JPH04145044A - Production of high-purity terephthalic acid - Google Patents

Abstract

PURPOSE:To produce high-purity terephthalic acid by oxidizing p-xylene in the liquid phase in the presence of acetic acid solvent, carrying out hydrogenating treatment using hydrous acetic acid as a solvent, providing crystallized high-purity teretphtalic acid, refiltering the separated mother liquor and recycling the mother liquor for use. CONSTITUTION:p-Xylene is oxidized in the liquid phase with O2 in the presence of a catalyst containing Co and Mn in acetic acid solvent to provide crude terephthalic acid, which is then catalytically treated with a group VIII noble metal in the presence of hydrogen using acetic acid containing 1-50wt.% water as a solvent. The resultant reaction solution is cooled to deposit and separate crystals of the terephthalic acid. Thereby, the high-purity terephthalic acid is separated. On the other hand, the separated mother liquor is refiltered to recycle the obtained mother liquor for use as a solvent for the liquid-phase oxidative reaction. As a result, the objective terephthalic acid of excellent color quality is obtained. Since the mother liquor is recycled, yield is improved. The amount of waste water is also extremely reduced substantially without requiring waste water treating equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing high-purity terephthalic acid with excellent white discoloration and useful as a polymer intermediate raw material for polyester resins, fibers, films, etc.

[Prior art] Terephthalic acid is produced by oxidizing paraxylene, and is usually produced using acetic acid as a solvent and a heavy metal salt catalyst such as cobalt or manganese, or a catalyst in which a promoter such as a bromine compound or acetaldehyde is added thereto. is used.

Crude terephthalic acid obtained by liquid phase oxidation is usually 4-
It contains carpoxyhenzaldehyde (4CBA) and contains a large amount of impurities, so it is not suitable for reacting with glycol as it is to make polyester.

As a method for producing high-purity terephthalic acid from crude terephthalic acid containing impurities such as 4 CBA, many methods are known in which purification treatment is performed through reactions such as oxidation or reduction. For example, as a hydrogenation reduction purification method, Japanese Patent Publication No. 41-16860 describes a method of hydrogenating an aqueous solution of crude terephthalic acid at high temperature in the presence of a hydrogenation catalyst, and Japanese Patent Publication No. 51-32618 and Japanese Patent Publication No. 51-38698 discloses an improved method of this hydrogenation treatment.

[Problems to be Solved by the Invention] The above-mentioned Japanese Patent Publication No. 4 in which crude terephthalic acid solution is hydrogenated
In Japanese Patent Publication No. 1-16860, Japanese Patent Publication No. 51-32618, and Japanese Patent Publication No. 51-38698, water is used as an inert solvent for the reaction. However, since water is not a good solvent for organic substances, impurities such as p-)ruyl acid, which is a reduction product of 4 CBA in crude terephthalic acid, are easily mixed into the terephthalic acid crystals, and the color of terephthalic acid is It has the disadvantage that it cannot be improved sufficiently. Special Public Service 1977-
No. 49049 and Special Publication No. 53-24057 have p-
) An improved method for preventing the contamination of ruyl acid has been proposed, but such a method complicates the manufacturing process and requires complicated operations. Furthermore, even if such a method is adopted, it is necessary to substantially eliminate the contamination of p-)ruyl acid (4C of crude terephthalic acid).
It is necessary to keep the BA content to a low level. For this reason, the oxidation reaction conditions in the production process of crude terephthalic acid become severe, leading to an increase in combustion. Furthermore, the wastewater from which terephthalic acid has been separated contains many organic substances in addition to p-)ruyl acid and terephthalic acid, which are discharged together with the mother liquor, and must be treated to prevent water pollution before being discharged outside the factory as wastewater. I need.

The present invention overcomes the quality problems faced by the prior art, improves the method for purifying crude terephthalic acid containing a large amount of impurities such as 4CBA, and enables industrial implementation with simple operations.
The present invention provides an economically extremely advantageous method for producing high-purity terephthalic acid.9 [Means for solving the problems] The inventors have conducted intensive research into a method for producing terephthalic acid that has the above-mentioned problems. As a result, the crude terephthalic acid obtained by liquid-phase oxidation of paraxylene in an acetic acid solvent was subjected to hydrogenation treatment using aqueous acetic acid as a solvent, and the terephthalic acid was crystallized and the separated mother liquor was recycled. It was discovered that the separated mother liquor can be recycled as a solvent for liquid phase oxidation reaction by filtration treatment, leading to the present invention.

That is, the present invention provides a method for producing terephthalic acid by liquid-phase oxidation of p-dialkylbenzenes with molecular oxygen. Step (b) of producing crude terephthalic acid obtained by liquid phase oxidation of step (b).
Cooling the reaction solution in step (c) of contact treatment with a group III noble metal to precipitate and separate terephthalic acid crystals,
This is a method for producing high purity terephthalic acid, which is characterized by having a step of re-filtering the separated mother liquor and recycling the obtained filtrate to step (a).

The present invention will be explained in detail below.

The present invention purifies crude terephthalic acid obtained by oxidizing paraxylene by a liquid phase oxidation method. This process (
Cobalt, manganese and bromine compounds are usually used as catalysts for the oxidation step a). Alternatively, a method may be used in which a promoter such as acetaldehyde or methyl ethyl ketone is used instead of the bromine compound. Acetic acid is used as a solvent in this oxidation step.

Note that this acetic acid solvent may contain about 3 to 20'A of water. Air or oxygen is usually used as molecular oxygen, and generally the temperature is 170-230'' C1 pressure 10
The reaction is carried out at ~30 atmospheres.

Crude terephthalic acid obtained by liquid phase oxidation usually contains many impurities including 4CBA.

The present invention has a 4CBA content of 11,000 pp or more, especially 20
It is preferable to apply it to crude terephthalic acid of 00 ppm or more. This is because in the production of crude terephthalic acid, if the 4 CBA content is high, the oxidation reaction conditions can be relaxed, and the combustion loss of acetic acid etc. due to the oxidation reaction can be suppressed, which is extremely advantageous industrially.

In step 3), the crude terephthalic acid obtained by the above oxidation is dissolved in high-temperature hydrous acetic acid, and then subjected to catalytic hydrogenation treatment with a noble metal catalyst from group Ⅰ of the periodic table in the presence of hydrogen.

By this catalytic hydrogenation treatment, 4 CBA contained in the crude terephthalic acid is converted to p-toluic acid, and other coloring impurities are also converted to acetic acid soluble substances.

Noble metals belonging to Group 1 of the periodic table are effective as catalysts for catalytic hydrogenation treatment, with palladium, platinum, rhodium, ruthenium and the like being preferred, with palladium and platinum being particularly preferred. These metals do not necessarily have to be used alone and can be used in combination.

These catalytic metals are used supported on porous materials,
Activated carbon is usually used as the porous material. Coconut shell charcoal is particularly preferred as the activated carbon. The catalytic metal supported on the carrier is effective in a small amount, but an appropriate amount is required to maintain activity for long-term use, and 0.1 to 53!1% is preferable. The supported metal catalyst may be in the form of granules or powder.

Acetic acid is used as the solvent in step (b). The water concentration contained in acetic acid is in the range of 1 to 50% by weight, preferably 3 to 20% by weight. By using hydrated acetic acid in this range, the characteristics of acetic acid as a solvent can be utilized,
Not only can high-purity terephthalic acid with excellent color quality be obtained, but also high-purity terephthalic acid can be industrially produced extremely economically.

That is, by using acetic acid with a water concentration of 3% by weight or more, the solubility of terephthalic acid at high temperatures can be increased, and loss of acetic acid due to the hydrogenation reaction of acetic acid can also be suppressed. moisture is 5
0! If the i amount exceeds χ, the quality of the obtained terephthalic acid will deteriorate. In addition, if the water content exceeds 20% by weight, if the separated mother liquor after catalytic hydrogenation treatment is recycled to the oxidation process, the water concentration will increase in the oxidation process, resulting in an increase in the amount of impurities produced, and the terephthalic acid will become colored, impairing product quality. This is not desirable as it will make things worse. In this case, it may be considered to subject the separated mother liquor to distillation treatment, but this is not economical because it increases energy consumption.

The catalytic hydrogenation treatment of crude terephthalic acid is carried out under high pressure and high temperature in order to be carried out in a solution state. Since the solubility of terephthalic acid in a solvent depends on temperature, at low temperatures only a low concentration crude terephthalic acid solution can be processed, which is industrially disadvantageous, so the temperature is set at 24.
It is necessary to maintain the temperature above 0"C. However, if the temperature is too high, there is a risk of side reactions occurring and hydrogenolysis of acetic acid. The concentration of the crude terephthalic acid solution is preferably in the range of 10 to 30% by weight, and it is sufficient that the concentration is below the concentration at which terephthalic acid is completely dissolved at the selected temperature.The pressure is determined by the liquid phase of the solvent. Any pressure is sufficient as long as it is sufficient to maintain hydrogen pressure and has a hydrogen partial pressure suitable for catalytic hydrogenation, and is usually in the range of 30 to 80 kg/cm''. It is desirable that the amount of hydrogen is at least twice the molar amount of 4CBA.

Catalytic hydrogenation treatment may be carried out either batchwise or continuously.

The treatment time should be sufficient time for the hydrogenation reaction to substantially proceed, usually 1 to 300 minutes, preferably 2 to 1 minute.
The duration is 20 minutes.

Note that the terephthalic acid solution after the catalytic hydrogenation treatment is filtered at high temperature to remove insoluble components such as traces of fragments of the hydrogen-based catalyst and foreign substances in the terephthalic acid.

In step (c), the terephthalic acid solution subjected to the catalytic hydrogenation treatment is cooled to crystallize terephthalic acid, and then the crystals are separated into solid and liquid. By washing and drying the separated crystals, high purity terephthalic acid with extremely high whiteness can be obtained.

After the mother liquor from which the crystals have been separated is refiltered, a part of it is passed through step (a).
) and the remainder is recycled to the catalytic hydrogenation step (b). Terephthalic acid and p-)ruyl acid are dissolved in the refiltered filtrate, and are recovered as p-terephthalic acid in the oxidation step.

Refiltration of the separated mother liquor needs to be carried out at a temperature at which crystals do not precipitate, and a method of passing it through a porous filter medium is preferred. The reason why the Gagaru filtration treatment is necessary is that the group II noble metal catalyst used in the catalytic hydrogenation treatment has a strong inhibitory effect on the liquid phase oxidation reaction, so the separated mother liquor to be reused is not used in the catalytic hydrogenation treatment. This is because it is necessary to avoid contamination with the catalyst metal used. As the filtration treatment, a method of passing through a filter made of a porous material with an opening diameter of 0.1 to 5 μm is suitable. Particularly when filtering at high temperatures, it is desirable to use a porous material such as carbon, ceramic, glass, or sintered metal as the corrosion-resistant base material.

By using the separated mother liquor in the oxidation reaction, p-)luic acid and terephthalic acid contained in the separated mother liquor are not only recovered as crude terephthalic acid, but also acetaldehyde and ethanol, which are hydrogenation products of acetic acid, are recovered. ,
Ethyl acetate etc. are also oxidized to acetic acid. That is, according to the method of the present invention, the yield of terephthalic acid is improved.

[Effects of the Invention] The use of the method of the present invention in the production of terephthalic acid has the following advantages.

(1) Extremely useful as a raw material for polyester products for highly functional applications
High purity terephthalic acid with excellent color quality can be obtained for the first time.

(2) Since crude terephthalic acid containing 11,000 pp or more of 4 CBA can be used for catalytic hydrogenation treatment, the liquid phase oxidation reaction conditions can be relaxed and combustion losses of raw materials and solvent can be reduced. can do.

(3) By recycling the separated mother liquor after catalytic hydrogenation treatment as a solvent for liquid-phase oxidation reaction, terephthalic acid, p-)ruyl acid, etc. in the separated mother liquor are recycled together with acetic acid, so terephthalic acid can be recovered. rate will improve.

(4) In the method of the present invention, the amount of waste water from the terephthalic acid production equipment is extremely small, and waste water treatment equipment is substantially unnecessary.

As described above, the present invention has great industrial significance.

[Example] Next, the present invention will be explained in more detail with reference to Examples. However, the present application is not limited to these Examples. Olh, which indicates Naori quality, is 2 g of terephthalic acid crystals added to 25 ml of 2N hydrium hydroxide solution? This is the absorbance at a wavelength of 340 mm measured using a 50 mm wide glass cell for a containerized terephthalic acid solution.

Example 1 Crude terephthalic acid was obtained by liquid phase oxidation of paraxylene in the following manner.

1.11 g of cobalt acetate tetrahydrate was placed in advance in a pressure-resistant titanium oxidation reactor (inner volume 242) equipped with a stirring device, a reflux cooling device, a heating device, a raw material inlet, an air inlet, an exhaust gas outlet, and a reflux liquid reflux port. , manganese acetate tetrahydrate 2.15g, hydrobromic acid (47χ) 2.36g and acetic acid (moisture 10
χ) 1044g (cobalt 249ppm,
Manganese 458ppm, bromine 101044ppm. The reactor containing the catalyst and acetic acid was heated to 210"C, and 350g of paraxylene was continuously supplied at a constant rate for 45 minutes while blowing air at a temperature of 210°C and a pressure of 17kg/cm"G. and oxidized. During this time, the amount of air supplied was adjusted to maintain the oxygen concentration of the exhaust gas at approximately 2z. Five minutes after the supply of paraxylene was stopped, air blowing was stopped and the reactor was cooled. The cooled reaction slurry was taken out from the reactor and the crystals separated by filtration were washed with acetic acid and dried to obtain crude terephthalic acid. As a result, the quality of crude terephthalic acid was 4, CBA content 3,000 ppm, 0
Dano 1.5, and the yield was 96.5 mo IL2.

Next, this crude terephthalic acid was subjected to catalytic hydrogenation treatment as described below.

Stirring device, reflux cooling device, heating device, raw material inlet, gas inlet, reaction liquid outlet, exhaust gas outlet, bottom with an average of 3μ
A pressure-resistant model equipped with a part of the carbon filter, a pressure-resistant receiver that receives the filtrate through the carbon filter and the connecting valve, and a reflux liquid reflux port, and a hanging titanium wire mesh catalyst cage that can be raised and lowered by an electromagnetic induction device. 120 g of crude terephthalic acid and 1080 g of acetic acid (containing 10 x water) were placed in a titanium reaction vessel (inner volume 2j2), and the gas in the vessel was replaced with hydrogen, and then the pressure was increased to 5 kg/cm2G with hydrogen and the temperature was raised. Catalyst is coconut shell activated carbon (4-8 mesh)
15 g of a granular palladium catalyst (containing 0.5 wt % palladium) on which palladium was supported was placed in the catalyst cage and attached to the reaction vessel, and the catalyst was held at a position above the level of the reaction liquid. When the temperature reaches 240°C, the catalyst cage is lowered and the temperature is increased to 240°C with the catalyst immersed in the reaction solution.
Hydrogen at 16Nf under pressure 30kg/cm2G
The air was blown for 20 minutes at a constant flow rate of /h. After 20 minutes, the catalyst was withdrawn from the reaction solution and the hydrogen injection was stopped, the catalytically hydrogenated high-temperature solution was filtered through a carbon filter at the bottom of the container, and the filtration mother liquor was collected in a pressure receiver. The pressure receiver was gradually cooled to 100°C to crystallize purified terephthalic acid. Next, the pressure receiver was opened, and the slurry inside was filtered through a glass filter with a standard diameter of 10 to 16 μm, and the crystals were rinsed with pure water at 100° C. and then dried to obtain a product. As a result, the recovery rate of the product based on the crude terephthalic acid crystals was 98.2 mol χ. As a result of analyzing the obtained terephthalic acid by polarography, 4CBA was not detected, and p4ruyl acid was analyzed by gas chromatography after methyl esterification, but this was also not detected.

Moreover, 0D340 was 0.1.

The filtered mother liquor from which the crystals were separated was heated to 100°C and 0.5μ
When para-xylene was oxidized in liquid phase in the same manner as above using the acetic acid solution obtained by re-filtering with a carbon filter of It's no different than if you did
The yield of crude terephthalic acid was 97.1 mol χ. This increase in yield is due to the terephthalic acid contained in the filtration mother liquor and p.
-1 This is because terephthalic acid was recovered from ruyl acid.

Furthermore, when the mother liquor from which the terephthalic acid crystals were separated by hydrogenation treatment was directly used as a solvent for liquid phase oxidation, the oxidation reaction proceeded extremely slowly and only poor quality crude terephthalic acid was obtained (yield of crude terephthalic acid 86 mol 2, 4CBA content in crude terephthalic acid 1.8 mol χ). The obtained terephthalic acid could not be purified to a high degree even by hydrogenation treatment, and could not be practically used as a raw material for purification.

Patent applicant: Mitsubishi Gas Chemical Co., Ltd. Agent: Patent Attorney Sadafumi Kohori

Claims (1)

[Claims] When producing terephthalic acid by liquid-phase oxidation of para-xylene with molecular oxygen, (a) para-xylene is oxidized with molecular oxygen in the presence of a catalyst containing cobalt and manganese in an acetic acid solvent; Step (b) of producing crude terephthalic acid obtained by phase oxidation.
Step (c) of contact treatment with a group III noble metal; the reaction solution of step (b) is cooled to precipitate and separate terephthalic acid crystals; the separated mother liquor is refiltered; the resulting filtrate is recycled to step (a). A method for producing high-purity terephthalic acid, characterized by having a step of using