JPS62212341A - Purification of 2,6-naphthalenedicarboxylic acid - Google Patents

Abstract

PURPOSE:To enable the purification of the titled compound, by dissolving crude 2,6-naphthalenedicarboxylic acid in an aqueous solution of NaOH, K2CO3, etc., adding a water-soluble salt or hydroxide of the same cation and precipitating the objective compound as di-Na salt or di-K salt. CONSTITUTION:Crude 2,6-naphthalenedicarboxylic acid produced by the oxidization of 2,6-dialkylnaphthalene is dissolved in an aqueous solution of NaOH, KOH, Na2CO3 or K2CO3 of >=11 pH. A water-soluble salt or hydroxide of the cation same as the ion used above is added to the solution to precipitate the objective compound in the form of di-Na salt of di-K salt. The amount of the water-soluble salt or hydroxide of the above common cation is <=5mol/l as a cation concentration and below the solubility of the added component. preferably, the solution is added with 1-3wt% NaCl before or after salting-out teatment and is subjected to activated carbon treatment. EFFECT:A colorless objective compound having a purity of >=99.8% can be produced by combining the above process with activated carbon treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides 2,6-dialkylnaphthalene or its oxidized intermediate obtained by oxidizing 2,6-dialkylnaphthalene or its oxidized intermediate with molecular oxygen.
, 6-naphthalene dicarboxylic acid (hereinafter referred to as 2.6-NDCA)
(abbreviated as )).

2.6-ND CA is a raw material for producing polyethylene 2,6-sphthalate, polyester, polyamide, etc., which are used to produce films and textile products with excellent heat resistance.

Chixia and I 2.6-NDCA is produced by air oxidation of 2,6-dialkylnaphthalene in glacial acetic acid in the presence of a cobalt and manganese catalyst and a bromine catalyst at high temperature and pressure. However, since aldehydes and ketones, brominated derivatives of 2.6-NDCA, oxidized polymers, and colored substances produced as by-products of the oxidation reaction are mixed into the produced 2,6-NDCA, the resulting crude 2.6 - The purity of NDCA is typically 95%.

If 2.6-N OOA containing such impurities is used as a raw material for producing polyethylene 2.6-naphthalate, polyester, polyamide, etc., the degree of polymerization of the above polymer may decrease or the films and fibers made from the above polymer may deteriorate. Physical properties such as heat resistance may deteriorate, or the quality may deteriorate due to coloring.

Therefore, it has been conventionally required that the purity of 2.6-N DC A be as high as 99% or higher.

2. (The following methods for producing and purifying i-NDCA have been proposed.

2.6-diitubrobylnaphthalene or its oxidized intermediate is combined with at least 5 fatty acid monocarboxes having 3 or less carbon atoms.
Oxidized with molecular oxygen in a solvent containing 0% by weight,
．． In a method for producing 6-naphthalene dicarboxylic acid, oxidation of 2,6-diitubrobylnaphthalene or its oxidized intermediate is carried out using (i) a heavy metal consisting of cobalt and/or manganese and (11) a catalyst consisting of bromine; 2.6-diitubrobylnaphthalene or its oxidized intermediate 1 mole, the presence of a heavy metal as a component of the catalyst in a proportion of at least 0.2 mole "T-τ.S"; Method for producing 6-naphthalene dicarboxylic acid (Special ll Sho 6O-89445).

2. Oxidizing 6-diituprobylnaphthalene or its oxidized intermediate with molecular oxygen in ii containing at least 50% by weight of an aliphatic monocarboxylic acid having 3 or less carbon atoms;
In the method for producing 2.6-naphthalene dicarboxylic acid, the oxidation of 2.6-diituprobylnaphthalene or its oxidized intermediate is carried out using a heavy metal consisting of cobalt and/or manganese and (ii) a catalyst consisting of bromine. A method for producing an aliphatic mono-2,6-naphthalene dicarboxylic acid having 3 or less carbon atoms (JP-A-60-89446).

Dissolve crude 2.6-ND CA in aqueous alkaline solution,
Heat treatment is performed by stirring at 100 to 250°C for 1 to 5 hours,
Next, after decolorizing with a solid adsorbent, acidic gas such as carbon dioxide or sulfur dioxide is injected to lower the pH to 2.6.
- A method of precipitating NDCA as a monoalkali salt (Japanese Patent Publication No. 52-20993).

After treating an alkaline aqueous solution of crude 2.6-NDCA with an oxidizing agent such as an alkali perhalogenate or an alkali permanganate, carbon dioxide gas or 1iIK acid gas is blown into the 2.6-NDCA solution.
- A method for separating NDCA as a monoalkaline salt (JP-A-48-68554).

After performing a catalytic hydrogenation treatment on an alkaline aqueous solution of crude 2.6-NDCA at a temperature below 220°C in the presence of a metal catalyst such as palladium, platinum, ruthenium, or nickel, carbon dioxide gas is blown into the aqueous solution of 2.6-NDCA. A method for separating monoalkaline salts (JP-A-5O-160248).

A method of dissolving crude 2.6-NDCA in an aqueous solution of sodium acetate and then concentrating and crystallizing it to separate the monoalkali salt of 2.6-NDCA (Japanese Patent Laid-Open No. 105639/1983).

In both methods, 2.6-NDC is dissolved in an alkaline aqueous solution, I) H is adjusted, and 2.6-NDC
This method is a combination of a method of precipitating and purifying the monoalkali salt of A and a heat treatment method or a redox treatment method.

However, by adjusting the pH mentioned above, 2.6-NDCA
The method for purifying is to adjust the pH to 6.5 to 7.5 by injecting carbon dioxide or sulfur dioxide gas or adding mineral acid while heating a relatively highly concentrated alkaline aqueous solution of 2.6-NDCA. Since this is a method in which monoalkali salts are precipitated by cooling to 20°C, monoalkali salts and dialkali salts and 2.
Due to the delicate equilibrium relationship with 6-NDCA, there is a drawback that the crystal composition and precipitation 1 are not constant depending on conditions such as pH, temperature, and concentration.

In addition, other carboxylic acids whose PKa is close to 2.6-NDCA are contained in 2,6-NDCA obtained by oxidizing 2,6-dialkylnaphthalene, so 1) H
It is difficult to purify 2.6-N DC A to high purity by means of control alone. Furthermore, after separating the monoalkali salt precipitated by the pHlX section, it is necessary to remove the mother liquor attached to and contained in the crystals by washing with water.
Since the monoalkali salt of 6-NDCA is water-soluble, it has the disadvantage that the purification rate of 2.6-NDCA decreases due to washing.

``Attempts to purify 2,6-ND only by crystallization of monoalkali salts''
Since CA cannot be purified to a high degree of purity, it has become necessary to combine it with other methods such as heat treatment, oxidation treatment, reduction treatment, etc.

However, heat treatment requires high temperature and high pressure, and when oxidation and reduction reactions are used together, there is a problem that many new by-products are generated and become impurities, and measures to remove them are required. It was incomplete.

On the other hand, 2.6-NDCA has a melting point of 300°C or higher, so it cannot be produced by distillation, and methanol,
Ethanol, acetone, benzene, xylene, dioxane. Since it is insoluble in most organic solvents such as acetonitrile and acetic acid, it cannot be purified by recrystallization.

The present inventors first studied a method of crystallizing and purifying 2,6-NDCA as a dialkali salt without performing any chemical reactions such as oxidation or reduction.

As a result, it was found that since the dialkali salt of 2.6-N D CA has a very high solubility in water, it is necessary to increase the solution concentration during recrystallization. However, this method has the disadvantage that since the concentration of impurities is high, when crystallization is performed, impurities are mixed into the crystals, making it impossible to obtain highly pure crystals.

Also, because of its high water solubility, it has the disadvantage that the crystals cannot be washed sufficiently. Furthermore, when carried out on an industrial scale, it is necessary to recover the dialkali salt of 2,6-NDCA contained in the P solution and cleaning solution, but since a large amount of water is evaporated, a very large latent heat of vaporization is required. The energy loss is also large. In addition, during concentration, there is intense foaming development, which makes concentration difficult, and as the purity of 2.6-ND CA in the P solution decreases, crystal precipitation becomes difficult.
There was a drawback that the recovery rate of CA decreased.

In order to solve all of the above-mentioned problems, the present inventors have discovered that 2. operations such as chemical reactions, concentration, and cooling sections are not required;
As a result of intensive research on the purification method of 6-NDCA, 2.
Crude 2.6 obtained by oxidizing 6-dialkylnaphthalene
- NDC is dissolved in an alkaline aqueous solution selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and a water-soluble salt or hydroxide of the same cation as the alkali aqueous solution used is dissolved in 2.6-N D CA
Highly purified 2.6
The inventors have discovered a method for purifying 2,6-N D CA that involves precipitating CA as a disodium salt or dipotassium salt, and have accomplished the present invention based on this finding.

1匪5且1 The method of the present invention involves washing or extracting 2,6-NDCA obtained by oxidizing 2,6-dialkylnaphthalene with acetic acid, water or an aqueous solution of mineral acid, and then 2,6-NDCA. (hereinafter abbreviated as crude 2.6-ND CA) in an alkaline aqueous solution selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate having a pH of 9 or more, preferably pi-111 or more, Same cation as the alkaline aqueous solution used (hereinafter abbreviated as common cation)
A water-soluble salt or hydroxide of 2.6-ND CA is added to an aqueous solution in which 2.6-ND CA is dissolved, and 2.6-ND CA is precipitated as a disodium salt or a dipotassium salt, that is, by a salting-out method. This is a method for producing NDCA.

Water-soluble salts or hydroxides of common cations are water-soluble salts or hydroxides of sodium or potassium,
Salts or hydroxides that dissolve 10% by weight or more, preferably 15% by weight or more in water at ℃, such as sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, potassium bicarbonate, and sodium sulfate. , potassium sulfate, sodium nitrate, potassium nitrate, dipotassium phosphate, sodium hydroxide, and potassium hydroxide.

Salting out in the method of the present invention involves adding the crude 2.6-
This is carried out by adding NDC to an aqueous alkaline solution in which NDC is dissolved. The amount of the water-soluble salt or hydroxide added is such that the concentration of cations is 10 m0R11 or less, preferably 5 soil/j or less, and the solubility of the additive or less. If the solubility is exceeded, the additive will be mixed into the salted-out crystals, resulting in poor results. Further, even if it is added so that the cation concentration is 10110#/1 or more, the salting-out effect will not be enhanced, and the specific gravity and viscosity of the solution will increase, making solid-liquid separation difficult.

The solubility of dialkali salts of 2.8-N D CA decreases rapidly as the concentration of common cations increases, such as sodium ions in the case of disodium salts and potassium ions in the case of dipotassium salts.

For example, the solubility of 2,6-N DC A in a sodium hydroxide aqueous solution with pH 12 at 20°C is 11% when the sodium ion concentration is 1.511101/1, but when the sodium ion concentration is 2.2 mon/1 In case of 1%, the solubility is 1.7% in button 01/l, 4
At IIlOft/l, the solubility is 0.4%, and the sodium ion concentration is 5.4107)/! Then the solubility is 0
．． This decreases to 2%.

That is, crude 2.6-ND with a purity of 90 to 95% obtained by oxidizing 2.6-dialkylnaphthalene in a solvent such as acetic acid in the presence of cobalt and/or manganese and a bromine catalyst.
After dissolving CA in the alkali aqueous solution mentioned above, adding a water-soluble salt or hydroxide of the same cation as the alkali aqueous solution used can precipitate dialkali salt crystals of 2.6-NDCA with a purity of 99% or more. I can do it.

To explain the purification method of the present invention in detail, 2.6-dialkylnaphthalene such as 2.6-dimethylnaphthalene or 2.6-diitubrobylnaphthalene is purified in a solvent containing 70% or more of lower aliphatic monocarboxylic acid. In the presence of cobalt and/or manganese and a bromine catalyst, the crude 2.6
- NDCA is added to and dissolved in an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, or potassium carbonate with a pH of 9 or higher. The amount of alkali used is 2.6-N
It is sufficient to neutralize DCA by 5 or more, but when using an excessive amount of alkali, use an insoluble hydroxide to remove the heavy metals (cobalt and/or manganese) contained in crude 2.6-NDCA. Alternatively, since it can be separated as a basic carbonate, it is preferable to use an aqueous alkaline solution in excess of about 20%. Further, the concentration of alkali may be at a pH of 9 or higher, and is particularly preferably at a pH of 11 or higher. After removing heavy metal hydroxides, etc., when a water-soluble salt or hydroxide of the common cation used for dissolving 2.6-NOOA is added to the P solution, salting out occurs immediately. - Crystals of dialkali salt of NDCA are precipitated.

In salting out, water-soluble salt or hydroxide added:
．． The concentration of 6-N DC A can be adjusted within a wide range depending on purification purposes. For example, when salting out an alkaline aqueous solution with a low concentration of 2.6-N D CA, salting out is carried out by increasing the m degree of the common cation;
When salting out an alkaline aqueous solution with a high concentration of CA, salting out can be carried out without increasing the concentration of common cations too much.

By increasing the concentration of the common cation, 2.6-NDCA
The recovery rate can be over 97%, but if the concentration of common cations is too high, the purity may decrease, so crude 2.
If the purity of 6-NDCA is low, the concentration of the cation should be adjusted appropriately.

When the purity of crude 2.6-NDCA is particularly low, it is preferable to dissolve the crystals obtained in the first salting out in an alkaline aqueous solution again and salt out.

2.6-Since the solubility of the alkali salt of NDCA changes largely depending on the concentration of common cations rather than the influence of the concentration in the salting-out process, there is no need for heating or cooling treatment during salting-out, and there is no need to concentrate. Nor. Since the temperature of the solution at the time of salting out is usually 20 to 40°C, energy loss may be small even in industrial implementation.

In the method of the present invention, adsorption treatment using activated carbon can be performed before and after the salting-out treatment.

It is preferable to perform the salting-out treatment first and then the activated carbon treatment, since the number of activated carbon needles used can be reduced. Activated carbon can be used in any of granular, granular, spherical, crushed, and powdered forms, but powdered activated carbon with a large surface area works effectively.

↓ To describe the method of activated carbon treatment specifically, if it is performed before salting out treatment, activated carbon is directly added to a crude alkaline aqueous solution of 2.6-NDC CA, stirred for at least 30 minutes, and then activated carbon is added. Although it may be separated, in order to effectively utilize the activated carbon, it is preferable to pass through a filler of activated carbon for adsorption treatment.

The temperature of the adsorption treatment using activated carbon is 5 to 100°C, and the temperature of the adsorption treatment is 10 to 30°C. Adding about 1 to 3% by weight of sodium chloride to the aqueous alkaline solution of ancestral 2,6-NDCA enhances the adsorption capacity of activated carbon, making it possible to reduce the amount of activated carbon used.

For example, crude 2.6-NDC is added to an aqueous sodium hydroxide solution.
After dissolving A, salting out using sodium chloride, washing the obtained crystals with sodium chloride water, and dissolving in water will give the appropriate sodium chloride degree, so if you treat it with activated carbon, the consumption of activated carbon will be small. , is an advantageous method.

Depending on the conditions of the salting-out treatment, the P solution subjected to salting-out treatment may contain 2.6
- NDCA may remain. In this case, add a small amount of mineral acids such as dilute hydrochloric acid, sulfuric acid, nitric acid, etc. [i-N D CA precipitates. The 2,6-NDC'A thus precipitated was dissolved again in an alkaline aqueous solution and then subjected to salting out treatment to yield 2.6-NDC'A.
l) The dialkali salt of CA can be recovered.

According to the method of the present invention, the solubility of the dialkali salt of 2.6-N D CA decreases to about 0.2% by increasing the concentration of common cations, so no heating concentration operation is necessary. 2,6-NDCA without increasing the concentration of impurities in the alkaline solution of 2,6-NDCA.
Crystals of the dialkali salt of NDC A can be obtained.

In addition, since the dialkali salt of 2.6-NDCA is poorly soluble in water-soluble salts of common cations or aqueous solutions of hydroxides, the salting-out results should be cleaned using a solution with an appropriate salt concentration. is possible.

Further, according to the method of the present invention, 2.6-NDCA of sufficient quality as an industrial raw material, that is, 2.6-NDCA with a purity of 99% or more, can be recovered by a single salting-out treatment. Also, especially high quality 2. When G-NDCA is required, colorless 2.6-NDCA with a purity of 99.8% or more can be recovered by combining activated carbon treatment.

The recovery rate of 2,6-NDCA by the method of the present invention is usually 9
It is about 5%.

Hereinafter, the purification method of the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to these Examples.

The purity of 2.6-N DC A was determined by high performance liquid chromatography, the bromine element was analyzed by fluorescent X-ray analysis, and the colored components were determined by the OD value of a 25% methylamine solution.

(1) High Performance Liquid Chromatography Waters, Model 510 HPLG measuring device Column: L r ChrO8Or
b - RP-8 (5-, Merck & Co.) and Radial Pack Cartridge C-8 (Waters Co.) connected column mobile phase: I))-13 water/acetonitrile =
45/55 (volume ratio) solution, flow rate: 0.6c
c/min Internal standard: 2-naphthoic acid Detection wavelength: 260nm ■ Fluorescence X1! Analysis method: Rigaku Denki Fluorescence X-ray analyzer (Model 3080E 2) Measurement and detection using X-ray tube dirhodium 50KV-5011A Insect: PC detector Crystal: Germanium sample GIOG is molded into a tablet with a diameter of 301I1m and analyzed.

Detection limit: 3PPm ■ Analysis of colored components 25% methylamine aqueous solution 10ai! 1 g of the sample is dissolved in the solution, and the optical density is measured using a 1001 m quartz cell at a wavelength of 100 m.

Example 1 2 kg of glacial acetic acid and 0.1 g of cobalt acetate tetrahydrate were placed in a titanium-lined stainless steel 51 autoclave equipped with a reflux condenser, a gas blowing tube, a temperature measuring tube, and a stirrer.
, manganese acetate tetrahydrate 0.2Kg, ammonium bromide 50
Add Q and 0.2Kg of 2.6-diitubropylnaphthalene and mix at 180-190°C with stirring at 20Kg/
Blow compressed air at a rate of 600 fl/hr with ci,
Allowed time to react. After the reaction was completed, the mixture was cooled to 80° C., the precipitate was filtered, washed with hot acetic acid, 6% hydrochloric acid (2Il) was added, and the mixture was stirred for 1 hour.

After filtration and washing, dry 165g of crude 2.6-ND
Obtained GA. Its purity was 94.6%, and the OD value of the 25% methylamine solution, which indicates the content of coloring components, was 0.66. Moreover, the content of bromine element was 4600 PPm.

Incidentally, the yield of 2,6-NDCA based on the raw material 2,6-diituprobylnaphthalene was 76.7%.

209 of the crude 2.6-NDCA thus obtained was converted into 7
．． In addition to 105 g of 61% sodium hydroxide aqueous solution,
After stirring and dissolving at 5°C, insoluble matter was removed from door to door. 23 to P liquid
(When adding 1 liter of sodium chloride and stirring at 25°C, 2.
Disodium salt crystals of 6-NDCA were precipitated. The precipitated crystals were separated from each other, washed with a 1% by weight sodium chloride aqueous solution 90Q, and then dissolved in 300 g of water. While stirring, add 10% hydrochloric acid to adjust the pH to 1.5, and
．． 6-NDCA crystals were precipitated. After each house is washed with water until no chlorine ions are detected, dried and
2.6-NDCA of 2.6-NDCA was obtained.

The purity of the obtained 2,6-NDCA was 99.2%, and the OD value of the 25% methylamine solution, which indicates the content of coloring components, was 0.060. In addition, the content of bromine element is 4PPn
It was +. In addition, purification 2. for crude 2.6-NDCA.
The recovery rate of 6-NDCA was 95.4%.

Example 2 20 (J of 0) of crude 2.6-NDCA obtained in Example 1
．． After adding it to 235 g of a 15% by weight aqueous potassium carbonate solution containing 5 g of sodium chloride and dissolving it by stirring at room temperature, 2
．． Activated carbon treatment was carried out by passing through a bed filled with powdered activated carbon. After washing the activated carbon layer with 12G of 0.5% by weight aqueous sodium chloride solution, 50(l) of potassium chloride was added with stirring at 25°C for salting out treatment, and 2.6-
Dipotassium salt crystals of ND CA were precipitated.

After each house, the crystals were washed with a 25% by weight potassium chloride aqueous solution 80 (), and the obtained crystals were dissolved in 30017 water, and 10% by weight sulfuric acid water was added with stirring to adjust the pH of the liquid to 1.5. After the precipitated 2,6-ND CA crystals were distributed from house to house,
Rinse thoroughly with water until the washing liquid becomes neutral, and dry.17.
8 g of 2.6-NDCA was obtained.

The purity of the obtained 2,6-NDCA was 99.8%, and the OD value of the 25% methylamine solution, which indicates the content of coloring components, was 0.015. Moreover, bromine element was not detected. In addition, purified 2.6-ND relative to crude 2.6-NDCA
The recovery rate of CA was 93.9%.

Claims (4)

[Claims] (1) Crude 2,6-naphthalene dicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene was dissolved in an aqueous alkali solution selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and used. Water-soluble salt or hydroxide of the same cation as the alkaline aqueous solution
, 6-naphthalene dicarboxylic acid is added to an aqueous solution in which 2,6-naphthalene dicarboxylic acid is precipitated as a disodium salt or a dipotassium salt.
Method for purifying naphthalene dicarboxylic acid. (2) The purification method according to claim 1, which comprises dissolving the precipitated disodium salt or dipotassium salt of 2,6-naphthalene dicarboxylic acid in water and subjecting it to adsorption treatment with activated carbon. (3) Before salting out the aqueous alkaline solution of crude 2,6-naphthalene dicarboxylic acid to precipitate 2,6-naphthalene dicarboxylic acid as a disodium salt or dipotassium salt,
The purification method according to claim 1, which comprises adsorption treatment using activated carbon. (4) The purification method according to claim 2 or 3, which comprises adding 1 to 3% by weight of sodium chloride to the solution to be adsorbed with activated carbon.