JPH09157214A - Production of aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously recover a catalyst useful in producing an aromatic carboxylic acid in high recovery ratio and to reuse the catalyst. SOLUTION: In this method for producing an aromatic carboxlic acid by oxidizing an aromatic compound containing an alkyl-substituted group in a solvent of acetic acid in the presence of a catalyst comprising cobalt acetate, manganese acetate and a bromine compound in a liquid phase, (1) a residue containing cobalt acetate and manganese acetate is obtained from an oxidation reaction mixture, (2) water and an alkali hydroxide are added to the residue, (3) then the aqueous solution and an alkali carbonate are continuously added to a carbonating tank, a retention time is 20-200 minutes, a slurry containing cobalt carbonate and manganese carbonate is continuously or intermittently taken out from the carbonating tank, (4) cobalt carbonate and manganese carbonate are separated from the slurry and (5) are reacted with acetic acid, and (6) prepared cobalt acetate and manganese acetate are reused.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent,
The present invention relates to a method for producing an aromatic carboxylic acid, which comprises continuously and efficiently recovering a metal component of a liquid phase oxidation catalyst.

[0002]

BACKGROUND OF THE INVENTION Alkyl aromatic compounds, such as para-xylene, are produced in a process for producing terephthalic acid by liquid phase oxidation with molecular oxygen in the presence of a catalyst consisting of cobalt, manganese and bromine compounds in an acetic acid solvent. Since the reaction mother liquor after the separation of the terephthalic acid contains the acetic acid solvent and the metal component of the catalyst, it is desirable to recover and reuse it.

Conventionally, the acetic acid solvent is reused after raising the reaction mother liquor to recover it and then distilling it to remove water. On the other hand, for the metal component of the catalyst, the residue obtained by the above-mentioned pumping is mixed with water to dissolve the metal component in water to form an aqueous solution (hereinafter referred to as "catalyst stock solution"), to which alkali carbonate is added. Is recovered as a carbonate. As a preferred method for recovering the metal catalyst as the carbonate, the catalyst stock solution and the alkali carbonate are added at such a ratio that the pH of the retained liquid in the precipitation reaction zone is kept substantially constant within the range of 7.6 to 10. A method of continuously introducing and continuously withdrawing and collecting a liquid containing a precipitate from the precipitation generation reaction region (Japanese Patent Publication No. 56-31139), and sodium carbonate having a pH of the stock solution of 6.5 to 7.5. After the aging treatment for at least 20 minutes, the pH was further adjusted to 8.
There is known a method of adding alkali carbonate until the number becomes 5 or more (Japanese Patent Publication No. 56-25195).

[0004]

Most of the alkali carbonate added in the above reaction is consumed not only for carbonation of the catalyst metal in the catalyst stock solution but also for neutralization of organic acids. Generally, carbon dioxide is generated in the reaction between an alkali carbonate and an organic acid,
Most of the pH of the reaction solution is released outside the system in the acidic range, whereas most of it is dissolved in the solution in the alkaline range.
The carbon dioxide gas dissolved in the liquid newly reacts with the alkali carbonate and becomes a factor to increase the consumption amount of the alkali carbonate.
Particularly, in the continuous method as described in Japanese Patent Publication No. 56-311939, an increase in consumption of alkali carbonate is unavoidable, which is economically disadvantageous and cannot be said to be a preferable method.

The method of Japanese Patent Publication No. 56-25195 is
Most of the carbon dioxide gas generated by the neutralization of organic acids, etc. is released to the outside of the system by adjusting the pH to the neutral range by adding alkali carbonate in the first step, but there is an effect of saving alkali carbonate. Therefore, in order to industrially treat a large amount of stock solution of the catalyst, a plurality of reaction tanks are required, and further, the operation tends to be complicated.

[0006]

In view of the above circumstances, the inventors of the present invention have conducted various studies on a method for reducing the amount of alkali carbonate required for carbonate formation in the case of carrying out a carbonation reaction, and as a result,
The neutralization reaction of the organic acid in the catalyst stock solution and the carbonation reaction of the catalytic metal component are performed separately by a two-step method, the alkali hydroxide is used for the first-step neutralization reaction, and the second-step carbonation reaction is performed. By continuously performing the process under specific conditions, the consumption of total alkali including alkali carbonate is reduced, which is economical, and at the same time, the recovery rate of the catalyst component is high, and the separation and separation of the obtained carbonate particles is improved. Has been found to be excellent, and has reached the present invention.

That is, the gist of the present invention is to obtain an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent in an acetic acid solvent in the presence of a catalyst consisting of cobalt acetate, manganese acetate and a bromine compound. In the method for producing an aromatic carboxylic acid by liquid phase oxidation with oxygen,
When the catalyst is recovered and reused, (1) the aromatic carboxylic acid and acetic acid solvent are removed from the oxidation reaction mixture to obtain a residue containing cobalt acetate and manganese acetate, and (2) water and water are added to the residue. Add and mix alkali oxide and its pH is 4.0-
An aqueous solution of 6.5 is obtained, and (3) the aqueous solution and the alkali carbonate are then made substantially constant in a carbonation tank within a pH range of 8.0 to 9.5. It is continuously supplied at a rate such that it is maintained, the residence time is set to 20 to 200 minutes, and the slurry containing cobalt and manganese carbonate is continuously or intermittently withdrawn from the carbonation tank, (4)
Cobalt and manganese carbonates are separated from the slurry, (5) the separated cobalt and manganese carbonates are reacted with acetic acid, and (6) the obtained cobalt acetate and manganese acetate are reused as the catalyst component. And a method for producing an aromatic carboxylic acid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent is used as a raw material. The alkyl substituent has usually 1 to 8 carbon atoms.
Although those having a degree of about 1 to 3 are used, those having 1 to 3 carbon atoms such as methyl group, ethyl group, n-propyl group and i-propyl group are preferable.
Alkyl group. The partially oxidized alkyl group having a carbon number of about 1 to 8 is usually used, and examples thereof include a formyl group, a carboxyl group and a hydroxyalkyl group. The number of these substituents is not limited to one, and two or more may be substituted. Further, in the case of having a plurality of substituents, each substituent may be the same or different. The aromatic nucleus includes not only a single ring such as a benzene ring but also a polycyclic aromatic nucleus such as a naphthalene ring.

The aromatic compounds containing the above alkyl substituents or partially oxidized alkyl substituents include toluene, ethylene, isopropylbenzene, 4,4'-dimethylbiphenyl, o-, m- or p-xylene. o
-, M- or p-diisopropylbenzene, pseudocumene (1,2,4-trimethylbenzene), 2,6
-Aromatic compounds substituted with an alkyl group such as dimethylnaphthalene and 2,6-diisopropylnaphthalene; benzaldehyde, o-, m- or p-tolualdehyde, 2,
Formyl group-substituted aromatic compounds such as 4-dimethylbenzaldehyde and 2,4,5-trimethylbenzaldehyde; Hydroxyalkyl group-substituted aromatic compounds such as benzyl alcohol; o-, m- or p-toluic acid, o Examples thereof include compounds substituted with a carboxyl group such as-, m- or p-carboxybenzaldehyde, 2,6-naphthalenedicarbaldehyde and 1-naphthalenedicarbaldehyde, and mixtures thereof, but are not limited thereto. Absent.

The most typical example of the method for producing an aromatic carboxylic acid, which is the subject of the present invention, is the case where liquid phase oxidation of paraxylene is used to produce terephthalic acid. The case of producing this terephthalic acid will be particularly described below, but also in the case of producing an aromatic carboxylic acid by using other raw material compounds, the liquid phase oxidation of the present invention is performed except that the reaction conditions are appropriately set to optimum conditions. The catalyst recovery method can be applied as it is.

When para-xylene is subjected to liquid phase oxidation with molecular oxygen in the presence of a catalyst consisting of cobalt acetate, manganese acetate and a bromine compound in an acetic acid solvent, the bromine compound used is hydrogen bromide, sodium bromide or the like. Is mentioned. As the amount of the catalyst added, cobalt acetate and manganese acetate are usually 10 to 5 as each metal in the solvent.
000 ppm, and the bromine compound is usually 30 to 10,000 ppm as bromine with respect to the solvent. The raw material paraxylene is usually used in a proportion of 1 to 50% by weight with respect to the acetic acid solvent. Also, acetic acid may contain up to about 30% by weight of water. As the molecular oxygen supplied to the oxidation reactor, pure oxygen, air, a mixture of pure oxygen and an inert gas, or the like is used, and the ratio of oxygen is usually 3 to 20 mol with respect to 1 mol of paraxylene. To do. The reaction conditions are usually a reaction temperature of 150 to 260 ° C., a reaction pressure of ^{2 to} 50 kg / cm ² , and a residence time of 10 to 200 minutes. The desired aromatic carboxylic acid, terephthalic acid, produced by the oxidation reaction is usually solid-liquid separated from the oxidation reaction mixture by crystallization, centrifugation or the like.

Since the main component of the reaction mother liquor after the separation of terephthalic acid is acetic acid, a part of the reaction mother liquor can be directly returned to the reaction system and reused. The acetic acid solvent and water are evaporated and separated. The hydrous acetic acid thus pumped up is reused after removing some water in the distillation column. On the other hand, the residue after the lifting is usually made into an aqueous solution by adding 1 to 10 times by weight of water to the residue to dissolve the metal component of the catalyst in the residue. At this time, when a small amount of terephthalic acid or other reaction by-products contained in the residue is precipitated as a solid content, it is preferable to separate it. The obtained aqueous solution (hereinafter referred to as "stock solution") usually contains 20 to 10000 ppm of cobalt acetate and 20 of manganese acetate as catalyst components.
In addition to containing 10000ppm, residual acetic acid 1-8
%, And acidic by-products such as terephthalic acid, benzoic acid, orthophthalic acid, and isophthalic acid, and having an pH of 3 or less.

The cobalt and manganese components in the catalyst stock solution are usually separated and recovered after reacting with alkali carbonate to form carbonate particles. The carbonation reaction in the present invention is characterized by being carried out in two steps. In the first-step reaction, the pH of the stock solution is adjusted to 4.0 to 6.5, preferably 5.0 to 5.0 by adding and mixing an alkali hydroxide to the catalyst stock solution.
Adjust to 6.3. Further, if it is empirically easy to adjust to a desired pH range, alkali hydroxide and water or an alkali hydroxide aqueous solution is directly added and mixed to the above residue, and fine adjustment of pH is performed if necessary. May be performed and such methods are also an aspect of the invention. PH here is 4.0
If the amount is less than 1, the neutralization of the organic acid containing acetic acid as a main component is insufficient, so that the amount of dissolved carbon dioxide gas generated in the next carbonation reaction increases, and the consumption of alkali carbonate increases, which is not preferable. On the other hand, if the pH exceeds 6.5, the hydroxide of the metal component is generated, the amount of undissolved substances in the subsequent acetic acid step is increased, and the particles of carbonate generated in the next carbonation reaction are added. It is not preferable because the diameter is small and the filterability in the separation is lowered.

Examples of the alkali hydroxide used in the above include sodium hydroxide, potassium hydroxide and the like, but the generation of carbon dioxide gas due to the reaction with an organic acid is small, the alkali potency is high, and the price is low. Sodium hydroxide is preferred. The alkali hydroxide may be used in the form of a solid or an aqueous solution, but it is preferably used as an aqueous solution of 5 to 20% by weight.

The catalyst stock solution and the aqueous alkali hydroxide solution may be mixed in a pipe before being supplied to the neutralization tank, but since carbon dioxide is generated, it is usually carried out in a neutralization tank having a stirrer. Preferably, it is carried out by a batch method in which an alkaline aqueous solution is added to the catalyst stock solution charged in the neutralization tank to adjust the target pH, or a method in which each is continuously supplied at a rate such that the target pH is maintained constant. Be seen. The temperature in the neutralization tank or in the pipe for neutralization is usually 40 to 70.
C., preferably 50 to 60.degree. Further, the stirring speed and the residence time of the neutralization tank are not particularly limited as long as the neutralization liquid is uniformly mixed.

As described above, the target pH of 4.0 to 6.5 is obtained.
Then, an alkali carbonate is continuously added to and mixed with the catalyst stock solution aqueous solution adjusted to pH 7.0 to adjust the pH of the mixed solution to 8.0.
The slurry containing the carbonates of cobalt and manganese is made into slurry by holding it at 9.5, preferably 8.0 to 9.0 for a certain period of time. That is, in the present application, the alkali carbonate and the catalyst stock solution are mixed within the above pH range. If the pH is less than 8, the amount of alkali carbonate used will be small, but the reaction rate of carbonation will be low, and the catalyst components discharged together with the separation waste liquid without reaction will be increased, and the recovery rate will be low, which is not preferable. . On the other hand, if the pH exceeds 9.5, not only is it economically disadvantageous because the alkali consumption increases, but also the catalytic metal component easily forms hydroxides and oxides, and it becomes acetic acid in the next acetic acid process. Is not preferable because it causes a decrease in the dissolution rate.

The alkali carbonate to be added includes lithium carbonate, sodium carbonate, potassium carbonate and the like, and sodium carbonate is generally used. The alkali carbonate may be used in the form of a solid or an aqueous solution, but it is preferably used in an aqueous solution of 5 to 30% by weight. Specifically, a carbonation tank is provided, and the neutralized catalyst stock solution aqueous solution and the alkali carbonate aqueous solution are supplied to the carbonation tank from separate nozzles within a pH range of 8.0 to 9.5. It is desirable to continuously feed each at a rate such that it remains substantially constant.
This is because if the catalyst stock solution and the alkali carbonate are mixed in the pipe before being supplied to the reaction tank, the pipe may be clogged due to precipitation of carbonate crystals, which is not preferable.

As the pH measuring device for the liquid in the carbonation tank, a throwing type, a submersion type, a circulation type or the like is usually used.
Since the carbonate that precipitates during the reaction may adhere to the sensor and not give a normal indication, use a pH meter with a cleaning function such as a chemical cleaning method, an ultrasonic cleaning method, a jet cleaning method, or a brush cleaning method. It is preferably used. It is advantageous that the temperature in the carbonation tank is as high as possible from the viewpoint of increasing the reaction rate or increasing the particle size of the carbonate produced, but if the temperature is raised too high, the heat of the carbonate will increase. Since alteration is likely to occur, it is usually 45
~ 65 ° C, preferably 50 ~ 60 ° C.

Since the carbonate particles produced by the reaction have a large true specific gravity and tend to settle in the lower part of the reaction tank, it is necessary to stir the slurry sufficiently to uniformly disperse the slurry. As the stirring blade, generally known blades such as a turbine type, paddle type, propeller type and paddle type can be used without particular limitation. Further, it is also one of the effective means for dispersion to use the circulation mixing with a pump for extracting the carbonate slurry and transferring it to the next step. Further, the retention time of the liquid in the carbonation tank (residence time when continuously carried out) is 20 to 200 minutes, preferably 30 to 18 minutes.
It is 0 minutes, and if it is shorter than this, unreacted substances increase and cause loss of catalyst components. On the other hand, if the length is longer than this, a large carbonation tank is required, the pH response becomes dull, and it becomes difficult to control the reaction pH at a constant level. Is not practical because it gets worse.

The slurry containing the carbonates of cobalt and manganese produced by the carbonation reaction is sent to the solid-liquid separation step to separate the carbonates of cobalt and manganese. Especially when carrying out the carbonation reaction continuously, the solid-liquid separation step is carried out continuously or intermittently so that the liquid amount in the carbonation tank is always kept substantially constant or close to it. And separate the cobalt and manganese carbonates. Solid-liquid separation can be carried out using any of a sedimentation separator, a pressure filter, a vacuum filter, a centrifuge, etc., such as filtration, filter cake washing, cake discharge, and filter washing. It is effective to use a candle type pressure filter in order to carry out a series of operations continuously and efficiently.

The slurry to be supplied to the candle-type pressure filter is once received in a storage tank, and the storage tank is used as an aging tank for completing the reaction of the unreacted catalytic metal in the carbonation reaction zone. You can also combine.
The residence time in the storage tank is usually set to 30 to 120 minutes, preferably 60 to 90 minutes in order to smoothly perform a series of filtration operations. The filtration pressure in the filter is usually 0.1 to 5 kg.
/ Cm ² , and the filtration area is usually 0.3 to 23 m ² per 1 m ³ / hr of the flow rate of the treated slurry, but these are appropriately determined so that the treatment can be performed in a desired time cycle.

The material of the filter cloth for filtration is polypropylene type, polyester type, polyamide type, aramid type,
Fluorine-based materials are available, but generally polypropylene, which is a versatile material, is sufficient in terms of price. The mesh size of the filter cloth is usually selected from the range of 3 to 40 μm in consideration of loss due to leakage of carbonate particles. However, supplying the slurry to the filter,
When the circulation operation for returning the filtrate to the storage tank is carried out until the cake layer is formed on the surface of the filter cloth and the leakage of particles is eliminated in the initial stage of the filtration, it is not necessary to reduce the opening more than necessary. If a filter cloth with an opening of less than 3 μm is used, the filtration resistance increases due to clogging when repeatedly used,
It is not preferable because smooth slurry treatment cannot be performed. The adhered thickness of the separated carbonate cake on the filter cloth surface is
In consideration of cake releasability, it is usually 5 to 50 mm, preferably 10 to 20 mm. Metal components other than catalyst components such as alkali carbonate and iron attached to the filter cake, and water-soluble impurities such as organic impurities are washed and removed by circulating water through the cake layer. Is usually 2 to 50 times, preferably 5 to 20 times the volume of the carbonate cake by volume.

The salt cake of the cobalt and manganese carbonates separated above is peeled from the surface of the filter cloth, and then water is usually added in a slurry tank or the like so that the carbonate concentration is usually 5 to 50.
It is re-slurried to a weight percent, preferably 10 to 30 weight percent. The slurry is then sent to a step of dissolving in acetic acid, and by adding acetic acid in an amount not less than twice the amount of carbonate to produce acetic acid, cobalt acetate and manganese acetate are produced and dissolved, and then the metal of the catalyst is dissolved. Reused as a solution of ingredients. The acetic acid reaction is usually 100 to 15 with stirring.
The temperature is 0 ° C., preferably near the boiling point of acetic acid, and the reaction time is usually 30 to 300 minutes, preferably 60 to 180 minutes.

[0024]

The present invention will be described below in more detail with reference to examples. In Examples and Comparative Examples, the total Na consumption is
The total amount of sodium required for neutralization (kg / hr) and the amount of sodium required for carbonation reaction (kg / hr) is shown, and the reaction pH is the pH of the solution in the carbonation reaction tank.
The average particle size of the carbonate represents the average particle size of the carbonate particles obtained by the carbonation reaction measured by a laser diffraction method, and the recovery rate means the catalyst in the carbonation reaction. It is expressed by multiplying the reaction rate of the component and the dissolution rate of the catalyst component dissolved in acetic acid in the acetic acid.

Example 1 300 ppm of cobalt acetate as a Co atom, 200 ppm of manganese acetate as a Mn atom and B with respect to a solvent
Hydrous acetic acid containing 1000 ppm of hydrobromic acid as an r atom (water content; 20% by weight) was used as a solvent, the solvent / paraxylene weight ratio was 3, the reaction temperature was 210 ° C., the pressure was 25 kg /
The para-xylene was continuously oxidized in a titanium reaction vessel at cm ² and a residence time of 120 minutes. Then, the terephthalic acid particles were separated from the obtained reaction mixture using a vacuum filter,
The separated liquid was introduced into the evaporator to lift up the solvent. About 1 part by weight of the obtained residue was added with about 2 parts by weight of water to form a water slurry, which was filtered to obtain an aqueous catalyst solution (Co; 286
0ppm, Mn; 1860ppm, acetic acid; 3.9%, benzoic acid; 8120ppm, orthophthalic acid; 4450p
pm, isophthalic acid; 890 ppm, others; 1000
ppm or less, pH = 3.0) was obtained.

A neutralization tank (baffle, stirring blade, pH) of 2500 kg / hr of this aqueous solution and a 15% by weight aqueous solution of caseiso-da was added so that the flow rate of the aqueous solution of caseiso-da would be 5.
(Equipped with a meter) and continuously neutralized at 55 ° C. At this time, the flow rate of the aqueous caseiso-da solution is 4
It was 20 kg / hr. The liquid is extracted from the neutralization tank, and this liquid and a 20 wt% sodium carbonate aqueous solution are continuously introduced into the carbonation tank (equipped with baffles, stirring blades, and pH meters) from separate introduction paths. did. The pH of the solution in the carbonation tank at this time was 8.7. The temperature at this time was maintained at 55 ° C., and the residence time was 60 minutes. The flow rate of the soda carbonate aqueous solution at this time was 560 kg / hr.

Next, in order to filter and separate the slurry continuously discharged from the carbonation tank, it was once taken out to a storage tank (temperature 55 ° C., residence time 60 minutes). 10 ppm of cobalt was dissolved in the liquid of this slurry, and the reaction rate was 9
It was 9.5%. The average particle size of carbonate particles is 28μ.
m. A slurry is extracted from this storage tank in batches, and a candle-type pressure filter equipped with five same-type filters having a length of 2500 mm and a filtration area of 0.6 m ² (total filtration area 3 m ² , filter cloth polypropylene, opening) 30 μm). Five times the volume of water was circulated through the obtained carbonate cake to wash it, and then mixed with water to obtain a slurry having a concentration of about 20% by weight. This slurry was supplied to an acetic acid dissolution tank and dissolved at a temperature of 105 ° C for 180 minutes. The composition after acetic acid is
Co 4.2%, Mn 2.8%, acetic acid 26%, and the dissolution rate was 9 with respect to the amount of carbonate cake supplied to the acetic acid dissolution tank.
It was 9.9% by weight. At this time, the recovery rate of the catalyst component in the catalyst recovery system was 9 based on the above reaction rate and acetic acid dissolution rate.
It was 9.4% by weight.

Examples 2 to 3 In the same manner as in Example 1 except that the pH in the neutralization tank was changed, the total amount of Na consumed for the neutralization and the carbonation reaction and the average of carbonates were changed. The particle size and the recovery rate of the catalyst component were obtained. The results are shown in Table 1. Examples 4 to 5 In the same manner as in Example 1 except that the reaction time in the carbonation tank was changed, the total amount of Na consumed for the neutralization and the carbonation reaction and the average of carbonates were changed. The particle size and the recovery rate of the catalyst component were determined. The results are shown in Table 1.

Comparative Example 1 In the same manner as in Example 1 except that neutralization was not performed in the neutralization tank, the total amount of Na consumed for the carbonation reaction, the average particle size of the carbonate, and the recovery of the catalyst component were carried out. I asked for the rate. Table 1 shows the results.
Shown in Comparative Examples 2-3 In the same manner as in Example 1 except that the reaction time in the carbonation tank was changed, the total amount of Na consumed for the neutralization and the carbonation reaction, the average particle size of the carbonate, and the catalyst components The recovery rate was calculated. The results are shown in Table 1. Comparative Example 4 In the same manner as in Example 1 except that the pH in the neutralization tank was 7, the total amount of Na consumed for the neutralization and the carbonation reaction, the average particle size of carbonate,
And the recovery rate of the catalyst component were determined. The results are shown in Table 1.

Comparative Examples 5 to 6 The total amount of Na consumed for the neutralization and carbonation reaction was the same as in Example 1 except that the pH of the solution in the carbonation tank was changed.
The average particle size of the carbonate and the recovery rate of the catalyst component were determined. The results are shown in Table 1.

[0031]

[Table 1]

[0032]

INDUSTRIAL APPLICABILITY According to the present invention, cobalt acetate and manganese acetate which are catalysts used in the liquid phase oxidation of an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent to produce an aromatic carboxylic acid. Since it has a low alkali consumption and can be continuously recovered and reused at a high recovery rate, it has a great industrial utility value.

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Claims (3)

[Claims] 1. A liquid phase oxidation of an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent with molecular oxygen in the presence of a catalyst composed of cobalt acetate, manganese acetate and a bromine compound in an acetic acid solvent. In the method of producing an aromatic carboxylic acid by the method, (1) when the catalyst is recovered and reused, the aromatic carboxylic acid and the acetic acid solvent are removed from the oxidation reaction mixture to obtain a residue containing cobalt acetate and manganese acetate. (2) Water and alkali hydroxide are added to the residue and mixed to obtain an aqueous solution having a pH of 4.0 to 6.5, (3)
Then, the aqueous solution and the alkali carbonate are continuously added to a carbonation tank at such a ratio that the pH of the solution in the carbonation tank is kept substantially constant within the range of 8.0 to 9.5. The slurry containing cobalt and manganese carbonate is continuously or intermittently withdrawn from the carbonation tank, and the residence time is 20 to 200 minutes, and (4) cobalt and manganese carbonate is separated from the slurry, (5) A method for producing an aromatic carboxylic acid, characterized in that the separated cobalt and manganese carbonates are reacted with acetic acid, and (6) the obtained cobalt acetate and manganese acetate are reused as the catalyst component. . 2. The method according to claim 1, wherein a candle pressure separator is used for separating cobalt and manganese carbonates from the slurry. 3. The method according to claim 1, wherein para-xylene is liquid-phase oxidized to produce terephthalic acid.