KR100896516B1 - Preparation method of terephthalic acid - Google Patents

Abstract

The present invention relates to a method for producing terephthalic acid, and more particularly, to a method of preparing terephthalic acid by oxidizing paraxylene using a metal catalyst of cobalt and manganese under an acetic acid solvent, and bromine as a reaction initiator. It relates to a method for producing terephthalic acid wherein the oxidation reaction temperature is 165 to 180 ℃.

When terephthalic acid is prepared by oxidizing paraxylene using the method for producing terephthalic acid of the present invention, the loss of acetic acid solvent is low, the organic impurity concentration is low, and the yield is high.

Terephthalic Acid, Acetic Acid, Cobalt, Manganese, Bromine, Paraxylene

Description

Production method of terephthalic acid {PREPARATION METHOD OF TEREPHTHALIC ACID}

1 shows a continuous terephthalic acid production reactor.

[Industrial use]

The present invention relates to a method for producing terephthalic acid, and more particularly, to a method for producing terephthalic acid with low loss of acetic acid solvent, low concentration of organic impurities, and high yield.

[Prior art]

Terephthalic acid is a compound widely used as a raw material for producing polyesters such as polyethylene terephthalate and the like. A widely used method for producing terephthalic acid is a method of reacting paraxylene with oxygen in air under acetic acid solvent.

There are many criteria for evaluating the superiority of the method for producing terephthalic acid. Among them, various economic aspects such as the quality of terephthalic acid to be manufactured, that is, purity and manufacturing cost, are considered to be important criteria.

First of all, in terms of quality, various standards such as concentration, color, and fluorescence of organic impurities contained in terephthalic acid particles are representative criteria for evaluating the quality of terephthalic acid. In particular, 4-carboxybenzaldehyde and paratoluic acid, which are intermediates produced during terephthalic acid manufacturing process, have only one functional group, unlike terephthalic acid, and are known as representative organic impurities that serve to terminate the polymerization reaction in the polymerization process. Therefore, the lower the production rate of 4-carboxybenzaldehyde and paratoluic acid as described above in the terephthalic acid manufacturing process is considered to be an excellent method for producing terephthalic acid.

In terms of manufacturing costs, the loss of acetic acid, which is used as a reaction medium, is the biggest economic loss, except for the investment cost. Acetic acid is oxidized with oxygen in the air introduced into the reactor in the presence of a reaction catalyst to produce carbon monoxide, carbon dioxide, methyl acetate, and the like. The carbon dioxide and carbon monoxide thus produced are discharged to the atmosphere along with the exhaust gas through a condenser at the top of the reactor. Therefore, it can be seen that the higher the concentration of carbon monoxide and carbon dioxide in the gas discharged from the reactor, the greater the loss of acetic acid. Therefore, the amount of acetic acid that is lost by measuring the content of the exhaust gas, such as carbon dioxide, carbon monoxide in the exhaust gas in this way, the amount of acetic acid that is lost, such as this leads to a problem of increasing the manufacturing cost.

However, although the price of cobalt among cobalt and manganese used as a catalyst is relatively high, since most catalysts are recovered together with a solvent through a solvent recovery process, the effect on the cost of terephthalic acid production is very small compared to acetic acid.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing terephthalic acid, which has low loss of acetic acid solvent, low concentration of organic impurities, and high yield.

In order to achieve the above object, the present invention uses a metal catalyst of cobalt and manganese under acetic acid solvent, and using bromine as a reaction initiator to prepare a terephthalic acid by oxidizing paraxylene, the oxidation reaction temperature is Provided is a method for producing terephthalic acid at 165 to 180 ° C.

Hereinafter, the present invention will be described in more detail.

The method for producing terephthalic acid of the present invention is a method of producing terephthalic acid by oxidizing paraxylene using a metal catalyst of cobalt and manganese under acetic acid solvent, and bromine as a reaction initiator. It is characterized by being 180 ° C.

Conventional reports have reported that the use of only cobalt as a catalyst can oxidize paraxylene, but the actual reaction of paraxylene by oxidizing paraxylene using only cobalt as a catalyst results in continuous paraxylene. There is a problem that can not maintain the oxidation reaction.

In general, metal catalysts such as cobalt and manganese and bromine may be introduced into the reactor in various forms of compounds. For example, cobalt and manganese may be added in any form of hydroxide or acetate, respectively, and bromine may be added in various forms such as bromic acid, tetrabromoethane and sodium bromide. In addition, cobalt and manganese may be dissolved in water or acetic acid and added to the reactor in the form of a liquid catalyst.

In the present invention, cobalt, manganese and acetic acid may be added to the reactor in the various forms described above, but most preferably, cobalt is added in the form of hydroxide, manganese in the form of acetate and bromine in the form of bromic acid. Do.

In the method for producing terephthalic acid of the present invention, when the oxidation reaction temperature is less than 165 ° C., there is a problem in that the content of impurities such as 4-carboxybenzaldehyde is increased in the produced terephthalic acid, thereby reducing the purity of the produced terephthalic acid. In addition, when the oxidation reaction temperature exceeds 180 ℃, the content of impurities such as 4-carboxybenzaldehyde is lowered in the terephthalic acid produced, but the loss of acetic acid is increased, the content of carbon dioxide, carbon monoxide, etc. in the exhaust gas is not preferable.

The concentration of cobalt in the acetic acid solvent used in the method for producing terephthalic acid of the present invention is preferably 400 to 2500 ppm. The concentration of cobalt is more preferably 600 to 2000 ppm. When the concentration of cobalt in the acetic acid solvent is less than 400 ppm, the oxidation reaction does not proceed smoothly, so that the content of organic impurities such as 4-carboxybenzaldehyde or paratoluic acid increases, thereby decreasing the purity of the produced terephthalic acid and lowering the yield. There is a problem. In addition, if the concentration of cobalt in acetic acid solvent exceeds 2500 ppm, the content of 4-carboxybenzaldehyde, which is an impurity in terephthalic acid, decreases, but the loss of acetic acid increases, so that the content of carbon dioxide and carbon monoxide in the exhaust gas increases. It is not desirable.

In addition, in the method for producing terephthalic acid of the present invention, the concentration of the metal catalyst of the cobalt and manganese is characterized in that 400 ppm to 4000 ppm in the acetic acid solvent. If the metal catalyst concentration of cobalt and manganese is less than 400 ppm in acetic acid solvent, the oxidation reaction of paraxylene does not proceed smoothly. If the metal catalyst concentration of cobalt and manganese exceeds 4000 ppm in acetic acid solvent, There is a problem in that it is not economical because the reactivity is not increased in proportion to the content of the concentration of the catalyst.

In addition, in the method for producing terephthalic acid of the present invention, it can be seen as another feature that the molar ratio of cobalt to manganese in the metal catalyst is 1: 1 to 25: 1. If the molar ratio of cobalt to manganese in the metal catalyst of the cobalt and manganese is less than 1, there is a problem in that the content of 4-carboxybenzaldehyde, which is an impurity in terephthalic acid, is not increased because the oxidation reaction of paraxylene does not proceed smoothly. If the molar ratio of cobalt to manganese in the metal catalysts of the cobalt and manganese exceeds 25, the loss of acetic acid increases, so that the content of carbon dioxide and carbon monoxide in the exhaust gas increases.

In addition, in the method for producing terephthalic acid of the present invention, it can be seen as another feature that the molar ratio of the bromine to the metal catalyst of cobalt and manganese is 0.3: 1 to 1: 1. In the molar ratio of bromine to cobalt and manganese metal catalysts, when the molar ratio of bromine to cobalt and manganese metal catalysts is less than 0.3, the loss of acetic acid is reduced, thereby reducing the content of carbon dioxide and carbon monoxide in the exhaust gas, but oxidizing reactions. There is a problem in that the purity and yield of the terephthalic acid produced by increasing the content of organic impurities such as 4-carboxybenzaldehyde or paratoluic acid is not smoothly disclosed. In addition, when the molar ratio of bromine to the metal catalyst of cobalt and manganese exceeds 1, the oxidation of acetic acid is promoted and the loss of acetic acid is increased.

In addition, in the method for producing terephthalic acid of the present invention, it can be seen as another feature that the residence time in the reactor of the acetic acid solvent and the prepared terephthalic acid is 30 to 120 minutes. As the residence time of the acetic acid solvent and the produced terephthalic acid in the reactor increases, the amount of exhaust gas such as carbon dioxide and carbon monoxide increases and the content of impurity phosphorus such as 4-carboxybenzaldehyde decreases. If the residence time of the acetic acid solvent and the prepared terephthalic acid in the reactor is less than 30 minutes, the residence time is too short, there is a problem that the purity and yield of terephthalic acid is lowered because the content of 4-carboxybenzaldehyde as impurities is high, the residence time is 120 minutes Exceeds the loss of acetic acid increases, but also causes a problem that the performance of the reactor is reduced due to the exhaust gas, such as carbon dioxide, carbon monoxide.

The terephthalic acid produced by the method for producing terephthalic acid of the present invention is purified through a hydrogenation or secondary oxidation reaction to produce terephthalic acid with higher purity.

As described above, the method for producing terephthalic acid of the present invention has a low loss of acetic acid solvent, a low concentration of organic impurities, and a high yield.

As the reactor, it is preferable to use the continuous terephthalic acid production reactor shown in FIG. The method for producing terephthalic acid using this reactor is as follows.                     

First, a liquid mixed reactant composed of acetic acid, para xylene, and a catalyst is introduced into the oxidation reactor at a predetermined flow rate using a metering pump. Air, which is a reactant in the gas phase, is compressed to a desired pressure using a compressor, and then injected into the oxidation reactor by a predetermined amount through a flow control valve.

The oxidation reactor is heated to a reaction temperature by using a heating jacket, and a pressure control valve is installed at the rear of the condenser to control the reaction temperature and pressure. The terephthalic acid and acetic acid slurry reacted under such conditions is sent to storage container 1 until the steady state is reached, and after the steady state is reached, it is sent to storage container 2 for sampling. After filtering, washing and drying the collected terephthalic acid slurry, the quality and content of organic impurities such as 4-carboxybenzaldehyde and paratoluic acid contained in terephthalic acid are analyzed.

On the other hand, the excess gas and vapor generated in the oxidation reactor or participating in the reaction passes through the condenser, and the vapor phase condenses and returns to the oxidation reactor, but most of the gas which has been dropped by the condenser is released into the atmosphere, and some of the remaining steam The removal process is followed by an online analysis. Here, the concentrations of oxygen, carbon dioxide, carbon monoxide, etc. contained in the exhaust gas in which the steam is completely removed are measured. As described above, carbon dioxide and carbon monoxide are produced as a result of the oxidation reaction of acetic acid used as a reaction medium, which causes a loss of acetic acid, which greatly affects the economics of the terephthalic acid manufacturing process.

Hereinafter, preferred examples and comparative examples of the present invention are described. The following examples and comparative examples are described for the purpose of more clearly expressing the present invention, but the contents of the present invention are not limited to the following examples and comparative examples.

(Examples 1-3 and Comparative Examples 1-2)

First, to investigate the effect of reaction temperature on the oxidation reaction of para xylene, the quality and process change of terephthalic acid obtained by varying the temperature of the reactor were examined. Reaction conditions and results thereof are shown in Table 1 below.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Reaction temperature (℃) 165 175 180 150 190  Catalyst condition Cobalt (ppm) 2500 1500 1000 2500 600 Cobalt / Manganese (Molar Ratio) 20 20 20 20 20 Bromine / cobalt and manganese (molar ratio) 0.7 0.7 0.7 0.7 0.7  Response result 4-carboxybenz aldehyde (ppm) 680 550 480 2100 420 Emission Gas (%) 2.14 2.52 2.87 1.80 4.58

In Examples 1 to 3, as the oxidation reaction temperature is 165 to 180 ° C., the oxidation reaction proceeds smoothly, and as the reaction temperature increases, the content of 4-carboxybenzaldehyde in the produced terephthalic acid is decreased. However, as in Comparative Example 1, when the reaction temperature is 155 ° C., the oxidation occurs, but the concentration of 4-carboxybenzaldehyde contained in terephthalic acid is high, and thus it may not be a condition for producing high quality terephthalic acid. In addition, 4-carboxybenzaldehyde content is too high as a result of the first oxidation reaction, which increases the cost of the subsequent purification process and increases the organic impurities in the terephthalic acid, the final product after the purification process, which is not preferable. have.

In addition, as in Comparative Example 2, when the reaction temperature is 190 ℃, the content of 4-carboxybenzaldehyde is less, but there is a problem that the content of carbon dioxide, carbon monoxide, etc. in the exhaust gas may be increased to damage the reactor.

(Examples 4 to 9 and Comparative Examples 3 to 5)

The concentration and molar ratio of the metal catalyst at the reaction temperature of 170 ° C. were varied as described in Table 2 below, and the results are also shown in Table 2 below. In Examples 3 to 5 and Comparative Example 4 described in Table 2 below, the concentration of the entire metal catalyst was kept constant at 2000 ppm, and only the molar ratio was changed.

Example 3 Example 4 Example 5 Comparative Example 3 Comparative Example 4 Reaction temperature (℃) 170 170 170 170 170  Catalyst condition Cobalt (ppm) 1900 1800 1500 2000 1000 Cobalt / Manganese (Molar Ratio) 19 9 3 - One Bromine / cobalt and manganese (molar ratio) 0.7 0.7 0.7 0.7 0.7  Response result 4-carboxybenz aldehyde (ppm) 580 610 680 - 1200 Emission Gas (%) 2.43 2.3 1.9 - 1.3

In addition, the concentration and the molar ratio of the metal catalyst at the reaction temperature of 180 ℃ was changed as described in Table 3, and the results are also shown in Table 3 below. In Examples 7 to 9 and Comparative Example 5 described in Table 3 below, the concentration of the total metal catalyst was fixed at 600 ppm, and only the molar ratio of cobalt and manganese was changed.                     

Example 7 Example 8 Example 9 Comparative Example 5 Reaction temperature (℃) 180 180 180 180  Catalyst condition Cobalt (ppm) 570 540 300 200 Cobalt / Manganese (Molar Ratio) 19 9 One 0.5 Bromine / cobalt and manganese (molar ratio) 0.7 0.7 0.7 0.7  Response result 4-carboxybenz aldehyde (ppm) 570 560 780 2110 Emission Gas (%) 2.43 2.34 1.66 1.57

As shown in Tables 2 and 3, as the value of cobalt / manganese (molar ratio) is smaller, the content of 4-carboxybenzaldehyde increases, but the content of exhaust gases such as carbon dioxide and carbon monoxide decreases. In other words, the higher the concentration of manganese than the cobalt, the oxidation reaction is inhibited. In Comparative Example 3, the experiment was performed without adding manganese as a catalyst, but the experimental results could not be obtained. Therefore, in order to oxidize paraxylene, it was found that manganese must be present in addition to cobalt as a metal catalyst.

(Examples 10 to 12 and Comparative Examples 6 to 7)

Table 4 shows the conditions and results of the experiment to determine the effect of the concentration of bromine on the oxidation reaction of para xylene.

Example 10 Example 11 Example 12 Comparative Example 6 Comparative Example 7 Reaction temperature (℃) 180 180 180 180 180  Catalyst condition Cobalt (ppm) 540 540 540 540 540 Cobalt / Manganese (Molar Ratio) 9 9 9 9 9 Bromine / cobalt and manganese (molar ratio) 0.3 0.7 1.0 0.1 1.5  Response result 4-carboxybenz aldehyde (ppm) 750 560 510 3450 500 Emission Gas (%) 2.15 2.31 2.87 1.23 3.75

As shown in Comparative Example 6 shown in Table 4, when the concentration of bromine is lowered, the loss of acetic acid is reduced, but it can be seen that 4-carboxybenzaldehyde is increased, which is not preferable. In addition, as in Comparative Example 7, when the concentration of bromine is too high, the combustion of acetic acid is promoted to increase the loss of acetic acid, and it is known that a large amount of fluorescent substance is contained in the produced terephnal acid.

(Examples 13 to 15 and Comparative Examples 8 to 9)

The effect of the residence time of the acetic acid solvent and the prepared terephthalic acid in the reactor on the oxidation reaction of para xylene was tested under the same conditions as in Table 5 and the results are shown in Table 5 below.

Example 13 Example 14 Example 15 Comparative Example 8 Comparative Example 9 Reaction temperature (℃) 180 180 180 180 180 Retention time (minutes) 30 90 120 20 150  Catalyst condition Cobalt (ppm) 540 540 540 540 540 Cobalt / Manganese (Molar Ratio) 9 9 9 9 9 Bromine / cobalt and manganese (molar ratio) 0.3 0.7 1.0 0.7 0.7  Response result 4-carboxybenz aldehyde (ppm) 750 560 510 2780 330 Emission Gas (%) 2.15 2.31 2.87 1.22 3.50

As shown in Table 5, as the residence time increases, the amount of exhaust gas such as carbon dioxide and carbon monoxide increases, and the content of impurities such as 4-carboxybenzaldehyde decreases. In Comparative Example 8, the residence time was too short, and thus the content of impurities such as 4-carboxybenzaldehyde was relatively high. I could see that.

As described above, the method for producing terephthalic acid of the present invention has a low loss of acetic acid solvent, a low concentration of organic impurities, and a high yield.

Claims (6)

Under the acetic acid solvent, using a metal catalyst of cobalt and manganese, using bromine as a reaction initiator to oxidize para xylene to produce terephthalic acid, The oxidation reaction is carried out at 165 to 180 ℃, the concentration of cobalt in the acetic acid solvent is 400 to 2500 ppm, the concentration of the metal catalyst in the acetic acid solvent is 400 ppm to 4000 ppm, the molar ratio of cobalt to manganese in the metal catalyst Is 1: 1 to 25: 1, The molar ratio of bromine to metal catalyst is 0.3: 1 to 1: 1, and the residence time in the reactor of the acetic acid solvent and terephthalic acid prepared is 30 to 120 minutes. delete delete delete delete delete

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