KR100780751B1 - High efficiency high purity terephthalic acid production method using composite bromine catalyst system - Google Patents

Abstract

The present invention relates to a method for producing terephthalic acid, and more particularly, in the preparation of terephthalic acid by oxidizing paraxylene using a complex metal catalyst of cobalt, manganese and bromine in the presence of acetic acid solvent and oxygen, 150 to 200 Corrosion of the reaction plant by lowering the concentration of bromine to less than 500 ppm and the total catalyst input to 350 ppm to 1000 ppm by selecting bromoacetic acid as a new precursor of bromine under conditions of temperature of 10 ° C. and pressure of 10 to 50 kgf / cm ² . It relates to a method for producing terephthalic acid to ensure the safety of the process and improved yield and economics.

Description

Preparing method of terephthalic acid of high efficiency and high degree of purity using composition of multi-bromic catalytic system}

The present invention relates to a method for producing terephthalic acid, and more particularly, to a method for preparing terephthalic acid by oxidizing paraxylene using a complex metal catalyst of cobalt, manganese and bromine in the presence of acetic acid solvent and oxygen.

Paraxylene oxidation is a major reaction for producing terephthalic acid.High purity terephthalic acid is mainly used as a main raw material for polyester fibers, PET resins, film paints and engineering plastics, and has excellent heat resistance, abrasion resistance, insulation, and mechanical strength. Applications are expanding to many applications such as electrical, electronics, industrial materials, building materials, and mechanical parts. In addition, high-purity terephthalic acid is growing in demand not only for existing textile products, but also for packaging, audio, video tape films, general PET bottles, carbonated water, beer, milk packaging containers, tire cords, and automotive parts. In particular, the demand for high-purity terephthalic acid has grown at an annual rate of 8.5% globally over the past five years.

Korean Patent Application No. 1999-0048900 relates to a method for producing terephthalic acid by oxidizing paraxylene, wherein paraxylene is oxidized by oxygen in an acetic acid solvent under a catalyst of cobalt, manganese and bromine to produce terephthalic acid. In the case, the reaction temperature of 200 ~ 220 ℃, under the reaction conditions of the reaction pressure of 10 ~ 50kg / ㎠ it characterized in that the 4-carboxybenzaldehyde is lowered below 200ppm. However, if the oxidation reaction temperature exceeds 200 ℃ impurities contained in the produced terephthalic acid is lowered, but the loss of acetic acid is increased, the content of carbon dioxide, carbon monoxide, etc. in the exhaust gas is not preferable.

In addition, the Republic of Korea Patent Application No. 2000-0085076 relates to a manufacturing method of the crude terephthalic acid, in the manufacturing method of the concentration of cobalt atoms 50 ~ 600ppm, the weight ratio of manganese atoms and cobalt atoms 0.5: 1 ~ 6: 1 , Characterized by a step of oxidizing the reaction mixture under a temperature of 180-210 ° C. and a pressure of 10-50 kgf / cm ² at a concentration of 400-3000 ppm of bromine atom. According to the present invention, high purity crude terephthalic acid having a low content of reaction by-products can be produced in a very high yield. However, since bromine enters a high concentration of 400-3000 ppm, investment and maintenance costs increase due to the corrosiveness of bromine, and there is a possibility of environmental pollution problems such as increased wastewater treatment costs. If it is not completely removed during the purification process and remains in the product, it acts as a catalyst poison in the subsequent reduction process with acetic acid.

In addition, Korean Patent Application No. 2000-0060048 relates to a method for preparing high purity terephthalic acid, wherein 4-carboxybenzaldehyde is less than 500 ppm under a catalyst system prepared by mixing tetrabroethane and bromic acid as a precursor of bromine. It is characterized by lowering. According to the present invention, by using two or more kinds of precursors of bromine to ensure economic efficiency in the liquid phase oxidation of paraxylene at a temperature between 180 ~ 220 ℃ by using a high-purity method to significantly reduce the catalyst cost and increase the reaction rate Terephthalic acid can be obtained. However, when looking at the precursor of bromine used in the present invention, tetrabroethane has the disadvantage that the price is expensive and the reaction activity is lower than other bromine precursors, and bromic acid has a strong corrosiveness to be applied to the process It has the disadvantages of corrosive process equipment, dangerous handling and high vapor evaporation. In particular, the evaporation of bromic acid lowers the effective concentration of bromine, causing a rapid increase in the concentration of reaction intermediates and impurities, causing a problem of the quality of terephthalic acid, and causing corrosion of process equipment and a large amount of by-products. This results in economic losses .

In addition, the Republic of Korea Patent Application No. 2002-0056129 relates to a method for producing terephthalic acid, using a metal catalyst of cobalt and manganese in acetic acid solvent, bromine as a reaction initiator, the oxidation reaction temperature is 165 ~ 180 ℃ It is characterized by that. However, in the present invention, the variables affecting the oxidation reaction are presented as the concentration of the catalyst, the composition of the catalyst, and the reaction time, but there is a problem that the influence of the pressure and the reaction time is not considered.

Therefore, the present invention is a method for producing terephthalic acid by reacting paraxylene with an oxygen-containing gas in the presence of acetic acid solvent, reducing the corrosion of the reaction equipment, and reduce the cost of waste water treatment due to environmental pollution, catalyst during the reduction process In order to reduce the cost of the process by reducing the content of bromine atoms acting as a poison and to reduce the cost of the process, and also to reduce the content of bromine atoms, the catalyst system optimized the ratio of cobalt / manganese / bromine as a catalyst It is an object of the present invention to provide a method for producing terephthalic acid, which is selected to maintain a high yield of terephthalic acid.

In order to achieve the above object, the present invention is a method for producing terephthalic acid by reacting paraxylene with an oxygen-containing gas in the presence of acetic acid solvent, using a catalyst system with an optimized ratio of cobalt / manganese / bromine, reaction solvent It provides a method for producing terephthalic acid, characterized in that the content of the bromine atom in less than 500ppm.

In addition, the bromine is characterized by being prepared by mixing manganese bromide and bromine acetic acid as a precursor of bromine.

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

The present invention provides a method for producing terephthalic acid by oxidizing paraxylene using a complex metal catalyst of cobalt, manganese and bromine in the presence of acetic acid solvent and oxygen.

In the present invention, the reaction solvent uses acetic acid containing up to 10% by weight of water.

In the present invention, as the oxygen-containing gas used for the paraxylene oxidation reaction, a gas containing 10 to 95% by volume of oxygen in an inert gas is used, and preferably air is used. The total amount of oxygen-containing gas supplied to the reactor is supplied in the range of 3 to 100 moles of oxygen molecules per mole of paraxylene. When air is used as the oxygen-containing gas, the oxygen concentration in the exhaust gas discharged from the reactor during the oxidation reaction is maintained at 1.5 to 6% by volume, and the reaction temperature is maintained at 150 to 190 ° C. Inject gas containing gas to 10 to 50 bar.

Cobalt used as a catalyst for paraxylene oxidation in the present invention may be added in various forms such as cobalt acetate, cobalt hydroxide, cobalt bromide, cobalt carbonate, and at least one compound thereof is selected and added. In particular, it is preferred to be added in the form of cobalt acetate and cobalt bromide.

The addition amount of the cobalt compound is preferably such that the concentration of the total cobalt atoms is 10 to 1000 ppm, preferably 50 to 300 ppm based on the solvent.

In addition, the manganese used as a catalyst for the paraxylene oxidation in the present invention may be introduced in various forms such as manganese acetate, manganese hydroxide, manganese bromide, manganese carbonate, one or more compounds selected from these added do. In particular, it is preferred to be added in the form of one or a mixture of manganese acetate and manganese bromide.

The amount of the manganese compound added is such that the ratio of the total weight of the manganese atoms and the total weight of the cobalt atoms is 1: 0.1-10, preferably 1: 0.3-3.

When the cobalt and manganese compounds are used below the content, the conversion to the intermediate material paratoluic acid is not performed, resulting in a lower yield of terephthalic acid, which is a final target product. On the contrary, when the content exceeds the above content, the catalyst cost increases, the operating cost increases due to the oxidation of the solvent, product contamination due to the oxidation of manganese, and the purity of terephthalic acid occurs.

In the present invention, bromine that acts as a catalyst for the paraxylene oxidation reaction, its addition amount and the form of the bromine compound is an important factor in the present invention. Bromine is introduced into various forms such as bromic acid, cobalt bromide, manganese bromide and bromine acetic acid to serve as an initiator to initiate the oxidation reaction of paraxylene. At least one compound of the various bromine compounds mentioned above is selected and added to the reaction. In particular, it is preferred to be added in the form of one or a mixture of manganese bromide and bromic acetic acid. When manganese bromide is used as the bromine compound, the manganese bromide will simultaneously play the role of manganese and bromine in the catalyst system.

The higher the amount of bromine in the catalyst, the higher the initial reaction activity, but the higher the catalyst cost and the higher the corrosion costs due to the bromine effect, which incurs additional costs due to the corrosion of the process equipment and the need for a recovery process for bromine reuse. have. In the existing processes, the addition amount of bromine compound was 400-3000 ppm, but in the present invention, the addition amount of bromine is 50 ppm or more and less than 500 ppm based on the solvent, and the paraxylene oxidation reaction is performed. When the amount of bromine is less than 50 ppm, radicals are not formed for the initiation of the reaction of paraxylene, so it is difficult to convert to terephthalic acid through oxidation, and when 500 ppm or more is added, especially when a large amount of bromine is added more than 1000 ppm Due to this problem, especially environmental pollutants such as methyl bromide are also produced.

In addition, when manganese bromide and bromine acetic acid are used as the bromine compound while lowering the addition amount of bromine to less than 500 ppm, terephthalic acid yield does not decrease when the manganese bromide addition amount is 1: 0.5 to 1: 3. When the addition amount of bromine is less than 500 ppm and the addition ratio of bromic acetic acid and manganese bromide is less than 1: 0.5, the yield of terephthalic acid is greatly reduced. In addition, when the addition ratio of bromic acetic acid and manganese bromide exceeds 1: 3, the catalyst cost increases and reactor corrosion greatly increases.

In the present invention, the total content of cobalt, manganese, and bromine atoms acting as a catalyst for paraxylene oxidation is added at 350-1000 ppm, preferably 500-800 ppm, based on the acetic acid solvent. If the total content of cobalt, manganese and bromine atoms in the catalyst is less than 350 ppm, paraxylene oxidation does not occur sufficiently, and the yield of terephthalic acid is greatly lowered. In addition, when the total content of cobalt, manganese and bromine atoms in the catalyst is more than 1000ppm, problems such as increased catalyst cost, product loss due to increased side reactions, and large amounts of environmental pollutants such as methyl bromide will occur.

In addition, in the para xylene oxidation of the present invention, the residence time of the para xylene, the acetic acid solvent and the prepared terephthalic acid in the reactor is 10 to 120 minutes. If the residence time of the paraxylene, acetic acid solvent and the prepared terephthalic acid in the reactor is less than 10 minutes, the residence time is too short, so that the oxidation reaction does not reach the final product, terephthalic acid, resulting in higher content of 4-carboxybenzaldehyde as an impurity, thereby increasing the purity of terephthalic acid and Yield is lowered. In addition, when the residence time of the para xylene, the acetic acid solvent and the prepared terephthalic acid in the reactor exceeds 120 minutes, the loss of acetic acid increases and causes an increase in operating costs.

In addition, the present invention is characterized in that the 4-carboxybenzaldehyde content in the prepared terephthalic acid is less than 500ppm. When the content of 4-carboxybenzaldehyde in the prepared terephthalic acid is more than 500ppm, the quality of the terephthalic acid is lowered, so an additional process for removing the 4-carboxybenzaldehyde is required, resulting in an increase in cost. When 4-carboxybenzaldehyde, which is an impurity in terephthalic acid generated through oxidation reaction, is present at less than 500 ppm, it is sufficient to be used as high purity terephthalic acid through the subsequent crystallization and purification process.

Hereinafter, the present invention will be described in more detail with reference to Preparation Examples and Examples. These preparations and examples are for illustrative purposes only and are not intended to limit the scope of the invention to the following examples and comparative examples.

[Production Example 1]

2.58 g of paraxylene, 100.7 g of acetic acid and 1 g of distilled water were added to a 450 mL titanium reactor equipped with a stirrer, a heater, and an air inlet, followed by cobalt acetate, manganese acetate, manganese bromide, and bromine acetic acid. The catalyst was added so that the concentrations of the cobalt atom and the bromine atom were as shown in Table 1 on the basis of the solvent.

The reaction was carried out for 30 minutes by setting the reaction temperature of 170 ℃, the reaction pressure 30 bar, the stirring speed to 500rpm. After the completion of the reaction, the reaction product was cooled to 35 ° C. and the slurry product was recovered. 10 times the volume of distilled water was added to the slurry, cooled at 10 ° C. for 1 day, and the solid components were dried to recover terephthalic acid, thereby preparing Examples 1 to 8 and Comparative Example 1. And the reaction temperature was raised 5 degreeC, and the comparative example 2 and the comparative example 3 were manufactured.

Table 1 shows the paraxylene conversion and terephthalic acid selectivity determined by measuring the dry mass of the terephthalic acid thus obtained.

Catalyst concentration Co / Mn Response result Co (ppm) Mn (ppm) Br (ppm) PX conversion rate (%) TPA selectivity (%) Example 1 72 144 329 0.50 81.9 98.2 Example 2 72 144 129 0.50 59.9 99.2 Example 3 93 189 459 0.49 74.8 98.7 Example 4 93 189 259 0.49 29.5 97.4 Example 5 143 189 359 0.76 83.3 99.4 Example 6 143 189 259 0.76 83.3 99.1 Example 7 221 244 329 0.91 97.2 - Example 8 221 244 129 0.91 99.9 - Comparative Example 1 200 400 601 0.50 64.6 96.7 Comparative Example 2 250 250 501 1.00 81.5 98.9 Comparative Example 3 250 500 501 0.50 87.8 99.5

In Examples 1 and 3, the bromine content was less than 500 ppm, but the conversion of paraxylene was higher than that of Comparative Example 1 having a bromine content of 600 ppm, which means an increase in total terephthalic acid slurry recovery. In addition, as a result of analyzing the recovered slurry, the concentration of terephthalic acid in the slurry was 98.0% or more, indicating higher terephthalic acid selectivity than Comparative Example 1.

In the case of Examples 2 and 4, when the cobalt concentration in the solvent is 70 and 90 ppm, respectively, compared to the case of Examples 1 and 3, it can be seen that the para-xylene conversion is greatly reduced when the concentration of bromine is further reduced. .

In Examples 5 to 8, all of the bromine content is less than 500ppm, but showed a higher para xylene conversion compared to Comparative Example 1 having a bromine content of 600ppm.

In the case of Examples 6 and 8, when the cobalt concentration in the solvent is 140 and 220 ppm, respectively, compared to the case of Examples 5 and 7, even if the concentration of bromine was further reduced, the results of paraxylene conversion did not decrease. From this, it was found that when the cobalt concentration in the solvent is 140 ppm or more and the ratio of cobalt atoms to manganese atoms is 0.7 or more, the content of bromine can be greatly reduced.

In Examples 5 and 6, the concentration of terephthalic acid in the recovered slurry was higher than 99%, indicating higher terephthalic acid selectivity than Comparative Example 1.

In the case of Example 8, that is, in the case of cobalt 220ppm, manganese 240ppm, bromine 130ppm, the content of manganese and bromine is less than that of Comparative Example 1, but the reaction temperature of 5? Compared to the results of Comparative Example 2 and Comparative Example 3 that was raised showed a much higher para xylene conversion, it was found that the highest para xylene conversion among the examples.

That is, when the bromine concentration in the catalyst is less than 500ppm, when the total catalyst content is more than 590ppm and less than 800ppm showed a higher para xylene conversion compared to Comparative Example 1.

[Production Example 2]

A catalyst was added so that the concentrations of cobalt, manganese, and bromine precursors in the above examples using a mixture of manganese bromide and bromine acetic acid as the precursors of bromine are as shown in Table 2 on the basis of the solvent, and were carried out under the reaction conditions of Preparation Example 1. Examples 9-14 and Comparative Example 4 were prepared. And the reaction temperature was raised 5 degreeC, and the comparative example 5 and the comparative example 6 were manufactured.

Catalyst concentration MnBr ₂ / BrAc Response result Co (ppm) Mn (ppm) Br (ppm) PX conversion rate (%) TPA selectivity (%) MnBr ₂ BrAc Example 9 72 144 129 200 0.65 81.9 98.2 Example 10 93 189 259 200 1.30 74.8 98.7 Example 11 143 189 259 100 2.59 83.3 99.4 Example 12 221 244 129 200 0.65 97.2 - Example 13 159 317 52 150 0.35 18.7 87.5 Example 14 159 317 52 300 0.17 17.1 83.5 Comparative Example 4 200 400 0 601 0 64.6 96.7 Comparative Example 5 250 250 0 501 0 81.5 98.9 Comparative Example 6 250 500 0 501 0 87.8 99.5

In Examples 9, 10, and 11, the content of cobalt, manganese, and bromine is lower than that of Comparative Example 4, but all show higher para xylene conversion compared to Comparative Example 4. In addition, as a result of analysis of the recovered slurry, all of the terephthalic acid concentration in the slurry was 98% or more, indicating higher terephthalic acid selectivity than that of Comparative Example 4.

This suggests that using a mixture of manganese bromide and bromic acetic acid can yield a higher yield of terephthalic acid than using only bromic acetic acid as a precursor for bromine.

In the case of Example 12, the content of manganese and bromine is smaller than that of Comparative Example 4, but the paraxylene conversion is much higher than that of Comparative Examples 4 and 6, which of course increase the reaction temperature by 5 ° C as well as Comparative Example 4. . Through this, it can be seen that using a mixture of manganese bromide and bromic acetic acid rather than using only bromic acetic acid as a precursor of bromine is more helpful in increasing the yield of terephthalic acid than the effect of increasing the reaction temperature.

Examples 13 and 14 show very low paraxylene conversion, although the bromine atom content is not lower than the previous examples 9, 10, 11, 12. Through this, when the ratio of manganese bromide to bromine acetic acid as bromine precursor is less than 0.5, it can be seen that the yield of terephthalic acid can be significantly lowered regardless of the bromine atom content.

As described above, the method for producing terephthalic acid of the present invention can reduce wastewater treatment costs due to environmental pollution concerns, and can significantly reduce the content of highly corrosive bromine atoms in the reaction solvent, thereby reducing corrosion of the reaction equipment. In addition, it is possible to reduce the cost of the process to ensure economic feasibility. In addition, despite reducing the content of bromine atoms, it is possible to provide a catalyst system in which the ratio of cobalt / manganese / bromine is optimized to prepare high purity terephthalic acid in a very high yield.

Claims (7)

In a method for producing terephthalic acid by oxidizing paraxylene, acetic acid containing up to 10% by weight of water as a reaction solvent, a gas containing 10 to 95% by volume of oxygen in an inert gas, and cobalt / manganese / bromine A method for producing terephthalic acid, characterized in that the use of the catalyst system made, the content of the bromine atom in the reaction solvent to less than 500ppm. The method for producing terephthalic acid according to claim 1, wherein the cobalt concentration is 10 to 1000 ppm and the ratio of the total weight of manganese atoms and cobalt atoms is 1: 0.1 to 10. The method for preparing terephthalic acid according to claim 1, wherein the bromine is prepared by mixing manganese bromide and bromine acetic acid as a precursor of bromine. The method for producing terephthalic acid according to claim 3, wherein the ratio of bromic acetic acid and manganese bromide is 1: 0.5 to 1: 3. The method for preparing terephthalic acid according to claim 1, wherein the total catalyst concentration is 350 ppm to 1000 ppm based on the acetic acid solvent. The method for producing terephthalic acid according to claim 5, wherein the total catalyst concentration is 500 ppm to 800 ppm. The method of claim 1, wherein the content of 4-carboxybenzaldehyde in the prepared terephthalic acid is less than 500ppm.