JP4626031B2 - Method for producing high purity pyromellitic acid and high purity pyromellitic anhydride - Google Patents

Description

【００１７】
【発明の効果】
以上の実施例から明らかなように、本発明の方法により粗ピロメリット酸または粗無水ピロメリット酸を純水に溶解させ、活性炭処理と再結晶することで副生物を殆ど含まず着色の無い高純度ピロメリット酸が得られ、また更に加熱脱水することで副生物を殆ど含まず着色の無い高純度無水ピロメリット酸とすることできる。
本発明方法は、高品質の高純度ピロメリット酸や高純度無水ピロメリット酸を容易に得ることができ、工業的に優れた方法であるので、本発明の工業的意義は大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing high-purity pyromellitic acid which is a raw material for paints and the like, and a method for producing high-purity pyromellitic anhydride which is a raw material for highly heat-resistant polyimide resins, cross-linking agents for foamed polyester, special plasticizers, etc It is.
[0002]
[Prior art]
As methods for producing pyromellitic acid, there are known a method obtained by liquid phase oxidation of durene and a method of liquid phase oxidation of 2,4,5-trimethylbenzaldehyde and the like. As a method for obtaining pyromellitic acid, there is known a method of dehydrating in the presence of an aliphatic acid anhydride such as acetic anhydride. However, this method has a disadvantage of increasing cost because acetic anhydride is used.
Further, as a method for producing pyromellitic anhydride, a method for vapor phase oxidation of durene or 2,4,5-trimethylbenzaldehyde is known.
[0003]
Japanese Patent Publication No. 1-42953 describes a method of sublimating crude pyromellitic acid or crude pyromellitic anhydride and cooling it from a mixed gas phase to obtain pyromellitic anhydride. However, this method requires a large-scale apparatus necessary for sublimation purification.
Japanese Patent Application Laid-Open No. 62-59280 describes a method for producing pyromellitic anhydride by heating pyromellitic acid at a specific temperature.
[0004]
[Problems to be solved by the invention]
The pyromellitic acid and pyromellitic anhydride obtained by the above method contain a small amount of by-products such as trimellitic acid (TMA) and methyl trimellitic acid (MTMA), and are often colored. For this reason, JP-A-62-59280 describes that pyromellitic acid recrystallized with water is dehydrated, but the obtained pyromellitic anhydride is slightly colored, and further high quality pyroanhydride is obtained. There is a demand for merit acid and pyromellitic acid.
An object of the present invention is to provide a method for producing high-purity pyromellitic acid and high-purity pyromellitic anhydride that contain little by-products and have no coloration.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that crude pyromellitic acid and crude pyromellitic anhydride containing by-products obtained from 2,4,5-trimethylbenzaldehyde and colored are 70 to High-purity pyromellitic acid is obtained by heat-dissolving in water at 160 ° C., contact treatment with activated carbon, crystallization by cooling, and filtration, and high-purity by heat-dehydration in the range of 170 ° C. to 260 ° C. It has been found that pyromellitic anhydride can be easily produced, and has reached the present invention.
That is, the present invention provides a crude pyromellitic acid obtained by subjecting 2,4,5-trimethylbenzaldehyde to liquid phase oxidation, a crude pyromellitic anhydride obtained by subjecting crude pyromellitic acid obtained by the liquid phase oxidation to anhydride, or 2 The crude pyromellitic anhydride obtained by vapor phase oxidation of 1,4,5- trimethylbenzaldehyde is heated and dissolved in water at 70 to 160 ° C., contacted with activated carbon, cooled, crystallized, and filtered. A method for producing high-purity pyromellitic acid, and a method for producing high-purity pyromellitic anhydride, characterized by heat-dehydrating the obtained high-purity pyromellitic acid at 170 ° C. to 260 ° C.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The purified raw material in the present invention was obtained by vapor phase oxidation of crude pyromellitic acid obtained by liquid phase oxidation of durene, 2,4,5-trimethylbenzaldehyde or the like, or durene, 2,4,5-trimethylbenzaldehyde or the like. Crude pyromellitic anhydride or a product obtained by converting the crude pyromellitic acid obtained by the liquid phase oxidation into an anhydride can be used. In particular, it is preferable to use crude pyromellitic acid obtained by liquid phase oxidation of 2,4,5-trimethylbenzaldehyde or the like as a purification raw material.
[0007]
Ion exchange water or distilled water is used as water for dissolving crude pyromellitic acid or crude pyromellitic anhydride. The ratio of crude pyromellitic acid or crude pyromellitic anhydride to water is 1: 2 to 1:10 by weight, preferably 1: 3 to 1: 8. If the proportion of water is too large, the yield will be poor, so the minimum amount of water that dissolves crude pyromellitic acid or crude pyromellitic anhydride is preferred.
The melting temperature is in the range of 70 to 180 ° C, preferably 80 to 160 ° C.
[0008]
The temperature at which the dissolved crude pyromellitic acid or crude pyromellitic anhydride aqueous solution is brought into contact with activated carbon is 70 to 180 ° C, preferably 80 to 160 ° C. The dissolution temperature and the activated carbon treatment temperature are preferably the same.
Activated carbon is used in the form of granular or powdery coconut shell or coal and liquid phase. Those having good decolorization performance are preferable, and commercially available Kuraray Coal GLC, GL, Fuji activated carbon and the like can be exemplified.
The activated carbon treatment of the crude pyromellitic acid or the crude pyromellitic anhydride aqueous solution can be performed in a batch system, a semi-batch system, or a continuous system. When processing by a batch type, activated carbon is preferable 1 to 30 weight% with respect to crude pyromellitic acid or crude pyromellitic anhydride. In the case of continuous treatment, a fixed bed or a suspension bed can be applied. The activated charcoal treatment time is preferably in the range of 0.2 to 10 hours.
[0009]
Crystallization is performed by cooling the solution treated with activated carbon. At this time, a method of crystallization under reduced pressure is preferable, and the final crystallization temperature is 20 to 40 ° C.
The crystallized crystal is separated by a centrifugal separator, a vacuum filter, or the like, washed with water as necessary, and further dried to obtain high-purity pyromellitic acid. By this crystallization operation, impurities such as trimellitic anhydride and methyl trimellitic anhydride are mostly transferred to the mother liquor side, and purified highly pure pyromellitic acid is obtained as crystals.
[0010]
High-purity pyromellitic anhydride is obtained by heat-dehydrating the obtained high-purity pyromellitic acid in the range of 170 ° C. to 260 ° C., preferably 180 ° C. to 240 ° C. If it is 170 ° C. or less, the dehydration efficiency is low, and if it is 260 ° C. or more, it may be colored. The heating time is 1 to 20 hours, preferably 3 to 10 hours.
As an apparatus for heating and dehydrating high-purity pyromellitic acid, any apparatus such as a fluidized bed, a fixed bed, a batch type, a semi-continuous type, and a continuous type may be used as long as the solid is uniformly heated.
Although the pressure can be carried out under normal pressure, increased pressure, or reduced pressure, normal pressure or reduced pressure is preferable in consideration of the simplicity of the apparatus, water discharge efficiency, and the like.
[0011]
【Example】
Next, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited by the following examples.
In the following examples, the degree of coloring of pyromellitic anhydride and the like was indicated by a methanol-dissolved color. The methanol dissolution color was determined by the following method. That is, 5 g of a sample was dissolved in 100 ml of methanol, the absorbance at a wavelength of 430 nm was measured, and 100 times the measured value was taken as the methanol-dissolved color.
[0012]
Reference example (production of crude pyromellitic acid)
To the first stage reactor of a continuous two-stage reactor connected to two 2 L Zr autoclaves having a reflux condenser, a stirrer, a heating device, a raw material inlet, a gas inlet, and a reactant outlet 1450.3 g of water, 15.3 g of 100% hydrogen bromide, 34.4 g of manganese bromide (tetrahydrate) and 0.1 g of ferric bromide were mixed, bromine ion concentration 2.3 wt%, manganese ion concentration 0 A catalyst solution having a concentration of 44% by weight and an iron ion concentration of 13 ppm was charged, and 1000 g of a catalyst solution having the same composition as that in the first stage was charged in the second stage reactor. Nitrogen was injected from the gas inlet, the pressure was increased to 1 MPa, and the temperature was increased to 220 ° C. with a heating device. Subsequently, 2,4,5-trimethylbenzaldehyde was separately supplied to the first stage reactor at a rate of 90 g / h, and a catalyst solution (same composition as the reactor charged solution) was separately supplied at a rate of 780 g / h. Simultaneously with the supply of 2,4,5-trimethylbenzaldehyde, the introduction of air from the gas inlet was started, and the flow rate was controlled so as to keep the oxygen in the exhaust gas from the reactor at 2.5%. Next, while maintaining the liquid level in the first stage reactor constant, liquid transfer from the first stage reactor to the second stage reactor was started, and at the same time, 58 g of water and 100% hydrogen bromide were fed into the second stage reactor. Supply a catalyst solution with a bromine ion concentration of 3.3 wt% mixed with 2 g at a rate of 60 g / h, start air feeding from the gas inlet, and reduce the oxygen in the exhaust gas from the reactor to 4.5% The flow rate was controlled to maintain. While keeping the liquid level in the second-stage reactor constant, 1150 g / h reaction product was extracted from the second-stage reactor. During this time, the pressure in the reactor was maintained at 3.2 MPa for the first stage and 2.9 MPa for the second stage.
The reaction product solution obtained above is subjected to hydrogenation reaction at 150 ° C. and 1 Mpa in the presence of 0.5% Pd / C catalyst, and after cooling, the resulting crystals are separated by filtration and dried to obtain crude pyromellitic acid. Got.
The resulting crude pyromellitic acid contained 1.6% by weight trimellitic acid and 0.97% by weight methyl trimellitic acid, and the purity was 96.7% by weight.
[0013]
Example 1
To 2200 g of pure water, 300 g of crude pyromellitic acid and 50 g of commercially available activated carbon Kuraray Coal GL (10 to 30 mesh) were added, dissolved at 80 ° C., and held for 0.5 hours. Then, it cooled and isolate | separated the crystal | crystallization at 40 degreeC. The obtained crystals were rinsed with an equal amount of water and dried at 120 ° C. for one day to obtain high purity pyromellitic acid.
200 g of the obtained high-purity pyromellitic acid was heated at 250 ° C. with stirring for 10 hours to perform dehydration to obtain high-purity pyromellitic anhydride. Table 1 shows the measurement results of the obtained high purity pyromellitic acid and high purity pyromellitic anhydride.
[0014]
Example 2
Instead of the commercially available activated carbon Kuraray Coal GL, Kuraray Coal GLC (10-30 mesh) was used, and the others were the same as in Example 1. The results are shown in Table 1.
[0015]
Comparative Example 1
The procedure was the same as in Example 1 except that the activated carbon treatment was not performed. The results are shown in Table 1.
[0016]
[Table 1]

[0017]
【The invention's effect】
As is apparent from the above examples, crude pyromellitic acid or crude pyromellitic anhydride is dissolved in pure water by the method of the present invention, and recrystallized with activated carbon treatment so that it contains almost no by-product and is highly colored. Purified pyromellitic acid can be obtained, and further, by heat dehydration, it can be made highly pure pyromellitic anhydride containing almost no by-products and having no coloring.
Since the method of the present invention can easily obtain high-quality high-purity pyromellitic acid and high-purity pyromellitic anhydride and is an industrially excellent method, the industrial significance of the present invention is great.

Claims (2)

Crude pyromellitic acid obtained by liquid phase oxidation of 2,4,5-trimethylbenzaldehyde , crude pyromellitic anhydride obtained by converting crude pyromellitic acid obtained by liquid phase oxidation into an anhydride, or 2,4,5- Crude pyromellitic anhydride obtained by gas-phase oxidation of trimethylbenzaldehyde is heated and dissolved in water at 70 to 160 ° C., contacted with activated carbon, crystallized by cooling, and filtered. Manufacturing method. A method for producing high-purity pyromellitic anhydride, which comprises heat-dehydrating the high-purity pyromellitic acid obtained in claim 1 at 170 ° C to 260 ° C.