JPH0578366A - Production of high-purity pyromellitic anhydride - Google Patents

Abstract

(57) [Summary] [Purpose] To produce high-purity pyromellitic dianhydride with high yield. [Structure] Tetraalkylbenzene is gas-phase oxidized to produce pyromellitic dianhydride, and the gas produced by the oxidation reaction is cooled to precipitate and collect pyromellitic dianhydride. A method for producing high-purity pyromellitic dianhydride, which comprises washing with a medium solvent such as 4-dioxane and then recrystallizing using a good solvent such as γ-butyrolactone. [Effect] According to the method of the present invention, high-purity pyromellitic dianhydride can be obtained while keeping the yield of pyromellitic dianhydride high, and it can be used as a polymer raw material or the like requiring high purity. is there.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high-purity pyromellitic dianhydride.

[0002]

2. Description of the Related Art Pyromellitic dianhydride can be obtained by catalytic gas phase oxidation of a tetraalkylbenzene having four lower alkyl groups such as methyl, ethyl, propyl, etc. in the presence of a catalyst with a molecular oxygen-containing gas. The pyromellitic dianhydride thus obtained contains impurities even if the collection method is carefully selected. The impurities are those in which one or two of the rings constituting the acid anhydride of pyromellitic dianhydride are opened, trimellitic acid in which the carboxyl group is reduced, phthalic anhydride, etc., and these have the same properties as pyromellitic dianhydride. Many are similar and difficult to separate and remove. However, pyromellitic dianhydride is often required to have high purity because it is used for many polymer materials. For this reason,
Although methods such as a recrystallization method, a complex method, and a vacuum sublimation method have been proposed (Japanese Patent Laid-Open No. 62-93291), it is pointed out in the above publication that they all have some drawbacks.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to obtain pyromellitic dianhydride with high yield and high purity.

[0004]

According to the present invention, tetraalkylbenzene is vapor-phase oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate and collect pyromellitic dianhydride. This is a method for producing high-purity pyromellitic dianhydride in which the collected pyromellitic dianhydride is washed with a medium solvent and then recrystallized with a good solvent. In another invention, tetraalkylbenzene is vapor-phase oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate pyromellitic dianhydride, which is then collected by a collector, and then collected. As a solution in which at least a part of pyromellitic dianhydride is dissolved by pouring a good solvent, this is taken out from the collector, and this solution is cooled or concentrated or a medium solvent or a solvent is added to precipitate most of pyromellitic dianhydride. After letting it
Solid-liquid separation is performed, and the separated solid is washed with 1,4-dioxane and then recrystallized using a good solvent. This is a method for producing high-purity pyromellitic dianhydride.

Examples of tetraalkylbenzene include durene, tetraethylbenzene, and compounds in which 1 to 3 of the alkyl groups are methyl groups or ethyl groups, and the other are ethyl groups or isopropyl groups different from them. A known method in which such gas phase oxidation of tetraalkylbenzene is carried out in the presence of a catalyst containing vanadium at 300 to 450 ° C. also using an oxygen-containing gas can be adopted. This reaction yields pyromellitic dianhydride in relatively good yield, although it depends on the type of tetraalkylbenzene used as a raw material, but it contains some impurities. As impurities, pyromellitic acid in which the ring constituting the acid anhydride is opened,
The main components are trimellitic acid and phthalic anhydride, which have reduced carboxyl groups, and the purity of pyromellitic dianhydride obtained by cooling and precipitating the reaction product gas obtained by gas phase oxidation is 80% or more. In many cases, it is in the range of 85 to 98%.

Since the gas phase oxidation reaction is carried out at a high temperature, pyromellitic dianhydride is contained in the reaction product gas in a gaseous state and flows out from the reactor. By cooling this, pyromellitic dianhydride is deposited. .. By adjusting this cooling temperature, impurities such as phthalic anhydride having a relatively high vapor pressure are not precipitated as much as possible, and only pyromellitic anhydride having a low vapor pressure can be selectively precipitated. However, there is a limit, and the purity cannot be sufficiently high by itself. The collection can be performed by a collector such as a bag filter, but a collector of the type that deposits on the cooling surface or a type that deposits inside the cooler is preferable. The collected pyromellitic dianhydride is continuously or intermittently withdrawn. One preferable method of extracting is a method of extracting by washing with a good solvent described later, but the method is not limited to this, and scraping, melt extraction or the like may be used. When it is drawn out by washing, it is preferable to carry out at a high temperature equal to or lower than the boiling point of the good solvent to dissolve at least a part of the solvent, and preferably to extract it in a state where most of it is dissolved. Here, the good solvent used does not need to be highly pure, and may be, for example, a filtrate separated by recrystallization described later.

[0007] The collected pyromellitic dianhydride is melted, made into powder, or made into flakes or the like and taken out, but since it contains impurities, it is washed. Further, in the case of extracting the collected pyromellitic dianhydride in a state in which at least a part thereof is dissolved using a good solvent, it is cooled or concentrated or dissolved by adding a medium solvent or a poor solvent. After the pyromellitic dianhydride present is precipitated as much as possible, solid-liquid separation, for example, centrifugation is performed to separate the solid. In this case, if two or more operations such as concentration and cooling are added, the solid recovery rate is further improved. here,
The medium solvent has a medium ability to dissolve pyromellitic dianhydride, such as 1,4-dioxane, and the poor solvent has a poor ability, such as benzene and toluene. 1,4-dioxane is preferred. The loss of pyromellitic dianhydride can be minimized by adding a medium solvent or poor solvent and cooling or concentrating.

The washing of pyromellitic dianhydride, which is taken out by a method such as scraping from the collector and melt-extracting, or pyromellitic dianhydride which is solid-liquid separated after the dissolution-extracting, can be similarly performed. Then, for washing, an intermediate solvent having a relatively low solubility of pyromellitic dianhydride and a high solubility with respect to a ring-opened product is used. Preferred medium solvents having such properties include 1,4-dioxane, ethyl acetate, methyl isobutyl ketone, methyl ethyl ketone, and acetone, but 1,4-dioxane is a purification effect and recovery of pyromellitic dianhydride. It is advantageous in terms of yield. 1,4-dioxane has a characteristic of dissolving more ring-opened pyromellitic acid than pyromellitic dianhydride, and the difference is particularly large at 50 ° C or higher. Therefore, the washing is preferably carried out by heating at 50 ° C. or higher, and the amount used is insufficient to completely dissolve pyromellitic dianhydride, but 1 part by weight of pyromellitic dianhydride containing impurities is used. To 1 to 10 parts by weight, preferably 2 to
4 parts by weight is suitable. Washing can be performed by adding a medium solvent such as 1,4-dioxane and stirring for about 10 minutes to several hours. After the washing is completed, in order to reduce dissolution loss of pyromellitic dianhydride, at room temperature or 0 ° C. A method such as cooling to a certain degree and solid-liquid separation by means such as filtration or centrifugation is suitable. If necessary, operations such as washing and drying can be performed after solid-liquid separation.

Although the purity of pyromellitic dianhydride is sufficiently improved by washing, it is recrystallized by using a good solvent in order to obtain a higher purity and to improve the color tone and adjust the properties such as the crystal shape. .. A good solvent has a large ability to dissolve pyromellitic dianhydride, and acetic anhydride, lactones,
There are cyclohexanone, propylene carbonate, etc., but .gamma.-butyrolactone, cyclohexanone or propylene carbonate is preferable. These may be one kind or a mixture of two or more kinds. For example, γ-
The solubility of butyrolactone in pyromellitic dianhydride is 18 g / 100 g at 30 ° C and 70 g / 1 at 150 ° C.
Although it is about 00 g, it improves the color tone compared to other solvents,
It has a high ability to increase the crystal properties, especially bulk density, and to make the particle shapes uniform. In addition, cyclohexanone and propylene carbonate have a similar ability as compared with other solvents. The amount of the good solvent used is at least an amount sufficient to dissolve most of pyromellitic dianhydride upon heating, but in the case of γ-butyrolactone,
The amount is 1 to 5 parts by weight, preferably 1 to 4 parts by weight, per 1 part by weight of pyromellitic dianhydride after washing.

Recrystallization is performed at 100 ° C. or higher, preferably 130
To about 180 ° C to dissolve pyromellitic dianhydride, remove any insoluble matter if necessary, then cool it to room temperature or about 0 ° C, and filter or centrifuge. A method such as solid-liquid separation is suitable. If necessary, activated carbon or the like can be added during recrystallization.

The solid phase obtained by this recrystallization is purified pyromellitic dianhydride, and if necessary, further washed with benzene, acetic anhydride or the like and dried to obtain a product having a purity of 99.9% or more. be able to. The liquid phase obtained by the solid-liquid separation of this recrystallization is a filtrate composed of a solution of a good solvent, but since it contains a large amount of pyromellitic dianhydride, it is advantageous to recover it by distillation or the like. Is. In another embodiment, when a good solvent is flown through a collector and the collected pyromellitic dianhydride is dissolved or dispersed in this and withdrawn, this filtrate is allowed to flow as a part or all of the good solvent. Is also advantageous. The solvent used for washing is 1,
It can be separated into a medium solvent such as 4-dioxane and a solid substance such as pyromellitic dianhydride, and this can be reused.

[0012]

EXAMPLES Examples of the present invention will be shown below. In addition,% is% by weight. Example 1 Tetraethylbenzene was charged together with air into a reactor filled with a catalyst supporting vanadium pentoxide to produce pyromellitic dianhydride. This reaction product gas flows out of the reactor at about 400 ° C., is cooled to 250 ° C. by a heat exchanger, and then is charged into a collector equipped with cooling fins inside.
Here, the mixture was cooled to 120 ° C. to precipitate pyromellitic dianhydride, and then discharged. This collector is equipped with two
When collection of one group is completed, it is switched to another collection group. The solvent consisting of the γ-butyrolactone solution is poured into the collector where collection is completed, and most of it is circulated until it is dissolved and a small amount is dispersed. The amount of the solvent is about 2 parts by weight per 1 part by weight of the collected pyromellitic dianhydride, and the temperature during circulation is about 150 ° C. The purity of pyromellitic dianhydride in the collected crystals is 92.7%.
Met. To 1 part by weight of the solution extracted from the collector, 1 part by weight of 1,4-dioxane was added, and then 40
After cooling to ℃, the precipitated crystals were centrifuged. The separated crystals were charged into a washing tank, 3 times the amount of 1,4-dioxane was added, and the mixture was stirred at 50 ° C. for 1 hour for washing. This was centrifuged at room temperature, and the separated crystals were placed in a recrystallization tank. In the recrystallization tank, 3 times the amount of γ-butyrolactone was added, heated to 150 ° C., stirred for 1 hour to dissolve the crystals, and then cooled to 40 ° C. to precipitate the crystals. The obtained crystals were rinsed with 30 parts by weight of ethyl acetate, and then the precipitated crystals were centrifuged. Dried and purified pyromellitic dianhydride, crystals 100 collected by a collector
It was obtained at a rate of 85 parts by weight per part by weight. The whole of the filtrate separated by recrystallization was used as a γ-butyrolactone solution which was poured into a collector. The filtrate obtained by centrifuging the solution extracted from the collector and the filtrate separated by washing were sent to a distillation column for solvent recovery to recover 1,4-dioxane and γ-butyrolactone. .

The compositions of the crystals collected by the collector, the crystals after washing and the final purified product are shown below. Before washing After washing Purified product Pyromellitic anhydride 92.7% 96.9% 99.9% Pyromellitic acid monoanhydride 0.7 0.5-Pyromellitic acid 2.2 1.0-Trimellitic acid 1.8 1.1-Phthalic anhydride 1.2 0.3-Other 1.4 0.2-Crystalline powder Powder granular color brown brown light yellow white

[0014]

According to the method of the present invention, a high-purity pyromellitic dianhydride can be obtained while maintaining a high yield of pyromellitic dianhydride, and a polymer requiring high purity can be obtained.
It can be used as a raw material.

Claims (7)

[Claims] 1. Tetraalkylbenzene is vapor-phase-oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate and collect pyromellitic dianhydride, which is taken out and taken out. A method for producing high-purity pyromellitic dianhydride, which comprises washing mellitic acid with a medium solvent having a medium solubility in pyromellitic dianhydride and then recrystallizing it with a good solvent. 2. The high-purity pyromellitic dianhydride according to claim 1, wherein the medium solvent is one or more selected from the group consisting of 1,4-dioxane, ethyl acetate, methyl ethyl ketone, acetone and methyl isobutyl ketone. Manufacturing method. 3. The method for producing high-purity pyromellitic dianhydride according to claim 1, wherein the good solvent is one or more selected from the group consisting of γ-butyrolactone, propylene carbonate and cyclohexanone. 4. Tetraalkylbenzene is vapor-phase oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate pyromellitic dianhydride, which is then collected by a collector.
Pour a good solvent into the collector to dissolve at least a portion of pyromellitic dianhydride, take it out of the collector, cool or concentrate this solution, or add a medium or poor solvent to pyromellitic dianhydride. A method for producing high-purity pyromellitic dianhydride, which comprises precipitating most of the acid, then solid-liquid separation, and washing the separated solid with a medium solvent, followed by recrystallization with a good solvent. .. 5. The medium solvent is one or more selected from the group consisting of 1,4-dioxane, ethyl acetate, methyl ethyl ketone, acetone and methyl isobutyl ketone, and the good solvent is γ-butyrolactone, propylene carbonate.
The method for producing high-purity pyromellitic dianhydride according to claim 4, which is one or more selected from the group consisting of carbonate and cyclohexanone. 6. Tetraalkylbenzene is vapor-phase oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate and collect pyromellitic dianhydride, which is taken out and taken out. A method for producing high-purity pyromellitic dianhydride, which comprises washing mellitic acid with 1,4-dioxane and then recrystallizing it with γ-butyrolactone. 7. Tetraalkylbenzene is vapor-phase-oxidized to produce pyromellitic dianhydride, and the oxidation reaction product gas is cooled to precipitate pyromellitic dianhydride, which is then collected by a collector.
Gamma-butyrolactone was poured into a collector to obtain a solution in which at least a part of pyromellitic dianhydride was dissolved, and the solution was taken out from the collector and cooled or concentrated, or 1,4 dioxane was added thereto to obtain pyromellitic dianhydride. After precipitating most of the acid, solid-liquid separation is performed, and the separated solid is 1,4
A method for producing high-purity pyromellitic dianhydride, which comprises washing with dioxane and then recrystallizing with γ-butyrolactone.