high, 90% or more in all of Examples 7-9. If only the residual filtrate treatment is compared, it can be seen that as the mass of the solvent removed by distillation generally increases, the recovery rate increases. However, the higher the recovery rate, the lower the purity and color quality, but it is not very significant.

Example 9 had a very high recovery rate of 72.9% even after distilling 85.2%, but the purity and color (98.41% purity, Col-b 12.4) were low, resulting in similar values to crude 2,6-naphthalene dicarboxylic acid before purification. Seemed. However, the recrystallization of the crystal obtained from the residual filtrate can sufficiently improve the purity and chromaticity.

Therefore, according to the present invention, 2,6-naphthalene dicarboxylic acid having excellent purity and color can be recovered in high yield. Furthermore, by reusing the solvent used in the refining process, by-products of the reaction process can be used as solvents, not only environmentally friendly and energy-saving, but also naphthoic acid and formyl remaining in impure 2,6-naphthalene dicarboxylic acid. By removing naphthoic acid, a catalyst compound, etc., there is an effect that the 2,6-naphthalene dicarboxylic acid can be purified easily, quickly and economically.

Claims (11)

a) mixing a crude solvent of 2,6-naphthalene dicarboxylic acid with an amine compound and a mixed solvent of a protic polar solvent which is a soluble solvent and an aprotic solvent which is an insoluble solvent, b) a dissolution step of dissolving by heating the mixture obtained in step a), c) cooling the obtained mixed solution to precipitate 2,6-naphthalene dicarboxylic acid amine salt in a crystalline state to crystallize, and then filtering, and d) deamination of a 2,6-naphthalene dicarboxylic acid amine salt in a crystalline state by heat treatment to recover 2,6-naphthalene dicarboxylic acid, Iii) repeating step c) by injecting and dissolving a mixed solvent in the 2,6-naphthalene dicarboxylic acid amine salt crystal deposited after step c); Ii) concentrating the remaining filtrate remaining after step c) to further crystallize the 2,6-naphthalene dicarboxylic acid amine salt, filtering and recovering it, and then performing any one or more of steps. doing, 2,6-naphthalene dicarboxyl with at least 99.6% purity, less than 3.2 color-b, less than 3 ppm bromine, less than 10 ppm and 3 ppm cobalt and manganese, respectively; Purification of Acids. The method for purifying 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the steps a) and b) are performed stepwise or simultaneously occur in one reactor. The method of claim 1, wherein the mixed solution of step c) is used by removing the solvent in the mixed solution and concentrating it before cooling. The method for purifying 2,6-naphthalene dicarboxylic acid according to claim 1, wherein an alkyl acetate solvent is further added to the mixed solution or crystallization tank of step c). The method of claim 1, wherein the mixed solvent of step b) and iii) is a 2,6-naphthalene dicar, characterized in that the mixed solvent in which the soluble solvent and the insoluble solvent are mixed in a weight ratio of 1: 1 to 1:20. Purification of Acids. 6. The 2,6-naphthalene according to any one of claims 1 to 5, wherein the soluble solvent is alcohol, water, or a mixed solvent in which alcohol and water are mixed in a weight ratio of 1:10 to 100: 1. Method for Purifying Dicarboxylic Acid. The method of claim 6, wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, propanol and isopropanol. The method of claim 1, wherein the insoluble solvent is selected from acetone; And alkyl acetate selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate and isopropyl acetate; And a mixture thereof. 2. The method for purifying 2,6-naphthalene dicarboxylic acid. 2. The purification of 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the 2,6-naphthalene dicarboxylic acid and the amine compound of step a) are mixed in an equivalent ratio of 1.0: 0.9 to 1.0: 1.5. Way. The method for purifying 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the dissolution of step b) is performed at 25 to 150 ° C. The method for purifying 2,6-naphthalene dicarboxylic acid according to claim 1, wherein the cooling in step c) is performed at -10 to 50 ° C.

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