JP2002069073A - Method for producing highly pure pyromellitic anhydride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing highly pure colorless pyromellitic anhydride almost free from a by-product and having high quality. SOLUTION: The objective pyromellitic anhydride is recovered as purified crystal by dissolving crude pyromellitic acid or crude pyromellitic anhydride in water under heating, cooling the solution to crystallize pyromellitic acid, heating and dehydrating the obtained crystal, evaporating the obtained pyromellitic anhydride and cooling the vapor of the pyromellitic anhydride.

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 high-purity pyromellitic anhydride, which is a raw material of a polyimide resin having high heat resistance, a crosslinking agent for expanded polyester, a special plasticizer, and the like.

[0002]

2. Description of the Related Art As a method for producing pyromellitic acid, there are known a method in which durene is obtained by liquid phase oxidation and a method in which 2,4,5-trimethylbenzaldehyde and the like are liquid phase oxidized.
As a method for dehydrating and purifying the crude pyromellitic acid to obtain pyromellitic anhydride, a method of dehydrating in the presence of an aliphatic acid anhydride such as acetic anhydride is known, but this method uses acetic anhydride. Therefore, there is a disadvantage that the cost is increased. Further, as a method for producing pyromellitic anhydride, a method of 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 required for sublimation purification. JP-A-62-59280 describes a method for producing pyromellitic anhydride by heating pyromellitic acid at a specific temperature.

[0004]

The pyromellitic acid and pyromellitic anhydride obtained by the above method include a small amount of trimellitic acid (TMA) and methyltrimellitic acid (MTMA).
Etc., and are often colored.
For this reason, JP-A-62-59280 describes that pyromellitic acid recrystallized with water is dehydrated, but the purity, color, particle size, etc. of the obtained pyromellitic anhydride are insufficient. In addition, higher quality pyromellitic anhydride is required. An object of the present invention is to provide a method for producing high-quality, high-purity pyromellitic anhydride containing little by-products and having no coloring.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, dissolved pyromellitic acid or pyromellitic anhydride in water by heating and cooled as pyromellitic acid. By crystallizing and filtering, pyromellitic acid containing almost no impurities is obtained, which is dried by heating, and further, pyromellitic anhydride is evaporated under reduced pressure, and the vapor is cooled to recover as purified crystals. The present inventors have found that high-quality, high-purity pyromellitic anhydride having a large particle size without coloring can be industrially advantageously produced, and arrived at the present invention. That is, the present invention heat-dissolves crude pyromellitic acid or crude pyromellitic anhydride in water to crystallize by cooling as pyromellitic acid, heats the obtained crystal to anhydrate, evaporates the pyromellitic anhydride, This is a method for producing high-purity pyromellitic anhydride, characterized in that the vapor of pyromellitic anhydride obtained is cooled and recovered as purified crystals.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Purifying raw materials in the present invention include crude pyromellitic acid obtained by liquid-phase oxidation of durene, 2,4,5-trimethylbenzaldehyde and the like, durene,
Crude pyromellitic anhydride obtained by vapor-phase oxidation of 4,5-trimethylbenzaldehyde or the like, or an anhydride of crude pyromellitic acid obtained by the liquid phase oxidation can be used.
In particular, it is preferable to use crude pyromellitic acid obtained by subjecting 2,4,5-trimethylbenzaldehyde or the like to liquid phase oxidation as a purification raw material.

As the water for dissolving the crude pyromellitic acid or the crude pyromellitic anhydride, ion-exchanged water or distilled water is used.
The ratio of crude pyromellitic acid or crude pyromellitic anhydride to water is in the range of 1: 2 to 1:10 by weight, preferably in the range of 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 dissolution temperature is in the range from 70 to 180C, preferably from 80 to 160C.

[0008] Crystallization is performed by cooling the liquid in which the purified raw material is dissolved. At this time, a method of crystallization under reduced pressure is preferable, and the final crystallization temperature is in the range of 20 to 40 ° C. The crystallized crystals are separated by a centrifugal separator, a vacuum filter or the like, rinsed if necessary, and dried to obtain high-purity pyromellitic acid. In this crystallization operation, impurities such as trimellitic anhydride and methyl trimellitic anhydride are largely transferred to the mother liquor, and purified high-purity pyromellitic acid is obtained as crystals.

Next, the purified pyromellitic acid is heated at 170 ° C.
To 260 ° C., preferably 180 ° C. to 240 ° C. to obtain pyromellitic anhydride. 17
At 0 ° C. or lower, the dehydration efficiency is low, and at 260 ° C. or higher, coloring may occur. The heating time is 1 to 20 hours, preferably 3 to 10 hours. As an apparatus for heating and dehydrating pyromellitic acid, any apparatus such as a fluidized bed, a fixed bed, a batch system, a semi-continuous system, and a continuous system may be used as long as the system uniformly heats a solid. The pressure can be reduced to normal pressure, increased pressure, or reduced pressure. However, considering the simplicity of the apparatus and the water discharge efficiency, normal pressure or reduced pressure is preferable.

Next, the pyromellitic anhydride which has been dehydrated is evaporated and cooled, whereby it is recovered as purified crystals. The pressure for evaporation is 150 Torr or less, preferably 120 Torr or less, and the temperature is 250 to 40.
It is in the range of 0 ° C. Pyromellitic anhydride has a melting point of 287
° C and a vaporization operation in a liquid state is preferable.
The pyromellitic anhydride is evaporated at a temperature of 90 to 350 ° C. The cooling temperature of the vapor of pyromellitic anhydride is usually 20
The temperature is 0 ° C or lower, preferably 100 ° C or lower. The cooling method is preferably performed in a gas phase part in the apparatus for evaporating pyromellitic anhydride by heating under reduced pressure, or a cooling part having a plate-shaped cooling surface in a cooling part communicating with the gas phase part. The crystals of pyromellitic anhydride adhering to the surface can be easily recovered by a suitable scraping device. The time required for evaporation is preferably short, in order to suppress thermal decomposition as much as possible, and is usually in the range of 0.2 to 8 hours, preferably 0.5 to 5 hours. If it exceeds this range, trimellitic anhydride or the like will be generated, and the purity of pyromellitic anhydride will decrease. Evaporation, cooling, and recovery of pyromellitic anhydride are batch, semi-continuous,
Any form such as a continuous type can be applied.

[0011]

Next, the present invention will be described specifically 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 the methanol-soluble color. The methanol dissolution color was determined by the following method. Sample 5
g was dissolved in 100 ml of methanol, and the wavelength was 430 nm.
Was measured and 100 times the measured value was taken as the methanol-soluble color.

Reference Example (Production of Crude Pyromellitic Acid) Continuous connection of 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 having a capacity of 2 L. 14. 1450.3 g of water and 100% hydrogen bromide in the first reactor of a two-stage reactor.
3 g, 34.4 g of manganese bromide (tetrahydrate) and 0.1 g of ferric bromide, a bromine ion concentration of 2.3% by weight,
Manganese ion concentration 0.44% by weight, iron ion concentration 13
ppm of the catalyst solution was charged, and 1000 g of the catalyst solution having the same composition as the first stage was charged into the second stage reactor. Nitrogen was injected from the gas inlet, the pressure was increased to 1 MPa, and the heating device was 220 °
Temperature. Then, 2,4,5-trimethylbenzaldehyde and a catalyst solution (the same composition as the solution charged in the reactor) were separately supplied to the first-stage reactor at a rate of 90 g / h and 780 g / h. Air supply was started from the gas inlet simultaneously with the supply of 2,4,5-trimethylbenzaldehyde, and the flow rate was controlled so that the oxygen in the exhaust gas from the reactor was kept at 2.5%. Next, while the liquid level in the first-stage reactor was kept 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 g of water were added to the second-stage reactor.
% Hydrogen bromide mixed with 2 g of bromine ion concentration 3.3% by weight
Is supplied at a rate of 60 g / h, and the introduction of air from the gas inlet is started to reduce the oxygen in the exhaust gas from the reactor to 4.5.
The flow rate was controlled to maintain the percentage. While keeping the liquid level in the second-stage reactor constant, 1150 g / h of a reaction product was withdrawn from the second-stage reactor. During this time, the pressure of the reactor was maintained at 3.2 MPa in the first stage and 2.9 MPa in the second stage. The reaction product solution obtained above was treated with 0.5% Pd / C catalyst in the presence of 15%
A hydrogenation reaction was performed at 0 ° C. and 1 MPa, and after cooling, the obtained crystals were separated by filtration and dried to obtain crude pyromellitic acid.
The obtained crude pyromellitic acid contains 1.6% by weight of trimellitic acid and 0.97% by weight of methyltrimellitic acid,
Purity was 96.7% by weight.

COMPARATIVE EXAMPLE 1 300 g of the crude pyromellitic acid obtained in Reference Example was mixed with pure water 22
The solution was dissolved in 00 g at 80 ° C., kept in that state for 0.5 hour, cooled, and the crystals were separated at 40 ° C. The obtained crystals were rinsed with an equal amount of water and dried at 120 ° C. for one day. 200 g of the pyromellitic acid after drying was heated at 250 ° C. for 10 hours while stirring to dehydrate. Table 1 shows the measurement results of the obtained pyromellitic acid and pyromellitic anhydride.

Example 1 The same treatment as in Comparative Example 1 was carried out, and 150 g of the obtained pyromellitic anhydride was subjected to simple distillation at 305 ° C. and 70 Torr. Distillation time is 1 hour, recovery of pyromellitic anhydride is 95%
Met. Table 1 shows the results.

Example 2 In Example 1, simple distillation was carried out at 50 Torr and 297 ° C. The distillation time was 1 hour, and the recovery of pyromellitic anhydride was 90%. Table 1 shows the results.

Comparative Example 2 200 g of the crude pyromellitic acid obtained in Reference Example was heated at 250 ° C. for 10 hours with stirring without recrystallization and rinsing.
Dehydration was performed. 150 g of the obtained pyromellitic anhydride
Was subjected to simple distillation at 305 ° C. and 70 Torr. Distillation time is 1
Over time, the recovery of pyromellitic anhydride was 95%. Table 1 shows the results.

[0017]

[Table 1]

[0018]

As is clear from the above examples, the pyromellitic acid obtained by dissolving crude pyromellitic acid or crude pyromellitic anhydride in pure water and recrystallization by the method of the present invention. After heating and dehydrating, by distillation,
A high-quality, high-purity pyromellitic anhydride containing almost no by-products and no coloring can be produced. INDUSTRIAL APPLICABILITY The method of the present invention can easily obtain high-quality, high-purity pyromellitic anhydride and is an industrially superior method, so that the present invention has great industrial significance.

Claims (2)

[Claims] (1) Crude pyromellitic acid or crude pyromellitic anhydride is dissolved in water by heating and crystallized by cooling as pyromellitic acid, the obtained crystals are dried by heating, and the pyromellitic anhydride is evaporated to obtain A method for producing high-purity pyromellitic anhydride, comprising cooling the recovered pyromellitic anhydride vapor and recovering it as purified crystals. 2. The method according to claim 1, wherein the pyromellitic anhydride is evaporated under a reduced pressure of 150 Torr or less at a temperature in the range of 250 ° C. to 400 ° C.