JP2734121B2 - Method for producing aromatic carboxylic acid - Google Patents

Description

The present invention relates to a method for producing an aromatic carboxylic acid by oxidizing an aromatic compound containing an alkyl substituent or a partially oxidized alkyl substituent.

[Prior Art] Aromatic carboxylic acids are important chemical products, and in particular, aromatic dicarboxylic acids are widely used as raw materials for resins and polymers. For example, terephthalic acid, which is a typical aromatic dicarboxylic acid, is important as a raw material for a polyester resin.

Conventionally, water-soluble catalysts such as cobalt acetate, manganese acetate, and bromine compounds have been used for the production of aromatic carboxylic acids (for example, JP-A-60-184043). However, there is a problem that aromatic carboxylic acids produced using such a water-soluble catalyst cannot be satisfactory in purity and hue. Conventionally, purification treatment such as hydrogenation treatment is performed to improve purity and hue.

FIG. 2 is a process chart showing a conventional method for producing an aromatic carboxylic acid. In a reaction apparatus 1, a reaction solution 5 composed of a starting material 2, a reaction medium 3 and a catalyst 4 is oxidized by air 6. After the completion of the reaction, the reaction solution 5 containing the precipitated reaction product
To the separator 7a for solid-liquid separation. The reaction product thus obtained is led to a purifying apparatus 8, dissolved in water 9 under high temperature and high pressure conditions, and subjected to hydrogenation treatment with hydrogen gas 10 for purification. After the purification treatment, the aqueous solution in which the reaction product is dissolved is led to the crystallizer 11 for crystallization to precipitate crystals. Next, the precipitated crystals are led to a separator 7b together with water 9 to be subjected to solid-liquid separation, whereby the aromatic carboxylic acid 12 is isolated. In the figure, 13 is an exhaust gas, 14a and 14b are separated liquids, and 15 is a stirring blade. The separation liquid (mother liquor) 14a containing the catalyst 4 separated by the separator 7a is:
The reaction medium 3 and the catalyst 4 are circulated through the reactor 1.

As described above, in the conventional production method, since the reaction product is precipitated in the reaction solution 5 in the reactor 1, the catalyst 4
Crystals with low purity and poor hue are precipitated by entrapping other impurities. For this reason, in order to produce a high-purity aromatic carboxylic acid, a complicated purification step is required, such as dissolving the reaction product in water, performing a hydrogenation treatment, and further performing crystallization. Production of aromatic carboxylic acids has been complicated.

[Problems to be solved by the invention]

An object of the present invention is to propose a method for producing a high-purity aromatic carboxylic acid by a simple process in order to solve the above problems.

[Means for solving the problem]

The present invention provides for oxidizing an aromatic compound containing an alkyl or partially oxidized alkyl substituent with a molecular oxygen-containing gas in an aqueous reaction medium in the presence of a water-insoluble metal oxide catalyst, While the aromatic carboxylic acid generated by the oxidation reaction is dissolved in the aqueous reaction medium under heating and pressure, the water-insoluble metal oxide catalyst is subjected to solid-liquid separation, and the obtained mother liquor is cooled to obtain an aromatic compound. A method for producing an aromatic carboxylic acid, comprising depositing an aromatic carboxylic acid.

The compound used as a starting material in the method for producing an aromatic carboxylic acid of the present invention is an aromatic compound containing an alkyl substituent or a partially oxidized alkyl substituent. Examples of the alkyl substituent include an alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, a propyl group, and an isopropyl group. Partially oxidized alkyl substituents include, for example, aldehyde groups, carboxyl groups, hydroxyalkyl groups, and the like. The aromatic ring is not limited to a single ring, and a polycyclic ring may be used.
These starting materials may be obtained by any method. Specific examples of such compounds include tolueneben, benzaldehyde, benzyl alcohol, o-xylene, m-xylene, p-xylene, trimethylbenzene, o-toluic acid, m-toluic acid, p-toluic acid, and o-toluic acid. Aldehyde, m-tolualdehyde, p-tolualdehyde, 2-carboxybenzaldehyde, 3-
Examples thereof include carboxybenzaldehyde, 4-carboxybenzaldehyde, methylnaphthalene, dimethylnaphthalene, diisopropylnaphthalene, 2,6-diformylnaphthalene, 1-naphthaldehyde, 2-naphthaldehyde, and a mixture thereof. Examples of the mixture include a mixture of p-xylene and p-toluic acid.

These starting materials are generally used in an amount of 1 to 900 parts by weight, preferably 100 parts by weight of the aqueous reaction medium, and preferably in such a proportion that the starting materials are dissolved in the aqueous reaction medium under the oxidation reaction conditions.

The present invention uses a water-insoluble metal oxide catalyst as a catalyst. Specific examples of such metal oxide catalysts include RuO ₂ , MnO ₂ , Al ₂ O ₃ , SiO ₂ , V ₂ O ₅ , and Nb ₂ O ₃ . Of these, RuO ₂ is preferred. One metal oxide catalyst may be used alone, or two or more metal oxide catalysts may be used in combination. The metal oxide catalyst may contain a small amount of many compounds.

The metal oxide catalyst may be used in the form of a powder or a granule, or may be used by being supported on a carrier. Examples of the carrier include activated carbon, alumina, zeolite, graphite, silica, magnesium oxide, clay, barium sulfate, calcium carbonate and the like.

The metal oxide catalyst is the sum of the starting materials and the aqueous reaction medium
0.01 to 10 parts by weight, preferably 0.03 to 3 parts per 100 parts by weight
It is preferred to use it in parts by weight.

Examples of the molecular oxygen-containing gas used in the present invention include oxygen, a mixed gas of oxygen and an inert gas such as nitrogen gas, and air, but the use of air is sufficient. The method of supplying the molecular oxygen-containing gas is not particularly limited, and for example, a method of continuously supplying the molecular oxygen-containing gas to the reaction system, a method of performing the reaction under pressure of the molecular oxygen-containing gas, and the like can be adopted. However, a method of continuously supplying a molecular oxygen-containing gas is preferable.

In the present invention, water or a solution containing water as a main component is used as a reaction medium, and in these aqueous reaction media,
The aromatic compound is oxidized with a molecular oxygen-containing gas in the presence of the catalyst to produce an aromatic carboxylic acid.

The aromatic carboxylic acid produced is a carboxylic acid corresponding to the aromatic compound used as a starting material.For example, when p-xylene, p-toluic acid or a mixture thereof is used as a starting material, terephthalic acid is produced. You.

The reaction temperature is usually 150 to 280 ° C, preferably 210 to 260 ° C,
The reaction time is usually 0.5-5 hours, preferably 1-3 hours,
The reaction pressure is at least a pressure at which the mixture can maintain a liquid phase at the reaction temperature, and is usually 15 to 65 kg / cm ² · G, preferably 30 to 60 kg / cm ² · G.

The reaction can be carried out under any combination of conditions within the above reaction conditions and the ratio of the starting materials to the aqueous reaction medium. Therefore, the reaction can be carried out in a state in which the starting material and the aromatic carboxylic acid to be formed are completely dissolved in the aqueous reaction medium, or in a state in which a part of them is present as a solid. It is preferable to carry out the reaction in a state where the generated aromatic carboxylic acid is completely dissolved. By performing the reaction in a completely dissolved state, the catalyst and the intermediate produced by the oxidation reaction do not mix in the target aromatic carboxylic acid crystals,
A higher purity aromatic carboxylic acid can be obtained.

The reaction is preferably carried out with stirring in order to sufficiently bring the starting material, the catalyst and the molecular oxygen-containing gas into contact.

The reactor can be pressurized so that water and starting materials do not evaporate at high temperature, and efficiently disperse gas (molecular oxygen-containing gas), liquid (water, starting material), and solid (catalyst, starting material). Reactors that can be used are preferred. Specifically, a tank-type or tube-type reactor can be preferably used.

The reaction system is not particularly limited, and any of a continuous system or a batch system can be adopted.

In the present invention, after the completion of the reaction, the metal oxide catalyst present as a solid in the aqueous reaction medium and the generated aromatic carboxylic acid are separated. Aromatic carboxylic acids are usually hardly soluble or insoluble in water under normal temperature and pressure,
Under normal temperature and normal pressure, the metal oxide catalyst and the aromatic carboxylic acid cannot be separated. However, under the conditions of high temperature and high pressure, the amount of the aromatic carboxylic acid dissolved in water increases, and under the conditions of high temperature and high pressure, the solid-liquid separation of the metal oxide catalyst and the aromatic carboxylic acid is performed by means such as filtration and centrifugation. It can be done easily.

As a condition of high temperature and high pressure to a solid-liquid separating the metal oxide catalyst and the aromatic carboxylic acid is typically the temperature is 230 to 280 ° C., the pressure is 40~80kg / cm ² · G, preferably the temperature is 240 to 260 ° C., The pressure is preferably 50-60 kg / cm ² · G. Under such high-temperature and high-pressure conditions, the aromatic carboxylic acid is usually dissolved in water by about 10% by weight, so that solid-liquid separation can be easily performed. In addition, since solid-liquid separation can be performed any number of times, the metal oxide catalyst and the aromatic carboxylic acid can be completely separated. The separated metal oxide catalyst can be reused as it is or after a regeneration treatment.

When the catalyst is used as a fixed bed, the reaction occurs only by passing the reaction solution, and the aromatic carboxylic acid as a product flows out in a state where the catalyst is separated into solid and liquid.

Next, the mother liquor thus solid-liquid separated is crystallized at a temperature lower than the temperature at the time of solid-liquid separation, preferably at a temperature of 200 to 70 ° C., to precipitate an aromatic carboxylic acid. The precipitated aromatic carboxylic acid can be isolated by means such as filtration and centrifugation.

The aromatic carboxylic acid produced in this way is already precipitated in a state where the catalyst and other solids are separated,
The inclusion of impurities is extremely small and the purity is high. Therefore, it can be used as a raw material of a polyester resin or the like only by crystallization without performing purification treatment such as hydrogenation treatment. The aromatic carboxylic acid produced by the production method of the present invention can be further subjected to a known purification treatment to obtain a higher purity.

〔Example〕

FIG. 1 is a process chart showing one embodiment of the method for producing an aromatic carboxylic acid of the present invention. In the figure, 1 is a fixed bed type reaction apparatus, 3 is an aqueous reaction medium, and a water insoluble metal oxide catalyst is used as a catalyst 4 as a catalyst 4 in a fixed bed. In the reactor 1, the starting material 2 is heated at 240 to 250 ° C. and 50 to 55 kg / cm ^2.
The reaction solution 5 completely dissolved in the reaction medium 3 under the conditions of high temperature and high pressure of G is oxidized by air 6 in the presence of the catalyst 4. The reaction product produced by the oxidation reaction is passed through a fixed bed of the catalyst 4 while being completely dissolved in the reaction medium 3 under the conditions of high temperature and high pressure as described above, and is separated therefrom. Lead to. At this time, since the catalyst 4 exists as a fixed bed, the catalyst 4 and the mother liquor in which the reaction product is dissolved can be completely solid-liquid separated. The mother liquor led to the crystallizer 11 is crystallized at a temperature lower than the temperature at the time of the oxidation reaction to precipitate crystals. Next, the precipitated crystals are led to a separator 7 together with the reaction medium 3 and subjected to solid-liquid separation to isolate the aromatic carboxylic acid 12. In the figure, 13 is an exhaust gas, 14 is a separated liquid, and 15 is a stirring blade.

In this production method, since the aromatic carboxylic acid is separated from the catalyst in a state of being dissolved in the aqueous reaction medium, the purity of precipitated crystals is increased, and the purification step can be significantly reduced. In addition, by performing the oxidation reaction under the condition that the generated aromatic carboxylic acid does not precipitate, the catalyst and the intermediate of the oxidation reaction do not mix in the crystal of the aromatic carboxylic acid. Carboxylic acids can be produced. That is, as is clear from the comparison between FIG. 1 and FIG.
The purification process of the aromatic carboxylic acid can be greatly reduced, and a high-purity aromatic carboxylic acid can be produced by a simple process.

Example 1 p-xylene (hereinafter, abbreviated as PX) 15 ml, p-toluic acid (hereinafter abbreviated as p-TA) 5 g, as a catalyst ruthenium oxide (RuO ₂₎ 0.5 g and water 200ml The 500ml made of titanium After charging in an autoclave and purging with nitrogen, the temperature was raised.
When the temperature in the reactor reached 240 ° C., air was supplied at a rate of 50 Nl / hour for 3 hours to perform an oxidation reaction. The pressure at this time was 55 kg / cm ² · G.

After 3 hours, the catalyst was separated by filtration under the conditions of 240 ° C. and 55 kg / cm ² · G. The reaction solution after the catalyst separation was gradually cooled to precipitate terephthalic acid crystals, which were separated by filtration at normal temperature and normal pressure.

The thus obtained crystals were dried at 80 ° C. for 12 hours, and then analyzed by liquid chromatography, and terephthalic acid (hereinafter abbreviated as TA), p-TA, 4-carboxybenzaldehyde (hereinafter, 4-CBA) were analyzed. Abbreviated). The results are as follows.

TA; 53.8 mol% / (PX + p-TA) P-TA; 0.5 mol% / (PX + p-TA) 4-CBA; 50 ppm / TA According to the present invention, the alkyl substituent or partially oxidized. The aromatic compound having an alkyl substituent is oxidized with a molecular oxygen-containing gas in an aqueous reaction medium in the presence of a water-insoluble metal oxide catalyst, and the aromatic carboxylic acid generated by the oxidation reaction is heated, After being dissolved in the aqueous reaction medium under pressure, the water-insoluble metal oxide catalyst is solid-liquid separated,
Since the obtained mother liquor is cooled to precipitate an aromatic carboxylic acid, a high-purity aromatic carboxylic acid can be produced by a simple process.

[Brief description of the drawings]

FIG. 1 is a process chart showing a method for producing an aromatic carboxylic acid according to one embodiment of the present invention, and FIG. 2 is a process chart showing a conventional method for producing an aromatic carboxylic acid. In the respective drawings, the same reference numerals indicate the same or corresponding parts. 1: reaction device, 2: starting material, 3: reaction medium, 4: catalyst, 5: reaction solution, 6: air, 7, 7a, 7b: separator, 8: purification device, 9: water, 10: hydrogen gas, 11: crystallizer, 12: aromatic carboxylic acid, 13: exhaust gas, 14, 14a, 14b: separated liquid, 15: stirring blade.

Claims (1)

(57) [Claims] An aromatic compound containing an alkyl or partially oxidized alkyl substituent is oxidized by a molecular oxygen-containing gas in an aqueous reaction medium in the presence of a water-insoluble metal oxide catalyst. The aromatic carboxylic acid generated by this oxidation reaction is heated and dissolved in the aqueous reaction medium under pressure, the water-insoluble metal oxide catalyst is subjected to solid-liquid separation, and the obtained mother liquor is cooled. A method for producing an aromatic carboxylic acid, comprising precipitating an aromatic carboxylic acid.