JPS6115864B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and producing pyromellitic acid and/or pyromellitic anhydride from a mixture of aromatic polycarboxylic acids and/or their anhydrides. Conventionally, among aromatic polycarboxylic acids, pyromellitic acid and pyromellitic anhydride have not been commercialized on a large scale, despite their use as raw materials for heat-resistant resins, due to difficulties in obtaining raw materials in large quantities and production technology issues. I'm late. The reason why this industrialization has been delayed is that in addition to the above, pyromellitic acid, which is produced
Pyromellitic anhydride is often required to be a highly purified product due to its usage, and it is impossible to produce only a single aromatic polycarboxylic acid due to manufacturing technology, and it is difficult to produce only a single aromatic polycarboxylic acid. Another reason is that no method has been found to efficiently extract only the target product from a mixture containing . Originally, aromatic polycarboxylic acids and their anhydrides have high boiling and melting points, making it difficult to purify them by ordinary distillation. In particular, acids having three or more carboxyl groups in the benzene nucleus or their anhydrides have high boiling points, such as trimellitic anhydride at 250°C at 2 mmHg and pyromellitic anhydride at 310°C at 30 mmHg.
It is very difficult to use the distillation purification method industrially. The method conventionally attempted to separate pyromellitic acid and pyromellitic anhydride from a mixture of aromatic polyhydric carboxylic acids is a recrystallization method using solvents such as ketones and ethers. In order to selectively crystallize only the target product from group polyhydric carboxylic acids with high purity, it is necessary to use a large amount of solvent and repeat the recrystallization operation, which involves complicated operations such as recovering and reusing the solvent. There were many cases and it was not practical. Some aromatic polycarboxylic acids form stable crystalline complexes with aromatic hydrocarbons.
A method of separating aromatic polyvalent carboxylic acids using this property has also been proposed, but this is difficult unless the concentration of the target separation substance in the sample is high, and a concentration operation is required as a pretreatment. Further, there were drawbacks such as a decrease in separation yield. As an improved method for these, Japanese Patent Publication No. 11133/1986 describes a method of purifying pyromellitic anhydride by recrystallizing it using a mixed solvent of ether such as ethyl ether, tetrahydrofuran, or dioxane and benzene, toluene, or xylene. Although this method can yield high-purity pyromellitic anhydride when relatively high-purity crude pyromellitic anhydride is used as a starting material, it is possible to obtain pyromellitic anhydride with a low content of pyromellitic acid or aromatic anhydride. When a polyhydric carboxylic acid mixture is used as a starting material, there is a drawback that highly pure pyromellitic acid or pyromellitic anhydride cannot be obtained in high yield by one-stage recrystallization. Therefore, the object of the present invention is to eliminate the above-mentioned drawbacks, and to produce highly pure polyhydric carboxylic acids in one step of recrystallization even when the raw material is an aromatic polycarboxylic acid mixture with a relatively low content of pyromellitic acid or pyromellitic anhydride. The object of the present invention is to provide a method for obtaining pyromellitic acid or pyromellitic anhydride in high yield. In order to achieve the above object, the inventors of the present invention have carefully measured and studied various properties of aromatic polycarboxylic acids and their anhydrides. It was discovered that by dissolving the anhydride and gradually adding a poor solvent such as benzene or alkylbenzene, highly pure pyromellitic acid or pyromellitic anhydride could be precipitated in one step and separated in high yield. He has completed his invention. That is, the method of the present invention involves separating and producing pyromellitic acid and/or pyromellitic anhydride from a mixture of aromatic polycarboxylic acids and/or aromatic polycarboxylic acid anhydrides containing pyromellitic acid and/or pyromellitic anhydride. aliphatic carboxylic acid having 3 or less carbon atoms and/or
By using the following aliphatic carboxylic acid anhydride as a solvent and dissolving the aromatic polycarboxylic acid and/or aromatic polycarboxylic acid anhydride, benzene and/or alkylbenzenes are added. This is a method for producing pyromellitic acid and/or pyromellitic anhydride, which precipitates pyromellitic acid and/or pyromellitic anhydride. Specific examples of the mixture of aromatic polycarboxylic acids containing pyromellitic acid used in the present invention include the reaction product obtained when diurene is oxidized by an oxidation reaction such as air oxidation or nitric acid oxidation, O- These include distillation stillage from distillation and purification of phthalic anhydride obtained by oxidizing xylene. All of these have different compositions depending on the raw materials, reaction reagents, reaction conditions, etc., but they have physical properties similar to those of pyromellitic acid, and are difficult to separate using conventional separation methods, such as phthalic acid, isophthalic acid, and terephthalic acid. It is a mixture containing benzenedicarboxylic acids, benzenetricarboxylic acids such as trimellitic acid and trimesic acid, benzenetetracarboxylic acids other than pyromellitic acid, and benzenepentacarboxylic acids. In addition, in the mixture of aromatic polyhydric carboxylic acids, the benzene nucleus contains an alkyl group other than a carboxyl group such as a methyl group, an oxidation intermediate such as an aldehyde group, an alkanol group, and in some cases a nitro group.
It may also contain aromatic derivatives having halogen groups and the like. As the aliphatic carboxylic acid having 3 or less carbon atoms and its anhydride used in the present invention, for example, acetic acid, propionic acid, acetic anhydride, propionic acid anhydride, etc. can be used. From an economic point of view, acid anhydrides are particularly advantageous, and acetic anhydride is advantageous from an economical point of view. As the precipitant, benzene, alkylbenzenes, or a mixture of two or more thereof are used. As the alkylbenzenes, alkylbenzenes having one or two alkyl groups having 4 or less carbon atoms are used, such as toluene,
Xylenes, ethylbenzene, diethylbenzene, iso-propylbenzene, tert-butylbenzene, etc. are used. When employing a method of producing an O-xylene complex for further purification after precipitation purification, it is convenient in the post-process to use O-xylene as a precipitant. When carrying out the present invention, the amount of the solvent, that is, the aliphatic carboxylic acid having 3 or less carbon atoms and/or its anhydride, to be used for the mixture of aromatic polycarboxylic acids that are the raw materials is determined by the composition of the raw materials and the temperature at the time of dissolution. Although it varies depending on the type of solvent, in general, about 1 to 10 parts of solvent is sufficient for 1 part of raw material. The amounts of benzene and alkylbenzenes used as precipitants also vary depending on the above conditions, but generally 1 to 10 parts of the precipitant is appropriate for 1 part of the solvent used. The conditions for dissolving the mixture of aromatic polyhydric carboxylic acids in acetic acid, propionic acid and/or acetic anhydride, and pyromellitic anhydride are, of course, possible at room temperature if sufficiently finely divided raw materials are used, but the solvent used Heating to a temperature below the boiling point of the substance results in a faster dissolution rate and is more efficient. Additionally, if there are components that are insoluble in the solvent, removal operations such as sedimentation or centrifugation may be necessary, and in some cases, impurity adsorbents such as activated carbon may be added to remove components that are difficult to separate using normal operations. Impurities can be removed and it is useful for increasing the purity of the obtained pyromellitic acid and pyromellitic anhydride. Next, the method of adding a precipitant such as benzene or alkylbenzenes is to gradually add this type of precipitant to a uniformly dissolved solution, and after addition, leave it to stand for several hours or more, or slowly stir it. When the crystals are grown, a highly pure precipitate is obtained. The obtained precipitates of pyromellitic acid and pyromellitic anhydride are separated by a known separation method such as centrifugation, washed with an appropriate solvent, and then dried to obtain the desired pyromellitic acid and pyromellitic anhydride with high purity. can get. If a product of even higher purity is required, the same recrystallization method can be repeated. According to the method of the present invention, mixtures of aromatic polycarboxylic acids and their anhydrides with a low content of pyromellitic acid or pyromellitic anhydride, such as distillation residues from the production of phthalic anhydride from O-xylene, can also be used. High purity pyromellitic acid and pyromellitic anhydride can be separated and produced in high yield in one step.
Particularly when a high-purity product is required, solvent recovery can be advantageously carried out by using O-xylene as a precipitant and combining it with a purification method based on O-xylene complex formation. Next, the present invention will be explained in more detail with reference to Examples. Example 1 Distillation residue obtained when phthalic anhydride obtained by air oxidation of O-xylene was separated by distillation (composition,
300 parts (32% phthalic anhydride, 40% trimellitic anhydride, 14% pyromellitic anhydride, 5% anthraquinone, 7% other polyhydric carboxylic acids (all percentages by weight)) were dissolved in 500 parts acetic anhydride. Next, 2 parts of activated carbon was added, and a part of the insoluble matter was separated by suction. To the obtained liquid, 100 parts of benzene was gradually added, stirred well, and left for 5 hours. Separate the precipitated crystals using a glass filter, wash thoroughly with benzene, and dry under reduced pressure (60℃,
5mmHg). The amount of crystals obtained was 41 parts, and as a result of gas chromatography analysis by diazomethane esterification, the purity was 98% and the melting point was 289-290°C. The crystals were then dissolved in 200 parts of acetone,
When O-xylene is added, an O-xylene complex of pyromellitic anhydride is precipitated. This precipitate is O-
After washing with xylene, high purity pyromellitic anhydride was obtained by heating to 120°C while sufficiently reducing the pressure with a vacuum pump. As a result of gas chromatography analysis after esterification of this high-purity product, the purity was
99.8%, and the melting point was 291°C. Examples 2 to 9 Table 1 shows the analysis results of the recovery rate of pyromellitic anhydride and the purity of the obtained pyromellitic anhydride when pyromellitic anhydride was separated by changing only the type of solvent and precipitant in Example 1. Shown below.

[Table] Example 10 Reaction product obtained by air oxidation of diurene (composition: pyromellitic anhydride 80.1%, trimellitic anhydride 14.9%, trimesic acid 1.4% (wt%)) 100
1 part was dissolved in 200 parts of acetic anhydride, and impurities and insoluble matter were removed using activated carbon in the same manner as in Example 1. Next, 150 parts of O-xylene was added, and after thorough stirring, the mixture was left to stand at room temperature for 5 hours, then cooled to 5° C. and left to stand for 12 hours. After suctioning the formed crystals, 2 of the formed crystals are removed.
The sample was washed with twice the volume of O-xylene, the pressure was reduced to 5 mmHg or less using a vacuum pump, and the sample was gradually heated from room temperature to 100°C to dry. The amount of crystals obtained was 70.1 parts, and gas chromatography analysis by diazomethane esterification showed a purity of 99.2% and a melting point of 290-291°C.

Claims (1)

[Claims] 1. In a method for separating and producing pyromellitic acid and/or pyromellitic anhydride from a mixture of aromatic polycarboxylic acids and/or aromatic polycarboxylic acid anhydrides containing pyromellitic acid and/or pyromellitic anhydride, the carbon number After dissolving the aromatic polycarboxylic acids and/or the aromatic polycarboxylic anhydride using an aliphatic carboxylic acid having 3 or less and/or an aliphatic carboxylic anhydride having 3 or less carbon atoms as a solvent, Pyromellitic acid and/or pyromellitic anhydride, characterized in that pyromellitic acid and/or pyromellitic anhydride is selectively precipitated by adding benzene and/or an alkylbenzene having one or two alkyl groups having 4 or less carbon atoms. manufacturing method.