KR100527416B1 - Method for producing high purity isophthalic acid - Google Patents

Abstract

The present invention can easily process the PIA mother liquor, recover useful substances contained in the PIA mother liquor, reduce the amount of water discharged, recycle the water used as the solvent, and use high purity isophthalic acid without additional investment and cost. Regarding the manufacturing method,

The method is

a) separating the liquid oxidation reaction solution into an oxidation mother liquor and crude isophthalic acid by crystallization, and evaporating the oxidation mother liquor to form acetic acid vapor or its condensate,

b) Crude isophthalic acid is dissolved in water, followed by catalytic hydrogenation, catalysis or oxidation of the resulting isophthalic acid solution in water to form a purified solution, and the purified solution is cooled to crystallize isophthalic acid. Separating the purified solution into crystals of the mother liquor and isophthalic acid, and

c) The acetic acid vapor or condensate thereof prepared by evaporating the oxidation reaction mother liquor in step a) is fed to the middle stage of the distillation column, and the mother liquor separated from the purified solution in step b) is fed to the top of the distillation column. Distillation and withdrawing acetic acid containing aromatic carboxylic acid from the bottom of the distillation column.

Description

Method for producing high purity isophthalic acid

TECHNICAL FIELD This invention relates to the manufacturing method of high purity isophthalic acid which is a main raw material for the polyester resin used for industrial members, a component, and a general molded article.

Isophthalic acid is generally a molecule of m-phenylene compounds (mainly m-xylene) at high temperature and high pressure in an acetic acid solvent in the presence of bromine compounds as cobalt and manganese catalysts and as co-catalysts or in the presence of promoters such as acetaldehyde with cobalt catalysts. It is prepared by oxidation with phase oxygen, mainly air.

However, isophthalic acid prepared by the liquid phase oxidation generally has a low whiteness and contains a large amount of impurities such as 3-carboxybenzaldehyde (3CBA) and m-toluic acid, so the isophthalic acid is used to prepare a polyester by reacting with glycol. It is not suitable for the following.

In order to purify the crude isophthalic acid containing impurities such as 3CBA to produce high purity isophthalic acid, a purification method for oxidizing or reducing isophthalic acid or simply recrystallization is known. Commercially predominant methods are to obtain a high purity isophthalic acid by subjecting the crude isophthalic acid aqueous solution to catalytic hydrogenation at high temperature and then cooling and crystallizing the resulting solution.

In this method, however, the high-purity isophthalic acid is separated and the remaining mother liquor (hereinafter referred to as "PIA mother liquor") contains not only isophthalic acid in an amount corresponding to their solubility, but also aromatic carboxylic acids such as m-toluic acid and benzoic acid. . In order to dispose of the PIA mother liquor, it is necessary to treat it with an aromatic carboxylic acid having a large biochemical oxygen demand (BOD). Further disposal means loss of valuable materials such as isophthalic acid and m-toluic acid which can be converted to isophthalic acid. Moreover, the catalytic treatment step requires more water than the amount of high purity isophthalic acid produced.

The concentration of aromatic carboxylic acid in the PIA mother liquor depends on the quality of crude isophthalic acid, catalytic hydrogenation conditions, crystallization conditions or separation conditions. Generally, the PIA mother liquor contains about 500-700 ppm of isophthalic acid, about 100-1000 ppm of m-toluic acid and about 10-500 ppm of benzoic acid. The PIA mother liquor is generally supplied to a wastewater treatment apparatus, treated with activated sludge and then discharged.

The apparatus used to produce isophthalic acid commercially is a huge plant and therefore the amount of mother liquor to be discharged is large. For example, the throughput of mother liquors discharged per unit in a typical commercial plant is 5-100 m 3 / h, increasing investment in wastewater treatment units and their operating costs.

Furthermore, the isophthalic acid and m-toluic acid contained in PIA mother liquor are useful materials for producing high purity isophthalic acid, and the cost of producing high purity isophthalic acid increases due to the cost of wastewater treatment equipment and the cost of discharging the useful materials. do.

It is therefore an object of the present invention to provide a process for the preparation of high purity isophthalic acid that can easily process a PIA mother liquor.

Another object of the present invention is to prepare high purity isophthalic acid which can recover the useful materials contained in PIA mother liquor without reducing the investment and cost, reducing the drainage and recycling the water used as solvent. To provide a way.

According to the present invention, there is provided a method of liquid-oxidizing an m-phenylene compound in an acetic acid solvent to form crude isophthalic acid and purifying the crude isophthalic acid to produce high purity isophthalic acid.

The method is

a) separating the liquid oxidation solution into an oxidation mother liquor and crude isophthalic acid by crystallization, and evaporating the oxidation mother liquor to form acetic acid vapor or a condensate thereof,

b) Crude isophthalic acid is dissolved in water and the resulting isophthalic acid solution dissolved in water is subjected to catalytic hydrogenation, catalysis or oxidation to form a purified solution, the purified solution is cooled to crystallize isophthalic acid and the Separating the purified solution into crystals of the mother liquor and isophthalic acid, and

c) The acetic acid vapor or condensate thereof produced by evaporating the oxidation reaction mother liquor in step a) is fed to the middle stage of the distillation column, and the mother liquor separated from the solution purified in step b) is fed to the top of the distillation column. Distillation and withdrawing acetic acid containing aromatic carboxylic acid from the bottom of the distillation column.

MEANS TO SOLVE THE PROBLEM The present inventors continued earnest research about the manufacturing method of the high purity isophthalic acid which has the said problem, and came to complete this invention. After separating high purity isophthalic acid (crystal of isophthalic acid) in step 2), the remaining PIA mother liquor is recycled to the distillation step to remove the reaction-formed water from the oxidation reaction hydrous acetic acid and distilled as reflux. By feeding to the top of the column, useful components contained in the mother liquor can be recovered and the discharge load can be greatly reduced.

Hereinafter, the present invention will be described in detail.

In step a) crude isophthalic acid is produced by liquid phase oxidation of the m-phenylene compound. The m-phenylene compound refers to a compound having a carboxyl group in the m-position, or an oxidizable substituent that can be converted into a carboxyl group by air oxidation in the liquid phase in the m-position. The substituent includes a methyl group, ethyl group, propyl group, isopropyl group, formyl group and acetyl group. The two substituents may be the same or different from each other. Xylene is most commonly used as m-phenylene compound.

Hydrous acetic acid is used as a solvent for the oxidation reaction. The catalyst is selected from compounds of transition metals such as manganese, cobalt, iron, chromium and nickel. Furthermore bromine compounds are used in some cases as promoters. The catalyst is not particularly limited as long as it can form manganese ions, cobalt ions, iron ions, chromium ions or nickel ions in the oxidation reactor. The promoter is not particularly limited as long as it can form bromine ions in the oxidation reactor.

If no bromine catalyst is used, acetaldehyde or methyl ethyl ketone can be used as an accelerator to bond with the cobalt catalyst.

As the oxidizing agent, molecular oxygen or generally air is used. Air whose oxygen concentration has been reduced by adding oxygen gas, or air whose oxygen concentration has been reduced by adding an inert gas such as nitrogen gas may be used.

The liquid phase oxidation reaction temperature is generally 160 ° C-220 ° C, and the pressure may be any range in which hydrous acetic acid can maintain a liquid phase as a solvent. In the oxidation reaction method which does not use a bromine catalyst, the temperature below 160 degreeC is used in most cases.

Liquid phase oxidation is generally carried out in one or more reactors. After completion of the oxidation reaction, the reaction mixture obtained is fed into one reactor or a series of sequentially depressurized reactors of two or more and cooled by flash cooling action of the solvent to a temperature corresponding to the pressure of the reactor. Most of the isophthalic acid formed precipitates as crystals to form a slurry.

The slurry is separated into crude isophthalic acid cake and oxidation mother liquor, for example, via a rotary vacuum filter or by centrifugation or other suitable method.

Some of the oxidation reaction liquor is recycled on its own or as oxidized or reduced-treated and then as solvent in step a). Residues of the oxidation mother liquor are usually evaporated using an evaporation can or a thin film evaporator to remove the water and other by-products produced by the oxidation reaction, mainly steam and evaporation containing acetic acid, water and low boiling by-products. Separated into residue. The vapor is fed to the distillation column in step c) and various processes are carried out to recover the catalyst, useful components against the evaporation residue and the components which are not useful are discharged.

The crude isophthalic acid cake is washed with acetic acid or water if necessary and dried in a drier to remove the adhered solvent to obtain crude isophthalic acid.

In general, crude isophthalic acid obtained by liquid phase oxidation contains a large amount of impurities, including 3CBA, and their OD ₃₄₀ value as color indicator is generally lower than the standard used as the raw material for direct molding, so the purification step is generally in need.

There are various methods of purifying crude isophthalic acid to obtain high purity isophthalic acid, such as catalytic hydrogenation, catalysis, oxidation and crystallization. Any method may be used in the present invention, but catalytic hydrogenation is most commonly used and will be described below.

Catalytic hydrogenation is carried out in the presence of a metal selected from Group VIII metals. Group VIII metals include palladium, platinum, ruthenium and rhodium, with palladium being particularly preferred. The metal catalyst may be used in combination. The catalyst is generally used in the form of a catalyst supported on a carrier. The carrier is generally selected from porous materials, and carbon-based carriers are preferred in terms of the quality of the material, and activated carbon, particularly granular coconut husk charcoal, is preferred. Since the catalytic action is effective even in a very small amount, the amount of the catalyst supported on the carrier is not particularly limited. However, it is preferable to use in an amount of 0.1-1% by weight in order to allow the catalyst to work for a long time.

Catalytic hydrogenation is carried out in an aqueous solution under high temperature, high pressure, and in catalytic hydrogenation, the temperature is at least 180 ° C., preferably 200-260 ° C., in the presence of hydrogen.

In catalytic hydrogenation, the pressure can be set in any range as long as the liquid phase is maintained and an appropriate hydrogen partial pressure can be maintained for the catalytic hydrogenation treatment, and generally 10-60 atmospheres is preferred.

The hydrogen supply used for catalytic hydrogenation requires at least 2 moles of hydrogen per mole of 3CBA.

The catalytic hydrogenation time is not particularly limited as long as the hydrogenation reaction proceeds substantially. The hydrogenation treatment in the packed column is generally 1-60 minutes, preferably 2-20 minutes.

Catalytic hydrogenation is generally carried out in a continuous manner.

In order to prevent the isophthalic acid product from containing a fine powder induced by the wear of a catalyst carrier such as activated carbon, generally two to six groups connected in series after filtering the catalytic hydrogenated aqueous solution of isophthalic acid As the pressure is sequentially reduced by feeding to a crystallizer or batch crystallizer, the aqueous solution is cooled by evaporation of water and precipitated isophthalic acid crystals to form a slurry.

The slurry is separated into isophthalic acid cake and PIA mother liquor by crystal separation such as rotary vacuum filtration or centrifugation.

The separation temperature of the slurry is not particularly limited, but is generally about 70-160 ° C.

When separating at high temperature, the cake obtained is slurried again with water to separate the slurry.

Step c) comprises a distillation column in which the oxidation mother liquor is dehydrated to recycle the acetic acid solution. The steam or condensate introduced from step a) contains acetic acid and low boiling by-products as well as water formed as by-products by oxidation. Water is usually separated from the system via a distillation column.

In step c), steam or condensate from the evaporator or thin film evaporator is fed to the middle stage of the distillation column and dehydrated acetic acid is obtained from the bottom of the column to the extent that it can be recycled by the oxidation reaction.

In general, some of the distillate from the top of the column is discharged out of the system to achieve a set separation efficiency, and the remainder is recycled to the top of the column.

In this step, the reflux ratio [= amount recycled (m ³ / h) / discharge amount (m ³ / h)] is generally set at about 1 / 1-10 / 1.

In the present invention, the PIA mother liquor from step b) is fed to the top of the column as reflux. The amount of PIA mother liquor that can be processed in step c) is an amount equivalent to the maximum reflux amount. As the reflux ratio increases, the amount of PIA mother liquor that can be naturally processed increases. On the other hand, if the distillation column is operated at an unnecessary large reflux ratio, losses occur, ie the amount of energy required is increased.

If the amount of PIA mother liquor to be treated is less than the reflux, the discharge is recycled in an amount corresponding to the deficiency. If the amount of PAI mother liquor exceeds the reflux, the PIA mother liquor is concentrated. Various heat sources recovered into the plant can be effectively used for concentration, but it is economical to use the latent heat of the vapor distilled from the top of the distillation column.

On the other hand, when the concentrated PIA mother liquor is supplied to the top of the distillation column as reflux, bubbling occurs at the top of the distillation column, as described in the comparative example below, and extremely bubbling occurs. In this case, the distillation effect is significantly reduced.

The bubbling phenomenon is caused when crystals such as isophthalic acid are present in the distillation column. The bubbling phenomenon is prevented by the following method.

(1) The solid component (mainly composed of isophthalic acid crystals) is separated and removed from the PIA mother liquor which is introduced by suitable means such as filtration. This method is simple, but the unit operation required for separation is added, and the processing of the separated isophthalic acid crystals is complicated.

(2) Metal ions are added to the PIA mother liquor supplied at the top of the column. Cobalt or manganese is effective as metal ions added to the PIA mother liquor. If they are added in amounts equivalent to or greater than the molar amount of isophthalic acid crystals present in the PIA mother liquor, the bubbling phenomenon can be completely prevented.

The method (2) was first discovered by the inventors. Cobalt and manganese, as is well known, are catalysts used in the oxidation step and their presence in acetic acid exiting from the bottom of the distillation column does not cause any problems in the oxidation reaction.

Even when the PIA mother liquor is supplied without concentration, the PIA mother liquor obtained in step c) may contain a small amount of isophthalic acid crystals according to solid component separation means or some other conditions. It is therefore desirable to provide a step of filtering the PIA mother liquor or adding metal ions in an amount sufficient for the measured isophthalic acid crystals.

If the PIA mother liquor or its condensate is fed to the top of the distillation column, the PIA mother liquor is approximately equivalent to the distillation temperature from the top of the column, in particular between the temperature of the distillate and the temperature range 50 ° C. below the temperature of the distillate. It is desirable to control the temperature to reduce the irregularity of the temperature in the distillation column.

According to the method, as shown in the following examples, even when the PIA mother liquid supplied to the column top contains aromatic carboxylic acid in an amount of several thousand ppm, the amount of aromatic carboxylic acid in the water distilled from the column top is small and the PIA mother liquid Most of the useful components in the can be recovered in the form of aqueous acetic acid solution from the bottom of the distillation column.

Even when the water flowing out from the top of the column is directly supplied into the wastewater treatment apparatus, the load of the wastewater treatment is significantly reduced as compared with the case where the PIA mother liquor is supplied without treatment.

Furthermore, the load of the wastewater treatment can also be reduced by the method of recycling the distilled water from the top of the column to step b) and using it as a solvent for dissolving crude isophthalic acid.

As shown in the examples, the distilled water discharged from the top of the column contains only a small amount of aromatic carboxylic acid, low boiling by-products and acetic acid, and thus can be used as a solvent for catalytic hydrogenation treatment, and it is desirable to provide an adsorption process using activated carbon. Do.

Example

The present invention is explained in more detail with reference to the following examples. The PIA mother liquor used as a raw material in the examples showed the following components as analyzed by high performance liquid chromatography and gas chromatography, and was somewhat opaque at room temperature.

For distillation, a sieve tray-type fractionation column with an internal diameter of 32 mm and a 70-stage perforated plate was used, and hydrous acetic acid having a water content of 18% was continuously supplied to the middle stage of the distillation column. It was. Concentrated acetic acid was withdrawn continuously from the bottom.

Example 1

Hydrous acetic acid was charged to the bottom of the distillation column and heated to stabilize the system at full reflux. Then hydrous acetic acid with a water content of 18% was fed to the middle stage of the distillation column and concentrated acetic acid was withdrawn from the bottom. The reflux ratio was set at 6. When the operation is continued for about 20 hours and the entire system is confirmed to be in a steady state, the PIA mother liquor is converted to the amount of liquid that has been refluxed through the reflux line while switching to draining the entire water from the top of the column. Supply in substantial quantities. Then, when the operation was continued for about 12 hours, the concentration of aromatic carboxylic acid in the distilled water discharged from the column top was as follows.

The analytical value indicates that about one tenth of the concentration of aromatic carboxylic acid in the PIA mother liquor and most of the aromatic carboxylic acid is recovered in the form of acetic acid solution from the bottom of the column.

Comparative Example 1

The supplied PIA mother liquor was preheated and concentrated to an amount of 1/3 of the starting amount and the experiment of Example 1 was repeated. The concentrated PIA mother liquor is opaque due to precipitation of isophthalic acid crystals.

The concentrated PIA mother liquor containing the opaque portion was analyzed and the following results were obtained.

Shortly after the start of the feed, bubbling was visually observed in the tray above the distillation column. At the same time solids were observed in the tube walls, which intensified with time.

Example 2

The experiment of Comparative Example 1 was repeated except that the concentrated PIA mother liquor was replaced with a filtrate prepared by filtration of the concentrated PIA mother liquor through a 3G glass filter. The filtrate was analyzed to obtain the following results.

At the point of continuous operation for about 12 hours, the concentration of aromatic carboxylic acid in the distilled water discharged from the column top is as follows.

The analytical value was about 1/5 of the aromatic carboxylic acid concentration in the PIA mother liquor, and most of the aromatic carboxylic acid was recovered from the column bottoms in the form of acetic acid solution. Furthermore, the bubbling phenomenon observed in the tray on the top of the distillation column in Comparative Example 1 is believed to be due to isophthalic acid crystals.

Example 3

The experiment of Comparative Example 1 was repeated except that manganese acetate was supplied as 1,740 ppm as a manganese atom into the feed solution. The amount corresponds approximately to the molar amount of isophthalic acid in the feed liquid. At the time of operation for about 12 hours, the concentration of aromatic carboxylic acid in the distilled water discharged from the column top is as follows.

Comparative Example 2

The experiment of Example 3 was repeated except that manganese acetate was supplied to 870 ppm as a manganese atom in the feed. The amount added is approximately equivalent to about 1/2 of the molar amount of isophthalic acid in the feed liquid. Shortly after bubbling, bubbling was visually observed in the tray on the top of the distillation column, the bubbling phenomenon was much more relaxed than in Comparative Example 1.

The results of Example 3 and Comparative Example 2 are as follows. The isophthalic acid crystals in the feed are converted to soluble compounds with manganese ions, with no bubbling. If the amount of manganese ions is equivalent to or greater than the molar amount of isophthalic acid, bubbling can be completely prevented.

Example 4

The experiment of Comparative Example 1 was repeated except that 1,867 ppm of cobalt acetate was added to the feed as a cobalt atom. The amount corresponds approximately to the molar amount of isophthalic acid in the feed liquid. The operation proceeded slowly, and no phenomenon was observed in the distillation column. At the time of operation for about 12 hours, the concentration of aromatic carboxylic acid in distilled water from the top of the column is as follows.

Comparative Example 3

The experiment of Example 3 was repeated except that the amount of cobalt acetate was replaced with 934 ppm as the cobalt atom. This amount roughly corresponded to about half the molar amount of isophthalic acid in the feed. Shortly after the start of the feed, bubbling was visually observed in the tray above the distillation column, but the bubbling was much less relaxed than in Comparative Example 1.

The results of Example 4 and Comparative Example 3 are as follows. Isophthalic acid crystals in the feed are converted to soluble compounds with cobalt ions, with no bubbling. If the amount of cobalt ions is equivalent to or greater than the molar amount of isophthalic acid, bubbling can be completely prevented.

Example 5

Catalytic hydrogenation was carried out in Example 1 using distilled water obtained from the top of the column and crude isophthalic acid produced on a commercial scale as raw material. For further comparison, the experiment was performed using pure water.

The result of analyzing crude isophthalic acid used as a raw material is shown next.

300 g of crude isophthalic acid and 900 g of water were charged in a 2 L stainless steel pressure vessel. The pressure vessel was equipped with a stirrer, a heater and a gas inlet, and furthermore equipped with an electronic catalyst cage that could be moved up and down by external operation.

The catalyst cage was filled with 16 g of palladium / carbon catalyst as a wet amount. The packed catalyst was used continuously for about one year in a commercial scale catalytic hydrogenation plant, followed by washing the contaminants with dilute aqueous ammonia solution and then rinsing thoroughly.

The catalyst cage was suspended at the upper position of the pressure resistant vessel made of stainless steel. By supplying hydrogen gas through the gas inlet pipe, the atmosphere was thoroughly cleaned several times and filled with hydrogen gas at a pressure of 10 kg / cm 2 G. When the liquid in the stainless steel vessel was heated with stirring and it was confirmed that the temperature stabilized at 235 ° C, the catalyst cage was moved downward until it was submerged in the liquid. After 20 minutes, the catalyst cage was moved to the top, then the liquid was allowed to cool. The liquid was cooled to near room temperature and the resulting slurry was filtered through a G3 glass filter. The resulting cake was washed with pure water having a temperature of about 90 ° C. and dried at 110 ° C. to obtain high purity isophthalic acid.

High purity isophthalic acid obtained using pure water or distilled water obtained in Example 1 was obtained.

In this test, no phenomena occurred in the reaction, and the difference in the result of evaluating the obtained isophthalic acid was also within an acceptable error range.

The experimental results of the Examples and Comparative Examples can be summarized as follows.

(1) When PIA mother liquor was fed to the top of the distillation column as reflux and all distilled water was discharged from the top of the column, the concentration of aromatic carboxylic acid in the distilled water was reduced to about 1/10 of the feed mother liquor.

(2) When the PIA mother liquor is concentrated and then fed to the top of the distillation column as reflux, isophthalic acid crystals precipitated in the PIA mother liquor form a core, causing bubbling at the top of the distillation column.

(3) When the isophthalic acid crystals are removed by filtration and the concentrated PIA mother liquor is fed to the top of the distillation column, bubbling does not occur in the distillation column.

(4) When manganese ions or cobalt ions are added to PIA mother liquor concentrated in the same amount as isophthalic acid in PIA mother liquor, bubbling does not occur in the distillation column.

(5) Distilled water discharged from the top of the column can be used as a solvent for catalytic hydrogenation of isophthalic acid.

According to the process of the invention, when the PIA mother liquor is fed for reflux in an acetic acid dehydration column, most of the aromatic carboxylic acids in the PIA mother liquor can be discharged in their solution form in acetic acid from the bottom of the dehydration column, the acetic acid being oxidized Recycled to the stage. As a result, useful ingredients such as isophthalic acid and m-toluic acid are effectively used, which results in an improved yield of isophthalic acid and a significant reduction in the load of wastewater treatment in the production of high purity isophthalic acid.

Furthermore, by using distilled water recovered from the top of the distillation column as water in the purification step, the amount of waste water is reduced, and as a result, the load on the waste water treatment apparatus is significantly reduced.

Industrial applicability of the present invention is great because the present invention can recover useful components in PIA mother liquor without additional investment or cost.

Claims (5)

In the manufacturing method of high purity isophthalic acid which produces | generates crude isophthalic acid by liquid-phase oxidation of m-phenylene compound in an acetic acid solvent, and refine | purifies the crude isophthalic acid, a) separating the liquid oxidation reaction solution into an oxidation reaction mother liquor and crude isophthalic acid by crystallization, and evaporating the oxidation reaction mother liquor to form acetic acid vapor or a condensate thereof; b) Crude isophthalic acid is dissolved in water, followed by catalytic hydrogenation, catalysis or oxidation of the resulting isophthalic acid solution in water to form a purified solution, and the purified solution is cooled to crystallize isophthalic acid. And separating the purified solution into crystals of the mother liquor and isophthalic acid; And c) acetic acid vapor or condensate prepared by evaporating the oxidation reaction mother liquor in step a) is fed to an intermediate stage of the distillation column, At least one of manganese compound and cobalt compound is added to the mother liquor separated from the purified solution in step b) and then fed to the top of the distillation column, and the concentrated acetic acid containing aromatic carboxylic acid is discharged from the bottom of the distillation column. Method of producing a high-purity isophthalic acid comprising a. The method of claim 1 wherein the purified solution is a solution obtained by catalytic hydrogenation of a crude isophthalic acid solution dissolved in water. The method of claim 1, wherein the mother liquor from step b) is fed to the top of the distillation column after removing the solids component from the mother liquor in advance. A process according to claim 1, characterized in that distilled water from the top of the distillation column is used as dissolved water for crude isophthalic acid in step b). A process according to claim 1, wherein some of the oxidation reaction mother liquor is distilled and fed to an intermediate stage of the distillation column and the remainder is used as solvent in the liquid phase oxidation.