JP3788634B2 - Production method of high purity terephthalic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing high-purity terephthalic acid, and more particularly to a mother liquor substitution method in which a mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals obtained by a liquid phase oxidation reaction is substituted with water.
[0002]
[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 (mother liquor) and a catalyst such as cobalt or manganese is used, or A catalyst obtained by adding a promoter such as a bromine compound or acetaldehyde to this is used.
However, since this reaction product contains 4-carboxybenzaldehyde (4CBA), p-toluic acid, and various coloring impurities, a highly advanced purification technique is required to obtain high-purity terephthalic acid.
[0003]
As a method for purifying crude terephthalic acid obtained by the liquid phase oxidation reaction, the crude terephthalic acid is dissolved in an aqueous solvent under high temperature and high pressure, and catalytic hydrogenation treatment, oxidation treatment, recrystallization treatment or terephthalic acid crystals are combined. Various methods such as high-temperature dipping treatment in a partially dissolved slurry are known.
In particular, the process of dissolving hydroterephthalic acid in water and carrying out catalytic hydrotreating using a Group VIII noble metal catalyst under high temperature and pressure has been a large-scale commercial process for producing high-purity terephthalic acid for several decades. Has a history.
[0004]
However, in the method for performing the catalytic hydrotreating step, a long process flow is one of the major problems. That is, in this process, even if only the main process flow is excluded from complicated and troublesome units such as solvent recovery and catalyst recovery, one or more oxidation reactors, several sequential sequential crystallizations It is connected to a reactor, a crude separator, a crude dryer, a remelting tank, a catalytic hydrogenation reactor, several purification sequential crystallizers, a purification separator, and a purification dryer.
[0005]
A major factor for the long process flow is that the solvent for the reaction for producing crude terephthalic acid by oxidation is acetic acid, and the solvent for the reaction for purification by catalytic hydrogenation is water.
In order to carry out such solvent substitution from acetic acid to water, the crude terephthalic acid produced by oxidation must be completely separated from the acetic acid solvent and then redissolved in an aqueous solvent. If the separation of crude terephthalic acid and acetic acid is incomplete and the solvent acetic acid adheres to the crude terephthalic acid and is supplied to the catalytic hydrotreating process, acetic acid itself is rarely subject to chemical changes by catalytic hydrotreating Therefore, the acetic acid solvent adhering to the crude terephthalic acid is mixed with the aqueous solvent of the catalytic hydrogenation treatment and discharged out of the system.
This means that the valuable material of acetic acid is lost and lost, and the acetic acid that flows out must be made harmless to the environment, so that the economic loss is great.
[0006]
In order to suppress this economic loss, acetic acid adheres to the crude terephthalic acid sent to the catalytic hydrogenation process by combining a crude separator and a crude dryer that separates the mother liquor from the slurry containing crystals from the oxidation process. Entrainment needs to be cut off almost completely, and current commercial scale equipment uses such a combined flow of separators and dryers.
The most commonly used method for separating mother liquor from slurry containing crystals is a centrifuge or rotary vacuum filter, both of which are widely used when separating mother liquor from crude terephthalic acid crystal slurry. Yes.
[0007]
The centrifuge is a method that introduces acetic acid slurry as a raw material into a basket that rotates at high speed, overflows the mother liquor from the top, and induces crystals to the bottom, which is preserved from the structural restrictions of the centrifuge that rotate at high speed. The disadvantage is that the maintenance is complicated.
In addition, since the rinsing of the crude terephthalic acid crystal cannot be easily performed, the mother liquor cannot be completely removed. Therefore, it is necessary to provide a drying step downstream of the centrifugation step to remove acetic acid remaining on the crude terephthalic acid crystal. There is.
[0008]
In the rotary vacuum filter, as the filter medium rotates, the crude terephthalic acid crystals stored at the bottom of the housing adhere to the filter medium and rise and rotate. Generally, after passing through the rinse point, the crystals are peeled off as cakes. .
Since this method does not require high-speed rotation, maintenance and maintenance are relatively easy. However, it is difficult to completely remove the mother liquor adhering to the crude terephthalic acid crystal by rinsing, so a dryer is required downstream. This is similar to a centrifuge.
[0009]
As a method for separating crystals and removing mother liquor in place of a centrifuge or a rotary vacuum filter, Japanese Examined Patent Publication No. 33-5410 discloses a slurry obtained by recrystallizing crude terephthalic acid with water at a high temperature (above 165 ° C.). A method is described in which terephthalic acid crystals are precipitated by gravity against a slow upward flow of high-temperature water, and the adhered mother liquor is washed.
This method recrystallizes terephthalic acid crystals with an aqueous solvent and then separates the crystals from the mother liquor at high temperatures (under pressure). Basically, the mother liquor replacement method replaces the mother liquor of the terephthalic acid slurry with a fresh solvent. It is.
[0010]
Since this mother liquor replacement method uses gravity for sedimentation of crystals, it is superior in that no special power is required, and the fact that the apparatus itself is used is also attractive. However, it has the disadvantages that the mother liquor replacement rate is low and that it is difficult to scale up the experimental results as they are.
In order to improve the mother liquor substitution rate, it is sufficient to increase the upward flow of high-temperature water. For this purpose, a large amount of solvent (water) must be used. As a result, a large amount of small-sized crystals overflows from the top of the vertical basket.
[0011]
In order to overcome such drawbacks, Japanese Patent Application Laid-Open No. 57-53431 combines the gravity sedimentation process of terephthalic acid crystals divided by a plurality of horizontal partition plates with a large number of holes and the particle transport process. A mother liquor replacement method is proposed. Such a partition plate is intended to prevent channeling or backmixing of the fluid in the apparatus and increase the mother liquor replacement rate. However, such a partition plate is provided in the mother liquor replacement using gravity sedimentation for handling the slurry. This means that crystals are deposited on the partition plate, the opening is blocked and bulking occurs, and much effort is required to stabilize the operation.
[0012]
Japanese Patent Application Laid-Open No. 1-160942 proposes a mother liquor replacement tower having a structure in which a number of shelves partitioned in the horizontal direction are provided and terephthalic acid crystals are dropped by scraping blades that rotate relatively slowly on each shelf. In the example in which the acetic acid solvent (mother liquor) of crude terephthalic acid was substituted with water using the substitution tower, a high level of mother liquor substitution rate estimated to be 99% or more was achieved.
However, this example is a laboratory-scale apparatus, and the amount of terephthalic acid slurry supplied is about 1 ton / h. If this is scaled up to a commercial scale, approximately 100 times the amount of terephthalic acid slurry as in this example can be obtained. If the size of the mother liquor replacement column corresponding to this throughput is assumed, the cross-sectional area about 100 times that of the replacement column of this embodiment is required. In other words, the rate at which the terephthalic acid crystal settles in the apparatus is determined by the characteristics of gravity and solvent, so that the cross-sectional area of the mother liquor displacement column is increased by about 100 times under the condition that it is constant regardless of the size of the mother liquor displacement column. In order to achieve a high-level mother liquor replacement tower as described above, a huge mother liquor displacement tower is required.
[0013]
[Problems to be solved by the invention]
If the mother liquor of the acetic acid solvent slurry of the crude terephthalic acid crystal obtained by the liquid phase oxidation reaction is replaced with water using a mother liquor displacement tower, the resulting aqueous slurry of crude terephthalic acid is led to a catalytic hydrotreating unit, A separator and a dryer for separating the mother liquor from the slurry from the oxidation step in the process flow can be eliminated.
However, as described above, a series of commercial scale mother liquor replacement methods for producing high-purity terephthalic acid, that is, a practical technology that can replace the functions of crude terephthalic acid mother liquor separator and dryer in the current process flow, has not yet been completed. I have not seen it.
[0014]
An object of the present invention is to replace a mother liquor of an acetic acid solvent slurry of crude terephthalic acid crystals obtained by a liquid phase oxidation reaction with water, and send the obtained mother liquor of an aqueous slurry of crude terephthalic acid as it is to a catalytic hydrotreating apparatus. To complete the method and shorten the process flow in a high-purity terephthalic acid production plant, thereby reducing the amount of investment and the cost of operation.
[0015]
Where the boundary between economic loss due to acetic acid loss and the accompanying wastewater treatment load must be determined by the various economic environments in the manufacturing plant, it is difficult to draw a precise line. Specifically, if the mother liquor replacement rate is 99% or more, it is judged that there is a possibility of implementation on a commercial scale. If the mother liquor replacement rate can reach a level exceeding 99.9%, it is judged that the possibility of implementation is certain. Therefore, a specific goal of the present invention is to complete a mother liquor replacement method that is more efficient than the conventional mother liquor replacement method, and to achieve a mother liquor replacement rate of 99% or more, preferably 99.9% or more.
[0016]
[Means for Solving the Problems]
As a result of many years of research to overcome these technical ideas and progress over the preceding decades and the technical obstacles, the present inventors have found that a layer of terephthalic acid crystals is deposited below the mother liquor replacement column. And by supplying water from the bottom, it was found that a high mother liquor replacement rate of 99% or more can be achieved with a small and simple device, and a patent application was filed (Japanese Patent Application No. 7-118299). ).
Further, the present inventors have studied and provided a stirring shaft (arm type stirring blade) having a plurality of arms extending in the horizontal direction in the deposition layer of the terephthalic acid crystal, and rotating this gently to make the deposition layer minute. By maintaining a good fluidity and pulsating the deposited layer of terephthalic acid in some way, the displacement and channeling of the substitution water in the deposition layer can be suppressed, and the dispersion of the substitution water can be improved. The present inventors have found that the operability of the substitution tower is dramatically improved and have reached the present invention.
[0017]
That is, the present invention relates to a method for producing high-purity terephthalic acid in which an acetic acid solvent slurry of terephthalic acid crystals obtained by liquid phase oxidation of p-alkylbenzene is replaced with an aqueous solvent slurry and then subjected to catalytic hydrogenation. The acetic acid solvent slurry is introduced into the upper part of the tower, a deposited layer of terephthalic acid crystals is formed in the lower part of the tower by sedimentation of terephthalic acid crystals, and replacement water sufficient to form an upward flow of water from the bottom to the inside of the tower is supplied. A terephthalic acid crystal deposition layer is extracted from the bottom of the tower by a screw conveyor , an arm type stirring blade is provided in the deposition layer, and the fluidity of the deposition layer is maintained by gently rotating the stirring blade. This is a method for producing pure terephthalic acid.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An acetic acid solvent slurry of crude terephthalic acid crystals used for mother liquor substitution is produced by oxidizing a p-phenylene compound such as p-alkylbenzene, typically paraxylene, and usually a heavy metal salt catalyst such as cobalt or manganese, or this. A catalyst obtained by adding a promoter such as a bromine compound or acetaldehyde is used. Acetic acid containing about 3 to 20% water is used as the solvent. As molecular oxygen, air or oxygen is usually used, and the reaction is generally carried out in one or more stages at a temperature of 170 to 230 ° C. and a pressure of 10 to 30 atm.
[0019]
The slurry-like reaction effluent after the liquid phase oxidation step contains 4CBA, p-toluic acid, catalyst and other various impurities in addition to the terephthalic acid crystals. The reaction effluent is introduced into a crude sequential crystallizer having one or more stages, and the terephthalic acid dissolved in the solvent is further crystallized while being gradually cooled, and the temperature is lowered to a predetermined temperature.
Thereafter, the acetic acid solvent slurry of terephthalic acid crystals is supplied to the mother liquor displacement tower and led into the upward flow of water in the tower, and the oxidation reaction mother liquor moves upward along with the rising liquid flow of water together with a small amount of fine terephthalic acid crystals. Most terephthalic acid crystals settle in the column.
[0020]
The precipitated terephthalic acid crystals are extracted as a slurry from the bottom of the tower. In the present invention, a deposited layer is formed at the bottom of the tower, and replacement water is supplied from the inside of the deposited layer. In order to improve the dispersion in the deposit layer and prevent channeling and drift of the substitute water, the replacement water supply method is as if it is supplied as a sprinkler from the arm type stirring blade provided in the deposit layer. It is effective to adopt a method of supplying via a ring header provided inside. The deposited layer in the lower part of the tower is extracted by a known engineering technique by a continuous or intermittent technique.
As a result, the individual terephthalic acid crystals in the deposited layer move downward. On the other hand, since an upward flow of water exists in the tower, the terephthalic acid crystal and water contacted countercurrent, and the various acetic acid by-product impurities contained in the acetic acid solvent and acetic acid solvent adhering to the crystal surface. Etc. are cleaned efficiently.
As a result, an aqueous solvent slurry of terephthalic acid crystals containing almost no acetic acid solvent is extracted from the bottom of the column, and this slurry can be used for various purification methods that are already known without any additional treatment. The aqueous solvent slurry can be dissolved under high temperature and high pressure and sent to a process for producing high-purity terephthalic acid through a catalytic hydrotreating process using a Group VIII noble metal catalyst.
[0021]
The main conditions for carrying out the present invention are described below.
The mother liquor displacement column should have a mother liquor substitution rate of 99% or higher, preferably 99.9% or higher. The main condition for this is to maintain the fluidity of the terephthalic acid crystal deposition layer. In addition, it is necessary to appropriately take the length (height) of the terephthalic acid crystal deposition layer and the linear velocity (rising linear velocity) of the water rising in the tower.
[0022]
The length of the deposited layer is determined as a result of several operating factors such as the supply rate of terephthalic acid slurry from the top of the tower, the supply rate of water from the bottom of the tower, and the extraction rate of terephthalic acid slurry from the bottom of the tower. In actual operation, it is achieved by detecting the interface between the crystal sedimentation portion and the deposition layer in the mother liquor displacement column and adjusting the extraction speed of the terephthalic acid crystal deposition layer so as to keep it at a predetermined position.
The longer the deposited layer, the greater the cleaning effect and the higher the mother liquor replacement rate. Conversely, the shorter the deposited layer, the lower the mother liquor replacement rate. Since there is a possibility of blocking due to the static pressure of the acid crystal itself, an unnecessary length must be avoided.
[0023]
The mother liquor replacement rate is also shown as a function of the tower diameter. To achieve a mother liquor replacement rate of 99% or more, the length of the deposited layer needs to be at least one fifth of the diameter of the mother liquor replacement tower. The ascending linear velocity represents the flow rate of water rising countercurrently to the terephthalic acid crystals in the deposited layer, and is conveniently defined on the basis of the superficial level of the deposited layer portion. According to our experience, if the rising linear velocity is increased, the mother liquor replacement rate also increases, but if it exceeds approximately 3 m / h, the mother liquor replacement rate decreases rapidly.
[0024]
In the design of the mother liquor replacement column, the lower limit of the ascending linear velocity should be a value exceeding 0, that is, an ascending flow should be substantially formed, and the upper limit is approximately 3 m / h.
Setting the ascending linear velocity to a value larger than this upper limit not only causes a reduction in the substitution rate, but also some terephthalic acid crystals do not settle sufficiently and are taken upward together with the ascending liquid flow. The amount of use increases, and this causes an increase in the water concentration in the acetic acid mother liquor recovered from the top of the column.
[0025]
The temperature of the mother liquor replacement column is not particularly limited, but it is necessary to consider several factors relating to the entire high-purity terephthalic acid production apparatus.
For one, replacing the mother liquor at a higher temperature has the effect of improving the quality of the terephthalic acid obtained. That is, in a general terephthalic acid production apparatus, most of the terephthalic acid produced by the reaction already exists as crystals when it is introduced from the oxidation reactor into the crude sequential crystallizer. In the crystallizer, the remaining temperature of the terephthalic acid dissolved in the mother liquor is successively crystallized by successively lowering the temperature. It is a common phenomenon that crystals obtained at higher temperatures have higher purity than crystals obtained at lower temperatures, but in the case of terephthalic acid crystallization, 4CBA present as an impurity is terephthalic. It is known to co-crystallize with an acid, and the rate of co-crystallization has the property of rapidly increasing as the temperature decreases. Therefore, if the mother liquor replacement is performed at a higher temperature, there is an advantage that the purity of the crude terephthalic acid in the obtained water slurry is improved and the quality of the high-purity terephthalic acid obtained through the catalytic hydrotreating process is improved.
[0026]
The other is that the catalytic hydrotreating reaction is carried out at a higher temperature, specifically at a temperature exceeding 250 ° C., so that the mother liquor replacement is carried out at a lower temperature results in a loss of thermal energy. Since the oxidation reaction is generally performed at around 200 ° C., if the mother liquor replacement is performed at a temperature much lower than that, it is necessary to repeatedly lower the temperature and raise the temperature, thus resulting in energy loss. Therefore, the mother liquor replacement column is as close as possible to the oxidation reaction. It is desirable to perform at temperature.
[0027]
The mother liquor replacement column in the present invention is a very simple device and has few power parts, so that it can be easily carried out at high temperature and high pressure. However, when the temperature is high, the amount of terephthalic acid dissolved in the acetic acid solvent mother liquor flowing out from the top of the mother liquor displacement column inevitably increases. Since this mother liquor is recycled and used as a solvent for the oxidation reaction, it does not directly lead to the loss of terephthalic acid, but causes a substantial reduction in the production volume of the reactor.
Considering these various conditions, it is preferable that the temperature of the mother liquor replacement step is generally a low temperature within 120 ° C. of the oxidation reaction temperature, that is, about 80 to 180 ° C.
The pressure in the mother liquor replacement column is a pressure that maintains the temperature of acetic acid and water. When the temperature is determined, the lower limit pressure is automatically determined, and is about 0 to 15 kg / cm ² G.
[0028]
It is important to maintain the fluidity of the terephthalic acid crystal deposition layer in the mother liquor replacement tower. This is because when the deposited layer formed by the precipitation of terephthalic acid crystals becomes completely compacted, the properties as a slurry are lost, and the slurry cannot be extracted from the mother liquor replacement tower by an engineering method. In order to prevent this, it is necessary to constantly flow the deposited layer of terephthalic acid crystals. Further, by maintaining the fluidity of the deposited layer, the dispersion of the supplied substitution water is promoted, and further, the substitution water can be prevented from drifting up and channeling in the terephthalic acid crystal deposition layer.
Of course, when the fluidity of the deposited layer becomes intense, mass transfer in the deposited layer is promoted, so that the purification capacity of the mother liquor replacement column, that is, the mother liquor displacement rate is lowered. In order not to lower the mother liquor replacement rate more than necessary, it is essential to suppress the fluidity of the deposited layer to a very small level.
[0029]
An arm type stirring blade is the most effective method for imparting minute fluidity to the deposited layer. It is also effective to give pulsation to the deposited layer by some method.
The arm type stirring blade may be anything as long as the arm extends in the horizontal direction from the stirring shaft, and when viewed from above the stirring shaft, there are no particular restrictions on the number and shape of the arms such as a single letter, a cross, or a saddle type. The number of steps of the arm is determined by the height of the deposited layer, and the cross section of the arm is not particularly limited as long as it does not require significant power to shear the deposited layer, such as a circle, a triangle, or a diamond.
The rotation speed of the arm type stirring blade is preferably 0.1 to 20 rotations per minute, and more preferably 0.5 to 10 rotations per minute.
As for the blade diameter of the arm type stirring blade, a length for fluidizing the entire deposited layer of terephthalic acid crystal is required. In an actual apparatus, the blade diameter is preferably 0.7 to 0.99 times the diameter of the mother liquor replacement tower, and more preferably 0.8 to 0.99 times the diameter of the mother liquor displacement tower.
[0030]
The pulsation of the sedimentary layer is as follows: supply replacement water is supplied and intermittently repeated when it is supplied, stopped, pulsation is provided by adding a pulser to the supply replacement water line, the bottom of the mother liquor replacement tower, that is, terephthalic acid There is a method of providing a pulsation by installing a pulsar directly in a portion where crystals are deposited.
By providing such an arm type agitating blade and rotating it gently to maintain the minute fluidity of the deposited layer, and by pulsating the deposited layer of terephthalic acid in some way, The displacement and channeling of the replacement water are suppressed, the dispersion of the replacement water is improved, and the operability of the mother liquor replacement tower is dramatically improved.
[0031]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by these examples.
[0032]
Example 1
An experiment was conducted in which the mother liquor of the acetic acid solvent slurry of the crude terephthalic acid crystal, which is the raw material slurry obtained by the liquid phase oxidation reaction, was replaced with water using the apparatus shown in FIG.
In FIG. 1, the mother liquor replacement tower 1 is a SUS container. At the upper part of the mother liquor replacement tower, there is a raw material slurry introduction pipe 3 which is connected to a raw material slurry supply pump 2. There is a mother liquor discharge pipe 4 at the top of the tower. The bottom of the mother liquor replacement tower has a semi-elliptical dish shape structure and is connected to the slurry tank 9.
The slurry tank 9 is circulated and agitated by a circulation pump 12 installed outside. A branch pipe to the slurry extraction pump 13 and a branch pipe to the water supply pump 14 are connected in the middle of the return pipe from the circulation pump 12.
[0033]
A screw conveyor guide tube 6 is inserted and connected to the bottom of the column, and is obliquely cut upward to form a deposited layer extraction port 7.
A screw conveyor 5 is contained inside the screw guide tube 6, one end reaching the crystal extraction port 7, and the other end reaching the upper portion of the slurry tank 9. The screw conveyor 5 is connected to a motor 8 installed outside.
The shoreline a shown in the horizontal direction at the center of the mother liquor replacement column 1 is the upper surface of the terephthalic acid crystal deposition layer, and the length from the shoreline a to the upper end of the screw guide tube 6 is the length (height of the deposition layer). )
[0034]
In FIG. 1, first, the water supply pump 14 was driven, and 100 ° C. water was poured into the system. After water began to overflow from the mother liquor discharge pipe 4, the circulation pump 12 and the slurry extraction pump 13 were operated. Further, the motor 11 was operated to rotate the arm type stirring blade 10 at a speed of 4 revolutions per minute.
Next, the raw material slurry supply pump 2 was operated to supply a raw material slurry at 150 ° C. via the raw material slurry introduction pipe 3. As the raw slurry, an acetic acid solvent slurry of terephthalic acid produced on a commercial scale was used. The raw slurry is a reaction product oxidized by blowing air into a hydrous acetic acid solvent at a reaction temperature of 195 ° C. using cobalt, manganese and bromine compounds with para-xylene as an oxidation reaction catalyst. The reaction product was converted into a slurry cooled to 150 ° C. through several stages of crystallizer, and the slurry was supplied to the mother liquor displacement tower 1.
When the height of the deposited layer reached a predetermined position while being detected by the powder level detector, the motor 8 was operated to rotate the screw conveyor 5 for extracting the crystal to start extracting the crystal.
[0035]
After the system was in a steady state, each flow rate was adjusted and set as follows.
Raw material slurry supply pump 2 783 kg / h (crystal concentration 32.4%)
Slurry discharge pump 13 762 kg / h (crystal concentration 33.3%)
Water supply pump 14 586kg / h
The rotational speed of the motor 8 was adjusted while monitoring with a powder level detector so that the height of the deposited layer was maintained at a predetermined position. Under this condition, the rising linear velocity of water in the tower is 0.88 m / h based on the empty tower.
[0036]
Samples were taken at each point of the device at the time of continuous operation for 3 days, and the results of analyzing each composition were as follows.
(1) Raw material slurry mother liquor (the sample collected from the raw material slurry supply pump 2 is cooled to room temperature and allowed to stand)
Acetic acid 85.2%
Water 14.5%
Unknown 0.3%
(2) Extracted slurry (the sample collected from the slurry extracting pump 13 was cooled to room temperature and allowed to stand)
Acetic acid 0.102%
From this, the mother liquor replacement rate based on acetic acid is 99.9%.
[0037]
Comparative Example 1
In Example 1, when the operation was carried out with the rotation of the arm type stirring blade stopped, the fluidity of the sediment layer disappeared and channeling of the upward flow of the replacement water occurred, and further bulking occurred at the bottom of the tower and The extraction of crystals became unstable, and operation was impossible.
[0038]
【The invention's effect】
In the method for producing high-purity terephthalic acid of the present invention, a mother liquor displacement apparatus is provided by which an extremely high mother liquor substitution rate is obtained and the fluidity of the deposit layer is maintained by gently rotating an arm type stirring blade provided in the deposit layer. Dramatically improved drivability.
This mother liquor replacement method eliminates the need for a mother liquor separator and dryer for the crude terephthalic acid obtained by the liquid phase oxidation reaction. The mother liquor replacement column is a small and simple device, and can be easily scaled up from a laboratory scale device to a commercial scale device. Furthermore, since the mother liquor replacement column can be easily operated at high temperature and high pressure, it is possible to obtain higher quality and high purity terephthalic acid and to reduce the number of crystallizers of crude terephthalic acid.
[0039]
For this reason, the process flow, which is one of the major problems in the conventional high-purity terephthalic acid production method, is shortened, and the construction cost in the production of high-purity terephthalic acid is significantly reduced and the operation is facilitated.
In addition, in the high purity terephthalic acid production method of the present invention, the cost of use consumed in the mother liquor separator and dryer of the crude terephthalic acid is reduced, and an extremely high mother liquor replacement rate is obtained. The outflow amount of acetic acid, which is a solvent for the liquid phase oxidation reaction, is reduced, and the load on wastewater treatment hardly increases.
Therefore, according to the present invention, highly purified terephthalic acid which is extremely advantageous commercially can be produced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a mother liquor replacement apparatus used in Examples.
[Explanation of symbols]
1: Mother liquor replacement tower 2: Raw material slurry supply pump 3: Raw material slurry introduction tube 4: Mother liquor discharge tube 5: Screw conveyor for crystal extraction 6: Screw conveyor guide tube 7: Crystal extraction port 8: Motor 9: Slurry tank 10: Arm Stirring blade 11: Motor 12: Circulation pump 13: Slurry extraction pump 14: Water supply pump a (coast line): Deposited layer upper surface b: Deposited layer of terephthalic acid crystal

Claims (6)

In a method for producing high-purity terephthalic acid in which an acetic acid solvent slurry of terephthalic acid crystals obtained by liquid phase oxidation of p-alkylbenzene is replaced with an aqueous solvent slurry and then subjected to catalytic hydrogenation, A solvent slurry is introduced, a sedimentation layer of terephthalic acid crystals is formed at the bottom of the tower by sedimentation of terephthalic acid crystals, and replacement water sufficient to form an upward flow of water is supplied from the bottom to the inside of the tower. Production of high-purity terephthalic acid, wherein the crystal deposit layer is extracted by a screw conveyor , an arm type stirring blade is provided in the deposition layer, and the fluidity of the deposition layer is maintained by gently rotating the stirring blade. Law The method for producing high-purity terephthalic acid according to claim 1, wherein the replacement water is intermittently supplied. The method for producing high-purity terephthalic acid according to claim 1 or 2, wherein the replacement water is supplied while being pulsed. The method for producing high-purity terephthalic acid according to claim 1, wherein a pulse is applied to the bottom of the mother liquor displacement column. The method for producing high-purity terephthalic acid according to claim 1, wherein the rotational speed of the arm type stirring blade is 0.1 to 20 revolutions per minute. The method for producing high-purity terephthalic acid according to claim 1, wherein replacement water from the bottom of the deposition layer is supplied in a sprinkler-like manner from a stirring blade provided in the deposition layer.

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