JPH01249746A - Purification of 2,6-naphthalenedicarboxylic acid dimethyl ester - Google Patents

Abstract

PURPOSE:To purify the subject compound in a high efficiency, by distilling crude compound in the presence of a specific solvent such as dipentyl phthalate in vacuum, or distilling in the presence of a solid adsorbent such as slaked lime or combining the above methods. CONSTITUTION:Crude 2,6-naphthalenedicarboxylic acid dimethyl ester is purified by distilling in vacuum under an absolute pressure of 0.1-100mmHg in the presence of a solvent having a boiling point of 300-500 deg.C under normal pressure and a melting point of <=60 deg.C and essentially nonreactive with the subject compound (e.g., dibutyl phthalate or trioctyl phosphate). As an alternative method, the compound can be purified by distilling in the presence of a solid adsorbent which is essentially insoluble in crude 2,6-naphthalenedicarboxylic acid dimethyl ester (e.g., magnesia). When the above two methods are used in combination, the distillation operation is facilitated and the acid value of the subject compound can be decreased to <=0.05mgKOH/g. The subject compound is useful as a raw material for polyesters.

Description

[Detailed description of the invention] [Industrial application field] 2.6-naphthalene dicarboxylic acid dimethyl ester is
It is useful as a raw material for polyalkylene-2,6-naphthalene dicarboxylate, which is a polyester with excellent physical properties.

[Prior Art] Conventionally, as a method for producing 2,6-naphthalene dicarboxylic acid dimethyl ester, there has been a method in which, for example, 2,6-naphthalene dicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene or the like is esterified with methanol. Are known. However, the crude 2,6-
Naphthalene dicarboxylic acid dimethyl ester is usually significantly colored due to impurities, and when dimethyl ester is used as a raw material for a polymer, the color tone of the polymer is poor and the value of the product is low. Therefore, it is necessary to remove impurities from this dimethyl ester.

As a method for purifying dimethyl 2.6-naphthalenedicarboxylate, operations such as crystallization, adsorption, distillation, etc., or a method combining these operations are known.

Crystallization and adsorption operations require a large amount of solvent, are complicated to operate, and have other disadvantages, and it is difficult to obtain products of satisfactory quality.

Distillation is considered to be the best industrial purification method, but when directly distilling 2,6-naphthalene dicarboxylic acid dimethyl ester, its boiling point is high and its melting point is 19.
Since the temperature is as high as 0°C, it is necessary to make the distillation temperature sufficiently higher than 190°C. Therefore, since distillation takes place at high temperatures,
There are problems such as the generation of new impurities such as colored substances and methyl naphthoate due to thermal decomposition of dimethyl 2,6-naphthalene dicarboxylate during distillation, and the inability to lower the acid value. For this reason, for example,
The issue states that the temperature of the distillation pot should be kept below 340°C, and JP-B No. 58-29291 states that the acid value of 2,6-naphthalene dicarboxylic acid dimethyl ester should be kept low from 1 to 50 to keep the esterification rate low. It is stated that. Further, JP-A No. 51-82246 describes the addition of a small amount of naphthoic acid derivative in order to prevent the trouble of clogging the vacuum line due to precipitation of dimethyl 2,6-naphthalene dicarboxylate.

[Problem that the invention seeks to solve]

There are the following two problems in the distillation of crude 2,6-naphthalene dicarboxylic acid dimethyl ester.

(1) Since the distillation temperature of 2.6-naphthalene dicarboxylic acid dimethyl ester is high, troubles such as clogging due to sublimation of 2.6-naphthalene dicarboxylic acid dimethyl ester are likely to occur, and the temperature of the condensing section, vacuum line, connecting section, etc. Controls require careful attention and are difficult to drive.

In addition, since the distillation temperature of 2,6-naphthalene dicarboxylic acid dimethyl ester is high, its vapor pressure is high and the degree of vacuum cannot be increased, so there is a limit to lowering the bottom temperature, and thermal decomposition at the bottom of the column is also limited. In fact, it cannot be ignored.

(2) The acid value of the distillate is as high as 0.5 to 3 mg KOII/g, which is insufficient as a polymer grade, and further treatment is required to lower the acid value.

For example, in Japanese Patent Publication No. 46-3057, distillation is carried out by adding an alkali salt such as sodium carbonate and an organic acid salt such as potassium acetate in order to lower the acid value.

Since this method uses a strongly alkaline salt, this alkali salt dissolves in 2,6-naphthalene dicarboxylic acid dimethyl ester and causes thermal decomposition of 2,6-naphthalene dicarboxylic acid dimethyl ester at high temperatures. An organic acid salt is added at the same time, which requires an expensive organic acid salt.

[Means for Solving the Problems] As a result of intensive studies on the distillation purification method for dimethyl 2,6-naphthalene dicarboxylic acid, the present inventor found that the above two problems can be solved by the following method. This heading led to the present invention.

As a method to solve the problem (1), the boiling point at normal pressure is 300 to 500°C, and the melting point is 60°C or less,
It is effective to distill in the presence of at least one solvent (hereinafter simply referred to as "solvent") that does not substantially react with 2.6-naphthalene dicarboxylic acid dimethyl ester.

That is, by simultaneously distilling 2,6-naphthalene dicarboxylic acid dimethyl ester and the solvent, the melting point is lowered, so that sticking to the condenser and vacuum piping is prevented, and the condensation temperature can be significantly lowered. 2 more
, 6-naphthalene dicarboxylic acid dimethyl ester, the bottom temperature does not rise to the thermal decomposition temperature of 2,6-naphthalene dicarboxylic acid dimethyl ester, and the decomposition of 2,6-naphthalene dicarboxylic acid dimethyl ester does not occur. can be avoided.

As a method for solving the problem (2), it is effective to add a virtually insoluble alkaline solid adsorbent to 2,6-naphthalene dicarboxylic acid dimethyl ester and distill it. That is, by melting 2,6-naphthalene dicarboxylic acid dimethyl ester in the presence of a solid adsorbent or adsorbing the remaining acid component, the acid value in 2,6-naphthalene dicarboxylic acid dimethyl ester can be lowered. In addition, since the solid adsorbent is insoluble in dimethyl 2,6-naphthalene dicarboxylic acid, it can be distilled without causing thermal decomposition.

The above two methods are new methods that solve the problems of the conventional methods, but in the presence of the solvent (1), (2
It is more effective to add a solid adsorbent of ) and distill under a vacuum of 0.1 to 100 mmHg.

That is, according to the present invention, (1) When purifying crude 2,6-naphthalene dicarboxylic acid dimethyl ester by distillation, the boiling point at normal pressure is 300 to 500°C, the melting point is 60°C or less, and 2°6
- in the presence of at least one solvent that does not substantially react with naphthalene dicarboxylic acid dimethyl ester, at an absolute pressure of 0.1
2.6- A method for purifying 2,6-naphthalene dicarboxylic acid dimethyl ester, which comprises distilling the naphthalene dicarboxylic acid dimethyl ester by adding a virtually insoluble solid adsorbent thereto, and (3) crude dimethyl 2,6-naphthalene dicarboxylate. When purifying esters by distillation, the boiling point at normal pressure is 300 to 500°C, the melting point is 60°C or less, and 2°6
- addition of a virtually insoluble solid adsorbent to 2,6-naphthalene dicarboxylic acid dimethyl ester in the presence of at least one solvent that is virtually unreactive with naphthalene dicarboxylic acid dimethyl ester, at a pressure of 0.1 to 100 mm Hg absolute; This is a method for purifying 2,6-naphthalene dicarboxylic acid dimethyl ester, which is characterized by distilling the 2,6-naphthalene dicarboxylic acid dimethyl ester.

The crude 2,6-naphthalene dicarboxylic acid dimethyl ester used in the present invention may be obtained by any method. For example, 2,6-naphthalene dicarboxylic acid obtained by oxidizing 2,6-dialkylnaphthalene as described above and methyl esterifying it by a known method is advantageously used.

The solvent used in the present invention has a boiling point of 3 at normal pressure.
00-500℃, 300-400℃ close to the boiling point of 2,6-naphthalene dicarboxylic acid dimethyl ester
Solvents with a boiling point of °C are preferred. In the presence of this solvent 2
．． By distilling 6-naphthalene dicarboxylic acid dimethyl ester, sublimation of 2,6-naphthalene dicarboxylic acid dimethyl ester is suppressed, and troubles due to blockages in the condenser and vacuum piping are eliminated. If co-distillation is carried out using a solvent with a boiling point below 300° C., the composition of 2,6-naphthalene dicarboxylic acid dimethyl ester in the distillate will be low and a large amount of the compound will be required, which is not efficient.

Also, when co-distilled with a solvent with a boiling point exceeding 500℃,
Since the distillation temperature is high, the target product is likely to be thermally decomposed. Moreover, since almost only 2,6-naphthalene dicarboxylic acid dimethyl ester is distilled out, troubles such as sublimation occur.

The solvent used in the present invention must also have a melting point of 60°C or less. If the melting point exceeds 60° C., the solvent must be heated to maintain it in a liquid state industrially, and the filtration operation must also be carried out with heating.

This solvent is also inert to 2,6-naphthalene dicarboxylic acid dimethyl ester, has good thermal stability, and does not produce thermal decomposition products during distillation. It is necessary to obtain.

Examples of solvents having the above-mentioned properties used in the present invention include phthalic acid derivatives such as dibutyl phthalate, dibentyl phthalate, dihexyl phthalate, and dioctyl phthalate; Examples include phosphoric acid derivatives such as phosphate, fatty acid derivatives such as dioctyl adipate and tributyl citrate, heat carriers such as alkyldiphenyl and hydrogenated triphenyl, or 0-methylbenzophenone and 0-terphenyl.

These solvents are not limited to one type, but it is particularly effective to use a mixture of two or more types. 2. When a solvent with a lower boiling point and a solvent with a higher boiling point than 6-naphthalene dicarboxylic acid dimethyl ester are simultaneously mixed and co-distilled, the lower boiling point compound initially covers the reactor wall to prevent sublimation, and the higher boiling point compound finally forms. is effective in extruding 2,6-naphthalene dicarboxylic acid dimethyl ester and improving the recovery rate.

The amount of solvent used is 0.05 to 20 times the weight of 2,6-naphthalene dicarboxylic acid dimethyl ester,
Preferably it is 0.1 to 10 times. If it is less than 0.05 times, the above-mentioned effect can hardly be expected, and if it exceeds 20 times, the amount of solvent will be too large and heat consumption will be large, which is not industrially preferable.

Note that this solvent can be heated to 2.6 by cooling the distillate.
- Naphthalene dicarboxylic acid ester precipitates and is easily separated.

In the present invention, a solid adsorbent insoluble in 2,6-naphthalene dicarboxylic acid dimethyl ester is used. As this solid adsorbent, alkaline solid adsorbents such as slaked lime, magnesia, calcium oxide, silica-alumina-magnesia, and Kyoward (product name of Kyowa Kagaku GE) are generally used.

The amount of solid adsorbent used should be theoretically equivalent to the acid value of crude 2,6-naphthalene dicarboxylic acid dimethyl ester, but since it is a solid, it should not be used in excess to achieve sufficient adsorption. It is necessary to add it, and it is usually added in an amount of 1% by weight or more, preferably in the range of 1 to 20% by weight. If the amount is less than 1% by weight, the adsorption effect will be small. The solid adsorbent used for -degree adsorption can be used repeatedly.

In the present invention, the adsorption temperature can range from room temperature to the distillation temperature, but in order to carry out the adsorption operation when 2,6-naphthalene dicarboxylic acid dimethyl ester is melted or dissolved in a solvent, the adsorption temperature is usually in the range of 100 to 300°C. conduct. An adsorption time of one hour or less is sufficient, and even if adsorption takes place for more than one hour, no further effect is expected.

The distillation method may be simple distillation or precision distillation using a number of stages. The pressure of distillation is 0.1 to 100 in absolute pressure.
mmHg, preferably 1 to 20 mmHg.

When distilled at a pressure exceeding 100 mmHg, the temperature becomes high, thermal decomposition of 2,6-naphthalene dicarboxylic acid dimethyl ester occurs, and the purity of 2,6-naphthalene dicarboxylic acid dimethyl ester decreases.

A pressure of less than 0.1 mmHg is not only not necessary for the distillation operation, but is also disadvantageous in terms of industrial equipment because it becomes expensive.

The distillation temperature is determined by the distillation pressure, and may be any temperature below which thermal decomposition of 2°6-naphthalene dicarboxylic acid dimethyl ester can be sufficiently suppressed.

Since decarboxylation of the dimethyl ester occurs gradually at temperatures above 300°C, the temperature is preferably below 300°C, more preferably from 150 to 280°C.

Distillation may be continuous or batchwise. As the distillation apparatus, a vacuum distillation pot, a tray distillation pot, a packed distillation pot, etc. are used.

When the purified 2,6-naphthalenedicarboxylic acid dimethyl ester distilled by the method of the present invention and the purified 2,6-naphthalenedicarboxylic acid dimethyl ester are separated by filtration from the solvent, other solvents (e.g. methanol, xylene, , toluene), and is preferably removed by filtration, washing, or recrystallization.

[Effects of the Invention] In the method of the present invention, pure white crystals of 2,6-naphthalene dicarboxylic acid dimethyl ester are obtained by performing co-distillation using the solvent of (1), and the purity is 99.9% or more. The acid value can be 0.4 mg KOII/g or less. In addition, by adding the solid adsorbent (2) and distilling it, the purity can be increased to 99.9% or more, and the acid value can be reduced to 0.1 mg KO.
It can be less than Il/g. Furthermore, in the method in which the solvent (1) and the solid adsorbent (2) are combined, the acid value can be reduced to 0.05 mg KOIl/g or less.

In the method of the present invention, by first distilling 2,6-naphthalene dicarboxylic acid dimethyl ester in the presence of at least one of the solvents, the melting point is lowered and sticking to the condenser is prevented. can be significantly reduced. As a result, the vapor pressure of 2,6-naphthalene dicarboxylic acid dimethyl ester is reduced, eliminating troubles caused by sublimate leakage into the vacuum line, and allowing the distillation line to be heated by accurately controlling the temperature with a heating medium. There is no need for
The driving benefits are huge.

Next, when the crude 2,6-naphthalene dicarboxylic acid dimethyl ester is purified by distillation, a solid adsorbent is added and distilled to lower the acid value in the obtained 2,6-naphthalene dicarboxylic acid dimethyl ester. Something happens. This also significantly reduces thermal decomposition of naphthalene dicarboxylic acid dimethyl ester during distillation.
-5- Further, by combining these two inventions, it becomes easier to cultivate plums by distillation, and the acid value of the obtained dimethyl 2゜6-naphthalene dicarboxylic acid is 0.0.
The present invention is an industrially extremely significant method because it can achieve a concentration of 5 mgKOH/g or less.

〔Example〕

EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

In the following Comparative Examples and Examples, the degree of coloration was measured by the following method. A solution of 2,6-naphthalene dicarboxylic acid dimethyl ester in 0-chlorophenol to a concentration of 10% by weight was placed in a cell with a length of 5CII+,
This is the optical density measured at a wavelength of 500 mμ using a spectrophotometer with 0-chlorophenol placed in a comparative cell.

Example 1 Acid value 8.45 (KOII mg/g), coloring degree 5.1
10 g of crude 2.6-naphthalenedicarboxylic acid dimethyl ester and 110 g of phthalic acid dipentyl ester from 2.
Place in a 0 cc three-loaf flask and heat at 140°C for 1 hour.
The mixture was heated and stirred.

Next, at an absolute pressure of 1 mmHg and a temperature inside the flask of 200°C,
2゜6-naphthalene dicarboxylic acid dimethyl ester and 7
Talic acid dipentyl ester was subjected to simple distillation. Tower top temperature 19
The liquid distilled at 0° C. was dissolved in 50 g of xylene, cooled, and recrystallized. After filtering the crystals, the filtered crystals were washed three times with xylene and dried. The obtained 2,6-naphthalene dicarboxylic acid dimethyl ester weighed 9.5 g (recovery rate 95%) and was a white crystal. The purified 2.6-naphthalene dicarboxylic acid dimethyl ester obtained by this method has an acid value of 0.364 (KOHmg/g) and a coloring degree of 0.0.
1, and the purity as determined by gas chromatography was 100%.

Example 2 Crude 2,6-naphthalene dicarboxylic acid dimethyl ester with acid value 8.45 (KOH/g) and coloring degree 5.12 50
Put 10g of g1 slaked lime into a 300cc three-lough flask,
The mixture was heated and stirred at 180° C. for 1 hour. Next, absolute pressure 5mmH
g. 2,6-naphthalene dicarboxylic acid dimethyl ester was subjected to simple distillation at a flask internal temperature of 205°C. Obtained 2
, 6-naphthalene dicarboxylic acid dimethyl ester is 4
0 g (recovery rate 80%), and was colorless crystal. The purified 2,6-naphthalene dicarboxylic acid dimethyl ester obtained by this method has an acid value of 0.095 (KOIImg/g)
The degree of coloration was 0°04, and the purity was 99.7%.

Example 3 Acid value 8.45 (KOIImg/g), coloring degree 5.1
Put 10 g of crude 2.6-naphthalenedicarboxylic acid dimethyl ester from Step 2, 110 g of phthalic acid dipentyl ester, and 2 g of slaked lime into a 300 cc three-lough flask, and heat at 140°C.
The mixture was heated and stirred for 1 hour. Next, 2,6-naphthalenedicarboxylic acid dimethyl ester and phthalic acid dipentyl ester were subjected to simple distillation at an absolute pressure of 1 mmHg and a temperature inside the flask of 200°C.

The liquid distilled at a top temperature of 190° C. was dissolved in 50 g of xylene, cooled, and recrystallized. After filtering the crystals, the filtered crystals were washed three times with xylene and dried. Obtained 2
, 6-naphthalene dicarboxylic acid dimethyl ester is 9
．． 5 g (recovery rate 95%), and white crystals.

The purified 2,6-naphthalene dicarboxylic acid dimethyl ester obtained by this method has an acid value of 0.032 (K weight 11 mg/g).
), the coloring degree was 0.01, and the gas chromatography purity was 100%.

Compared with Example 1 and Example 2, in this example, 2
The acid value of 46-naphthalene dicarboxylic acid dimethyl ester has decreased to 0.032 (mgKOII/g).

Example 4 Acid value 8.45 (K weight 1 mg/g), coloring degree 5.12
50 g of crude 2,6-naphthalenedicarboxylic acid dimethyl ester, 25 g of dibutyl phthalate, and 25 g of dioctyl phthalate 1 2.5 g of slaked lime at 300 c
The mixture was placed in a three-hole flask, and heated and stirred at 170°C for 1 hour. Next, the absolute pressure is 1 mmtlg, and the temperature inside the flask is 20
At 0°C, 2,6-naphthalenedicarboxylic acid dimethyl ester, phthalic acid dibutyl ester, and phthalic acid dioctyl ester were subjected to simple distillation. The liquid distilled at a top temperature of 170 to 200°C was dissolved in 50 g of xylene, cooled, and recrystallized. After drying the crystals, the separated crystals were washed three times with xylene and dried. The obtained 2,6-naphthalene dicarboxylic acid dimethyl ester weighed 49.5 g (recovery rate 99%) and was colorless crystal. The purified 2,6-naphthalene dicarboxylic acid dimethyl ester obtained by this method had an acid value of 0.03 g (KOII mg/g), a degree of coloration of 0.01, and a purity of 100%.

Compared to Example 3, in this example, 2,6- The recovery rate of naphthalene dicarboxylic acid dimethyl ester is improved by 4%.

Example 5 The pot residue (quicklime, colored substances, etc.) used in Example 4 was given an acid value of 8.
．． 45 (KOIImg/g), crude 2,6-naphthalene dicarboxylic acid dimethyl ester with coloring degree 5.12 50
g, 25 g of dibutyl phthalate, and 25 g of dioctyl phthalate were added, and the mixture was heated and stirred at 170° C. for 1 hour. Next, the absolute pressure was 1 mmHg, and the temperature inside the flask was 20 mmHg.
At 0°C, 2,6-naphthalenedicarboxylic acid dimethyl ester, phthalic acid dibutyl ester, and phthalic acid dioctyl ester were subjected to simple distillation. The liquid distilled at a top temperature of 170 to 200°C was dissolved in 50 g of xylene, cooled, and recrystallized. After filtering the crystals, the filtered crystals were washed with xylene for 3 minutes.
Washed twice and dried. The obtained 2゜6-naphthalene dicarboxylic acid dimethyl ester was 49.5 g (recovery rate 99%)
The purified 2,6-naphthalene dicarboxylic acid dimethyl ester obtained by this method had an acid value of 0.040 (KOIImg/g) and a degree of coloration of 0.
．． 01, purity was 100%. The results show that even if slaked lime is used once, the adsorption capacity does not decrease and it can be used repeatedly.

Comparative Example 1 A distillation operation of the heptalic acid dipentyl ester of Example 1 was carried out without the coexistence of a solvent. Distillation was carried out at an absolute pressure of 10 mm, 1 g, and a tower top temperature of 245° C. to obtain 2,6-naphthalene dicarboxylic acid dimethyl ester. When run without co-distillation with the solvent, 2,6-naphthalene dicarboxylic acid dimethyl ester often caused shutdowns due to blockage of the vacuum line. The temperature of the distillation pot exceeded 300°C and the distillate became colored, so the operation was stopped. The amount of 2,6-naphthalene dicarboxylic acid dimethyl ester obtained at this time was 3.6 g (recovery rate 36%) and was a yellow crystal. The purified 2,6-naphthalene dicarboxylic acid dimethyl ester obtained by this method has an acid value of 0.378 (KOI1m
g/g), the degree of coloration was 0.04, and the purity was 98%.

In this comparative example, since co-distillation with phthalic acid dipentyl ester was not performed as compared to Example 1, the target product was decomposed during distillation, resulting in a decrease in the purity of the target product. Furthermore, the recovery rate decreased by 60% due to sublimation of the target product.

Furthermore, compared to Example 2, since there was no alkaline solid adsorbent, the acid value of the target product was 10 times higher.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Agent: Patent Attorney Sadafumi Kohori

Claims (3)

[Claims] (1) When purifying crude 2,6-naphthalene dicarboxylic acid dimethyl ester by distillation, the boiling point at normal pressure is 300 to 500 °C, the melting point is 60 °C or less, and 2,6
- in the presence of at least one solvent that does not substantially react with naphthalene dicarboxylic acid dimethyl ester, at an absolute pressure of 0.1
A method for purifying 2,6-naphthalene dicarboxylic acid dimethyl ester, which comprises distilling under a pressure of ~100 mmHg. (2) When purifying crude 2,6-naphthalene dicarboxylic acid dimethyl ester by distillation, a substantially insoluble solid adsorbent is added to the 2,6-naphthalene dicarboxylic acid dimethyl ester before distillation. A method for purifying 6-naphthalene dicarboxylic acid dimethyl ester. (3) When purifying crude 2,6-naphthalene dicarboxylic acid dimethyl ester by distillation, the boiling point at normal pressure is 300 to 500°C, the melting point is 60°C or less, and 2,6
- addition of a virtually insoluble solid adsorbent to 2,6-naphthalene dicarboxylic acid dimethyl ester in the presence of at least one solvent that does not substantially react with the naphthalene dicarboxylic acid dimethyl ester, at a pressure of 0.1 to 100 mm Hg absolute; 1. A method for purifying 2,6-naphthalene dicarboxylic acid dimethyl ester, which comprises distilling the 2,6-naphthalenedicarboxylic acid dimethyl ester.