JPH072732A - Production of isophthalic acid of high purity - Google Patents

Abstract

PURPOSE:To produce isophthalic acid of high purity from the reaction mixture after catalytic hydrogenation of crude isophthalic acid with industrial advantage. CONSTITUTION:Isophthalic acid of high purity is obtained by catalytic hydrogenation treatment of crude isophthalic acid obtained in liquid-phase oxidation wherein the reaction mixture is separated from the catalyst, reduced in pressure and cooled down, then the isophthalic acid slurry comprising the crystals and the mother liquor is introduced into the solvent-replacing column at 180 to 120 deg.C and brought into contact with ascending stream of hot water introduced from the column bottom. A part of the mother liquor and fine crystals of isophthalic acid is taken out of the column top together with the ascending stream, while most parts of the crystals are pulled out of the bottom of the column as a slurry together with the hot water. Then, isophthalic acid crystals of high purity is separated from the bottom slurry.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high-purity isophthalic acid from crude isophthalic acid produced by liquid phase oxidation of m-dialkylbenzenes. High-purity isophthalic acid is useful as an intermediate raw 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 used as a liquid phase by molecular oxygen in the presence of a catalyst composed of a heavy metal and bromine in a solvent of an aliphatic carboxylic acid such as acetic acid. Methods of oxidation are known, m
Isophthalic acid is produced by liquid phase oxidation of dialkylbenzenes.

That is, Japanese Patent Publication No. 60-48497 describes a specific method for oxidizing m-dialkylbenzenes with air in the presence of a catalyst consisting of cobalt, manganese and bromine in metaxylene in an acetic acid solvent, which is widely used industrially. Have been implemented in. The isophthalic acid obtained by this method is inferior in whiteness of crystals and contains a large amount of impurities such as 3-carboxybenzaldehyde (3CBA). Even if it is used as a raw material as a polymer, the hue is not excellent, And it is not suitable for high-performance applications. Particularly in recent years, with the progress of industrial technology, quality requirements for polyester products as highly functional materials have become more and more severe, and isophthalic acid having high purity and excellent whiteness is desired as a polyester raw material.

As a method for purifying an aromatic carboxylic acid obtained by liquid phase oxidation, a method of catalytic hydrogenation treatment of an aqueous solution of a crude aromatic carboxylic acid at high temperature in the presence of a palladium catalyst is disclosed in JP-B-41-16860. , Japanese Patent Publication No. 47-49049,
It is described in JP-B-51-326618 and 51-38698. This catalytic hydrotreating method is mainly used for the purification of terephthalic acid, but it can also be applied to isophthalic acid. In Japanese Patent Laid-Open No. 4-21653, crude isophthalic acid is subjected to catalytic hydrogenation by using a mixed solvent of water and acetic acid. The method of chemical treatment is described.

[0005]

However, the purity of isophthalic acid obtained by crystallization of the reaction solution by the above-mentioned catalytic hydrotreating method is different from that of terephthalic acid, as will be shown later, and a product which is not always satisfactory is obtained. No, coloring and 3
Further purification is required in terms of CBA concentration. That inventors, using the OD ₃₄₀ as an index representing the whiteness of crystals, the results of comparing the high purity isophthalic acid from the reaction solution by the catalytic hydrotreatment a crude isophthalic acid, the reaction rate of the OD ₃₄₀ is about It was about 60% and required further purification.

Crystallization of the catalytic hydrogenation reaction solution is generally carried out by a multi-stage method, but impurities are more likely to remain dissolved than isophthalic acid in the crystallization step. Therefore, precipitation is particularly likely to occur in the middle and subsequent crystallizers. The concentration of impurities in isophthalic acid increases. Therefore, in the crystallizer in the middle stage and thereafter, the isophthalic acid crystals and the mother liquor are separated by the high-pressure separating means while the dissolved impurities do not precipitate at high temperature, but this high-pressure separating method requires complicated maintenance operations. The purpose of the present invention is to
The object is to industrially advantageously produce highly pure isophthalic acid having high purity and excellent whiteness by further purifying the reaction solution obtained by catalytic hydrogenation of crude isophthalic acid.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies as to a method for producing high-purity isophthalic acid having the above-mentioned problems. The quality of isophthalic acid obtained from the bottom of the column is dramatically improved by performing solvent replacement between the precipitated slurry and high-temperature water, and extracting some of the fine crystals of isophthalic acid together with the mother liquor from the top of the solvent replacement column. The present invention has been achieved and has reached the present invention.

That is, according to the present invention, in a method for producing high-purity isophthalic acid by subjecting crude isophthalic acid obtained by liquid phase oxidation to catalytic hydrogenation, a catalyst is separated from a reaction solution obtained by catalytic hydrogenation. Thereafter, an isophthalic acid slurry solution consisting of crystals of isophthalic acid crystals obtained by depressurizing and lowering the temperature of the reaction solution and a mother liquor is introduced into the solvent displacement tower at a temperature of 180 to 120 ° C. and introduced from the lower part of the solvent displacement tower. Contact with the rising stream of high temperature water, and a part of the mother liquor and fine isophthalic acid crystals are withdrawn from the top of the tower as a slurry liquid together with the rising stream of high temperature water, and most of the isophthalic acid crystals are collected as a slurry liquid together with the high temperature water in the tower. It is a method for producing high-purity isophthalic acid, which is characterized by extracting from the bottom and separating isophthalic acid crystals from the slurry liquid from the bottom of the column.

In the method of the present invention, the concentration of isophthalic acid in the slurry solution after the solvent replacement can be increased by adjusting the amount of substances flowing into and out of the solvent replacement column, whereby the fresh solvent introduced into the solvent replacement column can be increased. It is possible to reduce the amount of high-temperature water and reduce the load in the next crystal separation operation.

The present invention specifically comprises the following steps. (1) Catalytic hydrogenation treatment step The crude isophthalic acid obtained by liquid phase oxidation is dissolved in hot water, and catalytic hydrogenation is carried out in the presence of hydrogen at 180 to 260 ° C. with a Group 8 noble metal catalyst supported on a carbon support. The treated and treated solution is separated from the catalyst, the pressure of the solution is lowered, and the temperature is lowered to 180 to 120 ° C. by evaporation of water to precipitate isophthalic acid crystals to obtain an isophthalic acid slurry solution. (2) Solvent Replacement Step The isophthalic acid slurry solution is introduced into an ascending liquid stream of high temperature water at 180 to 120 ° C., and a fine portion of the mother liquor and isophthalic acid crystals is added to the ascending liquid stream of the high temperature water as a slurry solution at the top of the column. Most of the isophthalic acid crystals are allowed to settle in the high temperature water, and are extracted from the bottom of the column as a slurry solution together with a part of the high temperature water. (3) Separation and Drying Step The pressure of the slurry solution extracted from the bottom of the tower is lowered, the temperature is lowered to 110 to 80 ° C. by evaporation of water, and the crystals are separated at the temperature and then dried. Hereinafter, the content of the present invention will be described in detail.

The crude isophthalic acid used in the present invention is m
It is obtained by oxidizing dialkylbenzenes by a known liquid-phase oxidation method. The liquid phase oxidation reaction is usually carried out by a method in which a heavy metal such as cobalt and manganese and a bromine compound are present in an acetic acid solvent and air is used at a temperature of 150 to 240 ° C. and a pressure of 10 to 30 atmospheres. In addition, a liquid phase oxidation reaction may be used by a method of performing an oxidation reaction with oxygen in an acetic acid solvent in the presence of a cobalt catalyst at a temperature of 100 to 150 ° C. and a pressure of 5 to 20 atmospheres, or a method using a promoter such as acetaldehyde or methyl ethyl ketone. it can. Meta-xylene is usually used as a starting material for crude isophthalic acid, m-dialkylbenzenes, but the substituent is not limited to a methyl group, and may be an ethyl, propyl or i-propyl group, or an aldehyde or acetyl group. As long as it is oxidized to a carboxyl group as described above. Further, one of the substituents may be a carboxyl group.

The crude isophthalic acid obtained by the liquid phase oxidation method usually contains many impurities such as 3CBA. Three
CBA content is measured by the polarographic method. There is no particular restriction on the 3CBA content in the crude isophthalic acid used in the present invention. However, in the production of crude isophthalic acid, 3
Since the combustion loss of acetic acid due to the oxidation reaction can be suppressed by selecting the oxidation reaction conditions that increase the CBA content, the 3CBA content in the crude isophthalic acid in the liquid phase oxidation step is 500 pp.
It is industrially advantageous to set the condition to be m or more. The whiteness index OD ₃₄₀ is measured using a spectrophotometer. There is also no particular restriction on OD ₃₄₀ in the crude isophthalic acid used in the present invention.

In the method of the present invention, the crude isophthalic acid obtained by the above-mentioned oxidation is dissolved in water of a constant concentration, and this solution is supported on activated carbon in the presence of hydrogen at high temperature under pressure. Catalytic hydrotreating is carried out using a group noble metal catalyst. A noble metal belonging to Group 8 of the periodic table is used as a catalyst for the catalytic hydrogenation treatment, and palladium, platinum, ruthenium and rhodium are preferable, and palladium and platinum are particularly preferable. These metals do not necessarily have to be used alone and can be used in combination. A porous substance such as activated carbon is suitable as the simple substance of the catalytic metal, and coconut shell coal is particularly suitable as the activated carbon. Although the amount of the catalyst metal supported on the carrier is very small, the effect is exerted, but an appropriate amount is required to maintain the activity for long-term use, and usually 0.1 to 0.5% by weight is supported.

The catalytic hydrotreatment of crude isophthalic acid is carried out in a solution state, so that it is carried out under high pressure and high temperature. The catalytic hydrotreatment temperature is preferably 180 to 260 ° C. The concentration of the crude isophthalic acid is preferably in the range of 10 to 40% by weight, and the concentration is such that the isophthalic acid is completely dissolved at the selected temperature.
The pressure is preferably sufficient to maintain the liquid phase of the solvent, and is preferably a pressure capable of maintaining an appropriate hydrogenation partial pressure for the catalytic hydrogenation reaction,
It is usually in the range of 10 to 50 atm. In the catalytic hydrotreating of crude isophthalic acid, it is necessary to supply hydrogen in an amount of at least twice the molar amount of 3CBA. The treatment time is substantially sufficient for the hydrogenation reaction to proceed,
It is in the range of 60 minutes, preferably 2 to 20 minutes. Usually, the catalytic hydrotreatment is carried out continuously.

The catalytically hydrotreated reaction solution is made of sintered titanium or other sintered metal or carbon particles in order to prevent the outflow of fine powder due to wear of the activated carbon used as the catalyst carrier. Pass through a filter. After that, it is introduced into a crystallizer reaching 1 to 5 stages connected in series, or is introduced into a batch-type crystallizer, and by successively depressurizing, water is evaporated to crystallize isophthalic acid crystals, and a slurry solution is obtained. Becomes

In the present invention, an isophthalic acid slurry comprising crystals of isophthalic acid crystals and a mother liquor obtained by separating the catalyst from the reaction liquid which has been subjected to catalytic hydrogenation as described above, and then dropping and lowering the temperature of the reaction liquid. The solution is introduced into the solvent substitution tower, and the isophthalic acid slurry solution cooled to 180 to 120 ° C. is introduced into the solvent substitution tower. In the solvent displacement tower, it is required to disperse the isophthalic acid crystals in fresh high temperature water and settle them, and to discharge a part of the fine crystals of isophthalic acid out of the system together with the mother liquor. For that purpose, the object is achieved by a method of introducing the slurry solution into the rising liquid flow of the high temperature water introduced from the lower part of the tower.

In the present invention, by introducing the isophthalic acid slurry solution into the solvent displacement column, the contaminated fine crystals of isophthalic acid and the mother liquor are separated, and the concentration of isophthalic acid increases in the slurry liquid from the bottom of the column. Impurities are reduced. As described above, impurities are more likely to remain dissolved in the crystallization process than isophthalic acid, and especially in the middle stage and thereafter (2
(Since the second and subsequent stages), the concentration of impurities in the precipitated isophthalic acid becomes high, so by introducing the isophthalic acid slurry solution obtained from the middle-stage crystallizer into the solvent displacement column, without using high-pressure separation means. High-purity isophthalic acid can be obtained.

Further, in the solvent replacement step of the present invention, a function of increasing the concentration of isophthalic acid in the slurry solution after solvent replacement is added by skillfully adjusting the amount of substances flowing into and out of the solvent replacement column. With this function, the amount of fresh hot water introduced into the solvent displacement column can be reduced, and the load in the next crystal separation operation can be reduced. That is, the present invention is an extremely sophisticated method that simultaneously satisfies the two contradictory requirements of increasing the purity of crystalline isophthalic acid in the slurry solution as much as possible and simultaneously reducing the amount of hot water and reducing the load in the crystal separation operation. Is a technique.

The reduction of the amount of hot water and the reduction of the load in the separation operation can also be carried out by increasing the concentration of the isophthalic acid slurry solution introduced into the solvent displacement column. However, if the slurry concentration supplied to the solvent displacement tower is set high, the impurity concentration in the mother liquor in the crystallization process will be correspondingly high. This can be calculated based on the eutectic phenomenon in which the OD ₃₄₀ component described later is incorporated into the isophthalic acid crystal, and the experimental results of the present inventors also support this.

The specific operation of the solvent substitution column is performed as follows. The isophthalic acid slurry solution is introduced from the upper part of the tower into the rising liquid flow of the high temperature water introduced from the lower part of the tower.
The hot water is set to the same temperature as the isophthalic acid slurry solution. The pressure is sufficient to maintain the temperature of hot water, and is determined almost automatically when the temperature is determined. The linear velocity of the rising liquid flow of the high-temperature water varies depending on the structure of the apparatus, the size of the crystal, etc., but is preferably about 0.001 to 0.01 m / sec. If the linear velocity is too low, the separation of the mother liquor and the crystals will be insufficient, and the purity of isophthalic acid will decrease. On the contrary, if the linear velocity is too high, there is a drawback that the amount of hot water used increases.

The structure of the solvent displacement column is preferably column-shaped because the rising liquid flow of high-temperature water must rise at a certain linear velocity without backmixing. In order to achieve such an object, a column having a baffle in the column or a perforated plate column is suitable. A stirrer is not necessarily required in the tower, but in the process of suspending and settling the crystals in the hot water, the stirrer is used for the purpose of improving the contact between the hot water and the crystals and removing the mother liquor accompanying the crystals from the crystals. It is effective to provide them. In order to achieve such an objective, so-called RDC (Rotary Di
sk Contactor) is especially recommended.

The mother liquor extracted from the top of the solvent displacement column contains, as a slurry, isophthalic acid corresponding to the solubility at that temperature and fine crystals of isophthalic acid discharged along with the upward flow. This slurry is cooled to a temperature as low as possible by passing through 1 to 3 crystallization tanks installed in series to crystallize isophthalic acid crystals. The obtained isophthalic acid crystals are separated and recovered from the mother liquor by a suitable means such as filtration in a crystal recovery device, and returned to the oxidation reaction system for effective use.

The mother liquor discharged from the crystal collector contains isophthalic acid and other organic components corresponding to the solubility at that temperature, and part of it can be reused as water for catalytic hydrotreatment. it can. The balance will be sent to the wastewater treatment process, but if necessary, a process for recovering isophthalic acid will be installed.

The liquid stream withdrawn from the bottom of the solvent displacement column is a slurry solution of high temperature water containing purified isophthalic acid crystals, and must pass through 1 to 3 crystallization tanks installed in series. After cooling to 110 to 80 ° C. and further crystallizing isophthalic acid, the crystal is separated by a crystal separator and taken out, and passed through a drier to become high-purity isophthalic acid. The mother liquor discharged from the crystal separator only contains isophthalic acid corresponding to the solubility at that temperature, other organic impurities and inorganic impurities are extremely low concentration, and this mother liquor is a catalytic hydrotreating process. Will be reused in.

The purification status of isophthalic acid according to the present invention is
The change in OD ₃₄₀ , which is an index of the whiteness of crystals, is as follows. The OD ₃₄₀ was measured using 3 g
Dissolve in 35 g of N sodium hydroxide aqueous solution, filter, and use a spectrophotometer to measure 3 with a 50 mm long cell.
This is done by measuring the absorbance of the filtrate at 40 millimicron wavelength. It is said that the value of OD ₃₄₀ is closely related to the polymer hue when isophthalic acid is used as a polymer.

[0026] Individual compounds that affect OD ₃₄₀ (hereinafter, referred to as OD ₃₄₀ component) is not fully identified, an aromatic compound also becomes several tens or more types having primarily fluorene and fluorenone structure Seen as
The solubility of these compounds in water is presumed to be small, but the content of each compound is a low concentration that does not reach several tens of ppm at most, and it is considered that the compounds are completely dissolved in high temperature water. However, as shown in Comparative Example 2 below, many OD ₃₄₀ components are contained in the isophthalic acid crystals obtained by separating the reaction solution obtained by the catalytic hydrogenation treatment at 90 ° C.

This phenomenon cannot be explained by the solubility of the substance, but it can be grasped as a phenomenon generally called eutectic, and in the process of crystallization of isophthalic acid, the OD ₃₄₀ component is incorporated into the crystal with a certain distribution coefficient. Moreover, if the distribution coefficient changes exponentially with temperature, the change in OD ₃₄₀ can be explained well. That is, OD
The partition coefficient of the ₃₄₀ component into the isophthalic acid crystal is small at high temperatures, but it seems to increase at lower temperatures at an accelerating rate. Further, the content of the OD ₃₄₀ component is relatively low in a large crystal and increases as the crystal becomes finer. Therefore, it is found that the crystallization of isophthalic acid only in the high temperature region and the elimination of fine crystals by the solvent displacement column are effective in improving the quality of high-purity isophthalic acid.

The effect of refining by catalytic hydrotreatment is the quality of the crude isophthalic acid used in Example 1 described later and the result of crystallization of a slurry liquid obtained by catalytic hydrotreatment (Comparative Example 2). ) Is clear. According to this, the raw material crude isophthalic acid had an OD ₃₄₀ absorbance of 1.
5, the 3CBA concentration was 600 ppm, while the OD ₃₄₀ absorbance of the obtained purified isophthalic acid was 0.
67, and the 3CBA concentration is 22 ppm. The slurry liquid obtained by the catalytic hydrogenation treatment was crystallized to give 9 crystals.
OD ₃₄₀ and 3CB in mother liquor obtained when separated at 0 ° C
As a result of measuring A and adding it to the analysis value of purified isophthalic acid to calculate the reaction rate of the catalytic hydrogenation reaction, the reaction rate of OD ₃₄₀ was 60% and the reaction rate of 3CBA was 93%.

In the case of catalytic hydrogenation reaction of terephthalic acid, the reaction rate of 4CBA is usually 99% or more, and OD
_A high reaction rate of ₃₄₀ is obtained. It is considered that this is because the solubility of terephthalic acid in hot water is small, so that the catalytic hydrogenation reaction is performed at a high temperature of 260 to 290 ° C. Since the solubility of isophthalic acid in hot water is about 10 times higher than that of terephthalic acid, it is not necessary to raise the reaction temperature due to the limitation of the solubility, and it is not necessary to carry out the catalytic hydrogenation reaction at such a high temperature. Since it requires a lot of energy to heat, it is not economically advantageous.

As a means for increasing the reaction rate of the catalytic hydrogenation reaction, there is also a method of decreasing the space velocity of the reaction solution, that is, increasing the contact time with the catalyst to measure the progress of the reaction. It is economically disadvantageous because it requires a larger vessel.

As described above, in the present invention, the isophthalic acid crystal is simply prepared by introducing the slurry solution obtained by catalytically hydrotreating the crude isophthalic acid aqueous solution using the solvent displacement column into the rising liquid stream of high temperature water. Greatly improved the purity of
It is possible to continuously produce high-quality isophthalic acid of excellent quality.

[0032]

EXAMPLES Next, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.

Example 1 The raw material crude isophthalic acid used was one produced by air-oxidizing meta-xylene in a water-containing acetic acid solvent using a commercial-scale apparatus. The catalyst for this liquid-phase oxidation is manganese acetate,
Using cobalt acetate and hydrobromic acid, the reaction temperature is 205
C. and pressure are 16 atm. This crude isophthalic acid OD
₃₄₀ absorbance is 1.5, 3CBA concentration is 600pp
It was m.

A pressure-resistant stainless steel reactor having an inner diameter of 26 mm and a length of 350 mm equipped with an external heating device was charged with palladium.
200 ml of a catalyst having 5% supported on activated carbon was charged. This reaction tower is heated to 220 ° C., and 1200 g / hr of a 30% aqueous solution of crude isophthalic acid heated to 220 ° C. from the top of the tower.
Supplied. Hydrogen gas was supplied to the crude isophthalic acid aqueous solution from the hydrogen gas supply line at 0.3 normal liters per hour. The reaction liquid flowing out from the bottom of the reactor is cooled to room temperature through a buffer tank that is provided to adjust the difference between the supply rate and the withdrawal rate, and is then introduced into an external receiver by an intermittent withdrawal device consisting of a three-way valve and an actuator. It was extracted as a slurry solution.

For solvent replacement, an inner diameter of 25 mm and a height of 150
A 0 mm stainless steel solvent displacement tower was used. The slurry solution inlet is located 750 mm from the bottom surface, the hot water inlet is located 200 mm from the bottom surface, and receivers with an internal volume of 50 L are connected to the tower top and tower bottom outlets, respectively. Each receiver is equipped with a heating device, a reflux condenser, a stirring device, and a liquid level detector. Prior to operation, this solvent displacement tower was heated to 150 ° C., and 1740 g / hour from the hot water inlet.
Hot water heated to the same temperature as the tower was introduced, and when the tower was filled with hot water, it was discharged to the receiver through the outlets at the top and bottom of the tower. Further, the slurry solution which has been subjected to the catalytic hydrotreating step heated to the same temperature as the tower from the slurry solution inlet is supplied 24 hours per hour.
10 g of the slurry was introduced, and 1550 g of the slurry liquid was withdrawn from the bottom of the tower every hour. From the top of the tower, 2600 g of a slurry solution containing fine crystals was discharged every hour.

After lowering the temperature of the receiver connected to the bottom of the solvent displacement tower to 90 ° C. and holding it for about 15 minutes, the slurry solution was taken out and rapidly filtered with a sufficiently heated G3 glass filter. The crystals were washed with hot water and dried. As a result, the concentration of isophthalic acid in the slurry solution introduced into the settling tower was 30%, but the concentration of isophthalic acid in the slurry solution extracted from the bottom of the tower was 40%. Further, 80 g of isophthalic acid (a total amount of solution and fine crystals) was discharged from the top of the column every hour. This corresponds to 12% of the isophthalic acid introduced into the column. The analytical values of the crystals are shown in Table 1.

Example 2 The same experiment as in Example 1 was conducted with the temperature of the solvent displacement column set to 180 ° C. At this time, in order to keep the crystal settling rate in the upper part of the tower at the same level as in Example 1, the amount of hot water introduced was 15 per hour.
The amount of slurry solution introduced was set to 80 g, the amount of slurry solution introduced was set to 2850 g per hour, and the amount of slurry solution withdrawn from the bottom of the column was set to 1320 g per hour. As a result, the concentration of isophthalic acid in the slurry solution introduced into the settling tower was 30%, but the concentration of isophthalic acid in the slurry solution extracted from the bottom of the tower was 40%. Further, 314 g of isophthalic acid (total amount of solution and fine crystals) was discharged from the top of the column per hour, which corresponds to 37% of isophthalic acid introduced into the column. The analytical values of the crystals are shown in Table 1.

Example 3 The same experiment as in Example 1 was conducted by setting the temperature of the solvent displacement column to 120 ° C. At this time, in order to keep the crystal settling rate in the upper part of the tower at the same level as in Example 1, the amount of hot water introduced was 15 per hour.
The amount of the introduced slurry solution was set to 00 g, the amount of the slurry solution introduced was 1610 g per hour, and the amount of the slurry solution withdrawn from the bottom of the column was set to 1120 g per hour. As a result, the concentration of isophthalic acid in the slurry solution introduced into the settling tower was 30%, but the concentration of isophthalic acid in the slurry solution extracted from the bottom of the tower was 40%. Further, 24 g of isophthalic acid (a total amount of solution state and fine crystals) was discharged from the top of the column every hour. This corresponds to 5% of the isophthalic acid introduced into the column. The analytical values of the crystals are shown in Table 1.

Comparative Example 1 The same experiment as in Example 1 was conducted with the temperature of the sedimentation tower at 90 ° C. At this time, in order to keep the crystal settling rate in the upper part of the tower at the same level as in Example 1, the amount of introduced hot water was 1200 g / hr.
In addition, the amount of slurry solution introduced was set to 830 g / hr, and the amount of slurry solution withdrawn from the bottom of the column was set to 590 g / hr. As a result, the concentration of isophthalic acid in the slurry solution introduced into the settling tower was 30%, but the concentration of isophthalic acid in the slurry solution extracted from the bottom of the tower was 40%. Further, 8 g of isophthalic acid (a total amount of solution and fine crystals) was discharged from the top of the column every hour. This corresponds to 3% of the isophthalic acid introduced into the column. The analytical values of the crystals are shown in Table 1.

Comparative Example 2 The slurry solution from the catalytic hydrotreating step in Example 1 was
After holding at 0 ° C. for 15 minutes, the crystals were quickly filtered through a sufficiently heated G3 glass filter, and the crystals were washed with hot water and dried. The analytical values of the crystals are shown in Table 2.

[0041]

[Table 1] Solvent replacement Analytical value of purified isophthalic acid from the top of the tower Temperature of the tower OD ₃₄₀ 3CBA ℃ IPA% ppm ──────────────────────── ──────── Raw crude IPA 1.5 600 ─────────────────────────────── Example 1 150 12 0.21 5 Example 2 180 37 0.09 3 Example 3 120 5 0.39 11 ────────────────────────── ────── Comparative Example 1 90 3 0.58 18 Comparative Example 2 − 0.67 22

The following can be seen from the experimental data in Table 1. (1) When the solvent substitution was performed at 150 ° C., the OD ₃₄₀ was about one-third that of Comparative Example 2 in which the solvent substitution was not performed.
CBA was reduced by about a quarter. (2) The higher the solvent replacement temperature is, the better the quality is, but on the other hand, the amount of isophthalic acid discharged from the top of the column increases, and the load of crystal recovery in the downstream increases. (3) The quality becomes worse as the solvent replacement is performed at a lower temperature. 90
The quality of Comparative Example 1 in which the solvent replacement was performed at 0 ° C. was slightly better than that of Comparative Example 2 in which the solvent replacement was not performed.

[0043]

Industrial Applicability According to the method of the present invention, highly purified purified isophthalic acid is industrially advantageously produced from a reaction solution obtained by subjecting crude isophthalic acid to catalytic hydrogenation. For example, by introducing the isophthalic acid slurry solution from the crystallizer in the middle and subsequent stages of the crystallization step of the reaction solution obtained by catalytic hydrogenation treatment into the solvent displacement column, a high purity can be obtained without using a high pressure separation means. Isophthalic acid can be obtained. Moreover, since the concentration of the isophthalic acid slurry solution can be increased by using the solvent displacement tower, the load on the crystal separation operation can be reduced.

Claims (2)

[Claims] 1. A method for producing high-purity isophthalic acid by subjecting crude isophthalic acid obtained by liquid-phase oxidation to catalytic hydrogenation, which comprises separating the catalyst from the reaction solution obtained by catalytic hydrogenation, An isophthalic acid slurry solution consisting of crystals of isophthalic acid crystals obtained by depressurizing and lowering the temperature of the reaction solution and a mother liquor was introduced into a solvent substitution tower at a temperature of 180 to 120 ° C.,
The mother liquor and a part of fine isophthalic acid crystals were withdrawn from the top of the tower as a slurry liquid together with the rising liquid flow of the high temperature water by contacting with the upward flow of high temperature water introduced from the lower part of the solvent displacement tower, and most of the isophthalic acid crystals were A method for producing high-purity isophthalic acid, characterized in that isophthalic acid crystals are extracted from the bottom of the slurry as a slurry liquid with hot water, and the slurry liquid is discharged from the bottom of the tower. 2. The high-purity isophthalic acid according to claim 1, wherein the reaction solution obtained by the catalytic hydrogenation treatment is crystallized in multiple stages, and the isophthalic acid slurry solution obtained from the middle stage crystallizer is introduced into the solvent displacement column. How to manufacture