JPH0733705A - Purification of 2,6-naphtalenedicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide an easy, inexpensive and efficient purification process for getting 2,6-naphthalenedicarboxylic acid having high purity and good hue. CONSTITUTION:Crude 2,6-naphthalenedicarboxylic acid obtained by the oxidation of a 2,6-dialkylnaphthalene is added to more than neutralizing equivalent of an alkaline aqueous solution to form a solutions of the corresponding dialkail salt, and acetone is added to the formed solution of the corresponding dialkail salt to precipitate 2,6-naphthalenedicarboxylic acid from the solution in the form of a dialkail salt.

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) obtained by oxidizing 2,6-dialkylnaphthalene or its oxidation intermediate with molecular oxygen. It is about. NDCA provides a film or a fiber product excellent in heat resistance, mechanical strength and dimensional stability, and is therefore useful as a raw material for polyethylene naphthalate, polyamide and the like.

[0002]

It is known that NDCA is produced by air oxidation of 2,6-dialkylnaphthalene in an acetic acid solvent in the presence of a cobalt, manganese and bromine compound catalyst. However, the crude NDCA obtained by the oxidation reaction contains a trace amount of heavy metals, a coloring substance with an unknown structure, a bromine derivative, a reaction intermediate, and the like. Therefore, if the crude NDCA is used as a raw material, it can be obtained. Poor performance and coloration of the polymer appear. Therefore, there have been many NDCs as described below.
A purification method has been proposed. (1) Dissolve crude NDCA in an aqueous alkaline solution,
The mixture is stirred at 250 ° C. for 1 to 5 hours for heat treatment, then decolorized with a solid adsorbent, and then acid gas such as carbon dioxide or sulfurous acid is pressure-treated to lower the pH.
Method of precipitating as a monoalkali salt (Japanese Patent Publication No.
No. 20993) (2) A method in which an aqueous alkaline solution of crude NDCA is treated with an oxidizing agent such as alkali permanganate, and then carbon dioxide or sulfur dioxide is blown to separate NDCA as a monoalkali salt (JP-A-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, followed by blowing carbon dioxide or sulfurous acid gas to remove NDCA. Method for separating as mono-alkali salt (JP-A-50-160248) (4) Method for separating crude NDCA by dissolving in crude sodium acetate aqueous solution and then concentrating and crystallization to separate mono-alkali salt of NDCA. -105639 gazette) (5) So-called salt in which a water-soluble salt of the same cation is added to an alkaline aqueous solution of crude NDCA Method for isolating NDCA dialkali salt by precipitation (JP-A-62-212341) (6) Method for recrystallizing crude NDCA with a solvent such as dimethyl sulfoxide (JP-A-62-230747)

The above-mentioned methods (1) to (4) are used for the crude NDCA.
If the pH or the temperature of the alkaline aqueous solution in which the is dissolved is not strictly adjusted, there is a problem in that the amount and composition of the monoalkali salt of NDCA to be precipitated will not be constant. The above method (5) includes a salt used for salting out and a salt formed by acid precipitation of an alkali salt, and since the total amount of these salts is very large, a purification method on an industrial scale. As a result, it lacked practicality. Since the method (6) uses a large amount of an expensive solvent for recrystallization, there are problems such as an increase in cost due to the recovery loss thereof and the purity of the obtained NDCA is not sufficiently high.

[0004]

The above-mentioned conventional methods have various technical problems, while the purification by distillation requires NDC.
This is not possible because the melting point of A is 300 ° C. or higher, and since NDCA does not dissolve in general-purpose organic solvents such as methanol, acetone, benzene, etc., a purification method by solvent washing cannot be adopted. Therefore, the present invention solves these problems and is a simple, inexpensive and efficient NDCA.
The purpose of the present invention is to provide a purification method of.

[0005]

As a result of intensive efforts to solve the above problems, the present inventors have found that the crystallization method using acetone is effective for the efficient purification of NDCA. Has been completed. That is, the present invention is
A crude 2,6-naphthalenedicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene is added to an aqueous alkaline solution having a neutralization equivalent or more to form a solution of a corresponding dialkali salt, and acetone is added to the solution. The method of purifying 2,6-naphthalenedicarboxylic acid is characterized in that 2,6-naphthalenedicarboxylic acid is precipitated as a dialkali salt from the solution.

[Detailed Description of the Invention] 1. Oxidation Reaction The crude NDCA used in the present invention is obtained by oxidizing 2,6-dialkylnaphthalene with molecular oxygen. As 2,6-dialkylnaphthalene, 2,6
-Dimethylnaphthalene, 2,6-diisopropylnaphthalene and the like can be mentioned, and their oxidation intermediates can also be used. The conditions of the oxidation reaction are not particularly limited, but for example, NDCA can be obtained under the following reaction conditions. Cobalt and manganese are 0.5 to 5 as a catalyst to 1 mol of the raw material dialkylnaphthalene.
About 0 mol% is used. The ratio of cobalt to manganese is in the range of 1:99 to 99: 1. The bromine compound is suitable in an amount of 1 to 10 mol with respect to 1 mol of cobalt. Acetic acid or propionic acid is used as the solvent, and the amount thereof is 2 to 50 times by weight that of the raw material. Reaction temperature is 80
To 250 ° C, preferably 100 to 200 ° C, and the reaction time is usually in the range of 1 to 10 hours. Considering the reaction rate, the reaction pressure is preferably such a pressure that the oxygen partial pressure in the gas phase is constantly 0.2 to 40 kg / cm ^{2 in} absolute pressure. As molecular oxygen, in addition to pure oxygen, oxygen is nitrogen,
It is also possible to use those diluted to an arbitrary concentration with an inert gas such as helium or argon. The reaction may be either a batch system or a semi-continuous system, but in general, a semi-continuous system having a large yield per catalyst is advantageous. After the completion of the reaction, the produced crude NDCA is in the form of a solvent slurry, so it is filtered, collected, washed with water or an acid, washed with water and dried.

2. Formation of dialkali salt Crude NDCA is added to an aqueous solution in which more than the neutralization equivalent of alkali is dissolved and dissolved under heating or stirring at room temperature to form a solution of crude NDCA dialkali salt. Examples of the alkali used at that time include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonia and the like. The amount of alkali used is N
The amount is in the range of 1 to 2 equivalents with respect to DCA, but it is usually preferable to use about 1.01 to 1.50 equivalents so that the alkali is in a small excess. Alkali is used as an aqueous solution, and its concentration is usually 0.2 to 10% by weight,
In the case of ammonium salts, it is preferable to use a lower concentration than sodium or potassium salts. If the alkali concentration is too high, the NDCA dialkali salt will not dissolve and the purification efficiency will decrease, while if the concentration is too low, the amount of acetone used for precipitation of the dialkali salt will increase,
The recovery rate of NDCA decreases. The formation of dialkali salt
It may be carried out in air, but is preferably carried out in an inert gas such as nitrogen. The temperature for forming the dialkali salt may be room temperature, but it is generally under heating, for example, 4
It is preferable to carry out at a temperature of 0 to 100 ° C. This is because the solubility of the dialkali salt is improved and the efficiency of the reaction vessel is increased, and the recovery rates of a small amount of cobalt and manganese contained in the crude NDCA are improved. This heating is usually carried out for 0.5 to 5 hours, and the obtained aqueous solution of dialkali salt is subjected to crystallization operation after insoluble matter is removed by filtration.

3. Crystallization of dialkali salt By adding acetone to the aqueous solution of the NDCA dialkali salt obtained as described above, the dialkali salt is crystallized. Acetone can also be added while the aqueous solution is heated or cooled. Acetone is intermittently or continuously added to the aqueous solution little by little with stirring to precipitate white NDCA dialkali salt crystals.
The amount of acetone used varies depending on the concentration of the dialkali salt solution in water and cannot be generally stated. However, when the concentration is low, it may be high, and when the concentration is high, it may be low. Generally speaking, acetone has a pH of 0.02 relative to the amount of water present in the aqueous solution.
It is used in a range of about 5 to 5 times by weight. If you want to increase the recovery rate of NDCA, add an aqueous solution at 5 ° C after adding acetone.
It is preferable to cool to a certain degree. The precipitated NDCA dialkali salt is filtered off, washed with saturated saline and / or acetone, and dried. Acetone is easily recovered from the filtrate by distillation and can be reused, and a trace amount of unrecovered NDCA dialkali salt in the filtrate is added with acid to produce NDCA.
Used as a raw material for purification.

4. Activated carbon treatment The dialkali salt obtained above can be directly subjected to the acid precipitation operation described below, but in order to obtain a higher purity NDCA, it is preferable to perform activated carbon treatment. The activated carbon treatment may be carried out by dissolving the dialkali salt in water and using a flow system or a batch system. For example, in the case of the flow type, granular activated carbon is packed in a column, and the NDCA dialkali salt aqueous solution is passed through the flow in an up flow or a down flow. The temperature at that time is about room temperature to 60 ° C., and the liquid flow rate is 0.1 to 1
0.0 is suitable. On the other hand, in the case of the batch system, powdered activated carbon is added in an amount of about 1 to 10% by weight with respect to the dialkali salt, and the mixture is treated under stirring for 1 to 5 hours. The activated carbon used is not particularly limited, and any kind of activated carbon can be used.

5. Acid precipitation operation NDC obtained by the above crystallization operation or activated carbon treatment
For the dialkali salt A, acid is added to its aqueous solution to adjust the pH to 2
It is adjusted to the vicinity and converted to NDCA. At that time, the concentration of the dialkali salt is preferably maintained in the range of 0.5 to 30% by weight. When the concentration exceeds this range, the precipitated N
Since DCA forms a high-viscosity slurry, it becomes difficult to perform operations such as stirring, while if the concentration is too low, the operation efficiency becomes poor. However, since NDCA is insoluble in water, NDCA
There is no effect on the recovery of. As the acid used for acid precipitation,
Usually, it is sulfuric acid, hydrochloric acid or the like, and those diluted with water are used. Also, an acid gas such as carbon dioxide gas can be used. The generated NDCA is filtered, washed thoroughly, and dried.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. The purity of NDCA was determined by high performance liquid chromatography, and the hue was measured by dissolving 1 g of the sample in 10 ml of 40% methylamine aqueous solution and using a 10 mm quartz cell to measure absorbance at wavelengths of 400 nm and 500 nm (hereinafter referred to as OD).
Abbreviated). In order to show the improvement of the hue in an easy-to-understand manner, the hue improvement rate was calculated by the following formula. The bromine element was quantified by fluorescent X-rays and cobalt and manganese were quantified by atomic absorption.

[0012]

[Equation 1]

Crude NDCA obtained by an ordinary liquid-phase oxidation reaction was used as a purification raw material. This crude NDCA
Has a purity of 99.5% and an OD of 0.3563 (40
0 nm) and 0.0473 (500 nm), and N
The cobalt content in DCA was 3 ppm, the manganese content was 27 ppm, and the bromine element content was 200 ppm.

Example 1 20 equipped with a reflux condenser, a dropping funnel, a stirrer, and a thermometer
Crude NDCA 10 g (46 mmol) in a 0 cc four neck flask
Add 4.07g (102mm of sodium hydroxide)
ol) was dissolved in 65 g of water, and the mixture was heated and refluxed for 1 hour. The solution at this time was a light brown uniform solution. After cooling, 80 g of acetone was slowly added from a dropping funnel over about 15 minutes while stirring. White crystals were precipitated by the addition of acetone. After the addition of acetone was completed, the reaction mixture was cooled to about 5 ° C., and the precipitate was collected by filtration. The obtained white crystals were washed with 40 g of acetone and dried to obtain 11.74 g of NDCA disodium salt. On the other hand, the filtrate was adjusted to pH 2 with dilute hydrochloric acid to recover 0.18 g of NDCA. Acetone was almost quantitatively recovered from the filtrate by distillation.

5 g of the disodium salt obtained above was added to
The mixture was dissolved in 0 ml of water, insoluble matter existing in an extremely small amount was filtered off, and then a 10 wt% sulfuric acid aqueous solution was added to adjust the pH to about 2. The produced NDCA was collected by filtration, washed with water, dried,
White NDCA 4.08 g (9% recovery from crude NDCA
5.8%) was obtained. The purity of this NDCA is 100%
OD is 0.0833 at 400 nm (hue improvement rate of 76.6%) and 500 nm is 0.0069 (hue improvement rate of 85.4%), both cobalt and manganese content is 1 ppm or less, and elemental bromine is contained. The rate was 60 ppm.

Example 2 NDCA disodium salt 5 synthesized and isolated in Example 1
g, dissolved in about 150 ml of water, and insoluble matter present in an extremely small amount was filtered off. A column having a diameter of 10 mm was filled with 1.5 g (about 8 cc) of granular activated carbon (“Shirasagi KL” manufactured by Takeda Pharmaceutical Co., Ltd.), and water was circulated for washing. The aqueous disodium salt solution was passed through the column at room temperature and LHSV = 4. A 10 wt% sulfuric acid aqueous solution was added to the obtained treatment liquid to adjust the pH to 2. The produced NDCA was collected by filtration, washed with water, and dried to obtain 4.01 g of white NDCA (recovery rate from crude NDCA 94.2%). The purity of this NDCA is 1
00%, OD 400 nm is 0.0269 (hue improvement rate 92.5%), 500 nm is 0.0059 (hue improvement rate 87.5%), both cobalt and manganese content is 1 ppm or less, bromine The element content was 51 ppm.

Example 3 20 equipped with a reflux condenser, a dropping funnel, a stirrer, and a thermometer
5 g (23 mmol) of crude NDCA was placed in a 0 ml four-necked flask, and 100 g of 1.8 wt% ammonia water (NH
_3: 51 mmol) was added and reacted for 1 hour under reflux. After cooling, acetone 6 with a dropping funnel is added with stirring.
0 g was added slowly over about 15 minutes. White crystals were precipitated by the addition of acetone. After the addition of acetone was completed, the reaction mixture was cooled to about 5 ° C., and the precipitate was collected by filtration. The obtained white crystals were washed with 20 g of acetone and dried to obtain 5.63 g of white NDCA diammonium salt. 5 g of the obtained diammonium salt was dissolved in about 200 ml of water, and insoluble matters existing in a very small amount were filtered off. Diameter 10
Granular activated carbon (“Shirasagi K” manufactured by Takeda Pharmaceutical Co., Ltd.
L ") was charged in an amount of 1.5 g (about 8 cc), and water was passed to wash. The aqueous solution of diammonium salt was subjected to LHSV at room temperature.
= 4 and was passed through the column. 10 to the obtained treatment liquid
The pH was adjusted to 2 by adding a weight% sulfuric acid aqueous solution. The generated NDCA was collected by filtration, washed with water and dried to give a white ND.
CA 4.16g (Recovery rate from crude NDCA 94.2%)
was gotten. The purity of this NDCA is 100%.
D of 400 nm is 0.0194 (hue improvement rate 94.6
%), 500 nm is 0.0001 or less (hue improvement rate 10
0%), and the cobalt and manganese contents are both 1
The content of bromine was 40 ppm or less and the content of elemental bromine was 40 ppm.

Comparative Example 1 5 g (23 mmol) of crude NDCA was added and dissolved with 34.5 g (NaOH: 51 mmol) of a 5.9 wt% sodium hydroxide aqueous solution. The aqueous disodium salt solution was circulated at LHSV = 4 at room temperature through a column packed with activated carbon similar to that used in Example 2. A 10 wt% sulfuric acid aqueous solution was added to the obtained treatment liquid to adjust the pH to 2. The produced NDCA was collected by filtration, washed with water and dried to give 4.77 g of white NDCA.
(Recovery rate from crude NDCA 95.3%) was obtained. The purity of this NDCA is 100%, and the OD is 400 nm.
Is 0.1425 (hue improvement rate 60.0%), 500 nm
Was 0.0184 (hue improvement rate 61.1%), both the cobalt and manganese content was 1 ppm or less, and the bromine element content was 120 ppm.

Comparative Example 2 The same reactor as in Example 1 was charged with 5 g (23 mmol) of crude NDCA, an aqueous solution prepared by dissolving 2.04 g (51 mmol) of sodium hydroxide in 32 g of water was added, and the mixture was reacted for 1 hour while heating under reflux. It was Thereafter, the mixture was cooled and about 150 g of methanol was slowly added from a dropping funnel under stirring, but the reaction solution was only clouded at the time of addition, and crystals of the NDCA disodium salt did not precipitate.

Comparative Example 3 The same amount of the same raw materials as in Comparative Example 1 was charged in the same reactor as in Example 1, and an aqueous solution prepared by dissolving 2.04 g (51 ml) of sodium hydroxide in 23 g of water was added and heated under reflux. To react for 1 hour. Thereafter, the mixture was cooled and 70 g of methyl ethyl ketone was added from a dropping funnel with stirring, but the reaction solution was only separated into two layers and no precipitation of crystals was observed. Then, the reaction solution was cooled to about 5 ° C. with ice, and white crystals were precipitated. This is filtered, washed, dried and 2.25 g NDC
A disodium salt was obtained. This disodium salt 2.25
g was dissolved in 60 g of water, and a 10 wt% sulfuric acid aqueous solution was added to adjust the pH to about 2. The produced NDCA was collected by filtration, washed with water and dried to obtain 1.82 g of NDCA (recovery rate from crude NDCA: 36.4%). The purity of this NDCA is 100%, and the OD is 0.1079 at 400 nm.
(Hue improvement rate 69.7%), 500 nm is 0.0166
(Hue improvement rate 64.9%), both cobalt and manganese content is 1 ppm or less, and bromine element content is 120 p.
It was pm.

Comparative Example 4 The same amount of the same raw materials as in Comparative Example 1 was charged in the same reactor as in Example 1, and an aqueous solution prepared by dissolving 2.04 g (51 ml) of sodium hydroxide in 23 g of water was added and heated under reflux. To react for 1 hour. 4.2 g of sodium chloride in the obtained reaction solution
Was added little by little to precipitate the NDCA disodium salt. The deposited solid matter was filtered, washed with 30 g of a 19 wt% sodium chloride aqueous solution, and dried to recover 5.92 g of a solid matter. The solid (5.92 g) was dissolved in water (80 cc), and a 10 wt% sulfuric acid aqueous solution was added to adjust the pH to about 2. The produced NDCA is collected by filtration, washed with water and dried to obtain N.
DCA 4.00 g (recovery rate from crude NDCA 80.0
%)was gotten. The purity of this NDCA is 100%, and the OD is 0.1246 at 400 nm (hue improvement rate 6
5.0%), 0.0321 at 500 nm (Hue improvement rate 3
2.1%), both the cobalt and manganese contents were 1 ppm or less, and the bromine element content was 100 ppm.

[0022]

According to the present invention, acetone is used to
By crystallizing the DCA dialkali salt, NDCA with high recovery and high hue can be obtained with a high recovery rate. Such excellent effects of the present invention cannot be achieved by using a solvent other than acetone, for example, methanol, methyl ethyl ketone, or the like, a method by salting out, or the like.

Claims (3)

[Claims] 1. A crude 2,6-naphthalenedicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene is added to an alkaline aqueous solution having a neutralization equivalent or more to form a solution of a corresponding dialkali salt. 2,6-naphthalenedicarboxylic acid is precipitated as a dialkali salt from the solution by adding acetone to 2,6-
Method for purifying naphthalenedicarboxylic acid. 2. The method according to claim 1, wherein the alkaline aqueous solution is an alkaline aqueous solution selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and ammonia. 3. The method according to claim 1, wherein after the dialkali salt of 2,6-naphthalenedicarboxylic acid is dissolved in water, adsorption treatment with activated carbon is performed.