JPH07118201A - Purification of 2,6-naphthalene dicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide a purification method capable of not only efficiently removing impurities in crude 2,6-naphthalene dicarboxylic acid (NDCA) but also obtaining pure NDCA uniform and large in the diameters of the crystal granules. CONSTITUTION:A dialkylnaphthalene or its oxidation intermediate is oxidized with molecular oxygen in the presence of a cobalt-manganese catalyst in acetic acid solvent, and the produced crude NDCA dialkali salt is crystallized with a mineral acid or an acidic gas in the presence of water and a water-soluble organic solvent (e.g. an alcohol, a ketone or acetonitrile). The produced NDCA crystals are filtered out, sufficiently washed with water, and subsequently dried to recover the pure NDCA free from a coloring substance, a heavy metal, and 2-formyl-naphthoic acid which is a reaction intermediate. When the NDCA is treated with active carbon before the acidic crystallization, the NDCA crystals having a higher purity are obtained. On the acidic crystallization, the concentration of the NDCA dialkali salt is 0.2-15wt.% in the aqueous solution, and an organic solvent is used in an amount of 50-200g per 100g of the water.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying 2,6-naphthalenedicarboxylic acid (hereinafter abbreviated as NDCA). The process of the invention is particularly suitable for the purification of crude NDCA obtained by oxidizing 2,6-dialkylnaphthalene or its oxidation intermediate with molecular oxygen. NDC
A is polyethylene naphthalate because it gives films and textiles with excellent heat resistance, mechanical strength and dimensional stability.
Demand is increasing as a raw material for polyamide, polyamide, etc.

[0002]

2. Description of the Related Art It is known that NDCA is produced by subjecting 2,6-dialkylnaphthalene to air oxidation in an acetic acid solvent in the presence of a cobalt and manganese catalyst and a bromine catalyst. However, in the crude NDCA obtained by these oxidation reactions, a trace amount of heavy metals, a coloring substance with an unknown structure, a bromine derivative, a reaction intermediate, and the like are mixed.
Therefore, if this crude NDCA is used as a raw material as it is, there are problems such as deterioration of the performance of the polymer and coloring. Therefore, various NDCA purification methods have been studied and proposed.

(1) Crude NDCA is dissolved in an alkaline aqueous solution and heat-treated at 100 to 250 ° C. for 1 hour, followed by decolorizing treatment with a solid adsorbent, and then carbon dioxide gas or sulfurous acid gas is pressure-treated to lower the pH to form NDCA. Method of Precipitating as Mono-Alkali Salt (JP-A-48-49747) (2) After treating an alkaline aqueous solution of crude NDCA with an oxidizing agent such as alkali permanganate, carbon dioxide gas or sulfurous acid gas is blown in to mono-decompose NDCA. Method of separating as alkaline salt (Japanese Patent Laid-Open No. 48-68554) (3) Catalytic hydrogenation treatment of an alkaline aqueous solution of crude NDCA at a temperature of 220 ° C. or lower in the presence of a metal catalyst such as palladium, platinum, nickel or ruthenium. And then blowing carbon dioxide or sulfur dioxide to separate NDCA as a monoalkali salt (JP-A-50-16 No. 248) (4) A method in which crude NDCA is dissolved in an aqueous sodium acetate solution and then concentrated and crystallized to separate a monoalkali salt of NDCA (JP-A-50-105639). Purification by crystallization of monoalkali salt. It was not possible to purify NDCA to a high degree of purity by using only these (1) to (4).
The above method is a combination of a method of dissolving crude NDCA in an alkaline aqueous solution, adjusting the pH to precipitate a monoalkali salt of NDCA for purification, and a heat treatment method or a redox treatment method. However, in these methods, the pH is adjusted to 6.5 to 7.5 to precipitate the monoalkali salt, but the amount and composition of the precipitated salt are not constant depending on the conditions such as pH and temperature, and the operation is complicated. . Furthermore, the oxidation-reduction treatment results in the production of new by-products and higher costs.

(5) ND by so-called salting out by adding a water-soluble salt of the same cation to an alkaline aqueous solution of crude NDCA
Method for isolating CA dialkali salt (JP-A-62-212
341 publication). This method uses the salt used for salting out,
There is a salt formed by acidifying an alkali salt, the total amount of these is very large, and there are problems such as the treatment of these inorganic salts, so that a purification method on an industrial scale cannot be achieved. (6) Method of precipitating a dialkaline salt of crude NDCA by adding a water-soluble organic solvent (JP-A-2-24365)
No. 2). This method has a low recovery rate and a high cost. (7) On the other hand, a method of recrystallizing crude NDCA with a solvent such as dimethylsulfoxide (JP-A-62-230747) is also known, but the cost due to recovery loss is high because a large amount of expensive solvent is used. Moreover, it is not an industrial purification method because it was not purified as expected.

[0005]

The above methods (1) to (6) are for purifying as dialkaline salt or monoalkali salt of NDCA, respectively. After purification, acid precipitation is carried out by adding mineral acid or acid gas. Convert to NDCA. The NDCA precipitated by this acid precipitation contains a lot of very fine crystal grains, and in the conventional refining method for producing an alkali metal salt, in addition to the above-mentioned drawbacks, acid crystals are generated due to the fine crystals. NDCA filtration after precipitation is difficult, and there is a big problem in making an industrial scale purification method. The present invention is intended to provide a simple, inexpensive and efficient NDCA purification method which is excellent in filterability after acid precipitation.

[0006]

DISCLOSURE OF THE INVENTION The present invention is characterized by acidifying 2,6-naphthalenedicarboxylic acid dialkali salt in the presence of water and a water-soluble organic solvent to efficiently remove impurities in crude NDCA. The present invention provides a method for purifying 2,6-naphthalenedicarboxylic acid, which is capable of recovering purified NDCA having a uniform crystal grain size and large size as well as being easily removed.

2,6-naphthalenedicarboxylic acid dialkali salt is a crude NDCA, for example, a crude NDCA which is a liquid-phase oxidation reaction product by air or the like using cobalt, manganese, and bromine as a catalyst in a dialkylnaphthalene in an acetic acid solvent.
Is obtained by neutralizing with an aqueous solution of an alkali metal hydroxide, a carbonate, ammonia or the like. According to the method of the present invention, the colored substance and the reaction intermediate 2-formyl-6-naphthoic acid and heavy metals in the crude NDCA obtained by the oxidation reaction can be efficiently removed, and a highly purified purified NDCA can be obtained. it can.

(Oxidation reaction) Crude NDCA is a dialkylnaphthalene such as 2,6-dimethylnaphthalene or 2,6.
-It is obtained by oxidizing diisopropylnaphthalene or the like or an oxidation intermediate thereof with molecular oxygen in the presence of a cobalt and manganese catalyst and a bromine catalyst in an acetic acid solvent.

The oxidation reaction conditions are not particularly limited, but for example, the following conditions are used. About 0.5 mol% to 50 mol% of cobalt and manganese are used with respect to 1 mol of the raw material dialkylnaphthalene. The molar ratio of cobalt and manganese used is 1:99 to 99: 1. Bromine compound is 1 to 1 per mol of cobalt
Use 0 mol. Acetic acid or propionic acid is used as the solvent, and the amount used is 2 to 50 times by weight that of the raw material. The reaction temperature is 80 to 250 ° C., preferably 100 to 200 ° C., and the reaction time is usually 1 to 10 hours. As the molecular oxygen, in addition to pure oxygen, pure oxygen diluted with an inert gas such as nitrogen or helium argon to an arbitrary concentration can be used, but air is generally sufficient. Considering the reaction rate, the reaction pressure is such that the oxygen partial pressure in the gas phase is constantly 0.
The pressure is preferably 2-40 kg / cm ² . The reaction may be either a batch system or a semi-continuous system, but in general, a semi-continuous system in which the yield per catalyst is large is advantageous. Since the NDCA produced after the reaction is in the form of a slurry in the solvent, it is collected by filtration, washed with water or an acid, washed with water and dried.

(Production of dialkali salt) The dialkali salt is generally produced as an aqueous solution of NDCA dialkali salt by adding crude NDCA to an aqueous solution in which an alkali having a neutralization equivalent or more is dissolved and heating or stirring at room temperature to dissolve. is there. Examples of the alkali used include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and ammonia. The amount used is 1 to NDCA
Used in the range of 2 equivalents, but usually ND
Use about 1.01 to 1.50 equivalents to CA. The concentration of the alkaline aqueous solution is slightly different depending on the type of salt, and it is necessary to lower the concentration of ammonium salt than sodium and potassium salts, and it is used at about 0.2 to 10% by weight.

The temperature for forming the dialkali salt may be room temperature, but it is generally preferable to perform it under heating. Increased dialkali salt solubility and improved pot efficiency, and rough ND
This is because the recovery rate of cobalt and manganese contained in a small amount in CA is improved. This heat treatment is usually 0.5 to 5
Perform in time and remove any insoluble matter by filtration. The concentration of the NDCA dialkali salt in the aqueous solution obtained as described above is usually 0.2 to 15% by weight.

The NDCA dialkali salt can be easily obtained as purified NDCA by acid precipitation with a mixed solvent system of water and an organic solvent, but a higher purity product can be obtained by treatment with activated carbon prior to acid precipitation. be able to.

(Activated carbon treatment) The activated carbon treatment method is a flow type or a batch type. For example, in the case of the flow type, granular activated carbon is packed in a column and NDC is used by up-flow or down-flow.
Circulate the dialkaline salt aqueous solution. Processing temperature is room temperature ~
It is carried out at 60 ° C., but room temperature is usually sufficient. In the case of the batch method, 1 to 10 with respect to the NDCA dialkali salt in the aqueous solution.
Powdered activated carbon of about wt% is added, and the mixture is treated with stirring for 1 to 5 hours. The activated carbon treatment is more effective near neutral than by treatment with a strong base. The pH of the NDCA dialkali salt aqueous solution is usually 1 when 1.5 equivalent of alkali is used.
Since it is 2 or more, it is preferable to adjust the pH of the treatment liquid within the range of pH 8 to 10 by adding an acid to the extent that NDCA does not precipitate. There is no particular limitation on the type of activated carbon, and any type can be used.

(Acidation operation) Acidification of the NDCA dialkali salt is carried out in the presence of water and a water-soluble organic solvent. Usually ND
It is performed by mixing a water-soluble organic solvent with the CA dialkaline salt aqueous solution. As the water-soluble organic solvent, one having a high solubility in water is preferable, and specifically, an organic solvent having a solubility in water at 20 ° C. of 100 g / 100 g · H ₂ O or more, for example, methanol, ethanol, 2 -Alcohols such as propanol, ketones such as acetone and methyl ethyl ketone, and dimethyl sulfoxide, acetonitrile and the like can be used. These organic solvents may be used alone or in combination.

The concentration of the NDCA dialkali salt in the aqueous solution is usually 0.2 to 15% by weight, but in the case of the disodium salt, the concentration of the aqueous solution is preferably 2 to 10% by weight. Although the amount of the organic solvent is such that the NDCA dialkali salt does not precipitate, the amount varies depending on the concentration of the NDCA dialkali salt in the aqueous solution and the type of salt, but is used in an amount of about 50 to 200 g per 100 g of water in the aqueous solution. If the amount of the organic solvent used is too small, the effects of the present invention will not be fully exhibited.

In this way, the NDCA dialkali salt is dissolved in a mixed solvent of an organic solvent and water, an acid is added with stirring and acid precipitation is performed to obtain NDCA crystals. As the acid, a mineral acid such as hydrochloric acid or sulfuric acid or an acid gas such as sulfurous acid gas is used, but usually a mineral acid such as sulfuric acid is diluted with water before use. Although the dilution concentration is arbitrary and there is almost no problem with the effect of the present invention, normally, for example, sulfuric acid having a concentration of about 1 to 50% by weight is used. The acid is added until the pH of the reaction solution becomes around 2. The addition rate depends on the addition amount, but is usually 0.01 to 1
At 0 hours, stirring is continued for 3-30 minutes after acid addition. The temperature of the acid precipitation is from room temperature to the boiling point of the organic solvent, but it can be carried out at a high temperature above the boiling point under pressure. The NDCA crystals thus formed are filtered off, washed thoroughly with water and dried. The crystal grain size of the obtained NDCA is usually 1 to 50 μm.

[0017]

INDUSTRIAL APPLICABILITY According to the present invention, coloring substances, heavy metals, and the like in crude NDCA can be obtained by acidifying NDCA dialkali salts.
In addition to efficiently removing 2-formyl-6-naphthoic acid, which is a reaction intermediate, and having excellent filterability,
A large purified NDCA having a uniform crystal grain size can be recovered.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. The NDCA purity and 2-formyl-6-naphthoic acid content were measured by high performance liquid chromatography.
Then, the hue is sample 1 in 10 ml of 40% methylamine aqueous solution.
g was melted and 400 nm was used by using a 10 mm quartz cell.
It was measured by a method of measuring the absorbance at a wavelength of 00 nm (hereinafter abbreviated as OD). Further, the hue improvement was expressed as a hue improvement rate by the following formula.

[0019]

[Equation 1]

Quantitative determination of elemental bromine was carried out by fluorescent X-ray, Co and Mn.
Was determined by atomic absorption. Laser type particle size distribution measuring device (Leeds & Northrup: Microtrac)
It was used.

[0021]

[Reference example] reflux condenser, gas introduction pipe, raw material feed pump,
In a 500 ml titanium autoclave equipped with a back pressure regulator and an induction stirrer, acetic acid 150 g, cobalt acetate tetrahydrate 0.125 g, manganese acetate tetrahydrate 0.
123 g and 0.074 g of potassium bromide were charged, the atmosphere was replaced with nitrogen, and the pressure inside the system was adjusted to 30 kg / cm ² G. The reactor was heated to a temperature of 200 ° C., air was blown at 1.5 Nl / min and nitrogen at 3.6 Nl / min, and the reaction system was adjusted so that the internal pressure was maintained at 30 kg / cm ² G. . When the system became stable, a mixture of 15.61 g of 2,6-dimethylnaphthalene, 0.021 g of 2,6-diisopropylnaphthalene and 200 g of acetic acid was continuously supplied for 2.5 hours, and a mixture of acetic acid and water was discharged from the condenser to about 80 g. / Hour. After the supply of the raw materials was completed, the supply of the above mixed gas was continued for 1 hour or more while keeping the system at 200 ° C. and 30 kg / cm ² G. After completion of the reaction, the mixture was cooled to room temperature, the precipitated solid was collected by filtration, washed with acetic acid, washed with hot water, washed with distilled water, and then dried to obtain crude NDCA19.
79 g were obtained.

The crude NDCA has a purity of 99.5%,
OD is 0.883 at 400 nm and 0.11 at 500 nm
3, the Co content in NDCA was 6 ppm, and the Mn content was 36 ppm. The content of 2-formyl-6-naphthoic acid was 500 ppm, and the content of elemental bromine was 200 ppm.

[0023]

Example 1 A 500 ml four-necked flask equipped with a reflux condenser, a dropping funnel, a stirrer, and a thermometer was used as a reference example.
4.15 g (19.2 mmol) of CA was taken, and 1.55 g (38.8 mmol) of sodium hydroxide was added to 100 g of water.
An aqueous solution of sodium hydroxide dissolved in was added, and the mixture was heated under reflux for 1 hour. After cooling, the insoluble matter was filtered off to obtain an aqueous solution of NDCA disodium salt. After adding 100 g of acetone to this NDCA disodium salt aqueous solution with stirring, the mixture was stirred at room temperature (22
C.), 12 g of a 18.2 wt% sulfuric acid aqueous solution was added over 2 minutes. After completion of the addition, the mixture was stirred for 5 minutes for acid precipitation, and the precipitated NDCA crystals were filtered, washed with a small amount of water, and dried to obtain 4.11 g of purified NDCA (recovery rate 99.0%). The minimum particle size of the obtained NDCA was 3.13 μm, and the filtration was easy.

The obtained NDCA had a purity of 100% and an OD of 0.417 at 400 nm (hue improvement rate 53
%) 500 nm is 0.031 (hue improvement rate 73%), 2-formyl-6-naphthoic acid is 30 ppm, C
Both o and Mn were 1 ppm or less. The elemental bromine content was 100 ppm.

[0025]

Example 2 The same operation as in Example 1 was carried out except that 100 g of methanol was used instead of 100 g of acetone and the acid precipitation temperature was 50 ° C. As a result NDC
A 4.08 g (recovery rate 98.3%) was obtained, and the minimum particle size of the obtained NDCA was 2.21 μm, and filtration was easy.

The obtained NDCA had a purity of 100% and an OD of 0.437 at 0.437 (hue improvement rate 51
%) 500 nm is 0.040 (hue improvement rate 65%), 2
-Formyl-6-naphthoic acid is 20ppm, Co, Mn
Was less than 1 ppm. Bromine element content is 120
It was ppm.

[0027]

Example 3 In Example 1, 100 g of 2-propanol was added in place of 100 g of acetone, and the acid precipitation temperature was 70%.
The same operation as in Example 1 was performed except that the temperature was changed to ° C. As a result, 4.10 g of NDCA (recovery rate: 98.8%) was obtained, the minimum particle size of the obtained NDCA was 2.21 μm, and filtration was easy.

The obtained NDCA had a purity of 100% and an OD of 0.405 at 400 nm (hue improvement rate 54
%) 500 nm is 0.032 (hue improvement rate 72%), 2
-Formyl-6-naphthoic acid is 35 ppm, Co, Mn
Was less than 1 ppm. Bromine element content is 100
It was ppm.

[0029]

Comparative Example 1 Acid precipitation was carried out in the same manner as in Example 1 except that 100 g of water was additionally added instead of 100 g of acetone. As a result, NDCA 4.10 g
Although the recovery rate was 98.8%, the minimum particle size of NDCA was 0.15 μm or less, and filtration was time-consuming and difficult.

The purity of the obtained NDCA was 99.6%, the OD was 0.883 at 400 nm, and the OD was 500 at 500 nm.
There was no change at 113 and no improvement was made. 2-Formyl-6-naphthoic acid was 480 ppm, and Co and Mn were both 1 ppm or less. Elemental bromine content is 180ppm
Met.

[0031]

Example 4 In Example 1, the obtained crude NDCA disodium salt aqueous solution was adjusted to pH 9 using an 18.2 wt% sulfuric acid aqueous solution, and then 0.15 g of activated carbon (Shirasagi A: Takeda Yakuhin) was added thereto. In addition, after stirring at 60 ° C. for 2 hours, acid precipitation was carried out in the same manner as in Example 1 except that an aqueous solution of NDCA disodium salt in a filtrate obtained by filtering activated carbon was used. As a result ND
CA 3.97 g (recovery rate 95.7%) was obtained, and the minimum particle size of the obtained NDCA was 3.13 μm, and filtration was easy.

The obtained NDCA had a purity of 100% and an OD of 0.328 at 400 nm (hue improvement rate 63
%), 500 nm is 0.018 (hue improvement rate 84%), and 2-formyl-6-naphthoic acid is 5 ppm or less C
Both o and Mn were 1 ppm or less. The elemental bromine content was 90 ppm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Miwa Shirasaki 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72) Tomoya Sakata Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture 8-3-1, Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute

Claims (3)

[Claims] 1. A method for purifying 2,6-naphthalenedicarboxylic acid, which comprises subjecting a dialkali salt of 2,6-naphthalenedicarboxylic acid to acid precipitation in the presence of water and a water-soluble organic solvent. 2. A 2,6-naphthalenedicarboxylic acid which is characterized by adsorbing an aqueous solution of a dialkaline salt of 2,6-naphthalenedicarboxylic acid with activated carbon and then acidifying the salt in the presence of a water-soluble organic solvent. Acid purification method. 3. An acid is added to a mixed solvent solution of 2,6-naphthalenedicarboxylic acid dialkali salt in water and a water-soluble organic solvent to precipitate 2,6-naphthalenedicarboxylic acid. -A method for purifying naphthalenedicarboxylic acid.