JPS5949212B2 - Manufacturing method of terephthalic acid - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing terephthalic acid.

The method of producing terephthalic acid by reacting paraxylene with molecular oxygen in an acetic acid solvent in the presence of a heavy metal catalyst is well known as the SD method.

Terephthalic acid is separated by centrifuging the slurry obtained from this reaction, but the mother liquor at this time is usually sent to a distillation column to remove insoluble matter such as water and catalyst, and then acetic acid is recovered and reused. are doing. however,
Since the mother liquor contains active ingredients such as paraxylene, a catalyst, and an oxidation intermediate, it would be of great industrial value if this mother liquor could be recycled as it is to the oxidation reactor. However, the mother liquor contains a small amount of reaction inhibiting substances in addition to the active ingredients, so if the mother liquor is circulated as it is, the reaction contents such as side reactions will deteriorate and the quality of the obtained terephthalic acid will deteriorate. It was not possible to circulate. In view of the above-mentioned circumstances, the present inventors conducted various studies in order to obtain a method for producing terephthalic acid that does not deteriorate the reaction content even if the mother liquor is circulated to the reactor. We have completed the present invention by discovering that when the slurry produced is subjected to additional oxidation treatment without separation, terephthalic acid of good quality can be obtained without inhibiting the reaction even if the mother liquor is circulated to the oxidation reactor. .

That is, the present invention provides a method for continuously producing terephthalic acid by oxidizing paraxylene with molecular oxygen in an acetic acid solvent in the presence of cobalt, manganese, and a bromine compound. Using hydrogen, b)
At least a part of the condensable gas discharged from the oxidation reactor is guided to a distillation column to remove moisture and recover the solvent, and the slurry extracted from the oxidation reactor is heated to 0 to 5
Additional oxidation is carried out without supplying paraxylene in a temperature range as low as 0° C.; d) terephthalic acid is recovered by centrifuging the slurry obtained in the additional oxidation step in No. 9 above;
e) A method for producing terephthalic acid, characterized in that the solvent recovered in step) and the mother liquor after terephthalic acid has been separated in step d) are recycled to an oxidation reactor.

To explain the present invention in detail, the method for producing terephthalic acid, which is the object of the present invention, is a method in which paraxylene is reacted with molecular oxygen in a liquid phase in an acetic acid solvent in the presence of a catalyst containing a heavy metal. Any method is fine. The amount of the solvent used is usually 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 1 part by weight of the oxidized material, and if necessary, aldehydes, ketones, alcohols, para It may contain a reaction accelerator such as aldehyde or water.

Further, cobalt, manganese and bromine compounds are used as the catalyst, but any cobalt and manganese compound containing known cobalt and manganese elements may be used.
Specific examples include cobalt compounds such as cobalt acetate and cobalt naphthenate, and manganese compounds such as manganese acetate and manganese naphthenate.

Hydrogen bromide is used as the bromine compound. If you recycle the reaction mother liquor by using, for example, sodium bromide without using hydrogen bromide, some bromine will be lost during the reaction and Na+ will remain in the mother liquor. The Na+ concentration in the reaction system gradually increases due to the sodium bromide supplemented. Therefore,
The contents of the oxidation reaction deteriorate. The amount of catalyst used is usually 200-5000% of the cobalt compound relative to the solvent.
P, preferably 200-600 IP (as cobalt metal), the manganese compound is 10-1000 IP relative to the solvent
P1 is preferably 100 to 600 PI (as manganese metal), and the bromine compound is 400 to 10,00 PI to the solvent.
0P1 is preferably selected from the range of 600 to 2000P. When a catalyst within the above range is used, a good oxidation reaction can be carried out when carrying out the mother liquor recycling of the present invention. The reaction temperature in the present invention is usually 150 to 2
The temperature may be 50°C, but especially when using a catalyst within the above range, the temperature may be 170-230°C, preferably 205-230°C.
25°C is desirable.

Further, the reaction pressure is usually normal pressure to 200 atm, preferably normal pressure to 100 atm. Furthermore, air is usually used as the gas containing molecular oxygen to be supplied into the liquid phase.
The supply amount is, for example, 1 to 10 oxygen per mole of the oxidized material.
0 mol, preferably in the range of 3 to 100 mol.

The reaction slurry obtained by the above-mentioned oxidation reaction is then subjected to additional oxidation treatment. This treatment is for further oxidizing the oxidized intermediate contained in the reaction slurry, and the concentration of the molecular oxygen-containing gas supplied may be lower than in the oxidation reaction. It is usually preferable to utilize a portion of the waste gas from the oxidation reactor. The temperature of additional oxidation is 0 than the oxidation reaction temperature.
The temperature range is preferably lower than 50°C, preferably 0°C to 30°C. During additional oxidation, it is sufficient to add no additional oxidation catalyst. Additional oxidation treatment may be carried out by providing an additional oxidation tank, but
They may be carried out simultaneously using a cooling crystallization tank. The reaction slurry subjected to the additional oxidation treatment is cooled and crystallized according to a conventional method, and then separated into terephthalic acid and mother liquor using a centrifuge.

In the present invention, it is essential to circulate this mother liquor as it is to the oxidation reactor. The mother liquor may be circulated in its entirety, but
For example, 20-50% by weight may be purged and used mixed with fresh solvent and catalyst. On the other hand, in the present invention, since the mother liquor is circulated as it is to the reactor, it is necessary to remove water generated by the reaction.

If the water concentration becomes too high, the reaction will deteriorate, so
Generally, it is preferred that the water concentration be about 20% by weight or less. In the present invention, at least a portion of the condensable gas from the reactor is extracted, moisture is removed in a distillation column, and the solvent is recovered and reused. In this case, the distillation column is not necessarily installed independently from the reactor; for example, the distillation column is connected directly to the soil of the reactor, and moisture and non-condensable gases are removed from the top of the column. The reactive gas may be of the type that is returned to the reactor. The condensable gas extracted from the reactor is usually condensed in a condenser, most of it is returned to the reactor, and a part of the condensate is led to a distillation column. Distillation is usually carried out at normal pressure, for example at a temperature of 124°C at the bottom of the column.
, the temperature at the top of the tower is about 100°C.

The solvent recovered here is recycled to the oxidation reactor. Next, the continuous process of the present invention will be explained in detail with reference to FIG. FIG. 1 is a process diagram showing a method for producing terephthalic acid as an example of the present invention. Paraxylene is supplied to the oxidation reactor 1 through a pipe 2, and a solvent containing a catalyst is supplied through a pipe 3. Also, air is supplied from the pipe 4 to carry out the oxidation reaction. The reaction slurry is supplied to an additional oxidation container 7 through a pipe 6, and is subjected to an additional oxidation treatment by blowing diluted air through a pipe 8.

The additionally oxidized reaction slurry is completely crystallized in a crystallizer 9, and then terephthalic acid is separated in a centrifugal separator 10 and recovered through a pipe 13. On the other hand, the mother liquor is in pipe 11
is circulated through the pipe 5 to the oxidation vessel 1. Also,
A portion of the mother liquor is purged through pipe 12. The condensable gas generated from the top of the oxidation reactor 1 is condensed by the condenser 15, most of it is returned to the oxidation reactor, and the remaining condensate is led to the distillation column. In the distillation column 16, water is removed from the upper pipe 17, and the solvent is recovered from the lower part. The recovered solvent is circulated to the oxidation reactor 1 via a pipe 5. As mentioned above, both the recovered solvent and mother liquor are supplied to the oxidation reactor 1 through pipe 5, but new solvent and catalyst corresponding to the loss and purge are supplied through pipe 3, and continuous operation is performed. . According to the present invention, even if the mother liquor of the reaction slurry is circulated as it is to the oxidation reactor, the reaction content does not deteriorate, so terephthalic acid of good quality can be obtained. In addition, paraxylene in the mother liquor,
Active ingredients such as oxidation intermediates and catalysts can be used without waste,
It is extremely advantageous industrially. The reason why the reaction content does not deteriorate even when the mother liquor is circulated in the present invention is that reaction inhibiting substances are substantially eliminated by additionally oxidizing the slurry produced after the reaction. Next, the present invention will be explained in more detail with reference to Examples.

Example 1 4.4 ml of cobalt acetate (tetrahydrate) was placed in a titanium pressure-resistant reactor 1 with an internal volume of 102 equipped with a stirring device and an external heating device.
39, an acetic acid solvent (moisture 5 wt%) containing 4.689 manganese acetate (tetrahydrate) and 6.79 f1 of hydrobromic acid (47% aqueous solution) was charged, reaction temperature was 210°C, and reaction pressure was 24 Kf/ClM. Under the conditions of G, the raw material paraxylene was charged and 7509/Hrl air was introduced from the pipe 4 so that the oxygen concentration in the reactor waste gas was 4 to 5v01 (Fb), and the reaction was carried out semi-continuously for 1.5 hours. I did this.

Next, a newly prepared acetic acid solvent having the same catalyst composition as above was charged from pipe 3 to 2250f! /Hr, and the reaction slurry is supplied from the extraction pipe 6 at a rate of 36009/Hr.
A continuous oxidation reaction was conducted at a rate of r and the average residence time in the reactor 1 was 60 minutes. The reaction slurry extracted from the reactor 1 is sent to a titanium pressure-resistant container 7 (additional oxidation container) with an internal volume of 101 equipped with a stirring device and an external heating device, and is heated at a temperature of 195° C. and a pressure of 19 Kf/d-G. At an average residence time of 40 minutes, diluted air with an oxygen concentration of 14v01% is introduced from the inlet pipe 8 until the oxygen concentration in the additional oxidizer waste gas is 3 to 4v0.
It was blown in to give a concentration of 1%. After the additionally oxidized reaction slurry was sent to a crystallizer 9 and crystallized at 100° C., it was separated into terephthalic acid and a reaction mother liquor. After 3 hours from starting the continuous oxidation reaction, the solution prepared by replenishing the reaction mother liquor obtained in this way with the catalyst components that had disappeared through the reaction was transferred from the charging pipe 5 to 1250f! /Hr, and the remaining part is purged, and the catalyst-containing acetic acid solvent is supplied from the charging pipe 3 at 1100f! /Hr.

In order to prevent the water concentration in the mother liquor in reactor 1 from increasing due to this reaction mother liquor recycling, the condensable gas entrained in the reactor waste gas, which was refluxed in its entirety for up to 3 hours of continuous reaction, was condensed. A portion of the solution was extracted, and the same amount of acetic acid as contained in the extracted liquid (on an industrial scale, this is recovered from a distillation column, but in this example, a distillation column was not used) was newly added. The water concentration in the mother liquor in the reactor was adjusted to 18 wt%. The above mother liquor recycling reaction was carried out for 30 hours, and the solid-liquid separated terephthalic acid was suspended washed with 3 times the weight of acetic acid solvent at 80° C. for 20 minutes. The properties of the obtained terephthalic acid are shown in Table 1.

Comparative Example 1 (Reference Example) A continuous oxidation reaction was carried out in the same manner as in Example 1, except that the mother liquor was not recycled and the reflux liquid was not partially withdrawn.

The properties of the obtained terephthalic acid are shown in Table 1. As is clear from the above Example 1 and Comparative Example 1, in the case of additional oxidation treatment, the properties of the terephthalic acid obtained even when the reaction mother liquor is recycled to the oxidation reactor are different from those of Comparative Example 1 in which the mother liquor is not recycled. The properties were comparable to those of terephthalic acid obtained in .

Comparative Example 2 Para-xylene was supplied at 5009/Hrl, and the semi-continuous reaction time was 2 hours, and in the continuous reaction, the catalyst-containing acetic acid solvent was supplied at 15009/Hr, and the average residence time in reactor 1 was approximately 90 minutes. A continuous oxidation reaction was carried out for 30 hours in the same manner as in Comparative Example 1 except that additional oxidation in the oxidation vessel was not performed.

The properties of the obtained terephthalic acid are shown in Table 1.
Comparative Example 3 The obtained reaction mother liquor was poured into the charging tube at 830 f!4 hours after the start of the continuous reaction. /Hr and the catalyst-containing acetic acid solvent supplied from charging pipe 3 was reduced to 7509/Hr, and the water concentration in the mother liquor of reactor 1 was 18%. The sample was prepared in the same manner as above, and the mother liquor recycling reaction was carried out for 30 hours.

The properties of the obtained terephthalic acid are shown in Table 1. As shown in the above results, the terephthalic acid obtained when the reaction mother liquor without additional oxidation treatment is recycled to the reactor (Comparative Example 3) is the same as the terephthalic acid obtained in the reaction without mother liquor recycling and additional oxidation (Comparative Example 2). Compared to terephthalic acid, the content and transmittance of 4-carboxybenzaldehyde, which is an impurity oxidation intermediate, were significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a process for producing terephthalic acid as an example of the present invention, in which 1 is an oxidation reactor, 7 is a process for producing terephthalic acid, and
16 indicates an additional oxidation vessel, and 16 indicates a distillation column.

Claims (1)

[Claims] 1. In a method for continuously producing terephthalic acid by oxidizing paraxylene with molecular oxygen in an acetic acid solvent in the presence of cobalt, manganese and a bromine compound, a) hydrogen bromide is used as the bromine compound. , 2) At least a part of the condensable gas discharged from the oxidation reactor is guided to a distillation column to remove moisture and recover the solvent, and 3) the slurry extracted from the oxidation reactor is heated to a temperature 0 to 50°C lower than the reaction temperature. Additional oxidation is performed within a temperature range without supplying paraxylene, and d)
Terephthalic acid is recovered by centrifuging the slurry obtained in the additional oxidation step in c) above, and e) the solvent recovered in b) above and the mother liquor after terephthalic acid has been separated in d) are subjected to an oxidation reaction. A method for producing terephthalic acid characterized by circulating it in a vessel.