JP2010202552A - Crystallizer for aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallizer that enables long-term stable operation by solving the problems occurring in a crystallization step of an aromatic carboxylic acid, particularly in a crystallization step by a flush method. <P>SOLUTION: The crystallizer comprises: a crystallization tank for obtaining aromatic carboxylic acid slurry by precipitating an aromatic carboxylic acid crystal from a liquid containing an aromatic carboxylic acid; a feed pipe for feeding the liquid to the crystallization tank; and a discharge pipe for discharging the aromatic carboxylic acid crystal from the crystallization tank. The crystallizer is also equipped with a treatment apparatus for treating a gaseous composition produced inside the crystallization tank. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystallizer, and more particularly to a crystallizer used in an aromatic carboxylic acid production process.

  Terephthalic acid, which is a typical example of aromatic carboxylic acid, is a raw material in the presence of a heavy metal catalyst mainly composed of cobalt, manganese, and a bromine compound using a solvent containing an aliphatic carboxylic acid such as acetic acid and water. A method of producing para-xylene by liquid phase oxidation under pressure with a gas containing molecular oxygen is generally performed. In order to reduce the amount of trace impurities contained in terephthalic acid as much as possible due to the demands of commercial use of terephthalic acid, a further high-temperature and high-pressure additional oxidation reaction process was installed, and the terephthalic acid slurry after the oxidation reaction was separated. A method of installing a process of hydrotreating after drying is performed.

  After the above liquid phase oxidation, after additional oxidation, or after hydrorefining, the solid-liquid separation / washing / drying treatment is usually performed after the crystallization step. In order to reduce energy consumption, the crystallization process generally employs a flash system in which the pressure and temperature are rapidly reduced. In the flash method, crystallization is performed by lowering the temperature by evaporating a part of the solvent, so that the slurry concentration is increased and a clogged state is likely to occur in the crystallization tank or the transfer pipe. In addition, since a high-pressure liquid material is supplied to the crystallization tank, the pressure of the liquid material causes an impact on the stirring axis of the crystallization tank, vibration of the stirring tank, etc. As a result, the life of the stirring shaft may be shortened. There are problems such as damage to bearings and mechanical seals, making it difficult to continue long-term stable operation.

In order to solve these problems, Patent Document 1 proposes a method in which a baffle is provided in a stirring tank, and the liquid level of the slurry-like contents is arranged at the upper end of the baffle or above it. Moreover, in patent document 2, in the slurry stirring tank with a baffle provided with an insertion-type radiation liquid level gauge, the stirring tank which suppresses the production | generation of a lump by providing the lower end of the said liquid level gauge, or the upper end of a baffle below it. Has proposed. Further, Patent Document 3 proposes a method in which the supply of slurry to the crystallization tank is controlled by a pressure reducing valve, and an intermittent impact is applied and eliminated by intermittent opening / closing operation of the pressure reducing valve. However, in the case of Patent Documents 1 and 2, it is a countermeasure for the problem that occurs in the upper part of the crystallization tank, and in the case of Patent Document 3, it is a countermeasure in the lower part of the crystallization tank. Yes, it has not yet been solved completely.
Patent Document 4 proposes not a flash method but a method in which low-temperature water is added to lower the temperature and crystallize without increasing the slurry concentration. However, this method is not efficient in terms of energy utilization compared to the flash method.
As described above, there are still insufficient measures to solve all the problems such as blockage and equipment damage that occur in the crystallization process by the flash method.

JP 2004-168673 A JP 2004-167711 A JP-A-8-89706 JP 2000-86577 A

Among the background arts as described above, the present invention provides a crystallizer capable of improving long-term stable operation by improving the problems that occur in the crystallization process of aromatic carboxylic acid, particularly in the flash crystallization process. With the goal.

  As a result of intensive studies to solve the above problems, the present inventors have optimized the apparatus configuration and functions of a crystallizing apparatus for depositing aromatic carboxylic acid crystals from a liquid containing aromatic carboxylic acid. As a result, it has been found that long-term continuous operation is possible, product quality can be stabilized, equipment damage can be prevented and costs can be reduced, and the present invention has been completed.

That is, the gist of the present invention is a crystallization tank for obtaining an aromatic carboxylic acid slurry by depositing an aromatic carboxylic acid crystal from a liquid containing an aromatic carboxylic acid, a supply pipe for supplying the liquid to the crystallization tank, a crystal A crystallization apparatus having a discharge pipe for discharging an aromatic carboxylic acid slurry from a crystallization tank, comprising a processing apparatus for processing a gas phase composition generated in the crystallization tank. Equipment.
In the crystallization apparatus of the present invention, it is preferable that the processing apparatus includes a facility for separating a solid entrained in the gas phase composition from the gas composition, and the processing apparatus further includes the gas phase composition. It is preferable to use a system in which water and water are brought into countercurrent contact.
In the crystallization apparatus of the present invention, the crystallization tank is preferably a flash system, and the crystallization tank preferably has a stirrer and a baffle.
In the crystallization apparatus of the present invention, at least one of a crushing function of aromatic carboxylic acid crystals, a dispersing function of aromatic carboxylic acid slurry, a mixing function, and a conveying function is provided downstream of the discharge pipe. It is preferable.
Moreover, it is preferable that the piping which has two or more said crystallization tanks and connects between different crystallization tanks is equipped with the heating function which heats this piping.

Furthermore, another gist of the present invention is a crystallization tank for obtaining an aromatic carboxylic acid slurry by depositing an aromatic carboxylic acid crystal from a liquid containing an aromatic carboxylic acid, and a supply for supplying the liquid to the crystallization tank. A crystallization apparatus having a discharge pipe for discharging an aromatic carboxylic acid slurry from a pipe and a crystallization tank, wherein the crystallization apparatus has a plurality of supply pipes.
In the crystallization apparatus of the present invention, the crystallization tank is preferably a flash system, and the crystallization tank preferably has a stirrer and a baffle.
In the crystallization apparatus of the present invention, at least one of a crushing function of aromatic carboxylic acid crystals, a dispersing function of aromatic carboxylic acid slurry, a mixing function, and a conveying function is provided downstream of the discharge pipe. It is preferable.
Moreover, it is preferable that the piping which has two or more said crystallization tanks and connects between different crystallization tanks is equipped with the heating function which heats this piping.

  According to the present invention, in the crystallization tank, vibration of the stirring tank accompanying the flash operation, impact on the stirring shaft, and the like are suppressed, and the life of the lower part of the stirring shaft, the intermediate bearing, the mechanical seal, and the like can be extended. In addition, entrainment to the gas phase portion of the crystallization tank and entrainment loss to the exhaust gas are reduced, the heat efficiency of the cooling heat exchanger is improved, and blockage in the condensate tank and piping is suppressed. Furthermore, long-term stable operation is possible by reducing the blockage of piping due to lump in the supply pipe to the crystallization tank and downstream of the crystallization tank, product quality is stabilized, and economic loss is greatly reduced. The

It is a conceptual diagram which shows one Embodiment of the crystallization apparatus which concerns on this invention. It is a conceptual diagram of the aromatic carboxylic acid manufacturing flow to which this invention is applied.

Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.
Although the installation location of the crystallizer of this invention in an aromatic carboxylic acid manufacturing process is not limited, Usually, the following 2 locations are mentioned.
(Step 1) Obtained by pressure liquid phase oxidation with molecular oxygen in the presence of a catalyst in the presence of a catalyst, using an alkyl aromatic compound as a raw material, and a mixture of a lower aliphatic carboxylic acid and water, followed by additional oxidation as necessary. Crystallization of the resulting crude aromatic carboxylic acid slurry.
(Step 2) A step of dissolving the crude aromatic carboxylic acid obtained in Step 1 in water, reducing impurities by a hydrogenation reaction, and crystallizing the resulting solution.

[Crystallizer]
FIG. 1 is a conceptual diagram showing an embodiment of a crystallization apparatus according to the present invention. Although the crystallization method in the crystallization apparatus of the present invention is not limited, it is preferably a flash crystallization tank.
The crystallization tank 20 is obtained by a supply pipe 22 for supplying a liquid material 21, a stirrer 25 and a baffle 26 for stirring the liquid material in the tank, a processing device 30 for processing the gas phase composition in the tank, and crystallization. It is a container provided with a discharge pipe 23 for discharging the aromatic carboxylic acid slurry to the outside of the tank. Here, the liquid 21 means a crude aromatic carboxylic acid slurry generated by a liquid phase oxidation reaction in the step 1, and a solution obtained by reducing impurities by a hydrogenation reaction in the step 2. means. Therefore, the liquid 21 may already contain an aromatic carboxylic acid crystal, and if the aromatic carboxylic acid dissolved in the liquid 21 is crystallized in the crystallization tank 20, it is included in the present invention.

If necessary, a crushing pump 50 is installed downstream of the discharge pipe 23, where the aromatic carboxylic acid crystals in the aromatic carboxylic acid slurry are crushed and then transferred to a solid-liquid separator (not shown). The transfer piping from the discharge pipe 23 to the solid-liquid separation device is normally kept warm as a clogging prevention measure.
In the processing apparatus 30, the gas phase composition generated in the crystallization tank 20 is brought into countercurrent contact with the cleaning water 31, and the solid entrained with the gas is separated and returned to the crystallization tank 20. A heat exchanger 60 is installed downstream of the processing apparatus 30 (upper side in FIG. 1) to use the discharged hot gas, and the condensed liquid is stored in the condensation tank 40 and drained to be partially purged. It is transferred to the treatment process (purge water 42), and the rest is recovered and reused (recovered water 41).

  When crystallizing an aromatic carboxylic acid crystal using the crystallization apparatus of the present invention, it is preferable to provide a plurality of crystallization tanks 20. When a plurality of crystallization tanks 20 are provided, it is not always necessary that all the crystallization tanks have the same configuration as described above, but it is preferable that the final crystallization tank has the configuration of the crystallization apparatus of the present invention. In the case where a plurality of crystallization tanks 20 are provided, the liquid material 21 supplied to the crystallization tank 20 is obtained by the above-described crude aromatic carboxylic acid slurry generated by the liquid phase oxidation reaction or the additional oxidation reaction, or by a hydrogenation reaction. In some cases, not a solution obtained by reducing impurities but a liquid (aromatic carboxylic acid slurry) discharged from another crystallization tank 20 may correspond.

<Crystal tank>
Although the shape of the crystallization tank 20 is not limited, it is usually cylindrical, and the lower part of the tank is preferably a spheroid. Although the material of the crystallization tank 20 is not limited, Stainless steel, titanium, nickel alloy, etc. are mentioned. As the stainless steel, austenitic stainless steel is preferable. For example, SUS304, SUS304L, SUS316L, SUS317L, NAS254N, NAS354N manufactured by Nippon Yakin Kogyo Co., Ltd., Avesta (trademark) 254MO manufactured by SANDVIK, etc. are used. Examples of the nickel alloy include MAT21, MA22, MA276, MC alloy, MA625, MA600, MA-X manufactured by Mitsubishi Materials Corporation, and Hastelloy (trademark) C276, C22, B3, C4 manufactured by Haynes.
Etc. are used.

The crystallization tank 20 is usually provided with a stirrer 25 in order to make the concentration of the liquid substance uniform in the tank. As the shape of the stirring blade 25c in the stirrer 25, a propeller, a paddle, a turbine, a flat blade, an anchor, a helical ribbon, or the like can be adopted. As a method for performing uniform stirring, it is important to install a plurality of stirring blades 25c, to appropriately select the stirring blades 25c, and to appropriately set the stirring power. It is desirable to install two or more stirring blades 25c. However, it is sufficient that even one stirring blade 25c can maintain an appropriate dispersion force in combination with a stirring blade and stirring power. When a propeller, a flat blade or the like is used as the stirring blade 25c, the “plurality” and “two” can be read as “multiple stages” and “two stages”, respectively.
Stirring power by agitator 25 may be at 0.1 kw / ^{m 3} or more, but preferably at 0.2kw / ^{m 3} or higher, and usually 4 kw / ^{m 3} or less, preferably 3 kw / ^{m 3} or less.

<Supply pipe>
One of the features of the present invention is that a plurality of supply pipes 22 are provided for one crystallization tank 20. The number of supply pipes 22 is not limited and may be 2 or more, but is usually 6 or less, preferably 5 or less.
In the case of a flash type crystallization tank, when the high-pressure liquid material 21 is flushed into the low-pressure crystallization tank 20 through the supply pipe 22, a pressure difference is locally generated, so that the slurry is generated inside the crystallization tank 20. The concentration distribution becomes non-uniform, and a lump is easily generated. In addition, since the high pressure when the liquid material 21 is flushed is locally applied to the inner wall of the crystallization tank 20 and the stirrer 25, the impact causes the crystallization tank 20 to vibrate or the stirrer 25 (particularly the stirrer 25). The lower part of the wing 25c, the intermediate bearing, the mechanical seal, etc.) may be damaged. Further, when the high-pressure liquid material 21 is introduced into the crystallization tank, the liquid surface of the liquid material in the tank is disturbed, and the vapor phase composition (gas) that volatilizes to the heat exchanger 60 side accordingly. ) May increase. Further, when a plurality of crystallization tanks are used, the slurry may be supplied as the liquid material 21, but when supplying a high-concentration slurry, the supply pipe may be blocked.

As these countermeasures, by providing a plurality of supply pipes 22 for one crystallization tank 20, the formation of lumps in the crystallization tank 20 is reduced. Damage can be largely avoided, and furthermore, the amount of gas that volatilizes toward the heat exchanger 60 can be suppressed. Moreover, when using a some crystallization tank, the obstruction | occlusion by the slurry supplied as the liquid substance 21 can be suppressed.
When a plurality of crystallization tanks 20 are provided, it is not always necessary to provide a plurality of supply pipes 22 for all the crystallization tanks. For the purpose of suppressing the amount of gas that volatilizes toward the heat exchanger 60 side, it is preferable that the final crystallization tank having a large amount of volatile gas is configured as described above.
Although the installation position of the supply pipe is not limited, it is usually provided so as to be below the interface 24 (the liquid level of the liquid material 21). The material of the supply pipe 22 is not limited, but the same material as the crystallization tank 20 can be used.

<Baffle>
The crystallization tank 20 is preferably provided with a baffle 26 in order to make the liquid concentration uniform in the tank. The baffle is also called a baffle plate and usually means a plate-like object fixed to the inner wall of the crystallization tank 20 by welding. The shape of the baffle 26 is not limited, and examples thereof include a flat plate shape and a curved plate shape.
It is preferable to install a plurality of baffles 26 for one crystallization tank. The number of the baffles 26 is not limited, but is preferably at least 2 or more, preferably 3 or more, and 10 or less, preferably 8 or less. One baffle is not preferable because the flow of the liquid in the crystallization tank becomes non-uniform or the stirring efficiency decreases. The baffle 26 is preferably installed such that the upper end of the baffle 26 is held below the interface 24 and that the supply port 22 is within the height range of the baffle 26. By providing the baffle 26, the flow rate in the vertical direction and the degree of turbulence can be increased while suppressing the flow in the circumferential direction in the tank, and the stirring efficiency of the liquid material 21 can be increased. Further, normally, droplets of the liquid material 21 adhere to the inner wall surface of the tank above the interface 24, and when the adhered substance dries, solidifies, peels and falls into the tank, the outlet of the crystallization tank 20 and the discharge pipe 23 However, by providing the baffle 26 and considering its installation position, the liquid material 21 can be prevented from adhering to the inner wall surface of the tank.
Although the material of the baffle 26 is not limited, the thing similar to the crystallization tank 20 can be used.

<Shielding plate>
In the vicinity of the outlet of the supply pipe 22 in the crystallization tank 20, it is effective to disperse the impact in the case of a flash type crystallization tank by installing a shielding plate (not shown) perpendicular to the liquid material 21. . As a method of installing the shielding plate, a plurality of rods supporting the shielding plate are provided around the outlet of the supply pipe 22 and are vertically welded to the tank wall surface. Connect. The connecting position is not limited, but the distance from the outlet of the supply pipe 22 is preferably within half of the radius of the crystallization tank 20. The shielding plate is preferably installed perpendicularly to the line connecting the outlet of the supply pipe 22 and the stirring shaft 25b at the center of the crystallization tank 20, and facing the line. The shape of the shielding plate is not limited and may be any shape that can disperse impact, such as a round shape or a square shape, but a round shape is desirable. When the shielding plate is round, the diameter is larger than the diameter of the outlet of the supply pipe 22 and is preferably 2 times or more, and usually 5 times or less and 4 times or less. The shielding plate is preferably provided with a plurality of punched portions. The punching shape is not particularly limited as long as it can disperse the impact appropriately, such as a round shape, a square shape, and a triangular shape. The material of the shielding plate is not limited, but is preferably the same as the crystallization tank 20.

<Processing apparatus for processing a gas phase composition>
One of the features of the present invention is that a processing apparatus 30 for processing a gas phase composition generated in the crystallization tank 20 is provided at an exhaust gas discharge port at the top of the crystallization tank 20. Here, the gas phase composition refers to a mixture containing a gas and a solid accompanying the gas. Although the processing apparatus 30 used by this invention is not limited, It is preferable to provide the installation which isolate | separates the solid entrained in a gaseous-phase composition from this gaseous composition. Moreover, it is preferable that the processing apparatus 30 used by this invention is a system which makes a gaseous-phase composition and water contact countercurrent, and specifically, it is a scrubber. The structure of the scrubber employed is not limited, and a tray tower, a spray tower, a packed tower, etc. can be used, but a tray tower or a spray tower is preferred.

When a tray tower is used as the processing apparatus 30, a sieve tray is preferable as the tray. The number of trays used is not limited, but is preferably at least 2 or more, more preferably 3 or more, and usually 6 or less, preferably 5 or less. If the sheave tray has one stage, the cleaning effect (the effect of separating the solid entrained in the gas phase composition) may be insufficient. The washing water 31 is supplied from the upper part of the tray tower and is brought into countercurrent contact with the gas phase composition rising from the lower part of the tray tower, thereby separating the solids such as fine powder entrained in the gas phase composition from the gas phase composition. Then, it is dropped into the crystallization tank 20 together with the washing water 31. The linear velocity of the gas phase composition is appropriately set, but is usually 0.01 m / s to 1 m / s, and the ratio of the cleaning water 31 to the gas phase composition is approximately 5 to 20: 1 (weight ratio). It is preferable to do this.
Although the material of the processing apparatus 30 is not limited, the thing similar to the crystallization tank 20 can be used.

In crystallization by the flash method, a large amount of gas is generated as the liquid material 21 drops in pressure from the high pressure side to the low pressure side. Usually, since the generated gas is high temperature, in order to recover thermal energy from the gas, a heat exchanger 60 is installed downstream of the crystallization tank 20 (upward in FIG. 1) to recover energy. When the processing apparatus 30 is not provided, a solid such as fine powder accompanying the gas adheres to the shell side (the side that gives heat) of the heat exchanger 60 to reduce thermal efficiency and generate energy loss. In addition, a large amount of solid content is contained in the condensate produced by cooling by heat exchange to form a slurry, the solid content concentration in the condensation tank 40 increases, the piping downstream of the condensation tank 40 is blocked, cooling water Problems such as an obstacle in quality occur during reuse.
In the present invention, by installing the processing device 30 on the upper part of the crystallization tank 20, the fine powder in the gas phase composition is prevented from adhering to the heat exchanger 60, and the condensation tank 40 or downstream of the condensation tank 40 is suppressed. Blockage of the pipes can be suppressed.
In the case where a plurality of crystallization tanks 20 are provided, it is not always necessary to provide the treatment apparatus 30 in all the crystallization tanks, but it is preferable to provide the crystallization tanks with a large amount of volatilized gas. It is preferable to provide in a tank.

<Crushing pump>
The crystallization apparatus of the present invention is provided with at least one or more of an aromatic carboxylic acid crystal crushing function, an aromatic carboxylic acid slurry dispersing function, a mixing function, and a conveying function downstream of the discharge pipe 23. preferable. Although the specific apparatus for achieving these functions is not limited, it is preferable to provide the crushing pump 50. Since crystals with a small particle size are present in a high concentration in the liquid material (aromatic carboxylic acid slurry) after crystallization by the crystallization tank 20, the crystals are separated in the crystallization tank 20 and the discharge pipe 23. Aggregation occurs, crystals attached to the inner wall of the crystallization tank grow, or scale to the inner wall of the transfer pipe. If the crystal grown in this way is peeled off, there may be a problem that the crystal after the discharge pipe 23 is blocked. By providing the crushing pump 50, the above problem can be solved.

  The crushing pump 50 may be a device in which a crusher and a pump are individually installed, crushed by a crusher, and then transferred by a pump, but it is more efficient to use a device having both a crushing function and a pump function. is there. Here, the pump function includes a transfer function. When a device having both a crushing function and a pump function is used as the crushing pump 50, the crushing pump 50 is usually crushed to a predetermined size or less by three stages of rough cutting, secondary cutting, and fine cutting by selecting a blade for crushing. , Pressure transported. Furthermore, in addition to the crushing function and the pump function, it is preferable to use a multipurpose dispersion pump (also referred to as a high function slurry pump) having one or more of a dispersion function and a mixing function. Examples of such an apparatus include a scatter pump SD-K manufactured by Sanwa Hydrotech Co., Ltd.

When using the apparatus which has a crushing function and a pump function as the crushing pump 50, the rotary blade and the fixed blade are installed for crushing, and also the impeller is equipped for conveyance. There are single-stage and double-stage types of fixed blades, and the crushing size can be determined almost arbitrarily. In the present invention, the crushing size is usually 10 mm diameter or less, preferably 5 mm diameter or less, more preferably 4 mm diameter or less. It is preferable that the device is set as described above. If the size of the aromatic carboxylic acid crystals is too small, the capacity of the crushing pump tends to be excessive. On the other hand, if the crushing size is too large, reaggregation of crystals occurs, or crystals are deposited and separated on the inner wall of the pipe downstream from the crushing pump 50, so that the centrifugal pump may be blocked and cannot be used. Here, the centrifugal pump is used to transfer the aromatic carboxylic acid slurry stored in a storage tank installed downstream from the crushing pump to a solid-liquid separation device described later. In addition, the aromatic carboxylic acid slurry in the storage tank can be transferred to the solid-liquid separator without using a centrifugal pump.
Although the material of the crushing pump 50 is not limited, the thing similar to the crystallization tank 20 can be used.

In the case where a plurality of crystallization tanks 20 are provided, it is desirable that the crushing pumps 50 be installed downstream of the discharge pipe 23 for each crystallization tank, but not necessarily all. However, it is preferable to install a crushing pump 50 downstream of the final crystallization tank. A plurality of crushing pumps 50 may be installed in series. This is particularly effective when a hard lump (crystal) is included.
Moreover, it is preferable to heat the transfer pipe to the solid-liquid separation device after the discharge pipe 23 as a preventive measure against a situation where the aromatic carboxylic acid crystal closes the pipe by scaling, reaggregation, or the like in the transfer pipe. It is also preferable to heat the casing of the crushing pump 50. Specifically, heating is performed so that the temperature of the inner wall surface of the pipe is higher than the temperature of the liquid (aromatic carboxylic acid slurry) passing through the pipe, preferably 10 ° C. or higher, and usually 200 ° C. or higher. In other words, it is preferable that the temperature is not higher than 150 ° C. When the temperature of the inner wall surface of the pipe is low, reaggregation is likely to occur locally, and when the temperature is high, product quality is deteriorated and energy is lost.

  The heating medium for heating the pipe is not limited, but steam, hot oil, hot gas generated from other processes, and the like are used. Moreover, it is also preferable to use a heat insulating material, for example, inorganic fiber type heat insulating materials, such as glass wool and rock wool, and a foamed plastic type heat insulating material. Furthermore, the use of a double pipe is also preferable.

<Method for producing aromatic carboxylic acid>
[Oxidation process]
Next, an example of a method for producing an aromatic carboxylic acid to which the crystallization apparatus of the present invention is applied will be described.
Aromatic carboxylic acid is obtained by converting molecular oxygen from raw material alkyl aromatic compound using a heavy metal compound and, if necessary, a bromine compound as a catalyst in a solvent containing lower aliphatic carboxylic acid under a pressure exceeding normal pressure. It is obtained as an aromatic carboxylic acid slurry by performing liquid phase oxidation at 140 to 230 ° C. with the contained gas.

As the raw material alkyl aromatic compound, an aromatic compound having an alkyl group is used. The aromatic ring constituting the aromatic compound may be monocyclic or polycyclic. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. The alkyl group may have a functional group, and examples thereof include an aldehyde group, an acyl group, a carboxyl group, and a hydroxyl group. Specific examples of the alkyl-substituted aromatic compound include carbon such as m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, o-xylene, p-xylene, and trimethylbenzenes. Examples thereof include alkylbenzenes having 2 to 4 alkyl groups of 1 to 4, alkylnaphthalenes, alkylbiphenyls and the like.
Further, the aromatic compound having an alkyl group may have a substituent other than the alkyl group, and specifically, for example, 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-toluic acid, p-toluic acid. , 3-formylbenzoic acid, 4-formylbenzoic acid, 2-methyl 6-formylnaphthalene, and the like. These raw materials are used alone or in combination of two or more.

In the following description, a method for producing terephthalic acid will be described with reference to FIG. 2 as an example.
2 is charged with paraxylene, solvent 3, catalyst 4, and molecular oxygen 2 as raw materials 1 and continuously reacted. As the solvent 3, aliphatic carboxylic acids such as acetic acid, propionic acid, formic acid and butyric acid are used, and a solvent containing acetic acid as a main component is preferable. In the case of terephthalic acid, the amount of the solvent 3 used is desirably 1 to 10 times by weight, preferably 2 to 8 times by weight, and more preferably 3 to 6 times by weight with respect to the raw material 1. If the amount of acetic acid is too small, the concentration of the aromatic carboxylic acid slurry may become too high, causing troubles such as clogging, and temperature control in the oxidation reaction may be difficult. If the amount of acetic acid is too large, the amount of solvent in the system with respect to the production amount of the target aromatic carboxylic acid becomes large, and there is a need to increase the size of the equipment, which is not economically preferable.
The solvent 3 is preferably a mixture of acetic acid and water. Usually, water 1-2 is added to 100 parts by weight of acetic acid.
It is a mixture obtained by mixing 0 part by weight, preferably 5 to 15 parts by weight.
As the molecular oxygen 2, for example, a gas containing molecular oxygen such as air, oxygen diluted with an inert gas, or oxygen-enriched air is used. The supply amount is 3 to 100 times mol as molecular oxygen with respect to the raw material 1, and air is preferably used practically. The oxygen content of air at the inlet of the oxidation reaction apparatus 101 is 21% by volume. And it supplies so that the oxygen concentration in the waste gas discharged | emitted from a reactor may be 1-8 volume%, Preferably it is 1.5-3 volume%.

The catalyst 4 is not particularly limited as long as it has an ability to oxidize an alkyl aromatic compound and convert it into an aromatic carboxylic acid, but usually a heavy metal compound is used, and bromine as a catalyst auxiliary as necessary. A compound may be used. Examples of the heavy metal in the heavy metal compound include cobalt, manganese, nickel, chromium, zirconium, copper, lead, hafnium, cerium and the like. These can be used alone or in combination. It is particularly preferable to use a combination of cobalt and manganese. Examples of such heavy metal compounds include acetate, nitrate, acetylacetate, naphthenate, stearate, bromide and the like, and acetate and bromide are particularly preferred.
Examples of the bromine compound include inorganic bromine compounds such as molecular bromine, hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide, manganese bromide, methyl bromide, methylene bromide, bromoform, bromide. Examples thereof include organic bromine compounds such as benzyl, bromomethyltoluene, dibromoethane, tribromoethane, and tetrabromoethane. These bromine compounds are also used alone or as a mixture of two or more.
In the case of terephthalic acid production, the catalyst used when oxidizing the raw material paraxylene specifically includes a combination of cobalt, manganese and bromine, and in particular, a combination of cobalt acetate, manganese acetate and hydrogen bromide. preferable.
In the present invention, the catalyst composed of a combination of the above heavy metal compound and bromine compound is desirably composed of 0.05 to 10 moles, preferably 0.1 to 5 moles of bromine atom with respect to 1 mole of heavy metal. Such a catalyst is usually used in the range of 10 to 10,000 ppm by weight, preferably 100 to 3000 ppm by weight as the heavy metal catalyst in the solvent 3.

The temperature of the oxidation reaction is usually 140 ° C to 250 ° C, preferably 150 ° C to 230 ° C. If the reaction temperature is too low, the reaction rate decreases, and if the reaction temperature is too high, the amount of loss due to combustion of the acetic acid solvent increases. The reaction pressure needs to be equal to or higher than the pressure at which the mixture can maintain a liquid phase at least at the reaction temperature, and needs to be a pressure higher than normal pressure. Specifically, 0.2 to 6 MPa (absolute pressure) is preferable, and 0.4 to 3 MPa (absolute pressure) is more preferable. In order to facilitate the transfer of the produced aromatic carboxylic acid slurry, a higher pressure is better, which leads to suppression of side reactions, but a lower pressure is preferable from the viewpoint of pressure resistance of the reaction vessel, equipment cost, and the like.
The reaction is usually carried out continuously, and the reaction time (average residence time) is usually 30 to 300 minutes, preferably 40 to 150 minutes. If the reaction time is too short, the quality of the aromatic carboxylic acid may deteriorate due to insufficient oxidation reaction. If the reaction time is too long, the amount of loss due to combustion of a solvent such as acetic acid will increase. The capacity of 101 increases, which is not economical.
The water in the solvent is adjusted by purging a part of the condensate obtained by condensing exhaust gas out of the system because water is by-produced by the reaction.

  The structure of the oxidation reaction apparatus 101 may be a stirring tank or a bubble column. When a stirring tank is used, a complete mixing type stirring tank is preferable. In the case of the bubble column, the molecular oxygen 2 supplied from the lower part of the bubble column is extracted from the bubble column as a reaction gas accompanied by a large amount of solvent vapor after being used for the oxidation reaction. After a condenser is provided at the upper part of the bubble column to condense the exhaust gas mainly composed of the solvent and separate the condensed liquid, the exhaust gas discharged is treated in an exhaust gas treatment step. Note that the same method can be applied to the exhaust gas treatment method even when a stirring tank is used.

  In the exhaust gas treatment process, separation and recovery of the solvent 3 and the like, recovery of thermal energy, and the like can be performed. The exhaust gas is condensed (liquefied by cooling) with a condenser installed at the top of the oxidation reaction apparatus 101 to recover thermal energy and return a part of the condensate to the oxidation reaction apparatus 101. The exhaust gas that has passed through the condenser is introduced into a high-pressure absorption tower downstream (upper part) of the condenser, and the absorption liquid absorbs the exhaust gas components. Examples of the absorbing liquid include the same compound and / or water as the solvent 3, and examples of the component to be absorbed include water produced as a by-product in the oxidation reaction, the solvent 3, the unreacted raw material 1, and by-products. Subsequently, the mixture of the absorbing liquid and the remainder of the condensate separates water and components other than water by distillation separation or the like. The separated components other than water, that is, the solvent 3, the unreacted raw material 1, and the by-products are returned to the oxidation reaction apparatus 101 and reused. Components other than water may be returned to the oxidation reaction tank 101 as they are, but they may be used as the absorbing solution, and may be reused after increasing the purity of the solvent 3. Since the exhaust gas discharged from the high-pressure absorption tower maintains a high pressure state, the pressure energy is recovered by a gas expander or the like, and then detoxified and released. (Not shown)

As another example of the embodiment used in the present invention, a separation mother liquor mainly composed of water obtained by solid-liquid separation in a purification step described later by directly connecting a high pressure distillation column to the upper part of the oxidation reaction apparatus 101 instead of a condenser. May be introduced into the upper part of the high-pressure distillation column, and the same operation as that of the condenser may be performed. (Not shown)
In the present invention, in the oxidation step, additional treatment may be performed as necessary. The additional treatment means that the aromatic carboxylic acid slurry obtained by the above oxidation reaction is continuously supplied with the molecular oxygen without supplying the raw material 1 under either the low temperature condition or the high temperature condition than the oxidation reaction condition. Oxidation is one or more times in the presence. When performing additional processing, an oxidation reaction apparatus is added. Conventionally known conditions may be applied as the conditions for the additional oxidation.
In addition, when an additional process is performed on low temperature conditions, an aromatic carboxylic acid crystal will precipitate during the additional process on this low temperature condition. Therefore, in such a case, the oxidation reaction apparatus used for the additional treatment under the low temperature condition can be regarded as the crystallization tank 20 and can be applied to the crystallization apparatus of the present invention.

[Crystalling process]
The oxidation reaction slurry obtained after finishing the oxidation reaction or the additional oxidation reaction is then crystallized in the crystallizer 102 of the present invention described above. The crystallization apparatus of the present invention can be applied to this crystallization process. Crystallization may be performed either batchwise or continuously, but is usually stepped down by a plurality of crystallization tanks 20 in a continuous manner. The number of crystallization tanks 20 is usually 6 or less, preferably 5 or less.
The crystallization method in the crystallization apparatus of the present invention is not limited, but a flash method is preferable. The release pressure in the flash method is not limited. However, when a plurality of crystallization tanks are used, the pressure is usually reduced to a normal pressure to 20 MPa in the initial stage crystallization tank, and the pressure is lowered stepwise. The final pressure for releasing the crystallization tank may be normal pressure.

[Solid-liquid separation and washing process]
The crude terephthalic acid slurry obtained from the crystallizer is then solid-liquid separated by the solid-liquid separation / washing device 103 and separated into the terephthalic acid cake (aromatic carboxylic acid cake 8) and the mother liquor 13.
Solid-liquid separation can be carried out at normal pressure, reduced pressure, or increased pressure. In the case of pressure separation, the pressure is usually 0.01 MPa or more, preferably 0.03 MPa or more, more preferably 0.05 MPa or more. The upper limit is 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, and particularly preferably 2 MPa or less. It is also possible to install a pressurizing device such as a pump upstream of the solid-liquid separator and further pressurize and separate.

Since the mother liquor is attached to the solid content of the slurry that has been subjected to solid-liquid separation, washing is usually required.
The washing liquid is not limited as long as the liquid state can be maintained at the pressure and temperature in the solid-liquid separation device, but is preferably compatible with the solvent used in the oxidation reaction, and generally an acetic acid aqueous solution or water is used. The pressure at the time of washing is preferably the same as the pressure at the time of solid-liquid separation.
When solid-liquid separation and washing are performed under high temperature and high pressure, the solid content of the slurry after washing still has high energy (heat and / or pressure), so it is desirable to utilize this energy during drying. This can be achieved by a flash evaporation drying apparatus in which the solid content liquid is opened from high pressure to low pressure.

  It can also be carried out by a solid-liquid separation washing / drying apparatus capable of performing solid-liquid separation, washing and drying with one apparatus. There are no restrictions on the equipment, but a discharge valve is used at the bottom of the hopper where the solid content of the slurry is stored using a screen bowl decanter, solid bowl decanter, horizontal belt filter, rotary pressure filter, rotary vacuum filter, etc. And flash dry to extract into a lower pressure reservoir. If the drying is insufficient, a known drying apparatus may be installed for additional processing. A fluidized bed dryer, a rotary steam tube dryer or the like is preferably used.

The separated mother liquor 13 is branched into a recycled mother liquor and a purge mother liquor. Here, the mother liquid 13 includes washing water. The branching of the mother liquor 13 is preferably performed while maintaining a pressure exceeding the normal pressure, and more preferably a pressure that substantially maintains the operation pressure for solid-liquid separation. Although the branching ratio between the recycled mother liquor and the purge mother liquor can be arbitrarily adjusted according to the situation of the entire manufacturing process, the recycled mother liquor is usually 50% by weight or more, preferably 70% by weight or more of the mother liquor 13. By setting the ratio of the recycled mother liquor to the above lower limit or more, there is an advantage that the amount of the purge mother liquor is reduced, resulting in a reduction in mother liquor loss, and an advantage that the methyl bromide concentration in the oxidation reactor exhaust gas can be lowered. is there. The recycled mother liquor is preferably 95% by weight or less, preferably 90% by weight or less of the mother liquor 13. By setting the ratio of the recycled mother liquor to be equal to or less than the above upper limit value, there is an advantage that the accumulation of impurities in the system can be suppressed and the product quality can be improved.
Many components are contained in the purge mother liquor. These are aromatic carboxylic acids, unreacted raw materials, by-products, catalysts, solvents, water and the like. As a method for recovering and reusing these components, a plurality of recovery methods are used in combination depending on the properties and properties of the recovery object.

[Liquid substance adjustment process]
The terephthalic acid cake obtained by the above-described production method contains an oxidation intermediate, unreacted substances, impurities, and the like, and may not be used as a product as it is, so that further purification is preferably performed. As a purification operation, there is carried out a method in which 4-carboxybenzaldehyde, which is a main impurity in the reduction reaction by hydrogenation, is changed to p-toluic acid or the like, and solid-liquid separation is performed using a difference in water solubility with terephthalic acid. First, a crude terephthalic acid liquid (crude aromatic carboxylic acid liquid 9) is prepared in the liquid preparation tank 104. The type of the solvent 5 is not particularly limited, but it is desirable to include water from the solubility of organic substances, the boiling point, and the like, more preferably 90% by weight of water, more preferably about 100% by weight of water. In order to suppress water consumption, it is preferable to reuse the water generated in the terephthalic acid production process.

The concentration of terephthalic acid crystals in the liquid is 10% or more, preferably 15% or more, more preferably 20% or more, and usually 40% or less, preferably 35% or less, more preferably 30% or less. If the concentration is low, the apparatus becomes large and not economical. If the concentration is high, the fluidity of the slurry increases, special equipment is required, and the equipment cost increases.
The liquid material adjusting device 104 is operated at normal pressure, and the temperature is 50 ° C. or higher, preferably 70 ° C. or higher, usually 90 ° C. or lower, preferably 85 ° C. or lower. If the temperature is too high, cavitation occurs in a pressure pump (not shown) for transferring the crude aromatic carboxylic acid liquid 9 and it cannot be transferred well, and at a low temperature, the heat balance is disadvantageous.
As the stirring blade, a propeller, paddle, turbine, flat blade, anchor, helical ribbon, etc. can be adopted, preferably a propeller. When a propeller is used, the rotation speed is preferably 30 to 500 rpm, more preferably 50 to 300 rpm, more preferably 70-100 rpm is employed.
Furthermore, the residence time in the liquid preparation apparatus 104 is preferably 10 to 60 minutes, particularly preferably 15 to 30 minutes. If the residence time is too short, the preparation of the slurry concentration is insufficient, and if the residence time is too long, it requires large equipment and is not economical.
In order to prevent problems such as cavitation and clogging in the pressurizing pump, and the effect on the purification quality due to undissolved solids, a foreign matter removing device such as an automatic scraping strainer is provided at the outlet of the liquid preparation device 104. By installing a system (not shown) and separating a large particle having a diameter of 4 mm or more, stable operation becomes possible.

[Hydropurification process]
The crude aromatic carboxylic acid liquid 9 is heated to 230 ° C. or higher by a heating device (not shown), dissolved, and sent to the hydrogenation reaction device 105. The heating device is composed of a plurality of multi-tube heat exchange devices, and is heated with steam, hot oil, etc. recovered from the manufacturing process.
The crude aromatic carboxylic acid liquid 9 to be supplied to the hydrogenation reactor 105 is preferably in a completely dissolved state, but can be dissolved before contacting the stationary phase carrying the catalyst inside the hydrogenation reactor 105. That's fine. The hydrogenation reaction is performed by introducing hydrogen 6 in a state of being immobilized on a stationary phase using a noble metal supported on activated carbon or the like.
The reaction temperature is 230 ° C or higher, preferably 250 ° C or higher, and usually 330 ° C or lower, preferably 310 ° C or lower. The hydrogen partial pressure is usually 0.05 to 2 MPa, and is in contact with a Group 8 metal catalyst such as ruthenium, rhodium, palladium, platinum, osmium, iridium or the like alone or in a mixture usually for 1 to 100 minutes. The pressure at this time is usually 3 MPa or more, preferably 5 MPa or more. Moreover, it is 20 MPa or less normally, Preferably it is 15 MPa or less, More preferably, it is 12 MPa or less. These Group 8 metals are usually used by being supported on a carrier insoluble in a hot aromatic carboxylic acid aqueous solution, such as activated carbon. Among these, it is preferable from the viewpoint of the purification effect that palladium supported on activated carbon is used as a fixed bed.

[Crystalling process]
The hydrogenation reaction liquid 10 is crystallized to obtain a terephthalic acid slurry liquid, and then solid-liquid separation, washing and drying to obtain a product. The crystallization apparatus of the present invention can be applied to this crystallization process. The crystallization tank 106 is composed of a plurality of crystallization tanks connected in series, and cools in stages to crystallize. Usually 2 or more, preferably 3 or more. Moreover, it is 6 or less normally, Preferably it is 5 or less. The temperature is lowered stepwise in the crystallization tank, and the final crystallization condition is that the pressure is usually 0.1 MPa or more, preferably 0.3 MPa or more, more preferably 0.5 MPa or more, and the upper limit is preferably 3 MPa. Hereinafter, it is more preferably 1 MPa or less, particularly preferably 0.7 MPa or less. It is necessary to maintain a temperature and pressure at which dissolved p-toluic acid crystals do not precipitate. The high-pressure steam that is flushed and discharged during crystallization is recovered and reused as thermal energy, the condensed water is partially purged after wastewater treatment, and the rest is reused.

[Solid-liquid separation and washing process]
Subsequently, the terephthalic acid slurry liquid 11 is separated into terephthalic acid, a mother liquor, and a cleaning liquid by a solid-liquid separation / cleaning device 106, and the terephthalic acid is dried to become a product 12. From the mother liquor / cleaning solution, valuable substances such as p-toluic acid, which is an oxidation intermediate, are recovered by crystallization separation and returned to the oxidation step to be changed to terephthalic acid. A part of the mother liquor is reused as a solvent, or trace impurities remaining in the separated mother liquor are concentrated by reverse osmosis membrane treatment, ion exchange treatment, etc., and a portion of the permeated water is a crude aromatic carboxylic acid solvent. If it is reused, the amount of water used and the amount of drainage can be reduced.
The solid-liquid separation in the solid-liquid separation / washing device 106 can be performed at normal pressure, reduced pressure, or increased pressure. However, it is preferable to carry out while maintaining the above-described final crystallization pressure from the viewpoint of energy efficiency. As a separator, when drying is insufficient, such as a screen bowl decanter, a solid bowl separator, a rotary pressure filter, a rotary vacuum filter, a horizontal belt filter, etc., a known drying apparatus is further installed for additional processing. As the dryer, a pressure dryer by pressure-release evaporation, a normal fluidized bed dryer, a rotary steam tube dryer or the like is preferably used.

  The solid-liquid separation, washing and drying can be carried out with a single apparatus. Specific examples of the apparatus are known devices and are not particularly limited. However, the slurry solid content separated and washed using a screen bowl decanter, solid bowl decanter, horizontal belt filter, rotary pressure filter, rotary vacuum filter, etc. It is possible to employ a method in which a discharge valve is provided at the lower part of the stored hopper, and it is flash dried and extracted into a lower pressure reservoir. When the dried cake is insufficiently dried, it is preferably further dried using a fluidized bed dryer, a rotary dryer or the like.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
Example 1
In a high-purity terephthalic acid production facility, para-xylene and 5 parts by weight of acetic acid in para-xylene, 0.5 parts by weight of water in para-xylene, cobalt acetate, manganese acetate as catalyst, Hydrogen bromide was supplied, and the oxidation reaction was performed at a temperature of 190 to 195 ° C., a pressure of 1.0 to 1.7 MPa, and a reaction time (average residence time) of 90 minutes. With respect to the amount of catalyst used, the cobalt component and the manganese component were each 300 ppm by weight in terms of metal, and the bromine component was 700 ppm relative to the solvent. Air was used as a gas for performing an oxidation reaction with molecular oxygen. At this time, the oxygen content of the air was 21% by volume, and compressed air was supplied into the reactor so that the oxygen concentration in the gas discharged from the reactor (oxidation reaction tank) was 3-7% by volume. .

Subsequently, the obtained oxidation reaction slurry liquid was transferred to a low temperature additional oxidation reaction tank and subjected to low temperature additional oxidation at a temperature of 180 to 190 ° C. and a pressure of 1.0 to 1.2 MPa.
The slurry liquid after low-temperature additional oxidation is crystallized stepwise in two crystallization tanks provided in series, and finally the crystallization operation is carried out at 90 ° C. and a pressure of 0.05 MPa. A terephthalic acid slurry was obtained. Each of the two crystallization tanks used was a flash-type crystallization tank having a paddle type stirring blade, two supply ports, and a baffle. The number of baffles was 4 for the first unit (the side close to the low temperature additional oxidation reaction tank) and 5 for the second unit. The pipe connecting the first and second crystallization tanks was heated to 164 ° C. by high-pressure steam (the temperature of the slurry liquid in the pipe was 140 ° C.).

The obtained crude terephthalic acid slurry was subjected to solid-liquid separation and washing with a screen bowl decanter while maintaining the second crystallization conditions (temperature, pressure) to obtain crude terephthalic acid. The pipe from the outlet of the second crystallization tank to the screen bowl decanter was heated to 125 ° C. by pressurized steam (the temperature of the crude terephthalic acid slurry in the pipe was 90 ° C.). 75% of the reaction mother liquor separated into solid and liquid was recycled to the oxidation reactor, and the remainder was recovered after valuable materials such as catalyst and acetic acid were collected, sent to a wastewater treatment step, treated and discharged.
As a result of continuous operation under the above conditions, no damage was observed in the mechanical seal of the stirring blade installed in the flash crystallization tank or in the lower portion of the stirring blade and the intermediate bearing over 2 years. In addition, the supply pipe to each crystallization tank, the pipe between the crystallization tanks, and the pipe from the second crystallization tank to the solid-liquid separation apparatus were not clogged with a lump. Furthermore, reduction of entrainment loss to exhaust gas was able to be achieved.

(Example 2)
Crude terephthalic acid obtained by liquid phase oxidation of para-xylene was introduced into a purifier and mixed with water in a liquid preparation tank to obtain a crude terephthalic acid slurry liquid. The operating pressure was normal pressure, the temperature was 90 ° C., and the residence time was 15 minutes. The obtained crude terephthalic acid slurry liquid is passed through a plurality of serially connected liquid heating and dissolving devices (multi-tubular heat exchangers) using a pressure pump, and steam and heat transfer oil (hot oil) ) At 290 ° C. and 8.5 MPa to completely dissolve terephthalic acid, and then introduced into a purification tank equipped with palladium-activated carbon as a fixed bed together with hydrogen, and impurities 4-carboxybenzaldehyde is added to paratoluic acid. Converted to.

  The obtained aqueous terephthalic acid solution was crystallized stepwise in five crystallization tanks provided in series, and finally the crystallization operation was performed at 160 ° C. and a pressure of 0.65 MPa. Got. All of the five crystallization tanks used were flush type crystallization tanks having paddle type stirring blades, two supply ports, and five baffles. In addition, the pipes connecting all five crystallization tanks were heated with oil so as to be in the range of + 20 ° C. to + 150 ° C. with respect to the temperature of the slurry liquid in each pipe.

The obtained terephthalic acid slurry was subjected to solid-liquid separation, washing and drying with a screen bowl decanter while maintaining the crystallization conditions (temperature, pressure) of the final crystallization tank to obtain terephthalic acid. As the dryer, a fluidized bed dryer was used. The piping from the outlet of the final crystallization tank to the screen bowl decanter was heated to 164 ° C. by high-pressure steam (the temperature of the terephthalic acid slurry in the piping was 155 ° C.).
As a result of continuous operation under the above conditions, no damage was observed in the mechanical seal of the stirring blade installed in the flash crystallization tank or in the lower portion of the stirring blade and the intermediate bearing over 2 years. In addition, the supply pipe to each crystallization tank, the piping between the crystallization tanks, and the piping from the final crystallization tank to the solid-liquid separation apparatus were not clogged with a lump. Furthermore, reduction of entrainment loss to exhaust gas was able to be achieved.

(Example 3)
In the same manner as in Example 2, crude terephthalic acid was introduced into a purifier and hydrogenated to convert impurity 4-carboxybenzaldehyde into p-toluic acid.
The obtained aqueous terephthalic acid solution was crystallized stepwise in four crystallization tanks provided in series, and finally the crystallization operation was performed at 160 ° C. and a pressure of 0.63 MPa. Got. All of the four crystallization tanks used were flash type crystallization tanks having paddle type stirring blades and five baffles. In addition, each crystallization tank is equipped with a scrubber (countercurrent contact with water) equipped with a three-stage sieve tray at the upper part of the crystallization tank gas discharge pipe outlet so that fine powder in the exhaust gas is in countercurrent contact with water. Washed and removed and returned to the crystallization tank. Also, the pipes connecting all four crystallization tanks were heated with oil so as to be in the range of + 20 ° C. to + 120 ° C. with respect to the temperature of the slurry liquid in each pipe.

The obtained terephthalic acid slurry was subjected to solid-liquid separation, washing and drying with a screen bowl decanter while maintaining the crystallization conditions (temperature, pressure) of the final crystallization tank to obtain terephthalic acid. As the dryer, a fluidized bed dryer was used. The piping from the outlet of the final crystallization tank to the screen bowl decanter was heated to 164 ° C. by high-pressure steam (the temperature of the terephthalic acid slurry in the piping was 160 ° C.).
As a result of continuous operation under the above conditions, no damage was observed in the mechanical seal of the stirring blade installed in the flash crystallization tank or in the lower portion of the stirring blade and the intermediate bearing over 2 years. In addition, the supply pipe to each crystallization tank, the piping between the crystallization tanks, and the piping from the final crystallization tank to the solid-liquid separation apparatus were not clogged with a lump.
Furthermore, the product quality such as the particle size and transmittance of terephthalic acid was stabilized, and the entrainment loss to the exhaust gas was reduced.
In addition, heat efficiency due to fine powder adhering to the shell side of the heat exchanger for heat recovery from the exhaust gas does not decrease, the purity of the recovered cooling water is good, and there is a quality problem in reuse There wasn't.

20 Crystallization tank 21 Liquid material 22 Supply pipe 23 Discharge pipe 24 Interface 25 Stirrer 25a Motor 25b Stirring shaft 25c Stirring blade 26 Baffle 30 Processing device 31 Washing water 40 Condensing tank 41 Collected water 42 Purge water 50 Crushing pump 60 Heat exchanger DESCRIPTION OF SYMBOLS 101 Oxidation reaction apparatus 102 Crystallization apparatus 103 Solid-liquid separation and washing apparatus 104 Liquid substance preparation apparatus 105 Hydrogenation reaction apparatus 106 Crystallization apparatus 107 Solid-liquid separation and washing apparatus 1 Raw material 2 Molecular oxygen 3 Solvent 4 Catalyst 5 Solvent 6 Hydrogen 6 7 Crude aromatic carboxylic acid slurry 8 Crude aromatic carboxylic acid cake 9 Crude aromatic carboxylic acid liquid 10 Hydrogenation reaction liquid 11 Aromatic carboxylic acid slurry 12 Aromatic carboxylic acid 13 Mother liquor

Claims (8)

  A crystallization tank for obtaining an aromatic carboxylic acid slurry by depositing an aromatic carboxylic acid crystal from a liquid containing an aromatic carboxylic acid, a supply pipe for supplying the liquid to the crystallization tank, and an aromatic carboxylic acid from the crystallization tank A crystallization apparatus having a discharge pipe for discharging slurry, comprising a processing apparatus for processing a gas phase composition generated in the crystallization tank.   The crystallization apparatus according to claim 1, wherein the processing apparatus includes equipment for separating a solid entrained in the gas phase composition from the gas composition.   The crystallization apparatus according to claim 1 or 2, wherein the processing apparatus is a system in which a gas phase composition and water are brought into countercurrent contact.   A crystallization tank for obtaining an aromatic carboxylic acid slurry by depositing an aromatic carboxylic acid crystal from a liquid containing an aromatic carboxylic acid, a supply pipe for supplying the liquid to the crystallization tank, and an aromatic carboxylic acid from the crystallization tank A crystallization apparatus having a discharge pipe for discharging slurry, wherein the crystallization apparatus has a plurality of supply pipes.   The crystallization apparatus according to any one of claims 1 to 4, wherein the crystallization tank is a flash system.   The crystallization apparatus according to any one of claims 1 to 5, wherein the crystallization tank has a stirrer and a baffle.   In any one of Claims 1-6 provided with at least 1 or more functions among the crushing function of an aromatic carboxylic acid crystal | crystallization, the dispersion function of an aromatic carboxylic acid slurry, a mixing function, and a conveyance function downstream of this discharge pipe. The crystallizer described.   The crystallization apparatus according to any one of claims 1 to 7, wherein the crystallization apparatus has two or more crystallization tanks, and has a heating function for heating the pipes in pipes connecting different crystallization tanks. .

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