JPH02243652A - Method for purifying naphthalenedicarboxylate - Google Patents

Abstract

PURPOSE:To efficiently obtain high-purity naphthalenedicarboxylic acid by adding a water-soluble organic solvent to an aqueous solution of a dialkali salt of crude naphthalenedicarboxylic acid, depositing and separating the dialkali salt. CONSTITUTION:An alkali and water are added and reacted with naphthalenedicarboxylic acid (hereinafter abbreviated to NDCA), prepared by various methods and containing impurities to provide an aqueous solution of the dialkali salt. An organic solvent (e.g. methanol or acetone) having >=100g/100g-H2O solubility in water at 20 deg.C is then added to deposit and separate the dialkali salt of the NDCA. The NDCA is useful as a raw material for polymers, etc., and especially 2,6-NDCA is useful as a raw material for producing polyethylene-2,6-naphthalate, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for purifying naphthalene dicarboxylic acid salts.

[Prior art] Naphthalene dicarboxylic acid (hereinafter abbreviated as NDCA)
There are various isomers depending on the substitution position of the carbonyl group, and some of them are used as polymer raw materials, etc. Among these, 2.6-NDC
Polyethylene-2, which has excellent physical and chemical properties,
It is an industrially useful compound as a raw material for producing 6-naphthalate and the like.

Such NDCA can be achieved by, for example, a method of oxidizing an alkyl group such as a methyl group, an ethyl group, an isopropyl group, a di-substituted naphthalene such as a formyl group or an acyl group, or an oxidized intermediate thereof with molecular oxygen, or a method using Henkel. However, the crude NDCA products produced by these methods contain many impurities and require purification.

This will be explained in detail with respect to 2.6-NDCA, which is particularly useful industrially, as follows.

That is, as a method for producing 2.6-NDC, 2,6-dialkylnaphthalene having a methyl group, ethyl group, isopropyl group, etc. as an alkyl group is converted into Hn, C.

There is a method of oxidizing in the presence of an oxidation catalyst containing a heavy metal compound such as NaBr and a bromine compound such as NaBr. The crude 2,6-NDCA product obtained by this method contains many impurities such as coloring substances, reaction intermediates, and side reaction products, and cannot be used as a raw material for resins, etc. In some cases, its purification is necessary. In many of these impurities, one of the two alkyl groups in the raw material dialkylnaphthalene has been oxidized to an aldehyde group or a carboxyl group, or one alkyl group has been oxidized to a carboxyl group.
One of the groups is a reaction intermediate such as one oxidized to an aldehyde group, or an organic compound such as a side reaction product such as trimellitic acid.

However, the crude 2.
When 6-NDCA is made into a dialkali salt by adding an aqueous alkali solution of potassium, sodium, ammonium, etc., the reaction intermediate having a carboxyl group and the acid of the side reaction product also become an alkali salt and both become water-soluble. From the aqueous solution of these alkali salts, only the dialkali salt of 2.6-NDCA is separated and purified by methods such as cooling, concentration, salting out, and acid precipitation, and impurities are removed to obtain the target product, 2.6-NDCA. Obtaining high purity is not easy.

In addition, alkali salts of benzenecarboxylic acid compounds having three or more carboxyl groups, such as trimellitic acid, have high solubility in water and are less likely to precipitate than dialkali salts of 2.6-NDCA, so their separation is relatively difficult. Although it is easy to use, organic compounds in which only one alkyl group is oxidized to an aldehyde group do not form alkali salts and are unnecessary in water, so they are dispersed as fine particles or 2.6-NDCA. It is thought that it exists attached to the dialkali salt of , and its separation is difficult.

Furthermore, 2-alkyl-6-carboxynaphthalene and 2-alkyl-6-carboxynaphthalene
- In organic compounds such as carboxy-〇-formylnophthalene, the solubility of the alkali salt in water is 2.
．． It is thought that it is lower than the dialkali salt of 6-NDCA and precipitates easily, and it is difficult to remove it efficiently.

Therefore, as a method for purifying such a crude product of 2.6-NDCA, 2.8-NDCA is made into a dialkali salt aqueous solution, 1. This dialkali salt aqueous solution is concentrated to a saturated aqueous solution, and then cooled. (1) Method of precipitating dialkali salt by evaporating water and concentrating it (Japanese Unexamined Patent Publication No. 48-96.573, Japanese Patent Publication No. 52/1986)
-20.994), ■ A method of salting out by adding a salt such as NaCl and 2CO3 to this dialkali salt aqueous solution,
A method of precipitating a metal salt from an aqueous solution of a dialkali salt such as a method of precipitating a metal salt from an aqueous solution of a dialkali salt, and a method of precipitating a metal salt with an acid while adjusting the amount of (i) II
(No.), ■Make monoalkaline salt with CO2 etc. (Special Publication No. 52
20.993), etc., methods of precipitating and separating monoalkaline salts are known.

However, methods ① and ③ require a large amount of energy to evaporate or cool water, and the solubility difference with respect to temperature is small. The surrounding area becomes locally highly concentrated, and impurities precipitate out because they are surrounded by the precipitated dialkali salt, improving purity.Also, when adding salt as a saturated aqueous solution, the dialkali salt aqueous solution is concentrated to a saturated aqueous solution. There is a problem that the amount of salt increases as well as it is necessary to do so, and method (2) has the problem that impurities are likely to be precipitated at the same time even if acid precipitation is performed while adjusting the pH.
There were problems such as multiple steps and the need for an autoclave.

[Problems to be Solved by the Invention] As a result of intensive research in order to solve the problems in the conventional purification methods, the present inventors found that by adding a water-soluble organic solvent to an aqueous solution of dialkali salt of NDCA, water By lowering the solubility, the dialkali salt of N0CA is precipitated, and organic compounds that do not have a carboxyl group such as 2-alkyl-6-formylnaphthalene, which are present as impurities in crude NDCA and are unnecessary in water, -1 carboxyl group such as alkyl-6-carboxynaphthalene
Organic compounds that are relatively sparingly soluble in water, such as alkaline salts of organic compounds that have only one compound, are apparently easily dissolved in an aqueous solution and difficult to precipitate. The present invention was completed based on the discovery that it can be precipitated using the following methods.

Therefore, an object of the present invention is to provide a method for efficiently refining 1N ()CA produced by various methods and containing various impurities to obtain highly pure NDCA.

[Means for Solving the Problems 1] That is, the present invention provides an aqueous solution of a dialkali salt of NDCA with a solubility in water of 100 g/100 g at 20°C.
This is a method for purifying naphthalene dicarboxylic acid salts, which includes a step of adding an organic solvent of -+12o or higher to precipitate a dialkali salt of NDCA.

The crude NOCA to be purified in the method of the present invention is, for example, a di-substituted naphthalene having a furkyl group such as a methyl group, an ethyl group, an isopropyl group, a formyl group, an acyl group, etc., or an oxidized intermediate thereof. Crude NDCA obtained by oxidation with molecular oxygen, crude NDC produced by the Henkel method, etc., and preferably crude NDCA, which is industrially particularly useful among the many isomers of NDCA.
．． 6-NDC8. In addition, in the Henkel method, the method of the present invention is applied in the purification step of dialkali salt, which is a reaction intermediate.

The purification process to NDC basically consists of: ■ converting NDCA into a dialkali salt aqueous solution; ■ adding a water-soluble organic solvent to this NDCA dialkali salt aqueous solution to precipitate and separate the NDCA dialkali salt; ■ NDC^ It consists of a step of converting NDCA from NDCA salt, and if necessary, a decolorizing step using a solid adsorbent can be added between the steps (1) and (2) and/or the steps (2) and (2). The present invention relates to the step (2).

(2) Step N of forming a dialkali salt aqueous solution [) Add an alkali and water to the crude product of CA and react to form a dialkali salt aqueous solution of NDCA.

Here, the alkali includes hydroxides such as Na, K, N, etc., hydrogen carbonates such as carbonates, and ammonia. These good alkalis are
From the viewpoints of reaction rate, solubility, operability, cost, etc., NaOH or diOH is preferable, and the best one is KO]1. The amount of this alkali added is 1.
8 to 3 equivalents may be sufficient. On the other hand, if too much water is added, the amount of organic solvent to be added will increase, and the amount of treatment will increase, which is not preferable. Additionally, it may be heated to a temperature below 90° C. to increase the dissolution rate and increase ease of handling.

Furthermore, if there is any insoluble matter in the dialkali salt aqueous solution, it is preferable to include a step to remove it, or alternatively, step (2) may be included to remove it simultaneously with the solid adsorbent.

■ Adding a water-soluble organic solvent to precipitate and separate the dialkali salt The water-soluble organic solvent used to precipitate the dialkali salt of NDCA by adding it to the dialkali salt aqueous solution includes, for example, methanol, ethanol, and 2-propanol. Alcohols such as tools, ketones such as acetone and methyl ethyl ketone, amides such as N,N-dimethylformamide, N,N-dimethylacetamide, and other organic acids such as dimethyl sulfoxide and pyridine. Organic solvents can be used. That is, the organic solvent may be a mixture as long as it appears to be an aqueous solution, or may contain an organic solvent that is insoluble in water. The solubility of the organic solvent needs to be 100 g/100 g-u2° or more at 20°C, and preferably it can be dissolved in any proportion. From the viewpoint of reusing the organic solvent, it is preferable that the organic solvent has a boiling point difference of 5° C. or more with water, and it is more preferable that the organic solvent has a boiling point lower than that of water. Such organic solvents include:
Examples include acetone, methanol, ethanol, and the like. The amount of organic solvent to be used is as long as the amount of ω required to precipitate 10% or more, preferably 50% or more of the dialkali salt of NDCA in the aqueous solution, and if necessary, this organic solvent may be used in excess. good.

Although the dialkali salt aqueous solution obtained in the above step (2) may be used as it is, it is advantageous to keep it close to the saturated S degree. It is preferable to add the organic solvent little by little while stirring. Further, although operations such as cooling may be combined with this step, it is not necessary to provide a particular temperature difference.

The dialkali salt crystals of NDCA thus precipitated can be separated by suitable means such as centrifugation or filtration. At this time, the obtained dialkali salt crystals of NDCA are mixed with the same organic solvent as added, other water-soluble organic solvents, solvents such as organic solvents unnecessary for water, or mixtures thereof, or mixtures containing water, etc. It is preferable to perform reslurry cleaning or rinsing cleaning to remove the mother liquor remaining in the crystals. The used organic solvent can be recovered by appropriate means such as distillation and reused.

(2) Step of releasing NDCA from dialkali salt To release NDCA from dialkali salt, after dissolving the crystals of NDCA dialkali salt in water, a mineral acid such as HCI or an organic acid such as acetic acid may be added. Further, when the crystals are dissolved in water, step (2) may be added as necessary. The amount of acid used is the amount necessary for the dialkali salt aqueous solution to reach a pll of 6 to 3. The precipitated crystals are centrifuged,
Separate by appropriate means such as filtration. The obtained crystals are washed with water by re-slurry washing or rinsing to remove acids, etc. in the crystals, and then dried to give highly pure NDCA.

(2) Decolorization step using a solid adsorbent This decolorization step is a step in which a solid adsorbent is added to an aqueous dialkali salt solution, stirred, and then the solid adsorbent is separated and removed. Solid adsorbents include activated carbon, activated alumina,
Examples include activated magnesia, and activated carbon is preferred. The amount used may be from 0.5 to 30% by weight, based on the crude product of NDCA. Alternatively, the treatment method may be a method of forming a flow of an aqueous dialkali salt solution passing through a layer of solid adsorbent.

[Example] Hereinafter, the method of the present invention will be specifically explained based on Examples.

In the examples, "part" means "heavy" part, and "%" means "heavy mass %." Moreover, purity is a value measured by liquid chromatography.

Example 1 2.6-Diituprobylnaphthalene was oxidized in the presence of an oxidation catalyst containing heavy metals and bromine compounds, and the q product was filtered, washed, and dried to yield crude 2.6-NDC^. )qta. This crude 2.6-NDCA contained impurities and was dark yellow in color with a purity of 95.0%.

1,150 parts of a 5% KOH aqueous solution was added to 0 parts of this 2.6-NDCAI O, and heated to 70° C. with stirring to dissolve it. 5 parts of activated carbon was added, stirred, and then filtered.

Using 300 parts of the dipotassium salt aqueous solution obtained in this way, 450 parts of acetone was added to it at room temperature to
．． Crystals of 6-NDCA dipotassium salt were precipitated.

The obtained slurry liquid was suction-filtered, the crystals of the dialkali salt were rinsed with 100 parts of acetone, the crystals were dissolved in water again, and 5%-HCI was added until the OH of the aqueous solution reached 3. -N[)CA crystals were precipitated.

The 2,6-NDCA crystals precipitated in this way are suction filtered, re-slurried and rinsed with water to remove acids, etc. in the crystals, and then dried to produce pure white 2゜6-NDCA.
33 parts of crystals of A were obtained. The purity of the obtained 2,6-NDCA was 99.9%, and the yield was 35%.

Example 2 The same operation as in Example 1 was performed except that 700 parts of methanol was used in place of 450 parts of aretone, and pure white 2.6
-62 parts of NDCA crystals were obtained. Obtained 2゜6-ND
The purity of CA was 99.9% and the yield was 65%.

Example 3 The same operation as in Example 1 was performed except that 550 parts of N,N-dimethylacetamide was used in place of 450 parts of acetone to obtain 83 parts of pure white 2.6-NDCA crystals. The purity of the obtained 2,6-NDCA was 99.9%, and the yield was 87%.

Example 4 In Example 1, after concentrating 1.200 parts of dialkali salt aqueous solution after activated carbon treatment to a total volume of 680 parts,
Add 700 parts of acetone to this aqueous solution and add 2.6-N[
) Crystals of CA dialkali salt were precipitated, and the same operations as in Example 1 were performed to obtain pure white 2.6-NDCA crystals 66.
．． The obtained 2,6-NDCA had an N degree of 99.9% and a yield of 70%.

[Effects of the Invention] According to the method of the present invention, crude naphthalene dicarboxylic acid containing various impurities can be purified by a simple method,
Furthermore, it is possible to efficiently produce high-purity naphthalene dicarboxylic acid (
I can do it.

Patent applicant: Nippon Steel Chemical Co., Ltd.

Claims (1)

[Claims] In precipitating and purifying the dialkali salt of naphthalene dicarboxylic acid from an aqueous solution of the dialkali salt of naphthalene dicarboxylic acid, the solubility in water at 20°C is 100 g/
A method for purifying naphthalene dicarboxylic acid salts, which comprises adding 100 g-H_2O or more of an organic solvent to precipitate a dialkali salt of naphthalene dicarboxylic acid.