JP2003128598A - Method for controlling particle diameter of terephthalic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which the particle diameter of terephthalic acid can simply be controlled by hydrolysis of dimethyl terephthalate without pulverization or installing a crystallizing tank in a process for producing particles. SOLUTION: The dimethyl terephthalate is hydrolyzed. In the process, the hydrolysis reaction temperature, weight ratio of water/dimethyl terephthalate in the reaction system and the amount of impurities in terephthalic acid are controlled. Thereby, the average particle diameter of the produced terephthalic acid is controlled to >=50 μm with the dispersion thereof within 10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle size control method for producing terephthalic acid (TA), which is a raw material of polyester resin widely used for fibers, films, industrial members, general molded articles and the like. More specifically, it relates to a method for controlling the particle size of terephthalic acid obtained by controlling the reaction conditions when terephthalic acid is produced by hydrolyzing dimethyl terephthalate (DMT).

[0002]

Various methods for industrially producing terephthalic acid are known, and one of them is dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) as a starting material, which is hydrolyzed with water. A method is known (Japanese Patent Laid-Open No. 55-141433, German Patent 29161).
97, JP-A-8-231464, etc.).

Regarding the particle size of terephthalic acid, recently, instead of controlling the conditions for forming terephthalic acid crystals, a method of crushing the formed terephthalic acid crystals in a slurry state to change the particle size distribution (Japanese Patent Laid-Open No. 9- 25561
No. 9), a part of the terephthalic acid slurry is extracted, finely pulverized by a wet pulverizer, re-mixed, and solid-liquid separated to change the slurry characteristics (Japanese Patent Laid-Open No. H11 (1999) -111945).
-100350 gazette) etc. are proposed.

However, a method for producing terephthalic acid having a particle size that can be practically used without using a wet or dry pulverizing method or providing a crystallization tank in the process of producing particles has hitherto been known. The reality is that it has not been proposed.

[0005]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above-mentioned prior art, and its purpose is to adopt a crushing method or without providing a crystallization tank in the process of producing particles. It is to propose a method that can easily control the particle size of terephthalic acid by a hydrolysis method of dimethyl terephthalate.

[0006]

According to the research conducted by the present inventors, the above-mentioned problem is "when hydrolyzing dimethyl terephthalate to produce terephthalic acid, hydrolysis reaction temperature, water / terephthalate in reaction system By controlling the weight ratio of dimethyl acid and the amount of impurities in terephthalic acid produced, the average particle size of terephthalic acid produced is controlled to 50 μm or more and the variation thereof is controlled to within 10%. Method. "

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. In the present invention, the method of hydrolyzing DMT may be either batch or continuous without any problem. At this time, the hydrolysis reaction temperature, water / dimethyl terephthalate in the reaction system are used. It is important to control the weight ratio and the amount of impurities of terephthalic acid to be produced. By doing so, the average particle diameter of the terephthalic acid to be produced is preferably 50 μm or more, which is suitable when industrially used as a polyester raw material, preferably Is 100 μm
With the above, the variation is within ± 10%, preferably ± 5
It is possible to control within%.

That is, the hydrolysis reaction of DMT is carried out at a temperature of 2
The temperature is 30 ° C. or higher, preferably 230 to 260 ° C., and the pressure at that time is preferably 2.8 to 4.6 MPa (gauge pressure).
As the above, the hydrolysis reaction is performed under high temperature and high pressure. Furthermore, the existing weight ratio of water to DMT (water / DMT) is 1 or more, preferably 1 to 4, and the amount of impurities in the terephthalic acid after the reaction is 1000 ppm or less, preferably dimethyl terephthalate and terephthalate contained as impurities. The total amount of monomethyl acidate (MMT) is controlled to be 1000 ppm or less.

Here, if the conditions other than the hydrolysis reaction temperature are the same, the higher the reaction temperature, the larger the particle size of terephthalic acid obtained, and the variation in particle size is suppressed. On the other hand, when the reaction temperature is lower than 230 ° C., T
The particle size of A becomes minute and the particle size becomes unstable. Further, if the weight ratio of water / DMT is 1 or more, the particle size becomes large,
Variations in particle size are also suppressed. Furthermore, impurities in the produced TA (MMT which is an intermediate product of unreacted DMT or hydrolysis reaction)
If the total amount of T) increases, the particle size of TA becomes unstable, and if the amount of impurities exceeds the limit, it becomes too small to be used industrially.

[0010] These are because, when the reaction temperature is low or the amount of water is low while TA has a very low solubility in water, the generated TA is immediately precipitated in the system and the chance of growth is reduced. It is considered to be a thing. It is considered that the amount of impurities existing in the reaction system also tends to become a nucleus for TA precipitation, so that it tends to cause miniaturization rather than grain size growth.

Therefore, the preferred hydrolysis conditions are 230 ° C. or higher, more preferably 240 ° C. or higher, the feed water / DMT weight ratio is 1 or higher, more preferably 2 or higher, and the amount of impurities (DMT + MMT) in the produced TA is 100
It is desirable to select a reaction time that is 0 ppm or less, preferably 800 ppm or less, for example, a reaction time suitable for the conditions, and it is desirable to select more severe conditions industrially.

The terephthalic acid obtained by the method described above is discharged from the reactor in a state of being suspended in water, cooled, and solid-liquid separated. The obtained terephthalic acid cake can be obtained as a terephthalic acid powder by removing water by drying.

The terephthalic acid having a stable particle size obtained by such a method is suitable for almost all purposes, and can be used as a raw material for PET bottles for beverages and polyester films. It can handle various particle sizes of terephthalic acid required in the process.

[0014]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Each value in the examples was determined according to the following method. Particle size: Average particle size (μ) Dried TA sample suitable amount 4 with JET SIEVE device
2, 60, 80, 120, 200, 250, 300, 4
Sieve through a 00 mesh. The non-passage amount of each sieve is plotted on the normal probability paper, and the particle size of 50% of the non-passage amount is defined as the average particle size. DMT, MMT weight concentration (ppm): The mixture obtained by the hydrolysis reaction of DMT was dried, dehydrated, and then subjected to high performance liquid chromatography (apparatus: HPLC D-700 manufactured by Hitachi Ltd.).
0, packed column: RP-18; 2 tubes) to determine the concentration of each of DMT and MMT.

[Example 1] DMT1 was added to a batch type autoclave (AC) having a 100-liter titanium stirrer.
8 kg and 54 kg of pure water are added, and the liquid temperature is gradually raised to 180 ° C. in a sealed state to start stirring. Then increase the liquid temperature to 2
After the temperature was raised to 50 ° C. and kept for 30 minutes, the distillation pipe valve provided on the upper part of the AC was slightly opened and the liquid temperature was kept at 250 ° C., while the Me generated in the hydrolysis reaction during the distillation time of 2 hours.
About 27 Kg of excess water with OH is distilled off. The obtained TA water slurry is dehydrated and dried with a centrifuge and a dryer to obtain a product TA. Repeated experiments by this method 10
The average MMT of the impurities obtained in the TA was 500p.
pm and DMT were 50 ppm. Further, similarly, the average particle size of the TA sample with the number of repetitions of 10 was 180 μ, and the variation was ± 1.5%.

[Examples 2 to 7, Comparative Examples 1 and 2] Example 1
In Example 1, the same procedure as in Example 1 was carried out except that the reaction temperature, charged DMT, amount of water, and amount of water removed were changed as shown in Table 1. Table 1 shows the average amount of impurities in the obtained TA, the average particle size, and the variation thereof.

[Comparative Examples 3 to 5] The same procedure as in Examples 1 and 5 or Comparative Example 1 was repeated except that the reaction time was shortened to 1 hour to increase the average amount of impurities in TA. Table 1 shows the average amount of impurities in the obtained TA, the average particle size, and the variation thereof.

Comparative Example 6 The hydrolysis reaction was carried out in the same manner as in Example 1 except that the reaction temperature was lowered to 210 ° C., but the amount of impurities was extremely large and the TA particle size was extremely small. It was found that the TA was unbearable for use.

[0019]

[Table 1]

[0020]

According to the particle size controlling method of the present invention, terephthalic acid having a large particle size and a small variation can be efficiently obtained from dimethyl terephthalate, and its industrial value is extremely large.

   ─────────────────────────────────────────────────── ─── 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 BB31 BC35 BC40                       BE60 BS30

Claims (3)

[Claims] 1. When producing terephthalic acid by hydrolyzing dimethyl terephthalate, by controlling the hydrolysis reaction temperature, the water / dimethyl terephthalate weight ratio in the reaction system and the amount of impurities of terephthalic acid produced, A method for controlling the particle size of terephthalic acid, characterized in that the average particle size of the terephthalic acid produced is controlled to 50 μm or more and the variation thereof is controlled to within 10%. 2. The particle diameter control method according to claim 1, wherein the total amount of dimethyl terephthalate and monomethyl terephthalate contained as impurities in the produced terephthalic acid is 1000 ppm or less. 3. The particle size control method according to claim 1, wherein the hydrolysis reaction temperature is 230 ° C. or higher, and the weight ratio of water / dimethyl terephthalate in the reaction system is 1 or higher.