JP2924104B2 - Method for producing high-purity isophthalic acid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing isophthalic acid by liquid phase oxidation of meta-xylene.

High-purity isophthalic acid is useful as an intermediate material for polymers such as unsaturated polyester resins, alkyd resins, modified polyester fibers, and heat-resistant polyamides.

(Prior Art) As a method for producing an aromatic carboxylic acid, an aromatic hydrocarbon having an aliphatic substituent is prepared by the reaction of an aromatic hydrocarbon having a molecular oxygen in the presence of a heavy metal and bromine catalyst in a solvent of an aliphatic carboxylic acid such as acetic acid. A liquid phase oxidation method is known, and this method can also be applied to the production of isophthalic acid.

Japanese Patent Publication No. 60-48497 describes a specific method for oxidizing meta-xylene with air in the presence of a catalyst comprising cobalt, manganese and bromine in an acetic acid solvent, and is widely practiced industrially. Isophthalic acid obtained by such a method contains a large amount of impurities such as 3-carboxybenzaldehyde (3CBA), and if it is used as a raw material as a raw material, it does not have excellent hue and is not suitable for high-performance applications. . In particular, in recent years, with the advancement of industrial technology, quality requirements for polyester products as high-performance materials have become strict, and isophthalic acid having high purity and excellent whiteness has been desired as a polyester raw material.

To purify the crude isophthalic acid obtained by oxidation,
A method of hydrogenating and purifying an aqueous solution of crude isophthalic acid at a high temperature in the presence of a palladium catalyst as shown in JP-B-51-38698 and JP-B-51-32618 can be applied.

On the other hand, terephthalic acid is produced by oxidizing para-xylene by the same method as that for isophthalic acid. As described above, a method for directly producing high-purity terephthalic acid without performing hydrogenation purification or the like is performed. That is, JP-B-45-36732
Describes a method for producing terephthalic acid for direct polymerization by oxidizing para-xylene in a cobalt-manganese-bromine-based catalyst containing manganese in an amount of 1 to 20% by weight based on cobalt. . However, since this method uses a large amount of expensive cobalt, there have been proposed many methods for producing high-purity terephthalic acid by improving the oxidation conditions and the oxidation method to reduce the amount of catalyst and the amount of acetic acid burned (Japanese Patent Publication No. 57-57). 42053, JP-A-53-9736, JP-B-60
No. -50775, JP-B-53-30700, JP-A-54-70235,
JP-B-56-14101, JP-B-56-5377, JP-A-47-319
No. 47).

(Problems to be Solved by the Invention) The conventional method for purifying crude isophthalic acid to be hydrogenated in the presence of a palladium catalyst requires a separate hydrogenation reactor and crystallization apparatus, and requires a large amount of purification equipment. It requires investment and labor, and raises manufacturing costs.

The present inventors have attempted to apply the method for producing high-purity terephthalic acid by oxidizing para-xylene to the production of isophthalic acid by oxidizing meta-xylene, and as a result, have the following problems. It turned out that it cannot be directly applied to the production of isophthalic acid.

Oxidation of meta-xylene, that is, JP-A-47-319467
As described in the item, if post-oxidation is performed after the main oxidation reaction, the intermediate metatoluic acid and 3CBA can be almost eliminated, but if 3CBA is reduced below a certain amount, isophthalic acid with excellent whiteness is obtained. Is not obtained, but rather the coloring impurities increase and the quality deteriorates.

In recovering acetic acid by evaporating the separated mother liquor of the reaction solution, the recovery rate of acetic acid is poor, and the amount of acetic acid loss increases. This is because the solubility of isophthalic acid in acetic acid near the boiling point is about 10 times higher than that of terephthalic acid, and the amount of isophthalic acid dissolved in the mother liquor obtained by separating crystals increases. This is because the fluidity of the high-temperature melt-like high-boiling substance is reduced, and the operability of the evaporator is extremely deteriorated. For this reason, an evaporator such as a thin film evaporator cannot be suitably used.

An object of the present invention is to provide an expensive purification step without providing it.
An object of the present invention is to provide an industrially advantageous production method capable of obtaining high-purity isophthalic acid having excellent whiteness in a high yield only by an oxidation step and simple washing.

(Means for Solving the Problems) The present inventors focused on the oxidation characteristics of meta-xylene,
As a result of further intensive studies on the application of the above-mentioned method relating to the production method of high-purity terephthalic acid, a specific amount of acetic acid solvent and catalyst were used to oxidize to a certain limit by dividing into main oxidation and post-oxidation, and then to specific purification. By performing the treatment, high-purity isophthalic acid with excellent whiteness can be obtained, acetic acid can be efficiently recovered from the mother liquor from which crystals have been separated, and it can be recycled, and the amount of acetic acid combustion in the reactor can be reduced. The present invention has been completed and the present invention has been completed.

That is, the present invention relates to a method for producing isophthalic acid by oxidizing meta-xylene with an oxygen-containing gas in the presence of a cobalt-manganese-bromine-based catalyst in a acetic acid-containing solvent, comprising the steps of: ~
15 times, the total amount of cobalt and manganese per solvent weight
300-1500ppm, atomic ratio of manganese to cobalt is 0.
The catalyst is supplied so that the atomic ratio of bromine to the total amount of cobalt and manganese is 0.5 to 1.5 times, and the oxidation is performed while maintaining the temperature at 180 to 210 ° C and the oxygen concentration of the exhaust gas at 2 to 8% by volume. The reaction is performed, and the concentration of 3-carboxybenzaldehyde of the crude isophthalic acid obtained in the step is 500 to 100.
A first step of carrying out the oxidation reaction so that the total amount of isophthalic acid produced by the oxidation reaction and its intermediate is 10 to 35% by weight based on the weight of the solvent, within the range of 00 ppm, the oxidation reaction product obtained in the first step A second step of further oxidizing the mixture to a concentration of 3-carboxybenzaldehyde in the crude isophthalic acid of 100 to 800 ppm, separating the crude isophthalic acid, evaporating the mother liquor, purifying the mother liquor by distillation and collecting acetic acid, and a second step A method for producing high-purity isophthalic acid, comprising a third step of mixing the isophthalic acid crystal obtained in the above with purified acetic acid, stirring the mixture at a temperature of 100 ° C. or higher, and separating the purified isophthalic acid.

 Hereinafter, the present invention will be described in detail.

In the method of the present invention, first, in a first step, meta-xylene is oxidized with an oxygen-containing gas in a hydrous acetic acid solvent in the presence of a catalyst comprising a cobalt compound, a manganese compound and a bromine compound.

Meta-xylene is usually used as an oxidizing material,
The substituent is not limited to a methyl group, but may be ethyl, propyl, i
-A propyl group or any one which can be oxidized to a carboxyl group such as an aldehyde or acetyl group.
One of the substituents may be a carboxy group.

Meta-xylene is continuously supplied to the oxidation reactor. The feed rate is hourly per liter of solvent volume in the reactor
0.05-0.2 kg, reaction time is 10-120 minutes, preferably
The range is 20 to 90 minutes.

Hydrous acetic acid is used as a reaction solvent. The water concentration in acetic acid supplied to the oxidation reactor is 3 to 15% by weight, preferably 5 to 15% by weight.
It is in the range of 12% by weight. If the water concentration is too low, the color quality of isophthalic acid tends to deteriorate, and the burning amount of acetic acid increases. If the water concentration is too high, the oxidizing activity decreases and the reaction time becomes longer, and the quality deteriorates, which is not preferable.

The amount of the solvent used is such that the total amount of isophthalic acid produced by the oxidation reaction and its intermediates (methtoluic acid and 3CBA) is 10 to 35% by weight based on the weight of the solvent. Usually, the supply amount of the solvent in this case is 1 to 15 times by weight, preferably 3 to 12 times by weight based on meta-xylene. When the concentration of the total amount of isophthalic acid and its intermediates is lower than 10% by weight, a relatively large amount of solvent is required, so that a large crystal separator is required.
In addition, the amount of the solvent to be treated in the solvent recovery step increases, which is not economical. If this concentration is higher than 35% by weight, clogging is likely to occur in pipes, crystallizers, and the like from the post-oxidation reactor to the crystallizer of crude isophthalic acid, causing troubles in operation.

As the cobalt compound, manganese compound and bromine compound of the catalyst, well-known compounds used for liquid-phase oxidation, for example, carbonate and acetate tetrahydrate, bromide and the like of cobalt and manganese are used. The bromine compound is preferably an inorganic compound which dissociates into ions as soon as it is dissolved in a solvent. In particular, hydrobromic acid, cobalt bromide, manganese bromide and the like are used.

The metal concentration of the catalyst is 300 to 1500 ppm, preferably 400 to 1200 ppm by weight of the solvent in the total amount of cobalt and manganese.
And the atomic ratio of manganese to cobalt is 0.5 to 5 times, preferably 0.8 to 4 times.
The bromine is used at a concentration of 0.5 to 1.5 times, preferably 0.6 to 1.2 times, the atomic ratio to the total amount of cobalt and manganese. By setting the concentration of each metal component within the above range, the 3CBA concentration can be appropriately maintained through main oxidation and post-oxidation, and isophthalic acid having an excellent hue can be obtained, and the burning amount of acetic acid can be extremely reduced.

The reaction temperature of the first step is 180-210 ° C. The pressure is sufficient to maintain the liquid phase of the solvent, usually 10-25 kg / c
The reaction takes place in the range of m ² .

Air is usually used as the oxygen-containing gas. The oxygen concentration in the exhaust gas of the oxidation reaction is 2 to 8% by volume, preferably 3% by volume.
Air is supplied into the reaction solution so as to be maintained at ６6% by volume.

In the main oxidation reaction of the first step, 3CBA of crude isophthalic acid obtained by oxidation under the conditions in the range described above is added to 50%.
Operating factors such as residence time and reaction temperature are controlled so as to be in the range of 0 to 10000 ppm. If 3CBA is too low at this stage, the degree of oxidation will be excessive, resulting in an increase in coloring impurities, and the post-oxidation will have no effect, and the color quality will not be improved. Further, the amount of acetic acid combustion increases, which is extremely disadvantageous economically. On the other hand, if 3CBA exceeds this range, 3CBA is not sufficiently oxidized even after post-oxidation, and high-purity isophthalic acid cannot be obtained.

The above-mentioned 3CBA of the crude isophthalic acid was measured on the crude isophthalic acid crystal obtained by solid-liquid separation of the oxidation reaction mixture extracted from the reactor in the first step.

In the second step, first, the oxidation reaction product mixture of the first step is post-oxidized by an oxygen-containing gas. Usually, in the case of a continuous type, the post-oxidation is carried out by transferring from the main oxidation reactor of the first step to the crystallization tank, but can also be carried out in a cooling step following the main reaction of the first step. The post-oxidation reaction is performed at a temperature between the main oxidation reaction temperature in the first step and a temperature 30 ° C. lower than this temperature. Making the post-oxidation reaction temperature higher than the main oxidation reaction temperature is not only industrially disadvantageous because it requires heating, but also tends to cause deterioration in color quality. If the temperature is too low, the post-oxidation becomes insufficient, and high-purity isophthalic acid cannot be obtained.

As the oxidation-containing gas used for the post-oxidation, air can be used, but the oxidized exhaust gas of the first step can also be used.
The oxygen concentration in the exhaust gas in the second step is maintained at 2 to 7% by volume.

The post-oxidation treatment time may be sufficient to substantially allow the desired oxidation to proceed, and may be 1 to 300 minutes, preferably 2 to 300 minutes.
The range is ~ 120 minutes.

The most important point in the second step is to make the concentration of 3CBA in the oxidation reaction solution obtained in the post-oxidation 100 to 800 ppm, for the following reasons.

(1) The oxidized reaction mixture is cooled to crystallize isophthalic acid, and the solid isophthalic acid is separated into solid and liquid. The isophthalic acid is purified in the following third step.
By setting the concentration of 3CBA within the above range, isophthalic acid having high purity and excellent whiteness can be obtained in the third step.

If the concentration of 3CBA in the oxidation reaction solution obtained in the post-oxidation is higher than 800 ppm, high-purity isophthalic acid cannot be obtained even in the third step. If the concentration of 3CBA is lower than 100 ppm, purified isophthalic acid having excellent whiteness cannot be obtained.

(2) Acetic acid, water, a catalyst composition, benzoic acid, metatoluic acid,
In addition to 3CBA, isophthalic acid, phthalic acid, trimellitic acid, etc., high-boiling substances such as coloring substances are included. As a result of detailed studies by the inventors, the fluidity of the separated mother liquor at the high temperature of the evaporator residue largely depends on the contents of acetic acid, water, a catalyst composition, benzoic acid, 3CBA, metatoluic acid, trimellitic acid, etc. with respect to isophthalic acid. I understood that.

That is, if the 3CBA in the post-oxidation is lower than the above range, the fluidity at a high temperature is remarkably reduced due to a change in the composition of the residue of the separated mother liquor, so that acetic acid cannot be efficiently evaporated. Therefore, acetic acid can be efficiently recovered by setting the concentration of 3CBA within the above range.

The oxidation reaction solution obtained by post-oxidation is usually transferred to a crystallizer and finally cooled to 110 to 80 ° C. to precipitate isophthalic acid crystals. Next, the crystals are separated by a filtration operation and sent to the third step. The filtered mother liquor is evaporated to separate a high boiling substance in a melt state, and the condensate of the recovered vapor is purified by distillation to recover acetic acid. In this evaporation operation, a thin film evaporator is preferably used.
The mother liquor can be circulated to the oxidation reactor in the first step. In this case, the remainder of the mother liquor is evaporated and purified by distillation as described above to recover acetic acid.

When a thin film evaporator is used, it is preferable to distill a part of the mother liquor in advance in order to reduce the load, and to purify the bottom liquid in the thin film evaporator. As the thin film evaporator used in the present invention, for example, a type manufactured by Luwa is suitable, and the temperature is adjusted so that the concentration of the concentrated liquid is 130 to 230 ° C. The acetic acid aqueous solution separated from the mother liquor distillation column and the acetic acid from the thin film evaporator are preferably further rectified, and the rectification separates generated water. The recovered acetic acid is the first
It is used for the solvent in the step and the washing in the third step.

In the third step, isophthalic acid crystals separated from the reaction mixture of the second step are made into a suspension using purified acetic acid,
After stirring at a temperature of 100 ° C. or more, isophthalic acid crystals are separated.

The acetic acid used for washing the isophthalic acid crystals is purified acetic acid, and the acetic acid recovered in the second step can be used, and industrial acetic acid can be newly used. This acetic acid may be hydrous acetic acid, and the amount of purified acetic acid used is 1 to 5 times by weight of isophthalic acid.

A holding temperature of 100 ° C. or higher is sufficient for the stirring process,
It is not necessary to raise the temperature to the point where isophthalic acid is completely dissolved. The retention time is in the range of 10 to 60 minutes.
By drying after such a washing treatment, purified isophthalic acid having extremely excellent whiteness can be obtained.

The mother liquor from which the isophthalic acid crystals have been separated in the third step can be used as a solvent for the liquid phase oxidation in the first and second steps, whereby the isophthalic acid dissolved in the mother liquor is recovered in the oxidation step.

(Example) Next, the present invention will be described in more detail by way of examples.
However, the present invention is not limited by these examples.

Example 1 [First step] A first pressure-resistant titanium reactor equipped with a stirrer, a reflux cooling device, and a heating device and having a raw material inlet, an air inlet, an exhaust gas outlet, and a reflux liquid reflux port, was also used. Equipped with a stirrer, a reflux cooling device, and a heating device, a pressure-resistant titanium second reactor and crystallizer having an air inlet, an exhaust gas outlet, a reflux liquid reflux, and a reaction product inlet and outlet are provided. A continuous oxidation reaction of meta-xylene was performed.

100 parts by weight of meta-xylene was added to the first reactor, and 0.561 parts of aqueous cobalt acetate and 1.656 manganese acetate tetrahydrate were added thereto.
Parts, hydrobromic acid (47%) 1.117 parts and acetic acid (water 10%) 8
Feed continuously as a raw material liquid with a ratio of 96.7 parts (catalyst concentration is 147 ppm cobalt and 412 manganese manganese per solvent weight)
m, bromine 576 ppm) and oxidized while blowing air. The temperature was kept at 200 ° C. and the pressure was 16.5 kg / cm ² G, and the air supply was adjusted so that the oxygen concentration of the oxidizing exhaust gas was kept at 5% by volume. At this time, the feed rate of meta-xylene was 0.17 kg / h per liter of the solvent volume in the reactor, and the average residence time was about 30
And the total concentration of isophthalic acid and its intermediates in the oxidation reactor was 15.6%.

[Second step] The oxidation reaction mixture obtained in the first reactor is transferred to the second reactor, and subjected to post-oxidation with air at a temperature of 195 ° C, a pressure of 12 kg / cm ² G, and an average residence time of 50 minutes. went. At this time, the oxygen concentration of the exhaust gas was maintained at 3% by volume. (CO _{2 in the} exhaust gas in the oxidation process, which is an indicator of acetic acid combustion,
+ CO) The production amount was 0.41 mol per 1 mol of the starting meta-xylene.

The oxidation reaction mixture post-oxidized in the second
The crystal was transferred to a crystallizer at ℃ to precipitate isophthalic acid crystals. Isophthalic acid was separated by filtration from the obtained slurry while washing with isoacetic acid. The separated mother liquor is concentrated by distillation, and the distillation column bottom liquid is continuously fed for 6 hours to a thin film evaporator in which a heating medium held at 240 ° C. is circulated while controlling the flow rate of the heating medium so that the concentration of the concentrated liquid becomes 230 ° C. When acetic acid was further recovered by feeding to the reactor, high-boiling substances in the bottom could be separated well (total acetic acid content in the bottom was 4.3%). The acetic acid recovered from the mother liquor distillation column and the thin film evaporator was purified in a rectification column and used as a washing solution in the next step.

[Third Step] A suspension obtained by adding 1.5 weight times of purified acetic acid (water content: 10%) to the isophthalic acid crystals separated by filtration was transferred to a washing tank, and kept at 150 ° C. for 30 minutes with stirring. The suspension subjected to the washing treatment was cooled to 100 ° C., filtered again, and then dried to obtain 146 parts by weight of purified isophthalic acid. As a result, the yield of isophthalic acid with respect to the raw material meta-xylene is
93.0 mol%, and purified isophthalic acid having high purity and excellent whiteness was obtained.

Example 2 In Example 1, the catalyst concentration in the first step was increased to 1.5 times,
The oxidation reaction was performed at a temperature of 190 ° C. Post-oxidation treatment was performed in the same manner as in Example 1, and crystallization and washing treatment were performed. As a result, purified isophthalic acid having high purity and excellent whiteness was obtained. The filtered mother liquor was treated with a thin-film evaporator in the same manner as in Example 1, and acetic acid could be recovered smoothly (total acetic acid content in the bottom of the kettle was 5.5%).
Five%).

Comparative Example 1 In Example 2, an oxidation reaction was performed at a temperature of 215 ° C. in the first step. As a result, the concentration of 3CBA in the crude isophthalic acid crystal due to the post-oxidation in the second step was reduced. Acetic acid was recovered from the filtered mother liquor by a thin film evaporator in the same manner as in Example 1. As a result, the fluidity of the bottom remained poor, and the thin film evaporator became inoperable.

Example 3 60 parts by weight of meta-xylene was added to a first reactor, and 0.561 part of cobalt acetate tetrahydrate and 1.656 parts of manganese acetate tetrahydrate were added thereto.
1.551 parts of hydrobromic acid (47%) and acetic acid (water 10%) 49
Feed continuously as a raw material solution consisting of 6.2 parts (catalyst concentration is 276 ppm cobalt and 773 manganese manganese per solvent weight)
m, bromine 1500 ppm) and oxidized while blowing air. In this oxidation, the temperature was maintained at 190 ° C. and the pressure was 16.5 kg / cm ² G, and the air supply amount was adjusted so that the oxygen concentration of the oxidation exhaust gas was maintained at 5% by volume. The feed rate of meta-xylene was 0.09 kg / h / liter of acetic acid solvent held in the reactor, and the average residence time was about 55 minutes. The concentration of the total amount of isophthalic acid and its intermediate in the obtained oxidation reactor was 19.0%.

The oxidation reaction mixture obtained in the first reactor was transferred to the second reactor, where the temperature was 185 ° C., the pressure was 12 kg / cm ² G, and the average residence time was 50.
The post-oxidation was performed with air under the conditions of minutes. The oxidation concentration of the exhaust gas was kept at 3% by volume.

Thereafter, the same operation as in Example 1 was performed, and as a result, purified isophthalic acid having high purity and excellent whiteness was obtained. The filtered mother liquor was treated with a thin film evaporator in the same manner as in Example 1, and acetic acid was successfully recovered (total acetic acid content in the bottom of the kettle was 5.0%).
%).

Comparative Example 2 In Example 3, 1.795 parts of cobalt acetate and 0.442 parts of manganese acetate tetrahydrate (the ratio of manganese to cobalt)
0.25), except for the above.

As a result, the concentration of 3CBA in the oxidized isophthalic acid crystals after the second step was reduced. Acetic acid was recovered from the filtered mother liquor by a thin film evaporator in the same manner as in Example 1. As a result, the fluidity of the bottom remained poor, and the thin film evaporator became inoperable.

Comparative Example 3 The first step was the same as in Example 1, and after the second step
The test was performed at 5 ° C. and a pressure of 7 kg / cm ² G. As a result, although the filtered mother liquor was treated by a thin film evaporator and acetic acid could be collected smoothly (total acetic acid content in the bottom 4.8%), purified isophthalic acid was 3%.
CBA was highly concentrated and colored.

Comparative Example 4 The first step and the second step were the same as in Example 1, and the cleaning temperature in the third step was 90 ° C. As a result, coloring was observed in the purified isophthalic acid.

Table 1 shows the main operating conditions of each Example and Comparative Example, and the analysis results of the crystals of crude isophthalic acid and purified isophthalic acid.

The crude isophthalic acid in Table 1 was obtained by directly taking the oxidation reaction mixture from the first reactor and the second reactor into a pressure-resistant sample vessel, and performing solid-liquid separation while washing with acetic acid at 100 ° C.

 The method for measuring 3CBA and resin color is as follows.

3CBA: Quantitative value by polarography, high purity isophthalic acid requires 3CBA to be 50 ppm or less.

Resin color: Isophthalic acid: fumaric acid: neopentyglycol: propylene glycol = polymerized at a ratio of 57: 43: 50: 53 (molar ratio), and the resin color was obtained for a styrene solution (resin 60% by weight) of the obtained resin. Indicated by Hazen color number. The smaller the number of Hazen colors, the better the resin color, and the high purity isophthalic acid must be at least 30 or less.

(Effects of the Invention) According to the present invention, high-purity isophthalic acid having extremely excellent color quality can be industrially very easily obtained as a polymer material for unsaturated polyester resins, alkyd resins, heat-resistant polyamides and the like for high-performance applications. Can be In addition, the method of the present invention does not require an expensive purification step, so construction costs are small,
A small amount of acetic acid can be used, and high-purity isophthalic acid can be obtained in high yield.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code FI // C07B 61/00 300 C07B 61/00 300 (72) Inventor Tao Ohta 2-5-2-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. (72) Inventor Toshiaki Abe 6-38-3 Yokodai, Isogo-ku, Yokohama-shi, Kanagawa Examiner Koji Ito (58) Field surveyed (Int.Cl. ⁶ , DB name) C07C 63/24 C07C 51/265

Claims (1)

(57) [Claims] 1. A method for producing isophthalic acid by oxidizing meta-xylene with an oxygen-containing gas in a hydrous acetic acid solvent in the presence of a cobalt-manganese-bromine catalyst, comprising the steps of: ~
15 times, the total amount of cobalt and manganese per solvent weight
300-1500ppm, atomic ratio of manganese to cobalt is 0.
The catalyst is supplied so that the atomic ratio of bromine to the total amount of cobalt and manganese is 0.5 to 1.5 times, and the oxidation is performed while maintaining the temperature at 180 to 210 ° C and the oxygen concentration of the exhaust gas at 2 to 8% by volume. The reaction is performed, and the concentration of 3-carboxybenzaldehyde of the crude isophthalic acid obtained in the step is 500 to 100.
A first step of carrying out the oxidation reaction so that the total amount of isophthalic acid produced by the oxidation reaction and its intermediate is 10 to 35% by weight based on the weight of the solvent, within the range of 00 ppm, the oxidation reaction product obtained in the first step A second step of further oxidizing the mixture to a concentration of 3-carboxybenzaldehyde in the crude isophthalic acid of 100 to 800 ppm, separating the crude isophthalic acid, evaporating the mother liquor, purifying the mother liquor by distillation and collecting acetic acid, and a second step A method for producing high-purity isophthalic acid, comprising the step of mixing the isophthalic acid crystal obtained in the above with purified acetic acid, stirring the mixture at a temperature of 100 ° C. or higher, and separating the purified isophthalic acid.