JP2003128617A - Method for producing high purity terephthalic acid by high temperature separation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing high purity terephthalic acid at low energy consumption in a method for producing the terephthalic acid by hydrolysis of dimethyl terephthalate. SOLUTION: The high purity terephthalic acid is produced by transferring a substance of which the melting point is lower than a separation temperature along with water to the filtrate by subjecting terephthalic acid/water slurry after hydrolysis reaction to high temperature solid/liquid separation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to fibers, films,
TECHNICAL FIELD The present invention relates to a method for producing terephthalic acid, which is a main raw material of a polyester resin widely used for industrial members, packaging materials, general molded products, etc., and more specifically, it is obtained by hydrolyzing a mixture of DMT and / or MMT. The present invention relates to a method for producing high-purity terephthalic acid by solid-liquid separating terephthalic acid at high temperature.

[0002]

2. Description of the Related Art Methods for industrially producing terephthalic acid include a method of liquid phase oxidation of paraxylene (PX) with molecular oxygen, and a method of hydrolyzing dimethyl terephthalate. Both are known. Terephthalic acid produced by the PX liquid phase oxidation method contains para-toluic acid or 4-carboxybenzaldehyde as a main impurity. On the other hand, terephthalic acid produced by the DMT hydrolysis method contains MMT and DMT as main impurities. In the DMT hydrolysis method,
In order to reduce the amount of MMT and DMT, mainly 2
Two methods are known. The first method is a method of appropriately adjusting the reaction conditions of the hydrolysis reaction, and specifically, raising the reaction temperature or extending the reaction time. However, if the reaction temperature is increased, the pressure will increase exponentially with it, and the amount of capital investment will increase.
In addition, there is a drawback that the production efficiency is lowered when the reaction time is extended. A second method is a method in which crude terephthalic acid containing the above impurities is washed with demineralized water at high temperature to remove the impurities and obtain high-purity terephthalic acid. Japanese Patent Publication No. 55-141433 discloses D
DM contained in terephthalic acid obtained by TM hydrolysis method
A method is described in which T and MMT are pressure-fed to a countercurrent washer and the crystal sludge is countercurrently washed with demineralized water in the washer.
However, the purification method according to the above method requires a large amount of demineralized water and has to maintain a high temperature, which causes a problem that the running cost becomes very high.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing highly pure terephthalic acid by separating and removing DMT and MMT from terephthalic acid by a simpler method.

[0004]

DISCLOSURE OF THE INVENTION The present invention contains unreacted DMT and MMT as impurities in the production of terephthalic acid by hydrolyzing dimethyl terephthalate (DMT) and / or monomethyl terephthalate (MMT). After obtaining a mixture of the crude terephthalic acid to be reacted with a reaction mother liquor mainly consisting of water, terephthalic acid is precipitated at a temperature not lower than the melting point of the impurities and lower than the sublimation temperature of terephthalic acid, and then solid-liquid separated. The present invention relates to a method for producing terephthalic acid, which comprises removing impurities together with a reaction mother liquor to the filtrate side.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The DMT and / or MMT used in the present invention may be those produced by a depolymerization reaction of polyester with ethylene glycol and a subsequent transesterification reaction with methanol, , A paraxylene (p-X) and a paratoluic acid methyl ester (p-TE) may be used as a starting material, but industrially, a product obtained by the method is preferable.

In the method for producing terephthalic acid of the present invention, the hydrolysis reaction is carried out by DMT and / or MMT.
Is carried out in the reactor (either batch type or continuous type can be adopted without any problem) with or without a catalyst. In the hydrolysis reaction of DMT and / or MMT, the amount of water used is 0.1 to 100 times by weight that of DMT and / or MMT. If it is less than 0.1 times by weight, the hydrolysis reaction is not sufficiently carried out, while if it is more than 100 times by weight, the amount of water used is too large, resulting in energy loss and possibly cost increase. The hydrolysis reaction of DMT and / or MMT is performed at a temperature of 200 ° C. or higher and lower than 300 ° C. at a pressure of 3.0.
~ 4.6 MPa (gauge pressure), preferably temperature 230 ~
260 ° C., pressure 3.0 to 4.6 MPa (gauge pressure), more preferably temperature 250 to 260 ° C., pressure 4.0.
It is desirable to react at 4.6 MPa (gauge pressure) for several hours. The methanol produced by the hydrolysis reaction is discharged out of the system from the reactor head together with dimethyl ether produced as a by-product.

The terephthalic acid formed by the hydrolysis reaction has a very low solubility in water, so a certain amount of terephthalic acid is precipitated at the end of the reaction.
Further, in order to increase the recovery rate of terephthalic acid, it is possible to discharge the reaction mother liquor out of the system by means such as evaporation. Then, the melting point of the impurities (MMT: 222
℃, DMT: 141 ℃) or more, terephthalic acid sublimation temperature (300 ℃) or less, usually 170 ℃ or more 3
By performing solid-liquid separation at a temperature of less than 00 ° C, preferably 230 ° C or more and less than 300 ° C, and more preferably 230 to 260 ° C, the cake mainly consisting of terephthalic acid and mainly water are dissolved to dissolve DMT and / or MMT. The filtrate is separated into At this time, solid-liquid separation is performed by filtration, centrifugation, or a similar method. The obtained terephthalic acid cake can be obtained as terephthalic acid having a total content of impurities of DMT and MMT of 0.01 to 1,000 ppm. In addition, by reusing the above filtrate as reaction water for the hydrolysis reaction, the DMT and MMT contained in the filtrate can be reused as a raw material, reducing the amount of waste and improving the raw material basic unit. Can also contribute. The terephthalic acid produced by the method described above is suitable for almost all purposes of use. In particular, it can be used as terephthalic acid suitable for a packaging material such as polyethylene terephthalate (PET) which requires a high-purity raw material and a polyester film.

[0008]

EXAMPLES The contents of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. The impurities DMT and MMT contained after the hydrolysis reaction were quantified by a high performance liquid chromatograph (HPLC: D-7000 manufactured by Hitachi, packed column: RP-18; 2).

Example 1 DMT (1.0 kg) and distilled water (2.0 kg) were reacted at 280 ° C. under a pressure capable of maintaining a liquid phase for 2 hours. 280 after reaction
Solid-liquid separation was performed while maintaining the temperature of ° C, and 0.74 kg of solid terephthalic acid was taken out and dried. The amount of impurities in terephthalic acid obtained by the above operation is DMT = 2 pp
m, MMT = 21 ppm.

Example 2 1.0 kg of DMT and 2.0 kg of distilled water were reacted at 250 ° C. for 2 hours under a pressure capable of maintaining a liquid phase. 250 after reaction
Solid-liquid separation was performed while maintaining the temperature of ° C, and 0.77 kg of solid terephthalic acid was taken out and dried. The amount of impurities in terephthalic acid obtained by the above operation is DMT = 18 pp
m, MMT = 210 ppm.

Example 3 1.0 kg of DMT and 2.0 kg of distilled water were reacted at 250 ° C. for 2 hours under a pressure capable of maintaining a liquid phase. 180 after reaction
After cooling to 0 ° C, solid-liquid separation was performed while maintaining the temperature of 180 ° C, and 0.77 kg of solid terephthalic acid was taken out and dried. Impurities in terephthalic acid obtained by the above operation were DMT = 21 ppm and MMT = 4027 ppm.
Met.

Comparative Example 1 DMT (1.0 kg) and distilled water (2.0 kg) were reacted at 250 ° C. for 2 hours under a pressure capable of maintaining a liquid phase. 100 after reaction
After cooling to 0 ° C, solid-liquid separation was performed while maintaining the temperature of 100 ° C, and 0.77 kg of solid terephthalic acid was taken out and dried. The amount of impurities in terephthalic acid obtained by the above operation was DMT = 590 ppm, MMT = 6,027 p
It was pm.

[0013]

According to the present invention, highly pure terephthalic acid can be obtained easily and stably. Also,
The terephthalic acid produced according to the invention is suitable for almost all purposes of use. In particular, it can be used as terephthalic acid suitable for a packaging material such as polyethylene terephthalate (PET) which requires a high-purity raw material and a polyester film.

Continued front page    (72) Inventor Minoru Nakajima             77, Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Stock Association             Company Matsuyama Office F-term (reference) 4H006 AA02 AC46 AD15 BB31 BC10                       BC35 BC40 BC51 BJ50 BS30

Claims (10)

[Claims] 1. A crude terephthalic acid containing unreacted DMT and MMT as impurities in producing terephthalic acid by hydrolyzing dimethyl terephthalate (DMT) and / or monomethyl terephthalate (MMT),
After obtaining a mixture with a reaction mother liquor consisting mainly of water, terephthalic acid is precipitated at a temperature not lower than the melting point of the impurities and lower than the sublimation temperature of terephthalic acid, followed by solid-liquid separation to filter the impurities together with the reaction mother liquor. A method for producing terephthalic acid, which is characterized in that it is removed on the liquid side. 2. The amount of water used for carrying out the hydrolysis reaction is
The method for producing terephthalic acid according to claim 1, which is 0.1 to 100 times the weight of DMT and / or MMT. 3. The method for producing terephthalic acid according to claim 1, wherein the hydrolysis reaction is carried out at a reaction temperature of 200 ° C. or higher and lower than 300 ° C. 4. The method for producing terephthalic acid according to claim 1, wherein the solid-liquid separation is performed at 170 ° C. or higher and lower than 300 ° C. 5. The method for producing terephthalic acid according to claim 4, wherein solid-liquid separation is performed at 230 ° C. or higher and lower than 300 ° C. 6. The method for producing terephthalic acid according to claim 1, wherein the solid-liquid separation is carried out by filtration or centrifugation. 7. The total amount of impurities mainly composed of DMT and / or MMT contained in terephthalic acid is 0.01.
The method for producing terephthalic acid according to claim 1, wherein the amount is ˜1,000 ppm. 8. The method for producing terephthalic acid according to claim 1, wherein the filtrate separated by solid-liquid separation is reused as reaction water for the hydrolysis reaction. 9. The method for producing terephthalic acid according to claim 1, wherein DMT and / or MMT is produced by a depolymerization reaction of polyester with ethylene glycol and a subsequent transesterification reaction with methanol. 10. The terephthalic acid according to claim 1, wherein DMT and / or MMT is produced from a mixture containing para-xylene (p-X) and para-toluic acid methyl ester (p-TE) as a raw material. Manufacturing method.