KR100249678B1 - Process of producing highly pure terephtalic acid - Google Patents

Abstract

The present invention relates to a method for producing high purity terephthalic acid, and more particularly, two or more reactors in series in order to purify crude terephthalic acid containing 4-carboxybenzaldehyde (hereinafter, referred to as 4-CAB). It relates to a method for producing high purity terephthalic acid by connecting and operating.

It is an object of the present invention to provide a method for producing high purity terephthalic acid having improved powder fluidity and slurry fluidity of terephthalic acid while having a low content of 4-CAB, which is an impurity contained in crude terephthalic acid.

According to the present invention, the terephthalic acid slurry is dissolved into a nitric acid solvent or acetic acid solution by dissolving 4-terephthalate phthalic acid containing 4-CAB and a plurality of reactors connected in series and operated at a temperature lower than the temperature of the preceding reactor. Provided is a method for producing high purity terephthalic acid through a series operation of a reactor comprising a purification step of transporting and oxidizing and recovering the purified terephthalic acid slurry.

Description

High purity terephthalic acid production method

The present invention relates to a method for producing high purity terephthalic acid, and more particularly, two or more reactors in series in order to purify crude terephthalic acid containing 4-carboxybenzaldehyde (hereinafter, referred to as 4-CAB). It relates to a method for producing high purity terephthalic acid by connecting and operating.

Generally, p-xylene is subjected to liquid-air oxidation in acetic acid solution using an oil-soluble salt of a variable valence metal such as cobalt, manganese, and chromium as a catalyst to obtain a crude terephthalic acid. In the preparation of such terephthalic acid, the terephthalic acid contains a considerable amount of impurities including 4-CAB produced by incomplete oxidation of p-xylene, and high purity terephthalic acid in which such impurities are purified is used as a raw material of polyester.

The 4-CAB not only reduces the efficiency of the polymerization reaction by breaking the chain in the polyester polymer polymerization, but also affects the color. Therefore, efforts to lower the content of 4-CAB in the production of high-purity terephthalic acid have been steadily attempted since the development of the terephthalic acid manufacturing process, mainly to change the operating conditions of the reactor or the operation conditions of the crystal bath or vacuum filter during the purification process. Has been used.

Conventionally, there are two methods for purifying joterephthalic acid, which will be described below.

The first method is a method of dissolving joterephthalic acid in a high temperature, high pressure water solvent to purify by hydrogenation under a platinum group catalyst, the technical content of which is described in US Patent No. 3,584,039. This method is a method of crystallizing by cooling the aqueous solution of crude terephthalic acid purified by hydrogenation step by step in a plurality of crystal baths connected in series, it is possible to adjust the purity, particle size and particle size distribution of terephthalic acid by changing the temperature conditions of the crystal bath. have.

In the second method, crude terephthalic acid is dissolved in acetic acid solvent or acetic acid solution at high temperature and high pressure and purified through oxidation. This method is a method of obtaining terephthalic acid crystals by crystallizing the terephthalic acid slurry purified by oxidation reaction in a flash tank serving as a crystal tank, it is possible to adjust the particle size and particle size distribution of terephthalic acid according to the temperature and recycle flow rate of the flash tank.

By using the two methods, high purity terephthalic acid having a particle size and a content of 4-CAB within a range which hardly affects the reaction during polyester polymerization has been prepared. However, as a method for producing polyester, in particular, polyethylene terephthalate, a direct esterification technique has been developed, and glycols including high purity terephthalic acid and ethylene glycol are directly polymerized, and the amount of 4-CAB, which is an impurity contained in high purity terephthalic acid, and the high purity terephthalic acid. The particle size of has a great influence on the polymerization process.

In addition, when high purity terephthalic acid is mixed with glycols in a polyester polymerization process, the terephthalic acid is transferred to a polymerization reactor in a slurry state. The fluidity of the slurry can be easily mixed with glycols in the reactor to increase the efficiency of the reactor. Can be. Further, even when the prepared high purity terephthalic acid is transferred or stored in the polymerization process, the powder fluidity of the terephthalic acid should be excellent.

Slurry fluidity and powder fluidity of high purity terephthalic acid are greatly influenced by the average particle size and particle size distribution of terephthalic acid. In general, the average particle size is known to be suitable in the range of 50 ~ 150㎛, Terephthalic acid having a wide particle size distribution tends to have excellent slurry fluidity.

As a method for improving slurry fluidity and obtaining uniformity of the polymerization reaction, for example, a method of increasing the amount of glycols used for polymerization or injecting glycols in an amount close to the ratio of terephthalic acid has been used. A method of controlling slurry property by mixing terephthalic acid having an average particle size in a constant ratio has also been used. As another method, an attempt was made to improve slurry fluidity by adjusting a particle size and particle size distribution of terephthalic acid while changing operating conditions by installing a multi-stage crystal tank at the bottom of the reactor for purification.

However, despite various efforts to increase the fluidity of the slurry, a method for obtaining excellent slurry property by a simple method has not yet been devised.

It is an object of the present invention to provide a method for obtaining high purity terephthalic acid having a low content of 4-CAB, which is an impurity contained in Zoterephthalic acid, and improved powder and slurrity of terephthalic acid through a series operation of a reactor.

It is another object of the present invention to provide a method of reducing the number of crystal baths used while obtaining excellent powder fluidity and slurry fluidity by introducing a flash tank recycling method into the crystal bath during the crystallization reaction.

1 is an example of a schematic diagram of an apparatus for performing an oxidized plaque in a method according to the present invention.

2 is an example of configuration diagram of an apparatus for performing a crystallization reaction in the method according to the present invention.

* Explanation of symbols for main parts of the drawings

1: first stage reactor # 1 2: first stage reactor # 2

3: first stage reactor # 3 4: first stage reactor # 4

5: second stage reactor 5a: stirrer

6: flash tank 7: transfer pump

8: First Decision Group 9: Second Decision Group

10: 3rd crystal tank 11: transfer pump

According to the present invention, the terephthalic acid slurry is prepared by dissolving crude terephthalic acid containing 4-CAB in acetic acid solvent or acetic acid solution into a slurry state and a plurality of reactors connected in series and operated at a temperature lower than the temperature of the preceding reactor. Provided is a method for producing high purity terephthalic acid through a series operation of a reactor comprising a purification step of transporting and oxidizing and recovering the purified terephthalic acid slurry.

In addition, the terephthalic acid slurry passed through the purification step is transferred to a flash tank operated at a temperature of 60 ~ 100 ℃ connected to the reactor at the bottom of the crystallization and introduced into a transfer pump to recover a part and the rest is transferred back to the reactor As a result, the particle size and particle size distribution of the terephthalic acid can be further improved.

Looking at the configuration of the reactors in the present invention, when the reactor is two units are configured in the 1-1 type is installed in the first stage and one unit in the second stage, two reactors in the case of two It is composed of one type selected from one type or 1-1-1 type, and if there are four reactors, it is composed of any one type selected from 3-1 type or 2-2 type. It can be configured and operated in either 4-1 or 3-2 format. Various other reactor series combination operations are possible.

Referring to Figure 1, which is a block diagram of the reactor consisting of 4-1 of the high purity terephthalic acid production method according to the present invention will be described in detail.

p-xylene is prepared as joterephthalic acid by reaction with oxygen at a temperature of 140-240 ° C. in acetic acid solvent in the presence of a catalyst such as cobalt, manganese, or bromine. The crude terephthalic acid contains a large amount of impurities, and about 1,000 to 10,000 ppm of 4-CBA as an impurity exists in the crude terephthalic acid.

The crude terephthalic acid is dissolved in an acetic acid solvent or acetic acid aqueous solution in a weight ratio of about 20 to 40% and is present in a slurry state.

As shown in FIG. 1, four reactors are installed in the first stage and one reactor is installed in the second stage, and five reactors are connected in series in a 4-1 form, and the crude terephthalic acid slurry containing 4-CBA is included. Is transferred to the first stage reactor (1, 2, 3, 4) and undergoes the first purification step. The operating temperatures of the reactors 1, 2, 3 and 4 are about 190 to 280 ° C and the pressure is 14 to 18KG. The terephthalic acid slurry purified in the first purification step includes a transfer line 1a existing at the bottom of the first stage reactor # 1 (1) and a transfer line 2a located at the bottom of the first stage reactor # 2 (2). It is fed to the left side of the first stage reactor 5 through the combined transfer line 5b, and the transfer line 3a and the first stage reactor # 4 (4) which exist below the first stage reactor # 3 (3). The transfer line 4a existing at the bottom of the feed line is introduced to the right side of the second stage reactor 5 through the combined transfer line 5c.

At this time, the terephthalic acid slurry passed through the first purification step is transferred to the second stage reactor 5 by a pressure difference without a transfer pump and undergoes a second purification reaction. In the second purification stage, the first stage (1, 2, 3, 4) is purified at lower temperature and pressure conditions, wherein the temperature of the second stage (5) is 140 ~ 215 ℃, the pressure is 11 ~ 16KG. In the second stage reactor 5, a condenser is installed at the top of the reactor 5 to condense acetic acid vapor rising to the upper portion and return to the reactor 5, and to maintain uniform internal composition, the stirrer 5a ) Is installed to continuously stir the inside of the reactor (5). In addition, oxygen or air is not added separately in order to make the most of the existing dissolved oxygen.

In addition, the present invention is subjected to a recycling step to further improve the particle size and particle size distribution of terephthalic acid. After passing through the refining step, the terephthalic acid slurry is transferred to the flash tank 6 which is operated at a temperature of 60 to 100 ° C. through a transfer line 5d existing at the bottom of the second stage reactor 5, whereby the transfer pump is crystallized. (7) is introduced. After the purification and crystallization process, some of the high-purity terephthalic acid introduced into the transfer pump 7 is discharged and collected through the product transfer line 7a, and the rest is transferred to improve the particle size and particle size distribution. 7b) to the transfer line 1a, through the transfer line 7c to the transfer line 2a, via the transfer line 7e to the transfer line 3a, and through the transfer line 7f. ) Is recirculated to the second stage reactor (5), and is also introduced into the transfer line (5d) through the transfer line (7d) and recirculated to the flash tank (6) to proceed with the recrystallization reaction. The flash tank 6 is a device for suddenly lowering the temperature and pressure to precipitate the terephthalic acid crystal well, and the particle size and particle size distribution of the crystal vary depending on the temperature and pressure.

As described above, by operating two or more reactors in series according to the present invention, the concentration of 4-CBA contained in the crude terephthalic acid is preferentially reduced. For example, if the 4-CBA concentration in the joterephthalic acid is 3,000 to 10,000 ppm, the 4-CBA concentration after the first purification step is about 200 to 1,000 ppm, and once further purification in the second purification step, The concentration of 4-CBA is reduced below 100 ppm.

The average particle size of terephthalic acid can be adjusted by changing the operating conditions, especially the temperature conditions, of the reactors connected in series. Terephthalic acid particles grow in the crystallization process while staying in the reactor. Since all reactors are not ideal continuous stirred reactors, very small particles, usually particles of 25 μm or less, pass through the reactor without retention time. This adversely affects the particle size and particle size distribution. Therefore, the terephthalic acid slurry, which has been primarily purified, is connected in series with the first stage reactor and is transferred to a second stage reactor operated at a lower temperature than the first stage reactor to undergo a crystallization and recrystallization process. The particle size of terephthalic acid increases. The terephthalic acid slurry is continuously transferred to a flash tank connected to the lowermost reactor through a plurality of reactors connected in series operating at a lower temperature than the preceding reactor temperature, thereby increasing the average particle size of terephthalic acid. The particle size and particle size distribution are finally determined by the operating temperature of the flash tank and the slurry flow rate recirculated to the reactor through the transfer pump. As a result of analyzing the average particle size before and after the series operation by operating the reactor in series, it can be seen that the reactor is operated in series to improve about 10 to 30%.

Further, according to the present invention, 4-teraphthalic acid containing 4-CBA is dissolved in a water solvent, purified through a hydrogenation reaction in a hydrogenation reactor in the presence of a platinum catalyst at a temperature of 250 to 330 ° C, and then connected in series to the ends of the hydrogenation reactor. In the high purity terephthalic acid production method for crystallizing while passing through a plurality of crystal baths, the crystallization step of the crystallization step of transferring the purified terephthalic acid through the hydrogenation reaction to a plurality of crystal tanks connected in series, and the terephthalic acid passed through the crystallization step transfer pump A high purity terephthalic acid production method is provided, which is composed of a step of recovering and partially recovering the residue and transferring the rest to the crystal bath. At this time, the number of the crystal tank connected in series is characterized in that 1 to 3.

Referring to the crystallization reaction of the present invention in more detail with reference to Figure 2 composed of three crystal baths, the purified terephthalic acid through the hydrogenation reaction is first crystallized by the crystallization tank (8), the terephthalic acid is the transfer line It is introduced into the crystal bath 9 through 8a and the transfer line 8b and recrystallized, and the crystal bath 10 is passed through the transfer line 9a and the transfer line 9b connected to the lower part of the crystal bath 9. ) And undergoes the third crystallization step. Terephthalic acid after the three-step crystallization process is introduced into the transfer pump 11 through the transfer line (10a), a part is recovered, the rest is transferred to the transfer line (11a) from the transfer pump (11) via the transfer line (11c) ) Is combined with terephthalic acid being transferred to the crystallization tank 9 through the transfer line 8b, and is also combined with terephthalic acid being transferred to the transfer line 9a via the transfer line 11b, and then through the transfer line 9b. Recirculated to the crystal bath 10 is subjected to the recrystallization step.

Generally, in the case of hydrogenation purification, four to five crystal baths are passed to increase the purity of terephthalic acid after the hydrogenation reaction. In the present invention, the method of recycling the terephthalic acid slurry recycled through a transfer pump to the crystal bath reduces the number of crystal baths. In addition, the same quality effect as the existing method can be achieved, thereby reducing the investment cost.

In short, the crude terephthalic acid containing 4-CBA is purified and crystallized in two or more reactors connected in series to produce high purity terephthalic acid having excellent slurry fluidity and powder fluidity required for polyethylene terephthalate polymerization. In addition, since the reactor is operated in series, the reaction volume required for the reaction is reduced compared to when the reactor is connected in parallel due to the oxidation mechanism and reaction rate of 4-CBA. Consequently, when the same reactor is operated in series, the amount of terephthalic acid is also increased. Will increase.

In addition, this series operation method can be applied not only to the oxygenation purification process but also to the hydrogenation reactor used in the hydrogenation purification process and the subsequent connected crystal bath.

Hereinafter, the present invention will be described in more detail with reference to the following Examples, which should not be construed as being limited to the following Examples without departing from the gist of the present invention.

Example 1

Using cobalt, manganese acetate compound and bromine compound as a catalyst, p-xylene was oxidized in acetic acid solution to prepare a crude terephthalic acid slurry. The crude terephthalic acid contained terephthalic acid at about 30% by weight. After passing through a centrifuge, which is a solid-liquid separator, to first purify the impurities contained in the slurry, 500 ml of the crude terephthalic acid slurry was dissolved in 500 ml of acetic acid solution (90-100% acetic acid) and introduced into a reactor connected in series. It was.

1 is a block diagram of a device used in the present invention.

As shown in FIG. 1, four reactors are installed in the first stage and one reactor is installed in the second stage, and five reactors are connected in series in a 4-1 fashion.

Into the first stage reactor (1, 2, 3, 4) having a capacity of 2 L each, a crude terephthalic acid slurry containing about 6,000 ppm of 4-CBA is added to the first purification step. The reaction temperature of the first stage reactors (1, 2, 3, 4) is 205 ℃, the pressure is 15KG, and is maintained for 1.26 hours. The 4-CBA concentration in the terephthalic acid slurry after the first purification step was 200 ppm.

Transfer line 1a existing in the lower part of the first stage reactor # 1 (1) of the terephthalic acid slurry purified in the first purification step and transfer line 2a existing in the lower part of the first stage reactor # 2 (2) The combined transfer line 5b is introduced into the left side of the second stage reactor 5, and the transfer line 3a and the first stage reactor # 4 (4) existing in the lower portion of the first stage reactor # 3 (3). The transfer line 4a existing at the bottom of) is introduced into the right side of the second stage reactor 5 through the combined transfer line 5c and undergoes the second purification step. At this time, the slurry was transferred between the first stage reactors (1, 2, 3, 4) and the second stage reactor (5) by a differential pressure without a transfer pump. In the second stage reactor 5, a condenser is installed on the upper portion of the reactor 5 to condense acetic acid vapor rising to the upper portion and return to the reactor 5, and to maintain uniform internal composition, the stirrer 5a ) Is installed to continuously stir the inside of the reactor (5). The reaction temperature of the second stage reactor was 165 ℃, the pressure was 12KG, and stayed for 0.36 hours. The concentration of 4-CBA contained in the terephthalic acid slurry purified using this method was 90 ppm.

Comparative Example 1

500 ml of the crude terephthalic acid slurry produced in the same manner and in Example 1 was dissolved in 500 ml of an acetic acid solution (acetic acid content of 90 to 100%) and introduced into five reactors connected in parallel.

Purification was carried out by adding crude terephthalic acid slurry containing about 600 ppm of 4-CBA to five reactors connected in parallel, each having a volume of 2 L. The reaction temperature of the reactors was 205 ° C., the pressure was 15 KG, and the temperature was 1.61 hours. The concentration of 4-CBA contained in the terephthalic acid slurry purified using this method was about 180 ppm.

According to the present invention, high purity terephthalic acid was prepared by the method of Example 1, and the concentration, average particle size, and productivity of 4-CBA were compared with those of the conventional method. The average particle size of Table 1 refers to a diameter corresponding to 50% by weight accumulation from the value measured by dry classification with a standard body.

TABLE 1

As can be seen from Table 1, by connecting the reactor in series according to the present invention, the concentration of 4-CBA is significantly reduced and the production is increased, and it is possible to obtain an excellent effect in terms of particle size without installing a separate crystal bath. Able to know.

Example 2

A co-xylene was prepared by oxidizing p-xylene in acetic acid solution using a cobalt, a manganese acetate compound and a bromine compound as a catalyst to prepare a crude terephthalic acid slurry. The crude terephthalic acid contained about 30% by weight of terephthalic acid. After passing through a centrifuge which is a solid-liquid separator to first purify the impurities contained in the slurry, 500 ml of 4-teraphthalic acid slurry containing 4-CBA was dissolved in 500 ml of water and introduced into a 2-liter hydrogenation reactor to 250-. Purification through hydrogenation under a platinum catalyst at a temperature of 330 ° C. was added to a 1 L multistage crystal bath connected to a hydrogenation reactor.

2 is a block diagram of the apparatus used in the present invention.

As shown in Fig. 2, the crystal bath was installed in three steps. Then, the terephthalic acid purified through the hydrogenation reaction is introduced into a crystal bath 8 operated at a temperature condition of 240 ° C. at a flow rate of 15 g / min, and first crystallized, and the terephthalic acid is transferred to a transfer line 8a and a transfer line ( 8b) is introduced into a crystal bath 9 which is operated at a temperature of 190 ° C. at a flow rate of 12.9 g / min, and recrystallized, and a transfer line 9a and a transfer line connected to the lower part of the crystal bath 9 9b) was crystallized in the crystallization tank 10 which is operated under the temperature conditions of 150 degreeC by the flow rate of 11.2g / min.

The terephthalic acid after the three-step crystallization process is introduced into the transfer pump 11 via the transfer line 10a, and the terephthalic acid is being transferred from the transfer pump 11 through the transfer line 11c to the transfer line 8a. It is combined with terephthalic acid and recycled to the crystal bath 9 through the transfer line 8b to undergo a recrystallization step. In addition, the terephthalic acid passed through the transfer pump 11 is combined with the terephthalic acid being transferred to the transfer line 9a via the transfer line 11b and recycled to the crystal bath 10 through the transfer line 9b to undergo a recrystallization step. do.

Comparative Example 2

500 ml of the crude terephthalic acid slurry produced by the same method and conditions as in Example 2 was dissolved in 500 ml of water, charged into a 2 liter hydrogenation reactor, and purified through a hydrogenation reaction under a platinum catalyst at a temperature of 250 to 330 ° C., followed by a hydrogenation reactor. It was charged into a 5 stage crystal bath of 1 liter capacity connected to.

This Comparative Example 2 was carried out by adjusting the temperature conditions of the crystal bath of the five stages as shown in Table 2 below.

High purity terephthalic acid was prepared by the method of Example 2 according to the present invention and the average particle size is shown in Table 2 as compared with the method according to the conventional method.

TABLE 2

As can be seen in Table 2, by applying the terephthalic acid slurry recycling method of the present invention to the crystal bath, it is possible to produce a high-purity terephthalic acid having almost the same quality effect as the existing method in terms of particle size while reducing equipment investment costs.

According to the present invention, there is provided a method of obtaining high purity terephthalic acid having a low content of 4-CBA and improved powder fluidity and slurry fluidity of terephthalic acid through a series operation of a reactor. As such, the slurry fluidity of the high purity terephthalic acid is improved, so that when the terephthalic acid is mixed with glycols in the polyester polymerization process, the glycol is easily mixed with the glycols in the reactor, thereby increasing the efficiency of the reactor. In addition, the powder flowability is improved, and thus useful when transported or stored in the terephthalic acid polymerization process.

By connecting two or more reactors in series and recirculating the terephthalic acid slurry, the series operation of the reactors acts as a multistage crystal bath, thus producing terephthalic acid of the same or higher purity without the installation of a complex multistage crystal bath.

In addition, since the reaction volume required for the reaction is reduced compared to when the reactor is connected in series to operate in parallel, as a result, the production of terephthalic acid also increases when the same reactor is operated in series.

In addition, even in a hydrogenation purification process in which a crystal bath is used, the recycling method can be used to reduce the number of crystal baths while maintaining good powder and slurry fluidity of terephthalic acid.

Claims (4)

dissolving p-xylene in an acetic acid solvent or acetic acid solution with oxygen in the air using a cobalt, manganese, bromine compound catalyst to dissolve crude terephthalic acid in a purified acetic acid solvent or acetic acid solution into a slurry state; Refining step of transporting and oxidizing the terephthalic acid slurry to a plurality of reactors operated at a temperature lower than the reactor temperature of the preceding reactor connected in series, and the step of operating the reactor characterized in that the purified terephthalic acid slurry is recovered High purity terephthalic acid production method through. According to claim 1, wherein the reaction temperature of the first stage reactor of the reactor connected in series is 190 ~ 280 ℃, the reaction temperature of the second stage reactor is 140 ~ 215 ℃ high purity terephthalic acid through the series operation of the reactor Manufacturing method. The method of claim 1, wherein after passing through the purification step, the terephthalic acid slurry is transferred to a flash tank operated at a temperature of 60 ~ 100 ℃ connected to the lowest reactor crystallized and introduced into a transfer pump to recover a part and the rest of the Method for producing high purity terephthalic acid through the series operation of the reactor, characterized in that the transfer back to the reactor. According to claim 1, wherein the reactor is composed of two 1-1 type is installed in the first stage and one unit is installed in the second stage when there are two reactors, 2-1 type or 1 when the reactor is three It is composed of any one type selected from -1-1 type, and if there are four reactors, it is composed of any one type selected from 3-1 type or 2-2 type. Or 3-2 type of high purity terephthalic acid through the series operation of the reactor, characterized in that configured in any one type.

Images