KR20020029214A - The Preparation method of high purity terephthalic acid with composition of mult-bromic catalytic system - Google Patents

Abstract

PURPOSE: Provided is a process for producing terephthalic acid with high purity in the presence of a composite bromine catalyst using at least two precursors of the bromine, which reduces the cost of catalyst and increases the velocity of reaction. CONSTITUTION: The terephthalic acid is produced by oxidizing p-xylene by molecular oxygen at a temperature of 180-220deg.C in an acetic acid solvent in the presence of the composite catalyst comprising cobalt, manganese, and bromine component produced by mixing tetrabromo ethane and bromic acid as the precursors of the bromine, wherein the content of the bromine from the bromic acid precursor is 10-40wt% based on the total bromine content.

Description

The preparation method of high purity terephthalic acid with composition of mult-bromic catalytic system

The present invention relates to a method for preparing high purity terephthalic acid using a catalyst prepared from para-styrene using a heavy metal such as cobalt and manganese and bromine compounds in an oxygen-containing gas and an acetic acid solvent.

More particularly, the present invention relates to a method for producing high purity terephthalic acid, which can be used for producing polyester fibers without the need for an additional process by economically maintaining high purity by appropriately selecting a precursor of a bromine component.

Recently, in the production of polyester, rather than using the esterification reaction of dimethyl terephthalate, it is produced by the condensation polymerization process of terephthalic acid. However, in order to use the prepared terephthalic acid directly in the polymerization process, it must maintain a high purity. In the production of terephthalic acid, 4-carboxybenzaldehyde, which is a representative impurity, does not obtain a high molecular weight polyester because it serves as a terminator for polymerization when it cannot maintain a concentration below a predetermined level in the produced terephthalic acid.

In addition, when the amount of benzyl, fluorenone, and anthraquinone-based color forming precursors that affect the color is high, the quality of the final polymer may be affected. Therefore, in order to meet the inclusion criteria of terephthalic acid for polyester production, it is generally required to undergo a complex high purity process.

A method for constructing a catalyst system for producing high purity terephthalic acid has already been proposed through various manufacturing processes. According to British Patent 1241298, the oxidation of para xyrene under a catalyst of cobalt, manganese and bromine is carried out at 150-200 ° C. The most important parameter of this reaction is that the ratio of manganese to cobalt exceeds 1 on an atomic basis. It is stated that it should not be. However, the terephthalic acid produced through this process has a high content of 4-carboxybenzaldehyde, which is not suitable for use immediately in preparing polyester. This is due to the relatively low reaction temperature, which results in the formation of undesired oxidation intermediates, which are difficult to get into the crystals of the final product and are difficult to remove, and also cause problems with the color of the finally produced polyester after the polymerization has proceeded. Cause.

This problem can be solved by increasing the size of the reactor or increasing the reaction time. However, from the economic point of view, the cost of equipment increases and causes a new problem of enormous loss of acetic acid used as a solvent.

Japanese Patent No. 36732 deals with a case where the content of manganese is less than 20% by weight of cobalt in a cobalt, manganese, bromine-based catalyst system. When the reaction proceeds in such a catalyst system, high purity terephthalic acid may be obtained using a relatively small amount of catalyst at a reaction temperature of 170-190 ° C. at less than 3000 ppm based on a solvent.

Although the permeability in the alkaline solution is improved when terephthalic acid is produced through this preparation process, it is reported that the content of 4-carboxybenzaldehyde and the side reaction of the solvent reach a serious level. In addition, to lower the content of 4-carboxybenzaldehyde, the yield of the product is significantly reduced. In addition, under high temperature reaction conditions, 4-carboxybenzaldehyde is increased, solvent loss is increased, and the permeation coefficient is lowered.

In order to solve the above problems, the present invention, in the production of terephthalic acid produced by the oxidation reaction of para xylene, to maintain a high purity in the final product at a minimum catalyst cost through the selection of a suitable bromine precursor, the technical problem I put it.

In the present invention, in the liquid phase oxidation of para xylene, cobalt, manganese, and bromine components are used to make a high purity terephthalic acid by producing a catalyst system. By constructing a catalyst system that can ensure high purity and maintain high purity, that is, by using a catalyst prepared by mixing tetrabroethane and bromic acid, the content of 4-carboxybenzaldehyde, a representative by-product, can be lowered to 500 ppm or less without a separate treatment process. The present invention relates to a method for preparing high purity terephthalic acid by implementing an optimal reaction condition.

Hereinafter, the present invention will be described in detail.

The oxidation reaction is carried out at a reaction temperature of 180-220 ° C. by supplying paraxylene and air in an acetic acid solvent. The oxidation reaction uses a known process. Acetic acid containing up to approximately 30% water is used as the solvent in the oxidation reaction.

The catalyst used for oxidizing paraxylene to terephthalic acid uses a mixed catalyst system consisting of a combination of a cobalt component, a manganese metal catalyst and a bromine component.

Cobalt compounds that may be applied to the present invention include cobalt acetate, cobalt naphthalate, cobalt carbonate, cobalt bromide. The amount of catalyst used in this process is 200 to 600 ppm of cobalt atoms, more preferably 250 to 500 ppm, and most preferably 300 to 400 ppm on a solvent basis.

Manganese compounds containing manganese components include manganese acetate, manganese naphthalate, manganese carbonate, manganese bromide, and the like, and an appropriate amount of 0.5 to 1.5 times the weight of cobalt atoms, and most preferably 0.7 to 1.3. If it is out of the above range, the desired high purity terephthalic acid cannot be obtained. In addition, if too little cobalt and manganese components are used, conversion to the intermediate paratoluic acid is not achieved, resulting in a lower yield of the final target product.

As the bromine component, at least one or more of compounds such as bromic acid, manganese bromide, cobalt bromide, sodium bromide, potassium bromide, ammonium bromide and tetrabromethane should be selected and used. However, some bromine compounds have relatively low catalytic activity, so if the bromine precursor is incorrectly selected, the intended effect is difficult to expect.

Tetra bromethane and bromic acid were used in this process. Tetra bromethane is a precursor of bromine, which is generally used in the existing process. Although it is advantageous in terms of stability, it is expensive and its reaction activity is inferior to that of bromic acid. Acids have the advantage of being inexpensive and excellent, whereas they have strong corrosiveness, which has the disadvantage of corrosive process equipment when applied as a single precursor to the process.

The amount of bromine component used is 400 to 2000ppm on solvent basis, most preferably 700 to 1500ppm, and in such a ratio, 2 times or more is preferable on the basis of cobalt, and most preferably 2.5 times or more is added. In particular, when tetrabroethane and bromic acid are mixed to form a catalyst system, it is preferable that the concentration of bromine having bromine as a precursor is 10 to 40% of the total bromine component.

If it is less than 10%, a problem of high cost of the catalyst occurs, and if it is more than 40%, the effective concentration of bromine is lowered due to evaporation of bromic acid, and the concentration of reaction intermediates and impurities rapidly increases, causing problems of quality of terephthalic acid. In addition, this can lead to problems of corrosion of process equipment and generation of by-products. This results in economic losses.

Cobalt bromide and manganese bromide both play the role of cobalt or manganese and bromine in the catalyst system.

The amount of cobalt, manganese and bromine needs to be adjusted in the total amount in the range of 1650 to 1800 ppm in consideration of side reactions and economic aspects. When the total amount of the catalyst is less than 1650ppm, the conversion rate is lowered, the yield of the target product is lowered.

In this invention, a portion of tetra bromethane, which is generally used as a precursor of bromine component, is replaced by bromic acid, which is advantageous in terms of cost, and the applied pressure is reduced by 10 to 10 by a gas containing oxygen to keep the reactant in a liquid phase. It was performed in the range of 20 kg / cm 2.

A gas containing oxygen refers to a gas containing oxygen in an inert gas in the range of 0 to 95%, and specifically refers to air. The total amount of air supplied to the reaction system is preferably supplied in the range of 1 to 100 moles, and more preferably in the range of 3 to 100 moles per mole of parastyrene. Here, when air is used as the gas containing oxygen, the volume-based concentration of oxygen is supplied to be discharged at about 1.5 to 8% in the gas phase discharged through the reaction, and preferably at about 3 to 5%.

Since the reactant obtained through the reaction is obtained in the form of a slurry containing terephthalic acid as a solid, a crystallization step of separating it from the liquid phase is required. A general crystallization method is a method of washing the obtained slurry using water or acetic acid. The slurry washed with water or acetic acid contains terephthalic acid as a suspension solution, and the solid product obtained by separating the liquid phase and the solid phase is dried to obtain the desired product terephthalic acid.

As described in more detail through the following examples, the examples should not be regarded as limiting the present invention.

<Example 1>

The total amount of catalyst used was expressed as the sum of cobalt, manganese, and bromine components. In the case of bromine, the concentration of each catalyst was expressed in ppm units based on the solvent.

Into a 2-liter titanium reactor equipped with a reflux condenser, a stirrer, a heater, a para xylene and an air inlet, 598 g of acetic acid and 30.8 g of distilled water were added, and then a catalyst was added as shown in Table 1 below.

Cobalt acetate 1.26 g Manganese acetate 0.67 g Tetrabromethane 0.574 g Bromic acid 0.067 g

The temperature was adjusted to 195 ° C. and the reaction pressure was adjusted to 15 kg / cm 2, followed by setting the stirrer to 700 rpm. The reaction was carried out for 2 hours while supplying paraxylene at 100 g / hr and supplying air such that the volume-based concentration of oxygen in the outlet was 4%. Thereafter, the reaction was terminated, and additionally, oxygen was further supplied for 2 minutes.

After cooling to 100 ° C., the reactant in the form of a slurry was recovered, cooled with 3 times distilled water, stirred at 80 ° C. for 20 minutes, and the liquid and solid phases were separated and dried.

The composition of each system and the production concentration of 4-carboxybenzaldehyde, which are impurities, are shown in Table 2.

Example 2

In Example 2, all the conditions were carried out in the same manner as in Example 1 except that 0.517 g of tetrabromethane and 0.121 g of bromic acid were added thereto to proceed with the reaction. The results are shown in Table 2.

Example 3

In Example 3, all the conditions were carried out in the same manner as in Example 1 except that 0.453 g of tetrabromethane and 0.181 g of bromic acid were added. The results are shown in Table 2.

Example 4

In Example 4, all the conditions were carried out in the same manner as in Example 1 except that 0.388 g of tetrabromethane and 0.242 g of bromic acid were added to the reaction. The results are shown in Table 2.

Comparative Example 1

In Comparative Example 1, all the conditions were carried out in the same manner as in Example 1 except that 0.179 g of tetrabromethane and 0.424 g of bromic acid were added thereto. The results are shown in Table 2.

division Catalyst condition Response result Co (ppm) Mn (ppm) Br (ppm) Br from TBE (ppm) BrfromHBr (ppm) Total of Catalysts (ppm) 4-CBA (ppm) Example 1 500 250 1000 900 100 1700 338 Example 2 350 350 1000 800 200 1650 349 Example 3 350 350 1000 700 300 1700 391 Example 4 350 260 1000 600 400 1610 470 Comparative Example 1 350 550 1000 300 700 1900 651

According to the present invention, high purity terephthalic acid is used as an efficient method to significantly reduce the catalyst cost and increase the reaction rate by using two or more kinds of precursors of bromine in order to secure economic efficiency in the liquid phase oxidation of para xylene at a temperature between 180-220 ° C. You can get it.

Claims (2)

In preparing tetrapephthalic acid by oxidizing paraxylene by molecular oxygen in a solvent of acetic acid under a catalyst of cobalt, manganese and bromine components, 4-carboxyl was prepared by mixing tetrabroethane and bromic acid as a precursor of bromine. Method for producing high purity terephthalic acid using complex bromine catalyst system, characterized in lowering benzaldehyde to 500ppm or less The method for producing high purity terephthalic acid according to claim 1, wherein the amount of bromine having bromic acid as a precursor in the bromine mixture catalyst system is 10 to 40 wt% based on the total bromine component content.