JP5173474B2 - Method for producing terephthalic acid - Google Patents

Description

  The present invention relates to a method for producing terephthalic acid by replacing a first dispersion medium of a raw slurry containing a first dispersion medium and terephthalic acid crystals with a second dispersion medium.

  Terephthalic acid is produced by a liquid phase oxidation reaction of a p-phenylene compound typified by p-xylene. In the liquid phase oxidation reaction, acetic acid is usually used as a solvent, and a catalyst obtained by appropriately adding a promoter such as a bromine compound or acetaldehyde to a metal catalyst such as cobalt or manganese is used as a catalyst. However, the reaction product of the liquid phase oxidation reaction contains oxidation reaction intermediates such as 4-carboxybenzaldehyde and p-toluic acid, by-products such as benzoic acid, and various coloring impurities. In order to obtain high-purity terephthalic acid from the crude terephthalic acid obtained by separation from the reaction product while avoiding the contamination of these impurities, a high-level purification technique is required.

As a purification technology of crude terephthalic acid obtained by liquid phase oxidation reaction, crude terephthalic acid is dissolved in water or hydrous acetic acid under high temperature and high pressure, catalytic hydrogenation treatment, decarbonylation treatment, oxidation treatment, recrystallization, Alternatively, a method in which a high temperature immersion treatment is performed in a dispersed state in which a part of terephthalic acid crystals is dissolved is known. In any of these methods, an operation for separating the terephthalic acid crystals from the slurry is necessary in order to remove impurities.
Most of the impurities in the slurry are dissolved in the dispersion medium at a high temperature. However, when the terephthalic acid crystals are separated from the slurry when the slurry is cooled to about 100 ° C., these impurities are contained in the terephthalic acid crystals. It becomes difficult to obtain high-purity terephthalic acid crystals. Therefore, it is necessary to separate the high-purity terephthalic acid from the slurry after the liquid phase oxidation reaction under high temperature and pressure conditions.

  Centrifugation is the most commonly used method for separating terephthalic acid crystals from a slurry, and is also used for slurries after liquid phase oxidation or for purification. Yes. However, there are problems that it is difficult to rinse the crystal during or after centrifugation, and that the amount of dispersion medium attached to the crystal tends to increase.

  On the other hand, as a method for removing the impurities from the terephthalic acid crystal slurry, in recent years, there has been proposed a dispersion medium replacement method using a displacement tower utilizing the precipitation action of terephthalic acid crystals due to gravity (see Patent Document 1). . Furthermore, in order to avoid channeling and backmixing of the fluid in the substitution tower and to increase the substitution efficiency of the dispersion medium, it has been proposed to install a shelf in the substitution tower (see Patent Document 2). However, handling a slurry and providing a shelf in a substitution tower using gravity settling tends to cause accumulation on the shelf, clogging of the opening and bulking, and a great deal of labor is required to stabilize the operation. Therefore, there is room for further improvement in order to increase the replacement efficiency.

  Therefore, the present inventors provided a stirrer at the lower part of the displacement column, and further increased the terephthalic acid content in the slurry in the lower region to be higher than the terephthalic acid content in the slurry in the intermediate region. In the past, a substitution tower having a simple structure that does not require the above and having a high substitution efficiency has been proposed (see Patent Document 3). However, in the substitution tower, (i) a slurry inlet comprising a terephthalic acid crystal and a first dispersion medium, (ii) a second dispersion medium inlet, and (iii) a substitution slurry comprising a terephthalic acid crystal and a second dispersion medium. The flow control is very complicated because there are four outlets, namely, the outlet for extraction and (iv) the outlet for extracting the first dispersion medium, and it is difficult to continue operation stably while maintaining high replacement efficiency. Met. In particular, in the case of a substitution tower having an actual apparatus size with an inner diameter of 1 m or more, it has been more difficult to maintain a high displacement efficiency of the dispersion medium.

  Furthermore, the present inventors have proposed a method for stably operating the displacement tower by controlling the position of the rapid temperature change zone in the vertical temperature distribution in the displacement tower (Patent Document 4). reference.). However, although the operation state is stabilized by using the position of the temperature change zone as an indicator of the operation condition, the current situation is that higher replacement efficiency is desired, and the method is not described.

  It is known that a stirrer in which a stirring shaft passes through the lower wall and extends to the lower portion of the stirring tank is used in an oxidation reactor or a crystallization tank in the production of aromatic carboxylic acid (see Patent Documents 5 and 6). Compared with conventional agitators that have a drive unit at the top of the tank and a stirring shaft that penetrates the top wall of the tank over the entire length of the oxidation reactor and crystallization tank, the structure of the agitator can be simplified and reduced in size. In addition, although the driving power can be reduced and the upper space of the oxidation reactor and the crystallization tank can be effectively used, there is no description about application to a dispersion medium displacement column.

JP-A-55-87744 JP-A-57-53431 JP-A-8-231465 Japanese Patent Laid-Open No. 10-45667 JP 2000-44510 A JP 2002-275122 A

  Accordingly, an object of the present invention is a method for producing high-purity terephthalic acid using a substitution tower having a simple structure that does not require a plate, and maintains the substitution efficiency of the dispersion medium in the slurry extremely high. Then, it is providing the manufacturing method of the terephthalic acid which can make the quality of the obtained terephthalic acid, especially a hue value low, and can continue a driving | operation stably.

  As a result of intensive studies to solve the above-mentioned object, the present inventors can obtain extremely high substitution efficiency and can be easily managed by replacing the dispersion medium with a substitution tower under specific conditions. And reached the present invention.

That is, the present invention provides a method for producing terephthalic acid comprising a substitution step of substituting a dispersion medium of a slurry containing a first dispersion medium and terephthalic acid crystals (hereinafter referred to as a raw slurry) using a substitution tower.
The mixed liquid inside the substitution tower is in the upper region [region above the raw slurry inlet. ], Middle region [region from the raw slurry inlet to the upper surface of the boundary region described later. ], Boundary area [area between the middle area and the lower area described later. ], And lower area [area below the lower surface of the boundary area. And the following conditions (1) to (3)
Condition (1): the inner diameter of the substitution tower is 1 to 7 m,
Condition (2): height _{L A} of the intermediate region is 0.3 to 4 times the internal diameter of the replacement column,
And the height L _B (the height from the lower surface of the boundary region to the stirring blade of the stirring device, or the height from the lower surface of the boundary region to the lower tangential line of the replacement column when the stirring blade is not used) 0.3 to 1.5 times the inner diameter of
Condition (3): the height L of the boundary region is 0.1 to 1 m,
The filling,
The raw slurry is introduced from the lower surface of the upper region of the displacement tower, the second dispersion medium is introduced into the lower region of the displacement tower, and the first dispersion medium is mainly extracted from the upper region of the displacement tower. This is a method for producing terephthalic acid containing the substitution step, wherein an operation of extracting a slurry containing terephthalic acid crystals and a second dispersion medium (hereinafter referred to as substitution slurry) from the lower region is performed according to the following condition (4). .
Condition (4): 15 ≦ X ≦ 500
[In the formula, X represents the amount of change in terephthalic acid content per unit height (% by mass / m) in the boundary region, and is represented by the formula (C _B -C _A ) / L. Such C _A represents the terephthalic acid content (% by mass) at the intermediate position of the intermediate region, C _B represents the terephthalic acid content (% by mass) at the intermediate position of the lower region, and L represents the height of the boundary region ( m). ]

  According to the present invention, impurities are efficiently removed from a slurry of terephthalic acid crystals obtained by a liquid phase oxidation reaction of a p-phenylene compound, a catalytic hydrogenation treatment of crude terephthalic acid, a recrystallization treatment, etc., and a high purity and high quality is obtained. In particular, terephthalic acid having a low hue value can be obtained.

The dispersion medium of the slurry containing the first dispersion medium and terephthalic acid (hereinafter sometimes abbreviated as TA) crystal (hereinafter referred to as the original slurry) according to the present invention is replaced using a substitution tower. The production method of terephthalic acid containing a substitution step is
The mixed liquid inside the substitution tower is in the upper region [region above the raw slurry inlet. ], Middle region [region from the raw slurry inlet to the upper surface of the boundary region described later. ], Boundary area [area between the middle area and the lower area described later. ], And lower region [region from the lower surface of the boundary region to the stirring blade of the stirring device or the lower tangential line of the displacement tower. And the following conditions (1) to (3)
Condition (1): the inner diameter of the substitution tower is 1 to 7 m,
Condition (2): height _{L A} of the intermediate region is 0.3 to 4 times the internal diameter of the replacement column,
And the height L _{B of the} lower region is 0.3 to 1.5 times the inner diameter of the substitution tower,
Condition (3): the height L of the boundary region is 0.1 to 1 m,
The filling,
The raw slurry is introduced from the lower surface of the upper region of the displacement tower, the second dispersion medium is introduced into the lower region of the displacement tower, and the first dispersion medium is mainly extracted from the upper region of the displacement tower. In this TA production method, the operation of extracting a slurry containing TA crystals and a second dispersion medium (hereinafter referred to as a substitution slurry) from the lower region is performed in accordance with the following condition (4).
Condition (4): 15 ≦ X ≦ 500
[In the formula, X represents the amount of change (mass% / m) of TA content per unit height in the boundary region, and is represented by the formula (C _B -C _A ) / L. TA content of such C _A middle position of the intermediate area represents the (mass%), C _B represents TA content in the intermediate position of the lower region (mass%), L is the boundary area height (m) Represents. ]

As the raw slurry, a slurry containing TA crystals obtained by a liquid phase oxidation reaction of a p-phenylene compound can be used.
Hereinafter, the liquid phase oxidation reaction will be briefly described.

  The liquid phase oxidation reaction is, for example, a reaction of a p-phenylene compound using a molecular oxygen-containing gas in the presence of a catalyst comprising at least a heavy metal compound and a bromine compound and hydrous acetic acid having a water concentration of about 1 to 15% by mass. A method is mentioned. Here, the p-phenylene compound is a compound having substituents at the 1-position and 4-position of benzene, and examples of such substituents include alkyl groups such as a methyl group, an ethyl group, a propyl group, and a butyl group. Etc. In particular, p-xylene is preferred as the p-phenylene compound.

  As a heavy metal compound which is one of the catalyst components, at least one of a cobalt compound and a manganese compound is essential, and a nickel compound, a cerium compound, a zirconium compound, etc. may be used together if necessary. . Examples of the cobalt compound, manganese compound, nickel compound, cerium compound, and zirconium compound include organic acid salts, hydroxides, halides, and carbonates of the respective metals. Particularly, acetates and bromides are preferably used. . Specific examples of such heavy metal compounds include cobalt acetate, cobalt hydroxide, cobalt fluoride, cobalt chloride, cobalt bromide, cobalt iodide, cobalt carbonate, manganese acetate, manganese hydroxide, manganese fluoride, manganese chloride, bromide. Manganese, manganese iodide, manganese carbonate, nickel acetate, nickel hydroxide, nickel fluoride, nickel chloride, nickel bromide, nickel iodide, nickel carbonate, cerium acetate, cerium hydroxide, cerium fluoride, cerium chloride, bromide Examples include cerium, cerium iodide, cerium carbonate, zirconium acetate, zirconium hydroxide, zirconium fluoride, zirconium chloride, zirconium bromide, zirconium iodide, and zirconium carbonate.

  The bromine compound, which is one of the catalyst components, may be any compound that dissolves in hydrous acetic acid in the reaction system and generates bromide ions, such as hydrogen bromide, sodium bromide, cobalt bromide, etc. Inorganic bromine compounds, and organic bromine compounds such as bromoacetic acid and tetrabromoethane. Among these, hydrogen bromide, cobalt bromide, and manganese bromide are preferably used, and it is more preferable to use hydrobromic acid in which hydrogen bromide is dissolved in an aqueous solution.

The reaction temperature of the liquid phase oxidation reaction is preferably 160 to 230 ° C, more preferably 180 to 210 ° C. The reaction pressure may be any pressure that allows the reaction system to maintain a liquid phase at the above reaction temperature, and is usually preferably 0.78 to 3.04 MPa, more preferably 0.98 to 1.86 MPa.
Examples of the molecular oxygen-containing gas include air, oxygen diluted with an inert gas, and oxygen-enriched air. Air is usually preferable from the viewpoint of equipment and cost.

  The slurry containing TA crystals obtained by the above method can be used as the raw slurry of the present invention. Further, the crude TA obtained by the liquid phase oxidation reaction is subjected to known catalytic hydrogenation treatment (see, for example, Japanese Patent Publication No. 41-16860), decarbonylation treatment (see, for example, US Pat. No. 3,456,001), oxidation treatment. (See, for example, JP-B-52-46212), recrystallization treatment (see, for example, JP-A-49-102636), high-temperature dipping treatment (see, for example, JP-A-54-90136), and the like. A slurry obtained by performing the purification treatment can also be used as a raw slurry.

  In the present invention, the content of TA in the raw slurry is usually preferably 20 to 45% by mass, and more preferably 30 to 40% by mass. Moreover, it is preferable to introduce | transduce a raw slurry into a substitution tower at 140-240 degreeC, It is more preferable to introduce at 170-210 degreeC, It is further more preferable to introduce at 180-200 degreeC.

Although there is no restriction | limiting in particular as a 1st dispersion medium, Water or a water-containing acetic acid can be used preferably, and it is preferable that the water concentration of a water-containing acetic acid is 1-15 mass%. In particular, when the slurry after the liquid phase oxidation reaction is used as it is as a raw slurry, hydrous acetic acid having a water concentration of about 1 to 15% by mass becomes the first dispersion medium. In this case, the first dispersion medium contains impurities. Specifically, the impurities include oxidation reaction intermediates such as 4-carboxybenzaldehyde and p-toluic acid, by-products such as benzoic acid, and various kinds. Coloring impurities and the like.
On the other hand, the second dispersion medium to be substituted with the first dispersion medium is usually preferably water or hydrous acetic acid, and the water concentration of the hydrous acetic acid is preferably 1 to 15% by mass. For the purpose of the present invention, it is preferable to use a sufficiently purified second dispersion medium. The second dispersion medium is preferably introduced into the substitution tower at 60 to 220 ° C., more preferably 100 to 200 ° C., and still more preferably 140 to 180 ° C. It is preferable that the temperature of the second dispersion medium is lower than the temperature of the raw slurry because the specific gravity of the slurry in the lower region, which will be described later, becomes higher than the specific gravity of the raw slurry, and the present invention tends to be stably implemented.

The upper region of the substitution tower refers to the region above the inlet of the raw slurry and is a liquid phase mainly composed of the first dispersion medium (which may contain the second dispersion medium), which is introduced from the lower surface of the upper region. In this state, the first dispersion medium of the raw slurry remains (TA crystals in the raw slurry settle to an intermediate region and a lower region described later). By extracting the first dispersion medium continuously or intermittently from the upper region, the impurities in the raw slurry are extracted together with the first dispersion medium. In order to efficiently perform the extraction operation of the first dispersion medium, it is preferable that the raw slurry inlet is extended from the top of the tower to below the height of the first dispersion medium extraction port. The ratio between the introduction flow rate of the first dispersion medium in the raw slurry and the extraction flow rate of the first dispersion medium is a mass ratio per unit time. The introduction flow rate of the first dispersion medium in the raw slurry: the extraction flow rate of the first dispersion medium. = 1: 1 to 1: 1.5 is preferable, and 1: 1.01 to 1: 1.2 is more preferable.
The inlet is preferably cylindrical from the viewpoint of the dispersion state of the raw slurry. In addition, from the viewpoint of increasing the contact efficiency between the raw slurry and the second dispersion medium, it is preferable that the opening of the inlet is installed downward. Furthermore, it is preferable to install a dispersion plate (shielding plate) for liquid flow dispersion in front of the opening. By the dispersion plate, the raw slurry is introduced widely and uniformly into the substitution tower, so that the dispersion medium can be replaced more efficiently.

The intermediate region below the inlet of the raw slurry is a region where TA crystals in the raw slurry introduced from the lower surface of the upper region are subjected to gravity and freely settled toward the lower region described later. The temperature in the intermediate region is preferably 70 to 230 ° C, more preferably 100 to 220 ° C, and further preferably 150 to 200 ° C.
The lower region is a region in which the TA crystals that have settled from the intermediate region are mixed with the second dispersion medium to form a uniform dispersion state. The temperature of the lower region is preferably 60 to 220 ° C, more preferably 100 to 200 ° C, and further preferably 150 to 180 ° C.

The lower region of the substitution tower is provided with an inlet for the second dispersion medium, and is also provided with an outlet for removing the substituted slurry that is substituted with the second dispersion medium. Furthermore, when using a stirrer, it is preferable to install near or below the lower tangential line. Since the second dispersion medium does not contain TA crystals and has a low specific gravity, in order to sufficiently mix the second dispersion medium and the replacement slurry, the inlet of the second dispersion medium should be installed below the lower region. Is preferred. Further, since the substitution slurry has a high specific gravity, the substitution slurry outlet is preferably located below the lower region, and is preferably located as far as possible from the introduction port of the second dispersion medium.
The ratio of the introduction flow rate of the second dispersion medium and the extraction flow rate of the second dispersion medium in the replacement slurry is a mass ratio per unit time, and the introduction flow rate of the second dispersion medium: the second dispersion medium in the replacement slurry. It is preferable to set the extraction flow rate of 1: 1 to 1.5: 1 as a guide, and more preferable to set 1.0: 1 to 1.2: 1 as a guide.

The lower region is stirred by the stirring device, and the introduction flow rate of the second dispersion medium and the removal flow rate of the replacement slurry are adjusted, and the TA content (C _B ) in the lower region [measured at an intermediate position of the lower region. ] TA content (C _A ) in the intermediate region [measured at an intermediate position in the intermediate region. ], The boundary region is formed between the intermediate region and the lower region. Here, _{C A} is preferably usually 1 to 40 wt%, more preferably 3 to 20 mass%. C _B is C _A or more, preferably 6 to 51% by mass, and more preferably 10 to 45% by mass. The presence of such a boundary region makes it difficult for the first dispersion medium to mix with the second dispersion medium beyond the boundary region, and as a result, high replacement efficiency can be maintained. In order to obtain a high substitution efficiency, it is preferable that the TA content in the lower region is 5% by mass or more higher than the TA content in the intermediate region. Further, the position of the boundary region can be increased by increasing the introduction flow rate of the second dispersion medium or decreasing the extraction flow rate of the replacement slurry. By adjusting the position of the boundary region to a certain height or higher, the replacement efficiency can be maintained and improved.

  The stirring device is not particularly limited as long as it is a device that substantially uniformizes the inside of the lower region. Even with various types of stirrers with stirring blades, an external circulation device that generates a mixed flow in the lower region may be used. Examples of the stirring blade include a propeller blade, a turbine blade, a paddle blade, a disk turbine blade, and an inclined paddle blade. In the case of using an external circulation device, a circulation pipe is installed outside the displacement column, the internal liquid in the lower region is extracted, and returned to the lower region through the circulation pump. It is also preferable that a stirring device with a stirring blade be interposed in the middle of this external circulation. It is also preferable to put a baffle in the lower part of the substitution tower to assist stirring. In a stirrer having a stirring blade, it is not necessary to stir the entire tank as in an oxidation reactor or a crystallization tank. No need for strong stirring power because it only stirs.

  In the present invention, the action of replacing the first dispersion medium of the raw slurry with the second dispersion medium appears in the boundary region. In order to obtain higher and more stable replacement efficiency, it is necessary to form the boundary region stably. From this point of view, when the stirring device is a stirrer equipped with stirring blades, for example, it is not preferable that the stirring shaft supporting the stirring blades extends from the upper part of the substitution tower to the lower region through the boundary region. When the stirring shaft exists in the boundary region in this way, the boundary region becomes discontinuous, and the influence of the rotation of the stirring shaft, the vibration of the stirring shaft, the influence of heat transfer through the stirring shaft, the influence of the stirring shaft as a wall, Since the boundary region is disturbed due to the influence of the TA crystal adhering to the stirring shaft, it becomes difficult to stabilize the boundary region. Therefore, it is preferable to stir with a stirrer installed below the displacement tower and not use the boundary region, or to use an external circulation device.

  Making a temperature difference between the middle region and the lower region is also effective in forming the boundary region. This is because the specific gravity of acetic acid or water, which is a dispersion medium, becomes smaller as the temperature is higher. If the temperature in the middle region is higher than that in the lower region, the movement of the dispersion medium in the boundary region is reduced and the boundary region is stabilized. To do. Therefore, the temperature of the intermediate region is preferably 3 ° C. or higher, more preferably 5 ° C. or higher, and more preferably 10 ° C. or higher than the temperature of the lower region. The temperature of the intermediate region is determined by the heat input of the raw slurry and the amount of heat input corresponding to the rising flow rate of the second dispersion medium, and the temperature of the lower region is determined by the heat input of the second dispersion medium and the amount of heat of the TA crystal that settles in the substitution tower. Determined.

  The TA content of the replacement slurry can be controlled by adjusting the introduction flow rate of the second dispersion medium and the extraction flow rate of the replacement slurry. The adjustment of these flow rates is important for stable operation, and the adjustment of the second dispersion medium introduction flow rate and the displacement slurry extraction flow rate is a relative relationship between the TA content in the lower region and the TA content in the intermediate region. As a result, it relates to the replacement efficiency of the dispersion medium and the difficulty of handling the replacement slurry. The TA content in the intermediate region is determined by the amount of TA crystals processed in the substitution tower. The amount of TA crystal treated is obtained by dividing the amount of TA crystal introduced as a raw slurry into the substitution tower by the cross-sectional area of the intermediate region of the substitution tower. In addition, the TA content in the lower region is arbitrarily set within a range where it can exist as a slurry having a uniform content by stirring with a stirrer installed in the lower part of the substitution tower, the second dispersion medium introduction flow rate, and the removal flow rate of the substitution slurry. it can.

The substitution tower used in the present invention is an apparatus used for commercial scale TA production, and its inner diameter is in the range of 1 to 7 m [Condition (1)]. Since the processing capacity of the substitution tower is mainly determined by the amount of TA crystal processing per unit cross-sectional area, the inner diameter of the substitution tower may be determined according to the production capacity of the TA production facility. If an attempt is made to process a TA crystal that exceeds the processing capacity, free precipitation of the TA crystal in the intermediate region is hindered, and the replacement efficiency decreases.
The shape of the replacement tower is preferably a cylinder, and the upper mirror part and the lower mirror part can be exemplified by a spherical shape, an elliptical shape, a conical shape, etc. Especially, the lower mirror part is an ellipse that tends to make the lower region uniformly dispersed. The shape is preferred. Since the substitution tower used in the present invention does not require a shelf or the like, there is no risk of TA crystal deposition or blockage. However, in the present invention, the installation of the shelf is not necessarily denied.
In addition, the operation temperature of a substitution tower should just be the temperature below the boiling point of each dispersion medium under operation pressure.

The height L _A (m) of the intermediate region of the substitution tower means a distance from the introduction position of the original slurry (position of the introduction port of the original slurry) to the upper surface of the boundary area.
In order to stabilize the boundary region, it is necessary to maintain a distance at which the TA crystal introduced into the displacement column can freely settle. Therefore, the height L _A (m) needs to be in the range of 0.3 to 4 times the inner diameter of the displacement column [Condition (2)], preferably 0.5 to 2.2 times the inner diameter of the displacement column. Is double. If L _A (m) is less than 0.3 times the inner diameter of the substitution tower, TA crystals cannot be freely settled, and the boundary region is disturbed by the momentum of the raw slurry that jumps out from the inlet of the raw slurry, and the substitution efficiency is high. It tends to decrease. On the other hand, if L _A (m) exceeds 4 times the inner diameter of the substitution tower, the substitution tower becomes very large, making it difficult to make an actual apparatus.

In the present invention, as described above, the height L _B (m) corresponds to the distance from the lower surface of the boundary region to the stirring blade of the stirring device, or when the stirring blade is not used, such as when using an external circulation device. This corresponds to the distance from the lower surface of the boundary region to the lower tangential line of the replacement tower. The lower tangential line refers to the boundary line between the straight body portion and the lower mirror portion of the replacement tower.
In order to stabilize the boundary region, it is necessary to maintain the state in which the TA crystal is uniformly dispersed in the lower region having a high TA content, while keeping the boundary region from shaking and undulating.
Therefore, the height L _B (m) needs to be in the range of 0.3 to 1.5 times the inner diameter of the replacement column [Condition (2)], preferably 0.5 to 1 of the inner diameter of the replacement column. Double the range. When the height L _B (m) is less than 0.3 times the inner diameter of the substitution tower, when a stirring blade is used, the discharge flow or the swirling flow from the stirring blade affects the boundary region and the boundary Since the region is disturbed, the replacement efficiency is lowered. In addition, when an external circulation device is used, it is necessary to lower the return position of the circulation line, and the discharge flow circulated from the circulation line return port adversely affects the extraction of the replacement slurry. The TA content cannot be kept uniform, and as a result, the replacement efficiency decreases. On the other hand, when the height L _B (m) exceeds 1.5 times the inner diameter of the displacement column, the stirring efficiency in the lower region is reduced, and TA crystals in the lower region are dispersed unevenly. Replacement efficiency decreases. Further, when an external circulation device is used, the displacement tower becomes very large, and it becomes difficult to make an actual device, which is not preferable.

In the present invention, a boundary region is generated between the intermediate region and the lower region in the mixed liquid inside the substitution tower. The position of the boundary region is determined by the introduction flow rate and TA content of the raw slurry, the introduction flow rate of the second dispersion medium, the withdrawal flow rate of the replacement slurry, and the TA content.
The height L of the boundary region is determined by the inner diameter of the substitution tower, the difference in TA content between the middle region and the lower region, the temperature difference between the middle region and the lower region, the grain size of the TA crystal, and the like. In order to obtain high replacement efficiency, it is necessary to set the above conditions appropriately so that the height L of the boundary region is in the range of 0.1 to 1 m [Condition (3)].

In the present invention, in order to make the replacement efficiency extremely high, it is necessary that the change amount X (mass% / m) of the TA content per unit height in the boundary region satisfies the following condition (4).
Condition (4): 15 ≦ X ≦ 500
[Wherein, X is represented by the formula (C _B -C _A ) / L. Such C _A , C _B and L are as described above. ]

X means how much the TA content in the intermediate region and the TA content in the lower region are changed across the boundary region. When X is less than 15, extremely high substitution efficiency cannot be obtained. The minimum value of L is 0.1, and considering the preferable ranges of C _A and C _B , the maximum value of the difference (C _B -C _A ) is 50. The realistic value was 500.
X is preferably in the range of 16 to 500, more preferably in the range of 30 to 400, and even more preferably in the range of 30 to 200. By adjusting the introduction flow rate of the second dispersion medium and the extraction flow rate of the replacement slurry, the change amount X can be maintained in the above range.

  In the substitution tower of the present invention, it is preferable to provide a weak flow of the second dispersion medium from the bottom to the top of the substitution tower. This is to prevent the first dispersion medium from diffusing into the lower region of the substitution tower. The velocity of the flow from the bottom to the top of the second dispersion medium is indicated by “rising linear velocity (empty standard)” obtained by dividing the rising flow rate of the second dispersion medium by the cross-sectional area of the displacement tower. The ascending linear velocity is preferably 0.01 to 1.2 m / h, more preferably 0.3 to 1.2 m / h, and further preferably 0.6 to 1 m / h. .

  Hereinafter, an example of an apparatus and a dispersion medium replacement method used in the present invention will be briefly described with reference to FIGS. The raw slurry is a slurry containing terephthalic acid crystals obtained by liquid phase oxidation reaction of a p-phenylene compound or purification treatment of crude terephthalic acid.

See Figure 1:
From the raw slurry tank 8, the raw slurry is introduced into the displacement tower 1 via the raw slurry introduction port 3 by the raw slurry feed pump 12. At this time, the raw slurry is dispersed in the substitution tower by the dispersion plate 4 positioned at the tip of the raw slurry introduction port 3.
Of the dispersed raw slurry, the TA crystals generally settle down below the substitution tower 1, and the first dispersion medium and fine TA crystal particles are extracted from the first dispersion medium outlet 5 and the first dispersion medium is extracted. It overflows into a tank (overflow dispersion medium tank) 9.
See Figure 2:
The dispersed TA crystal settles freely in the intermediate region 23, sinks to the lower region 24, and is stirred by the stirring device 13 installed near the lower tangential line of the substitution tower. As a result, the lower region 24 has a uniform TA content and a higher TA content than the intermediate region 23.
See Figure 1:
The second dispersion medium is introduced from the second dispersion medium tank 11 via the second dispersion medium feed pump 14 and from the second dispersion medium inlet 6 on the lower side surface of the substitution tower. Further, the slurry in the lower region is extracted from the replacement slurry extraction port 7, and the extracted replacement slurry is sent to the replacement slurry tank 10.
See Figure 2:
When performing the above operations, the boundary region 25 appears between the intermediate region 23 and the lower region 24. This boundary region has an upper surface 26 in contact with the intermediate region 23 and a lower end surface 27 in contact with the lower region 24, and has a certain range of height L.

See Figure 3:
When an external circulation device is used, the replacement slurry extracted from the replacement slurry extraction port 7 is circulated by the agitation pump 28 and returned to the lower region from the return port 29 of the circulation line. Thereby, the TA content in the lower region 24 is uniform, and the TA content is higher than that in the intermediate region 23. A part of the circulating replacement slurry is extracted and sent to the replacement slurry tank 10.

EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited at all by these examples. In addition, the substitution rate of the dispersion medium determined in the following examples is the amount of benzoic acid contained as a by-product in the raw slurry dispersion medium, in the dispersion medium that has been substituted and overflowed from the first dispersion medium outlet 5. Is the amount of benzoic acid contained in.
Moreover, the hue value (OD ₃₄₀ ) of terephthalic acid was measured as follows.
<Measuring method of hue value (OD ₃₄₀ ) of terephthalic acid>
Hue values were measured using a spectrophotometer with the following specifications.
Model: Spectrophotometer U-3010 (manufactured by Hitachi High-Technologies Corporation)
Wavelength: 340nm
Cell: Quartz, optical path length 50mm
Measurement method: Using 3.2 g of TA crystal as a sample, dissolve in 40 ml of 2 mol / L potassium hydroxide aqueous solution, put the resulting solution in a cell, and measure the absorbance at 340 nm. However, if there is a precipitate when the sample is dissolved, it is precipitated by centrifugation, and the supernatant is put into a cell and the absorbance is measured.

(Production Example 1)
In hydrous acetic acid, p-xylene was subjected to a liquid phase oxidation reaction (reaction temperature 200 ° C., reaction pressure 16 atm) with air in the presence of a catalyst composed of cobalt, manganese and bromine to obtain a crude TA slurry (TA content 34 mass%, Water concentration of 11% by mass of hydrous acetic acid as the first dispersion medium), and the obtained crude TA slurry was led to a crystallization tank connected in series and released in order, cooled to 190 ° C. and then the raw slurry The tank 8 was supplied.

Example 1
A titanium cylindrical tower having an inner diameter of 1.5 m and having a long structure in the vertical direction was used as the replacement tower 1 using the equipment shown in FIG.
Water as the second dispersion medium was introduced into the lower region of the substitution tower using the second dispersion medium feed pump 14. In the middle, the heat exchanger 15 heated to 160 ° C. The substitution tower 1 was filled, water was overflowed from the first dispersion medium outlet 5, and at the same time, the stirring device 13 was operated.
Next, introduction of the raw slurry produced in Production Example 1 was started using the raw slurry feed pump 12. At this time, the raw slurry was heated to 190 ° C. by the heat exchanger 17 and then introduced into the substitution tower 1. After confirming that the lower region 24 having a high TA content was formed below the substitution tower 1, extraction of the substitution slurry was started.

Each introduction flow rate and withdrawal flow rate were as follows.
Introduction flow rate of raw slurry: 13.90 t / h
Introduction flow rate of second dispersion medium: 9.93 t / h
Extraction flow rate of the first dispersion medium: 10.40 t / h
Removal flow rate of displacement slurry: 13.42 t / h

At this time, the TA content of the raw slurry is 34.1% by mass, the TA content of the replacement slurry is 33.6% by mass, and the rising linear velocity of the dispersion medium inside the replacement column is 0.63 m / h. there were.
Was confirmed by the results of the sampling in the vertical direction temperature distribution and replacement tower fluid in the substitution tower, the height L _A of the intermediate region is 3m, the height L _B from the lower surface of the boundary region to the stirring blade of the stirrer Was 0.9 m, and the height L of the boundary region was 0.3 m. Moreover, the TA content _{C A} of the intermediate region is 7.9 wt%, the temperature is from 169 to 185 ° C. (intermediate position: 180 ° C.) are, TA content of the lower region _{C B} 33.6 wt% The temperature was 163 ° C. The difference (C _B -C _A ) was 25.7 (mass%), and the change amount X (mass% / m) in the boundary region was 86.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. The replacement slurry is sent to a solid-liquid separation process using a centrifuge, a rotary vacuum filter, etc. through a crystallization process, separated into a TA wet cake and a mother liquor, and the wet cake is dried to obtain TA crystals. Thereafter, the hue value was measured. The results are shown in Table 1.

<Table 1>
Elapsed time (h) Replacement rate (%) Hue value
4 95.6
6 95.8
8 95.9
10 95.7 1.20

(Example 2)
In Example 1, the experiment was performed in the same manner as in Example 1 except that each introduction flow rate and extraction flow rate were changed as follows.
Introduction flow rate of raw slurry: 14.19 t / h
Introduction flow rate of second dispersion medium: 6.58 t / h
Extraction flow rate of the first dispersion medium: 10.71 t / h
Extraction flow rate of displacement slurry: 10.06 t / h

At this time, the TA content of the raw slurry is 33.5% by mass, the TA content of the substitution slurry is 45.0% by mass, and the rising linear velocity of the dispersion medium inside the substitution column is 0.66 m / h. there were.
Was confirmed by the results of the sampling in the vertical direction temperature distribution and replacement tower fluid in the substitution tower, the height L _A of the intermediate region is 3m, the height L _B from the lower surface of the boundary region to the stirring blade of the stirrer Was 0.9 m, and the height L of the boundary region was 0.25 m. Also, a TA content _{C A} 7.8 wt% of the intermediate region, the temperature is 173 to 185 ° C. (intermediate position: 181 ° C.) a and, TA content of the lower region _{C B} 45.0 wt% The temperature was 165 ° C. The difference (C _B -C _A ) was 37.2 (mass%), and the change amount X (mass% / m) in the boundary region was 149.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 2.

<Table 2>
Elapsed time (h) Replacement rate (%) Hue value
4 98.3
6 98.0
8 98.2
10 98.1 1.08

(Example 3)
In Example 1, the experiment was performed in the same manner as in Example 1 except that each introduction flow rate and extraction flow rate were changed as follows.
Introduction flow rate of raw slurry: 14.00 t / h
Introduction flow rate of second dispersion medium: 20.91 t / h
Extraction flow rate of the first dispersion medium: 10.49 t / h
Removal flow rate of displacement slurry: 24.42 t / h

At this time, the TA content of the raw slurry is 34.0% by mass, the TA content of the replacement slurry is 18.6% by mass, and the rising linear velocity of the dispersion medium inside the replacement column is 0.64 m / h. there were.
Was confirmed by the results of the sampling in the vertical direction temperature distribution and replacement tower fluid in the substitution tower, the height L _A of the intermediate region is 3m, the height L _B from the lower surface of the boundary region to the stirring blade of the stirrer Was 0.9 m, and the height L of the boundary region was 0.3 m. Also, a TA content _{C A} 8.0 wt% of the intermediate region, the temperature is one hundred and sixty-four to one hundred and eighty-five ° C. (intermediate position: 179 ° C.) a and, TA content of the lower region _{C B} 18.6 wt% The temperature was 161 ° C. The difference (C _B -C _A ) was 10.6 (mass%), and the change amount X (mass% / m) in the boundary region was 35.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 3.

<Table 3>
Elapsed time (h) Replacement rate (%) Hue value
4 94.6
6 94.9
8 94.7
10 94.8 1.31

Example 4
In Example 1, the experiment was performed in the same manner as in Example 1 except that each introduction flow rate and extraction flow rate were changed as follows.
Introduction flow rate of raw slurry: 13.98 t / h
Introduction flow rate of second dispersion medium: 28.23 t / h
Extraction flow rate of the first dispersion medium: 10.49 t / h
Extraction flow rate of displacement slurry: 31.72 t / h

At this time, the TA content of the raw slurry is 33.8% by mass, the TA content of the replacement slurry is 14.2% by mass, and the rising linear velocity of the dispersion medium inside the replacement column is 0.63 m / h. there were.
Was confirmed by the results of the sampling in the vertical direction temperature distribution and replacement tower fluid in the substitution tower, the height L _A of the intermediate region is 3m, the height L _B from the lower surface of the boundary region to the stirring blade of the stirrer Was 0.9 m, and the height L of the boundary region was 0.35 m. Also, a TA content _{C A} 8.0 wt% of the intermediate region, the temperature is one hundred and sixty-four to one hundred and eighty-five ° C. (intermediate position: 179 ° C.) a and, TA content of the lower region _{C B} 14.2 wt% The temperature was 161 ° C. The difference (C _B -C _A ) was 6.2 (mass%), and the amount of change X (mass% / m) in the boundary region was 18.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 4.

<Table 4>
Elapsed time (h) Replacement rate (%) Hue value
4 93.6
6 93.4
8 93.7
10 93.8 1.42

(Comparative Example 1)
In Example 1, the experiment was performed in the same manner as in Example 1 except that each introduction flow rate and extraction flow rate were changed as follows.
Introduction flow rate of raw slurry: 14.04 t / h
Introduction flow rate of second dispersion medium: 32.18 t / h
Extraction flow rate of the first dispersion medium: 10.53 t / h
Removal flow rate of displacement slurry: 35.68 t / h

At this time, the TA content of the raw slurry is 33.7% by mass, the TA content of the replacement slurry is 12.6% by mass, and the rising linear velocity of the dispersion medium inside the replacement column is 0.63 m / h. there were.
Was confirmed by the results of the sampling in the vertical direction temperature distribution and replacement tower fluid in the substitution tower, the height L _A of the intermediate region is 3m, the height L _B from the lower surface of the boundary region to the stirring blade of the stirrer Was 0.9 m, and the height L of the boundary region was 0.35 m. Also, a TA content _{C A} 7.9 wt% of the intermediate region, the temperature is 161-185 ° C. (intermediate position: 177 ° C.) a and, TA content of the lower region _{C B} 12.6 wt% The temperature was 160 ° C. The difference (C _B -C _A ) was 4.7 (mass%), and the amount of change X (mass% / m) in the boundary region was 13.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 5.

<Table 5>
Elapsed time (h) Replacement rate (%) Hue value
4 90.8
6 90.1
8 89.9
10 90.4 1.75

(Production Example 2)
A crude TA slurry obtained by subjecting p-xylene to a liquid phase oxidation reaction with air (reaction temperature 200 ° C., reaction pressure 16 atm) in water-containing acetic acid in the presence of a catalyst composed of cobalt, manganese and bromine was crystallized, and solidified. Liquid TA is separated and dried to obtain crude TA crystals. The obtained crude TA crystals are heated and dissolved in an aqueous solvent to perform a catalytic hydrogenation reaction, and the raw slurry thus obtained is connected to a crystallization tank connected in series. Then, the pressure was released successively, cooled to 160 ° C., and supplied to the raw slurry tank 8.

(Example 5)
Using the equipment shown in FIG. 1, a cylindrical column made of SUS316 having an inner diameter of 5 m and having a long structure in the vertical direction was used as the replacement column 1.
Water as the second dispersion medium was introduced into the lower region of the substitution tower using the second dispersion medium feed pump 14. In the middle, the heat exchanger 15 heated to 100 ° C. The substitution tower 1 was filled, water was overflowed from the first dispersion medium outlet 5, and the stirring device 13 was started at the same time. Next, introduction of the raw slurry was started using the raw slurry feed pump 12. At this time, the raw slurry was heated to 160 ° C. by the heat exchanger 17 and then introduced into the substitution tower 1. After confirming that the lower region 24 having a high TA content was formed below the substitution tower 1, extraction of the substitution slurry was started.

Each introduction flow rate and withdrawal flow rate were as follows.
Introduction flow rate of raw slurry: 109.9 t / h
Introduction flow rate of second dispersion medium: 80.6 t / h
Extraction flow rate of first dispersion medium: 79.4 t / h
Removal flow rate of displacement slurry: 111.0 t / h

At this time, the TA content of the raw slurry is 32.7% by mass, the TA content of the replacement slurry is 32.1% by mass, and the rising linear velocity of the dispersion medium inside the replacement column is 0.39 m / h. there were.
Was confirmed by the results of sampling of the temperature distribution and replacement tower fluid in the vertical direction in the substitution tower, the height of the height L _A of the intermediate region 5.3 m, from the lower surface of the boundary region to the stirring blade of the stirrer L _B is 2.5 m, the height L of the boundary region was 0.7 m. Moreover, the TA content _{C A} of the intermediate region is 8.0 wt%, the temperature is from 105 to 155 ° C. (intermediate position: 0.99 ° C.) are, TA content of the lower region _{C B} 32.1 wt% And the temperature was 103 ° C. The difference (C _B -C _A ) was 24.1 (mass%), and the amount of change X (mass% / m) in the boundary region was 34.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 6.

<Table 6>
Elapsed time (h) Replacement rate (%) Hue value
4 96.3
6 96.7
8 96.4
10 96.5 0.125

(Comparative Example 2)
In Example 5, the experiment was performed in the same manner as in Example 5 except that the introduction flow rate and the extraction flow rate were changed as follows.
Introduction flow rate of raw slurry: 110.0 t / h
Introduction flow rate of second dispersion medium: 130.3 t / h
Extraction flow rate of first dispersion medium: 79.6 t / h
Removal flow rate of displacement slurry: 160.7 t / h

At this time, the TA content of the raw slurry is 32.7% by mass, the TA content of the substitution slurry is 22.2% by mass, and the rising linear velocity of the dispersion medium inside the substitution column is 0.40 m / h. there were.
Was confirmed by the results of sampling of the temperature distribution and replacement tower fluid in the vertical direction in the substitution tower, the height of the height L _A of the intermediate region 5.2 m, from the lower surface of the boundary region to the stirring blade of the stirrer L _B is 2.3 m, the height L of the boundary region was 1.0 m. Also, a TA content _{C A} 8.0 wt% of the intermediate region, the temperature is 103-155 ° C. (intermediate position: 148 ° C.) a and, TA content of the lower region _{C B} 22.2 wt% And the temperature was 102 ° C. The difference (C _B -C _A ) was 14.2 (mass%), and the amount of change X (mass% / m) in the boundary region was 14.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 7.

<Table 7>
Elapsed time (h) Replacement rate (%) Hue value
4 91.5
6 90.9
8 91.6
10 91.1 0.139

(Example 6)
Using the equipment shown in FIG. 4, the raw slurry inlet is changed to a dispersion ring 30 provided with a plurality of slurry inlets, the stirring shaft extends from the upper part of the tower to the lower part of the tower, and each introduction flow rate. The experiment was performed in the same manner as in Example 1 except that the extraction flow rate was changed as follows.
Introduction flow rate of raw slurry: 13.89 t / h
Introduction flow rate of second dispersion medium: 9.89 t / h
Extraction flow rate of the first dispersion medium: 10.39 t / h
Removal flow rate of displacement slurry: 13.39 t / h

At this time, the TA content of the raw slurry is 33.9% by mass, the TA content of the replacement slurry is 33.5% by mass, and the rising linear velocity of the dispersion medium inside the replacement tower is 0.62 m / h. there were.
Was confirmed by the results of sampling of the temperature distribution and replacement tower fluid in the vertical direction in the substitution tower, the height of the height L _A is 3m middle region, from the lower surface of the boundary region to the lower tangential line of the replacement column L _B is 0.9 m, the height L of the boundary region was 0.3 m. Also, a TA content _{C A} 7.8 wt% of the intermediate region, the temperature is from 169 to 185 ° C. (intermediate position: 179 ° C.) a and, TA content of the lower region _{C B} 33.5 wt% The temperature was 163 ° C. The difference (C _B -C _A ) was 25.7 (mass%), and the change amount X (mass% / m) in the boundary region was 86.

  Run for 10 hours, analyze the concentration of benzoic acid in the dispersion medium of the raw slurry introduced into the substitution tower 1 and the concentration of benzoic acid in the dispersion medium in the first dispersion medium tank (overflow dispersion medium tank) 9 The substitution rate of the medium was determined. After obtaining TA crystals in the same manner as in Example 1, the hue value was measured. The results are shown in Table 8.

<Table 8>
Elapsed time (h) Replacement rate (%) Hue value
4 93.5
6 93.2
8 93.4
10 93.8 1.44

  From Tables 1-4, 6, and 8, when the method of the present invention is followed, the first dispersion medium can be replaced with the second dispersion medium with high substitution efficiency, and therefore the terephthalic acid crystals finally obtained are also high. The purity was low, the hue value was low, and yellowing of terephthalic acid could be suppressed. On the other hand, it can be seen from Table 5 that when the TA content change rate X (mass% / m) in the boundary region is less than 15, the substitution rate decreases and the hue value increases. Also, in Table 7, it can be seen that the substitution rate decreases and the hue value increases as compared with Table 6.

An example of the substitution tower in this invention. An example of the positional relationship of the upper area | region in a displacement tower, an intermediate | middle part area | region, a boundary area | region, a lower area | region, and a stirring apparatus. It is an example of the substitution tower whose stirring is an external circulation system, and is an example of the positional relationship between the lower end face of the boundary region and the lower tangential line. An example of the substitution tower in which the stirring shaft of the stirring device is in contact with the boundary region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Replacement tower 2 ... Original slurry receiving port 3 ... Original slurry introduction port 4 ... Dispersion plate 5 ... First dispersion medium removal port 6 ... Second Dispersion medium introduction port 7 ... Replacement slurry extraction port 8 ... Original slurry tank 9 ... First dispersion medium tank (overflow dispersion medium tank)
DESCRIPTION OF SYMBOLS 10 ... Replacement slurry tank 11 ... Second dispersion medium tank 12 ... Raw slurry liquid feed pump 13 ... Stirrer 14 ... Second dispersion medium liquid feed pump 15 ... Heat exchanger 16 ... On-line density meter 17 ... Heat exchanger 18 ... Upper region 19 ... Intermediate region 20 ... Lower region 21 ... Intermediate position 22 of boundary region ... Upper region 23 ... Intermediate region 24 ... lower region 25 ... boundary region 26 ... upper surface 27 of boundary region ... lower surface 28 of boundary region ... stirring pump 29 ... circulation line return port 30 ... Raw slurry inlet (dispersing ring)
D ··· Inner diameter L of displacement column _A ··· Height L of intermediate region ··· Height L of boundary region _B ··· Height from bottom surface of boundary region to stirring blade of stirring device Or the height from the lower surface of the boundary area to the lower tangential line of the displacement tower when no stirring blade is used

Claims (7)

In the method for producing terephthalic acid comprising a substitution step of substituting the dispersion medium of the slurry containing the first dispersion medium and terephthalic acid crystals (hereinafter referred to as the original slurry) using a substitution tower,
The mixed liquid inside the substitution tower is in the upper region [region above the raw slurry inlet. ], Middle region [region from the raw slurry inlet to the upper surface of the boundary region described later. ], Boundary area [area between the middle area and the lower area described later. ], And lower area [area below the lower surface of the boundary area. And the following conditions (1) to (3)
Condition (1): the inner diameter of the substitution tower is 1 to 7 m,
Condition (2): The height L _A of the intermediate region is 0.3 to 4 times the inner diameter of the displacement column, and the height L _B (the height from the lower surface of the boundary region to the stirring blade of the stirring device, or the stirring blade) Is used, the height from the lower surface of the boundary region to the lower tangential line of the displacement tower is 0.3 to 1.5 times the inner diameter of the displacement tower,
Condition (3): the height L of the boundary region is 0.1 to 1 m,
The filling,
The raw slurry is introduced from the lower surface of the upper region of the displacement tower, the second dispersion medium is introduced into the lower region of the displacement tower, and the first dispersion medium is mainly extracted from the upper region of the displacement tower. Including the substitution step, wherein the operation of extracting a slurry containing terephthalic acid crystals and a second dispersion medium (hereinafter referred to as substitution slurry) from the lower region is performed according to the following condition (4) ;
The ratio of the introduction flow rate of the first dispersion medium and the extraction flow rate of the first dispersion medium in the raw slurry is a mass ratio per unit time of 1: 1.01 to 1: 1.2,
Production of terephthalic acid in which the ratio of the introduction flow rate of the second dispersion medium and the extraction flow rate of the second dispersion medium in the substitution slurry is 1.01: 1 to 1.2: 1 in mass ratio per unit time. Method.
Condition (4): 15 ≦ X ≦ 500
[In the formula, X represents the amount of change in terephthalic acid content per unit height (% by mass / m) in the boundary region, and is represented by the formula (C _B -C _A ) / L. Such C _A represents terephthalic acid content in the intermediate position of the intermediate region (mass%), C _B represents a terephthalic acid content in the intermediate position of the lower region (wt%), L is the boundary area height ( m). ]   The method for producing terephthalic acid according to claim 1, wherein the introduction temperature of the raw slurry is 140 to 240 ° C.   The method for producing terephthalic acid according to claim 1 or 2, wherein the first dispersion medium is water or hydrous acetic acid, and the second dispersion medium is water or hydrous acetic acid.   The method for producing terephthalic acid according to claim 1 or 2, wherein the first dispersion medium is hydrous acetic acid and the second dispersion medium is water.   The manufacturing method of the terephthalic acid of any one of Claims 1-4 whose temperature of the intermediate position of an intermediate part area | region is 3 degreeC or more higher than the temperature of the intermediate position of a lower area | region.   The method for producing terephthalic acid according to any one of claims 1 to 5, wherein the lower region is stirred using a stirring device and / or an external circulation device.   The method for producing terephthalic acid according to claim 6, wherein the lower region is stirred using a stirring device installed so as not to contact the boundary region at all.

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