JP3024459B2 - Process for producing dimethyl 2,6-naphthalenedicarboxylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dimethyl 2,6-naphthalenedicarboxylate useful as a raw material for high-performance polyester.

[0002]

2. Description of the Related Art 2,6-Naphthalenedicarboxylic acid, which is a raw material of dimethyl 2,6-naphthalenedicarboxylate, generally comprises 2-acyl-6-alkylnaphthalene, 2,6-dialkylnaphthalene or 2,6-diacylnaphthalene. A method is known in which a catalyst is produced by oxidation with molecular oxygen in an acetic acid solvent in the presence of a catalyst such as a cobalt, manganese or bromine compound catalyst. Next, dimethyl 2,6-naphthalenedicarboxylic acid is produced by the method of esterifying 2,6-naphthalenedicarboxylic acid with methanol as described above, but 2,6-naphthalenedicarboxylic acid is hardly soluble in methanol. The esterification reaction rate is extremely slow, and various methods for speeding up the reaction using an esterification catalyst have been proposed. For example, Japanese Patent Publication No. 49-174 discloses a method using a mineral acid such as sulfuric acid, and Japanese Patent Publication No. 55-33704 discloses a method using copper, manganese,
Methods using rhenium, copper oxides, chromium oxides, etc. Japanese Patent Application Laid-Open No. 50-83360 discloses a method using ferric sulfate, mercury sulfate, indium sulfate, zinc sulfate, and the like, JP-A-50-83361, JP-A-50-84553 and JP-A-50-88058. Is a method using molybdenum compounds such as molybdenum oxides, sulfides, cyanides, thiocyanides, molybdic acid, and phosphomolybdic acid. Methods using tellurium, tungstosilicic acid, and the like have been proposed.

[0003]

However, these known methods are not always satisfactory from the viewpoint of industrial equipment and operation, and have various problems. For example, in the method using a mineral acid such as sulfuric acid, the corrosion resistance of the reactor is required, so that the equipment cost increases, and furthermore,
Since dimethyl ether is produced as a by-product, the loss of methanol is also large. Further, the esterification reaction is accelerated to some extent by the above-mentioned method using various metals or metal compounds as a catalyst, but when 2,6-naphthalenedicarboxylic acid is used as a raw material as described above, it is industrially satisfactory. Reaction rate and reaction yield are not obtained. Further, among these metal compound catalysts, tetra-iso-propyl titanate, tetra-n-butyl titanate, and phosphomolybdic acid catalysts are known to be relatively effective for the esterification reaction. For example, when 2,6-naphthalenedicarboxylic acid is used as a raw material as described above, a satisfactory reaction rate cannot be obtained, and an insoluble solid adheres to the inner wall of the reactor to block the reactor. It has been found that this method is not suitable for an industrial production method.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted various studies on the use of an esterification catalyst in order to develop a practical method, and found that 2,6-naphthalenedicarboxylic acid used as a raw material was used. It has been found that the activity of the catalyst and the amount of plugs vary greatly with the quality of the catalyst. As a result of intensive studies on the cause, it was found that cobalt and manganese contained in 2,6-naphthalenedicarboxylic acid had a large effect on the activity of the esterification catalyst and the formation of clogs. The esterification catalyst was found to be effective by using cobalt and manganese salts of 2,6-naphthalenedicarboxylic acid having a controlled manganese content as a raw material. The production amount can also be significantly reduced, and as a result, 2,6-
It has been found that dimethyl naphthalenedicarboxylate can be obtained, and the present invention has been completed. That is, the present invention
When producing 2,6-naphthalenedicarboxylic acid dimethyl by reacting 2,6-naphthalenedicarboxylic acid and methanol, the cobalt content is 200 pp as a raw material.
m and a manganese content of 200 ppm or less 2,
It is intended to provide a method for producing dimethyl 2,6-naphthalenedicarboxylate, which comprises using 6-naphthalenedicarboxylic acid.

[0005] The 2,6-naphthalenedicarboxylic acid used as a raw material in the present invention may be produced or purified by any method as long as the contents of cobalt and manganese are each 200 ppm or less. As described above, 2,6-naphthalenedicarboxylic acid produced by subjecting 2-acyl-6-alkylnaphthalene, 2,6-dialkylnaphthalene or 2,6-diacylnaphthalene to liquid phase oxidation using a cobalt or manganese catalyst. In the case of an acid, it usually contains several thousand ppm of cobalt and manganese. If used as a raw material as it is, not only will the activity of the esterification catalyst be impaired, but also a large amount of insoluble solids will be produced in the reactor, which will lead to industrial production of dimethyl 2,6-naphthalenedicarboxylate. What must not be done is as described above. In the method of the present invention, it is essential to use 2,6-naphthalenedicarboxylic acid containing 200 ppm or less of cobalt and manganese as raw materials. In order to satisfy the requirements of the present invention, it is effective to further wash the 2,6-naphthalenedicarboxylic acid produced and separated and recovered by a usual method with water, acetic acid, methanol or a mixed solvent thereof, particularly Washing with water is more advantageous in terms of washing effect, safety and economy.

In the present invention, known catalysts can be used as the esterification catalyst. In particular, the effect of the present invention is remarkable when tetra-n-butyl titanate, tetra-iso-propyl titanate or phosphomolybdic acid is used. The amount of these esterification catalysts to be used is 0.01 to 5% by weight, preferably 0.03 to 2% by weight, based on 2,6-naphthalenedicarboxylic acid. If the amount is less than 0.01% by weight, the esterification reaction rate is low, which is not preferable.
Further, if the amount is more than 5% by weight, the reaction rate and the reaction yield are not so much improved, so that it is not economical.

The amount of methanol used in the esterification reaction is 1 to 10 times, preferably 4 to 6 times by weight based on 2,6-naphthalenedicarboxylic acid. An excessively small amount of methanol is not preferable because the esterification reaction becomes small. Further, even if the amount is increased more than necessary, the reaction rate and the reaction yield do not improve so much, and unreacted methano-
This is economically disadvantageous due to the large amount of collected waste. The esterification temperature is usually from 200C to 350C, preferably from 220C
280 ° C. If the temperature is lower than 200 ° C., the rate of esterification decreases, which is not preferable. On the other hand, if the temperature is higher than 350 ° C., the amount of by-products of the polymer and dimethyl ether increases, and the yield decreases, which is not preferable. The reaction time varies depending on the amount of the catalyst and the reaction temperature, but is usually about 10 minutes to 5 hours. The reaction system may be any of a batch system, a semi-batch system, and a continuous system.

[0008]

According to the present invention, when 2,6-naphthalenedicarboxylic acid, which is difficult to esterify, is reacted with methanol to produce dimethyl 2,6-naphthalenedicarboxylate, the content of cobalt and manganese as raw materials is reduced. By using a small amount of 2,6-naphthalenedicarboxylic acid, a high reaction rate and a high yield can be achieved, and its industrial significance is extremely large.

[0009]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. COMPARATIVE EXAMPLE 1 A 100 ml sus-316 reactor was charged with a raw material containing 6.0 g of 2,6-naphthalenedicarboxylic acid containing 2530 ppm of cobalt and 3810 ppm of manganese, 36.0 g of methanol, and 2 parts of tetra-iso-propyl titanate catalyst. 0.5% by weight with respect to 2,6-naphthalenedicarboxylic acid was charged, and the reaction was carried out at 230 ° C. for 1 hour with shaking. After the completion of the reaction, a large amount of solid matter adhered to the inner wall of the reactor. The contents were taken out of the reactor and dissolved in dimethylformamide, and analyzed by gas chromatography. As a result, the yield of dimethyl 2,6-naphthalenedicarboxylate was 21.5 mol%.

Comparative Example 2 A reaction was carried out in the same manner as in Comparative Example 1 except that a raw material 2,6-naphthalenedicarboxylic acid containing 480 ppm of cobalt and 2500 ppm of manganese was used. As a result, as in Comparative Example 1, a large amount of solids adhered to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 27.1 mol%.

Comparative Example 3 A reaction was conducted in the same manner as in Comparative Example 1 except that tetra-n-butyl titanate was used as a catalyst in an amount of 1.0% by weight based on 2,6-naphthalenedicarboxylic acid. As a result, as in Comparative Example 1, a large amount of solids adhered to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 33.2 mol%.

Comparative Example 4 As a catalyst, phosphomolybdic acid was used in an amount of 0.1% by weight based on 2,6-naphthalenedicarboxylic acid, and the reaction time was 3 hours.
The reaction was carried out in the same manner as in Comparative Example 1, except that the time was 0 minutes.
As a result, as in Comparative Example 1, many solids were found to adhere to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 83.5 mol%.

Example 1 The same 2,6-naphthalenedicarboxylic acid as used in Comparative Example 1 was washed with 10 times the volume of water for 1 hour under stirring, then filtered and dried. The cobalt content in the obtained 2,6-naphthalenedicarboxylic acid was 126 ppm, and the manganese content was 148 ppm. A reaction was carried out in the same manner as in Comparative Example 1 using the 2,6-naphthalenedicarboxylic acid having a small content of cobalt and manganese as a raw material. As a result, no solid matter was found to adhere to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 95.1 mol%.

Example 2 A reaction was carried out in the same manner as in Comparative Example 3 except that 2,6-naphthalenedicarboxylic acid having a low content of cobalt and manganese used in Example 1 was used. As a result, no solid matter was found to adhere to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 94.8 mol%.

Example 3 A reaction was carried out in the same manner as in Comparative Example 4 except that 2,6-naphthalenedicarboxylic acid having a small content of cobalt and manganese used in Example 1 was used. As a result, no solid matter was found to adhere to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 95.0 mol%.

Example 4 2,6-Naphthalenedicarboxylic acid containing 2530 ppm of cobalt and 3810 ppm of manganese used in Comparative Example 1 was stirred for 1 hour with a 10: 1 weight ratio of a 1: 1 mixed solvent of water and acetic acid for 1 hour. After washing, it was filtered and dried.
The cobalt content in the obtained 2,6-naphthalenedicarboxylic acid was 155 ppm, and the manganese content was 173 ppm. 2,6- with low cobalt and manganese content
The reaction was carried out in the same manner as in Example 1 using naphthalenedicarboxylic acid as a raw material. As a result, no solid matter was found to adhere to the inner wall of the reactor, and the yield of dimethyl 2,6-naphthalenedicarboxylate was 94.7 mol%.

Continuation of the front page (56) References JP-A-51-8252 (JP, A) JP-A-50-84553 (JP, A) JP-A-4-54152 (JP, A) JP-A-5-163206 (JP) (A) JP-A-1-121237 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 69/76 CAPLUS (STN) REGISTRY (STN) WPIDS (STN)

Claims (1)

(57) [Claims] 1. A method for producing dimethyl 2,6-naphthalenedicarboxylate by reacting 2,6-naphthalenedicarboxylic acid with methanol to produce 2,6-naphthalenedicarboxylic acid having a cobalt content of 200 ppm or less and a manganese content of 200 ppm or less. -A process for producing dimethyl 2,6-naphthalenedicarboxylate, wherein the esterification reaction is carried out at a temperature of from 200 to 350 ° C. using naphthalenedicarboxylic acid and phosphomolybdic acid as a catalyst.