JPH09208518A - Method for producing high-purity naphthalene dicarboxylic acid - Google Patents

Abstract

(57) [Abstract] [Purpose] A method for producing a high-purity naphthalenedicarboxylic acid with improved hue from a crude naphthalenedicarboxylic acid obtained by an oxidation reaction of a dialkylnaphthalene at a high recovery rate and industrially advantageously. provide. SOLUTION: A crude naphthalenedicarboxylic acid obtained by an oxidation reaction of dialkylnaphthalene is dissolved in an aqueous solution containing aliphatic amines, and heavy metal components contained as impurities in naphthalenedicarboxylic acid are removed to 100 ppm or less. The amines are distilled off by heating the obtained aqueous solution to obtain naphthalenedicarboxylic acid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity naphthalenedicarboxylic acid from crude naphthalenedicarboxylic acid obtained by oxidation of dialkylnaphthalene. Naphthalenedicarboxylic acid is useful as a raw material for polyethylene naphthalate (PEN) resin, which has excellent performance.

[0002]

Polyesters obtained by polymerizing naphthalene dicarboxylic acid and diols such as ethylene glycol have excellent tensile strength and heat resistance,
It has industrially important uses as a material for films, fibers, bottles, etc. In particular, polyethylene naphthalate (PEN), which is obtained by polymerizing 2,6-naphthalenedicarboxylic acid and ethylene glycol, is expected to grow in demand in the near future as an excellent industrial resin that replaces polyethylene terephthalate.

Naphthalenedicarboxylic acid can be obtained by oxidizing dialkylnaphthalene in a solvent of acetic acid in the presence of a heavy metal such as Co or Mn and a bromine compound with molecular oxygen at high temperature and high pressure. However, it is inevitable that the crude naphthalenedicarboxylic acid thus obtained contains catalyst metals such as Co and Mn in the range of several hundred ppm to several thousand ppm. Formylnaphthoic acid and methylnaphthoic acid, which are intermediate products of the oxidation reaction, trimellitic acid generated by decomposition of the naphthalene ring, naphthalenedicarboxylic acid bromide added with bromine, and naphthoic acid and naphthalenetricarboxylic acid derived from impurities in the raw material dialkylnaphthalene. An acid or the like is contained as an impurity. In addition to this, there are also coloring components whose structure is unknown. When naphthalene dicarboxylic acid containing these impurities is used as a raw material for the polymerization with diols, the obtained polyester has lower heat resistance and softening point, and deterioration in quality such as coloring. In particular, when formylnaphthoic acid is contained in a certain amount or more, the degree of polymerization does not increase, and gelation and coloring occur, so it is important to control the amount thereof. That is, high-purity naphthalene dicarboxylic acid having an extremely low content of impurities is required to obtain high-quality polyester.

Since naphthalenedicarboxylic acid is decomposed by heating at a high temperature, distillation is impossible, and since it is hardly soluble in a general solvent, it is difficult to purify it by usual simple recrystallization. Therefore, an industrial method for obtaining high-purity naphthalenedicarboxylic acid has not been established yet, and at present, crude naphthalenedicarboxylic acid is reacted with alcohols such as methanol to be purified as naphthalenedicarboxylic acid ester. However, as a raw material of polyethylene naphthalate, naphthalenedicarboxylic acid is preferable rather than naphthalenedicarboxylic acid ester, and it is necessary to establish a purification method thereof.

As a method for dissolving naphthalenedicarboxylic acid in a solvent and purifying it, US Pat. No. 5,256,817 proposes to dissolve it at a high temperature of 300 ° C. or higher in water or an acetic acid aqueous solution as a solvent to carry out hydrogenation and crystallization. doing. In this method, a high temperature is required to dissolve naphthalenedicarboxylic acid, and therefore side reactions such as generation of naphthoic acid by decarboxylation reaction and generation of tetralindicarboxylic acid by nuclear hydrogenation reaction easily occur, and yet formylnaphthoic acid The removal treatment by hydrogenation is insufficient and remains in the crystal after crystallization. In JP-A-62-230747, crude 2,6-naphthalenedicarboxylic acid is dissolved in a solvent such as dimethyl sulfoxide, dimethylacetamide, or dimethylformamide,
A purification method by crystallization is shown. However, when the solubility in the solvent is low and the solution is hydrogenated,
Since the solvent is also hydrogenated, it cannot be hydrotreated, and it is difficult to remove formylnaphthoic acid, which is a particular problem during polymerization. Japanese Unexamined Patent Publication (Kokai) No. 5-32586 discloses a purification method by dissolving in pyridine and crystallizing. However, the solubility of 2,6-naphthalenedicarboxylic acid has a small temperature dependency, so that there is a drawback that the recovery rate is low.

In addition to the method for purifying naphthalenedicarboxylic acid as it is as described above, a method for purifying it by dissolving naphthalenedicarboxylic acid in an alkali to form an alkali salt to improve the solubility has been proposed. For example, Japanese Patent Publication Sho 52-2
In 0993 and Japanese Examined Patent Publication No. 48-68554, crude naphthalenedicarboxylic acid is dissolved in an alkaline aqueous solution such as KOH or NaOH, and precipitated as a monoalkali salt by acid precipitation using carbon dioxide gas or sulfurous acid gas. 2,6-naphthalenedicarboxylic acid is liberated by contacting with water and disproportionation. However, in these methods, when the monoalkali salt is precipitated, salts of other impurities such as 2,6-formylnaphthoic acid are also precipitated at the same time, and it is necessary to treat and recover a large amount of alkali and acid. There was a flaw. In Japanese Patent Publication No. 52-20994 and Japanese Patent Laid-Open No. 48-68555, crude 2,6-naphthalenedicarboxylic acid is dissolved in an aqueous alkaline solution such as KOH or NaOH, and the dialkali salt is crystallized by cooling or concentrating. A method of obtaining purified 2,6-naphthalenedicarboxylic acid by disproportionation has been proposed. However, in this method, the solubility of the dialkali salt is less dependent on temperature, and the solubility of the dialkali salt in water is very large even at a low temperature, so that the recovery rate is low, and further there is a problem that it is difficult to remove a trace amount of alkali in the crystal. .

Various methods have been proposed for purifying amines instead of alkalis. In JP-A-50-135062, crude 2,6-naphthalenedicarboxylic acid is dissolved in an aqueous aliphatic amine solution having a carbon number of 6 or less, crystallized as a diamine salt by cooling or concentration, and purified by thermal decomposition. A method for obtaining 6-naphthalenedicarboxylic acid is shown. However, in this method, the solubility of the diamine salt in water is very high even at a low temperature, and therefore the recovery rate is low, which is an industrial problem. Further, in JP-A-5-294892, naphthalenedicarboxylic acid is dissolved in a mixed solvent of amines and alcohols for crystallization, and the precipitated naphthalenedicarboxylic acid amine salt is thermally decomposed at a temperature not lower than the boiling point of the amine, A method for obtaining purified naphthalenedicarboxylic acid is shown. This method also has a drawback that the recovery rate is low because the solubility of the amine salt of naphthalenedicarboxylic acid in the lower alcohol is very high.

In Japanese Patent Laid-Open No. 142542/1975, crude 2,6-naphthalenedicarboxylic acid is dissolved in an aqueous amine solution, and then the amine compound is distilled off to precipitate 2,6-naphthalenedicarboxylic acid. A method for obtaining 6-naphthalenedicarboxylic acid is shown. This method uses a lot of water,
It has a drawback that it consumes a lot of energy, and the recovery rate in Examples is as low as 63.8 to 72.4%. Furthermore, when the present inventors conducted a detailed study of this method, in the region where the industrially recoverable 2,6-naphthalenedicarboxylic acid was obtained, 2,6-naphthalenedicarboxylic acid with a sufficiently good hue was obtained. Could not get acid.

[0009]

As described above, in the conventional method for purifying naphthalenedicarboxylic acid using an amine,
Since the naphthalene dicarboxylic acid is exposed to a high temperature in order to thermally decompose or distill off the amine compound, coloring is promoted at that time, so that it is difficult to obtain a high quality product. Further, the recovery rate of naphthalenedicarboxylic acid is generally low, and its improvement is required. An object of the present invention is to provide a method for industrially advantageously producing a highly pure naphthalenedicarboxylic acid having an improved hue from a crude naphthalenedicarboxylic acid obtained by an oxidation reaction of a dialkylnaphthalene with a high recovery rate. It is in.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a naphthalenedicarboxylic acid amine salt obtained by a reaction of naphthalenedicarboxylic acid and an aliphatic amine is dissolved in water. After removing the heavy metal components and heating the aqueous solution to distill off the amines, it was found that naphthalene dicarboxylic acid with high purity and good hue can be obtained with a high recovery rate, and the present invention was reached.

That is, according to the present invention, crude naphthalenedicarboxylic acid obtained by the oxidation reaction of dialkylnaphthalene is dissolved in an aqueous solution containing aliphatic amines, and 100 ppm of a heavy metal component contained as an impurity is added to naphthalenedicarboxylic acid.
A method for producing high-purity naphthalenedicarboxylic acid, which comprises removing naphthalenedicarboxylic acid by distilling amines off by heating the resulting aqueous solution after removal as described below.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The crude naphthalenedicarboxylic acid used as a raw material in the present invention is not particularly limited as long as it is obtained by an oxidation reaction of dialkylnaphthalene. Examples of the dialkylnaphthalene used in the oxidation reaction include dimethylnaphthalene, diethylnaphthalene, dipropylnaphthalene, diisopropylnaphthalene, and the like.
There are 10 isomers depending on the position of the alkyl group.
Among them, as a raw material of polyester, 2,6-substituted products and 2,7-substituted products are useful, and 2,6-naphthalenedicarboxylic acid is particularly preferably used. These dialkylnaphthalene are present in the presence of an oxidation catalyst mainly composed of heavy metals and bromine,
Crude naphthalene dicarboxylic acid is obtained by oxidation with molecular oxygen.

Examples of aliphatic amines capable of dissolving crude naphthalenedicarboxylic acid include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethyldimethylamine, diethylmethylamine, propylamine, isopropylamine, dipropylamine, Diisopropylamine, butylamine, isobutylamine, sec-butylamine, tert-
Butylamine, dibutylamine, diisobutylamine,
Alkylamines such as tributylamine, pentylamine, dipentylamine, tripentylamine, 2-ethylhexylamine, piperidine, N-methylpiperidine,
Examples thereof include alicyclic amines such as pyrrolidine, ethyleneimine, and hexamethyleneimine. Of these, methylamines and ethylamines are preferable because of their ease of handling and availability. Among these, trimethylamine and triethylamine, which have low decomposition temperatures of amine salts when forming amines with naphthalenedicarboxylic acid, are particularly preferable. Also, two or more kinds of these amines may be mixed and used.

In the method of the present invention, first, crude naphthalene dicarboxylic acid is dissolved in an aqueous solution containing these aliphatic amines. The amount of the amine compound used is equivalent to or more than the carboxylic acid group of the crude naphthalene dicarboxylic acid. The economical amount of industrial use is 1.0 to 1.2 equivalents.
The optimum amount of water is affected by the type and amount of the amine compound, the temperature at which the crude naphthalenedicarboxylic acid is dissolved, and the type and amount of the impurities contained, but usually 0.5 to 50 times the weight of the naphthalenedicarboxylic acid, preferably Is 1 to 20 times the weight. The temperature at which crude naphthalenedicarboxylic acid is mixed with an aqueous solution containing the above amines to form and dissolve an amine salt is about 10 to 100 ° C.

In the present invention, it is necessary to remove the heavy metal component contained as an impurity in the amine salt aqueous solution so as to be 100 ppm or less with respect to naphthalenedicarboxylic acid before carrying out the amine distillation operation. When it is higher than 100 ppm, the hue of the finally obtained naphthalene dicarboxylic acid is poor, and it is more colored than the raw material naphthalene dicarboxylic acid. This has nothing to do with the recovery rate of naphthalene dicarboxylic acid, and coloring is inevitable even if the recovery rate is lowered. The cause of this coloring is that the heavy metal component contained as an impurity promotes the generation of a new coloring component in the amine distillation operation. As described in JP-A-50-142542, it is not possible to remove isomers of naphthalenedicarboxylic acid, bromine derivatives, aldehydes, and originally existing coloring components as impurities by simply performing a solid adsorbent treatment. Even if it is possible, it is not always possible to remove the heavy metal component to 100 ppm or less, and therefore it is difficult to control the coloration during amine distillation. The smaller the content of the heavy metal component is, the more the generation of a new coloring component is suppressed, but when the content is more than 100 ppm, the degree of coloring is particularly remarkable. Therefore, it is necessary to remove heavy metal components to 100 ppm or less.

The heavy metal components contained in the crude naphthalene dicarboxylic acid are mainly cobalt and manganese which are catalyst components for the dialkylnaphthalene oxidation reaction, and other than this, metal components added as co-catalysts and titanium derived from the material of the reactor, There are iron, nickel, chromium, etc. Cobalt and manganese are several hundred to several thousand in crude naphthalene dicarboxylic acid.
ppm, especially its removal is important. When crude naphthalenedicarboxylic acid is dissolved in an aqueous amine solution, most of these heavy metal components are precipitated as insoluble matter. The insoluble heavy metal component is first removed by filtration. The pore size of the filter used for filtration is 10 μm or less, preferably 5 μm or less, more preferably 1 μm or less. In industrial equipment, it is preferable to gradually reduce the pore size of the filter by multistage filtration because it prevents clogging and enables stable operation for a long period of time.

Heavy metal components that cannot be completely removed by filtration using these filters can be further removed by solid adsorbent treatment. As the solid adsorbent, activated carbon,
Activated alumina, activated clay, ion exchange resin, etc. are used. In order to use the solid adsorbent in industrial equipment, it is carried out by filling a column and continuously supplying an aqueous solution containing an amine salt of naphthalenedicarboxylic acid. When the amine aqueous solution is directly supplied to the column packed with the solid adsorbent without performing the filtration operation to perform the operation of removing the insoluble heavy metal component, the load on the solid adsorbent is large because the amount of the insoluble heavy metal component that must be removed is large. Large, heavy-metal removal effect cannot be obtained for a long time.
In addition, a large amount of insoluble heavy metal components accumulate in the column and the column is clogged, making stable operation impossible. When the solid adsorbent treatment is performed by a batch operation, the amine aqueous solution and the solid component must be separated by filtration, and in that case, the amount of the solid component that must be treated as compared with the first filtration operation. Undesirably increases.

The aqueous solution of the amine salt of naphthalenedicarboxylic acid from which the heavy metal components have been removed to 100 ppm or less is then subjected to formylnaphthoic acid removal treatment in order to remove formylnaphthoic acid, which is particularly problematic during polymerization. It is preferable. A noble metal catalyst is usually used for the formylnaphthoic acid removal treatment, and the noble metal catalyst is poisoned by heavy metal components. By removing the heavy metal component to 100 ppm or less, the life of the catalyst used for the formylnaphthoic acid removal treatment carried out before the amine distillation operation can be maintained for a long period of time.

An example of the formylnaphthoic acid removal treatment is hydrogenation treatment. Hydrogenation is a reaction to convert the formyl group of formylnaphthoic acid to a methyl group, and as a catalyst on a large surface area carrier such as activated carbon, silica, or alumina.
A material in which one or more metals are dispersed among Pt, Pd, Rh, Ru, Ni, and Co is used. Preferably, a catalyst in which Pd or Pt is dispersed on activated carbon is used. In the presence of these catalysts, a solution of crude naphthalenedicarboxylic acid dissolved in an aqueous amine solution is subjected to formylnaphthoic acid removal treatment. The reaction system may be a batch system or a continuous flow system, but industrially the continuous flow system is preferred. The reaction conditions at that time vary depending on the catalyst species used, the amount of catalyst, and the residence time, but the reaction temperature is usually 70-25.
It is desirable that the temperature at 0 ° C. is the same as the temperature at which the crude naphthalenedicarboxylic acid is dissolved in the aqueous amine solution. Hydrogen partial pressure is 0.
It is carried out at 01 to 30 kg / cm ² , preferably 0.01 to 10 kg / cm ² . Under severe reaction conditions of 250 ° C or higher, tetralindicarboxylic acid may be produced as a side reaction by nuclear hydrogenation of the naphthalene ring, or naphthoic acid may be produced by decarboxylation or decarbonylation reaction.

The amine compound is distilled off from the aqueous solution containing the amine salt of naphthalenedicarboxylic acid thus obtained. To distill off the amine compound, the amine aqueous solution is externally heated to distill only the amine or the amine together with water, the method is to distill by heating while supplying superheated steam or water, inert gas such as nitrogen gas. There are a method of distilling off the amine while blowing gas, a method of distilling off the amine under reduced pressure, and the like, and two or more kinds of these methods may be combined to distill out only the amine or the amine and water. If the temperature for distilling off the amine is too low, the decomposition rate of the amine salt will be slow, so 50 ° C or higher is preferable, and 80 ° C or higher is particularly preferable. On the other hand, if the temperature is too high,
The naphthalene dicarboxylic acid that is produced may deteriorate or become colored, so it is usually kept at 250 ° C or lower.

By distilling the amine compound from the aqueous solution containing the amine salt of naphthalenedicarboxylic acid by the above method, the amine salt of naphthalenedicarboxylic acid is decomposed,
Almost all of the generated amine can be recovered by cooling and collecting it. The collected amine can be purified and reused if necessary. As the amine is distilled, free naphthalene dicarboxylic acid precipitates from the aqueous solution containing the amine salt of naphthalene dicarboxylic acid.
The amount of precipitated naphthalene dicarboxylic acid is proportional to the amount of amine distilled off. In order to obtain naphthalenedicarboxylic acid with a high recovery rate, the amine distillation amount may be increased. In order to establish an economical industrial process, it is preferable to carry out the distillation operation at a recovery rate of 90% or more. The purified naphthalenedicarboxylic acid that precipitates by heating can be recovered by an operation such as filtration or centrifugation. Further, it is also possible to perform an operation such as washing with water at appropriate times to remove impurities adhering to the crystals. High-purity naphthalenedicarboxylic acid can be obtained by further drying the crystals thus obtained.

[0022]

EXAMPLES The method of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The purity and properties of the raw materials and the crystals of purified naphthalenedicarboxylic acid were analyzed by gas chromatography after the methyl esterification treatment for organic substances and by ICP emission spectroscopy after the wet decomposition treatment for inorganic substances.
The hue was evaluated by dissolving 1 g of the sample in 10 ml of 1N-sodium hydroxide aqueous solution and measuring the absorbance at a wavelength of 500 nm (hereinafter abbreviated as OD ₅₀₀ ) using a 10 mm quartz cell.

The abbreviations used in the following Examples, Comparative Examples and each table 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 NTCA naphthalene tricarboxylic acid Br-2,6-NDCA 2,6-naphthalenedicarboxylic acid bromide TDCA tetralindicarboxylic acid LE low boiling HE high boiling TEA triethylamine

Production Example 1797 g of glacial acetic acid was mixed with 3.8 g of cobalt acetate (tetrahydrate), 32.0 g of manganese acetate (tetrahydrate) and 7.43 g of hydrogen bromide (47% aqueous solution) to dissolve them, to prepare a catalyst solution. did. 740 g of the above catalyst liquid 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 is 2,
A raw material liquid was prepared by mixing 180 g of 6-dimethylnaphthalene, charging the raw material supply tank, and heating to dissolve 2,6-dimethylnaphthalene. The pressure in the reaction system was adjusted to 18 Kg / cm ² G with nitrogen, and the temperature was raised to 200 ° C with 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. The oxygen concentration in the reactor offgas
While adjusting the supply air flow rate so that it becomes 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 completion of the reaction, the autoclave was cooled to room temperature, the reaction product was taken out, suction filtered with a glass filter, washed with water and acetic acid, and then dried. As a result, the composition shown in Table 1 and the rough hue 2,
6-NDCA was obtained. Co is 340ppm in this crude 2,6-NDCA,
It contained 2400ppm of Mn. The crude 2,6-NDCA was used as a raw material in the following Examples and Comparative Examples.

Example 1 Crude 2,6-NDCA 200 g, water 1070 g, TEA was placed in a 2 L glass four-necked flask equipped with a reflux condenser, a stirrer and a temperature measuring tube.
205.9 g (1.1 equivalent to 2,6-NDCA) was added and stirred for 30 minutes. The heavy metal component that did not dissolve and was filtered through a sintered metal filter with a pore size of 10 μm, and then with a pore size of 5 μm.
Filtration was carried out using the above filter to obtain a dissolved aqueous solution of 2,6-NDCA.TEA. 70 g of this solution was placed in a 300 ml stainless steel autoclave equipped with a stirrer, a pressure filter, and a gas outlet, and after nitrogen replacement, it was heated to 200 ° C and water was added at the same temperature at a rate of 100 g / hr. While adding, the same amount of distillate as the amount of water sent was withdrawn from the top of the reactor for 2 hours.
The total amount of distillate was about 21 times the amount of NDCA in the solution.
Then, pressure filtration was performed at the same temperature, the obtained crystals were washed with water and acetic acid, and then vacuum dried at 120 ° C. for 5 hours. Yield 94.7% (=
Crystals of purified 2,6-NDCA having the composition and hue shown in Table 1 were obtained (crude yield based on 2,6-NDCA). Co is 10p in this 2,6-NDCA
It contained 68 ppm of pm and Mn.

Example 2 Pore size in the step of obtaining an aqueous solution of 2,6-NDCA · TEA
Pore size after filtering with a 10 μm sintered metal filter
The same operation as in Example 1 was carried out except that the product was filtered through a 1 μm nitrocellulose membrane filter to obtain purified 2,6-NDCA crystals having the composition and hue shown in Table 1. This 2,6-NDCA
The content of Co was less than 1ppm and the content of Mn was 20ppm.

Example 3 Pore size in the step of obtaining an aqueous solution of 2,6-NDCA · TEA
After filtering through a 10 μm sintered metal filter, the pore size is 1 μm.
The same operation as in Example 1 except that the solution was filtered through a m-nitrocellulose membrane filter and 70 g of the solution was passed through a glass column filled with activated carbon to obtain a solution of 2,6-NDCA.TEA in solution. Then, purified 2,6-NDCA crystals having the composition and hue shown in Table 1 were obtained. Co in this 2,6-NDCA is
It was 1 ppm or less and Mn was 0.5 ppm or less.

Example 4 Pore size in the step of obtaining an aqueous solution of 2,6-NDCA · TEA
After filtering through a 10 μm sintered metal filter, the pore size is 1 μm.
The same procedure as in Example 1 was repeated, except that the solution was filtered through a m 2 nitrocellulose membrane filter, and 70 g of the solution was passed through a glass column filled with activated clay to obtain a solution of 2,6-NDCA · TEA in solution. The operation was performed to obtain purified 2,6-NDCA crystals having the composition and hue shown in Table 1. Co in this 2,6-NDCA is
It was 1 ppm or less and Mn was 0.5 ppm or less.

Comparative Example 1 The same operation as in Example 1 except that no filtration operation was performed in the step of obtaining a 2,6-NDCA.TEA dissolved aqueous solution, and a 2,6-NDCA.TEA dissolved aqueous solution was obtained. Then, purified 2,6-NDCA crystals having the composition and hue shown in Table 2 were obtained. The 2,6-NDCA contained 330 ppm of Co and 2360 ppm of Mn.

Comparative Example 2 Pore size in the step of obtaining an aqueous solution of 2,6-NDCA · TEA
Purification of the composition and hue shown in Table 2 was performed in the same manner as in Example 1 except that filtration was performed using a 10 μm sintered metal filter.
Crystals of 2,6-NDCA were obtained. Co in this 2,6-NDCA is 210pp
The content of m and Mn was 1620ppm.

Example 5 13 mm filled with 5 g of 0.5% Pd / C catalyst having a uniform particle size of 2 to 3 mm
A mixed gas of 33.3% by volume of hydrogen and 66.7% by volume of nitrogen in a fixed bed pressure distribution reactor equipped with a φ × 316 mm stainless steel reaction tube, a gas-liquid separator, and a raw material feed pump was mixed at 10 Kg / cm ²
2,6-NDCA., Obtained by the same operation as in Example 4 while keeping the reaction tube at 150 ° C. under the same gas flow rate of 50 ml / min.
A hydrolyzed solution of TEA was circulated at 30 g / hr for hydrogenation. The hydrolyzed aqueous solution of 2,6-NDCA.TEA after the hydrogenation treatment was distilled off by the same procedure as in Example 1 to obtain purified 2,6-NDCA crystals having the composition and hue shown in Table 2. Obtained. This 2,6-
Co in NDCA was 1 ppm or less and Mn was 0.5 ppm or less.

Comparative Example 3 Using the dissolved aqueous solution of 2,6-NDCA.TEA obtained in Comparative Example 1, hydrogenation treatment and distillation treatment were carried out in the same manner as in Example 5, and the composition shown in Table 2 was obtained. Colored crystals of 2,6-NDCA were obtained. The 2,6-NDCA contained 270 ppm of Co and 2200 ppm of Mn.

[0033]

[Table 1] Production Example Example 1 Example 2 Example 3 Example 4 Organic matter (%) (%) (%) (%) (%) 2,6-NDCA 98.593 99.746 99.721 99.938 99.927 2-NA 0.056 0.003 0.006 0.002 0.003 2,6-MNA 0.010 0.003 0.002 0.002 0.002 TMAC 0.630 0.002 0.001 0.001 0.002 2,6-FNA 0.263 0.210 0.235 0.020 0.020 TDCA 0.000 0.000 0.000 0.000 0.000 LE 0.097 0.011 0.009 0.010 0.015 Br-2,6-NDCA 0.165 0.013 0.012 0.013 0.015 NTCA 0.164 0.003 0.003 0.002 0.002 HE 0.022 0.014 0.011 0.012 0.014 Total 100.000 100.000 100.000 100.000 100.000 OD ₅₀₀ 0.256 0.261 0.256 0.060 0.100

[0034]

[Table 2] Comparative Example 1 Comparative Example 2 Example 5 Comparative Example 3 Organic matter (%) (%) (%) (%) 2,6-NDCA 99.726 99.721 99.837 99.828 2-NA 0.006 0.008 0.007 0.008 2,6-MNA 0.002 0.003 0.120 0.124 TMAC 0.001 0.002 0.001 0.002 2,6-FNA 0.221 0.231 0.006 0.006 TDCA 0.000 0.000 0.003 0.002 LE 0.012 0.011 0.011 0.011 Br-2,6-NDCA 0.018 0.011 0.003 0.002 NTCA 0.002 0.004 0.002 0.002 HE 0.012 0.009 0.012 0.015 Total 100.000 100.000 100.000 100.000 OD ₅₀₀ 0.452 0.338 0.200 0.321

[0035]

The crude naphthalene dicarboxylic acid obtained by oxidizing the dialkylnaphthalene by the method of the present invention,
Dissolve heavy metal components by using an aqueous solution of aliphatic amines, and heat to distill off amines to obtain highly pure naphthalene dicarboxylic acid with improved hue easily with high recovery rate. You can Further, after removing the heavy metal components, hydrogenation is carried out, and by distilling off the amines, formylnaphthoic acid, which is particularly problematic during the polymerization, is removed, and the life of the hydrogenation catalyst is prolonged. High-purity naphthalene dicarboxylic acid is industrially produced very advantageously. Therefore, the industrial significance of the present invention is extremely large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Takakawa 22 Wadai, Tsukuba, Ibaraki Prefecture Mitsubishi Gas Chemical Co., Ltd.

Claims (3)

[Claims] 1. A crude naphthalenedicarboxylic acid obtained by an oxidation reaction of dialkylnaphthalene is dissolved in an aqueous solution containing aliphatic amines, and a heavy metal component contained as an impurity in naphthalenedicarboxylic acid is removed to 100 ppm or less. Then, the amine is distilled off by heating the obtained aqueous solution, which is a process for producing a high-purity naphthalene dicarboxylic acid. 2. The method for producing a high-purity naphthalenedicarboxylic acid according to claim 1, wherein the removal of heavy metal components is carried out by filtration, or by filtration followed by treatment with a solid adsorbent. 3. The process for producing high-purity naphthalenedicarboxylic acid according to claim 1 or 2, wherein after the heavy metal components are removed, hydrogenation is performed to distill off amines.