JPS5933579B2 - Method for producing terephthalic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing terephthalic acid by liquid phase oxidation of paraxylene or its oxidized intermediate with a molecular oxygen-containing gas.

More specifically, it relates to a bromine catalyst component that can produce high-quality terephthalic acid with a low content of 4-carboxybenzaldehyde in this liquid phase oxidation reaction, and can reduce the loss of bromine catalyst due to the reaction. Traditionally, terephthalic acid has been produced by oxidizing paraxylene with molecular oxygen-containing gas under high temperature and pressure in an acetic acid solvent in the presence of an oxidation catalyst containing cobalt, manganese, and bromine. It has been adopted.

The bromine catalyst components of this oxidation catalyst include cobalt bromide,
Bromine compounds of heavy metals such as manganese bromide, bromine compounds of alkali metals such as sodium bromide and potassium bromide, inorganic bromine compounds such as ammonium bromide and hydrobromic acid: ethane tetrabromide, benzyl bromide, tetrabromo paraxylene,
The use of organic bromine compounds such as monobromoacetic acid and bromoform is disclosed in Japanese Patent Publication No. 34-2666, Japanese Patent Publication No. 49-25936, Japanese Patent Application Publication No. 48-5738, Japanese Patent Application Publication No. 49-135940, Kaisho 51-43
It has been proposed in Publication No. 734, etc. Among these publicly known documents, Japanese Patent Publication No. 49-25936, Japanese Patent Publication No. 48
-5738 publication, JP-A-49-135940 publication,
JP-A No. 51-43734 uses hydrobromic acid, tetrabromoparaxylene, monobromoacetic acid, or bromoform as the bromine catalyst component, and furthermore, these bromine catalyst components have specific harmful effects on the cobalt catalyst component. It has been described that by using a catalyst system consisting of cobalt, manganese and bromine with a specific composition formulated in the same manner as above, it is possible to produce high quality terephthalic acid as a raw material for the production of polyethylene terephthalate by a direct polymerization method. However, when using a bromine compound of cobalt or manganese as a bromine catalyst component in an oxidation catalyst containing cobalt, manganese, and bromine, the catalyst solution supplied to the reactor or the mother liquor from which terephthalic acid has been separated after the reaction must be recycled and reused. In some cases, the catalyst composition consisting of the cobalt catalyst component, the manganese catalyst component, and the bromine catalyst component in these catalyst solutions or circulating mother liquors cannot be adjusted to a specific composition that allows high-quality terephthalic acid to be produced.

Furthermore, when a bromine compound of another metal is used as a bromine catalyst component, the metal ion may have a negative effect on the oxidation reaction rate and the quality of terephthalic acid. Furthermore, when hydrobromic acid is used as the bromine catalyst component, the oxidation reaction is carried out under high temperature and pressure, so even if a corrosion-resistant material such as titanium is used, there is a major drawback in that the equipment is severely corroded. . On the other hand, in order to industrially and economically produce high-quality terephthalic acid, the mother liquor containing the oxidation catalyst obtained by separating terephthalic acid from the oxidation reaction product mixture is usually recycled and reused.

When circulating and reusing the mother liquor, the concentration of each catalyst component in the mother liquor generally decreases, and the concentration of the bromine catalyst component decreases at a particularly large rate, so the concentration and composition ratio of each of these catalyst components must be readjusted. It is necessary. When bromine compounds such as tetrabromide ethane, monobromoacetic acid, and bromoform are used as bromine catalyst components, these bromine compounds are decomposed in the reaction system and a considerable portion of them is lost from the reaction system. The decrease in component concentration is particularly significant. Therefore, when these bromine compounds are used as bromine catalyst components, the amount of bromine catalyst used increases,
As a result, there is a drawback that it is difficult to economically produce terephthalic acid. In addition, when a benzyl-position bromine compound such as benzyl bromide, α・α・α7・α7-tetra-bromoparaxylene is used as a bromine catalyst component,
These bromine compounds have strong lachrymatory and irritating properties, and therefore have the drawback of interfering with operations such as preparation of catalyst solution and adjustment of catalyst composition in circulating mother liquor. The present inventors have developed an oxidation catalyst containing cobalt, manganese, and bromine used in the liquid phase oxidation reaction of paraxylene or its oxidized intermediate, in order to solve the various problems of the conventional bromine catalyst components described above. As a result of searching for a new bromine catalyst component, it was discovered that these problems could be solved by using a bromoalkyl lower aliphatic carboxylate having a carbon number in the range of 4 to 6, and the present invention was achieved. It is.

According to the method of the present invention, by using a bromoalkyl lower aliphatic carboxylate as a bromine catalyst component in a catalyst containing cobalt, manganese, and bromine, the loss during oxidation reaction is greater than that of conventional bromine catalyst components. The proportion of the bromine catalyst component that is added to the bromine catalyst component is reduced, and the rate of decrease in the concentration of the bromine catalyst component contained in the mother liquor obtained by separating terephthalic acid is also reduced. As a result, when the reaction mother liquor is recycled and reused, the amount of the bromine catalyst component used can be reduced, and terephthalic acid can be produced more economically. In addition, by using the bromine catalyst component of the present invention, terephthalic acid can be obtained which has a lower content of 4-carboxybenzaldehyde and a lower optical density at 340 mμ compared to bromine catalyst components made of conventional organic bromine compounds. It has the characteristic of being Therefore, by selecting the reaction conditions such as the concentration of each catalyst component, its composition, reaction temperature, and the ratio of acetic acid solvent to the oxidized product as described below, polyethylene can be produced by direct polymerization through a one-step oxidation reaction. It is possible to economically produce high-quality terephthalic acid that can be used as a raw material for producing terephthalate. That is, the present invention provides a method for producing terephthalic acid by liquid-phase oxidation of para-xylene or its oxidized intermediate with a molecular oxygen-containing gas in an acetic acid solvent in the presence of an oxidation catalyst containing cobalt, manganese, and bromine. , is a method for producing terephthalic acid, characterized in that a bromoalkyl lower aliphatic carboxylate having a carbon number in the range of 4 to 6 is used as a bromine catalyst component.

In the method for producing terephthalic acid of the present invention, the oxidizable material used as a raw material is paraxylene or an oxidized intermediate thereof.

For example, specific examples include paraxylene, paratolualdehyde, paratolylic acid, and the like. Among these oxidizable substances, it is particularly preferable to apply the method of the present invention to paraxylene. The liquid phase oxidation reaction of paraxylene or its oxidized intermediate according to the method of the present invention is carried out in an acetic acid solvent.

The acetic acid medium used in this liquid phase oxidation reaction does not need to be pure acetic acid, and usually acetic acid containing 5 to 15% by weight of water is used. The water concentration in the mother liquor in the reaction system during the oxidation reaction is generally maintained in the range of 5 to 15% by weight, preferably in the range of 7 to 12% by weight. Further, the amount of the acetic acid solvent used is usually in the range of 2 to 10, preferably 3 to 6 in weight ratio to paraxylene. The molecular oxygen-containing gas used in the oxidation reaction of the present invention is usually air, but may also be oxygen gas or a mixed gas of oxygen gas and other inert gas in any proportion.

The amount of molecular oxygen-containing gas supplied during the oxidation reaction is such that the oxygen concentration in the exhaust gas from the oxidation reaction system is usually 2 to 8%;
It is preferably supplied in a range of 3 to 6%. In the method for producing terephthalic acid of the present invention, the oxidation reaction of paraxylene or its oxidized intermediate is carried out in the presence of a catalyst containing cobalt, manganese and bromine.

Here, as the cobalt catalyst component and the manganese catalyst component, a cobalt compound and a manganese compound that can be dissolved in an acetic acid solvent to generate cobalt ions and manganese ions, respectively, are used in the reaction system. As the cobalt catalyst component, it is preferable to use a cobalt salt of an organic carboxylic acid such as cobalt acetate, cobalt propionate, cobalt benzoate, or cobalt naphthenate. Preference is given to using salt.
The bromine catalyst component of the oxidation catalyst containing cobalt, manganese and bromine used in the process of the present invention is a bromoalkyl lower aliphatic carboxylate having a carbon number in the range of 4 to 6.

Specifically, the lower aliphatic carboxylic acid bromoalkyl compounds include, for example, monobromopropyl formate, dibromopropyl formate, monobromoethyl acetate, dibromoethyl acetate, monobromopropyl acetate, dibromopropyl acetate,
Examples include monobromoethyl propionate, dibromopropyl propionate, monobromoethyl butyrate, dibromoethyl butyrate, and the like. Among them, dibromoethyl acetate,
It is particularly preferred to use at least one bromoalkyl lower aliphatic carboxylate selected from the group consisting of dibromopropyl acetate, monobromoethyl acetate and monobromopropyl acetate as the bromine catalyst component, and dibromoethyl acetate is particularly preferred. This is particularly preferred. In the method of the present invention, the amounts of each catalyst component constituting the oxidation catalyst containing cobalt, manganese, and bromine are as follows.

Among the catalyst components, the amount of cobalt catalyst component used is usually 0.1 x 1 cobalt atom per acetic acid solvent 17.
In the range of 0-5 to 5.0 x 10-5 gram atoms. In addition, the amount of manganese catalyst component used is usually 0 as the atomic ratio of manganese to cobalt atoms in the cobalt catalyst component.
．． It ranges from 001 to 1,0. The amount of the bromine catalyst component used is usually in the range of 1 to 4 as the atomic ratio of the bromine atoms to the sum of the cobalt atoms and manganese atoms in the cobalt catalyst component and the manganese catalyst component. Furthermore, the oxidation catalyst containing cobalt, manganese, and bromine used in the method of the present invention may contain other metal catalyst components as necessary in addition to the above-mentioned essential three components, the cobalt catalyst component, the manganese catalyst component, and the bromine catalyst component. There is no problem even if it contains. In the method for producing terephthalic acid according to the method of the present invention, the liquid phase oxidation reaction of paraxylene or its oxidized intermediate is carried out under high temperature and pressurized conditions.

The reaction temperature is usually in the range of 170 to 230°C, preferably in the range of 180 to 220°C. The pressure during the oxidation reaction is arbitrary as long as it maintains the oxidation reaction product mixture in the reaction system in a liquid phase. The liquid phase oxidation reaction of the present invention is carried out under stirring. The stirring intensity at this time is arbitrary, but it is preferable that the stirring intensity is moderate because it affects the oxidative decomposition of the acetic acid solvent during the oxidation reaction.By suppressing the oxidative decomposition of acetic acid, terephthalic acid can be produced In order to improve the economical efficiency during this process, it is preferable to use strong stirring to improve the contact between gas and liquid. For example, in order to suppress the oxidative decomposition of acetic acid during the oxidation reaction, the stirring intensity is usually in the range of 1.0 to 10 horsepower, preferably in the range of 1.5 to 5.0 horsepower per m5 of the oxidation reaction mixture. be. In the method of the present invention, terephthalic acid is obtained by treating the oxidation reaction product mixture obtained by the liquid phase oxidation reaction according to a conventional method.

For example, a method for crystallizing and separating terephthalic acid from a mono-oxidation reaction product mixture in a multi-stage crystallization tank operated under slow cooling conditions, and a method in which most of the mother liquor in the 2-oxidation reaction product mixture is cooled too much from the reaction temperature. A method of replacing terephthalic acid with heated acetic acid under high temperature and pressure, followed by immersion treatment under high temperature and pressure, and then separating terephthalic acid, and directly flashing the trioxidation reaction product mixture under normal pressure to crystallize terephthalic acid. Examples include a method of post-separation. Regardless of the post-treatment performed by any of these methods, the mother liquor separated from the oxidation reaction product mixture contains cobalt catalyst components, manganese catalyst components, and bromine catalyst components, making it possible to economically process terephthalic acid. For production, it is preferable to reuse the mother liquor by recycling it to the oxidation reaction system. When the mother liquor is recycled and reused, the water concentration contained in the mother liquor can be adjusted to the above-mentioned preferred range by operations such as distillation, as necessary. A portion of the mother liquor can also be purged to avoid impurity build-up due to use. In the method of the present invention, when lower aliphatic bromoalkyl carboxylates having carbon numbers in the range of 4 to 6 are used as the bromine catalyst component, the bromine catalyst component is lower than when other organic bromine compounds are used. Since the residual rate in the mother liquor is high, it is particularly preferable to circulate and reuse the mother liquor. Furthermore, in the method of the present invention, one step can be carried out by selecting the reaction conditions such as the concentration of each catalyst component of the oxidation catalyst, their composition ratio, reaction temperature, and the ratio of acetic acid solvent to the oxidized product within the preferred ranges shown below. High quality terephthalic acid, which can be used as a raw material for producing polyethylene terephthalate by direct polymerization, can be produced by the acidification reaction.

The conditions are that the amount of the cobalt catalyst component of the oxidation catalyst containing cobalt, manganese and bromine used is 0.1 x 10-5 to 5.
The amount of manganese catalyst component used is in the range of 0.001 to 1.0 as the atomic ratio of manganese to cobalt atoms in the cobalt catalyst component, and the amount of manganese catalyst component used is in the range of 0.001 to 1.0. The amount used is 1 as the atomic ratio of bromine atoms to the sum of cobalt atoms and manganese atoms in the cobalt catalyst component and manganese catalyst component.
The range is from 1 to 4. The weight ratio of the acetic acid solvent to paraxylene or its oxidized intermediate is in the range of 3 to 6, and the reaction temperature is in the range of 180 to 220°C. Further, the water concentration in the mother liquor of the oxidation reaction system is preferably maintained in the range of 7 to 12% by weight, and the oxygen concentration in the exhaust gas from the oxidation reaction system is preferably maintained in the range of 3 to 6%. . Next, the method of the present invention will be specifically explained using examples.

In addition, in the Examples and Comparative Examples, the optical density (0D) of noterephthalic acid at 340 mμ is defined as the cell length of 1CTr1,
This is the optical density measured using a cell. Also, 4-carboxybenzaldehyde (4-CB) in terephthalic acid
The content of A) is a value measured by polarography. In addition, the bromine content in the reaction mother liquor is 5 ml of reaction mother liquor.
30 ml of a 15% by weight aqueous sodium hydroxide solution was added to the solution, heated under reflux for 30 minutes, and then quantified using a conventional silver nitrate titration method, and the amount of bromine loss was calculated from the results. Example 1 1.057 g of cobalt acetate tetrahydrate was placed in a titanium-lined rotary stirring autoclave with an internal volume of 500 m1.
(0.0042 mol), manganese acetate tetrahydrate 0.52
7 (0.0021 mol), α/β dibromoethyl acetate 1
．． 16y (0.0047 mol) and acetic acid 199.57
and 10.5 y of water were added, the autoclave was closed, and air was blown at a speed of 31 m/m at a temperature of 200°C and a pressure of 15 kg/Cd while rotating and agitating the para-xylene at 217 (0.20 y). The reaction was carried out for 2 hours while feeding at a rate of mol/Hr).

After the reaction was completed, the mixture was separated, washed with water, and dried to obtain terephthalic acid 62y (yield: 93%). The analysis results for terephthalic acid are shown in Table 1. Moreover, the loss rate of bromine at this time was 12%. Comparative Examples 1 to 3 In Example 1, 0.82 (0.0024 mol) of tetrabromide ethane (Comparative Example 1) and 1.317 (0.0094 mol) of monobromoacetic acid (Comparative Example 2) were used as bromine compounds, respectively.
) and bromoform 0.807 (0.0032 mol)
Terephthalic acid was obtained in the same manner as in Example 1 except for (Comparative Example 3).

Table 1 shows the analysis results of terephthalic acid and the bromine loss ratio.
Examples 2 to 8 All the procedures in Example 1 were repeated except that the compounds shown in Table 2 and their amounts were used as bromine compounds. Terephthalic acid was obtained in the same manner as in Example 1.

Table 2 shows the analysis results of terephthalic acid and the bromine loss ratio.
Examples 9 to 11 In Example 1, the amounts of cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and α/β-dibromoethyl acetate used as catalysts were all as shown in Table 3. Terephthalic acid was obtained in the same manner as in Example 1.

Claims (1)

[Claims] 1. A method for producing terephthalic acid by liquid-phase oxidation of paraxylene or its oxidized intermediate with a molecular oxygen-containing gas in an acetic acid solvent in the presence of an oxidation catalyst containing cobalt, manganese, and bromine. A method for producing terephthalic acid, characterized in that a bromoalkyl lower aliphatic carboxylate having a carbon number in the range of 4 to 6 is used as the bromine catalyst component. 2. At least one bromoalkyl lower aliphatic carboxylate selected from the group consisting of dibromoethyl acetate, dibromopropyl acetate, monobromoethyl acetate, and monobromopropyl acetate is used as the bromine catalyst component. The method according to claim 1. 3. The method according to claim 1, characterized in that dibromoethyl acetate is used as the bromine catalyst component.