JPS5910650B2 - Production method of high purity terephthalic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-quality terephthalic acid by which polyethylene terephthalate can be produced by a so-called direct polymerization method in which esterification with ethylene glycol is followed by polymerization.

Conventionally, a widely used method for producing terephthalic acid is a method in which paraxylene is oxidized with a molecular oxygen-containing gas in an acetic acid solvent in the presence of an oxidation catalyst containing a heavy metal. Furthermore, various methods have been proposed for producing high-quality terephthalic acid, which can produce polyester by direct polymerization using this one-step oxidation reaction. However, by any of these methods, it is difficult to economically produce high-quality terephthalic acid that can be used for producing polyester by direct polymerization. For example, in order to produce high-quality terephthalic acid that can be used directly for polymerization, especially by a one-step oxidation reaction, the solvent ratio, catalyst composition, reaction temperature, supply amount of molecular oxygen-containing gas ( The oxidation reaction conditions, such as oxygen gas content) and residence time, must be severe. As a result, even if high-quality terephthalic acid can be produced, in both cases the oxidative decomposition of the acetic acid solvent increases significantly, making it impossible to economically produce high-quality terephthalic acid. Therefore, in conventional methods, high-quality terephthalic acid for direct polymerization is obtained by catalytic hydrogenation of crude terephthalic acid, which contains significant amounts of impurities such as oxidized intermediates such as 4-carboxybenzaldehyde and colored substances. It has usually been produced by performing purification treatments such as catalytic decarbonylation treatment and recrystallization treatment.

However, although high-quality terephthalic acid can be produced by performing purification treatments such as catalytic hydrogenation treatment, catalytic decarbonylation treatment, or recrystallization treatment, the purification treatment operations are complicated. Therefore, manufacturing costs inevitably increase. Therefore, terephthalic acid purified by these methods does not fully satisfy the requirements for terephthalic acid for direct polymerization from an economic point of view. Also, regarding a method for purifying crude terephthalic acid produced by an oxidation reaction of paraxylene by a method other than the above,
Many methods have been proposed.

For example, crude terephthalic acid obtained by oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid solvent in the presence of a cobalt II catalyst is suspended in a lower aliphatic carboxylic acid such as acetic acid. A method of heat-treating a suspension at high temperatures is disclosed in Japanese Patent Publication No. 4413135 and Japanese Patent Application Laid-open No. 49-2
0141, etc., and a method similar to these methods has also been proposed in Japanese Patent Publication No. 47-7538.
However, as is clear from the description of the examples in the specification of the above-mentioned publication, none of these methods yields high-quality terephthalic acid that can be used in the production of polyester by direct polymerization. . or,
JP-A-51-127037 (a corresponding patent to Belg. 84O624) describes the production of paraxylene at a temperature of 160 to 180°C in the presence of a catalyst consisting of a cobalt compound, a manganese compound and a bromine compound. The oxidation reaction product mixture containing crude terephthalic acid obtained by oxidizing with a molecular oxygen-containing gas is heated to a temperature 50°C lower and 25°C higher than the oxidation reaction temperature in state X without separating the mother liquor. After holding, the terephthalic acid was separated, and then the separated terephthalic acid was suspended in the mother liquor or fresh acetic acid solvent, and the suspension was maintained at a temperature of at least 100°C or more, specifically up to about 160°C. It is described that by separating post-terephthalic acid, oxidative decomposition of acetic acid can be suppressed, and terephthalic acid that can be directly used in polymerization methods can be produced.

However, in this method, the first stage treatment is carried out in the state of X without decomposing the reaction mother liquor from the oxidation reaction mixture containing crude terephthalic acid, so the purification effect is not sufficient, and the obtained terephthalic acid is In particular, the content of colored impurities other than 4-carboxybenzaldehyde and impurities such as toluic acid is high, and the optical density is high. However, polyethylene terephthalate with good hue has not been obtained. In addition, the terephthalic acid obtained by this method is in the form of columnar or needle crystals, and has a major drawback in that it does not have good slurry properties with ethylene glycol when used directly in polymerization methods. High purity and excellent hue are not sufficient requirements for terephthalic acid for producing polyester by direct polymerization. When direct polymerization is employed, it is necessary to mix terephthalic acid with equimolar amounts of ethylene glycol and react in the form of a suspension. In such a solid-liquid heterogeneous reaction system, the polymerization raw material terephthalic acid is required to have good slurry properties such as stirring and mixing properties and suspension transport properties. In order to improve the slurry properties of ethylene glycol suspensions of high purity terephthalic acid,
It is necessary that the crystal shape of terephthalic acid be close to spherical and that its average particle size be large. Therefore, in addition to being highly pure and having an excellent hue, terephthalic acid used in the production of polyester by direct polymerization has the following properties:
Good slurry properties are required. As a method for improving the slurry properties of terephthalic acid,
Japanese Patent Publication No. 11488 proposes a method of heat treating fine particles of high-purity terephthalic acid in a solvent with low solubility for terephthalic acid, such as acetic acid or a mixed solvent of acetic acid and water; Similarly, the publication states that coarse particles of high-purity terephthalic acid are suspended in a solvent such as acetic acid or water that has low solubility for terephthalic acid, and then pumped and stirred using a circulation pump outside the stirring tank. A method is proposed.

However, in the former method, fine particulate terephthalic acid with an average particle size of several μm or less, such as terephthalic acid once generated by acid precipitation from an aqueous solution of an alkali terephthalic acid salt by the Pengel method, is mixed with acetic acid or acetic acid and water. By suspending the terephthalic acid in a mixed solvent, etc., and heating the suspension to a temperature close to the boiling point of the solvent, the average particle size of the finely divided terephthalic acid crystals is increased, and the shape becomes nearly spherical. It is something. In the latter method, terephthalic acid crystals, which are coarse particles with an average particle size of 50 to 200 mμ and have an elongated shape, are suspended in a solvent with low solubility, and the suspension is By stirring the terephthalic acid crystals with a pump at a temperature around room temperature without heating, the average particle size of the terephthalic acid crystals is reduced, the apparent density is improved, and terephthalic acid crystals with an increased roundness are obtained. In any of these methods, the terephthalic acid used as a raw material is either fine-particle high-purity terephthalic acid produced by acid precipitation method or coarse-particle high-purity terephthalic acid produced by crystallization method. The slurry property is improved by processing the high purity terephthalic acid in a suspension state. Crude terephthalic acid containing a considerable amount of oxidized intermediates or colored substances such as 4-carboxybenzaldehyde is subjected to complicated purification methods such as catalytic hydrogenation, catalytic decarbonylation, or recrystallization as described above. It can be purified through simple purification operations, and at the same time, it is possible to produce high-purity terephthalic acid that has a nearly spherical crystal shape, a large average particle size, and good slurry properties. If so, the oxidative decomposition of the acetic acid solvent during the oxidation reaction stage can be significantly suppressed, making it economically advantageous compared to the method of directly producing high-quality terephthalic acid through the one-step oxidation reaction described above. become.

The present inventors have developed an economical method of producing high-quality terephthalic acid through a one-step oxidation reaction of paraxylene, which causes less oxidative decomposition of the acetic acid solvent and which can be used as a raw material for the production of polyester by direct polymerization. The present invention was arrived at as a result of intensive study on a method that can produce the same.

In other words, the object of the present invention is to provide a production method that can economically produce high-quality terephthalic acid by oxidizing paraxylene in one step in an acetic acid solvent, thereby reducing oxidative decomposition of the acetic acid solvent and allowing direct polymerization. The goal is to provide the following. To summarize the present invention, (4) paraxylene is molecule-formed in an acetic acid solvent in the presence of an oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound at a temperature of 170 to 230° C. and under pressure. The content of 4-carboxybenzaldehyde in the crude terephthalic acid contained in the oxidation reaction product mixture obtained by the oxidation reaction is in the range of 500 to 3000 ppm, and Obtaining an oxidation reaction product mixture having an optical density of 0.3 or less, (B)
Without cooling the mixture to a temperature 30°C lower than the oxidation reaction temperature, 60% by weight or more of the mother liquor contained therein is separated and recycled to the oxidation reactor, and the remaining mixture is added with crude terephthalate. An acetic acid suspension of crude terephthalic acid obtained by adding heated acetic acid in an amount such that the weight ratio of the acetic acid solvent to the acid is in the range of 2 to 10 is first stirred at a temperature in the range from the oxidation reaction temperature to 240°C. (D) Then, a secondary dipping treatment is performed under stirring at a temperature in the range of 150 to 220°C and at least 10°C lower than the temperature of the primary dipping, (g) the obtained terephthalic acid is The present invention relates to a method for producing high-purity terephthalic acid, which is characterized by separating terephthalic acid from an acetic acid suspension.

More specifically, the present invention provides that the content of 4-carboxybenzaldehyde in the crude terephthalic acid obtained in the liquid phase oxidation of paraxylene with a molecular oxygen-containing gas is contradictory to the oxidative decomposition rate of the acetic acid solvent in the oxidation reaction. This is based on the discovery that there is a correlation between the content of 4-carboxybenzaldehyde in crude terephthalic acid, the optical density of its alkaline aqueous solution, and the immersion effect.

Furthermore, by oxidizing paraxylene under relatively mild oxidation conditions to obtain a crude terephthalic acid-containing oxidation reaction mixture containing a considerable amount of impurities such as 4-carboxybenzaldehyde, the oxidative decomposition of the acetic acid solvent was achieved. 4-carboxybenzaldehyde content within a specific range, namely 50
If the oxidation reaction product mixture contains crude terephthalic acid with a content of colored impurities in the range of 0 to 3000 ppm and an optical density at 340 mμ of a specific value, that is, 0.3 or less, the oxidation reaction product mixture is A two-step immersion process that can be easily carried out under specific temperature and solvent ratio conditions for the oxidation reaction product mixture obtained by replacing and separating a certain amount of the mother liquor contained therein with heated acetic acid without cooling. Through processing, high-quality terephthal has a spherical shape, large particle size, and good slurry properties with ethylene glycol, and can be used in the production of polyester by direct polymerization. This is based on the discovery that acids can be produced. Furthermore, the terephthalic acid obtained by the method of the present invention has a content of 4-carboxybenzaldehyde of 300 ppm or less, such as high-quality terephthalic acid that has conventionally been considered to be usable in direct polymerization methods, and
A polyester that can be directly polymerized and has a good color tone even though the content of 4-carboxybenzaldehyde is higher than that of high-purity terephthalic acid, which has an optical density at 40 mμ of 0.05 or less and has a higher optical density at 340 mμ. can be manufactured. In the method for producing terephthalic acid of the present invention, as is conventionally known, paraxylene is molecularized in an acetic acid solvent under high temperature and pressurized conditions in the presence of an oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound. Oxidized by oxygen-containing gases.

Here, the oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound is an oxidation catalyst that can generate cobalt ions, manganese ions, and bromide ions in the reaction system. Typically, oxidation catalysts consisting of cobalt compounds, manganese compounds and bromine compounds are used. In addition to the three essential catalyst components consisting of a cobalt compound, a manganese compound, and a bromine compound, other metal catalyst components may be included. In the method of the present invention, when using an oxidation catalyst consisting of a cobalt compound, a manganese compound, and a bromine compound, the amount used is not particularly limited, but the amount of the cobalt compound used is 0.1 x 10 - as cobalt atoms per 1 ton of acetic acid solvent. 5 to 5.0 x 10-5 gram atoms, and the amount of manganese compound used is 0.001 to 1.0 as an atomic ratio to the cobalt compound.
The amount of the bromine compound used is preferably in the range of 1 to 4 as an atomic ratio to the sum of cobalt atoms and manganese atoms. In the method of the present invention, the acetic acid solvent used in the oxidation reaction does not need to be pure acetic acid, and acetic acid containing water in the range of 5 to 15% by weight is usually used.

The amount of acetic acid solvent used is usually in the range of 2 to 10, preferably 3 to 6 in weight ratio to paraxylene. The water concentration in the mother liquor in the reaction system during the oxidation reaction is usually maintained in the range of 5 to 15% by weight, preferably 7 to 12% by weight. The molecular oxygen-containing gas used in the oxidation reaction of the present invention is usually air, but may also be oxygen gas or a mixed gas of oxygen gas and other inert gas in any proportion.

The amount of molecular oxygen-containing gas supplied during the oxidation reaction is such that the oxygen concentration in the exhaust gas from the oxidation reactor is usually 2 to 8%.
It is preferably supplied in a range of 3 to 6%. In the method of the present invention, the oxidation reaction of paraxylene is carried out under high temperature and pressurized conditions.

The reaction temperature must be in the range of 170 to 230°C, particularly preferably in the range of 180 to 220°C. When the oxidation reaction temperature is lower than 170℃,
The oxidation reaction was incomplete and the content of 4-carboxybenzaldehyde in the crude terephthalic acid rapidly increased, and the crude terephthalic acid was The optical density becomes extremely large. These qualities depend on oxidation conditions other than temperature,
For example, if the content of 4-carboxybenzaldehyde to which the purification method of the present invention is applied is 3000 ppm or less and 34
It becomes difficult to produce an oxidation reaction product mixture containing crude terephthalic acid that satisfies the optical density at 0 mμ of 0.3 or less.
As a result, in the subsequent immersion treatment process of the oxidation reaction product mixture, the purification effect is significantly reduced, and not only is it impossible to obtain high-quality terephthalic acid that can be directly polymerized, but also the oxidation reaction is necessary to purify this terephthalic acid. Since a large amount of heat is required to raise the temperature to a higher temperature and heat it to a high temperature, it also lacks economic efficiency. Furthermore, when the oxidation reaction temperature is higher than 230°C, the oxidation becomes too intense and impurities are produced that cannot be estimated from the content of 4-carboxybenzaldehyde or the optical density at 340 mμ of crude terephthalic acid.
Even if the optical density at μ is 0.3 or less, it will not be possible to remove it by the primary immersion treatment. As a result, even if this crude terephthalic acid is subjected to the two-step dipping treatment of the present invention, polyester with good color tone cannot be produced from this terephthalic acid, and oxidative decomposition of the acetic acid solvent increases, making it uneconomical. It also becomes lacking. The pressure during the oxidation reaction is arbitrary as long as it is sufficient to maintain the oxidation reaction product mixture in the reaction system in a liquid phase.

However, as will be explained later, when using an oxidation reactor with a distillation column connected to the top and performing the oxidation reaction while distilling off water produced by the oxidation reaction, the reaction pressure maintains the boiling of the reaction solvent. It is necessary to keep it within the possible range. The liquid phase oxygen oxidation reaction of paraxylene of the present invention is usually carried out under stirring.

The stirring intensity at this time is arbitrary, but is preferably moderate because it affects the properties of impurities in the crude terephthalic acid and the oxidative decomposition of the acetic acid solvent in the oxidation reactor. In order to make the impurities in crude terephthalic acid easily removable in the subsequent primary immersion treatment and to improve the economic efficiency of producing terephthalic acid by suppressing the oxidative decomposition of acetic acid, it is necessary to It is preferable to strongly stir the reaction mixture to improve gas-liquid contact.
For example, in order to suppress the decomposition of acetic acid during the oxidation reaction, the stirring intensity is usually 1.5 mm per cubic meter of the oxidation reaction mixture.
Ranges from 0 to 10.0 horsepower, 1.5 to 5.
It is particularly preferable that it be in the range of 0 horsepower. In the method of the present invention, the oxidation reactor for the oxidation reaction of para-xylene is an ordinary oxidation reactor having a condensing reflux device connected to the upper part, which can condense and reflux the acetic acid solvent vaporized by the reaction heat into the reactor. It is also possible to use an oxidation reactor with a distillation column connected to the top.

In these oxidation reactors, the water by-produced in the oxidation reaction can be easily distilled out of the reaction system by utilizing the reaction heat, and the water concentration in the mother liquor in the reaction system can be adjusted to a suitable level. It is preferable to use an oxidation reactor with a distillation column connected to the upper part in the method of the present invention because it can be easily controlled within a certain range. In the method of the present invention, the oxidation reaction product mixture obtained by the oxidation reaction of paraxylene has a content of 4-carboxybenzaldehyde in crude terephthalic acid of 500 to 3000.
4 carboxy in the crude terephthalic acid contained in this oxidation reaction product mixture. When trying to reduce the content of benzaldehyde to less than 500 ppm,
Increasing the acetic acid solvent ratio (to para-xylene weight) in the oxidation reaction, increasing the oxidation reaction temperature, changing the catalyst concentration, increasing the catalyst concentration, decreasing the water concentration in the mother liquor in the reaction system, molecular It is necessary to make the oxidation reaction conditions harsher by at least one of these methods, such as increasing the amount of oxygen-containing gas supplied or increasing the oxygen gas concentration in the exhaust gas.

As a result, the impurities change qualitatively, and even if this oxidation reaction product mixture is purified by the purification treatment of the present invention, the color tone of the polyester produced by the direct polymerization method deteriorates, and the oxidative decomposition of the acetic acid solvent The content of 4-carboxybenzaldehyde in the crude terephthalic acid contained in the oxidation reaction product mixture needs to be 500 ppm or more, as the 4-carboxybenzaldehyde content in the crude terephthalic acid contained in the oxidation reaction product mixture must be 500 ppm or more. It is. On the other hand, when the content of 4-carboxybenzaldehyde in the crude terephthalic acid contained in the oxidation reaction product mixture exceeds 3000 ppm, 4-
Impurities attributable to reaction intermediates other than carboxybenzaldehyde rapidly increase, and even if the method of the present invention is applied to this, the purification effect decreases significantly, making it difficult to produce polyethylene terephthalate by direct polymerization method. Therefore, the content of 4-carboxybenzaldehyde in the reaction product mixture must be 300 ppm or less.
In addition, 4 in the crude terephthalic acid contained in the reaction product mixture
- Even if the content of carboxybenzaldehyde is within the above range, if the optical density of crude terephthalic acid at 340 mμ is greater than 0.3, direct polymerization will not occur in the subsequent primary dipping treatment and secondary dipping treatment. It is not possible to obtain terephthalic acid of the highest possible quality. Therefore, it is necessary that the optical density of crude terephthalic acid in the oxidation reaction product mixture at 340 mμ be 0.3 or less. Furthermore, in order to further reduce the oxidative decomposition of the acetic acid solvent and to more economically produce high-quality terephthalic acid, the oxidation reaction product mixture used in the method of the present invention should contain the crude terephthalic acid contained therein. The oxidation reaction product mixture is preferably one in which the content of 4-carboxybenzaldehyde is in the range of 600 to 2,500 ppm and the optical density of crude terephthalic acid at 340 mμ is 0.2 or less. here,
4- in the crude terephthalic acid contained in the oxidation reaction product mixture
The content of carboxybenzaldehyde is the content of carboxybenzaldehyde in the crude terephthalic acid obtained by removing a portion of the high-temperature, high-pressure oxidation reaction product mixture from the oxidation reactor, cooling it, over-separating it, washing it with acetic acid, washing it with water, and drying it at room temperature. This is a value measured by polarography for 4-carboxybenzaldehyde. In addition, the optical density at 340 mμ means that the crude terephthalic acid 7.5P is dissolved in a 2N potassium hydroxide aqueous solution 50i1
Cell length 1C when dissolved in L1 at 340mμ!
It is an optical density measured using a cell of n. In the method of the present invention, the content of 4-carboxybenzaldehyde in the crude terephthalic acid contained in the oxidation reaction product mixture by the oxidation reaction of paraxylene is 500 to 3000 p.
pm range and the optical density of crude terephthalic acid is 0.
In order to produce an oxidation reaction product mixture of 3 or less,
As mentioned above, the acetic acid solvent ratio to paraxylene, oxidation reaction temperature, catalyst composition, catalyst concentration, water concentration in the mother liquor in the reaction system, supply amount of molecular oxygen-containing gas (oxygen gas concentration in exhaust gas), stirring This can be achieved by appropriately selecting oxidation reaction conditions such as strength within the above range.

In the method of the present invention, as described above, 60% by weight or more of the mother liquor is separated from the oxidation reaction product mixture obtained by the oxidation reaction and recycled to the oxidation reactor, and the oxidation reaction product mixture containing the remaining crude terephthalic acid is separated. A primary immersion treatment is performed in which a suspension of crude terephthalic acid in acetic acid obtained by adding heated acetic acid to the mixture is stirred at a high temperature.

Separation of the mother liquor from the oxidation reaction product mixture must be carried out without cooling below a temperature of 30°C below the oxidation reaction temperature, and must be carried out without cooling below a temperature of 20°C below the oxidation reaction temperature. is particularly preferred. or,
The separation rate of the mother liquor from the oxidation reaction product mixture at that time is
It is necessary that the amount is 60% by weight or more of the mother liquor contained in the oxidation reaction product mixture. When the mother liquor is separated from the oxidation reaction product mixture at a temperature 30°C or more lower than the reaction temperature, 4-carboxybenzaldehyde and colored impurities contained in the mother liquor are occluded in the crude terephthalic acid.
The content of 4-carboxybenzaldehyde in the crude terephthalic acid increases, and the optical density at 340 mμ increases. As a result, not only does the burden on purification in the next primary immersion treatment process increase, but also when the separated mother liquor is recycled to the oxidation reactor and when performing the primary immersion treatment of the remaining oxidation reaction product mixture. Since it becomes necessary to heat the product again, it becomes uneconomical in terms of the amount of heat used. In addition, if the separation ratio of the mother liquor from the oxidation reaction product mixture is lower than 60% by weight, a large amount of impurities such as 4-carboxybenzaldehyde dissolved in the mother liquor will be contained in the dipping tank, so the dipping treatment may be difficult. Not only does it become impossible to obtain a sufficient purification effect, but also these impurities cause condensation, further promoting coloring. The mother liquor separated by the above method is recycled and reused in the oxidation reaction system.

At that time, if there is a large amount of water in the mother liquor, if necessary, the water can be distilled off until the water concentration in the mother liquor reaches an appropriate range, and then recycled and reused. It can also be recycled and reused after being refilled. In the oxidation reaction, as mentioned above, an oxidation reactor with a distillation column directly connected to the top is used, and the water concentration in the mother liquor in the reaction system is maintained within a certain range while removing the water by-produced by the oxidation reaction by distillation. In the case where the reaction is carried out while the reaction is being carried out, the separated mother liquor can be recycled and reused as it is in the oxidation reactor without being subjected to dehydration treatment in a distillation column outside the system, which is suitable. In the method of the present invention, a separation method using centrifugal force such as an ordinary centrifuge or hydrocyclone is used to separate the mother liquor from the oxidation reaction product mixture, but separation under high temperature and pressure is easy. It is preferable to use a hydrocyclone that can perform

For example, in the method of the present invention, the method of separating the mother liquor from the oxidation reaction product mixture using a hydrocyclone was proposed by the present applicant in Japanese Patent Application No. 52-96176. Separation can also be achieved by displacement with heated acetic acid fed as a side stream to the cyclone. The resulting suspension of crude terephthalic acid in acetic acid can also be used as it is in the next primary dipping treatment. In the method of the present invention, heated acetic acid is added to the remaining oxidation reaction product mixture obtained by separating 60% by weight or more of the mother liquor from the oxidation reaction product mixture, and a primary immersion treatment is performed.

In this case, when the crude terephthalic acid is suspended in acetic acid, the weight ratio of the acetic acid solvent to the crude terephthalic acid in the suspension must be in the range of 2 to 10, particularly preferably in the range of 3 to 8. Further, the temperature during the primary dipping treatment needs to be in the range from the oxidation reaction temperature to 240°C, and preferably in the range from 10°C higher than the oxidation reaction temperature to 230°C. Furthermore, if the temperature during the primary dipping treatment is lower than the oxidation reaction temperature, a sufficient purification effect will not be obtained, and if it is higher than 240°C, the optical density at 340 mμ of terephthalic acid and the hue of polyethylene terephthalate produced by direct polymerization will decrease. begins to decline. If the weight ratio of the acetic acid solvent to the crude terephthalic acid in the crude terephthalic acid suspension in this primary immersion treatment is less than 2, the purification effect of the primary immersion treatment will be difficult to appear; Not only is this method ineffective, but it also requires a large amount of heated acetic acid, making it uneconomical in terms of the amount of heat used.

Further, during this immersion treatment, the content of water in the acetic acid solvent of the suspension of crude terephthalic acid in acetic acid is usually in the range of 3 to 25% by weight, and the content of water in the acetic acid solvent of the suspension is In particular, a content in the range of 5 to 20% by weight is preferable because the purification effect by dipping treatment, especially the effect of removing 4-carboxybenzaldehyde, becomes greater. In the method of the present invention, in order to obtain a sufficient purification effect by the primary immersion treatment of crude terephthalic acid in acetic acid suspension, the acetic acid solvent ratio and treatment temperature to crude terephthalic acid in the suspension should be within the above ranges. It is necessary.

The ratio of the acetic acid solvent to the crude terephthalic acid in the suspension, the treatment temperature, and the content of water in the acetic acid solvent are mutually related to influence the purification effect of the crude terephthalic acid, and an even better purification effect can be obtained. In order to achieve this, the acetic acid solvent ratio and treatment temperature must be within the ranges described above, and the general formula [where t represents the temperature (°C) of the primary immersion treatment, and X represents the weight ratio of the acetic acid solvent to crude terephthalic acid, m indicates the water content (% by weight) in the acetic acid solvent.

] It is preferable to perform the primary immersion treatment under conditions that satisfy the following. In the method of the present invention, the primary immersion treatment is carried out under the above conditions and with stirring.

Although the stirring intensity at that time is arbitrary, in order to obtain an excellent purification effect, it is preferable to perform the primary immersion treatment under appropriate stirring conditions. Further, in order to obtain sufficient effects from the primary immersion treatment, the immersion time is preferably 30 minutes or more.

In the method of the present invention, heated acetic acid is added to the remaining oxidation reaction product mixture obtained by separating 60% by weight or more of the mother liquor from the oxidation reaction product mixture, and the acetic acid solvent ratio to crude terephthalic acid in the suspension is adjusted. After being adjusted to the specific range, it is subjected to a primary immersion treatment.

In this case, it is particularly preferable to use the following heated acetic acid as the heated acetic acid added to the remaining oxidation reaction product mixture, since the heat of reaction can be utilized for heating the solvent. That is, when a reactor with a condensing reflux device connected to the upper part is used as an oxidation reactor, a part of the acetic acid refluxed from the condensing reflux device can be used as the heated acetic acid, and a distillation column can be directly connected to the upper part of the acetic acid. When connected oxidation reactors are used, part of the acetic acid refluxing from the bottom of the distillation column or acetic acid extracted from the side of the distillation column can also be used as the heated acetic acid. The latter method is particularly preferred because acetic acid having a water content suitable for immersion treatment can be obtained by appropriately selecting the position from which acetic acid is extracted from the distillation column. In the method of the present invention, the terephthalic acid suspension in acetic acid that has been subjected to the primary immersion treatment by the method described above is then subjected to a secondary immersion treatment.

In this secondary dipping treatment, the acetic acid of terephthalic acid obtained by selectively extracting impurities such as oxidized intermediates such as 4-carboxybenzaldehyde and colored substances from the crude terephthalic acid into an acetic acid solvent by the primary dipping treatment is By immersing the suspension at a specific temperature lower than the primary immersion temperature, the impurities extracted into the acetic acid solvent during the primary immersion treatment are prevented from being incorporated into the terephthalic acid again, and crystals of terephthalic acid are formed. The purpose is to prepare terephthalic acid crystals that are spherical in shape, large in particle size, and have good slurry properties with ethylene glycol. The temperature of this secondary immersion treatment must be in the range of 150 to 220°C and at least 10°C lower than the temperature of the primary immersion, especially in the range of 160 to 200°C and lower than the temperature of the primary immersion. Preferably the temperature is at least 20°C lower. Temperature of secondary immersion treatment is 150℃
If it is lower, it becomes impossible to obtain terephthalic acid crystals that are spherical in shape, have a large particle size, and have good slurry properties with ethylene glycol, and the content of impurities such as 4-carboxybenzaldehyde in terephthalic acid increases. It becomes like this. In addition, the temperature of the secondary immersion treatment was 220℃.
Even if the temperature rises above .degree. C., terephthalic acid with a spherical shape, large particle size, and good slurry properties with ethylene glycol cannot be obtained, and many fine powder crystals such as columnar or acicular crystals are produced. Even if the temperature during the secondary immersion treatment is within the above range of 150 to 220°C, the temperature difference between the temperature during the primary immersion treatment and the temperature during the secondary immersion treatment is 10°C.
If the temperature is less than 0.degree. C., it will be difficult to obtain terephthalic acid which has a spherical shape, a large particle size, and good slurry properties with ethylene glycol. In the method of the present invention, this secondary immersion treatment is carried out under the above-mentioned temperature conditions and with stirring.

In order to obtain crystals of purified terephthalic acid that are spherical in shape, have a large particle size, and have good slurry properties with ethylene glycol, it is preferable to perform a secondary dipping treatment under moderate stirring conditions. . If the stirring intensity becomes too high, the particle size becomes small, and if the stirring intensity becomes too small, needle-like or columnar crystals of terephthalic acid will be produced. In order to fully express the effect of the secondary immersion treatment, the immersion time is preferably 30 minutes or more, since the secondary immersion treatment is performed following the acetic acid suspension of terephthalic acid that has been subjected to the primary immersion treatment. As mentioned above, it is necessary to lower the temperature within the system.

At this time, the temperature in the system is reduced by flashing the acetic acid suspension of terephthalic acid from the primary immersion treatment tank into the secondary immersion treatment tank, which is maintained at a lower pressure than the primary immersion treatment tank. Although it is possible to lower the temperature rapidly, it is also possible to adopt a method of slow cooling. According to the method of the present invention, high quality terephthalic acid can be obtained by treating a suspension of terephthalic acid in acetic acid that has been subjected to the secondary immersion treatment according to a conventional method.

For example, a suspension of terephthalic acid in acetic acid that has been subjected to a secondary immersion treatment is rapidly cooled by flashing it under normal pressure, or a suspension of terephthalic acid in acetic acid is taken out by slow cooling. High quality terephthalic acid can be obtained by separating terephthalic acid from the suspension by centrifugation or the like, followed by washing and drying. An example of an apparatus for producing high quality terephthalic acid for direct polymerization according to the method of the invention is shown in the accompanying drawing.

The method of the present invention will be specifically explained using the apparatus shown in this figure.
A reaction mixture consisting of paraxylene, an oxidation catalyst and an acetic acid solvent, and air are continuously supplied to the oxidation reactor 10 from a reaction mixture supply line 12 and an air supply line 13, respectively. The oxidation reactor 10 is equipped with a stirrer 11, and by stirring the reaction mixture in the oxidation reactor at a predetermined temperature for a fixed residence time, para-xylene is oxidized to terephthalic acid and oxidized. The reaction product mixture becomes a suspension of crude terephthalic acid in acetic acid. The suspension of crude terephthalic acid in acetic acid, which is the oxidation reaction product mixture, is passed through the oxidation reaction product mixture extraction line 14 and the valve 15 from the oxidation reactor 10.
is fed into the first receiver 30 through the In the first receiver 30, the oxidation reaction product mixture is kept warm so as not to be cooled below a temperature 30°C lower than the oxidation reaction temperature, preferably below a temperature 20°C lower, and is stirred by a stirrer 31. When the oxidation reaction mixture is withdrawn from the oxidation reactor 10 into the first receiver 30, the acetic acid vapor generated when a pressure drop occurs passes through the line 32 and the cooler 33 in the upper part of the first receiver and condenses into the line 34. reflux to the first receiver through the On the other hand, the water produced as a by-product in the oxidation reaction is led to the tray distillation column 20 directly connected to the upper part of the oxidation reactor 10, together with the exhaust gas from the oxidation reactor and vaporized acetic acid vapor. The water concentration in the mother liquor in the oxidation reactor can be maintained constant by distilling and separating the oxidized water using the reaction heat while performing the oxidation reaction. The exhaust gas containing concentrated water vapor from the top of the distillation column 20 due to distillation is condensed through a line 21 and a cooler 22, and the condensed water-monoacetic acid solution enters a condensate receiver 23. A portion of the water-monoacetic acid solution containing mainly water in the condensate receiver 23 is removed through the condensate withdrawal line 26, and the other portion is refluxed to the top of the distillation column 20.
Gas that is not condensed by the cooler 22 is discharged from the exhaust gas line 25. On the other hand, the oxidation reaction product mixture in the first receiver 30 is transferred to the terephthalic acid acetic acid suspension withdrawal line 35, the pump 36 and the hydrocyclone supply line 3.
The mother liquor in the oxidation reaction product mixture is separated at a predetermined ratio at a predetermined temperature, and the separated mother liquor is returned to the oxidation reactor 10 through a separated mother liquor return line 41. The remaining oxidation reaction product mixture from which the mother liquor has been separated at a predetermined ratio is passed through a liquid cyclone 40.
Acetic acid suspension extraction line 4 of crude terephthalic acid at the bottom of
2 and heated to a predetermined temperature in a heat exchanger 43 together with heated acetic acid containing water of a predetermined concentration taken out from a heated acetic acid withdrawal line 27 on the side of the distillation column at the top of the oxidation reactor 10, and then heated to a predetermined temperature in a heat exchanger 43. It is supplied to the dipping tank 50. In the primary dipping tank 50, the weight ratio and temperature of the acetic acid solvent to the crude terephthalic acid in the suspension of crude terephthalic acid in acetic acid are maintained within a specific range, and the suspension of crude terephthalic acid in acetic acid is
The primary immersion treatment is performed while stirring for a predetermined period of time. The acetic acid suspension of crude terephthalic acid that has been subjected to the primary dipping treatment is supplied to the secondary dipping tank 60 through the extraction line 52 at the bottom of the primary dipping tank 50, the valve 53, and the secondary dipping tank supply port 54. Ru. In the second dipping tank 60, the suspension of terephthalic acid in acetic acid is subjected to a secondary dipping treatment while being stirred for a predetermined time by a stirrer 61 at a specific temperature lower than that in the first dipping tank. When transferring the terephthalic acid suspension in acetic acid from the primary dipping tank to the secondary dipping tank, a drop in pressure occurs as the temperature of the system drops. At this time, a part of the acetic acid solvent in the secondary dipping tank is vaporized and
5 and condenser 66 and reflux into the secondary soaking tank. Therefore, the temperature can be adjusted by adjusting the pressure of the secondary immersion tank. The acetic acid suspension of terephthalic acid that has been subjected to the secondary dipping treatment is carried out through a extraction line 62, a valve 63 and a line 64 at the bottom of the secondary dipping tank.
and is sent to the second receiver 70 through. The pressure in the second receiver 70 is normally maintained at atmospheric pressure and the temperature is maintained at or below the boiling point of acetic acid at atmospheric pressure, and the acetic acid suspension of terephthalic acid is stirred in the second receiver 70. Machine 71
It is stirred by The acetic acid suspension of terephthalic acid in the second receiver is fed to the centrifuge 80 through the withdrawal reline 72 at the bottom of the second receiver, the pump 73 and the centrifuge feed line JMOV. Terephthalic acid is obtained from the take-off line 81 of the centrifuge 80, and acetic acid solvent is obtained from the solvent take-off line 82. The terephthalic acid taken out from the centrifuge is further washed with acetic acid and water, if necessary, and then dried to obtain high quality terephthalic acid. Further, the acetic acid solvent recovered from the centrifuge is reused as it is or after being purified by distillation or the like if necessary. The terephthalic acid production apparatus shown in the attached drawings detailed above is one example of the apparatus for carrying out the method of the present invention, and the method of the present invention is not limited thereto. . According to the method of the present invention, even in crude terephthalic acid obtained by oxidizing under relatively mild oxidation conditions that can significantly suppress the decomposition of the acetic acid solvent, the content of 4-carboxybenzaldehyde is is within the specified range and the optical density at 340 mμ is within the specified range,
By a simple two-stage dipping operation carried out under the above-mentioned special conditions, it is possible to produce high-quality terephthalic acid that can be used in the production of polyester by direct polymerization. Since the oxidative decomposition of the acetic acid solvent can be reduced, there is an advantage that the manufacturing cost is low.

Next, the method of the present invention will be specifically explained using examples.

Note that the following Examples and Comparative Examples were all carried out using the apparatus shown in the attached drawings. In addition, terephthalic acid (TA
) in 4-carboxybenzaldehyde (4-CBA)
The content of terephthalic acid was measured by polarography, and the optical density (0.D.) of terephthalic acid was determined by measuring the optical density (0.D.) of terephthalic acid by measuring 1% of a 2N potassium hydroxide aqueous solution containing 15% by weight of terephthalic acid.
This is a value measured at 340 mμ using my cell. The shape of terephthalic acid crystals was determined visually using an optical microscope.
The average particle size of the crystals was determined by sieving terephthalic acid in a standard pool, performing a Gaudin-Schulman plot of the distribution under the sieve, and showing the 50% particle size. Polyethylene terephthalate (PET) can be prepared by putting 50 r of terephthalic acid and 75 V of ethylene glycol in a flask and heating it for 20 min in a nitrogen stream.
After esterification at 0°C, a temperature of 285°C and a pressure of 0.1 m7 using 20 ~ antimony trioxide as a catalyst! T.H.
It is obtained by polycondensation under the following conditions. The color tone of polyethylene terephthalate was indicated by the b value [yellow (A) to blue-white] among the external colors measured by reflected light with a color difference meter. b
The smaller the value, the better the color tone. Example 1 10.81<g of acetic acid and 1.0g of water were placed in an oxidation reactor 10 with a distillation column.
2k9, cobalt acetate 6011, manganese acetate 30y1, tetrabromoethane 31f, and the temperature of the reactor was set to 1.
Maintaining the temperature at 90°C and the pressure at 11 kg/Crli, 3 kg/Hr of baraxylene, 15.8 kg/Hr of acetic acid, and 2.0 kg/Hr of water were added.
While continuously feeding a mixture consisting of 6 kg/Hr, cobalt acetate 18 r/Hr, manganese acetate 97/Hr, and tetrabromoethane 9.3 t/Hr to the oxidation reactor from the reaction mixture supply lane 12, the oxygen concentration in the exhaust gas was is 5
% air to about 4%.

Air supply line 13 with a proportion of 2NM3A-paraxylene
A continuous oxidation reaction was carried out.

At this time, a part of the heated acetic acid in the distillation column 20 is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26 to reduce the water concentration in the reaction mixture to 10%. Had to keep it in weight. Also, the reaction mixture is 1f
! Stirring was carried out at a stirring intensity of 3 horsepower per I. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15, and first receiver 30 while maintaining the temperature at 190°C based on the signal from the liquid level gauge, which is set so that the residence time is 1 hr. 70% by weight (8.41<g/Hr) of the sample was separated, and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

85% by weight of heated acetic acid was added to the concentrated reaction mixture from the column side of the distillation column connected to the reactor through line 27 at 14.8
After adding at a rate of kg/Hr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the ratio of solvent to terephthalic acid was 4 by weight, and the concentration of water in the solvent was 14% by weight. The temperature of the primary immersion tank is 220℃ and the pressure is 18kg/Cf! The mixture was stirred as i. After a residence time of 1 hr in the first soaking tank, the terephthalic acid acetic acid suspension mixture was mixed at a temperature of 190°C and a pressure of 8kg/C.
The mixture is sent to a secondary soaking tank 60 maintained at rA, and after residence for 1 hour while stirring the mixture, is sent to a second receiver 70.
After bringing the pressure to normal pressure, solid-liquid separation was performed using a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Example 2 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 with a distillation column.
kg, cobalt acetate 487, manganese acetate 2437, and tetrabromoethane 257, and the temperature of the reactor was set to 21.
Maintaining 0°C and pressure at 15 kg/Cd, paraxylene 3 kg/Hr, acetic acid 20.7 kg/Hr, water 2.3 kV
hr, cobalt acetate 19y//FLrl manganese acetate 1
While a mixture consisting of 0y/Hr and tetrabromoethane 10y/Hr is continuously fed into the oxidation reactor from the reaction mixture supply line 12, air is added to about 4.6NM3A9-paraxylene so that the oxygen concentration in the exhaust gas is 7%. A continuous oxidation reaction was carried out by feeding air from the air supply line 13 at a rate of .

At this time, a part of the heated acetic acid in the distillation column 20 is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26 to bring the water concentration in the reaction mixture to 10% by weight. I kept it. The reaction mixture was also stirred at a stirring intensity of 3 horsepower per m3. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the first receiver 30, which are kept at 200°C, based on the signal from the liquid level gauge, which is set so that the residence time is 1 hr, and the mother liquor is The separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

18.2 90% by weight heated acetic acid is passed through line 27 from the column side of the distillation column connected to the reactor to the concentrated reaction mixture.
After adding at a rate of k9/Hr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the ratio of solvent to terephthalic acid was 5 by weight, and the concentration of water in the solvent was 10% by weight. Stirring was carried out at a temperature of 220° C. and a pressure of 18 kg/Cd in the first immersion tank. After the residence time in the first dipping tank was set to 1 hr, the terephthalic acid suspension mixture in acetic acid was sent to the second dipping tank 60 maintained at a temperature of 190° C. and a pressure of 8 kg/Cd, and the mixture was stirred. After residence for 1 hour, the mixture was sent to a second receiver 70, brought to normal pressure, separated into solid and liquid using a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Example 3 Acetic acid 10.8 k9 and water 1.2 were added to the oxidation reactor 10 with a distillation column.
kg, cobalt acetate 487, manganese acetate 0.0257
, 25r of tetrabromoethane was charged, the temperature of the reactor was maintained at 190°C and the pressure was maintained at 11k9/Cd, paraxylene was charged at 3kg/Hr, acetic acid was charged at 31.4kg/Hrl, water was charged at 5
．． 4kg/Hrl cobalt acetate 9.67/Hrl manganese acetate 0.05y/Hr and tetrabromoethane 57/
While continuously feeding Hr into the oxidation reactor from the reaction mixture supply line 12, air was continuously fed from the air supply line 13 at a ratio of about 4.2NM3/K9-paraxylene so that the oxygen concentration in the exhaust gas was 5%. An oxidation reaction was carried out.

At this time, a part of the heated acetic acid in the distillation column 20 is passed through the heated acetic acid withdrawal line 27 on the side of the distillation column, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26, so that the water concentration in the reaction mixture is reduced to 10% by weight. %. Also, the reaction mixture is 1
Stirring was carried out at a stirring intensity of 3 horsepower per m3. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15, and first receiver 30 while maintaining the temperature at 190°C based on the signal from the liquid level gauge, which is set so that the residence time is 1 hr, and 80% by weight of the mother liquor. % (9.6k9/Hr) and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

85% by weight of heated acetic acid was added to the concentrated reaction mixture from the column side of the distillation column connected to the reactor through line 27 at 34.4 mL.
After adding kgAr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the solvent ratio to terephthalic acid was 8 by weight, and the water concentration in the solvent was 15.
Weight%. Stirring was carried out at a temperature of the first immersion tank of 210° C. and a pressure of 15k9/Cd. After the residence time in the first dipping tank was set to 1 hr, the terephthalic acid acetic acid suspension mixture was sent to the second dipping tank 60 maintained at a temperature of 160° C. and a pressure of 5 kg/Cd, and the mixture was stirred. After staying for 1 hour, it is sent to the second receiver 70 and brought to normal pressure.
After solid-liquid separation with a centrifuge 80 and washing, the solid portion of terephthalic acid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Example 4 10.8 kg of acetic acid and 1 and 2 pieces of water were placed in an oxidation reactor 10 equipped with a distillation column.
kg, 60y of cobalt acetate, 157y of manganese acetate, and 31y of tetrabromoethane, and the temperature of the reactor was set to 80℃.
and the pressure was maintained at 10 kg/Cd, and the baraxylene 3k
g/Hrl acetic acid 29.6kg/Hrl water 7.2kg/H
rl cobalt acetate 6y/Hrl manganese acetate 1.57/
While a mixture of Hr and tetrabromoethane 32/Hr- is continuously fed into the oxidation reactor from the reaction mixture supply line 12, air is added at a rate of approximately 3.3NM3/Kg-para so that the oxygen concentration in the exhaust gas is 2%. A continuous oxidation reaction was carried out by feeding xylene through the air supply line 13 at a ratio of xylene.

At this time, a part of the heated acetic acid in the distillation column 20 is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26, so that the water concentration in the reaction mixture is reduced to 10% by weight. %. Also, the reaction mixture is 1FF
! Stirring was carried out at a stirring intensity of 3 horsepower per J. The reaction product mixture is kept at 180°C based on the liquid level signal set so that the residence time is 1 hr, and is passed through line 14 and valve 1.
5 and the first receiver 30 to a hydrocyclone 40 to separate 90% by weight (10.8 k9/Hr) of the mother liquor, and the separated mother liquor was returned to the reactor through a separated mother liquor return line 41. 80% by weight heated acetic acid was added to the concentrated reaction mixture from the column side of the distillation column connected to the reactor through line 27 at a rate of 35.61<g/Hr, and then heated in a heat exchanger 43 to form the first immersion. It was sent to tank 50. In this mixture, the ratio of solvent to terephthalic acid was 8 by weight, and the concentration of water in the solvent was 20% by weight. Temperature of primary immersion tank 2
Stirring was carried out under conditions of 10° C. and a pressure of 15 kg/Cd. After a residence time of 1 hr in the first soaking tank, the terephthalic acid suspension mixture in acetic acid was heated to a temperature of 160°C and a pressure of 51°C.
The mixture was sent to a secondary soaking tank 60 maintained at <g/Cd, and after residence for 1 hr while stirring the mixture, was sent to a second receiver 70, brought to normal pressure, and solid-liquid separated by a centrifuge 80. After washing, the solid portion of terephthalic acid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Example 5 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 with a distillation column.
1<g, 90y of cobalt acetate, 30f of manganese acetate, and 427g of tetrabromoethane were charged, and the temperature of the reactor was set to 17g.
Maintaining 0°C and pressure at 9k9/Crli, paraxylene 3kg/h1-, acetic acid 29.61<g/Hrl water7.
While continuously feeding a mixture consisting of 2k9/Hrl cobalt acetate 97/Hr-, manganese acetate 37/Hr and tetrabromoethane 4.2f/Hr to the oxidation reactor from the reaction mixture supply line 12, the oxygen concentration in the exhaust gas was Air was fed through the air supply line 13 at a ratio of about 3.3 NM3/Kg-varaxylene so that the ratio was 2%, and a continuous reaction was carried out.

At this time, a part of the heated acetic acid in the distillation column 20 is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26 to bring the water concentration in the reaction mixture to 10% by weight. I kept it. The reaction mixture was stirred at a stirring intensity of 3 horsepower per d. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15, and first receiver 30 while maintaining the temperature at 170°C based on the signal from the liquid level gauge, which is set so that the residence time is 1 hr, and the 90% weight of the mother liquor is % (10.8 kg/Hr) and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

80% by weight heated acetic acid was passed through line 27 from the column side of the distillation column connected to the reactor to the concentrated reaction mixture.
kg/? After adding T4, it is heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the solvent ratio to terephthalic acid is 8 by weight, and the water concentration in the solvent is 2.
It became 0% by weight. Stirring was carried out at a temperature of the first immersion tank of 210° C. and a pressure of 151<9/CF7f. After a residence time of 1 hr in the primary soaking tank, the terephthalic acid suspension mixture in acetic acid was heated to a temperature of 190°C and a pressure of 81<f! /
The mixture is sent to a secondary soaking tank 60 maintained at Cd, and after residence for 1 hour while stirring, the mixture is sent to a second receiver 70 and brought to normal pressure, and solid-liquid separation is performed by a centrifuge 80. After washing, the solid of terephthalic acid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Comparative Example 1 10.8kg of acetic acid, 1.2kg of water, 60y of cobalt acetate, 6f7 of manganese acetate, and 317% of tetrabromoethane were charged into the oxidation reactor 10 with a distillation column, and the temperature of the reactor was set to 240°C and the pressure was set to 25kg/Crill. Hold and paraxylene 3kg/
While continuously feeding a mixture consisting of Hr, acetic acid 23.6 kfI/Hrl water 4 kg/Hrl cobalt acetate 187/Hr manganese acetate 1.87/Hr and tetrabromoethane 963 f/Hr from the reaction mixture supply line 12 to the oxidation reactor. Air was fed through the air supply line 13 at a rate of about 4.2 NM3/Kg paraxylene so that the oxygen concentration in the exhaust gas was 5%, and a continuous oxidation reaction was carried out.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26, so that the water concentration in the reaction mixture is 10% by weight. I kept it. The reaction mixture was also stirred at a stirring intensity of 3 horsepower per m3. The reaction product mixture is heated to line 14 and valve 1 while maintaining the temperature at 240°C based on the signal from the liquid level gauge set in 5 so that the residence time is 1 hr.
5 and the first receiver 30 to a hydrocyclone 40 to separate 70% by weight (8.4 kg/Hr) of the mother liquor, and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41. 1. To the concentrated reaction mixture, 85% by weight of heated acetic acid was added from the column side of the distillation column connected to the reactor through line 27 at 24 kg/Hr, and then heated with heat exchanger 43,
It was sent to the primary dipping tank 50.

In this mixture, the ratio of solvent to terephthalic acid was 6 by weight, and the concentration of water in the solvent was 14% by weight. The temperature of the primary immersion tank is 230℃ and the pressure is 20kg/Crl.
The mixture was stirred as i. Residence time in the primary immersion tank is 1 hr.
After that, the terephthalic acid suspension mixture in acetic acid was heated to a temperature of 20°C.
The mixture is sent to a secondary soaking tank 60 maintained at 0°C and a pressure of 10 kg/Cd, and after residence for 1 hour while stirring the mixture, is sent to a second receiver 70, brought to normal pressure, and then transferred to a centrifuge 80. After solid-liquid separation and washing, the solid portion of terephthalic acid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Comparative Example 2 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 with a distillation column.
kg, cobalt acetate 547, manganese acetate 2.77, and tetrabromoethane 327, and the temperature of the reactor was set to 20
Maintaining 0°C and pressure at 12 kg/CrA, paraxylene 3 kg/Hrl acetic acid 15.8 kν1, water 2.6 kg/
Hr, cobalt acetate 117/Hrl manganese acetate 0.5
While continuously feeding a mixture consisting of 7/Hr- and tetrabromoethane 6.47/Hr into the oxidation reactor from the reaction mixture supply line 12, about 4.2NM3 of air was added so that the oxygen concentration in the exhaust gas was 5%. /Kg-paraxylene was fed through the air supply line 13 to carry out a continuous oxidation reaction.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26 to maintain the water concentration in the reaction mixture at 10% by weight. Ta. The reaction polymer was stirred at a stirring intensity of 3 m3/m3. ] θ The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15, and first receiver 30 while being maintained at 200°C based on the signal from the liquid level gauge whose residence time is set to 1 hr, and the mother liquor is 80% by weight, (9.6kg/H
r), and the separated mother liquor is sent to the separated mother liquor return line 41.
was returned to the reactor.

16 kg of 85% by weight heated acetic acid was passed through line 27 from the column side of the distillation column connected to the reactor to the concentrated reaction mixture.
/Hr, then heated in a heat exchanger 43 and fed into a primary dipping tank 50. In this mixture, the ratio of solvent to terephthalic acid was 4 by weight, and the concentration of water in the solvent was 14.
Weight%. Stirring was carried out at a temperature of 220° C. and a pressure of 18 kg/Cd in the first immersion tank. After the residence time in the first dipping tank was set to 1 hr, the terephthalic acid suspension mixture was sent to the second dipping tank 60 maintained at a temperature of 180°C and a pressure of 8 kg/Cwi, while stirring the mixture. After residence for 1 hr, the mixture was sent to a second receiver 70, brought to normal pressure, separated into solid and liquid using a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Comparative Example 3 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 with a distillation column.
kg, cobalt acetate 30f1, manganese acetate 22y, and cobalt bromide 78.5t, and the temperature of the reactor was set to 160℃.
℃ and pressure at 7 kg/Cd, paraxylene 3k
9/Hrl acetic acid 43.7kg/Hrl water 2.3k9/H
rl cobalt acetate 3f7/Hrl manganese acetate 2y/H
While continuously feeding a mixture of 8y/Hr of cobalt bromide and cobalt bromide into the oxidation reactor from the reaction mixture supply line 12, air was pumped in at a rate of about 4.2NM3/Kg-Par so that the oxygen concentration in the exhaust gas was 5%. A continuous oxidation reaction was carried out by feeding xylene through the air supply line 13 at a ratio of xylene.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26 to bring the water concentration in the reaction mixture to 10% by weight. I kept it. Also, the reaction mixture was
Stirring was carried out at a stirring intensity of horse power. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15 and first receiver 30 while maintaining the temperature at 160°C based on the signal from the liquid level gauge, which is set so that the distillation time is 1 hr.
0% by weight (10.8 kg/Hr) was separated, and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

95% by weight heated acetic acid was passed through line 27 from the column side of the distillation column connected to the reactor to the concentrated reaction mixture.
After adding at a rate of k9/Hr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the ratio of solvent to terephthalic acid was 10 by weight, and the concentration of water in the solvent was 5% by weight. The temperature of the first immersion tank was set to 230° C. and the pressure was set to 20 kg/i for stirring. After a residence time of 1 hr in the first dipping tank, the terephthalic acid suspension mixture in acetic acid was sent to the second dipping tank 60 maintained at a temperature of 200°C and a pressure of 10 kg/d, while stirring the mixture. After residence for 1 hr, the mixture was sent to a second receiver 70, brought to normal pressure, separated into solid and liquid using a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Comparative Example 4 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 with a distillation column.
kg, cobalt acetate 60y1, manganese acetate 30r1, sodium bromide 37t, and the temperature of the reactor was set to 180℃.
and the pressure was maintained at 10 kg/Cd, paraxylene 3k
g/Hr, acetic acid 29.6kg/Hrl water 7.2kg/Hr
rl cobalt acetate 6f/Hrl manganese acetate 3t/Hr
While continuously feeding a mixture consisting of sodium bromide and sodium bromide 4y/Hr- into the dioxide reactor from the reaction mixture supply line 12, about 4.2NM3//1<g of air was added so that the oxygen concentration in the exhaust gas was 5%. - Paraxylene was fed through the air supply line 13 in a continuous oxidation reaction.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid extraction line 27 on the distillation column side, and a part of the reflux liquid is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 10% by weight. %. The reaction mixture was stirred at a stirring intensity of 3 horsepower per d. The reaction product mixture is kept at 180°C and connected to line 14 and valve 1 based on the signal from the liquid level gauge set at 5 so that the residence time is 1 hr.
5 and the first receiver 30 to the hydrocyclone 40 to separate 90% by weight (10.8 kg/Hr) of the mother liquor,
The separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

80% by weight heated acetic acid was passed through line 27 from the column side of the distillation column connected to the reactor to the concentrated reaction mixture.
After adding at a rate of kg/Hr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. ] In this mixture, the ratio of solvent to terephthalic acid was 8 by weight, and the concentration of water in the solvent was 20% by weight.

The temperature of the primary immersion tank is 220℃ and the pressure is 18kg/C.
The mixture was stirred as d. Residence time in the primary immersion tank is 1 hr.
After that, the terephthalic acid suspension mixture in acetic acid was brought to a temperature of 1
The mixture was sent to a secondary soaking tank 60 maintained at 90°C and a pressure of 8 kg/CF7l, and after residence for 1 hour while stirring, was sent to a second receiver 70, brought to normal pressure, and then centrifuged by a centrifuge 80. Solid-liquid separation was performed, and terephthalic acid in the solid portion of the washing liquid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Comparative Example 5 Acetic acid 10.8 in oxidation reactor 10 with distillation column
1.2 kg of water, 36 V of cobalt acetate, 3.6 t of manganese acetate, 18.67 t of tetrabromoethane, and the temperature of the reactor was set to 220°C and the pressure was set to 181<g/Cd.
Paraxylene 3kg/Hr, acetic acid 15.8k
g/Hr-, water 2.6kg/Hr-, cobalt acetate 10
．． 8? /Hrl A mixture consisting of 1.1f7/Hr of manganese acetate and 5.6t/Hr of tetrabromoethane was continuously fed into the oxidation reactor from the reaction mixture supply line 12, while adjusting the oxygen concentration in the exhaust gas to 2%. Air was fed through the air supply line 13 at a ratio of about 3.3 NM3/Kg-paraxylene to carry out a continuous oxidation reaction.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26, so that the water concentration in the reaction mixture is 10% by weight. I kept it. Also, the reaction mixture is 3 per i
Stirring was carried out at a stirring intensity of horse power. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15, and first receiver 30, while maintaining the temperature at 190°C based on the signal from the liquid level gauge, which is set to have a residence time of 1 hr.
0% by weight (8.4 kg/Hr-) was separated, and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

85% by weight of heated acetic acid was added to the concentrated reaction mixture from the column side of the distillation column connected to the reactor through line 27 at 14.8
After adding at a rate of kg/Hr, it was heated in a heat exchanger 43 and sent to the primary immersion tank 50. In this mixture, the ratio of solvent to terephthalic acid was 4 by weight, and the concentration of water in the solvent was 14% by weight. Stirring was carried out at a temperature of 220° C. and a pressure of 18 kg/Cd in the first immersion tank. After a residence time of 1 hr in the first soaking tank, the terephthalic acid acetic acid suspension mixture was heated to a temperature of 190°C and a pressure of 8 kg/Crl.
The mixture was sent to a secondary soaking tank 60 maintained at a constant temperature of 1 hr, and after residence for 1 hr while stirring, was sent to a second receiver 70 where it was brought to normal pressure, solid-liquid separation was performed using a centrifuge 80, and after washing. The solid portion of terephthalic acid was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. Example 6: Fill the oxidation reactor 10 with a distillation column with 10.8k9 of acetic acid, 1.2kg of water, 907 cobalt acetate, 15V of manganese acetate, 36y of tetrabromoethane, and set the temperature of the reactor to 160°C and the pressure to 7k9/Cd. Paraxylene 3k9/Hr,
A mixture consisting of 29.6 kg/Hr of acetic acid, 7.2 kg/Hr of water, 97/Hr of cobalt acetate, 1.5 t/Hr of manganese acetate, and 3,6y/Hr of tetrabromoethane is continuously oxidized from the reaction mixture supply line 12. While being fed into the reactor, air was fed through the air supply line 13 at a rate of about 4.6 NM3/Kg-paraxylene so that the oxygen concentration in the exhaust gas became 7%, thereby carrying out a continuous oxidation reaction.

At this time, a part of the heated acetic acid in the distillation column is passed through the heated acetic acid withdrawal line 27 on the distillation column side, and a part of the reflux liquid is withdrawn from the condensed water withdrawal line 26, so that the water concentration in the reaction mixture is 10% by weight. I kept it. The reaction mixture was also stirred at a stirring intensity of 3 horsepower per m3. The reaction product mixture is sent to the hydrocyclone 40 through the line 14, valve 15 and first receiver 30 while being maintained at 160°C based on the signal from the liquid level gauge, which is set to have a residence time of 1 hr. % by weight (10.8k9/Hr) was separated, and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41. 80% by weight heated acetic acid is passed through line 27 to the concentrated reaction mixture from the column side of the distillation column connected to the reactor (35).
．． After adding at a rate of 6 kg/Hr, it was heated in a heat exchanger 43 and sent to the first immersion tank 50. In this mixture, the ratio of solvent to terephthalic acid was 8 by weight, and the concentration of water in the solvent was 20% by weight. The temperature of the first immersion tank was set to 210° C., the pressure was set to 151<9/Cr7L, and the mixture was stirred. After a residence time of 1 hr in the first soaking tank, the terephthalic acid suspension mixture in acetic acid was heated to a temperature of 190°C and a pressure of 8k9/min.
The mixture is sent to a secondary soaking tank 60 maintained at Cd, and after residence for 1 hour while stirring the mixture, is sent to a second receiver 70.
After bringing the pressure to normal pressure, solid-liquid separation was performed using a centrifugal separator 80, and after washing, terephthalic acid in the solid portion was dried. Table 1 shows the evaluation results of the obtained terephthalic acid. σσ Examples 6 to 7 and Comparative Example 7 In Example 1, the separation temperature of the mother liquor in the hydrocyclone 40 was 170°C (Example 6) and 180°C (Example 7).
) and 155°C (Comparative Example 7), terephthalic acid was produced in the same manner as in Example 1.

The evaluation results of the obtained terephthalic acid are shown in Table 2. Example 8 In Example 1, the raw materials fed from the reaction mixture supply line 12 contained acetic acid at 23.7 k9/Hr and water at 3.9 k9/Hr.
g/Hr, cobalt acetate 247/Hrl manganese acetate 127/Hrl and tetrabromoethane 12.4y
/Hr, and the heated acetic acid extraction line 27 on the distillation column side
Add 22.8 kg of 85% by weight heated acetic acid through
/Hr, and the temperature of the primary soaking tank was 220°C and the pressure was 18k9/c. The temperature of the secondary soaking tank was 180°C and the pressure was 7kg/Cd, but the same method as in Example 1. Terephthalic acid was produced by

The evaluation results of the obtained terephthalic acid are shown in Table 2. Example 9 In Example 8, the separation ratio of the mother liquor in the liquid cyclone 40 was set to 80% by weight, and the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 25.2 kg.
/Hr, and the reaction mixture supply line 12 to the reactor 10
Acetic acid in the raw materials supplied from
Manganese acetate 6y/Hr and tetrabromoethane 6y/Hr
．． Terephthalic acid was produced in the same manner as in Example 8 except that the ratio was 2y/Hr.

The evaluation results of the obtained terephthalic acid are shown in Table 2. Example 10 In Example 8, the separation ratio of the mother liquor in the liquid cyclone 40 was 90% by weight, and the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 26.4k9.
/Hr, and the reaction mixture supply line 12 to the reactor 10
Acetic acid in raw materials supplied from 23.4 kg/Hr, water 4.11 < g/Hr, cobalt acetate 67/Hr, manganese acetate 37/Hr, and tetrabromoethane 3.1
Terephthalic acid was produced in the same manner as in Example 8 except that the ratio was 7/Hr.

The evaluation results of the obtained terephthalic acid are shown in Table 2. Comparative Example 8 In Example 8, the separation ratio of the mother liquor in the liquid cyclone 40 was set to 50% by weight, and the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 21.6 kg/
Also, in the raw materials supplied to the reactor 10 from the reaction mixture supply line 12, 23.8 kI of acetic acid and 3.8 k of water were added.
9/Hrl cobalt acetate 307/Hrl manganese acetate 15f7/Hr and tetrabromoethane 15.5t
Terephthalic acid was produced in the same manner as in Example 8 except that /Hr- was used.

The evaluation results of the obtained terephthalic acid are summarized in Table 2. Example 11 In Example 1, the temperature of the primary dipping tank was set to 230°C and the pressure was set to 201<g/Cdl.The temperature of the secondary dipping tank was set to 200°C.
The temperature and pressure were set to 10 kg/Cd, and the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 5.61 to set the solvent ratio to terephthalic acid in the first immersion tank to be 2 by weight. <g/Hr, acetic acid in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 was set at 8.01<g/Hr, and water was set at 1.21<g/Hr. Terephthalic acid was produced in a similar manner.

Table 3 shows the evaluation results of the obtained terephthalic acid. Example 12 In Example 1, the temperature of the primary immersion tank was set to 230°C and the pressure was set to 201<g/Ctli, and the temperature of the second immersion tank was set to 2.
00°C and the pressure was 10 kg/Cd, and in order to make the solvent ratio to terephthalic acid in the primary dipping tank 3 by weight, 10.2 kg/Cd of heated acetic acid was added through the heated acetic acid extraction line 27 on the distillation column side. Terephthalic acid was produced in the same manner as in Example 1, except that the acetic acid and water in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 were 11.9 kg/Hr and 1.9 kg/Hr, respectively. Manufactured.

Table 3 shows the evaluation results of the obtained terephthalic acid. J/
Example 13 In Example 1, the temperature of the primary dipping tank was 230°C and the pressure was 20k9/Cdl. The temperature of the secondary dipping tank was 200°C.
In order to set the pressure to 10k9/Cd, and to make the solvent ratio to terephthalic acid in the primary dipping tank 4 by weight, the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 14.8 kg. /Hr, and terephthalic acid was produced in the same manner as in Example 1, except that the amount of acetic acid in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 was 15.8 kg/Hr, and the amount of water was 2.6 kg/Hr. was manufactured.

Table 3 shows the evaluation results of the obtained terephthalic acid. Vehicle Exchange Example 9 In Example 1, the temperature of the primary immersion tank was 230°C and the pressure was 20kg/Crli. The temperature of the secondary immersion tank is 200℃ and the pressure is 10kg/Cr! i,
In addition, in order to make the solvent ratio to terephthalic acid in the primary immersion tank 1.5 by weight, the amount of heated acetic acid added through the heated acetic acid extraction line 27 on the distillation column side was 3.3 kg/
Hr, acetic acid in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 is 6.0k9/Hr, and water is 0.
Terephthalic acid was produced in the same manner as in Example 1 except that the amount was 9 kg/Hr.

Table 3 shows the evaluation results of the obtained terephthalic acid. Example 14 In Example 1, the temperature of the primary immersion bath was set to 20
0℃ and pressure 13kg/Cdl Secondary soaking tank temperature 180℃ and pressure 7kf! /Cd, and in order to make the solvent ratio to terephthalic acid in the primary dipping tank 6 by weight, the amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was 24.0 kg/]1)- The acetic acid and water in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 are 23.6 kg/Hr and 4.0 kg/H, respectively.
Terephthalic acid was produced in the same manner as in Example 1 except that r was used.

Table 3 shows the evaluation results of the obtained terephthalic acid. Example 15 In Example 1, the temperature of the primary immersion tank was 200°C and the pressure was 13 kg/Crli, and the temperature of the secondary immersion tank was 18
The amount of heated acetic acid added through the heated acetic acid withdrawal line 27 on the distillation column side was set to 33.0°C and the pressure was set to 7 kg/Cd, and the solvent ratio to terephthalic acid in the primary soaking tank was set to 8 by weight. 2 kg/Hr, acetic acid in the raw materials supplied from the reaction mixture supply line 12 to the reactor 10 was changed to 31.4 kg/Hr, and water was changed to 5.4 kg/H1- in the same manner as in Example 1. Produced Jallic acid.

Table 3 shows the evaluation results of the obtained terephthalic acid. Examples 16 to 17 and Comparative Example 10 In Example 3, the temperature and pressure conditions of the primary immersion tank were changed to 190°C and 90°C in Example 16, respectively.
k! Terephthalic acid was produced in the same manner as in Example 3, except that in 9/Cdl Example 17, the temperature was 200°C and the pressure was 13k9/Cdl Comparative Example 10, the temperature was 180°C and the pressure was 71<g/Cd. did.

Table 4 shows the evaluation results of the obtained terephthalic acid. Example 18 In Example 3, the separation ratio of the oxidation reaction mother liquor by the liquid cyclone 40 was 90% by weight, the temperature of the primary immersion tank was 230°C, the pressure was 20kg/Cdl, and the temperature of the secondary immersion tank was 200°C. and pressure 10kg/Cwi. In addition, in order to make the solvent ratio to terephthalic acid in the primary immersion tank 6 by weight and the water concentration to 10% by weight, 90% by weight of heated acetic acid was added to 26% by weight through the heated acetic acid withdrawal line 27 on the distillation column side. .4 kg/Hr, and further acetic acid in the raw material supplied to the reactor 10 from the reaction mixture supply line 12.
4.9kv/Hr, water 2.7kg/Hr-, cobalt acetate 0.05y/Hr, and tetrabromoethane 2
．． Terephthalic acid was produced in the same manner as in Example 3 except that the voltage was 5 V/Hr.

Table 4 shows the evaluation results of the obtained terephthalic acid. Comparative Example 11 All the same procedures as in Example 17 except that the temperature of the primary immersion tank was 250°C and the pressure was 23 kg/Cd.
Terephthalic acid was produced in a similar manner.

Table 4 shows the evaluation results of the obtained terephthalic acid. Examples 19 to 21 and Comparative Examples 12 to 13 In Example 13, the temperature and pressure conditions of the secondary immersion tank were changed to 180°C and 7K in Example 19, respectively.
g/Cdl In Example 20, the temperature was 160°C and the pressure was 5
1<g/CriL, In Example 21, the temperature was 150°C and the pressure was 5k9/Cdl. In Comparative Example 12, the temperature was 230°C and the pressure was 14k9/c. In Comparative Example 13, the temperature was 140°C.
Example 13 except that the pressure was 5 kg/Cd.
Terephthalic acid was produced in a similar manner.

Table 5 shows the evaluation results of the obtained terephthalic acid.

[Brief explanation of drawings]

The accompanying drawings show a system diagram of an example of equipment used in carrying out the present invention. Explanations of the main symbols in the figure are as follows. 10...
... Oxidation reactor, 12 ... Reaction raw material mixture supply line, 13 ... Air supply line, 20 ...
・・・・・・Plate distillation column, 25・・・Exhaust gas line, 27・・・Heating acetic acid extraction line, 30・
...First receiver, 40 ... Liquid cyclone, 41 ... Separated mother liquor return line, 50 ...
...Primary dipping tank, 60...Second dipping tank, 70
...Second receiver, 80...Centrifugal separator.

Claims (1)

[Claims] 1 (A) Paraxylene containing molecular oxygen in an acetic acid solvent in the presence of an oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound at a temperature of 170 to 230°C and under pressure. 4- in the crude terephthalic acid contained in the oxidation reaction product mixture obtained by the oxidation reaction with gas.
Carboxybenzaldehyde content is 500 to 3
000 ppm and 340 ppm of crude terephthalic acid.
Obtaining an oxidation reaction product mixture having an optical density in mμ of 0.3 or less;
0% by weight or more is separated and recycled to the oxidation reactor, and (C) heated acetic acid is added to the remaining mixture in an amount such that the weight ratio of acetic acid solvent to crude terephthalic acid is in the range of 2 to 10. The resulting suspension of crude terephthalic acid in acetic acid is subjected to a primary immersion treatment while being stirred at a temperature ranging from the oxidation reaction temperature to 240°C, and (D) is then subjected to a primary immersion treatment at a temperature ranging from 150 to 220°C and at a temperature of the primary immersion. at least 10℃ below
A method for producing high-purity terephthalic acid, which comprises performing a secondary immersion treatment under stirring at a low temperature, and (E) separating terephthalic acid from the obtained suspension of terephthalic acid in acetic acid. 2 As the oxidation reaction product mixture obtained by the oxidation reaction, the content of 4-carboxybenzaldehyde in the crude terephthalic acid is in the range of 600 to 2500 ppm, and the optical density of the crude terephthalic acid at 340 mμ is 0.2
A manufacturing method according to claim 1, wherein the following oxidation reaction product mixtures are obtained: 3. The primary immersion treatment is carried out by dipping an acetic acid suspension of crude terephthalic acid in which the weight ratio of the acetic acid solvent to crude terephthalic acid is in the range of 3 to 8 at a temperature 10°C higher than the oxidation reaction temperature to 23°C.
A method according to claim 1, which is carried out at a temperature in the range of 0°C. 4. The manufacturing method according to claim 1, wherein the secondary dipping treatment is carried out at a temperature in the range of 160 to 200°C and at least 20°C lower than the temperature of the primary dipping. 5. As an oxidation reactor, an oxidation reactor with a distillation column connected to the upper part is used to distill and remove water by-produced by the oxidation reaction from the column section of the distillation column and from the bottom of the distillation column. The manufacturing method according to claim 1, wherein the oxidation reaction of para-xylene is carried out while refluxing acetic acid into an oxidation reactor. 6. As an oxidation reactor, an oxidation reactor with a distillation column connected to the upper part is used, and water produced by the oxidation reaction is removed by distillation from the column section of the distillation column, and water is removed from the bottom of the distillation column. The oxidation reaction of para-xylene is carried out while acetic acid is refluxed to an oxidation reactor, and the acetic acid extracted from the bottom or side of the distillation column is used as heated acetic acid, according to claim 1 or 5. manufacturing method.