JP2000191583A - Production of aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aromatic carboxylic acid in a method for replacing a dispersion medium in an aromatic carboxylic acid slurry with water, capable of efficiently removing water even by returning a diluted mother liquor to a reactor, retaining a solvent in the reactor and efficiently carrying out the formation reaction of an aromatic carboxylic acid. SOLUTION: In this method for producing an aromatic carboxylic acid by oxidizing an alkylaromatic compound in an reaction solvent containing an aliphatic carboxylic acid in the presence of an oxidation catalyst in a liquid phase in a reactor 1, the reactor 1 connected to a distillation column 2 is used. A slurry containing an aromatic carboxylic acid crystal from the reactor 1 is pulled out from L3, a mother liquor attached to the crystal is replaced with water in a multistage column 7, a diluted mother liquor is returned from L4 to the reactor 1. Stream generated in the reactor 1 is introduced into the distillation column 2, the reaction solvent is fractionated by distillation, returned to the reactor 1 and water is discharged to the outside of a system by a condenser 3. Consequently water is discharged in a highly maintained state of the reaction solvent in the reactor 1 to promote the formation of the aromatic carboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aromatic carboxylic acid by subjecting an alkyl aromatic compound containing an alkyl substituent or a partially oxidized alkyl substituent to liquid phase oxidation with an oxygen-containing gas.

[0002]

2. Description of the Related Art Aromatic carboxylic acids are used as basic chemicals. In particular, aromatic dicarboxylic acids are useful as raw materials for fibers, resins, plasticizers and the like. For example, terephthalic acid is frequently used as a raw material for polyester. Conventionally, as a method for producing an aromatic carboxylic acid, generally, in a reactor, a heavy metal compound and a bromine compound are used as catalysts, and a methyl group-substituted aromatic compound is molecularly dispersed in a reaction solvent containing a lower aliphatic carboxylic acid such as acetic acid. A method of contacting with an oxygen-containing gas and performing liquid phase oxidation is employed. In such a production method, an oxidation reaction is carried out by introducing an alkyl-substituted aromatic compound such as para-xylene, a mixture of acetic acid and a catalyst as a solvent, and an oxygen-containing gas such as air into a reactor, and performing oxidization reaction such as terephthalic acid. Of aromatic carboxylic acids.

The generated aromatic carboxylic acid such as terephthalic acid precipitates as a crystal and forms a slurry. The slurry is extracted from the reactor into a slurry receiving tank, and the crystals are recovered by solid-liquid separation to obtain a crude terephthalic acid or the like. A crude product is obtained. Oxidation reaction intermediates and impurities are entrained in the crystals of the crude product thus obtained, so that the crude product is dissolved, and the crystals of terephthalic acid or the like are subjected to a purification process such as an oxidation treatment or a reduction treatment to form crystals. Upon precipitation, a slurry containing crystals is obtained. When crystals are recovered from such a slurry, a purified product such as purified terephthalic acid is obtained.

Conventionally, in order to recover crystals from the slurry produced by the reaction, the slurry is extracted from the reactor into a slurry receiving tank, and solid-liquid separation is performed by a solid-liquid separation device such as a centrifuge or a rotary filter. The separated mother liquor is returned to the reactor, but part of the mother liquor adheres to the crystals,
This is collected and returned to the reactor. The mother liquor that adheres when viewed from the side of the separated crystal is an impurity and must be removed.

[0005] In order to remove the mother liquor attached to the crystals, the substrate is washed with a lower aliphatic carboxylic acid such as acetic acid used as a reaction solvent, and the washing effluent is returned to the reactor.
It was used as a reaction solvent. However, in this method, it is necessary to further replace the solvent attached to the crystal with water and send it to the purification step, which complicates the process and produces a large amount of a low-concentration solvent along with the solvent replacement. Have difficulty.

[0006] In order to improve such a point, a method has been proposed in which the mother liquor of the slurry is replaced with water and the separated mother liquor is returned to the reactor. In this method, a crystal is brought into contact with water in a countercurrent manner to remove a mother liquor attached to the crystal and returned to a reactor. As such a method, there is a method in which a crystal and water are brought into countercurrent contact using a multi-stage column (Japanese Patent Laid-Open No.
-160942), and a method of washing the crystal separated by using a rotary filter and washing water in a countercurrent manner (JP-A-6-327915).

However, in such a method, since the crystals are brought into countercurrent contact with water, a large amount of water is introduced into the reactor together with the mother liquor. Since water is generated in the aromatic carboxylic acid generation reaction, the reaction is suppressed if a large amount of water is present. Water generated in the reactor is removed as steam and removed by condensation. However, since acetic acid as a solvent is also removed at this time, a large amount of water cannot be introduced into the reactor.

Therefore, in the method of exchanging the dispersion medium with water,
Either a small amount of a portion having a high concentration is returned to the reactor, or a mother liquor concentrated by removing water from the diluted mother liquor by evaporation or the like is returned to the reactor. However, the method of returning a small portion with a high concentration has a problem that the loss of the solvent is large, a large amount of drainage occurs, and the method of concentrating and returning the mother liquor complicates the process. is there.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for replacing a dispersion medium of an aromatic carboxylic acid slurry with water, wherein water is efficiently removed even when a diluted mother liquor is returned to a reactor. An object of the present invention is to provide a method for producing an aromatic carboxylic acid capable of efficiently performing a reaction for producing an aromatic carboxylic acid while holding a solvent in a reactor.

[0010]

The present invention relates to the following method for producing an aromatic carboxylic acid. (1) A method for producing an aromatic carboxylic acid by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in a reactor in the presence of an oxidation catalyst, Using a reactor in which the gas phase is connected to a distillation column as a vessel, a slurry containing aromatic carboxylic acid crystals generated in the reactor is extracted, and a diluted mother liquor obtained by replacing the mother liquor attached to the crystals with water is obtained. It is returned to the reactor, the vapor generated in the reactor is introduced into the distillation column, the reaction solvent is fractionated by distillation, refluxed to the reactor, and water is discharged out of the system. A method for producing an aromatic carboxylic acid, wherein water is removed while maintaining a high concentration of carboxylic acid to promote the production of an aromatic carboxylic acid. (2) The water concentration in the mother liquor in the reactor is 1 to 20% by weight.
The method according to the above (1), wherein (3) The water concentration in the diluted mother liquor returned to the reactor is 15
The method according to the above (1) or (2), wherein the amount is 〜50% by weight. (4) The method according to any one of the above (1) to (3), wherein the replacement of the mother liquor attached to the crystal with water is performed by a method in which the crystal separated from the slurry is brought into contact with water. (5) The method according to the above (4), wherein the replacement of the mother liquor adhering to the crystals is carried out by flowing water in an upward flow through the multistage column and bringing the crystals separated from the slurry into contact with water. (6) The method according to the above (4), wherein the replacement of the mother liquor adhering to the crystals with water is based on a method of washing the crystals separated using a rotary filter by contacting the crystals with water. (7) The method according to any one of the above (1) to (6), wherein the water to be replaced with the mother liquor in the slurry is water distilled in a distillation column.

As the oxidizing raw material for producing an aromatic carboxylic acid in the method of the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent (hereinafter sometimes simply referred to as an oxidizing raw material) is used. Can be used. Such an aromatic compound may be monocyclic or polycyclic. Examples of the alkyl substituent include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group. Examples of the partially oxidized alkyl group include an aldehyde group, an acyl group, a carboxyl group, and a hydroxyalkyl group.

Specific examples of the aromatic compound having an alkyl substituent, that is, the alkyl-substituted aromatic hydrocarbon include, for example, m-diisopropylbenzene, p-diisopropylbenzene, m-cymene, p-cymene, m-xylene, An alkyl group having 1 to 4 carbon atoms such as p-xylene, trimethylbenzenes and tetramethylbenzenes is
Di or polyalkyl benzenes having from 2 to 4 di or polyalkyl naphthalenes having from 2 to 4 alkyl groups having 1 to 4 carbon atoms, such as dimethyl naphthalenes, diethyl naphthalenes and diisopropyl naphthalenes;
And polyalkylbiphenyls having 2 to 4 alkyl groups having 1 to 4 carbon atoms, such as dimethylbiphenyls.

The aromatic compound having a partially oxidized alkyl substituent is a compound in which the alkyl group in the above compound is partially oxidized and oxidized to the aldehyde group, acyl group, carboxyl group or hydroxyalkyl group. It is. Specific examples include, for example, 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-
Toluic acid, p-toluic acid, 3-formylbenzoic acid,
Examples include 4-formylbenzoic acid and 2-methyl-6-formylnaphthalenes. These are used alone or as a mixture of two or more.

In the method of the present invention, a heavy metal compound and a bromine compound are used as catalysts. Examples of such compounds are as follows. That is,
As the heavy metal in the heavy metal compound, for example, cobalt, manganese, nickel, chromium, zirconium, copper,
Lead, hafnium, cerium and the like can be mentioned. These can be used alone or in combination, but it is particularly preferable to use a combination of cobalt and manganese. Such heavy metal compounds include, for example, acetate, nitrate, acetylacetonate, naphthenate, stearate, bromide and the like, and particularly preferred are acetate and bromide.

As the bromine compound, for example, molecular bromine,
Inorganic bromine compounds such as hydrogen bromide, sodium bromide, potassium bromide, cobalt bromide and manganese bromide; methyl bromide, methylene bromide, bromoform, benzyl bromide, bromomethyltoluene, dibromoethane, tribromoethane and Organic bromine compounds such as tetrabromoethane can be mentioned. These bromine compounds are also used alone or as a mixture of two or more.

In the present invention, the catalyst comprising the combination of the heavy metal compound and the bromine compound is used in an amount of 0.05 to 10 mol, preferably 0.1 mol, of bromine atom per 1 mol of heavy metal atom.
Those having a range of 2 to 2 mol are desirable. Such a catalyst is usually used as a heavy metal concentration in a reaction solvent of 10 to 100.
It is used in the range of 00 ppm, preferably 100 to 5000 ppm.

In the method of the present invention, an aromatic compound to be oxidized is converted to a liquid phase in a reaction solvent containing a lower aliphatic carboxylic acid by a molecular oxygen-containing gas in a reaction solvent containing a lower aliphatic carboxylic acid. By oxidation, an aromatic carboxylic acid as a product is obtained.

The molecular oxygen-containing gas includes, for example, oxygen and air, but practically, air is preferably used. The molecular oxygen-containing gas is supplied in excess of the amount required to oxidize the aromatic compound serving as the oxidation raw material to the aromatic carboxylic acid. When air is used as the molecular oxygen-containing gas, aromatic compound 1 serving as an oxidation raw material
2 to 20 Nm ³ , preferably 2.5 to 15 kg / kg
It is desirable to supply Nm ^{3 to} the reaction system at a ratio of Nm ³ .

Specific examples of the lower aliphatic carboxylic acid used as the reaction solvent include acetic acid, propionic acid and butyric acid. The lower aliphatic carboxylic acid can be used alone as a reaction solvent, or can be mixed with water and used as a reaction solvent in the form of a mixture. Specific examples of the reaction solvent include, for example, acetic acid, propionic acid, butyric acid and mixtures thereof,
Alternatively, a mixture of these lower aliphatic carboxylic acids and water can be used. Among them, a mixture of acetic acid and water is preferable, and a mixture in which the water concentration is 1 to 20% by weight, preferably 5 to 15% by weight is desirable.

The temperature of the oxidation reaction is usually 100 to 250 ° C.,
Preferably, the range of 150 to 220 ° C is desirable. Also,
The reaction pressure may be any pressure as long as it can maintain the reaction system in a liquid phase, but is generally 0.1 to 4 MPa, preferably 0.4 to 3 MPa (gauge pressure).

By reacting in this manner, an aromatic carboxylic acid corresponding to the aromatic compound serving as an oxidation raw material is obtained. Specific examples of the aromatic carboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid; and aromatic dicarboxylic acids such as trimellitic acid and trimesic acid. Aromatic tricarboxylic acids such as pyromellitic acid; and the like. The method of the present invention is preferably applied to the production of an aromatic dicarboxylic acid or an aromatic carboxylic acid insoluble or hardly soluble in a reaction solvent, particularly preferably to the production of terephthalic acid.

In the present invention, a reactor having a gas phase connected to a distillation column is used as a reactor for performing the above reaction. In this distillation column, high-temperature and high-pressure oxidized exhaust gas is introduced from the gas phase part of the reactor, and distillation is performed by utilizing the heat generated in the reactor. In this case, a fraction containing a reaction solvent is passed from the bottom to the reactor. Reflux,
Water and non-condensable gases are discharged at the top. The distillation column may be independent of the reactor as shown in JP-A-54-14098, or may be installed at the top of the reactor as shown in JP-A-6-279353. The distillation column may be a tray column, but a packed column is preferable.In this case, a means for collecting fine solids such as crystals of an aromatic carboxylic acid or a catalyst, for example, a solids collecting tray is used to form a packed bed. Those provided on the lower side are preferred.

Into such a reactor, a reaction solvent containing an alkyl aromatic compound and an aliphatic carboxylic acid as a reaction raw material and an oxidation catalyst are introduced, and an aromatic carboxylic acid is introduced by introducing an oxygen-containing gas to perform liquid phase oxidation. Generates acid. The generated aromatic carboxylic acid precipitates as crystals in the mother liquor to form a slurry. The slurry is taken out of the reactor and is directly or pressurized, or is flashed in a flash tank to lower the temperature and pressure to separate crystals from the mother liquor in the slurry, and replace the mother liquor attached to the crystals with water.

The replacement of the mother liquor is performed by recovering the mother liquor contained in the slurry as much as possible and returning the mother liquor to the reactor, and dispersing the crystals in water to form a water slurry when the crystals are dispersed in water for the next purification step. This is performed to form a slurry that does not contain. In the purification step, in order to perform purification treatment such as hydrogenation in a state where the aromatic carboxylic acid is dissolved in water under heating,
It is necessary to remove as much as possible the reaction solvent such as lower aliphatic carboxylic acid contained in the reaction mother liquor. For this purpose, replacement of the mother liquor with water is performed. For this purpose, crystals are separated from the produced slurry, and the separated crystals are brought into contact with water to recover the mother liquor attached to the crystals and returned to the reactor.

The method of this substitution is not particularly limited as long as the mother liquor adhering to the crystals in the slurry can be replaced with water, but a method of separating the crystals from the slurry and contacting the separated crystals with water to replace them. preferable. As such a method, for example, a method using a multi-stage column as disclosed in JP-A-1-160942, or JP-A-6-327
In addition to a method using a rotary filter as shown in No. 915, a method in which crystals are separated by another solid-liquid separation device such as a centrifugal separator or a hydrocyclone and washed with water to replace the mother liquor can be used. .

In the method using a multi-stage column, the slurry is introduced into the upper portion of the column in which the partition plates are arranged in multiple stages, water is introduced into the lower portion, and water is caused to flow upward, so that the crystals are settled down from the mother liquor. This is a method of separating and replacing the mother liquor by bringing it into countercurrent contact with water, collecting the mother liquor diluted with water from the upper part, and obtaining a water slurry from the lower part, which can be replaced with a single device and operation. .

In the method using a rotary filter, a slurry is supplied to a rotary filter medium of a rotary filter to separate a mother liquor from crystals, and the separated crystals are washed with water to replace the mother liquor with water. At this time, washing by flowing the washing water in a countercurrent manner is preferable because replacement with a small amount of washing water is possible and a high-concentration diluted mother liquor is obtained. The mother liquor diluted with the washing drainage is collected, and the washed crystals are dispersed in water to obtain a water slurry. In addition, the same operation can be performed in the case of using another solid-liquid separation device such as a centrifuge or a liquid cyclone.

The reaction is carried out by returning the diluted mother liquor obtained by replacing the mother liquor in the slurry with water by the above substitution to the reactor. At this time, the water concentration of the returned diluted mother liquor is 1%.
The content is suitably 5 to 50% by weight, preferably 15 to 30% by weight. When such a diluted mother liquor is returned to the reactor to carry out the reaction, the water in the mother liquor evaporates together with the water produced by the reaction into steam by the heat of the reaction. At this time, the reaction solvent containing the lower aliphatic carboxylic acid also evaporates, and these vapors enter the distillation column together with the oxidized exhaust gas and undergo distillation.

By performing distillation in the distillation column, components containing the reaction solvent discharged along with the oxidized exhaust gas are distilled out and refluxed to the reactor. This fraction is refluxed to the reactor as a bottom liquid in a state where the unreacted alkyl aromatic compound, the generated aromatic carboxylic acid, the catalyst and the like are concentrated in addition to the reaction solvent.
The water vapor is condensed in a condenser provided at the top of the distillation column, fractionated as condensed water, and discharged out of the system. As a result, water introduced into the reactor as a diluted mother liquor is removed from the reactor, so that the water concentration of the reaction mother liquor in the reactor is maintained at the above-mentioned 1 to 20% by weight, preferably 5 to 15% by weight. it can.

As described above, even if the diluted mother liquor is introduced into the reactor, water can be easily removed from the reactor. In removing water, the reaction solvent is fractionated by distillation and refluxed to the reactor. The solvent is not removed out of the system, and the concentration of the reaction solvent in the reactor can be kept high. The reaction solvent is consumed by oxidation, but the consumed material can be replenished together with new raw materials. Since water is generated in the generation reaction of the aromatic carboxylic acid, the reaction is suppressed when water is introduced by returning the diluted mother liquor, but the reaction is promoted by removing water by distillation as described above. The reaction efficiency can be kept high.

The water fractionated in the distillation column can be used as water for replacing the mother liquor of the slurry, whereby water can be used effectively and the cost for obtaining washing water can be reduced. . In addition, the exhaust gas obtained from the distillation column is pressurized gas of a rotary filter, gas for cake peeling,
Alternatively, it can be used as a product transfer gas or the like, thereby similarly reducing the cost of obtaining these gases.

[0032]

According to the present invention, an oxidation reaction is carried out in a reactor connected to a distillation column, and a diluted mother liquor obtained by replacing the mother liquor in the slurry with water is returned to the reactor and distilled in the distillation column. To remove the water and reflux the reaction solvent to the reactor, so that in the method of replacing the dispersion medium of the aromatic carboxylic acid slurry with water, even if the diluted mother liquor is returned to the reactor, the water is efficiently removed. Is removed, and the solvent is held in the reactor, whereby the aromatic carboxylic acid generation reaction can be efficiently performed.

By maintaining the water concentration of the mother liquor in the reactor at 1 to 20% by weight, preferably at 5 to 15% by weight,
The generation reaction of the aromatic carboxylic acid can be controlled in an efficient range. Further, by adjusting the water concentration in the diluted mother liquor to be returned to the reactor to 15 to 50% by weight, preferably 15 to 30% by weight, the water concentration of the mother liquor in the reactor can be easily maintained in the above range. .

By using a multi-stage column for replacing the mother liquor in the slurry, the replacement can be carried out efficiently with a single apparatus and operation. In addition, by using a rotary filter, it is possible to efficiently replace the mother liquor with a small amount of water,
High concentration diluted mother liquor can be returned.

By using water fractionated in a distillation column as replacement water, water can be effectively used to increase product purity and reduce production costs.

[0036]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are flowcharts showing a method for producing terephthalic acid according to another embodiment. FIG. 1 shows an example using a multistage tower, and FIG. 2 shows an example using a rotary filter.

In FIG. 1, reference numeral 1 denotes a reactor, in which a distillation column 2 is provided at an upper portion thereof, and a condenser 3 is further provided thereon. The reactor 1 has a raw material supply path L
1, a gas supply path L2 and a slurry extraction path L3 in the lower part,
The mother liquor return path L4 communicates with the upper part. The distillation column 2 is filled with a packing layer 4 so that liquid and gas can pass therethrough. The condenser 3 is provided with a heat exchanger 5 and a condensed water receiver 6 thereunder. An exhaust gas passage L5 communicates with the upper part of the condenser 3, and a water drainage passage L6 communicates with the condensed water receiver 6.

Reference numeral 7 denotes a multi-stage tower having a plurality of fence steps 8a, 8
.. 8n are provided at intervals, and a plurality of scrapers 9a, 9b... 9o are provided on the top and bottom thereof so as to be rotated by a motor 11 through a shaft 10. An upper part of the uppermost barrier step 8a is connected to a slurry discharge path L3 via a pump 12, and a mother liquor return path L4 is connected to the reactor 1 from above. A drainage path L6 communicates with the lower part of the middle lower fence step 8m via the pump 13, a water supply path L7 below the lowermost shelf step 8n, and a water slurry extraction path L8 further below. .

In the production method using the above-described apparatus, a reaction solvent containing paraxylene and acetic acid as a reaction raw material and an oxidation catalyst are introduced into the reactor 1 from the raw material supply passage L1.
The terephthalic acid is generated by introducing an oxygen-containing gas from the gas supply path L2 and performing liquid phase oxidation. Since the generated terephthalic acid precipitates as crystals in the mother liquor to form a slurry, the slurry is withdrawn from the reactor 1 by the pump 12 through the slurry withdrawing passage L3, or as it is, or under pressure, or in a flash tank (not shown). The mixture is flushed to lower the temperature and pressure and introduced into the multi-stage column 7.

In the multistage tower 7, the slurry is introduced from the slurry discharge path L3 to the upper part of the uppermost fence step 8a, from the drainage path L6 to the lower part of the middle and lower fence steps 8m, and further from the water supply path L7 to the lowest shelf step. 8n, water is introduced into the lower part of the slurry, and water is caused to flow upward in such a flow velocity that the mother liquor in the slurry does not diffuse downward. By rotating the scrapers 9a, the crystals are settled and separated from the mother liquor. At the same time, it is brought into countercurrent contact with water to replace the mother liquor. This allows the slurry return path L4 from the top
, The mother liquor diluted with water is collected and returned to the reactor 1, and the water slurry is taken out from the lower part through the water slurry take-out path L8 and sent to the purification step. At this time, if necessary, water is supplied from the water supply passage L7 to form a water slurry.

When the diluted mother liquor obtained by the above substitution is returned to the reactor 1 to carry out the reaction, the water in the mother liquor evaporates together with the water produced by the reaction into steam by the heat of the reaction. At this time, the reaction solvent containing acetic acid also evaporates, and these vapors enter the distillation column 2 together with the oxidized exhaust gas and undergo distillation.

By performing distillation in the distillation column 2, a component containing a reaction solvent discharged along with the oxidized exhaust gas is distilled out and refluxed to the reactor 1. This fraction is refluxed to the reactor 1 in a state where unreacted para-xylene, generated terephthalic acid, catalyst and the like are concentrated in addition to the reaction solvent. Then, the steam enters the condenser 3 from the upper part of the distillation column 2, is cooled and condensed by the heat exchanger 5, is fractionated as condensed water in the condensed water receiver 6, and is sent to the multi-stage column 7 from the drainage line L 6. As a result, the water introduced into the reactor 1 as a diluted mother liquor is removed from the reactor 1, so that the water concentration of the reaction mother liquor in the reactor 1 is 1 to 20% by weight, preferably 5 to 15% by weight. And the reaction can be carried out efficiently. Part of the condensed water flows down from around the condensed water receiver 6 to the distillation column 2 and is used for distillation.

In FIG. 2, a rotary filter 15 is provided instead of the multistage tower. The rotary filter 15 is provided with a cylindrical rotary filter medium 17 in a casing 16, and the lower part is immersed in a slurry 19 of a slurry tank 18, and performs pressure filtration or pressure / pressure reduction under pressure to obtain a filter cake 2.
Numeral 0 is designed to be cleaned by a number of nozzles 21a, 21b... In the cleaning area.

In the above-described apparatus, the slurry 19 extracted from the reactor 1 to the slurry extraction path L3 enters the slurry tank 18 of the rotary filter 15, is filtered by the rotary filter medium 17, and the crystals are separated on the filter medium 17 and filtered. A cake 20 is formed. When the filter medium 17 comes to the washing area by rotation, the condensed water is supplied to the nozzles 21a, 21b,.

The washing water displaces the mother liquor when passing through the cake 20, and the mother liquor enters the filter medium 17 together with the washing waste water and mixes with the filtrate to form a diluted mother liquor 22. The diluted mother liquor 22 is taken out to the drainage chamber 23 via the suction passage L9, and is returned to the mother liquor return passage L
4 is returned to the reactor 1. The slurry in the slurry tank 18 is also returned to the reactor 1 from the slurry return path L10.
A part of the exhaust gas flows from the gas recovery passage L11 to the blower 24.
To the air supply chamber 25, and sprayed from the nozzle 26 onto the filter medium 17 in the separation area to separate the filter cake 20, and sent to the purification step. Other configurations and operations are the same as those in FIG.

[0046]

Embodiments of the present invention will be described below. Example 1 In FIG. 1, para-xylene was supplied to the reactor 1 from the raw material supply path L1 at 65 kg / hr, and acetic acid and a catalyst lost during the reaction and the like were supplied to cause a reaction. The reaction conditions at this time were a reaction temperature of 190 ° C. and a reaction pressure of 14 kg / cm ² G.
It is. A solution containing the generated terephthalic acid and the catalyst was pumped by the pump 12 through the slurry discharge passage L3 to 16 kg / cm ² G
And sent to the multistage column 7 under 15.5 kg / cm ² G. The terephthalic acid extracted from the slurry extraction passage L3 is 100 kg / hr, and the solvent containing the catalyst is 200 kg / hr.
kg / hr (water 20 kg / hr, acetic acid and other 180 kg
/ Hr).

At the lower part of the multi-stage tower 7, the water 2
00 kg / hr was supplied, and 50 kg / hr of condensed water extracted from the upper part of the distillation column 2 was supplied from the drainage line L6.
100 kg of terephthalic acid from the water slurry discharge passage L8
/ Hr and 225 kg / hr of water slurry were extracted. From the mother liquor return line L4, 225 kg / hr of an aqueous acetic acid solution containing a catalyst (45 kg / hr of water,
0 kg / hr) was withdrawn and returned to the reactor 1. Further, from the exhaust gas passage L5, the steam and the exhaust gas in which the acetic acid concentration in the condensate became 1 wt% or less were extracted by the distillation column 2. Even if the diluted mother liquor having the water concentration of 20 wt% as described above is returned to the reactor 1 through the mother liquor return line L4, the water concentration of the acetic acid solvent in the reactor 1 is set to 10 wt% by the distillation column 2. Thus, terephthalic acid was obtained under ordinary oxidation reaction conditions.

Example 2 In FIG. 2, the reaction was carried out under the same conditions as in Example 1, and the pressure of the solvent containing the generated terephthalic acid and the catalyst was increased to 16 kg / cm ² G by the pump 12 from the slurry discharge pipe L3. It was sent to a rotary filter 15 under 0.5 kg / cm ² G. The terephthalic acid extracted from the slurry extraction passage L3 is 100 kg / hr, and the solvent containing the catalyst is 20 kg / hr.
0kg / hr (water 20kg / hr, acetic acid and others 180k
g / hr). On the upper part of the rotary filter 15, 50 kg / hr of condensed water extracted from the upper part of the distillation column 2 through the drainage line L6 from the nozzles 21a, 21b... Is sprayed, and the filter cake 20 containing terephthalic acid / acetic acid is washed. Then, the filter cake was replaced with a filter cake containing terephthalic acid and water, and extracted from the cake discharge passage L12.

From the gas recovery passage L11, a part of the oxidized exhaust gas is withdrawn and pressurized by a blower 24 and supplied to an air supply chamber 25, whereupon a filter cake 20 containing terephthalic acid and water is filtered.
Is used from the nozzle 26 as a blow gas that separates from the rotary filter 15, and the rotary filter 15 is used at 15.5 kg / c.
Used to pressurize to m ² G. 15.5 kg / cm ² G of the rotary filter 15 and the pressure of the reactor 1 of 14 k
The mother liquor was sucked up from the suction passage L9 by a difference of g / cm ² G and sent to the reactor 1 from the mother liquor return passage L4. The solvent returned from the mother liquor return line L4 is 225 kg / hr (water 45
kg / hr, acetic acid and other 180 kg / hr).
When the amount of the slurry sent from the slurry discharge passage L3 to the rotary filter 15 was large, the overflowed slurry was returned from the slurry return passage L10. Exhaust gas path L5
, The concentration of acetic acid in the condensate is 1 wt%
The following steam and exhaust gas were extracted. The diluted mother liquor having the water concentration of 20 wt% as described above is returned to the mother liquor return path L4.
Even after returning to the reactor 1, the water concentration of the acetic acid solvent in the reactor 1 could be reduced to 10 wt% by the distillation column 2, and terephthalic acid could be obtained under ordinary oxidation reaction conditions.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment.

FIG. 2 is a flowchart of another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor 2 Distillation tower 3 Condenser 4 Packing layer 5 Heat exchanger 6 Condensed water receiver 7 Multi-stage tower 8a ・ ・ ・ Fence step 9a ・ ・ ・ Scraper 10 Shaft 11 Motor 12,13 Pump 15 Rotary filter 16 Casing 17 Rotation Filter medium 18 Slurry tank 19 Slurry 20 Filtration cake 21a, 21b ... Nozzle 22 Diluent mother liquor L1 Raw material supply path L2 Gas supply path L3 Slurry extraction path L4 Mother liquor return path L5 Exhaust gas path L6 Drainage path L7 Water supply path L8 Water slurry extraction path L9 Suction path L10 Slurry return path L11 Gas recovery path L12 Cake extraction path 23 Drainage chamber 24 Blower 25 Air supply chamber 26 Nozzle

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C07C 63/26 C07C 63/26 N 63/307 63/307 63/313 63/313 (72) Inventor Iida Tsukasa 2-5-2 Kasumigaseki, Chiyoda-ku, Tokyo Mitsui Chemicals, Inc. (72) Michio Umeda 1-2-1, Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term (reference) 4H006 AA02 AC46 AD15 BA05 BA08 BA10 BA11 BA14 BA16 BA20 BA21 BA32 BA34 BA37 BB17 BB31 BC10 BC36 BD20 BD33 BD35 BD42 BD52 BD82 BJ50 BS30 FC50 FC54 4H039 CA65 CC30

Claims (7)

[Claims] 1. A method for producing an aromatic carboxylic acid by subjecting an alkyl aromatic compound to liquid phase oxidation with an oxygen-containing gas in a reaction solvent containing an aliphatic carboxylic acid in a reactor in the presence of an oxidation catalyst. Using a reactor in which the gas phase is connected to a distillation column as a reactor, a slurry containing aromatic carboxylic acid crystals generated in the reactor is extracted, and the mother liquor attached to the crystals is replaced with water to obtain a diluted solution. The mother liquor is returned to the reactor, the vapor generated in the reactor is introduced into a distillation column, the reaction solvent is fractionated by distillation, refluxed to the reactor, and water is discharged out of the system. A method for producing an aromatic carboxylic acid in which water is removed while maintaining a high concentration of a reaction solvent to promote the generation of an aromatic carboxylic acid. 2. The method according to claim 1, wherein the concentration of water in the mother liquor in the reactor is 1 to 20.
2. The method of claim 1, wherein the amount is by weight. 3. The method according to claim 1, wherein the concentration of water in the diluted mother liquor returned to the reactor is 15 to 50% by weight. 4. The method according to claim 1, wherein the displacement of the mother liquor attached to the crystal with water is
4. The method according to claim 1, wherein the crystal separated from the slurry is brought into contact with water. 5. The method according to claim 4, wherein the displacement of the mother liquor adhering to the crystals is carried out by flowing water in an upward flow through the multistage column, and bringing the crystals separated from the slurry into contact with water. 6. The replacement of a mother liquor attached to the crystal with water,
5. The method according to claim 4, wherein the crystal separated by using a rotary filter is brought into contact with water and washed. 7. The water to replace the mother liquor in the slurry,
7. The method according to claim 1, wherein water distilled in a distillation column is used.