JPH07173100A - Production of high-purity 2,6-naphthalene-dicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide a production process for high-purity 2,6-naphthalene dicarboxylic acid with extremely reduced contents of coloring substances, heavy metals, bromine compounds and the like. CONSTITUTION:Crude crystals of 2,6-naphthalenedicarboxylic acid containing impurities is dissolved in water in the critical or sub-critical state, the solution is cooled lower than 300 deg.C to precipitate crystals. Then, the crystals are separated from the other liquor at 100 to 300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an impurity containing 2,
Crude 2,6-naphthalenedicarboxylic acid obtained by oxidizing 6-naphthalenedicarboxylic acid, especially dialkylnaphthalene with molecular oxygen is dissolved in water and crystallized to obtain high purity 2,6
-A method for producing naphthalenedicarboxylic acid.
2,6-naphthalenedicarboxylic acid is a compound useful as a raw material for highly functional resins such as polyethylene naphthalate (PEN resin).

[0002]

It is well known that naphthalenedicarboxylic acid is produced, for example, by oxidizing a dialkylnaphthalene such as dimethylnaphthalene or diisopropylnaphthalene with molecular oxygen in the presence of cobalt, manganese and bromine. There is. However, the crude naphthalene dicarboxylic acid obtained by these methods, impurities and coloring substances such as trimellitic acid, further cobalt due to the catalyst,
A purification step is necessary because it contains manganese and bromine compounds.

Conventionally, as a method for purifying naphthalenedicarboxylic acid, crude naphthalenedicarboxylic acid is dissolved in an alkaline aqueous solution, subjected to treatments such as oxidation, hydrogenation and decolorization by adsorption, and then acidified to obtain highly pure naphthalene dicarboxylic acid. A method for obtaining a dicarboxylic acid is known (JP-A-48-6).
No. 8554, JP-A-48-49747, JP-A-50-
105639, JP-A-50-160248, etc.). However, each of these methods uses a large amount of alkali and acid, and thus has a problem that a large amount of inorganic salt and waste water are generated. On the other hand, a method in which crude naphthalene dicarboxylic acid is dissolved in an organic solvent such as dimethylformamide or dimethylsulfoxide, treated with activated carbon and then recrystallized (Japanese Patent Laid-Open No. 62-23074) is also proposed. Since the solvent has a high boiling point, it is difficult to recover the solvent, and the toxicity is high.

A method has also been proposed in which crude naphthalenedicarboxylic acid is dissolved in an aqueous solution of dimethylamine or the like and then purified by depositing naphthalenedicarboxylic acid by distilling off the amine (Japanese Unexamined Patent Publication No. 50-142542). However, there are drawbacks such as a large amount of water being distilled off together since the amine used is azeotropic with water, and the recovery rate is low because the amine cannot be completely removed from the aqueous solution. Further, in order to improve these drawbacks, a method using a mixed solvent of amine and alcohol has been proposed (Japanese Patent Laid-Open No. 155807/1993), but in this method, it is caused by a catalyst such as a heavy metal. Not enough impurities are removed.

On the other hand, there has been proposed a method of washing with water at 80 to 90 ° C. to remove impurities containing cobalt and manganese (JP-A-1-121237). The incorporated impurities cannot be removed.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and comprises 2,6-naphthalenedicarboxylic acid containing impurities, particularly dialkylnaphthalene compounds in the presence of heavy metal salts and bromine compounds. A high-purity 2,6-naphthalenedicarboxylic acid having a very low content of coloring substances, heavy metals, bromine compounds, etc. is produced from 2,6-naphthalenedicarboxylic acid obtained by oxidation with a gas containing molecular oxygen. It is intended to provide a method.

[0007]

According to the present invention, crude crystals of 2,6-naphthalenedicarboxylic acid containing impurities are dissolved in water in a supercritical or subcritical state, and the resulting solution is heated to 300 ° C or lower. A method for producing high-purity 2,6-naphthalenedicarboxylic acid is provided, which comprises cooling the solution to precipitate a crystal and then separating the crystal from a mother liquor at a temperature of 100 to 300 ° C.

[0008]

DETAILED DESCRIPTION OF THE INVENTION As the crude crystals of 2,6-naphthalenedicarboxylic acid containing impurities used in the method of the present invention, those having a purity of 90% or more, generally 95 to 99% are used. Further, a substance having a purity of 99% or more, for example, 2,6-naphthalenedicarboxylic acid after a preliminary purification treatment with activated carbon or the like can be used as a treatment raw material. As such a crude 2,6-naphthalenedicarboxylic acid,
For example, crude crystals of 2,6-naphthalenedicarboxylic acid obtained by oxidizing dialkylnaphthalene compounds with molecular oxygen in the presence of cobalt, manganese and bromine in a solvent such as aliphatic lower monocarboxylic acid and water are used. Can be mentioned. The crude crystal of 2,6-naphthalenedicarboxylic acid obtained by the oxidation reaction of dialkylnaphthalene is
Cobalt, manganese, and bromine compounds derived from the catalyst, 6-carboxy-2-naphthaldehyde, trimellitic acid, nuclear brominated 2,6-naphthalenedicarboxylic acid, and other bromine compounds of unknown structure, and by-products from the reaction It contains impurities, coloring substances, etc., and usually has a light brown or brown color, but it may be directly used in the method of the present invention, or may be used after washing with a reaction solvent or the like.

Examples of the cobalt compound and the manganese compound used as a catalyst for the oxidation reaction include, for example, aliphatic carboxylates of cobalt and manganese such as formic acid, acetic acid, propionic acid, oxalic acid and maleic acid, and alicyclic rings such as naphthenic acid. Formula carboxylate, benzoic acid, terephthalic acid,
In addition to aromatic carboxylic acid salts such as naphthoic acid and naphthalene dicarboxylic acid, inorganic compounds such as acetic acid compounds, oxides, carbonates and halides can be mentioned. Of these, acetate and bromide are preferably used. Examples of the bromine compound include inorganic bromine compounds such as potassium bromide, ammonium bromide, molecular bromine and hydrogen bromide, and organic bromine compounds such as methyl bromide, ethyl bromide, bromoform, ethylene bromide and bromoacetic acid. Can be illustrated. The amount of the bromine compound used is such that the amount of bromine atoms is 0.1 to 10 times, preferably 0.1 times the total number of moles of cobalt and manganese atoms contained in the aliphatic carboxylic acid solvent.
It is in the range of 2 to 5 times.

The production of high-purity 2,6-naphthalenedicarboxylic acid from crude 2,6-naphthalenedicarboxylic acid according to the present invention is carried out by the following procedure. (1) A predetermined amount of crude 2,6-naphthalenedicarboxylic acid is dissolved in a predetermined amount of water in a supercritical or subcritical state. For supercritical or subcritical water, the temperature is 300 ° C or higher,
Usually 300 to 380 ° C, preferably 320 to 350 ° C
Use water. The pressure is a saturation pressure necessary for maintaining a liquid phase in the critical temperature range or lower, and a critical pressure or higher in the critical temperature range or higher, preferably the saturation pressure or the critical pressure or 10 kg / cm ² from the pressure. High pressure. If the temperature of the water for dissolving the crude 2,6-naphthalenedicarboxylic acid is too low, the solubility will be low, while if the temperature of the water is too high, the 2,6-naphthalenedicarboxylic acid will decompose, which is not preferable.

Although the amount of water used for dissolution varies depending on the dissolution temperature, it is more than the amount (saturated solubility) of water capable of completely dissolving the crude 2,6-naphthalenedicarboxylic acid, for example, the dissolution temperature is 350 ° C. In case of, coarse 2,6
5 parts by weight or more of water are required for 1 part by weight of naphthalenedicarboxylic acid. So far, the solubility of 2,6-naphthalenedicarboxylic acid in high temperature and high pressure water has been
Table 1 shows an example measured by the inventors, which has not been reported in a patent.

[0012]

[Table 1]

As shown in Table 1, surprisingly, the solubility of 2,6-naphthalenedicarboxylic acid in water suddenly rises in a high temperature range of 300 ° C. or higher near the critical point of water,
At around 370 ° C, which is the critical temperature of water, 30% by weight or more of 2,6-naphthalenedicarboxylic acid is dissolved. In addition,
Since water under a pressure above the critical pressure at temperatures above the critical temperature of water exhibits similar properties to the liquid phase of water below the critical temperature,
The temperature dependence of solubility can be treated continuously.

Generally, the molecules of the supercritical fluid are like balloons floating in the air, and the solid or liquid molecules existing at the interface are encased in a group (clustering) to be lifted into the fluid. Therefore, the lifted molecules can be dispersed in the supercritical fluid.
Dissolving in water in a supercritical state means making such a state.

(2) After the 2,6-naphthalenedicarboxylic acid is dissolved, it is 5 ° C., preferably 10 ° C., higher than the dissolution temperature under a pressure equal to or higher than the saturation pressure necessary to keep the obtained solution in the liquid phase. Or lower temperature, generally 300 ° C. or lower, specifically 300 to 100 ° C., preferably 270 to 180 ° C.,
More preferably, it is cooled in the range of 250 ° C to 200 ° C to precipitate crystals of 2,6-naphthalenedicarboxylic acid.
The temperature is preferably low in order to increase the recovery rate of 2,6-naphthalenedicarboxylic acid, but it is usually preferably 100 ° C. or higher in order to maintain sufficient solubility for impurities. As a cooling method, for example, a method of flushing a part of the solvent or heat exchange with low temperature water can be used.

(3) 2,6-from mother liquor in which impurities are dissolved
The crystals of naphthalenedicarboxylic acid are separated. Separation is usually carried out at a temperature equal to or lower than the cooling precipitation temperature of the above (2), generally 300 ° C. or lower, specifically 30.
It is in the range of 0 ° C to 100 ° C, preferably 270 ° C to 180 ° C, more preferably 250 ° C to 200 ° C. As a separation method, sedimentation separation, centrifugation, filtration or the like is performed, or after the mother liquor is replaced with pure water having the same pressure, water is removed by the above separation method or replacement water evaporation method.

The melting and crystallization operations consisting of (1) to (3) above can be carried out by either a continuous system or a batch system. Moreover, you may perform multistage melt | dissolution and crystallization which repeats this operation several times as needed. The obtained crystals of high-purity 2,6-naphthalenedicarboxylic acid are then, if necessary,
You may wash with water or another solvent. In this way, according to the method of the present invention, highly pure 2,6-naphthalenedicarboxylic acid having an extremely low content of impurities, for example, a bromine content of 100 ppm or less can be produced.

[0018]

In general, in the supercritical state, it is known that the solubility changes abruptly due to changes in temperature and pressure, but in the case of 2,6-naphthalenedicarboxylic acid, such a drastic change in solubility occurs. It was not expected to happen. The rapid change in the solubility of 2,6-naphthalenedicarboxylic acid from the temperature below the critical point to the critical point is 2.6
-It is speculated that this is a unique phenomenon that occurs because the melting point of naphthalenedicarboxylic acid and the critical point of water are almost the same. On the other hand, for coloring substances contained in crude crystals of 2,6-naphthalenedicarboxylic acid obtained by oxidizing dialkylnaphthalene compounds with molecular oxygen-containing gas depending on heavy metal salts and bromine compounds, impurities caused by catalysts, etc. Is 10
A sufficiently large solubility is maintained even at a temperature of 0 to 270 ° C. Therefore, the solubility of the 2,6-naphthalenedicarboxylic acid-water system has a particularly large temperature dependence,
By utilizing the large dissolving power of supercritical water or subcritical water, crystallization and purification of crude 2,6-naphthalenedicarboxylic acid can be carried out very easily.

The clustering described in (1) above is derived from the intermolecular force between the solute and water molecules, and the shape of the molecule,
It depends on the size and polarity. By the method of the present invention, the reason why the bromine compound, which cannot be sufficiently separated in the conventional method, particularly the nuclear brominated naphthalene dicarboxylic acid is well separated is that the bromide and the water molecule are present in the supercritical region or the subcritical region. It is presumed that this is because the intermolecular force between the two and the intermolecular force between the product and the water molecule are different from each other, and thus the clustering method is different, and thus the solubility is greatly different. That is, the method of the present invention is a method utilizing the properties of such a fluid in a supercritical state or a subcritical state exhibiting similar properties, and it is essential that the melting temperature condition is a supercritical state or a subcritical state. Is. Therefore, it is unexpected that the bromine compound, which has been particularly difficult to separate in the past, can be easily separated by the method of the present invention.

[0020]

EXAMPLES The present invention will be described in more detail with reference to examples. (Reference example) reflux condenser, gas introduction pipe, raw material feed pump,
In a 5 L titanium autoclave equipped with a back pressure regulator and an induction stirrer, 2050 g of acetic acid, 0.80 g (3.2 mmol) of cobalt acetate / tetrahydrate, 3.93 g (16.0 mmol) of manganese acetate / tetrahydrate. , Potassium bromide 0.95
g (7.98 mmol) was charged, the inside of the reaction system was replaced with nitrogen, and the pressure inside the system was adjusted to 25 kg / cm ² G with a back pressure regulator. Heat until the internal temperature reaches 200 ° C. Air from the liquid phase is 12 NL / min and nitrogen from the gas phase is 19 NL / min.
In minutes, the pressure was supplied so that the internal pressure was kept at 25 kg / cm ² G. When the system is stable, 2,6-dimethylnaphthalene /
600 g of a solution of acetic acid = 1/2 (weight ratio) was continuously supplied over 2 hours. After the supply of 2,6-dimethylnaphthalene was completed, the air was continuously supplied for 1 hour while maintaining the system temperature at 200 ° C. and 25 kg / cm ² G. After completion of the reaction, the autoclave was cooled to room temperature, the precipitated solid matter was collected by filtration, and warmed with warm water 6
It was washed with 00 g and 600 g of methanol. The solid was dried to obtain 255 g of a pale yellow solid. The liquid chromatography purity of this crude 2,6-naphthalenedicarboxylic acid was 97.7%, and the yield was 92%.

Example 1 To a 300 cc stainless autoclave in a constant temperature bath at 350 ° C., 25 g of the crude crystals of 2,6-naphthalenedicarboxylic acid obtained in Reference Example and water were filled (about 160).
g) Charged to a temperature of 350 ° C and 170 kg / cm ² G for 1.5
The crude crystals were kept for time and dissolved in water. Next, the temperature of the constant temperature bath was lowered to 250 ° C. over about 3 hours to precipitate crystals of 2,6-naphthalenedicarboxylic acid, and the autoclave was heated to 250 ° C. while keeping the pressure at the same pressure with a back pressure valve. Pure water was fed with a pump at 1.0 ml / min for about 6 hours to replace the liquid phase in the autoclave with pure water at the same temperature and pressure. The temperature and pressure were returned to room temperature and normal pressure, and the crystals in the autoclave were filtered and dried to obtain 12 g of high-purity 2,6-naphthalenedicarboxylic acid crystals. The analysis results of the obtained crystals are shown in Table 2 together with the values of the crude crystals used. 6-
Liquid chromatography was used for the analysis of carboxy-2-naphthaldehyde, inductively coupled plasma was used for the analysis of Co and Mn, and fluorescent X-ray (analyzed as AgBr by dry carbonization / extraction) was used for Br. As for the hue, 1 g of sample was dissolved in 10 ml of 25% methylamine aqueous solution,
400 nm and 500 n using a 10 mm quartz cell
The absorbance at the wavelength of m was measured and evaluated.

Comparative Example 1 In Example 1, after melting the crude crystals, the temperature in the constant temperature bath was set to about 5.
2,6-Naphthalenedicarboxylic acid was prepared in the same manner as in Example 1 except that the temperature was lowered to 80 ° C. to precipitate crystals of 2,6-naphthalenedicarboxylic acid, and then pure water at the same temperature was substituted. 16 g of crystals were obtained. Table 2 shows the analysis results of the obtained crystals.

[0023]

[Table 2]

Example 2 To a 300 cc stainless autoclave in a constant temperature bath at 300 ° C., 25 g of the crude crystals of 2,6-naphthalenedicarboxylic acid obtained in Reference Example and water were filled (about 190).
g) The mixture was charged and kept under the conditions of 300 ° C. and 90 kg / cm ² G for 1.5 hours to dissolve the crude crystals in water. Next, the temperature of the constant temperature bath was lowered to 250 ° C. over about 3 hours to precipitate crystals of 2,6-naphthalenedicarboxylic acid, and the autoclave was heated to 250 ° C. while keeping the pressure at the same pressure with a back pressure valve. Pure water was fed with a pump at 1.0 ml / min for about 6 hours to replace the liquid phase in the autoclave with pure water at the same temperature and pressure. The temperature and pressure were returned to room temperature and atmospheric pressure, and the crystals in the autoclave were filtered and dried to obtain 14 g of high-purity 2,6-naphthalenedicarboxylic acid crystals. The analysis results of the obtained crystals are shown in Table 3 together with the values of the crude crystals.

[0025]

[Table 3]

[0026]

According to the present invention, highly pure 2,6-naphthalenedicarboxylic acid can be easily produced by a simple process.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Okuyama 1 Toho Town, Yokkaichi City, Mie Prefecture Yokkaichi Research Institute, Mitsubishi Petrochemical Co., Ltd. (72) Inventor Mine Hokko 1 Toho Town, Yokkaichi City, Mie Prefecture Mitsubishi Oil Chemical Company In Yokkaichi Research Institute (72) Inventor Masahiko Yamagishi No. 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Oil Chemicals Incorporated Yokkaichi Research Institute

Claims (2)

[Claims] 1. A crude crystal of 2,6-naphthalenedicarboxylic acid containing impurities is dissolved in water in a supercritical or subcritical state, and the resulting solution is cooled to 300 ° C. or lower to precipitate crystals, and then the crystals are precipitated. A method for producing high-purity 2,6-naphthalenedicarboxylic acid, which comprises separating the crystals from a mother liquor at a temperature of 100 to 300 ° C. 2. The method according to claim 1, wherein the temperature for dissolving the crude crystals in water is 300 to 380 ° C.