JPH08231465A - Production of high-purity terephthalic acid - Google Patents

Abstract

PURPOSE: To provide a method for finally producing high-purity terephthalic acid, not installing a plate, etc., in a dispersion medium substitution column, subjecting a raw slurry consisting essentially of terephthalic acid crystal and a raw dispersion medium (a dispersion medium for liquid-phase oxidation reaction or a dispersion medium for purification treatment after the reaction) to dispersion medium substitution while pouring a dispersion medium for substitution from the lower part of the bottom of the column. CONSTITUTION: A raw slurry consisting essentially of terephthalic acid crystal particles obtained by liquid-phase oxidation or purification treatment after the liquid-phase oxidation and a raw dispersion medium is fed from the upper part of a dispersion medium substitution column and a dispersion medium for substitution is supplied from the lower part of the column, the solution at the lower part of the column is stirred into a scurried state uniformly as much as possible, the flow rate in supply of the dispersion medium for substitution and that in taking out the substituted slurry are regulated, both the solutions are brought into contact with each other in a liquid-liquid state while maintaining a slurry state in a concentration higher than that in the middle part of the column. The prepared substituted slurry is taken out from the bottom of the column, the liquid at the middle part of the dispersion medium substitution column is divided into plural flows in parallel or not divided to provide a method for producing high-purity terephthalic acid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for substituting a raw dispersion medium of a raw slurry to produce high-purity terephthalic acid. More specifically, it is a crude terephthalic acid slurry obtained by a liquid phase oxidation reaction, or a slurry obtained by subjecting crude terephthalic acid to catalytic hydrogenation or recrystallization treatment, wherein terephthalic acid crystal particles and an original dispersion medium are used. The present invention relates to a method for producing high-purity terephthalic acid by a dispersion medium replacement method capable of efficiently replacing the original dispersion medium of a raw slurry containing a large amount of impurities with another dispersion medium for substitution.

[0002]

2. Description of the Prior Art Terephthalic acid is produced by a liquid phase oxidation reaction of a p-phenylene compound such as p-alkylbenzene represented by p-xylene. Usually, acetic acid is used as a solvent and a catalyst such as cobalt or manganese is used. Alternatively, a catalyst obtained by adding a bromine compound or a promoter such as acetaldehyde thereto is used. However, this reaction product uses acetic acid as a solvent as described above, and the crude terephthalic acid slurry obtained by the liquid phase oxidation reaction contains 4-carboxybenzaldehyde (4CBA), paratoluic acid (p-TOL), benzoic acid, or the like, or In addition, since various coloring impurities are contained in a large amount, these impurities are also mixed in the crude terephthalic acid obtained by separating from the slurry, which is considerably high to obtain high-purity terephthalic acid. Requires purification technology.

As a method for purifying crude terephthalic acid,
A slurry in which crude terephthalic acid is dissolved in acetic acid, water, or a mixed solvent thereof at high temperature and high pressure, and catalytic hydrogenation treatment, decarbonylation treatment, oxidation treatment, recrystallization treatment, or terephthalic acid crystal is partially dissolved. Various methods such as high temperature immersion treatment in the state are known. In either case of production of crude terephthalic acid by liquid phase oxidation reaction or purification thereof, an operation of finally separating the terephthalic acid crystal from the dispersion medium is required.

However, most of the oxide intermediates such as 4CBA, p-TOL, benzoic acid, etc., or the coloring-causing substances, which are present as impurities in the oxidation reaction product slurry or the slurry obtained by purifying the crude terephthalic acid, are high in temperature. Although dissolved in the slurry dispersion medium,
When cooled to around 00 ° C. to form a slurry containing terephthalic acid crystals, these impurities are taken into the terephthalic acid crystals, making it difficult to obtain high-purity terephthalic acid.

Therefore, in order to separate the terephthalic acid having the highest possible purity from the dispersion medium, the crude terephthalic acid slurry after the above-mentioned oxidation reaction or the slurry after the purification treatment of the crude terephthalic acid is subjected to high temperature and pressure. It becomes necessary to do it under the conditions. The most commonly used method for separating the dispersion medium from the crystal-containing slurry is the centrifugal separation method, and the centrifugal separation method is also widely used for the slurry after the oxidation reaction or the slurry after the purification treatment. Has been done. The feature of the centrifugal separation method is that the slurry solution is introduced into the basket rotating at a high speed, the dispersion medium is overflowed from the upper part, and the crystals are guided to the lower part. However, due to the structure and function of the centrifugal separator. It is known that the continuous operation under high temperature and high pressure is accompanied by some difficulties due to the above restrictions.

First, since it is difficult to rinse the crystals during or after the centrifugation, the amount of the dispersion medium attached to the crystals tends to increase, and in order to solve the problem, the terephthalic acid crystals that have been centrifugally separated are usually used. A method of making the cake into a slurry with a fresh high-temperature solvent again is adopted, but there is a problem that the separation operation must be performed plural times. Furthermore, since high-speed rotation at high temperature and high pressure makes maintenance and maintenance of the centrifuge complicated and difficult, investment for it has increased, and it cannot be said that the technology in this field has become sophisticated. .

As a separation method replacing the centrifugal separation method, in recent years, a dispersion medium replacement device has been proposed which utilizes the sedimentation action of terephthalic acid crystals due to gravity. For example, JP-A-57-534
31 and JP-A-55-87744.
According to Japanese Patent Laid-Open No. 57-53431, a dispersion medium replacement device is provided with a horizontal shelf having a plurality of holes.
It is explained that without such a structure, the efficiency of replacement is not as good as desired due to channeling or back mixing of the fluid in the device. Also, in Japanese Patent Laid-Open No. 55-87744, a shelf for forming a slope is provided to improve the replacement performance. However, it is very difficult to provide such a tray when handling a slurry and when replacing the dispersion medium using gravity sedimentation.
That is, accumulation on shelves, blockage of open holes, and bulking occur, and a lot of labor is required to stabilize the operation, which is not a highly advanced technology.

[0008]

Therefore, an object of the present invention is to provide a raw slurry containing terephthalic acid crystal particles and a raw dispersion medium as main components by a gravity sedimentation method without providing a tray or the like in the dispersion medium substitution column. In addition, a method for efficiently performing the dispersion medium replacement while injecting the dispersion medium for replacement (dispersion medium for replacement) from the bottom of the dispersion medium replacement column bottom, and finally obtaining high-purity terephthalic acid It is the one trying to find out.

[0009]

Means for Solving the Problems As a result of intensive studies made by the present inventors in order to solve this problem, surprisingly, even if the apparatus does not have trays, a stirring apparatus is installed at the bottom of the dispersion medium replacement column. By setting the supply flow rate of the dispersion medium for substitution and the discharge flow rate of the substitution slurry at the bottom so that the concentration of the slurry at the bottom becomes higher than the concentration of the slurry at the middle of the device (tower), the substitution efficiency is dramatically improved. Turned out to be better. Conventionally, in the case of such a device having a stepless structure, it has been attempted to keep the inside of the device in a static state as much as possible in order to avoid back mixing. It was truly unexpected to say that doing it would be more efficient.

The gist of the present invention is as follows. (First) Liquid phase oxidation of a p-phenylene compound having a carboxyl group and / or a carboxyl group-forming oxidizable substituent at the para position, and the obtained crude terephthalic acid slurry is depressurized and cooled to 120 to 180 Slurry adjusted to ℃,
Alternatively, crude terephthalic acid obtained by separating from the crude terephthalic acid slurry is dissolved in water, acetic acid, or a mixed solvent thereof at high temperature and high pressure, purified, and subjected to pressure reduction and temperature reduction to 120 to 220 ° C. The temperature of the slurry is adjusted to the above, and the raw slurry containing terephthalic acid crystal particles and the raw dispersion medium as main components is introduced from the upper part of the dispersion medium substitution tower, and the substitution dispersion medium is introduced from the lower part of the tower to obtain the raw slurry. The original dispersion medium is replaced by extracting the original dispersion medium from the upper part of the tower, the lower part of the tower is stirred to make the slurry state as uniform as possible, and the replacement dispersion medium supply flow rate and the replacement slurry withdrawal flow rate are By adjusting, while maintaining a slurry state of a higher concentration than the middle part of the tower, withdrawing the replacement slurry containing terephthalic acid crystal particles and the dispersion medium for replacement as the main components from the lower part of the tower,
A method for producing high-purity terephthalic acid, which comprises separating terephthalic acid crystal particles from the substitution slurry. (2) The method for producing high-purity terephthalic acid according to the above 1, wherein the slurry in the middle part of the dispersion medium substitution column is divided into a plurality of parallel streams.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The contents of the present invention will be described in detail below. The method for producing high-purity terephthalic acid according to the present invention attempts to replace the raw dispersion medium by introducing a raw slurry containing terephthalic acid crystal particles and a raw dispersion medium as main components from the upper part of a continuously variable dispersion medium replacement tower. The other dispersion medium, the dispersion medium for substitution, is introduced respectively from the lower part of the tower, both liquids are placed in a liquid / liquid contact state, and in that state, terephthalic acid crystal particles are gravity settling means from the original dispersion medium to the dispersion medium for substitution. The present invention relates to a method of separating the terephthalic acid crystal particles by extracting the raw dispersion medium from the upper part of the tower and extracting the substitutional slurry consisting of the dispersion medium for substitution and the terephthalic acid crystal particles from the lower part of the tower.

Since the method according to the present invention utilizes the gravity settling phenomenon, it is preferable to maximize the slurry density at the bottom of the tower to form a stable state as the density gradient in the tower. The necessity of such a stable state will be described. It is natural that it is preferable to perform the dispersion medium replacement in a continuous operation in terms of work efficiency, but in the case of performing this continuous operation,
At the bottom of the tower, discharge the high-concentration slurry with the dispersion medium replaced,
It is necessary to supply the replacement dispersion medium for replacement of the dispersion medium at the same time. If this happens, a non-uniform state is likely to occur, such as a portion where the slurry concentration is partially diluted by the replacement dispersion medium at the bottom of the column. In this state, the middle part of the tower with a high slurry concentration (high specific gravity) is located above the lower part of the tower where the part with a low slurry concentration (low specific gravity) is non-uniform, forming a very unstable system. In the end, a large movement of the slurry occurs between the middle part of the tower and the lower part of the tower, and at that time, it becomes easy to induce the phenomenon that the raw slurry is also caught in the middle part of the tower, and the dispersion medium replacement function is not normally exhibited. become.

As a method for first solving the problem in the lower part of the tower, the present inventors make the replacement slurry in the lower part of the tower and the supplied dispersion medium for replacement promptly and as uniformly as possible. A mixing and stirring operation was added, but this addition causes the disturbance of the thick slurry that has started to settle due to the replacement of the dispersion medium, and as previously mentioned, a method not previously considered in the dispersion medium replacement operation utilizing the gravity sedimentation phenomenon. Is.

As a stirring method in the lower part of the dispersion medium substitution tower, it is not necessary to take a particularly limited means, but there is stirring by a stirring blade, and as the external stirring method of the same tower, a circulation pipe is installed outside the lower part of the tower. However, there is a method in which both the substitution slurry and the dispersion medium for substitution are extracted and returned to the lower part of the same tower again. When this circulation pipe is used, a method of further interposing a stirring device with stirring blades in the middle of circulation is also preferably adopted. However, it is important to prevent the influence of stirring from affecting the stability of the slurry in the middle part of the tower, and therefore, in addition to the method of lengthening the middle part of the tower process, the supply of the dispersion medium for replacement or the return of the circulation pipe is required. A method such as a method performed at a position as low as possible in the lower part of the tower is adopted as a simple means, but the method according to the present invention is not limited to these.

In order to suppress the back mixing, in the present invention, the supply flow rate of the dispersion medium for replacement and the discharge flow rate of the replacement slurry in the lower part of the tower are adjusted so that the slurry specific gravity in the middle part of the tower, that is, the slurry concentration, is adjusted to the lower part of the tower. The specific gravity of the slurry must be kept lower than the slurry concentration. The supply flow rate of the replacement dispersion medium and the discharge flow rate of the replacement slurry are almost the same during stable operation, but if these flow rates become too high, the liquid flow rate of the replacement dispersion medium will increase compared to the discharged crystal flow rate. From
The specific gravity of the lower part of the column is lowered, and may be lower than the specific gravity of the middle part of the column. Conversely, if the flow rate is too low, the concentration of the replacement slurry in the lower part of the column becomes extremely high, which makes it difficult to handle the slurry. Absent. More specifically,
The slurry concentration in the middle part of the tower is usually operated at 1 to 50% by weight, preferably 3 to 20% by weight, and the lower part of the tower is at or above the middle part slurry concentration and 1 to 50% by weight, preferably 1%.
It is operated under the condition of 0 to 40% by weight. In this case, the flow rate adjustment cannot be specified as a range of specific numerical values, and may be a flow rate that keeps the specific gravity of the lower part of the column higher than the specific gravity of the middle part of the column.

A second aspect of the present invention is a method for more efficiently carrying out the first aspect of the present invention, in which the slurry in the middle part of the dispersion medium substitution column in the first aspect of the invention is divided into a plurality of pieces parallel to the vertical direction. This is a dispersion medium replacement method that is performed by being divided. This division is also useful for preventing the influence of the agitation in the lower part of the tower and the non-uniformity of the specific gravity from reaching the middle part of the tower and the upper part of the tower as much as possible. Although there is a method of providing a partition plate in this case, in this method, it is preferable to form a densely aggregated passage by partitioning so that the cross-sectional shape and the cross-sectional area are almost the same.

The vertical division of the slurry in the middle part of the tower is
Ultimately, it is intended to settle the terephthalic acid crystal particles in a steady state rectified as much as possible.
In principle, by restricting the backmixing flow, which is unavoidable in each operation, to a small space, the backmixing phenomenon is suppressed as much as possible, and the dispersion medium replacement is attempted continuously. is there. On the contrary, if an attempt is made to replace the dispersion medium in a large area in the middle part of the tower without the above-mentioned division, the reverse mixing flow will occur almost throughout the middle part of the tower, which greatly promotes the back mixing phenomenon. Therefore, it is not preferable for the purpose of replacing the dispersion medium.

The raw slurry treated in the first and second aspects of the invention is a liquid phase oxidation reaction product slurry or a slurry obtained by purifying crude terephthalic acid, and contains terephthalic acid crystal particles and an original dispersion medium as main components. However, the main component of the raw dispersion medium constituting the raw slurry is a liquid phase oxidation reaction solvent or a purification treatment solvent. This liquid-phase oxidation reaction is usually
Acetic acid, water and the like are used, more preferably acetic acid containing water is used, and as the purification solvent, water, acetic acid and the like are usually used, but water is more preferably used. On the other hand, the dispersion medium for substitution may be the same material or composition as the original dispersion medium of the original slurry, that is, the liquid-phase oxidation reaction solvent or the purification treatment solvent, or may be a different material or composition, Is water, acetic acid or a mixture thereof.
It should be noted that it is desirable to use, as the dispersion medium for substitution, one from which impurities have been removed to the extent that the purification effect can be obtained at least by substitution.

In the apparatus of the present invention, it is preferable to provide a weak flow of the substitution slurry countercurrently with the precipitated terephthalic acid crystal particles, that is, from the lower part to the upper part of the device. This is a measure for preventing the raw dispersion medium from diffusing below the apparatus. The operating temperature of this device is not higher than the boiling point of each dispersion medium under operating pressure because the device of the present invention has a simple structure and is a closed system, and therefore can easily be operated under pressure. It can be preferably used.

Forced agitation of the bottom, performed by the inventors,
It is considered that the measures such as uniform dispersion and difference in slurry concentration contributed to the stabilization of the system, and therefore the substitution performance was improved. In addition, as a result of the inventors' continued study, by further dividing the flow of the liquid in the middle part of the tower vertically, and more preferably, by dividing the flow into almost the same cross-sectional shape and the same area to provide a long passage, It became clear that the performance of the replacement is improved. The reason why the replacement rate is improved by providing the long passages in the vertical direction is considered to be that such a structure has a rectifying action to suppress back mixing, but the detailed mechanism is unknown.

The dispersion medium substitution column to which the method according to the present invention can be roughly divided is composed of a column upper chamber, a column lower chamber and a column intermediate chamber, and the column upper chamber is composed of a raw dispersion medium and terephthalic acid crystal particles. Although it has an introduction part for the slurry, this introduction part may be opened to the inner wall of the upper part of the tower, but a cylindrical introduction part that extends and opens in the upper part of the tower does not interfere with the operation of extracting the raw dispersion medium. It is preferable in terms. Further, it is preferable that the tip end portion of the opening is installed downward because it is easy to make the original slurry and the replacement slurry come into uniform contact with each other. If a baffle plate (or a shielding plate) for liquid flow dispersion is installed at the tip of the opening, the raw slurry can be widely and uniformly supplied into the tower, and the dispersion medium replacement operation can proceed more smoothly. . The tower upper chamber is further provided with a raw dispersion medium extraction unit, and the raw dispersion medium containing almost no terephthalic acid crystal particles is extracted and introduced into a predetermined processing chamber. The shape of the terephthalic acid crystal particles targeted by the present invention is not particularly limited.

In the lower part of the tower, a replacement dispersion medium introduction part, a part for extracting the replacement slurry replaced with the replacement dispersion medium, a part for adjusting the replacement dispersion medium introduction flow rate and the replacement slurry removal flow rate, and the lower part chamber of the tower. A liquid stirring device is provided.
The replacement dispersion medium introduction part is a part for introducing a liquid that becomes a new dispersion medium by the replacement operation, and has a low specific gravity without containing terephthalic acid crystal particles, so that the mixing with the replacement slurry is facilitated, It is preferable to open downward. In addition, the withdrawal portion of the substitution slurry substituted with the substitution dispersion medium is preferably closer to the lower part of the lower column chamber in terms of position because the substitution slurry has a high specific gravity.

Adjustment of the flow rate of the disperse medium for substitution and the flow rate of withdrawal of the substitution slurry make it possible to control the specific gravity of the substitution slurry in the lower chamber of the tower. The installation of a control unit for adjusting the flow rates of both of these is important for stable replacement operation, and the control of the flow rate of the dispersion medium for replacement and the flow rate of withdrawing the replacement slurry is controlled by the slurry specific gravity in the lower tower chamber and the slurry in the middle tower chamber. It affects the relative relationship of the specific gravities, and as a result, is related to the dispersion medium replacement efficiency and the difficulty of handling the replacement slurry.

The lower chamber of the tower is equipped with the indoor slurry agitator. This stirrer is intended to make the dispersion state of the slurry in the lower part of the tower as uniform as possible.
The purpose of this homogenization is to prevent instability in the density gradient between the middle part of the tower and the lower part of the tower due to the partial reduction of the specific gravity of the slurry in the lower part of the tower. The sex is as described above.

This agitating device does not need to be a particularly limited device, but an ordinary agitator having an agitating blade may be installed in the lower chamber of the dispersion medium substitution column, but a baffle is provided to assist the agitation. It is also suitable to put
As another stirring means, a circulation pipe may be installed outside the lower part of the tower, and means for extracting the liquid inside the lower part of the tower and returning it to the lower part of the tower may be suitably used. As described above, interposing a stirrer is also a preferable means.

Next, the tower middle chamber is a passage that vertically connects the tower upper chamber and the tower lower chamber. As will be described later as the second invention, it is formed in a plurality of parallel and densely arranged passages. It is more preferable that the length is longer than that.
Here, since the long longitudinal passage has a vertical tubular structure without a shelf or the like, there is an advantage that there is no need to worry about the deposition or blockage of the terephthalic acid crystal particles as in the case of installing the shelf.

The operating temperature of the dispersion medium replacement according to the above method of the present invention is simple because the structure of the above apparatus is simple and the operation under pressure is easy. It may be below the boiling point. The temperature of the feed raw slurry and the temperature of the substitution dispersion medium may be the same or different, but if the temperature of the substitution dispersion medium is lower than the temperature of the feed raw slurry, the lower part of the tower The specific gravity of the slurry in the chamber becomes higher than that of the feed raw slurry, and a more stable system is formed, which is preferable.

In the second method according to the present invention, the slurry in the middle part of the dispersion medium substitution column is divided into a plurality of parallel streams, and the apparatus suitable for carrying out this method is as follows. The partition wall formed in the vertical direction, the cross-sectional shape is not particularly limited as long as it constitutes a plurality of parallel long passages, may be a tube bundle, honeycomb-shaped or lattice-shaped partition, the passage mode It is not limited by these. The reason why the replacement rate is improved by providing the narrow passage is not clear, but it is considered that the back mixing over a wide area is suppressed from being integrally generated, and the liquid has a rectifying action in the middle part of the tower.

The contents of the present invention will be described below with reference to examples.

【Example】

Example 1 An example of the method according to the present invention and an apparatus for carrying out the method will be described. The dispersion medium replacement device shown in FIG. 1 has a dispersion medium replacement tower A as a center, and a raw slurry tank 8 for a raw slurry supplied to this tower, a replacement dispersion medium tank 11, and a discharged replacement medium. An overflow dispersion medium tank 9 for receiving the original dispersion medium and a substitution slurry tank 10 for receiving the extracted substitution slurry are connected, and necessary liquid feeding and stirring pumps 12, 13 and 14 are installed. There is.
The dispersion medium replacement tower A is a stainless steel cylindrical tower having a vertically long structure and an inner diameter of 100 mm. An upper hollow chamber 2 and a lower hollow chamber 3 are formed on the upper end (column top) side and the lower end (column bottom) side, respectively, and serve as a raw slurry introduction chamber from the outside of the tower and a replacement slurry discharge chamber to the outside of the tower. ing. The raw slurry introducing section 4 is inserted into the upper hollow chamber 2. A raw slurry receiving port 4a connected to the raw slurry tank 8 and a raw slurry introducing port 4b extending below the upper hollow chamber are provided, and a shield plate 4c for assisting the slurry dispersion is installed at the tip of 4b. The raw slurry composed of the raw dispersion medium and the terephthalic acid crystal reaches the raw slurry introducing section 4 from the raw slurry tank 8 through the raw slurry transport pump 12.
The raw slurry is introduced into the upper hollow chamber 2 through the inlet 4b. Of the dispersed raw slurry, the terephthalic acid crystal particles generally settle down in the cylindrical tower 1, and a part of the terephthalic acid crystal particles, which is particularly fine, and the raw dispersion medium are in the upper hollow chamber 2. The raw slurry dispersion medium overflow portion 5 on the upper side surface overflows into the overflow dispersion medium tank 9. A stirring pump 13 is connected to the lower hollow chamber 3 of the tower, and a replacement slurry withdrawal section 7 is provided.
The liquid in the lower hollow chamber 3 is agitated by the circulating flow from a to the recycling return port 7b through the pump 13. Slurry that has been replaced from the hollow chamber 3 is extracted from a line branched through the discharge port of the stirring pump 13,
The extracted slurry is stored in the replacement slurry tank 10. The replacement dispersion medium to be replaced is supplied from the replacement dispersion medium tank 11 via the replacement dispersion medium transport pump 14 through the replacement dispersion medium supply port 6 on the side surface of the lower hollow chamber 3.

An experiment was conducted by using such an apparatus to replace the dispersion medium of the crude terephthalic acid crystal slurry obtained by the liquid phase oxidation reaction with fresh hydrous acetic acid. The raw slurry consisting of the raw material terephthalic acid crystal particles and the raw dispersion medium was produced by air-oxidizing paraxylene in a hydrous acetic acid solvent using a commercial-scale apparatus. In the oxidation step, manganese acetate, cobalt acetate, and hydrobromic acid were used as the oxidation reaction catalyst to carry out the oxidation reaction, and the crude terephthalic acid crystal finally cooled to 90 ° C via the crystallization step. The slurry was collected and used as the raw slurry of the raw material for the dispersion medium replacement experiment,
The concentration of terephthalic acid crystal particles was 30% by weight, the concentration of water in the dispersion medium was 11% by weight, and the concentration of manganese was 364 ppm. First, a terephthalic acid crystal was charged into the hollow portion 3 on the lower side of the tower, and fresh acetic acid containing 11% by weight of water was charged into the hollow portion 3 from the dispersion medium transport pump 14 for substitution through a heat exchanger 15.
The mixture was heated to 0 ° C. and supplied, and the stirring pump 13 was started to start stirring to disperse the terephthalic acid crystal concentration to 30% by weight. When the liquid level reaches the raw slurry dispersion medium overflow port 5, the raw slurry transport pump 12 is started to start the supply of the raw slurry, and at the same time, the replacement slurry tank 10 is started.
I started to pull out. The raw slurry of the raw material was heated to 160 ° C. by the heat exchanger 16 on the way. The supply amount and the withdrawal amount were as follows. Raw slurry supply amount 40.0 Kg / h Dispersion medium supply amount 33.4 Kg / h Overflow dispersion medium withdrawal amount 34.2 Kg / h Displacement slurry withdrawal amount 39.2 Kg / h Continuous operation for several hours After the liquid flow of No. 2 reached a steady state sufficiently, the liquid in the substitution slurry tank 10 was analyzed and the manganese concentration in the dispersion medium was 30 ppm.
Therefore, the dispersion medium substitution rate in this example was 92%.
At this time, the slurry concentration in the cylindrical tower (middle portion) was 8% by weight, and the slurry concentration in the lower hollow portion 3 was 30% by weight (Table 1).

(Comparative Example 1) As shown in FIG. 2, the apparatus used in Example 1 was used.
The entire amount of the slurry extracted from a is replaced with the replacement slurry tank 10
An experiment was conducted under the same conditions as in Example 1 except that the slurry was extracted into a tank and stirred by pump circulation.
The liquid manganese concentration in 0 was 100 ppm, and the dispersion medium substitution rate was 73%. At this time, the slurry concentration in the cylindrical tower 1 was 8% by weight, and the slurry concentration in the lower hollow chamber 3 was 3% (Table 1).

(Embodiment 2) As shown in FIG.
The crude terephthalic acid obtained by air-oxidizing para-xylene in the presence of cobalt, manganese, and bromine catalysts by using the dispersion medium replacement device used in 1. was purified by catalytic hydrogenation and recrystallization in a water solvent. An experiment was conducted to replace the dispersion medium of the purified terephthalic acid crystal particles with fresh water. The raw slurry used here uses a commercial-scale apparatus, paraxylene is oxidized in hydrous acetic acid in the oxidation step, and manganese acetate, cobalt acetate and hydrobromic acid are used as oxidation reaction catalysts, and air oxidation is performed. After crystallization, the crystals were separated and dried to dissolve the crude terephthalic acid crystal particles, which were dissolved in hot water and subjected to catalytic hydrogenation treatment with impurities using a palladium catalyst supported on activated carbon in the presence of hydrogen, followed by crystallization. It was obtained by cooling to 100 ° C. through the steps.

First, purified terephthalic acid crystals are charged into the hollow portion 3 on the lower side of the tower, and water is heated and supplied from the dispersion medium transport pump 14 for substitution through the heat exchanger 15 to 150 ° C., and the stirring pump 13 is used. Was started to start stirring, and the terephthalic acid crystal was dispersed so as to have a concentration of 30% by weight.
When the liquid level reached the raw slurry dispersion medium overflow portion 5, the raw slurry transport pump 12 was started to start the supply of the raw slurry and at the same time to start the extraction to the replacement slurry tank 10. The raw slurry of the raw material is 15
Heated to 0 ° C. The supply amount and the withdrawal amount were as follows. Raw slurry supply amount 40.0 Kg / h Dispersion medium supply amount 33.4 Kg / h Overflow dispersion medium withdrawal amount 34.2 Kg / h Displacement slurry withdrawal amount 39.2 Kg / h Dispersion of slurry introduced into dispersion medium substitution tower Impurity benzoic acid in the medium was 240 ppm. After the operation was continued for several hours and the liquid flow in the system reached a sufficiently steady state, the liquid in the displacement slurry tank 10 was analyzed and the benzoic acid concentration in the dispersion medium was 20 ppm. Therefore, the dispersion medium substitution rate in this example was 92%. At this time, the slurry concentration in the cylindrical tower was 6% by weight, and the slurry concentration in the lower hollow portion 3 was 30% by weight (Table 1).

(Comparative Example 2) As shown in FIG. 4, by using the dispersion medium replacement device used in Example 1, the entire amount of the slurry extracted from the replacement slurry extracting section 7a was extracted into the replacement slurry tank 10, but pump circulation was performed. When an experiment was performed under the same conditions as in Example 2 except that the stirring was not performed according to Example 2, the benzoic acid concentration in the liquid in the substitution slurry tank 10 was 70 ppm, and the dispersion medium substitution ratio was 71%. At this time, the slurry concentration in the tubular tower 1 was 6% by weight, and the slurry concentration in the lower hollow portion 3 was 3% by weight (Table 1). The raw slurry used here is the same as that used in Example 2.

(Embodiment 3) As shown in FIG. 5, a vertical partition plate 1 having a cross-shaped cross section is provided in the cylindrical tower of the dispersion medium replacement device of FIG.
An experiment was conducted in the same manner as in Example 2 by using an apparatus incorporating 7 (FIG. 8 shows a cross-sectional view of the cylindrical tower portion of FIG. 5, that is, the tower middle portion) in the same experimental procedure and conditions. As a result, the benzoic acid concentration in the liquid in the substitution slurry tank 10 was 7 ppm, and the dispersion medium substitution ratio was 97%. At this time, the slurry concentration in the cylindrical tower 1 was 6% by weight, and the slurry concentration in the lower hollow portion 3 was 30% by weight (Table 1).

(Example 4) As shown in FIG. 6, acetic acid, which is a mother liquor of an original slurry of terephthalic acid obtained by air-oxidizing paraxylene, was added to the dispersion medium replacement device used in Example 3.
An experiment was carried out in which the replacement dispersion medium was replaced with water. The raw slurry used was manganese acetate, cobalt acetate and hydrobromic acid as catalysts for the oxidation reaction, and the slurry was used after the reaction.
It was obtained by cooling to 0 ° C. An experiment was carried out under the same conditions and procedures as in Example 1 except that the concentration of the raw slurry was 30% by weight, the feed temperature of the raw slurry was 150 ° C., and the feed temperature of water for the dispersion medium for substitution was 150 ° C. The supply amount and the withdrawal amount were as follows. Raw slurry supply amount 40.0 Kg / h Dispersion medium supply amount 33.4 Kg / h Overflow dispersion medium withdrawal amount 34.2 Kg / h Displacement slurry withdrawal amount 39.2 Kg / h Continuous operation for several hours After the liquid flow in (1) reached a sufficient steady state, the acetic acid concentration in the dispersion medium of the slurry withdrawn to the substitution three tank was measured and found to be 1.8% by weight. Therefore, the dispersion medium substitution rate was 98%. At this time, the slurry concentration in the cylindrical tower was 6% by weight, and the slurry concentration in the lower hollow portion 3 was 30% by weight (first
table).

(Comparative Example 3) As shown in FIG. 7, the original slurry and the dispersion medium replacement device used in Example 4 were used, but the entire amount of the slurry extracted from the replacement slurry extracting section 7a was extracted into the replacement slurry tank 10. However, when an experiment was conducted under the same conditions as in Example 4 except that stirring by pump circulation was not carried out, the acetic acid concentration of the dispersion medium in the substitution slurry was 35% by weight, and the substitution rate of the dispersion medium was 61%. At this time, the slurry concentration in the tubular tower 1 was 6% by weight, and the slurry concentration in the lower hollow portion 3 was 3% by weight (Table 1).

[0038]

[Table 1]

The following can be said from the results of the above Examples and Comparative Examples. (1) The lower hollow portion is agitated to be uniform, and the supply flow rate of the replacement dispersion medium and the withdrawal flow rate of the replacement slurry are adjusted to make the concentration of the replacement slurry higher than the concentration of the slurry in the replacement tower. The replacement rate is improved (Example 1)
Comparative Example 1, Example 2 and Comparative Example 2, and Example 4 and Comparative Example 3). (2) In the same manner as in (1) above, the lower hollow portion was agitated to give a slurry concentration gradient, and a partition plate was installed inside the cylindrical tower to further improve the dispersion medium substitution rate. (Examples 1 and 2 and Examples 3 and 4)

[0040]

As described above, the terephthalic acid crystal particle-containing raw slurry which requires the dispersion medium replacement is introduced from the upper part of the long cylindrical dispersion medium replacement column, and the desired replacement dispersion medium is supplied from the lower part of the substitution column. Then, when the crystal particles in the original slurry are gravity settled to the lower side of the substitution tower to substitute the dispersion medium, the substitution slurry at the bottom of the substitution tower and the supplied dispersion medium for substitution are stirred to be in a uniform dispersion state, and, By adjusting the replacement slurry withdrawal flow rate and the replacement dispersion medium supply flow rate to make the concentration of the homogenized slurry higher than the slurry concentration inside the cylindrical tower, it is more preferable to partition in the middle part of the tower. By forming a plurality of liquid streams, the substitution ability of the dispersion medium can be made extremely high, and it can be said that this method is suitable for producing high-purity terephthalic acid by the dispersion medium substitution method. This form of the dispersion medium replacement method can be said to be a new development technology in which a replacement function is added to the gravity sedimentation concentration method.

[Brief description of drawings]

FIG. 1 shows an example of a dispersion medium replacement device used for carrying out a method according to the present invention and an example of the flow thereof.

FIG. 2 shows an example of a dispersion medium replacement device that does not mix and stir a replacement slurry and a dispersion medium for replacement, and an example of the flow thereof.

FIG. 3 shows an example of a dispersion medium replacement device used for carrying out the method according to the present invention and its flow.

FIG. 4 shows an example of a dispersion medium replacement device that does not mix and stir a replacement slurry and a dispersion medium for replacement, and an example of the flow thereof.

FIG. 5 shows an example of a dispersion medium replacement device used for carrying out the method according to the present invention and its flow.

FIG. 6 shows an example of a dispersion medium replacement device used for carrying out the method according to the present invention and its flow.

FIG. 7 shows an example of a dispersion medium replacement device that does not mix and stir a replacement slurry and a dispersion medium for replacement, and an example of the flow thereof.

FIG. 8 shows a transverse cross-sectional view of a central portion of a cylindrical tower of a dispersion medium replacement column that constitutes a dispersion medium replacement device used for carrying out the method according to the present invention.

[Explanation of symbols]

 A ... Dispersion medium replacement tower 1 ... Cylindrical tower 2 ... Upper hollow chamber 3 ... Lower hollow chamber 4 ... Raw slurry introduction part 4a ... Raw slurry Receiving port 4b ... Raw slurry introducing port 4c ... Shielding plate 5 ... Raw slurry dispersion medium overflow 6 ... Replacement dispersion medium supply port 7a ... Replacement slurry withdrawing unit 7b ...・ Recycle return port 8 ・ ・ ・ Original slurry tank 9 ・ ・ ・ Overflow dispersion medium tank 10 ・ ・ ・ Replacement slurry tank 11 ・ ・ ・ Replacement dispersion medium tank 12 ・ ・ ・ Original slurry transport pump 13 ・ ・ ・Stirring pump 14 ... Dispersion medium transport pump 15 ... Heat exchanger 16 ... Heat exchanger 17 ... Partition plate 17a ...

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Ogoshi 3-10 Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture Mitsubishi Gas Chemical Co., Ltd. Mizushima Plant (72) Inventor Fumiya Arama, Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture No. 10 Mitsubishi Gas Chemical Co., Ltd. Mizushima Plant

Claims (2)

[Claims] 1. A p-phenylene compound having a carboxyl group and / or a carboxyl group-forming oxidizable substituent at the para position is subjected to liquid-phase oxidation, and the resulting crude terephthalic acid slurry is depressurized and cooled to 120 to 120 ° C. Slurry adjusted to 180 ° C., or crude terephthalic acid obtained by separating from the crude terephthalic acid slurry is dissolved in water or acetic acid or a mixed solvent thereof at high temperature and high pressure, purified, and subjected to pressure reduction, A slurry whose temperature is lowered to 120 to 220 ° C. and which is a slurry whose main components are terephthalic acid crystal particles and an original dispersion medium is provided from the upper part of the dispersion medium replacement tower, and the replacement dispersion medium is also provided in the same tower. Introduce each from the lower part, replace the original dispersion medium of the original slurry and withdraw the original dispersion medium from the upper part of the tower, stir the lower part liquid of the same tower to make the slurry state as uniform as possible, and perform the dispersion for replacement. By adjusting the supply flow rate and the withdrawal flow rate of the replacement slurry, the replacement slurry containing terephthalic acid crystal particles and the dispersion medium for replacement as the main components is withdrawn from the lower part of the tower while maintaining a slurry state with a higher concentration than the middle part of the tower. A method for producing high-purity terephthalic acid, which comprises separating terephthalic acid crystal particles from the substitution slurry. 2. The method for producing high-purity terephthalic acid according to claim 1, wherein the slurry in the middle part of the dispersion medium substitution column is divided into a plurality of parallel streams.