JPH09278709A - Production of aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aromatic dicarboxylic acid excellent in quality and color tone of polymerization while extremely preventing combustion loss of acetic acid as a reaction solvent. SOLUTION: An alkyl aromatic hydrocarbon (e.g. p-xylene) is oxidized in an acetic acid solvent in the presence of a catalyst containing cobalt, manganese and bromine in a liquid phase at 140-180 deg.C to give the objective aromatic carboxylic acid. Preferably, the amount of the cobalt compound is 400-3,000wt. ppm calculated as cobalt metal based on the acetic acid solvent, the amount of the manganese component is 0.001-0.4 by the atomic ratio to cobalt and the amount of the bromine component is 0.1-5.0 by the atomic ratio to cobalt. A condensable component discharged from a reactor in the reaction is condensed and removed to give an oxidizing exhaust gas, which is partially supplied to a liquid phase of the reactor. The reaction pressure is preferably raised more than the pressure in which the oxidizing exhaust gas is neither circulated nor supplied, by using air as a molecular oxygen-containing gas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an aromatic carboxylic acid. More specifically, the present invention relates to a method for producing a high-quality aromatic carboxylic acid while largely preventing combustion loss of acetic acid, which is a reaction solvent, in a liquid phase oxidation reaction of an alkyl aromatic hydrocarbon.

[0002]

BACKGROUND ART As a method for producing an aromatic carboxylic acid such as terephthalic acid, industrially, an alkyl aromatic hydrocarbon such as paraxylene is used as a catalyst containing cobalt, manganese and bromine in an acetic acid solvent. The most general method is to carry out a liquid-phase oxidation reaction with molecular oxygen in the presence.

Taking the production of terephthalic acid by the liquid phase oxidation reaction of paraxylene as an example, it is one of the reaction intermediates.
-Carboxybenzaldehyde (hereinafter referred to as "4CBA"), or many impurities generated by side reactions are mixed in terephthalic acid, so the quality of the product terephthalic acid, especially the light at 340 nm when dissolved in an alkaline aqueous solution of terephthalic acid. The transmittance (hereinafter referred to as “transmittance”) changes. In the industrial production of high-purity terephthalic acid, generally, the quality of the product is judged and controlled by using the 4CBA content and the transmittance of the product terephthalic acid as indexes.

Generally, the quality of terephthalic acid can be controlled by selecting the oxidation reaction conditions such as the reaction temperature of the oxidation reactor, the amount of catalyst used, and the residence time. However, generally, in order to produce a high-quality terephthalic acid having a low 4CBA content and a high transmittance, it is necessary to make the conditions of the oxidation reaction severe, such as increasing the reaction temperature and increasing the catalyst concentration. Accompanying this, there is a problem that the acetic acid solvent burns or decomposes, the amount of loss increases, and the production cost of terephthalic acid increases.

When the reaction temperature of the oxidation reaction is lowered in order to prevent the loss due to the combustion or decomposition of acetic acid, at the same time, the reaction activity also largely decreases, and the 4CBA content present in the obtained terephthalic acid is high, and the permeation rate is high. Only poor quality terephthalic acid can be obtained. Looking at the publicly known documents, no reaction example applied to industrial production in a temperature range of 180 ° C. or lower is found, except in a special case where an oxidation reaction system using a reaction accelerator such as a co-oxidant is adopted. . In addition, 18
Even if the temperature range of 0 ° C. or less can be set, it is necessary to set conditions such as an extremely high catalyst concentration, which is a great disadvantage in terms of the quality and manufacturing cost of terephthalic acid.

In the above-mentioned method for producing an aromatic carboxylic acid by the liquid phase oxidation reaction of an alkylaromatic hydrocarbon, there are the following major improvements in recent years. Japanese Examined Patent Publication (Kokoku) No. 5-32381 discloses that a partial oxidation gas is circulated and supplied to the liquid phase part of the reactor to increase the oxygen partial pressure in the gas phase part of the reaction system to carry out the oxidation reaction.
A method for obtaining terephthalic acid having good transmittance is disclosed. In this method, the effect of improving the transmittance of terephthalic acid and the polymerization color tone is recognized. However, the equivalent 4C
The amount of acetic acid solvent burned or decomposed when producing terephthalic acid containing BA is almost the same as that in the conventional method.

Japanese Patent Publication No. 7-88211 discloses a method of circulating and supplying a part of oxidizing exhaust gas to a gas phase portion of a reactor. This method is shown to have the effect of suppressing foaming generated in the reactor and allowing the reaction to be carried out stably. However, when the oxidizing exhaust gas is circulated and supplied to the gas phase part, the acetic acid solvent is unlikely to be saturated, and compared with the case where the oxidizing exhaust gas is circulated and supplied to the liquid phase part, the effect of improving the transmittance of terephthalic acid is obtained. Hateful.

Japanese Unexamined Patent Publication No. 7-278048 discloses a method of circulating and supplying a part of oxidizing exhaust gas when a high-concentration oxygen-containing gas containing molecular oxygen at a higher concentration than air is used as an oxygen source gas. Has been done. However, it is extremely disadvantageous in terms of manufacturing cost to use a gas containing a high concentration of oxygen. Further, when the oxygen partial pressure in the gas phase of the reactor is kept constant, the circulation amount of the oxidizing exhaust gas must be increased as compared with the case where air is used, and the circulation blower capacity is increased or consumption power is increased. It is a cost disadvantage. Further, since the high-concentration oxygen-containing gas is used, the reaction pressure in the example becomes the same as the reaction pressure when the exhaust gas is not circulated and supplied in the oxidation reaction using air which is the condition of Comparative Example 1. The above-mentioned special fair 5-
As described in Japanese Patent No. 32381, it is difficult to obtain the effect of increasing the oxygen partial pressure in the gas phase portion of the reaction system.

In the above three improved inventions, as is clear from the examples, 4CBA contained in terephthalic acid is used.
The effect of improving the transmittance or polymerization color of terephthalic acid obtained when carrying out an oxidation reaction with a constant concentration is recognized, but the amount of acetic acid solvent lost by combustion or decomposition at that time can be reduced. Not not.

[0010]

SUMMARY OF THE INVENTION In view of the above circumstances, the present inventors have proposed a method for significantly reducing the amount of loss due to combustion of an acetic acid solvent in producing an aromatic carboxylic acid having particularly excellent quality and polymerization color tone. As a result of various studies, by circulating and supplying a part of the oxidizing exhaust gas to the liquid phase portion of the reactor,
The reaction pressure is higher than that when air is used as the molecular oxygen-containing gas and the oxidizing exhaust gas is not circulated, that is, the oxygen partial pressure in the gas phase of the reactor is efficiently increased to carry out the oxidation reaction. In doing so, by carefully selecting the combination of reaction temperature and catalyst composition, and further combining them, the combustion loss of acetic acid, which could not be achieved by the conventional method, was significantly reduced, and the quality such as transmittance was extremely excellent. It was found that an aromatic carboxylic acid can be produced, and the present invention has been completed.

That is, the gist of the present invention is to subject an aromatic aromatic hydrocarbon to liquid-phase oxidation of an alkylaromatic hydrocarbon in a solvent of acetic acid in the presence of a catalyst component containing cobalt, manganese, and bromine with a gas containing molecular oxygen. In the method for producing an acid, (1) the reaction temperature is 140 ° C. or higher and 180 ° C. or lower, and (2) the amount of the cobalt component is 400 ppm by weight or more and 3000 weight pp in terms of cobalt metal based on the acetic acid solvent.
m or less, and (3) the amount of the manganese component is 0.001 times or more and 0.4 times or less in terms of atomic ratio to cobalt.
(4) The amount of bromine component is 0.1 in terms of atomic ratio to cobalt.
In the presence of a catalyst component that is more than twice and less than 5.0 times, (5)
Part of the oxidizing exhaust gas obtained by condensing and removing the condensable components from the gas extracted from the reactor is circulated and supplied to the liquid phase part of the reactor, and (6) the reaction pressure is air as the molecular oxygen-containing gas, In addition, a method for producing an aromatic carboxylic acid is characterized in that the pressure is raised to a pressure higher than when the oxidizing exhaust gas is not circulated and supplied.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, an alkyl aromatic hydrocarbon used as a raw material is an aromatic monocarboxylic acid obtained by liquid phase oxidation,
An aromatic dicarboxylic acid, an aromatic hydrocarbon such as an aromatic carboxylic acid such as an aromatic tricarboxylic acid, a mono-, di-, or trialkylbenzene, or an aromatic hydrocarbon such as a mono-, di-, or trialkylnaphthalene, a part of which is an alkyl group. Includes those that have been oxidized. Examples of the alkyl aromatic hydrocarbon include paraxylene, metaxylene, orthoxylene, trimethylbenzene, toluene, methylnaphthalene, dimethylnaphthalene and the like. Examples of the aromatic carboxylic acid produced include terephthalic acid, isophthalic acid, orthophthalic acid, trimellitic acid, benzoic acid, naphthoic acid, and naphthalenedicarboxylic acid, but the method of the present invention is
It is preferably applied to the production of terephthalic acid or isophthalic acid, and in these cases, examples of the alkylbenzene as a raw material include paraxylene and metaxylene. Particularly preferred is a method for producing terephthalic acid from paraxylene as a raw material.

The amount of acetic acid solvent used is usually 2 to 6 times the weight of the alkyl aromatic hydrocarbon. The acetic acid solvent may contain a slight amount of water, for example, 10% by weight or less. As the molecular oxygen-containing gas, air, oxygen diluted with an inert gas, oxygen-enriched air, or the like is used, but air is preferable from the viewpoint of equipment and cost.

The catalyst contains respective components of cobalt, manganese and bromine, and specific examples thereof include cobalt compounds such as cobalt acetate, cobalt naphthenate and cobalt bromide. Examples of manganese compounds include manganese acetate, manganese naphthenate, manganese bromide and the like. For bromide compounds, hydrogen bromide,
Examples include sodium bromide, cobalt bromide, manganese bromide, tetrabromoethane and the like. These compounds may be used in combination.

The amount of the catalyst used is such that the amount of the cobalt component used is 400 weight ppm or more and 3000 weight ppm or less, preferably 500 weight p, based on acetic acid in terms of cobalt metal.
It is pm or more and 2000 weight ppm or less. The amount of the manganese component used is 0.001 times or more and 0.4 times or less in terms of atomic ratio with respect to cobalt. The absolute amount of manganese component is usually 1 ppm by weight or more and 250 ppm by weight or less, preferably 5 ppm by weight or more and 200 ppm by weight or less based on acetic acid in terms of manganese metal. The amount of the bromine component used is 0.1 times or more and 5.0 times or less, preferably 0.2 times or more and 2.0 times or less in terms of atomic ratio with respect to cobalt. If the amount of the catalyst used is out of the above range, the purity or the transmittance of the aromatic carboxylic acid to be obtained becomes insufficient, or the combustion of acetic acid becomes large, so that the effect cannot be obtained. In particular, the amount of the manganese component used is important. If the atomic ratio to cobalt is less than 0.001 times, the reaction activity is significantly reduced, and if it exceeds 0.4 times, the manganese component is precipitated and the aromatic carboxylic acid is precipitated. If mixed, the quality deteriorates or the loss of acetic acid increases.

As the catalyst component, components other than the cobalt, manganese and bromine components may be present. For example, when the sodium component is usually present in an amount of about 1 to 1000 ppm, the effect of preventing the precipitation of the manganese component or the quality of the aromatic carboxylic acid obtained, particularly the transmittance, is recognized. The sodium component may be added to the catalyst adjusting tank, or the sodium component accumulated in the system during the manufacturing process may be used as it is. Furthermore, if necessary, a co-oxidizing agent may be used together to accelerate the reaction.
As the co-oxidizing agent, aldehyde compounds such as acetaldehyde, ketone compounds such as methyl ethyl ketone, ester compounds such as propyl acetate and the like are used.

The reaction temperature is 140 ° C. or higher and 180 ° C. or lower, preferably 150 ° C. or higher and 175 ° C. or lower. If the temperature is lower than 140 ° C, the reaction rate decreases, and if the temperature exceeds 180 ° C, the loss due to combustion of the acetic acid solvent increases, which is not preferable. The reaction pressure is at least a pressure at which the mixture can maintain the liquid phase at least at the reaction temperature, and is usually 0.2 to 5 MPa. The reaction is usually carried out continuously, and the reaction time (average residence time) is usually 30 to 300 minutes. The water concentration in the reaction mother liquor is usually 5 to 25% by weight, preferably 7 to 20% by weight. The adjustment of the water concentration is usually performed by extracting the gas volatilized in the reactor and condensing the gas. This can be performed by discharging (purging) a part of the obtained condensable component reflux liquid to the outside of the system.

The reactor used in the present invention is usually a stirring tank type as shown in FIG. 1 which will be described later, but a stirrer is not always necessary and a bubble column type may be used. A reflux condenser is provided in the upper part of the reactor, and a molecular oxygen-containing gas supply port is provided in the lower part. After the molecular oxygen-containing gas supplied from the lower part is utilized for the oxidation reaction, it is extracted from the reactor as a gas component accompanied by a large amount of acetic acid vapor, and then the reflux condenser cools the acetic acid to separate it. , Emitted as oxidizing exhaust gas. The condensate is partially purged outside the system to control the water content, and the rest is refluxed to the reactor.

In order to increase the oxygen partial pressure in the gas phase of the reactor, which is an important operating factor of the present invention, the above-mentioned Japanese Patent Publication No. 5-3 is used.
2381, that is, the oxidizing exhaust gas obtained by condensing and removing the condensable components from the gas extracted from the reactor is branched into two streams, one of which is discharged out of the system and the other of which is reacted. A method of continuously circulating and supplying to the vessel is used. In the method of circulating a part of the oxidizing exhaust gas, the reaction pressure can be adjusted without seriously affecting other reaction conditions by adjusting the circulation amount. At this time, the reaction pressure needs to be higher than the pressure when air is used as the molecular oxygen-containing gas and the circulation supply is not performed under other conditions under the same conditions. At that time, the oxygen partial pressure in the gas phase portion of the reactor is usually 1 with respect to the oxygen partial pressure when air is not used as the molecular oxygen-containing gas and the circulation supply is not performed under the same conditions under other conditions. The circulation supply amount is adjusted so as to be 3 to 5 times, preferably 1.5 to 3 times.

As the oxidizing exhaust gas to be circulated, it is preferable to use a gas having a high pressure immediately after being condensed. Also,
The oxidizing exhaust gas to be circulated may be directly circulated from the oxidizing exhaust gas recycling line to the liquid phase part of the reactor as shown in FIG. 1 described later, and after being mixed with the oxygen-containing gas, it is supplied to the liquid phase part of the reactor as a mixed gas. It doesn't matter. The upper limit of the oxygen concentration in the oxidant exhaust gas is about 8% by volume from the viewpoint of explosion limit.
Therefore, it is usually 0.1 to 8% by volume, preferably 0.
It is operated in the range of 5 to 7% by volume.

In the present invention, a further important operating factor is that a part of the oxidizing exhaust gas obtained by condensing and removing the condensable components from the gas withdrawn from the reactor is circulated and supplied to the liquid phase portion of the reactor, and the reaction pressure is The reaction temperature and the catalyst composition of cobalt, manganese, and bromine under the reaction conditions that are higher than the pressure when the circulation supply is not performed under the same conditions using air as the molecular oxygen-containing gas. Carefully selected,
Furthermore, it is to combine them.

In the present invention, crystallization may be carried out immediately after the above-mentioned oxidation reaction, or crystallization may be carried out after additional treatment, if necessary. As the additional treatment, for example, the reaction mixture of the above-mentioned first oxidation reaction (first reaction zone) is additionally oxidized in the second reaction zone kept at 140 to 190 ° C. without supplying an alkylaromatic hydrocarbon. The method of performing the treatment (second oxidation treatment) is effective. Also, the second
The reaction mixture in the reaction zone is further mixed in the third reaction zone, usually 2
A method of performing additional oxidation treatment (third oxidation treatment) again at 10 ° C. or higher, preferably 220 to 280 ° C. without supplying an alkylaromatic hydrocarbon is also effective. It is usually desirable that the reaction mixture used for this additional oxidation treatment has a conversion rate to an aromatic carboxylic acid of 95% or more in the first oxidation reaction. The supply amount of the molecular oxygen-containing gas in each additional oxidation treatment is usually about 1/5 to 1/1000 of the first reaction, and the treatment time is usually 5 to 120 minutes.

The reason why the above-mentioned additional oxidation treatment is particularly effective in the reaction mixture containing an aromatic carboxylic acid obtained by the method of the present invention is, as in the present invention, 140 ° C. or higher,
Whether the precipitated particles of the aromatic carboxylic acid of the reaction mixture obtained at a low reaction temperature of 180 ° C. or lower have a smaller particle size than the particles of the aromatic carboxylic acid obtained under the conventional reaction conditions of more than 180 ° C. It is presumed that since the particles are agglomerated particles, they are likely to be subjected to the refining effect by the additional oxidation treatment.
The aromatic carboxylic acid obtained by the method of the present invention is dissolved in water and brought into contact with a platinum group catalyst in the presence of hydrogen for purification (see Japanese Patent Publication No. 41-16860). The processing technology described in (1) can be applied in the same manner.

[0024]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. During the implementation, "part" means "part by weight", and "ppm" means "weight pp."
m ". Example 1 (a) Reaction of reflux condenser 1, stirrer, heating device, catalyst, solvent and para-xylene supply line 3, oxygen-containing gas introduction line 4, reaction slurry extraction line 5, reflux liquid extraction line 8 and oxidizing exhaust gas Blower for circulating to the vessel
2 and a pressure-resistant main oxidation reactor 9 made of titanium (see FIG. 1) equipped with a circulation line 7, (b) a reflux condenser, a stirrer, a heating device, an oxygen-containing gas inlet and a reaction slurry inlet and outlet. The reaction was carried out using a continuous reaction apparatus comprising a titanium pressure-resistant additional oxidation reactor equipped with a (c) reflux condenser, a stirrer and a cooling crystallizer equipped with a reaction slurry inlet and outlet. .

That is, from the line 3 of the main oxidation reactor 9, 1 part of paraxylene, 4.6 parts of acetic acid containing 5% of water, 0.0105 parts of cobalt acetate.4 hydrate, 0 manganese acetate.4 hydrate. 0.0003 parts, hydrobromic acid (47% aqueous solution) 0.00
A mixture of 79 parts and 0.0004 parts of sodium hydroxide 5.615 parts / hr (Note: When the concentration of each catalyst component in the reaction system was calculated from the amount of catalyst charged, cobalt (Co)
1100ppm, Manganese (Mn) 33ppm, Bromine (Br) 1650ppm, Sodium (Na) 100p
pm). Further, 1.6 parts / hr of the reflux liquid was extracted from the line 8 and the water concentration in the reaction system was adjusted to about 10
%, And the paraxylene oxidation reaction was carried out under the conditions of a residence time of 100 minutes and a reaction temperature of 170 ° C. Air is supplied from line 4 as oxidizing gas so that the oxygen concentration in the oxidizing exhaust gas is 6% by volume, and the oxidizing exhaust gas from reflux condenser 1 is purged from line 6 and outside the system. The oxidizing exhaust gas is circulated through the line 7 to the main oxidation reactor 9 by the blower-2 so that the volume ratio of the circulating gas amount based on the non-condensable component to the oxidizing exhaust gas amount is 1.0. The reaction pressure is higher than the reaction pressure of 0.83 MPa when the exhaust gas is not circulated and supplied, and the reaction pressure of 1.10
Balance at MPa. At this time, the gas phase oxygen partial pressure is also
Increased from 0.015MPa without exhaust gas circulation to 0.03MPa

Then, a reaction slurry is taken out from the main oxidation reactor 9 through a line 5, and this slurry is continuously sent to an additional oxidation reactor 10 for a residence time of 45 minutes and a pressure of 0.9.
Under the conditions of 5 MPa and a reaction temperature of 176 ° C., air was supplied so that the oxygen concentration in the additional oxidation exhaust gas would be 6% by volume, and additional oxidation was performed. The reaction slurry after additional oxidation is subsequently sent to a cooling crystallizer for crystallization, and solid-liquid separation is carried out, and then the recovered crystals are subjected to suspension washing with acetic acid, solid-liquid separation is carried out again, and then dried. Terephthalic acid crystals were obtained. After carrying out such a continuous reaction for 24 hours, the transmittance and 4CBA content of the obtained terephthalic acid crystals were measured, and the combustion amount of the acetic acid solvent during the production was measured.
Shown in

Comparative Example 1 The catalyst composition was Co 300 ppm, Mn 300 ppm, Br.
900ppm, the reaction temperature of the main oxidation reaction is 195 ℃,
Table 1 shows the results of the reaction performed in the same manner as in Example 1 except that the reaction pressure was 2.07 MPa. This corresponds to the conditions of the embodiment described in Japanese Patent Publication No. 5-32381. Comparative Example 2 Table 1 shows the results of the reaction performed in the same manner as Comparative Example 1 except that the oxidizing exhaust gas was not circulated to the main oxidation reactor by the blower-2.

Comparative Example 3 Table 1 shows the results of the reaction carried out in the same manner as in Example 1 except that the oxidizing exhaust gas was not circulated to the main oxidation reactor by the blower-2. Comparative Example 4 The result of carrying out the reaction in the same manner as in Example 1 except that the circulation of the oxidizing exhaust gas to the main oxidation reactor by the blower-2 was circulated to the gas phase portion of the reactor instead of the liquid phase portion of the reactor, It shows in Table-1.

Comparative Example 5 The results of the reaction were carried out in the same manner as in Example 1 except that the reaction temperature was 195 ° C. and the reaction pressure was 2.07 MPa.
It is shown in FIG. Comparative Example 6 The reaction temperature was 195 ° C., the reaction pressure was 2.07 MPa,
Table 1 shows the results of the reaction performed in the same manner as in Example 1 except that the PX supply rate was increased so that the concentration of 4 CBA in the obtained terephthalic acid was the same as in Example 1.

Comparative Example 7 Co300 ppm, Mn, which is the catalyst composition (catalyst composition of Comparative Example 1) described in the example of Japanese Patent Publication No. 5-32381.
Example 1 except 300 ppm and Br 900 ppm
The results of the reaction carried out in the same manner as in Table 1 are shown in Table 1. In this example, the precipitation of the manganese component in the catalyst component was remarkable and the reaction state was unstable, so the reaction was stopped 2 hours after the start.

Comparative Example 8 The catalyst composition was Co1100 ppm, Mn500 ppm, B
Table 1 shows the results of the reaction performed in the same manner as in Example 1 except that r1650 ppm was used. In this example, although the reaction proceeded steadily, precipitation of manganese component was observed in the catalyst component, and the transmittance was poor as the quality of terephthalic acid.

[0032]

[Table 1]

The meanings of * 1 to * 7 in Table-1 are as follows. * 1 Exhaust gas circulation amount --- Indicates the volume ratio of the circulation gas amount based on the non-condensable component with respect to the oxidizing exhaust gas amount purged outside the system. * 2 Terephthalic acid transmittance --- Shows the transmittance at a light source of 340 nm and an optical path length of 10 mm when 7.5 g of terephthalic acid is dissolved in 50 ml of a 2N aqueous potassium hydroxide solution. * 3 Amount of acetic acid solvent burned --- The amount of CO and CO2 contained in the oxidizing exhaust gas from the reactor is analyzed, the amount of burned acetic acid is determined from this value, and the amount burned in the method of Comparative Example 1 is used as a standard (1 .0) is shown as a relative value. * 4 The exhaust gas was circulated by a blower in the gas phase part of the reactor. * 5 Shows the reaction pressure when part of the oxidation waste gas from the main oxidation reactor is not circulated to the reactor under the reaction conditions shown in the example. * 6 Since the reaction state was unstable, the reaction was stopped 2 hours after the start. * 7: shows the relative value when the feeding rate of para-xylene of Example 1 was 1.0.

Comparative Example 1 in Table 1 is the same as Japanese Patent Publication No. 5-3.
2381, that is, the oxidizing exhaust gas obtained by condensing and removing the condensable components from the gas extracted from the reactor is branched into two streams, one of which is discharged out of the system and the other of which is reacted. This is a reaction example in which the reaction pressure is raised and the oxygen partial pressure is raised by continuously circulating and supplying to the liquid phase portion of the vessel. In Comparative Example 1, the obtained terephthalic acid had a good transmittance as compared with Comparative Example 2 in which the oxidizing exhaust gas was not circulated, but the acetic acid combustion amount and the 4CBA content were the same. The results show that Examples 1 to 11 of Japanese Patent Publication No. 5-32381 and Examples 1 to 8 of JP-A-7-278048.
It was the same in. On the other hand, in Example 1 of the present invention, a method of increasing the oxygen partial pressure by circulating the oxidative exhaust gas to the reactor was combined with the carefully selected reaction temperature and catalyst composition revealed in the present invention, and a comparison was made. Similar to Example 1, the effect of improving the transmittance is recognized, and further,
At the same concentration of 4 CBA, a significant reduction effect of acetic acid combustion which was not achieved by the method of Comparative Example 1 was recognized.

Compared with Example 1, in Comparative Example 3 in which the oxidizing exhaust gas was not circulated and supplied to the reactor, the amount of acetic acid burned was significantly reduced, but the reaction activity was significantly reduced, so that the terephthalic acid in the obtained terephthalic acid was reduced. The 4CBA content was extremely high and the transmittance was significantly deteriorated. In Comparative Example 4 in which the oxidative exhaust gas was circulated to the gas phase portion instead of the liquid phase portion, the reaction results were almost the same as those in Comparative Example 3 in which the oxidizing exhaust gas was not circulated to the reactor. There is no effect of improving the transmittance. The reaction temperature was set to 1 in comparison with Example 1.
In Comparative Example 5 in which the temperature was changed to 95 ° C., the amount of acetic acid burned increased significantly. Compared to Example 1, the reaction temperature was changed to 195 ° C., and when the PX feed rate was increased so that the concentration of 4CBA in terephthalic acid obtained was the same as in Example 1, the transmittance was good. However, no effect of reducing the amount of acetic acid burned is observed. In contrast to Example 1, in Comparative Examples 7 and 8 in which the catalyst composition had cobalt and manganese concentrations outside the carefully selected range of the present invention, the reaction activity or the quality of the obtained terephthalic acid was greatly deteriorated.

Examples 2 to 6 and Comparative Examples 9 to 11 In the same manner as in Example 1, the main oxidation reaction temperature was set to 190 to 1
The reaction was carried out by changing the temperature to 30 ° C. The reaction conditions of the catalyst concentration and the paraxylene (PX) feed rate were selected so that the obtained terephthalic acid transmittance was almost constant (75 to 81%), and the results were compared. The temperature of the additional oxidation reaction is 0.15MP from the pressure of the main oxidation reactor when the pressure of the additional oxidation reactor is
The reaction temperatures (150 to 190 ° C.) were balanced when the pressure was set as low as a. Table-Results
It is shown in FIG.

[0037]

[Table 2]

From Table 2, in the temperature ranges shown in Examples 2 to 6, as shown in Example 1, the oxidative exhaust gas was circulated to the liquid phase portion of the reactor by the circulation of the gas phase portion of the reactor. By combining the method of increasing oxygen partial pressure with the reaction method of carefully selected reaction temperature and catalyst composition, a significant reduction effect of acetic acid combustion was realized. On the other hand, as shown in Comparative Examples 9 to 11, at the reaction temperature of 185 ° C. or higher, almost no decrease in the acetic acid combustion amount was observed, and at the reaction temperature of 130 ° C., the reaction activity was low and stable operation could not be performed.

[0039]

EFFECTS OF THE INVENTION According to the present invention, a method for significantly improving the quality, particularly the transmittance, of an aromatic carboxylic acid obtained by an oxidation reaction, which has been already reported, is maintained, and further, a reaction solvent is used. It became clear that the burning loss of some acetic acid could be largely prevented. This effect greatly exceeds the effects of the conventionally known inventions of the same kind of catalyst system, the effects described in Japanese Patent Publication No. 5-32381 or JP-A-7-278048, and the effects expected from these inventions. This is a special effect obtained only by the combination of the method of increasing the oxygen partial pressure in the gas phase of the reactor by circulating the oxidizing exhaust gas to the liquid phase of the reactor, the combination of the specific reaction temperature condition and the specific catalyst composition.

[Brief description of drawings]

FIG. 1 shows the oxidation reaction equipment used in the examples of the present invention.

[Explanation of symbols]

 1: Reflux condenser 2: Blower 3: Supply line of catalyst, solvent and paraxylene 4: Introduction line of oxygen-containing gas 5: Extraction line of reaction slurry 6: Purging line of oxidizing exhaust gas 7: Recycling of oxidizing exhaust gas Line 8: Reflux liquid extraction line 9: Main oxidation reactor 10: Additional oxidation reaction (second oxidation reaction) device 11: Oxygen-containing gas introduction line

Claims (13)

[Claims] 1. An alkyl aromatic hydrocarbon in an acetic acid solvent,
In the method for producing an aromatic carboxylic acid by liquid-phase oxidation with a gas containing molecular oxygen in the presence of a catalyst component containing cobalt, manganese, and bromine, (1) the reaction temperature is 1
The temperature is 40 ° C. or higher and 180 ° C. or lower, (2) the amount of the cobalt component is 400 wt ppm or more and 3000 wt ppm or less with respect to the acetic acid solvent in terms of cobalt metal, and (3) the amount of the manganese component is atoms relative to cobalt. 0.001 in ratio
(4) withdrawal from the reactor in the presence of a catalyst component having an amount of bromine component of 0.4 times or more and (4) an amount of bromine component of 0.1 to 5.0 times the atomic ratio of cobalt. Part of the oxidizing exhaust gas obtained by condensing and removing the condensable components from the gas is circulated and supplied to the liquid phase part of the reactor, (6) the reaction pressure is air as the molecular oxygen-containing gas, and the oxidizing exhaust gas is The method for producing an aromatic carboxylic acid is characterized in that the pressure is raised above the pressure when the circulation supply is not performed. 2. The method for producing an aromatic carboxylic acid according to claim 1, wherein the alkyl aromatic hydrocarbon is paraxylene. 3. The method for producing an aromatic carboxylic acid according to claim 1, wherein the amount of the cobalt component is 500 ppm by weight or more and 2000 ppm by weight or less based on the acetic acid solvent in terms of cobalt metal. 4. The amount of manganese component, calculated as manganese metal, is 1 ppm by weight or more and 250 ppm by weight based on the acetic acid solvent.
The method for producing an aromatic carboxylic acid according to claim 1, wherein: 5. The amount of bromine component is 0.2 times or more and 2.0 times or less in terms of atomic ratio with respect to cobalt.
A method for producing an aromatic carboxylic acid according to any one of 1. 6. The method for producing an aromatic carboxylic acid according to claim 1, wherein the reaction temperature is 150 ° C. or higher and 175 ° C. or lower. 7. The method for producing an aromatic carboxylic acid according to claim 1, wherein the oxygen concentration in the oxidizing exhaust gas is 0.1 to 8% by volume. 8. The oxygen partial pressure in the gas phase portion of the reactor is 1.3 to 5 of the oxygen partial pressure in the gas phase portion when air is used as the molecular oxygen-containing gas and the oxidizing exhaust gas is not circulated and supplied. The method for producing an aromatic carboxylic acid according to any one of claims 1 to 7, wherein the reaction pressure is doubled. 9. The method for producing an aromatic carboxylic acid according to claim 1, wherein the molecular oxygen-containing gas supplied to the reactor is air. 10. A sodium component as a catalyst component is 1 ppm by weight or more in terms of sodium metal based on an acetic acid solvent,
The method for producing an aromatic carboxylic acid according to claim 1, which has an amount of 1000 ppm by weight or less. 11. The method for producing an aromatic carboxylic acid according to claim 1, wherein the oxidation reaction is carried out in the absence of a co-oxidant for promoting the reaction. 12. A reaction mixture obtained by the method according to any one of claims 1 to 11 is maintained at a temperature of 140 to 190 ° C. in a second reaction zone without supplying an alkyl aromatic hydrocarbon. A method for producing an aromatic carboxylic acid, which comprises performing a second oxidation treatment with a gaseous oxygen-containing gas. 13. The reaction mixture obtained by the method according to claim 12, in a third reaction zone maintained at a temperature of 210 ° C. or higher, is fed with a molecular oxygen-containing gas without adding an alkylaromatic hydrocarbon. 3. A method for producing an aromatic carboxylic acid, which comprises performing an oxidation treatment.