JPH07258151A - Production of aromatic carboxylic acid and the apparatus therefor - Google Patents

Abstract

PURPOSE:To produce aromatic carboxylic acids in which the volume of the exhaustion gas occurring in the production of aromatic carboxylic acids has been greatly reduced and the danger of explosion has been avoided in the case of oxidation using pure oxygen gas. CONSTITUTION:An alkylbenzene is oxidized in liquid phase, as a solvent containing lower aliphatic carboxylic acid, the alkylbenzene, and the catalyst are fed from the inlet 6 and the mixed gas is introduced through the inlet 15 into the reactor 1. The reaction exhaustion gas from the reactor 1 is expelled through the exhaustion gas line 5, cooled down in the heat exchanger 11 and separated in the separator 12 into the condensed liquid fraction and the exhaustion gas free from the liquefying components. The condensed liquid fraction is recycled via the liquid-cycling line 7 into the reactor 1. The exhausted gas is recycled through the circulation line 3 to the reactor 1. At that time, a gas containing oxygen in a higher concentration than that of air is fed from the line 8 and mixed with the recycled exhaustion gas and the mixed gas is fed into the reactor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing an aromatic carboxylic acid, which comprises subjecting an alkylbenzene to liquid-phase oxidation with molecular oxygen in a solvent containing a lower aliphatic carboxylic acid to produce an aromatic carboxylic acid. The present invention relates to a method and an apparatus for producing an aromatic carboxylic acid capable of safely and easily reducing the amount of exhaust gas generated during a reaction.

[0002]

2. Description of the Related Art Conventionally, as a method for industrially producing an aromatic carboxylic acid such as terephthalic acid on a large scale, catalysts such as cobalt, manganese and bromine in a solvent containing a lower aliphatic carboxylic acid such as acetic acid have been used. In the presence, a method of liquid-phase oxidizing alkylbenzene such as p-xylene with molecular oxygen has been adopted.

When an aromatic carboxylic acid is produced by such a production method, a part of the lower aliphatic carboxylic acid which is a solvent is converted into carbon dioxide gas, carbon monoxide and other by-products during the reaction. Is well known. These byproducts are discharged from the reactor along with the reaction exhaust gas. The discharged by-products also contain harmful substances such as carbon monoxide and methyl bromide. Considering the environmental burden, when exhausting the reaction exhaust gas into the atmosphere, use some abatement equipment. It was necessary to devise the exhaust method by treating it or considering the landing concentration.

Usually, there are many large-scale apparatuses for producing aromatic carboxylic acids such as terephthalic acid, and when air is used as the molecular oxygen-containing gas, the amount of exhaust gas is considerably large. Therefore, the detoxification equipment for treating harmful substances contained in the exhaust gas and the collection equipment for collecting and effectively using the by-products have to be extremely large in scale, which is not economical. .

On the other hand, when pure oxygen gas is used as the molecular oxygen-containing gas, the amount of exhaust gas can be significantly reduced, but if the oxygen concentration in this gas phase portion is high in order to maintain the oxygen partial pressure in the gas phase portion. Inevitably, there is a problem that operating conditions are limited because the risk of explosion due to flammable substances such as lower aliphatic carboxylic acid contained in the solvent and the starting material alkylbenzene increases. As described above, in the conventional method, it is difficult to reduce the emission amount of the exhaust gas when the high-concentration oxygen-containing gas is not used as the molecular oxygen-containing gas, and the flammability is high when the high-concentration oxygen-containing gas is used. It was necessary to select reaction conditions that avoided the explosive range of the substance.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the conventional production of aromatic carboxylic acids, and oxygen in a gas containing molecular oxygen to be introduced into a reactor. Even if the concentration is about the same as the concentration in the air, it is possible to reduce the emission amount of exhaust gas generated by the production of aromatic carboxylic acid safely and easily and drastically. An object of the present invention is to provide a method and an apparatus for producing an aromatic carboxylic acid, which can avoid the risk of explosion which may be a problem when introducing the aromatic carboxylic acid.

[0007]

The present invention is the following method and apparatus for producing an aromatic carboxylic acid. (1) In the method for producing an aromatic carboxylic acid by contacting alkylbenzene with a molecular oxygen-containing gas in a solvent containing a lower aliphatic carboxylic acid to produce an aromatic carboxylic acid, the molecular oxygen-containing gas may be air. A method for producing an aromatic carboxylic acid, characterized in that a mixed gas of a high-concentration oxygen-containing gas containing molecular oxygen at a high concentration and a reaction exhaust gas is supplied to the reaction system. (2) The method according to (1) above, wherein a mixed gas of a reaction exhaust gas from which a condensable component has been removed and a high-concentration oxygen-containing gas is used as the mixed gas. (3) The method according to (1) or (2) above, wherein the aromatic carboxylic acid is terephthalic acid. (4) Reactor for contacting alkylbenzene with a gas containing molecular oxygen in a solvent containing a lower aliphatic carboxylic acid for liquid-phase oxidation, and a gas circulation system for circulating reaction exhaust gas discharged from the reactor to the reactor Aromatic carboxylic acid, characterized in that it is provided with a gas mixing means for supplying a high-concentration oxygen-containing gas containing molecular oxygen at a concentration higher than that of air to the gas circulation system path and mixing with the reaction exhaust gas. Manufacturing equipment. (5) The apparatus according to (4) above, wherein the gas circulation system has a condenser for removing condensable components from the reaction exhaust gas.

In the present invention, the alkylbenzene used as a raw material is an alkylbenzene such as a mono-, di- or tri-alkylbenzene which is converted into an aromatic carboxylic acid such as a mono-, di- or tri-aromatic carboxylic acid by liquid phase oxidation. It also includes those in which a part of the alkyl group is oxidized. For example, alkylbenzene as a raw material for producing terephthalic acid includes, for example, p-xylene and p-xylene.
-Toluic acid or a mixture thereof.

The reaction solvent used in the present invention is a solvent containing a lower aliphatic carboxylic acid, preferably a solvent containing a lower aliphatic carboxylic acid having 6 or less carbon atoms. Examples of such lower aliphatic carboxylic acid include acetic acid, propionic acid, butyric acid, isobutyric acid, n-valeric acid, trimethylacetic acid, caproic acid, or a mixture of these carboxylic acids and water. Of these, acetic acid or a mixture of acetic acid and water is preferable. When water is contained, the content of water in the solvent is preferably 20% by weight or less. The amount of the solvent containing such a lower aliphatic carboxylic acid used is preferably such that the concentration of the alkylbenzene as a raw material is 1 to 50% by weight based on the solvent.

In the oxidation reaction of the present invention, it is preferable to use an oxidation catalyst. As the oxidation catalyst, for example, a catalyst containing a transition metal and bromine, particularly a soluble catalyst containing cobalt, manganese and bromine is preferable, but other catalysts may be used. Cobalt and manganese compounds used in such catalysts include cobalt and manganese bromine salts,
Benzoates, naphthenates, carboxylates such as acetic acid, acetylacetonates, etc., and as bromine compounds, manganese, transition metal bromine salts such as cobalt, hydrobromic acid,
Examples include dibromoethylene and tetrabromoethane. The catalyst is used in an amount of 10 to 5,000 weight pp as cobalt atom in a solvent containing a lower aliphatic carboxylic acid.
It is preferable that m and manganese atoms are 10 to 5000 weight ppm and bromine atoms are 10 to 10,000 weight ppm.

In the present invention, alkylbenzene is brought into contact with a molecular oxygen-containing gas in a reaction solvent to undergo liquid phase oxidation to produce an aromatic carboxylic acid. At this time, as the molecular oxygen-containing gas, a mixed gas of a high-concentration oxygen-containing gas containing molecular oxygen at a higher concentration than air and a reaction exhaust gas generated by the oxidation reaction is used. Examples of the high-concentration oxygen-containing gas include pure oxygen, oxygen-rich air, a mixture of pure oxygen and an inert gas, and the like. The oxygen concentration in the high-concentration oxygen-containing gas is 23 to 100% by volume, preferably 50 to 100% by volume.

The mixing ratio of the high-concentration oxygen-containing gas and the reaction exhaust gas is 1: 0.01-10, preferably 1: 0.02-5, in the volume ratio of the high-concentration oxygen-containing gas: reaction exhaust gas. It is desirable to mix them so that the oxygen concentration therein is 15 to 30% by volume. By carrying out the oxidation reaction using a mixed gas having such an oxygen concentration, it is possible to avoid the risk of explosion that occurs when carrying out the oxidation reaction using a pure oxygen gas or a gas containing oxygen at a high concentration. . If you can select reaction conditions that avoid the risk of explosion,
The oxygen concentration in the mixed gas can be higher than the above value.

Alkylbenzene and gas containing molecular oxygen
The method of contact with (mixed gas) is not particularly limited, and alkyl
A gas containing molecular oxygen (mixed gas) in a solvent containing benzene.
It is possible to adopt a method of blowing air). Containing molecular oxygen
The gas (mixed gas) has molecular oxygen of alkylbenzene.
It is supplied so as to be in excess of the reaction equivalent required for oxidation.
For example, oxidize p-xylene to produce terephthalic acid.
If 0.1 to 3 Nm per kg of p-xylene
³Oxygen (converted value at 0 ° C and 1 atm) is supplied
The gas containing molecular oxygen (mixed gas)
Is preferred.

The temperature of the oxidation reaction in the present invention is usually 16
It is desirable that the temperature is 0 to 260 ° C., preferably 170 to 220 ° C., and the pressure is at least a pressure at which the reaction mixture can maintain a liquid phase at the reaction temperature, and usually 4 to 50 k
It is desirable to set it to g / cm ² G. Although the reaction time depends on the size of the apparatus and the like, it is usually desirable to set the residence time to about 10 to 200 minutes.

[0015]

The present invention will now be described with reference to the embodiments of the drawings.
FIG. 1 is a system diagram showing an aromatic carboxylic acid production apparatus of an example. In the figure, 1 is a reactor, which is equipped with an agitator 2a and a baffle plate 2b inside, and a gas circulation path 3 at the bottom.
And a reaction product discharge passage 4, a reaction exhaust gas passage 5 at the top,
The raw material introduction passage 6 and the condensate circulation passage 7 are connected to the intermediate portion. A high-concentration oxygen-containing gas supply passage 8 is connected to the gas circulation passage 3 so that a mixed gas can be prepared and constitutes a gas mixing means. The stirrer 2a has a stirring shaft supported at two intermediate positions (not shown) and the bottom.

The reaction exhaust gas passage 5 is connected to a separator 12 via a heat exchanger 11, the condensate in the separator 12 is circulated from the condensate circulation passage 7 to the reactor 1, and the condensable components are removed. The exhaust gas is circulated from the gas circulation path 3 to the reactor 1. The heat exchanger 11 and the separator 12 form a condenser. An exhaust gas passage 13 is connected to the top of the separator 12. The condensate circulation passage 7 has an exhausted condensate passage 1
4 is connected. Reference numeral 15 is a mixed gas blowing port, 16 is a compressor, and 17 is a circulation pump.

In the above apparatus, the agitator 2a and the baffle plate 2b can be omitted. A distillation column (not shown) may be provided instead of the heat exchanger 11 or together with the heat exchanger 11. Further, as the gas mixing means, a gas mixing tank (not shown) for mixing the circulating gas and the high-concentration oxygen-containing gas to prepare the mixed gas may be provided.

In order to produce an aromatic carboxylic acid by the above-mentioned apparatus, first, a solvent and a catalyst are put in a reactor 1, and alkylbenzene, a catalyst and a solvent are introduced into the reactor 1 through a raw material introducing passage 6, and A mixed gas is introduced from a mixed gas blowing port 15, and molecular oxygen is brought into contact with alkylbenzene in a solvent while stirring with a stirrer 2a,
Liquid phase oxidation. Since the baffle plate 2b is provided in the reactor 1, the lowering of the central liquid surface due to the rotating vortex when the stirrer 2a is driven is prevented, and the contact is performed efficiently.

The reaction exhaust gas is discharged from the reaction exhaust gas passage 5,
Cooling is performed in the heat exchanger 11 to condense the condensable components such as vapor contained in the reaction exhaust gas, and the separator 12 separates the condensate and the exhaust gas from which the condensable components have been removed. A part of the separated condensate is circulated through the condensate circulation passage 7 into the reaction liquid in the reactor 1 by driving the circulation pump 17. The rest of the condensate is discharged from the drained condensate passage 14. A part of the exhaust gas from which the condensable components have been removed is circulated as circulating exhaust gas from the gas circulation path 3 to the reactor 1 by the compressor 16.
At this time, a high-concentration oxygen-containing gas is supplied from the high-concentration oxygen-containing gas supply passage 8, mixed with the circulation exhaust gas in the gas circulation passage 3, and supplied as a mixed gas from the mixed gas blowing port 15 to the reactor 1.

By condensing the condensable component from the reaction exhaust gas,
When the condensate is circulated in the reactor 1, a part of the condensate is discharged to adjust the circulating amount of the condensate, whereby the water concentration in the solvent is adjusted. In such a system, the exhaust gas from which the condensable components have been removed in the separator 12 is circulated from the gas circulation path 3 to facilitate the adjustment of the water concentration in the solvent in the reactor 1. However, in some cases, reactor 1
The reaction exhaust gas discharged from the reactor may be directly circulated from the gas circulation path 3 to the reactor 1 without removing the condensable components.

In the exhaust gas from which the condensable components have been removed, the inert gas contained in the high-concentration oxygen-containing gas supplied from the high-concentration oxygen-containing gas supply path 8, unreacted oxygen, and lower fat as a solvent It contains carbon dioxide, carbon monoxide and other by-products generated by the decomposition of group carboxylic acids in the course of the reaction. The concentration of each component varies depending on the reaction conditions,
The main components are the inert gas, carbon dioxide gas, and carbon monoxide contained in the high-concentration oxygen-containing gas.

By preparing a mixed gas by changing the mixing ratio of the circulating exhaust gas and the high-concentration oxygen-containing gas or the oxygen content in the high-concentration oxygen-containing gas, the mixed gas in the mixed gas blowing port 15 The oxygen concentration can be controlled arbitrarily. In this case, the oxygen concentration is preferably 15 to 30% by volume, which is near the oxygen concentration in the air.
With such a concentration, even if a gas having a high oxygen concentration is introduced from the high-concentration oxygen-containing gas supply passage 8, the reaction can proceed under the same conditions as in the case of using air. Therefore, it is not necessary to particularly consider the limitation of reaction conditions due to the use of a gas having a high oxygen concentration.

When a gas having a high oxygen concentration is directly introduced into the reactor as in the conventional method, the oxygen partial pressure in the gas phase portion of the reactor must be increased in order to maintain the oxygen partial pressure in the gas phase portion. First, the reaction conditions are limited to avoid the risk of explosion due to combustible substances such as lower aliphatic carboxylic acids and alkylbenzenes. In the present invention, such a limitation is eliminated as described above.

The amount of the circulating gas depends on the amount of the molecular oxygen-containing gas introduced from the high-concentration oxygen-containing gas supply passage 8, the oxygen concentration, the control value of the oxygen concentration at the mixed gas blowing port 15 of the reactor 1, and the like. Although different, as described above, the volume ratio of the high-concentration oxygen-containing gas to the reaction exhaust gas is 1: 0.01 to 10,
It is desirable to set it to 1: 0.02-5.

Depending on the conditions under which the exhaust gas is circulated, the concentration of carbon monoxide in the circulating exhaust gas increases, and when mixed with the high-concentration oxygen-containing gas introduced from the high-concentration oxygen-containing gas supply passage 8, there is a danger of explosion. there is a possibility. In this case, the generation of carbon monoxide is suppressed by controlling the reaction conditions, or a part or all of the circulating exhaust gas is subjected to a catalytic oxidation treatment in advance, and a part or all of the carbon monoxide is converted to carbon dioxide gas. The danger of explosion can be avoided by the method of mixing with a gas containing a high concentration of oxygen.

The rest of the exhaust gas is discharged to the outside of the system through the exhaust gas passage 13. The amount of exhaust gas discharged is the inert gas contained in the high-concentration oxygen-containing gas introduced from the high-concentration oxygen-containing gas supply passage 8, unreacted oxygen, carbon dioxide gas generated in the reactor 1, carbon monoxide, and This is an amount equivalent to the total amount of other by-products. Since the amount of unreacted oxygen and the amount of by-products such as carbon dioxide gas generated can be controlled by the reaction conditions, the amount of exhaust gas discharged can be controlled by the high-concentration oxygen-containing gas supply passage 8 through the high-concentration oxygen-containing gas. It is determined by the amount of the inert gas contained in, that is, the oxygen concentration in the high-concentration oxygen-containing gas. Therefore, the higher the oxygen concentration in the high-concentration oxygen-containing gas to be introduced, the more the exhaust gas can be discharged. Even in this case, since the high-concentration oxygen-containing gas is mixed with the circulating exhaust gas and used for the reaction as described above, the danger of explosion can be avoided.

The reaction product thus produced is taken out from the reaction product take-out path 4 and subjected to solid-liquid separation into an aromatic carboxylic acid and a solvent by a usual method such as filtration and centrifugation. The obtained aromatic carboxylic acid is subjected to known post-treatments such as washing and drying, and then, if necessary, purified by a known method.

In the above production method, the condensate may be wholly or partly refluxed to the gas phase part instead of being refluxed to the liquid phase part of the reactor 1. In addition, gas mixing is done in the gas circulation path 3
Instead of the inside, a gas mixing tank may be provided.

An example of producing terephthalic acid using the apparatus shown in FIG. 1 will be described below. In each example, the concentration of carbon dioxide and carbon monoxide in the reaction exhaust gas was measured by an infrared gas analyzer, and the concentration of oxygen was measured by a magnetic wind oxygen analyzer. The concentration of 4-carboxybenzaldehyde (4CBA) in terephthalic acid was measured by a liquid chromatography method. The light transmittance of terephthalic acid is shown by the light transmittance (%) at 340 nm of a 2N potassium hydroxide aqueous solution containing terephthalic acid at a concentration of 13%.

Example 1 Terephthalic acid was produced using the apparatus shown in FIG. As the reactor 1, a stirring tank having a volume of 60 liter equipped with two baffles 2b and three stages of stirring blades was used. The manufacturing method is as follows: acetic acid 19 kg, water 1 kg, cobalt acetate 50.0 g,
24.0 g of manganese acetate and tetrabromoethane 3
4.0g was charged, and the reactor 1 was heated at a temperature of 187 ° C and a pressure of 1
Paraxylene was maintained at 1.1 kg / cm ² gauge.
3 kg / hr, acetic acid 13.8 kg / hr, water 0.72 k
g / hr, cobalt acetate 36.6 g / hr, manganese acetate 17.4 g / hr, tetrabromoethane 24.9 g /
While continuously feeding a mixture of hr, oxygen-rich air containing oxygen at a high concentration of 25% by volume was prepared by adding oxygen to the air so that the oxygen concentration in the exhaust gas would be 3.0% by volume. Aeration was performed from the gas supply passage 8 and a continuous oxidation reaction was performed under stirring.

At this time, a part of the exhaust gas discharged from the separator 12 is circulated from the gas circulation path 3 to the reactor 1 by the compressor 16 and mixed with the oxygen-rich air introduced from the high-concentration oxygen-containing gas supply path 8. The oxygen concentration in the mixed gas blowing port 15 is set to 21% by volume, which is almost the same as the oxygen concentration in the air. The yield of terephthalic acid thus obtained, the 4CBA content, the light transmittance, and the amount of exhaust gas discharged outside the system per kg of p-xylene are shown in Table 1.

Example 2 Under the reaction conditions of Example 1, the oxygen concentration in the high-concentration oxygen-containing gas to be supplied was raised to 50% by volume, and at the same time, the oxygen concentration of the mixed gas in the mixed gas inlet 15 was 21% by volume. Thus, terephthalic acid was produced by increasing the amount of circulating exhaust gas. The results are shown in Table 1.

Example 3 Under the reaction conditions of Example 1, the oxygen concentration in the high-concentration oxygen-containing gas to be supplied was raised to 95% by volume, and at the same time, the oxygen concentration of the mixed gas at the mixed gas inlet 15 was 21% by volume. Thus, terephthalic acid was produced by increasing the amount of circulating exhaust gas. The results are shown in Table 1.

Example 4 Under the reaction conditions of Example 2, the oxygen concentration in the mixed gas at the mixed gas injection port 15 was adjusted to 23% by volume.
Further, terephthalic acid was produced by changing the circulation amount of oxygen-rich air and the circulation exhaust gas so that the oxygen concentration in the exhaust gas was 3.3% by volume. The results are shown in Table 1.

Comparative Example 1 Under the reaction conditions of Example 1, terephthalic acid was produced using air as a molecular oxygen-containing gas and without circulating exhaust gas. The results are shown in Table 1.

[0036]

[Table 1]

[0037]

According to the method of the present invention, a mixed gas of a high-concentration oxygen-containing gas containing molecular oxygen at a concentration higher than that of air and a reaction exhaust gas is used as the molecular oxygen-containing gas. Since the amount of the inert gas introduced into the reactor is made smaller than that when air is used, the amount of exhaust gas discharged to the outside of the system can be reduced to produce the aromatic carboxylic acid. Moreover, since the oxygen concentration in the molecular oxygen-containing gas blown into the reactor can be controlled by using the mixed gas, for example, by making the oxygen concentration equivalent to that of air, the case where air is used as the molecular oxygen-containing gas It becomes possible to carry out the reaction under safe conditions that do not change at all, thus avoiding the risk of explosion.

According to the apparatus of the present invention, the gas circulation system for circulating the reaction exhaust gas discharged from the reactor to the reactor, and the high-concentration oxygen-containing gas containing molecular oxygen at a concentration higher than that of the air are used as the gas. Since it is equipped with a gas mixing means for supplying it to the circulation system and mixing it with the reaction exhaust gas, the above method avoids the risk of explosion and reduces the amount of exhaust gas discharged to the outside of the system to reduce aromatic carboxylic acid. It can be manufactured.

[Brief description of drawings]

FIG. 1 is a system diagram showing an aromatic carboxylic acid production apparatus of an example.

[Explanation of symbols]

 1 Reactor 2a Stirrer 2b Baffle plate 3 Gas circulation path 4 Reaction product extraction path 5 Reaction exhaust gas path 6 Raw material introduction path 7 Condensate circulation path 8 High-concentration oxygen-containing gas supply path 11 Heat exchanger 12 Separator 13 Exhaust path 14 Exhaust Condensation Liquid Channel 15 Mixed Gas Injection Port 16 Compressor 17 Circulation Pump

Claims (5)

[Claims] 1. In a solvent containing a lower aliphatic carboxylic acid,
A method for producing an aromatic carboxylic acid by contacting alkylbenzene with a molecular oxygen-containing gas to perform liquid-phase oxidation, wherein the molecular oxygen-containing gas is a high-concentration oxygen-containing gas containing molecular oxygen at a higher concentration than air. And a reaction exhaust gas, and a mixed gas is supplied to the reaction system. 2. The method according to claim 1, wherein a mixed gas of a reaction exhaust gas from which a condensable component has been removed and a high-concentration oxygen-containing gas is used as the mixed gas. 3. The method according to claim 1, wherein the aromatic carboxylic acid is terephthalic acid. 4. In a solvent containing a lower aliphatic carboxylic acid,
A reactor for contacting alkylbenzene with a gas containing molecular oxygen to perform liquid-phase oxidation, a gas circulation system for circulating the reaction exhaust gas discharged from this reactor to the reactor, and containing molecular oxygen at a concentration higher than that of air An apparatus for producing an aromatic carboxylic acid, comprising a gas mixing means for supplying a high-concentration oxygen-containing gas to the gas circulation system and mixing it with a reaction exhaust gas. 5. The apparatus according to claim 4, wherein the gas circulation line has a condenser for removing condensable components from the reaction exhaust gas.