JPS5842858B2 - 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 to oxidize paraxylene 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, according to any of these methods, it is difficult to economically produce high-quality terephthalic acid that can be used directly in polymerization methods.

For example, in order to produce high-quality terephthalic acid that can be used directly in the polymerization process, especially by a one-step oxidation reaction, the solvent ratio, catalyst composition, reaction temperature, supply amount of molecular oxygen-containing gas (exhaust gas The oxidation conditions, such as the content of oxygen gas in the

Even if high-quality terephthalic acid could be produced as a result,
In both cases, the oxidative decomposition of the acetic acid solvent increases particularly markedly, so that it is not possible to economically produce high-quality terephthalic acid.

Therefore, in conventional methods, high-quality terephthalic acid for direct polymerization is obtained by catalytic hydrogenation treatment, catalytic decarbonylation, etc. It was usually produced by performing purification treatments such as chemical treatment and recrystallization treatment.

However, although it is possible to produce high-quality terephthalic acid by performing purification treatments such as catalytic hydrogenation treatment, catalytic decarbonylation treatment, or recrystallization treatment, the refining treatment operations are complicated, so it is not necessary to produce terephthalic acid. This increases manufacturing costs.

Therefore, terephthalic acid purified by these methods does not fully satisfy the requirements for terephthalic acid for direct polymerization from an economic standpoint.

Furthermore, many methods have been proposed for purifying crude terephthalic acid produced by liquid-phase oxidation reaction of paraxylene by methods other than those described above.

For example, a suspension of 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, in a lower aliphatic carboxylic acid such as acetic acid. A method of heat-treating to a high temperature is disclosed in Japanese Patent Publication No. 4413135 and Japanese Patent Application Laid-open No. 49-2019.
141, etc., and a method similar to these methods has also been proposed in Japanese Patent Publication No. 7538/1983.

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. do not have.

Furthermore, JP-A No. 51-127037 (corresponding patent to Belgian Publication No. 127037, Belgian Patent Publication No. 840624) discloses that in the presence of a catalyst consisting of a cobalt compound, a manganese compound and a bromine compound, a temperature of 160 to 180° C. The oxidation reaction product mixture containing crude terephthalic acid obtained by oxidizing baraxylene with a molecular oxygen-containing gas was heated to 50°C below the oxidation reaction temperature without separating the mother liquor.
The terephthalic acid is separated after being kept at a lower temperature and 25° C. higher, the separated terephthalic acid is then suspended in the mother liquor or fresh acetic acid solvent, and the suspension is
℃ or higher, specifically, by separating terephthalic acid after holding it at a temperature of up to about 160℃, it is possible to suppress the oxidative decomposition of acetic acid and to produce terephthalic acid that can be used directly in the polymerization method. is listed.

However, in this method, the first stage treatment is carried out without separating 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. 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 employing the direct polymerization method, it is necessary to mix terephthalic acid with x equimolar amount of ethylene glycol and react in a suspension state.

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 a suspension of high-purity terephthalic acid in ethylene glycol, it is necessary that the crystal shape of the terephthalic acid be close to spherical and that its average particle size be large.

Therefore, the terephthalic acid used in the production of polyester by direct polymerization is required not only to have high purity and excellent hue, but also to have good slurry properties.

As a method for improving the slurry properties of terephthalic acid, Japanese Patent Publication No. 11488/1988 describes heating 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. A treatment method has been proposed, and Japanese Patent Publication No. 49-20303 similarly proposes a treatment method in which coarse particles of high-purity terephthalic acid are suspended in a solvent with low solubility for terephthalic acid, such as acetic acid or water. A method has been proposed in which pump agitation processing is performed using a circulation pump outside the agitation tank.

However, in the former method, fine particulate terephthalic acid with an average particle size of several μm or less, such as terephthalic acid that is once generated by acid precipitation from an aqueous solution of an alkali terephthalic acid salt in the Henkel method, is mixed with acetic acid or acetic acid and water. By suspending the terephthalic acid crystals in a mixed solvent, etc., and heating the suspension to a temperature close to the boiling point of the solvent, the average diameter of the fine particulate terephthalic acid crystals is increased and the shape of the crystals becomes nearly spherical. be.

In the latter method, terephthalic acid crystals, which are coarse particles with an average particle size of 50 to 200 μm 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 close to room temperature without heating, the average particle size of the terephthalic acid crystals is reduced, while 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 an acid precipitation method or coarse-particle high-purity terephthalic acid produced by a crystallization method. The slurry property is improved by treating the high purity terephthalic acid in a suspension state.

Crude terephthalic acid containing a considerable amount of oxidized intermediates such as 4-carboxybenzaldehyde and colored substances can be purified without using complicated purification methods such as catalytic hydrogenation, catalytic decarbonylation, or recrystallization as described above. If it can be purified by a simple purification process, and at the same time it is possible to produce high-purity terephthalic acid with a nearly spherical crystal shape, a large average particle size, and good slurry properties, oxidation Since the oxidative decomposition of the acetic acid solvent in the reaction stage can be significantly suppressed, this method is economically advantageous compared to the method of directly producing high-quality terephthalic acid through the one-step oxidation reaction described above.

The present inventors have developed a method for processing crude terephthalic acid containing a large amount of impurities such as 4-carboxybenzaldehyde, which is obtained by oxidizing baraxylene with a molecular oxygen-containing gas in the presence of an oxidation catalyst in an acetic acid solvent, through a simple processing procedure. By refining the terephthalic acid, we produce high-quality terephthalic acid with a nearly spherical crystal shape, a large average particle size, and good slurry properties, which can also be used in the production of polyester by direct polymerization. As a result of studying methods to do this, we have arrived at the present invention.

The object of the present invention is to obtain crystals having a nearly spherical shape suitable for producing polyester by direct polymerization from crude terephthalic acid obtained by oxidizing baraxylene with a molecular oxygen-containing gas in the presence of a catalyst in an acetic acid solvent. Another object of the present invention is to provide a method for producing terephthalic acid having a large average particle size and good slurry properties.

To outline the present invention, the present invention is obtained by oxidizing baraxylene with a molecular oxygen-containing gas under high temperature and pressurized conditions in an acetic acid solvent in the presence of an oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound. A method for purifying terephthalic acid by subjecting crude terephthalic acid as a suspension in an acetic acid solvent to an immersion treatment under heating, wherein the second immersion treatment is carried out at a temperature in the range of 170 to 240°C,
A secondary dipping treatment is then carried out at a temperature in the range of 150 to 220°C and at least 10°C lower than the primary dipping treatment temperature, and a stirring power in the range of 1.0 to 5.0 horsepower per m3 of the terephthalic acid suspension in acetic acid. The present invention also relates to a method for producing high-purity terephthalic acid, characterized in that the stirring is carried out at a linear velocity of 0.8 to 4 m/sec at the tip of a stirring blade.

That is, the present invention provides a method in which crude terephthalic acid containing a large amount of oxidized intermediates such as 4-carboxybenzaldehyde and colored impurities is subjected to a primary immersion treatment in the form of a suspension in an acetic acid solvent under the above-mentioned specific high temperature conditions. Furthermore, when performing a secondary dipping treatment on the terephthalic acid suspension to crystallize terephthalic acid crystals, the crystal shape can be changed by performing the secondary dipping treatment under the above-mentioned specific temperature and specific stirring conditions. This is based on the discovery that it is possible to produce high-quality terephthalic acid having a nearly spherical shape and a large average particle size and good slurry properties, thereby achieving the above object.

Conventionally, in a method for producing terephthalic acid by oxidizing baraxylene with a molecular oxygen-containing gas under high temperature and pressurized conditions in the presence of an oxidation catalyst in an acetic acid solvent, terephthalic acid crystals in the oxidation reaction product mixture are For the purpose of growing large crystals, it is usual to provide a series of multistage crystallization tanks operated under conditions of slow cooling and pressure reduction after the oxidation reactor.

In addition, in order to obtain sufficiently grown and large terephthalic acid crystals in these crystallization tanks, the oxidation reaction mixture is heated as slowly as possible within a range that allows the terephthalic acid to remain in suspension without precipitating. Stirring is necessary, and it was thought that if the stirring intensity was too strong, finely powdered terephthalic acid would be produced, which was undesirable.

However, according to the study results of the present inventors, the present invention involves performing a primary immersion treatment on crude terephthalic acid in an acetic acid solvent under specific high temperature conditions, and then dipping the terephthalic acid in the form of an acetic acid suspension. Surprisingly, contrary to conventional knowledge, by carrying out the secondary dipping treatment under specific temperature conditions and specific strong stirring conditions, The crystal shape of terephthalic acid is close to spherical and its average particle size is large, and in addition, impurities such as 4-carboxybenzaldehyde and colored substances that have been eluted by the next immersion are not reintroduced into the terephthalic acid crystals, resulting in high quality. Terephthalic acid is obtained.

In the method for producing terephthalic acid of the present invention, as is conventionally known, baraxylene is converted into molecular molecules 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 0.00% as cobalt atoms per 12 acetic acid solvents. lX1
in the range of 0' to 5.0 x 10-5 gram atoms;
The amount of the manganese compound used is in the range of o, ooi to 1.0 as an atomic ratio of the cobalt compound, and the amount of the bromine compound used is in the range of 1 to 4 as the atomic ratio to the sum of cobalt atoms and manganese atoms. is preferred.

In the method of the invention, the oxidation reaction of baraxylene is carried out in an acetic acid solvent.

The proportion of the acetic acid solvent used is usually in the range of 2 to 10, preferably 3 to 6, in terms of weight ratio to baraxylene.

The water concentration in the mother liquor in the reaction system during the oxidation reaction is usually 5 to 15% by weight, preferably 7 to 12% by weight.
maintained within the range.

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%.
, preferably in the range of 3 to 6%.

In the method of the present invention, the oxidation reaction of baraxylene is carried out under high temperature and pressurized conditions.

At this time, the reaction temperature is usually in the range of 170 to 230°C, preferably 180 to 220°C.

The crude terephthalic acid used as a raw material for purification in the method of the present invention is obtained by the oxidation reaction shown above, and may be crude terephthalic acid containing any range of 4-carboxybenzaldehyde.

However, in order to economically produce high-quality terephthalic acid, it is preferable to suppress the oxidative decomposition of the acetic acid solvent during the oxidation reaction stage, as described above.

To this end, it is preferable to use crude terephthalic acid as the raw material for purification of the present invention, which has a 4-carboxybenzaldehyde content in the range of 500 to 3000 ppm and an optical density at 340 mμ of 0.3 or less. It is particularly preferable to use crude terephthalic acid having a 4-carboxybenzaldehyde content in the range of 600 to 2500 ppm and an optical density at 340 mμ of 0.2 or less.

In order to produce crude terephthalic acid containing 4-carboxybenzaldehyde in a preferable specific range, that is, in order to suppress the oxidative decomposition of the acetic acid solvent in the oxidation reaction stage, the ratio of acetic acid solvent to baraxylene, Oxidation reaction conditions such as 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), and stirring intensity are within the above ranges. This can be achieved by appropriately selecting the following.

In addition, when separating crude terephthalic acid from the oxidation reaction product mixture, if the oxidation reaction product mixture is generally separated after being rapidly cooled, the content of 4-carboxybenzaldehyde in the crude terephthalic acid will increase, and the oxidation reaction product mixture will be oxidized. Avoid cooling too much from the reaction temperature (if separated, the content of 4-carboxybenzaldehyde in the crude terephthalic acid will decrease).

Therefore, in order to increase economic efficiency by suppressing the oxidative decomposition of the acetic acid solvent in the oxidation reaction step as much as possible, and to obtain crude terephthalic acid as a refining raw material with a content of 4-carboxybenzaldehyde within the above-mentioned preferred range, Preferably, the oxidation reaction product mixture is separated from the oxidation reaction temperature without significant cooling.

In addition, when crude terephthalic acid is separated from the oxidation reaction product mixture, most of the mother liquor is removed, and the crude terephthalic acid containing a portion of the mother liquor, for example, 40% by weight or less, can be used as the refined raw material, raw terephthalic acid. .

In the method of the present invention, the crude terephthalic acid is first immersed in a suspension state in an acetic acid solvent with stirring under high temperature and pressurized conditions, and then subjected to a second immersion treatment. .

The temperature during the primary immersion treatment in the method of the present invention is 170°C.
It is necessary that the temperature is in the range of 1 to 240℃, especially 1
Preferably the temperature is in the range 80 to 230°C and at least 10°C higher than the oxidation reaction temperature.

- If the temperature during the subsequent dipping treatment is lower than 170°C, a sufficient purification effect will not be obtained, and if it is higher than 240°C, the optical density of terephthalic acid and the hue of polyethylene terephthalate when directly polymerized will decrease.

In the method of the present invention, the weight ratio of the acetic acid solvent to the crude terephthalic acid in the suspension of crude terephthalic acid in acetic acid is usually in the range of 2 to 10, particularly in the range of 3 to 8. It is preferable that there be.

If the weight ratio of the acetic acid solvent to the crude terephthalic acid in the acetic acid suspension of crude terephthalic acid is too small, the purification effect of the primary immersion treatment will be difficult to show, and if the weight ratio of the acetic acid solvent is too large, a large amount of heat will be required for heating. As a result, it becomes uneconomical.

- The acetic acid solvent used for the subsequent immersion treatment may be acetic acid containing generally 3 to 25% by weight of water.

& When the content of water in the acetic acid solvent of the acetic acid suspension of crude terephthalic acid is in the range of 5 to 20% by weight, the purification effect of the second immersion treatment, especially the removal effect of 4-carboxybenzaldehyde, is significant ( Therefore, it is preferable.

In addition, in the immersion treatment of the present invention, the acetic acid solvent of the acetic acid suspension of crude terephthalic acid contains the reaction mother liquor present in the oxidation reaction product mixture in a weight ratio of 2.6 or less to the crude terephthalic acid. I can't help it.

The primary immersion treatment in crude terephthalic acid according to the method of the invention is carried out under stirring.

In order to obtain an excellent purification effect, the acetic acid suspension of crude terephthalic acid must be stirred with a stirring power of i, o horsepower or more per 1 m° of the suspension and at the tip of the stirring blade. It is preferable to perform stirring at a linear velocity of 0.8 m/sec or more, and in particular, the stirring power per 1 m° of the suspension is in the range of 1.3 to 4.0 horsepower, and the line at the tip of the stirring blade is Stirring is preferably carried out at a speed of 1.3 to 5.0 m/sec.

In the present invention, the terephthalic acid suspension in acetic acid that has been subjected to the primary dipping treatment by the above method is then subjected to a secondary dipping treatment.

In this secondary dipping treatment, an acetic acid suspension of terephthalic acid obtained by selectively extracting impurities such as oxidized intermediates such as 04-carboxybenzaldehyde and colored substances from the crude terephthalic acid into an acetic acid solvent by the secondary dipping treatment is used. By immersing the turbid liquid at a specific temperature lower than the primary immersion temperature, terephthalic acid crystals can be simultaneously crystallized without causing the impurities extracted into the acetic acid solvent by the second immersion treatment to be included in the terephthalic acid again. This method prepares terephthalic acid crystals having a nearly spherical crystal shape, a large average particle size, and good slurry properties.

In order to obtain terephthalic acid with crystal shape close to spherical, large average particle size, and good slurry properties through this secondary dipping treatment, the temperature and stirring intensity of the secondary dipping treatment are important requirements as shown below. becomes.

In the method of the present invention, the temperature of the secondary dipping treatment must be in the range of 150 to 220° C. and at least 10° C. lower than the temperature of the primary dipping treatment.

Furthermore, in order to obtain terephthalic acid crystals with a spherical crystal shape and good slurry properties, the temperature should be in the range of 160 to 200°C and at least 20°C higher than the primary dipping temperature.
Preferably, the temperature is low.

If the temperature of the secondary dipping treatment is lower than 150°C, terephthalic acid crystals with a nearly spherical crystal shape and a large average particle size cannot be obtained;
Impurities such as carboxybenzaldehyde are once again included in the terephthalic acid crystals.

Furthermore, if the temperature of the secondary dipping treatment is higher than 220° C., many particulate terephthalic acid crystals will be produced.

Even if the temperature during the secondary immersion treatment is in the range of 150 to 220°C, if the difference between the temperature during the secondary immersion treatment and the temperature during the secondary immersion treatment is less than 10°C, the crystal shape is nearly spherical (and has a large average particle size), making it difficult to obtain terephthalic acid.

In the method of the present invention, the secondary immersion treatment is carried out under stirring, and the stirring intensity is 1 m' of the terephthalic acid suspension in acetic acid.
The stirring power per unit is in the range of 1.0 to 5.0 horsepower, and the linear velocity at the tip of the stirring blade is 0.8 to 4.077.
In particular, the stirring power per unit of suspension of terephthalic acid in acetic acid must be in the range of 1.3 to 3.0 horsepower, and the linear velocity at the tip of the stirring blade must be in the range of 1/sec. 1
．． Preferably, the speed is in the range of 3 to 3.0 m/sec.

Even if the stirring power per 1r11' of terephthalic acid suspension in acetic acid is less than 1.0 horsepower, the linear velocity at the tip of the stirring blade is 0.
．． Even if the velocity is less than 8 m/sec, the terephthalic acid crystals do not have a nearly spherical shape, resulting in poor slurry properties.

In addition, the stirring power per terephthalic acid suspension Im' is 5
Even if it becomes larger than the horsepower, the linear velocity at the tip of the stirring blade is still 4.0.
Even if the speed is greater than m/sec, the average diameter of the terephthalic acid crystals becomes smaller and more fine particles of terephthalic acid are produced, resulting in poor slurry properties.

In the method of the present invention, the time for the secondary immersion treatment varies depending on the immersion temperature, stirring intensity, and other conditions, but is usually 2.
0 minutes to 2 hours, preferably 30 minutes to 1.
It is 5 hours.

After the suspension of terephthalic acid in acetic acid that has been subjected to the primary immersion treatment and then the secondary immersion treatment by the above method is rapidly cooled by slow cooling or flash method, high quality terephthalic acid is obtained by distributing it door to door according to the usual method. be able to.

The high-quality terephthalic acid produced by the method of the present invention not only has a low content of oxidized intermediates such as 4-carboxybenzaldehyde and impurities such as coloring substances, but also has crystals that are close to spherical in shape and have a large average particle size. , is a high-quality terephthalic acid with good slurry properties, and can be used in the production of polyester by direct polymerization.

An example of an apparatus for producing high quality terephthalic acid for direct polymerization according to the process 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, paraxylene is oxidized to terephthalic acid, and the oxidation reaction begins. The resulting mixture is a suspension of crude terephthalic acid in acetic acid.

A suspension of crude terephthalic acid in acetic acid, which is the oxidation reaction product mixture, is sent from the oxidation reactor 10 to the first receiver 30 through the oxidation reaction product mixture withdrawal line 14 and the valve 15 .

In the first receiver 30, the oxidation reaction product mixture is kept warm so as not to drop too much from the oxidation reaction temperature, and is heated by the stirrer 3.
1.

When withdrawing the oxidation reaction mixture from the oxidation reactor 10 into the first receiver 30, the acetic acid vapor generated if a pressure drop occurs is condensed through line 32 and cooler 33 in the upper part of the first receiver and is transferred through line 34 to the first receiver 30. Reflux into one receiver.

On the other hand, the water produced as a by-product in the oxidation reaction is led to the plate 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 is maintained constant by distilling and separating the water using the heat of reaction 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-acetic acid solution enters a condensate receiver 23.

A portion of the water-acetic acid solution mainly containing 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 supplied to the hydrocyclone 40 through the acetic acid suspension of terephthalic acid suspension line 35, the pump 36, and the hydrocyclone supply line 37, and the oxidation reaction product mixture is mixed at a predetermined temperature. The mother liquor inside is separated at a predetermined ratio, and the separated mother liquor is returned to the oxidation reactor 10 through the 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 taken out from the crude terephthalic acid suspension in acetic acid extraction line 42 at the bottom of the liquid cyclone 40 and transferred to the oxidation reactor 1.
Heated acetic acid extraction line 27 on the side of the distillation column at the top of 0
The water is heated to a predetermined temperature in a heat exchanger 43 together with heated acetic acid containing water of a predetermined concentration, which is taken out from the tank, and then supplied to the primary immersion 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 stirred by a stirrer 51. The primary immersion treatment is performed while stirring for a predetermined period of time.

- The acetic acid suspension of crude terephthalic acid subjected to the secondary 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 hole 54. be done.

In the secondary dipping tank 60, the terephthalic acid suspension in acetic acid is heated by a stirrer 61 at a specific temperature lower than in the primary dipping tank.
A secondary immersion treatment is performed while stirring for a predetermined time.

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 portion of the acetic acid solvent in the secondary dipping tank is vaporized and condensed through a line 65 and a cooler 66 at the top of the secondary dipping tank, and is refluxed into the secondary dipping tank.

Therefore, the temperature can be adjusted by adjusting the pressure of the secondary immersion tank.

A suspension of terephthalic acid in acetic acid that has been subjected to a secondary immersion treatment is
A withdrawal line 62 at the bottom of the secondary soaking tank is sent to a second receiver 70 through a valve 63 and a line 64.

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 in the second receiver 70 the suspension of terephthalic acid in acetic acid is stirred. 71.

The acetic acid suspension of terephthalic acid in the second receiver is fed to the centrifuge 80 through a withdrawal line 72, a pump 73 and a centrifuge-like feed line 77 at the bottom of the second receiver.

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.

Furthermore, the acetic acid solvent recovered from the centrifuge can be reused as 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 crude terephthalic acid obtained by oxidizing under relatively mild oxidation conditions that can significantly suppress the decomposition of the acetic acid solvent can be easily processed under the above-mentioned specific conditions. Through the two-stage dipping process performed in , it is possible to produce high-quality terephthalic acid that can be used in the production of polyester by direct polymerization, and moreover, it is possible to reduce the oxidative decomposition of the acetic acid solvent during the oxidation reaction. This has the advantage of lower manufacturing costs.

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 addition drawings.

In addition, the content of 4-carboxybenzaldehyde (4-CBA) in terephthalic acid (TA) was measured by polarography, and the optical density of terephthalic acid (0, D, )
is the value measured at 340 mμ using a 1 liter cell for a 2N potassium hydroxide aqueous solution containing terephthalic acid at a concentration of 15% by weight.

The shape of the terephthalic acid crystals was determined visually using an optical microscope, and the average particle size of the crystals was determined by sieving the terephthalic acid with a standard sieve and plotting the distribution under the sieve as a 50% particle size. .

Also, polyethylene terephthalate (PET) is composed of terephthalic acid 50S' and ethylene glycol 75f? was placed in a flask and esterified at 200°C in a nitrogen stream,
Using antimony trioxide of 201rI9 as a catalyst at a temperature of 2
It is obtained by polycondensation at 85° C. and a pressure of 0.1 mmHg or less.

The color tone of polyethylene terephthalate was indicated by the b value [yellow (-+) to blue (c)] among the external colors measured by reflected light with a color difference meter.

The smaller the b value, the better the color tone.

Example 1 10.8 kg of acetic acid and 1.2 kg of water were placed in an oxidation reactor 10 equipped with a distillation column.
kg, cobalt acetate 60P, manganese acetate 30g, and tetrabromoethane 31R, and the temperature of the reactor was set to 19
Maintaining the temperature at 0°C and the pressure at 11 kg/crA, 3 kg/hr of baraxylene, 15.8 kg/hr of acetic acid, and 2 kg/hr of water.
．． 6 kg/hr, cobalt acetate 18f/hr, manganese acetate 9t/hr and tetrabromoethane 9.3
f/hr to the reaction mixture supply line 12.
While feeding the air into the oxidation reactor more continuously, the air is adjusted to approximately 4.2 NM3/ so that the oxygen concentration in the exhaust gas is 5%! A continuous oxidation reaction was carried out by feeding 9-valaxylene through the air supply line 13.

At this time, a part of the heated acetic acid in the distillation column 20 is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 1.
It was kept at 0% by weight.

Further, the reaction mixture was stirred at a stirring intensity of 3 horsepower per 1 d.

The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the 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, and the 70% weight of the mother liquor is % (8,4 to 9/
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 kg/hr, it is heated in a heat exchanger 43,
It was sent to the 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% by weight.

The temperature of the primary immersion tank is 230℃ and the pressure is 20kg/c.
Let rA be 1m? Stirring was carried out at a stirring power of 2.5 horsepower and a linear velocity of 2.6 m at the tip of the stirring blade for 7 seconds.

After the residence time in the first dipping tank was lhr, 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/crA, and the mixture was mixed with 1 m Stirring was carried out at a stirring power of 2.0 horsepower and a linear velocity of 2.3 m/sec at the tip of the stirring blade.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, washed, and then the terephthalic acid in the solid portion was dried.

Table 1 shows the evaluation results of the obtained terephthalic acid.

Example 2.3 and Comparative Example 1.2 In Example 1, the operating conditions of the secondary immersion tank were 180°C, 7 to 11/ca (Example 2); 200°C
, 10 kg/crA (Example 3); 140°C, 5 kg
/c4 (Comparative Example 1); 230°C, 14 kg/crI
Terephthalic acid was produced in the same manner as in Example 1, except for using i (Comparative Example 2).

The evaluation results for terephthalic acid are shown in Table 1.

Comparative Example 3 Terephthalic acid was produced in the same manner as in Example 3 except that the temperature of the primary soaking tank was 200° C. and the pressure was 13 kg/crl.

The evaluation results for terephthalic acid are shown in Table 1. Example 4 10.8 kg of acetic acid and 1.0 kg of water were placed in an oxidation reactor 10 equipped with a distillation column.
2 kg, cobal acetate) 4.8 F, manganese acetate 0,
25 P, tetrabromoethane 25f? The temperature of the reactor was maintained at 190°C and the pressure was maintained at 11 kg/c4.
kg/hr, water 2.7 kg/hr, cobalt acetate 4.8? / hr, manganese acetate 0.05 fl/h
While continuously feeding a mixture of 2.5 t/hr of tetrabromoethane and 2.5 t/hr of air into the oxidation reactor from the reaction mixture supply line 12, air was added at a rate of about 4.2 NM3/hr so that the oxygen concentration in the exhaust gas was 5%. kg -varaxylene 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 20 is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 1.
It was kept at 0% by weight.

The reaction mixture was also stirred at a stirring intensity of 3 horsepower per 1771 inches.

The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the 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. % (10,8kg
/hr), and the separated mother liquor was returned to the reactor through the separated mother liquor return line 41.

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 at 26.4
After adding at kg/hr, it is heated in a 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 10% by weight.

The temperature of the primary immersion tank is 230℃ and the pressure is 20kg/c.
rA, the stirring power per 1 m3 was 2.5 horsepower, and the linear velocity of the stirring blade tip was 2.6 m/sec.

After the residence time in the primary dipping tank was 1 hr, the terephthalic acid acetic acid suspension mixture was sent to the secondary dipping tank 60 with a temperature of 200° C. and a pressure of 10 kg/cA, The mixture was stirred at a stirring power of 2.0 horsepower per 17 n'' and a linear velocity of the stirring blade tip of 2.3 m/sec.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried.

The evaluation results of the obtained terephthalic acid are shown in Table 2.

Example 5 and Comparative Examples 4 to 8 In Example 4, everything was carried out in the same manner as in Example 4, except that the stirring power of the secondary immersion tank and the linear velocity of the stirring blade tip were set to the values shown in Table 2. Terephthalic acid was produced.

The evaluation results for terephthalic acid are shown in Table 2.

Example 6 10.8 kg of acetic acid and 1.0 kg of water were placed in an oxidation reactor 10 equipped with a distillation column.
2kg, cobalt acetate 48g, manganese acetate 242, tetrabromoethane 25? and set the temperature of the reactor to 2.
Maintaining the temperature at 10°C and the pressure at 15 kg/crA, 3 kg/hr of baraxylene, 20.7 kg/hr of acetic acid, 2.3 ky/hr of water, 19 P/hr of cobalt acetate, tof/hr of manganese acetate, and 10 f of tetrabromoethane were added. /
While continuously feeding a mixture consisting of hr into the oxidation reactor from the reaction mixture supply line 12, air was added at a rate of about 4.6 NM3/kg so that the oxygen concentration in the exhaust gas was 7%.
A continuous oxidation reaction was carried out by feeding in the proportion of xylene from the air supply line 13.

At this time, a part of the heated acetic acid in the distillation column 20 is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 1.
It was kept at 0% by weight.

The reaction mixture was also stirred at a stirring intensity of 3 horsepower per 177 I''.

The reaction product mixture flows through line 14 and valve 1 based on the signal from the level gauge, which is set to have a residence time of 1 hr.
60% by weight (7.2 kg/hr) of the mother liquor is sent to the hydrocyclone 40 through the first receiver 30 at 5 and 200°C.
The separated mother liquor is sent to the separated mother liquor return line 41.
was returned to the reactor.

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 kg/hr, it is heated in a heat exchanger 43,
It was sent to the primary dipping tank 50.

In this mixture, the solvent ratio to terephthalic acid was 5 by weight, and the water concentration in the solvent was 10% by weight.

The temperature of the primary immersion tank is 220℃ and the pressure is 18 kg/c.
vr, the stirring power per 177 I″ was 2.5 horsepower, and the linear velocity of the tip of the stirring blade was 2.6 m/sec.

After a residence time of 1 hr in the primary dipping tank, the terephthalic acid acetic acid suspension mixture was sent to the secondary dipping tank 60 maintained at a temperature of 190° C. and a pressure of 8 kg/c4, and the mixture was ．． Stirring was carried out at a stirring power of 2.0 horsepower per liter and a linear velocity of 2.3 m at the tip of the stirring blade for 7 seconds.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, washed, and then the terephthalic acid in the solid portion was dried.

The analysis results of the obtained terephthalic acid are shown in Table 3.

Example 7 10.8 kg of acetic acid and 1.0 kg of water were placed in an oxidation reactor 10 with a distillation column.
2kg, cobalt acetate 60? , manganese acetate 3°? , tetrafromethane 31f was charged, and the temperature of the reactor was set to 1.
The temperature and pressure were maintained at 90°C and 11 kg/cyA, and 3 kg/hr of baraxylene and 15.0 kg/hr of acetic acid were added. s kg/hr,
Water 2.6 ky/hr, cobalt acetate 18 ff/
hr, manganese acetate 9 fl/hr and tetrabromoethane 9.3? /hr is continuously fed into the oxidation reactor from the reaction mixture supply line 12, while air is added to the oxidation reactor at a rate of approximately 4% to make the oxygen concentration in the exhaust gas 5%.
．． A continuous oxidation reaction was carried out by feeding through the air supply line 13 at a ratio of 2NM3/kg-baraxylene.

At this time, a part of the heated acetic acid in the distillation column 20 is withdrawn from the condensed water withdrawal line 26, and the water concentration in the reaction mixture is
o% by weight.

Also, the reaction mixture is 1. The mixture was stirred at a stirring intensity of 3 horsepower per -1 hour.

The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the 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, and the 70% weight of the mother liquor is %(g-4kg/
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 kg/hr, it is heated in a heat exchanger 43,
It was sent to the 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% by weight.

The temperature of the primary immersion tank was set to 220°C and the pressure was set to 18 kg/
Cni, the stirring power per m3 was 2.5 horsepower, and the linear velocity of the tip of the stirring blade was 2.6 m/sec.

After a residence time of 1 hr in the primary soaking tank, the mixture of terephthalic acid in acetic acid suspension was fed into a secondary soaking tank 60 maintained at a temperature of 190° C. and a pressure of 8 to 9/crti. Stirring was carried out at a stirring power of 2.0 horsepower per 171 L' and a linear velocity of 2.3 m/sec at the tip of the stirring blade.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried.

Table 3 shows the evaluation results of the obtained terephthalic acid.

Example 8 10.8 kg of acetic acid and 1.2 kg of water were placed in the oxidation reactor 10 equipped with a distillation column.
kg, cobalt acetate 48g, manganese acetate 0.25?
, tetrabromoethane 252 was charged, the temperature of the reactor was maintained at 190°C and the pressure was maintained at 11 kg/crrf,
Baraxylene 3 kg/hr, acetic acid 31.4 to 9/stone water 5.4 kg/hr, cobalt acetate 9.6? /hr
, manganese acetate 0.05? /hr and tetrabromoethane5? / hr is continuously fed into the oxidation reactor from the reaction mixture supply line 12, while air is added to the oxidation reactor at a rate of about 4 hr so that the oxygen concentration in the exhaust gas is 5%.
．． A continuous oxidation reaction was carried out by feeding through the air supply line 13 at a ratio of 2NM3/kg-baraxylene.

At this time, a part of the heated acetic acid in the distillation column 20 is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 1.
It was kept at 0% by weight.

The reaction mixture was also stirred at a stirring intensity of 3 horsepower per 177 I''.

The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the 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, and 80% by weight of the mother liquor. % (9.6kg/
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 34.4 mL.
After adding at kg/hr, it is heated in a heat exchanger 43,
It was sent to the primary dipping 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 15% by weight.

The temperature of the primary immersion tank is 210℃ and the pressure is 15kg/c.
fx, the stirring power per 1 m3 was 2.5 horsepower, and the linear velocity of the tip of the stirring blade was 2.6 m/sec.

After a residence time of 1 hr in the primary dipping tank, the terephthalic acid acetic acid suspension mixture was sent to the secondary dipping tank 60 maintained at a temperature of 160°C and a pressure of 5 kg/cni, and the mixture 1771'' Stirring was carried out at a stirring power of 2.0 horsepower and a linear velocity of 2.3 m/sec at the tip of the stirring blade.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried.

Table 3 shows the evaluation results of the obtained terephthalic acid.

Example 9 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 601, manganese acetate 151, and tetrabromoethane 31f, and the temperature of the reactor was set to 18 kg.
Maintaining the temperature at 0°C and the pressure at 10 kg/crrt, 3 kg/hr of baraxylene and 29.6 kg/hr of acetic acid.
Water 7.2 kg/hr, cobalt acetate 6f/hr, manganese acetate 1.5? /hr and tetrabromoethane 3S
'/hr to the reaction mixture supply line 12
While feeding the oxidation reactor more continuously, the air was pumped at a rate of approximately 3-3 NM"/2, so that the oxidation concentration in the exhaust gas was 2%.
A continuous oxidation reaction was carried out by feeding k19-valaxylene through the air supply line 13 at a ratio of k19-valaxylene.

At this time, a part of the heated acetic acid in the distillation column 20 is extracted from the condensed water extraction line 26, and the water concentration in the reaction mixture is reduced to 1.
It was kept at 0% by weight.

The reaction mixture was also stirred at a stirring intensity of 3 horsepower per 1771 inches.

The reaction product mixture is sent to the hydrocyclone 40 through the line 14, the valve 15, and the first receiver 30 while maintaining the temperature at 180°C based on the signal from the liquid level gauge, which is set to have a residence time of 1 hr, and is reduced to 90% by weight of the mother liquor. (10,8!9
/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.
After adding at kg/hr, it is heated in a heat exchanger 43,
It was sent to the primary dipping 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 was set to 210°C and the pressure was set to 15 kg/
ctrl, the stirring power per 1 m' was 2.5 horsepower, and the linear velocity of the stirring blade tip was 2.6 m/sec.

After a residence time of 1 hr in the first dipping tank, the terephthalic acid acetic acid suspension mixture was sent to a second dipping tank 60 maintained at a temperature of 160°C and a pressure of 5 to 9/Cm, and the mixture was Stirring was carried out at a stirring power of 2.0 horsepower per 1 d and a linear velocity of 2.3 m/sec at the tip of the stirring blade.

After residence in the second immersion tank, it was sent to a second receiver 70, brought to normal pressure, solid-liquid separated in a centrifuge 80, and after washing, the terephthalic acid in the solid portion was dried.

Table 3 shows the evaluation results of the obtained terephthalic acid.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show a system diagram of an example of equipment used in carrying out the present invention. The explanations of the upper symbols in the figure are as follows. DESCRIPTION OF SYMBOLS 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. Crude terephthal obtained by oxidizing baraxylene with a molecular oxygen-containing gas under high temperature and pressurized conditions in the presence of an oxidation catalyst containing a cobalt compound, a manganese compound, and a bromine compound in an acetic acid solvent. In a method for purifying terephthalic acid by subjecting the acid in suspension in an acetic acid solvent to an immersion treatment under heating, the second immersion treatment is carried out at a temperature in the range of 170 to 240°C, and then the second immersion treatment is performed. The suspension of terephthalic acid in acetic acid 1 at a temperature in the range of 150 to 220°C and at least 10°C lower than the primary soaking temperature.
The method is characterized in that the stirring power per m3 is in the range of 1-0 to 5.0 horsepower, and the stirring is carried out under conditions where the linear velocity of the tip of the stirring blade is 0.8 to 4 m/sec. Manufacturing method. The secondary immersion treatment is carried out at a temperature in the range 180 to 230°C and at least 10°C higher than the oxidation reaction temperature, and then the secondary immersion treatment is carried out at a temperature in the range 160 to 200°C and at least 20°C higher than the primary immersion temperature. ℃
The manufacturing method according to claim 1, which is carried out at a low temperature. 3. Perform the secondary immersion treatment using 1 m of the terephthalic acid suspension in acetic acid.
The manufacturing method according to claim 1, which is carried out under stirring conditions in which the stirring power per unit is in the range of 1.3 to 3.0 horsepower and the linear velocity of the tip of the stirring blade is in the range of 1.3 to 3.0 m/sec. . 4 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 primary dipping temperature, and the stirring power per cubic meter of the terephthalic acid suspension in acetic acid is 1.
The method according to claim 1, wherein the method is carried out under stirring conditions of 3 to 3.0 horsepower and a linear velocity of 1.3 to 3.0 m/sec at the tip of the stirring blade. 5 As raw material crude terephthalic acid, the content of 4-carboxybenzaldehyde is 500 to 3000 ppm
5. The production method according to any one of claims 1 to 4, which uses crude terephthalic acid which is in the range of 0.3 and has an optical density at 340 mμ of 0.3 or less.