JPH1180074A - Process for producing high-purity 2,6-naphthalenedicarboxylic acid - Google Patents

Abstract

(57) [Problem] To provide a method for industrially and advantageously producing a 2,6-naphthalenedicarboxylic acid having a good hue and a high purity from a crude 2,6-naphthalenedicarboxylic acid at a high recovery rate. I do. SOLUTION: An aliphatic or alicyclic amine salt of crude 2,6-naphthalenedicarboxylic acid is crystallized with a mixed solvent of water and acetonitrile, and the amine salt of 2,6-naphthalenedicarboxylic acid purified by crystallization is obtained. A high-purity 2,6-naphthalenedicarboxylic acid is produced by distilling an aliphatic or alicyclic amine by heating in the presence of water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a highly pure 2,6-naphthalenedicarboxylic acid from a crude 2,6-naphthalenedicarboxylic acid.

[0002]

2. Description of the Related Art 2,6-Naphthalenedicarboxylic acid is useful as a raw material for polyethylene naphthalate (PEN) resin having excellent performance. Polyesters obtained by polymerizing 2,6-naphthalenedicarboxylic acid and diols such as ethylene glycol have excellent heat resistance and mechanical strength, and are industrially important as materials for films, fibers, bottles, etc. It has various uses. In particular, demand for PEN produced by polymerizing 2,6-naphthalenedicarboxylic acid and ethylene glycol is expected to increase in the near future as an excellent industrial resin replacing polyethylene terephthalate.

[0003] As a method for producing 2,6-naphthalenedicarboxylic acid, 2,6-dialkylnaphthalene is prepared by adding Co or Co in an acetic acid solvent.
A method of oxidizing at high temperature and high pressure with molecular oxygen in the presence of a heavy metal such as Mn and a bromine compound is known. The 2,6-naphthalenedicarboxylic acid obtained by this oxidation reaction includes:
Intermediate products of the oxidation reaction, methyl naphthoic acid, formyl naphthoic acid, trimellitic acid generated by decomposition of the naphthalene ring, naphthalene dicarboxylic acid bromide to which bromine is added, and naphthoe derived from impurities in the raw material 2,6-dialkylnaphthalene Organic substances such as acids and naphthalene tricarboxylic acids, coloring components of unknown structure, and metal components such as Co and Mn derived from oxidation catalysts are contained as impurities.

When crude 2,6-naphthalenedicarboxylic acid containing these impurities is used as a raw material for polymerization with diols,
The resulting polyester causes adverse effects such as deterioration of physical properties such as heat resistance, mechanical strength, and dimensional stability, and deterioration of quality due to coloring of the polyester of the product. In particular,
The presence of monocarboxylic acids such as naphthoic acid, methylnaphthoic acid and formylnaphthoic acid inhibits polymerization and causes a decrease in the physical properties of the polyester.
It causes quality deterioration due to coloring of the polyester of the product. Therefore, in order to obtain a high-quality polyester, it is required to produce high-purity 2,6-naphthalenedicarboxylic acid containing extremely few impurities and coloring components.

[0005] Various methods have been proposed as a method for producing high-purity 2,6-naphthalenedicarboxylic acid by purifying crude 2,6-naphthalenedicarboxylic acid obtained by an oxidation reaction. As a method of dissolving and purifying crude 2,6-naphthalenedicarboxylic acid in a solvent, U.S. Pat.No.5,256,817 dissolves crude 2,6-naphthalenedicarboxylic acid at a high temperature of 300 ° C. or higher using water or an aqueous acetic acid solution as a solvent, It shows a method of purifying by hydrogenation treatment and crystallization. In this method, a high temperature is required to increase the solubility of 2,6-naphthalenedicarboxylic acid, so that there is a problem that naphthoic acid is generated by a decarboxylation reaction. Further, in order to remove formylnaphthoic acid, a hydrogenation treatment using an expensive noble metal catalyst is required, and at this time, tetralin dicarboxylic acid is easily generated by a nuclear hydrogenation reaction.

In Japanese Patent Application Laid-Open No. Sho 62-230747, crude 2,6-naphthalenedicarboxylic acid is dissolved in a solvent such as dimethylsulfoxide, dimethylacetamide, dimethylformamide and the like. Thus, a method for purification is shown. However, in this method, a large amount of activated carbon must be used for decolorization, the solubility in the solvent is low, a large amount of the solvent is required, and the recovery is low. JP-A-5-32586 discloses a purification method by dissolving in pyridines and crystallization. However, in this method, the recovery is low because the temperature dependence of the solubility of 2,6-naphthalenedicarboxylic acid is small.

In addition to the above-mentioned method of purifying crude 2,6-naphthalenedicarboxylic acid as it is, a method of purifying crude 2,6-naphthalenedicarboxylic acid as an alkali salt to improve the solubility and purify it has been proposed. In JP-B-52-20993 and JP-B-48-68554, crude naphthalenedicarboxylic acid is converted to KOH or N
After dissolving in an alkaline aqueous solution such as aOH and treating with a solid adsorbent, it is precipitated as a mono-alkali salt by acid precipitation using carbon dioxide gas or sulfur dioxide gas, and the mono-alkali salt is contacted with water to disproportionate. By doing so, 2,6-naphthalenedicarboxylic acid is released. But with these methods,
A large amount of solid adsorbent must be used for decolorization, and when mono-alkali salts are precipitated, salts of other impurities such as formylnaphthoic acid are also precipitated and mixed with 2,6-naphthalenedicarboxylic acid I do.

In Japanese Patent Publication No. 52-20994 and JP-A-48-68555, crude 2,6-naphthalenedicarboxylic acid is dissolved in an aqueous alkali solution such as KOH or NaOH and subjected to a decolorizing treatment with a solid adsorbent. A method of obtaining purified 2,6-naphthalenedicarboxylic acid by crystallization of a dialkali salt by cooling or concentration and further disproportionation thereof has been proposed. However, this method requires a solid adsorbent for decolorization,
Furthermore, the temperature dependence of the solubility of the dialkaline salt is small, and the recovery rate is low even at a low temperature because the solubility of the dialkaline salt in water is very large.

In Japanese Patent Application Laid-Open No. 2-243652, crude 2,6-naphthalenedicarboxylic acid is dissolved in an aqueous alkaline solution, and an organic solvent having a high solubility in water, such as alcohol or acetone, is added thereto to prepare 2,6. -A method of precipitating and purifying a dialkaline salt of naphthalenedicarboxylic acid is disclosed. However, in this method, since the precipitation rate of the crystal is high, impurities are easily taken in. When a high recovery rate is obtained, the effect of removing impurities is not sufficient. Further, a common problem in the above-mentioned method is that crude 2,6-naphthalenedicarboxylic acid has a
When releasing 2,6-naphthalenedicarboxylic acid, it is necessary to treat a large amount of alkali and acid, and it is difficult to remove a trace amount of alkali component in the crystal.

Apart from the above-mentioned method of purifying crude 2,6-naphthalenedicarboxylic acid into an alkali salt and purifying it, a method of dissolving the crude 2,6-naphthalenedicarboxylic acid in an aqueous amine solution and purifying the crude 2,6-naphthalenedicarboxylic acid into an amine salt has also been proposed. ing. JP 50-142542
In No. 2, a method of dissolving crude 2,6-naphthalenedicarboxylic acid in an aqueous amine solution and distilling out an amine compound to precipitate 2,6-naphthalenedicarboxylic acid to obtain a purified 2,6-naphthalenedicarboxylic acid is disclosed. It is shown. The present investigators have studied this method and found that a large amount of solid adsorbent treatment and reduction treatment are indispensable for decolorization and removal of the monocarboxylic acid. It was found that high purity 2,6-naphthalenedicarboxylic acid could not be obtained.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art as described above, and to convert 2,6-naphthalenedicarboxylic acid having a good hue and high purity from crude 2,6-naphthalenedicarboxylic acid. An object of the present invention is to provide a method for producing an acid at a high recovery rate and industrially advantageously.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found that an aliphatic or alicyclic amine salt of crude 2,6-naphthalenedicarboxylic acid can be converted into water and acetonitrile. By crystallization with a mixed solvent of 2, organic impurities, especially monocarboxylic acids, are almost completely removed, and an amine salt of 2,6-naphthalenedicarboxylic acid having an improved hue is obtained. Due to the large dependence, the amine salt of 2,6-naphthalenedicarboxylic acid was recovered at a high recovery rate, and the amine salt of 2,6-naphthalenedicarboxylic acid was heated and the amine was distilled off to obtain a highly pure hue. It has been found that 2,6-naphthalenedicarboxylic acid having a good value can be obtained at a high recovery rate, and the present invention has been achieved.

That is, the present invention is characterized in that a crude 2,6-naphthalenedicarboxylic acid is crystallized from an aliphatic or alicyclic amine salt with a mixed solvent of water and acetonitrile, and the high purity 2,6-naphthalenedicarboxylic acid is crystallized.
There is a method for producing naphthalenedicarboxylic acid, in which an amine salt obtained by this crystallization is heated to distill an aliphatic or alicyclic amine to produce high-purity 2,6-naphthalenedicarboxylic acid.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Crude 2,6-naphthalenedicarboxylic acid to be purified in the present invention is produced by an oxidation reaction of 2,6-dialkylnaphthalene. The method of the oxidation reaction is not particularly limited. Examples of the 2,6-dialkylnaphthalene used as a raw material for the oxidation reaction include 2,6-dimethylnaphthalene, 2,6-diethylnaphthalene, 2,6-dipropylnaphthalene, and 2,6-diisopropylnaphthalene.

The aliphatic or alicyclic amines (hereinafter referred to as amines) used for producing the amine salt of 2,6-naphthalenedicarboxylic acid in the present invention include, for example, methylamine, dimethylamine, trimethylamine, and the like. Ethylamine, diethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, propylamine, isopropylamine, dipropylamine, diisopropylamine, butylamine, isobutylamine, sec-
Butylamine, tert-butylamine, dibutylamine,
Aliphatic amines such as diisobutylamine, tributylamine, pentylamine, dipentylamine, tripentylamine, 2-ethylhexylamine, and alicyclic amines such as piperidine, N-methylpiperidine, pyrrolidine, ethyleneimine, and hexamethyleneimine. Can be Among these, methylamines and ethylamines are preferable from the viewpoint of easy handling and availability, and among them, trimethylamine and triethylamine, which have a low decomposition temperature when forming an amine salt with naphthalenedicarboxylic acid, are particularly preferable.
Further, two kinds of amines may be used in combination.

The step of purifying the crude 2,6-naphthalenedicarboxylic acid in the present invention comprises the steps of crystallizing the amine salt of the crude 2,6-naphthalenedicarboxylic acid from a mixed solvent of water and acetonitrile, and purifying the crude 2,6-naphthalenedicarboxylic acid by crystallization. Heating an amine salt of 6,6-naphthalenedicarboxylic acid to distill amines.

In the crystallization step, first, crude 2,6-naphthalenedicarboxylic acid is mixed with an amine, a mixed solvent of water and acetonitrile, and heated. By this operation, the crude 2,6-naphthalenedicarboxylic acid forms a salt with amines and is dissolved in a mixed solvent of water and acetonitrile. In the crystallization of the amine salt of the crude 2,6-naphthalenedicarboxylic acid, the mixing ratio was 1 to 9 with water.
9 to 1 part by weight of acetonitrile 99 to 1 part by weight, preferably 3 to 25 parts by weight of acetonitrile 97 to 1 part by weight
75 parts by weight.

The amine salt of 2,6-naphthalenedicarboxylic acid shows a large solubility in water alone, but has a small temperature dependence of the solubility and a high solubility even at a low temperature. Lower. Further, it is hardly soluble in acetonitrile alone and crystallization operation is impossible. In contrast, the present inventors have found that when a mixed solvent of water and acetonitrile is used, the aliphatic amine salt of 2,6-naphthalenedicarboxylic acid dissolves well at high temperatures, and the solubility decreases at low temperatures. .

That is, 2,6-naphthalenedicarboxylic acid ditriethylamine salt (2,6-NDCA.TEA) obtained by using triethylamine as an amine has a water concentration of 5, 10 or 20% by weight in a water-acetonitrile mixed solvent and water. Table 1 shows the results measured by the present inventors regarding the solubility in water.

[0020]

3. Mixing ratio of water to acetonitrile (wt%) 5 10 20 100 Solubility [g 2,6-NDCA.TEA / 100 g solvent] 25 (° C.) 0.7 4.3 11 110 50 (° C.) 0 14 44 135 75 (° C) 22 45 90 204 100 (° C) 110 140 170 240

For example, using 100 g of a water-acetonitrile mixed solvent having a water concentration of 10 wt%, 140 g of 2,6-naphthalenedicarboxylic acid ditriethylamine salt is dissolved at 100 ° C., and cooled to 25 ° C. for crystallization. Since the dissolution amount at 25 ° C. is 4.3 g, 97% of the crystals of 2,6-naphthalenedicarboxylic acid ditriethylamine salt are [(140-4.3) /140=0.97].
At a recovery rate of By mixing water and acetonitrile as a solvent in this way, water alone or acetonitrile alone can achieve a high recovery of 2,2
Crystallization of the amine salt of 6-naphthalenedicarboxylic acid becomes possible.

When the crude 2,6-naphthalenedicarboxylic acid and amines are heated and mixed in the solvent, an amine salt of 2,6-naphthalenedicarboxylic acid is rapidly formed and dissolved in the solvent. Here, the amount of the amine used is equivalent to or more than the carboxylic acid group of the crude 2,6-naphthalenedicarboxylic acid. As an economical amount to be industrially used, 1.0 to 1.2 equivalents to the carboxylic acid group is appropriate.

The mixed solvent of water and acetonitrile has the above-mentioned mixing ratio, and is mixed with crude 2,6-naphthalenedicarboxylic acid.
It is used in a weight of 0.2 to 100 times, preferably 0.5 to 10 times. The mixing ratio of water and acetonitrile and the amount used are within this range in consideration of the crystallization temperature, the recovery and purification of 2,6-naphthalenedicarboxylic acid amine salt, the operability during solid-liquid separation, and the economics. Arbitrarily selected.

The crude 2,6-naphthalenedicarboxylic acid is mixed with the above amines and a mixed solvent of water and acetonitrile,
The temperature at which the amine salt of 6-naphthalenedicarboxylic acid is formed and dissolved is 0 to 250 ° C, preferably 50 to 150 ° C.
It is. The pressure in the system at that time depends on the mixing ratio of the solvent used and the temperature, and is not particularly limited.

By the above operation, in the mixed solution of water and acetonitrile in which the crude aliphatic amine salt of 2,6-naphthalenedicarboxylic acid is dissolved, heavy metal components such as Co and Mn derived from the oxidation catalyst are precipitated as insolubles. It is desirable to remove this heavy metal component by filtration in order to obtain high quality purified 2,6-naphthalenedicarboxylic acid. Also purified by crystallization
Before the step of distilling the amine by heating the aliphatic amine salt of 2,6-naphthalenedicarboxylic acid, the amine salt of 2,6-naphthalenedicarboxylic acid is again dissolved in a solvent such as water, and filtration is performed at this stage. It can also be removed.

Next, purified crystals of the aliphatic amine salt of 2,6-naphthalenedicarboxylic acid were obtained by crystallization from a mixed solution of water and acetonitrile in which the crude aliphatic amine salt of 2,6-naphthalenedicarboxylic acid was dissolved. obtain. This crystallization utilizes the temperature dependency of the solubility of the 2,6-naphthalenedicarboxylic acid amine salt in the solvent, and the temperature difference, that is, the 2,6-naphthalenedicarboxylic acid amine salt is precipitated by cooling. Will be implemented. The cooling temperature is in the range of -50 to 100C. Generally, the cooling temperature that can be industrially easily carried out at the time of crystallization is preferably about 10 to 60 ° C, and in the present invention, 2,6-
The solubility of the naphthalenedicarboxylic acid amine salt in the solvent is small around room temperature, and the temperature dependence of the solubility is very large.
A 2,6-naphthalenedicarboxylic acid amine salt having a sufficient degree of purification can be obtained with a high recovery rate and an economical amount of solvent used.

By this crystallization operation, almost all organic impurities in the crude 2,6-naphthalenedicarboxylic acid are removed. Especially,
Monocarboxylic acids such as naphthoic acid, methylnaphthoic acid and formylnaphthoic acid and trimellitic acid are almost completely removed. In the method of the present invention, a formylnaphthoic acid which is liable to remain by a normal crystallization operation is removed, and thus a special operation for removing formylnaphthoic acid such as a hydrogenation reaction is not required.

In the present crystallization operation, the coloring component in the crude 2,6-naphthalenedicarboxylic acid is also removed, and a 2,6-naphthalenedicarboxylic acid amine salt having significantly improved hue is obtained. In order to further promote decolorization, the treatment may be performed with a solid adsorbent. For example, the 2,6-naphthalenedicarboxylic acid amine salt obtained by crystallization is again dissolved in a solvent such as water, and decolorization treatment is performed with a small amount of a solid adsorbent. If necessary, a purification treatment such as hydrogenation may be performed. If the solid adsorbent treatment is performed before the crystallization step, the decolorization load on the solid adsorbent increases, and a large amount of solid adsorbent is required, which is uneconomical. The crystallization method of the present invention may be either a batch method or a continuous method, but the continuous method is superior when a large amount is processed as an industrial process. The 2,6-naphthalenedicarboxylic acid amine salt obtained by crystallization is separated by a solid-liquid separation operation such as filtration or centrifugation.

Next, in order to remove the crystallization mother liquor adhering to the crystal surface, it has solubility in water and acetonitrile,
Wash with a solvent that has little solubility in the naphthalenedicarboxylic acid amine salt. Usually, acetonitrile alone or acetonitrile containing a small amount of water is used as a washing solvent. The crystallization mother liquor and the washing solution are recycled as crystallization raw materials or reused after extracting impurities. By repeating the above crystallization operation a plurality of times, a 2,6-naphthalenedicarboxylic acid amine salt having higher purity and improved hue can be obtained, but the number of times of crystallization takes into account the degree of purification and economical efficiency of the substance. Is determined.

The amine salt of 2,6-naphthalenedicarboxylic acid thus obtained is subjected to a step of distilling an amine by heating to obtain a purified 2,6-naphthalenedicarboxylic acid. As a method for distilling an amine from a 2,6-naphthalenedicarboxylic acid amine salt, a method of heating the 2,6-naphthalenedicarboxylic acid amine salt as it is and a method of heating the 2,6-naphthalenedicarboxylic acid amine salt in the presence of a solvent There is a method, and either method may be used. However, in the method of heating the 2,6-naphthalenedicarboxylic acid amine salt as it is, the organic impurities that cannot be completely removed in the crystallization step remain in the crystal. On the other hand, the method of distilling an amine by heating in the presence of a solvent has the effect of further removing organic impurities that could not be completely removed in the crystallization step, and a high-quality purified naphthalenedicarboxylic acid can be obtained. . The solvent used at this time is not particularly limited as long as it does not react with the 2,6-naphthalenedicarboxylic acid amine salt at the time of heating, but water is preferably used.

In a method for distilling an amine in the presence of water using water as a solvent, 2,6-naphthalenedicarboxylic acid amine salt purified by crystallization is dissolved in water. At this time, decolorization can be promoted by treating the solution with a small amount of a solid adsorbent. In addition, foreign matter and metal components can be removed by microfiltration of the solution. Next, the solution is heated to distill the amine together with water while supplying water or superheated steam. If the heating temperature is too low, the decomposition rate of the amine salt will be slow, and if it is too high, the precipitated 2,6-naphthalenedicarboxylic acid may be altered or colored, so
The temperature is 300 ° C, preferably 100 to 250 ° C. At this time, if distillation is performed while blowing an inert gas such as nitrogen gas, water containing a high concentration of amine is distilled out, and the recovery of 2,6-naphthalenedicarboxylic acid is improved.

In this method, the amine salt of 2,6-naphthalenedicarboxylic acid is decomposed, and the generated amines can be recovered by cooling and collecting almost all the amines. These amines can be purified if necessary and reused. As the amines are distilled off, free 2,6-naphthalenedicarboxylic acid precipitates in the aqueous solution containing the amine salt of 2,6-naphthalenedicarboxylic acid. The amount of precipitated 2,6-naphthalenedicarboxylic acid is proportional to the amount of distilled amine. By increasing the amount of distilled amine, 2,6-naphthalenedicarboxylic acid can be obtained with a high recovery of 90% or more. it can.

The above-mentioned amine distilling operation may be either a batch system or a continuous system. However, industrially, it is economical to distill the amine by a continuous system. Crystals of purified 2,6-naphthalenedicarboxylic acid generated by heating are recovered by operations such as filtration and centrifugation. In addition, a water washing operation is performed as needed to remove impurities adhering to the crystal. Further drying yields purified 2,6-naphthalenedicarboxylic acid.

[0034]

The method of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, the organic impurity components in the raw material and the crystals of the purified naphthalenedicarboxylic acid were analyzed by gas chromatography after the methyl esterification treatment, and the metal impurity components were analyzed by ICP emission spectrometry after the wet decomposition treatment. analyzed. For the hue, 1 g of a sample was dissolved in 10 ml of a 1N aqueous solution of sodium hydroxide, and the absorbance at 400 nm using a 10 mm quartz cell (hereinafter referred to as O
D ₄₀₀ ).

Abbreviations described in the following Examples, Comparative Examples and Tables are as follows. 2,6-NDCA 2,6-naphthalenedicarboxylic acid 2,6-NDCA / TEA 2,6-naphthalenedicarboxylic acid ditriethylamine salt 2-NA 2-naphthoic acid 2,6-MNA 2,6-methylnaphthoic acid 2, 6-FNA 2,6-Formylnaphthoic acid TMAC Trimellitic acid Br-2,6-NDCA 2,6-Naphthalenedicarboxylic acid bromide NTCA Naphthalenetricarboxylic acid LE Low boiling HE High boiling TEA Triethylamine TMA Trimethylamine

Production Example A catalyst solution was prepared by mixing and dissolving 3.8 g of cobalt acetate (tetrahydrate), 32.0 g of manganese acetate (tetrahydrate), and 7.43 g of hydrogen bromide (47% aqueous solution) in 1797 g of glacial acetic acid. did. 740 g of the above catalyst solution was charged into a 5 L titanium autoclave equipped with a stirrer, a reflux condenser and a raw material feed pump. The remaining catalyst liquid
It was mixed with 180 g of 2,6-dimethylnaphthalene, charged into a raw material supply tank, and heated to dissolve 2,6-dimethylnaphthalene, thereby preparing a raw material liquid. The pressure in the reaction system was adjusted to 18 kg / cm ² G with nitrogen, and the mixture was heated to 200 ° C. while stirring. After the temperature and pressure were stabilized, the raw material liquid and compressed air were supplied to the reactor to start the oxidation reaction. Oxygen concentration in reactor off-gas
While adjusting the supply air flow rate to be 0.1% by volume,
The raw material liquid was continuously supplied over 2 hours. After the supply of the raw material liquid was completed, the supply of air was continued for 9 minutes. After the completion of the reaction, the autoclave was cooled to room temperature to take out the reaction product, which was subjected to suction filtration with a glass filter, washed with water and acetic acid, and then dried. As a result, the composition and hue
2,6-NDCA was obtained. This crude 2,6-NDCA was used as a raw material in the following Examples and Comparative Examples.

Example 1 A crude 2,6-NDC obtained in Production Example was placed in a 300 ml pressure filtration apparatus.
A 50.0 g, TEA 50.0 g (1.07 equivalent to 2,6-NDCA), 1
Take 100 g of acetonitrile solution containing 0 wt% water,
To dissolve 2,6-NDCA, and a heavy metal component as an insoluble matter was removed by filtration with a 1 μm metal filter. The total amount of the filtrate is 30 equipped with a stirrer, a filter, and a gas outlet.
After transferring to a 0 ml autoclave and purging with nitrogen, the mixture was mixed at 100 ° C. for 30 minutes. After cooling to 25 ° C. over 8 hours, the crystals of 2,6-NDCA / TEA precipitated by this crystallization operation were separated by filtration and washed twice with 100 g of acetonitrile. At this time, the recovery rate of 2,6-NDCA / TEA was 95.6%. Next, 150 g of water was added to the obtained 2,6-NDCATEA crystal to form an aqueous solution, heated to 200 ° C, and water was added at the same temperature at a rate of 200 g / hr.
The operation of withdrawing the same amount of distillate from the upper part of the reactor while blowing in nitrogen so as to reach the total pressure was performed for about 2.5 hours. Total distillate volume is about 10 for 2,6-NDCA in solution
Double the amount. Then, the mixture was filtered under pressure at the same temperature to obtain 2,2.
The 6-NDCA crystals were washed with water and acetic acid, and then dried at 120 ° C. for 5 hours. As a result, purification of the composition and hue shown in Table 2 2,6-ND
44.5 g of CA were obtained. The recovery of 2,6-NDCA in all operations was 90.8%. This purified 2,6-NDCA had greatly improved hue, and almost no organic impurities were observed.

Example 2 5 w of acetonitrile solution containing 10 wt% of water was replaced with 100 g of acetonitrile solution.
A crystallization operation and a TEA distillation process were performed in the same manner as in Example 1 except that 100 g of an acetonitrile solution containing t% of water was used.
As a result, 46.2 g of purified 2,6-NDCA having the composition and hue shown in Table 2
was gotten. 2,6-NDCA / TEA recovery rate in crystallization operation is 99%
This is very high, and the recovery of 2,6-NDCA in all operations is
94.3%.

Example 3 20 watts of acetonitrile solution containing 10 wt% water was used instead of 100 g.
A crystallization operation and a TEA distillation process were performed in the same manner as in Example 1 except that 100 g of an acetonitrile solution containing t% of water was used.
As a result, 41.3 g of purified 2,6-NDCA having the composition and hue shown in Table 2
was gotten. The recovery of 2,6-NDCA / TEA in the crystallization operation was 88.6
%, And the recovery of 2,6-NDCA in all the operations was 84.2%.

Example 4 A crystallization operation and a distilling treatment of TMA were carried out in the same manner as in Example 1 except that 29.3 g of TMA (1.07 equivalent to 2,6-NDCA) was used instead of 50 g of TEA. As a result, 44.1 g of purified 2,6-NDCA having the composition and hue shown in Table 2 was obtained. The recovery rate at this time is 9
0.1%.

[0041]

[Table 2] Example 1 Example 2 Example 3 Example 4 Organic composition (%) (%) (%) (%) 2,6-NDCA 99.978 99.966 99.979 99.974 2-NA 0.000 0.000 0.000 0.000 2,6- MNA 0.000 0.000 0.000 0.000 TMAC 0.000 0.000 0.000 0.000 2,6-FNA 0.000 0.001 0.000 0.000 LE 0.002 0.004 0.002 0.002 Br-2,6-NDCA 0.000 0.001 0.000 0.000 NTCA 0.000 0.003 0.000 0.003 HE 0.020 0.025 0.019 0.021 Total 100.000 100.000 100.000 100.000 Metal content (ppm) (ppm) (ppm) (ppm) Co <1.0 <1.0 <1.0 <1.0 Mn 3.5 4.0 3.0 3.2 Hue value (OD ₄₀₀ ) 0.041 0.050 0.039 0.044

Comparative Example 1 Water 5 was used instead of 100 g of an acetonitrile solution containing 10 wt% of water.
A crystallization operation and a distilling treatment of TEA were performed in the same manner as in Example 1 except that 0 g was used. As a result, 20.1 g of purified 2,6-NDCA having the composition and hue shown in Table 3 was obtained. 2,6-NDCA ・ T in crystallization operation
The recovery of EA was remarkably low at 43.2%, with 2,6-N
The recovery of DCA was 41.0%.

Comparative Example 2 The same operation as in Example 1 was carried out except that 100 g of acetonitrile was used instead of 100 g of an acetonitrile solution containing 10 wt% of water. 6-NDCA did not dissolve at all, and purified 2,6-NDCA was not obtained.

[0044]

[Table 3] Production example Comparative example 1 Comparative example 2 Organic composition (%) (%) (%) 2,6-NDCA 98.312 99.968 Purified 2,6-NDCA 2-NA 0.064 0.001 Not obtained 2,6-MNA 0.010 0.000 TMAC 0.649 0.000 2,6-FNA 0.255 0.002 LE 0.104 0.004 Br-2,6-NDCA 0.182 0.000 NTCA 0.178 0.000 HE 0.246 0.025 Total 100.000 100.000 Metal amount (ppm) (ppm) (ppm) Co 500 <1.0 Mn 2500 3.2 Hue value (OD ₄₀₀ ) 0.930 0.045

[0045]

As is clear from the above examples, according to the present invention, 2,6-naphthalenedicarboxylic acid having good hue and high purity can be recovered from crude 2,6-naphthalenedicarboxylic acid at a high recovery rate. Is obtained. The features of the method of the present invention are as follows. 1) By crystallization with a mixed solvent of water and acetonitrile, organic impurities are almost completely removed, and an amine salt of 2,6-naphthalenedicarboxylic acid having an improved hue is obtained. 2) The solubility of the amine salt of 2,6-naphthalenedicarboxylic acid is highly temperature-dependent, and is small at low temperatures and high at high temperatures for the solvent used.
The amine salt of 6-naphthalenedicarboxylic acid is obtained with high recovery. 3) When this amine salt of 2,6-naphthalenedicarboxylic acid is heated in the coexistence of water to distill the amine, 2,6-naphthalenedicarboxylic acid having high purity and good hue can be obtained at a high recovery rate. 4) Almost all of the amines generated by heating the amine salt can be easily recovered by cooling and collecting, and can be recycled. Therefore, the present invention is an industrially excellent method, and the present invention has great industrial significance.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Minoru Takakawa 22nd Wadai, Tsukuba City, Ibaraki Pref. Mitsubishi Gas Chemical Company, Ltd.

Claims (3)

[Claims] 1. Production of high-purity 2,6-naphthalenedicarboxylic acid characterized by crystallizing a crude aliphatic or alicyclic amine salt of 2,6-naphthalenedicarboxylic acid with a mixed solvent of water and acetonitrile. Law. 2. The high-purity 2,6-naphthalenedicarboxylic acid according to claim 1, wherein the amine salt of 2,6-naphthalenedicarboxylic acid obtained by crystallization is heated to distill an aliphatic or alicyclic amine. Manufacturing method. 3. An amine salt of 2,6-naphthalenedicarboxylic acid, which is obtained by crystallizing an aliphatic or alicyclic amine salt of crude 2,6-naphthalenedicarboxylic acid with a mixed solvent of water and acetonitrile, and purifying by crystallization. Is heated in the presence of water to distill an aliphatic or alicyclic amine.