JPH0559099B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing terephthalic acid obtained by liquid phase oxidation of paraxylene or its oxidized intermediate. In particular, the present invention relates to a method for producing terephthalic acid for direct polymerization without complicated purification steps, that is, terephthalic acid that can be directly polymerized with ethylene glycol and used as a raw material for obtaining polyester. Normally, terephthalic acid for direct polymerization is required to be extremely pure, and in particular, it is required to have an impurity content of 500 ppm or less, typically 4-carboxybenzaldehyde (hereinafter referred to as 4-CBA). has been done. Therefore, conventionally, a complicated process has been used in which terephthalic acid obtained by liquid phase oxidation of paraxylene is dissolved in water and purified by treatment in a hydrogen atmosphere at high temperature and pressure. In view of the above circumstances, the present inventors have completed the present invention as a result of various studies on a method for obtaining high purity terephthalic acid for direct polymerization through a simpler purification process. That is, the present invention involves liquid-phase oxidation of para-xylene or its oxidized intermediate in an acetic acid solvent in the presence of a catalyst consisting of a heavy metal and a bromine compound with oxygen or an oxygen-containing gas to obtain a terephthalic acid slurry; After reducing the impurity concentration in the slurry mother liquor by additionally oxidizing the slurry and/or replacing part or all of this slurry mother liquor with fresh acetic acid, under the conditions that satisfy the following formula (): This is a method for producing terephthalic acid characterized by aging treatment. 500＞{R・a・(1.84−0.0083T)+1.29(
R・b+a)/R+1.29} × {(0.0138T−0.528)−(0.00344T−0.
394)lnθ}() (where, R is the weight ratio of the solvent to terephthalic acid, T is the treatment temperature (°C), a is the amount of 4-carboxybenzaldehyde in terephthalic acid (ppm), b
represents the amount of 4-carboxybenzaldehyde in the mother liquor (ppm), and θ represents the treatment time (minutes). ) Hereinafter, the content of the present invention will be described in detail. The solvent used in the present invention mainly consists of acetic acid and may normally contain 2 to 20% water. Heavy metals such as cobalt and manganese and bromine compounds such as hydrobromic acid, sodium bromide, and tetrabromoethane are used as oxidation catalysts, and paraxylene or its oxidized intermediates are oxidized in a liquid phase using oxygen or an oxygen-containing gas. do. The total amount of cobalt and manganese used in the catalyst is 200 to 2000 ppm (in the liquid), and the ratio of manganese metal to cobalt is 1.0 to 200 wt%.
The amount of the bromine compound to be used is 1.0 to 10.0 times that of cobalt in terms of atomic ratio. The reaction temperature is 180° C. or higher, preferably 190 to 230° C., and the reaction pressure is a pressure that can maintain the system in a liquid phase, that is, 10 to 50 kg/cm ² . The oxygen or oxygen-containing gas used in the present invention is a gas containing 10 to 100% molecular oxygen, and is usually air. The amount used is 3 to 5 mol per 1 mol of baraxylene, and adjusted so that the oxygen concentration in the waste gas is 2 to 8 vol%. Further, in the present invention, the amount of acetic acid solvent to be used relative to para-xylene is related to the treatment process conditions described later, but it is usually used in an amount of 2 to 8 times the weight of para-xylene. After liquid phase oxidation of paraxylene under the above oxidation conditions, the slurry containing terephthalic acid is subjected to additional oxidation treatment, that is, without supplying paraxylene, only oxygen or an oxygen-containing gas is supplied. By doing this, unoxidized substances in the liquid, i.e.
The concentration of impurities in the mother liquor of the slurry is reduced by oxidizing para-toluic acid, 4-CBA, and/or by replacing part or all of the mother liquor of the slurry with fresh acetic acid. After reducing the concentration of impurities, aging treatment is performed under conditions that satisfy the above formula (). Note that R in the above formula () is a solvent ratio, and indicates the weight ratio of the solvent to terephthalic acid. a is the amount of 4-CBA in terephthalic acid before treatment and is expressed in ppm. b is the amount of 4-CBA in the liquid, also expressed in ppm. T is the processing temperature (°C). To explain this aging process in more detail,
R, that is, the solvent ratio, also depends on the ratio of paraxylene to acetic acid solvent during liquid phase oxidation in the previous step, but in order to satisfy the formula (), the mother liquor in the slurry should be replaced with fresh acetic acid or It can be adjusted as desired by diluting or replacing the liquid with the condensate discharged from the condenser, or the hydrated acetic acid recovered by distillation. However, for economic reasons, 2 to 10 is usually preferred. The processing temperature T is any temperature that satisfies the equation (), but if it is below 150°C, the processing effect will be small and it is not practical. Therefore, usually 150~
Perform at a temperature of 280℃. In addition, the aging treatment time θ (holding time) is highly dependent on the treatment temperature, and is in the range of 30 to 300 minutes at temperatures below 200℃, and 120 minutes at temperatures above 200℃.
A retention time of minutes or less is sufficient. As described above, by employing the method of the present invention having such a configuration, impurities in terephthalic acid are reduced, and the desired high quality terephthalic acid for direct polymerization can be obtained. Furthermore, since the present invention can improve the quality of terephthalic acid through relatively simple processing, it can be implemented in either a batch method or a continuous method. Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples, but the present invention is not limited thereto. Example 1 Continuous production of para-xylene using a pressure-resistant titanium reactor equipped with a reflux condenser, a stirring device, a heating device, an inlet for a solvent containing raw materials and a catalyst, a gas inlet, and an outlet for the main reaction slurry. carried out oxidation. Catalyst solution contains 700ppm cobalt and manganese
An acetic acid solution containing 180 ppm of bromine, 2400 ppm of bromine (cobalt acetate, manganese acetate, and hydrobromic acid were used, respectively), and 5% by weight of water was used. This catalyst liquid was continuously supplied at a rate of 1000 parts/hr and paraxylene at a rate of 300 parts/hr. During this time, the reaction temperature is
By maintaining the temperature at 200℃ and continuously drawing out a portion of the condensate from the reflux condenser, the water content of the reaction system is reduced to 8.
It was kept at ~10% by weight. Further, the amount of air fed was adjusted so that the oxygen concentration in the exhaust gas was 3 to 5 vol%. The slurry thus obtained was continuously supplied to a titanium additional oxidation reactor, and additional oxidation was performed at a temperature of 190° C. and an average residence time of 30 minutes. Air was used as the oxygen source for additional oxidation, and the oxygen concentration in the exhaust gas was adjusted to be 8% or less. In addition, 4-CBA in the solid content of this slurry
The concentration is 1200ppm, and the amount of 4-CBA in the mother liquor is approximately
It was 80ppm. By replacing part of the mother liquor of the slurry after this additional oxidation with fresh acetic acid,
The solvent ratio R was 3.3, and the amount b of 4-CBA in the liquid was 10 ppm. Next, the slurry replaced with this new acetic acid is supplied to a titanium pressure-resistant container equipped with a stirring device, a heating device, a flow device, a slurry inlet, and a slurry outlet.
Aging treatment was performed at 220°C for an average residence time of 80 minutes.
After the aging treatment, the slurry was extracted, separated into solid and liquid, washed with acetic acid, and dried. The properties of the obtained terephthalic acid are shown in Table 1. Examples 2 to 6 Slurry after additional oxidation of Example 1 (a:
1200ppm, b: 80ppm), part of it was replaced with fresh acetic acid, and a slurry with the solvent ratio and the amount of 4-CBA in the liquid shown in Table 1 was made.
Each was aged at the temperatures shown in the same table. The quality of the obtained terephthalic acid is shown in Table 1. Comparative Examples 1 to 3 As in Examples 2 to 6, aging treatment was performed under the conditions shown in Table 1. () as seen in this example
When the value obtained by the formula exceeds 500, the quality of the obtained terephthalic acid deteriorates. Example 7 In Example 1, the composition of the catalyst liquid was changed to cobalt.
The same equipment and operation as in Example 1 were used except for using 220 ppm of manganese, 400 ppm of manganese, 1200 ppm of bromine (using cobalt acetate, manganese acetate, and tetrabromoethane, respectively), and 5% by weight of water. However, the reaction temperature was 210°C. Additional oxidation was also carried out in the same manner as in Example 1. The slurry after additional oxidation obtained in this way (4-CBA concentration in the solid content of the slurry is
The amount of 4-CBA in the mother liquor was 1800 ppm (approximately 200 ppm) by replacing that part with fresh acetic acid, so that the solvent ratio R was 4.3 and the amount b of 4-CBA in the solution was 10 ppm.
Next, using the aging device used in Example 1,
A ripening treatment was carried out with an average residence time of 30 minutes. The quality of the obtained terephthalic acid is shown in Table 1. Examples 8 to 10 Using the slurry after additional oxidation of Example 7, part of it was replaced with fresh acetic acid to make a slurry with the solvent ratio and the amount of 4-CBA in the liquid shown in Table 1,
Each was aged at the temperatures shown in the same table. The quality of the obtained terephthalic acid is shown in Table 1. Comparative Examples 4 to 6 A ripening treatment was performed under the same conditions as in Examples 8 to 10 as shown in Table 1. The quality of the obtained terephthalic acid is shown in Table 1. As seen in this example, it can be seen that when the value calculated by formula () exceeds 500, the quality of the obtained terephthalic acid deteriorates.

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Claims (1)

[Claims] 1. In an acetic acid solvent, in the presence of a catalyst consisting of a heavy metal and a bromine compound, paraxylene or an oxidized intermediate thereof is oxidized in the liquid phase with oxygen or an oxygen-containing gas to obtain a terephthalic acid slurry, and then After reducing the impurity concentration in the slurry mother liquor by additionally oxidizing this slurry and/or replacing part or all of the slurry mother liquor with fresh acetic acid, the following formula () is satisfied. A method for producing terephthalic acid characterized by aging treatment under certain conditions. 500＞{R・a・(1.84−0.0083T)+1.29(
R・b+a)/R+1.29} × {(0.0138T−0.528)−(0.00344T−0.
394)lnθ}() (where, R is the weight ratio of the solvent to terephthalic acid, T is the treatment temperature (°C), a is the amount of 4-carboxybenzaldehyde in terephthalic acid (ppm), b
represents the amount of 4-carboxybenzaldehyde in the mother liquor (ppm), and θ represents the treatment time (minutes). )