JP3484600B2 - Method for producing terephthalic acid and polyester - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to terephthalic acid for producing a polyester having a stable color tone (b value) with little coloring, and a method for producing the polyester.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter referred to as P
ET) and polybutylene terephthalate (hereinafter P
Polyester typified by BT) has excellent properties, and is used for fibers for clothing, fibers for industrial materials, and films,
Widely used as bottles and other plastic products. As an industrial production method of polyester, a direct polymerization method in which terephthalic acid (hereinafter referred to as TPA) and a glycol component are directly esterified and then polycondensation is performed is widely adopted. In the direct polymerization method, in order to obtain good quality in fibers, films, and other plastic products, it is important to reduce the coloring of the product polymer, control the color tone in a stable state, and reduce the variation.

As a means for controlling the color tone by reducing the coloring of the polymer, there is known a method of increasing the purity of TPA to prevent the coloring of the polyester due to the incorporation of impurities.
In order to raise the purity of A, it is necessary to repeat the refining step many times in the production thereof, which is industrially and economically disadvantageous. Therefore, conventionally, industrially, by adjusting the reaction temperature, by changing the addition amount of the metal compound as a catalyst, by optimizing the polyester production conditions,
The method of reducing the coloring and stabilizing the color tone is adopted. However, the method of adjusting the reaction temperature has a problem that the reaction rate varies depending on the temperature change and the degree of polymerization becomes unstable, which makes it difficult to control the polymerization. Further, in the method of changing the addition amount of the metal compound as the catalyst, when the amount of the catalyst is increased, the precipitation of the metal causes foreign matter to be generated in the polymer.

In order to solve such a problem, Japanese Unexamined Patent Publication No.
A proposal such as Japanese Patent No. 173268 has been made. However, adjusting the esterification rate also causes a change in the polycondensation reaction rate, which makes it difficult to control the polymerization.

On the other hand, there is a method of stabilizing the color tone by reducing the coloring of the polymer by limiting the raw materials to be used within a range that is not disadvantageous industrially and economically.
See 56529. This is because 4-carboxybenzaldehyde (hereinafter referred to as 4-CBA), which is a by-product during TPA synthesis, is known as an impurity in TPA that is said to affect the polymer color tone.
That is, the CBA amount is set to a certain amount or less. Also,
It is empirically known that the alkali solution permeability has a correlation with the coloration of the polymer, and it has been attempted to make the alkali solution permeability of TPA a certain value or more. However, TPA alkali solution permeability and 4-CBA
The polymer color tone could not be sufficiently stabilized only by controlling the amount.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of fluctuation of the degree of polymerization due to fluctuation of reaction rate and generation of foreign matters due to metal precipitation in the production of polyester, and to provide a polymer having a stable color tone with little coloring. For manufacturing
It is intended to provide a method for producing PA and a polyester having a stable color tone.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned object, the present inventors have found that the polymer, the color tone, and 9-fluorenone-2,6-dicarboxylic acid (hereinafter referred to as FL26) in TPA. It has been found that there is a certain relationship with the amount, and by controlling the amount of FL26, coloring of the polymer can be suppressed and the color tone can be controlled.

The present invention has been made on the basis of this finding, and the above-mentioned objects of the present invention are: (1) The amount of 9-fluorenone-2,6-dicarboxylic acid is 1
0 ppm or less, 4-carboxybenzaldehyde amount is 300 ppm or less, alkaline solution (concentration:
The light transmittance (quartz cell, optical path length: 10 mm) at 340 nm of 7.5 g / dl) is 87% or more, and 2
A terephthalic acid having a light transmittance (quartz cell, optical path length: 10 mm) at 340 nm of an alkaline solution of terephthalic acid (concentration: 7.5 g / dl) after heating at 80 ° C. for 3 hours is 70% or more.

(2) In the method for producing a polyester by mainly subjecting terephthalic acid and glycol to an esterification reaction and then polycondensing, the terephthalic acid described in the above item (1) is used. Manufacturing method.

(3) The glycol is ethylene glycol,
Alternatively, the method for producing a polyester according to the item (2), which is 1,4 butanediol.

It can be achieved by

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

First, the TPA of the present invention will be described.

Generally, TPA is obtained by air-oxidizing an alkylbenzene, especially paraxylene, in a lower aliphatic carboxylic acid. The present inventors have found that FL26 is produced as a by-product in this oxidation reaction via an intermediate such as 4-CBA, and this FL26 has a strong correlation with the polymer color tone. The effect of FL26 on the color tone of polyester, especially b value, varies depending on the type of polyester, but is usually in the range of +0.1 to +0.5 per ppm. Further, the b value of polyester is about −10 to 10 although it varies depending on the type of polyester. Therefore, in order to prevent the influence of FL26 on the polymer color tone (b value) from becoming excessive, the amount of FL26 in TPA is set to 10 ppm.
It is as follows. If it is 8 ppm or less,
Further, a polymer with less coloring can be obtained, which is preferable. However, reducing the amount of FL26 in TPA to less than 2 ppm is not preferable because it requires strict purification of TPA and is industrially disadvantageous. That is, FL2
As a range of 6 amounts, 2 ppm or more and 8 ppm or less are industrially preferable.

On the other hand, the fluctuation range of the polymer color tone (b value) required for polyester industrially used for fibers, films, bottles, and other molding materials is usually ± 0 though it varies depending on the use and the type of polyester. The range is from 0.5 to ± 3.5. Therefore, in order to stabilize the polymer color tone (b value), the fluctuation range of the amount of FL26 in TPA is 7 (± 3.
5) It is preferable to set the content to ppm or less. Further, if the fluctuation range of the FL26 amount is 2 (± 1) ppm or less, it is required that the fluctuation of the product color tone is small, the fiber, the transparent film,
It is suitable for bottle applications.

From the above points, the TPA of the present invention is FL2
6 is preferably 2 ppm or more and 10 ppm or less
It is PA.

Conventionally, the alkali solution permeability of TPA and the 4-CBA concentration in TPA, which have been known so far, have been used to stabilize the polymer coloration and color tone.
By managing the FL26 concentration in the combination,
Even better results can be obtained.

Permeability of TPA in alkaline solution means TPA
7.5 g was dissolved in 100 dl of 2N-KOH solution, and the transmittance (%) at a wavelength of 340 nm was obtained using a quartz cell having an optical path length of 10 mm. When the TPA alkali solution transmittance is 50% or less, the polymer is markedly colored. Usually, in order to obtain stable quality without fluctuation of the color tone of the polymer, it is 87% or more, preferably 89% or more, and if 94% or more, it is possible to obtain a stable polymer with less color tone. it can.

Further, it is possible to further know the tendency of polymer coloring by combining and controlling the alkali solution permeability after heating TPA at 280 ° C. for 3 hours.
In order to obtain a polymer with little coloration and stable color tone, the alkali solution permeability after heating at 280 ° C. for 3 hours is 73% or more, preferably 80% or more, 82%.
If it is above, an even better result can be obtained.

Further, when the amount of 4-CBA exceeds 300 ppm, it causes gelation and coloring of the polymer. Therefore, in order to stabilize the color tone of the polymer,
The amount of -CBA is 300 ppm or less. Preferably, the amount is 270 ppm or less and 230 ppm or less so that a polymer with less coloration can be obtained. However, even if the amount is 300 ppm or less, the change in the amount of 4-CBA causes the change in the color tone (b value). Therefore, the color tone (b
In order to suppress the fluctuation of the (value), the fluctuation width of the amount of 4-CBA can be controlled to ± 50 ppm or less to obtain more stable polymer color tone.

The TPA can be obtained by air-oxidizing an alkylbenzene, particularly paraxylene, in a lower aliphatic carboxylic acid, and the amount of FL26 is 2 to 10 ppm.
Alkaline solution transmittance of 87% or more, 280 ° C. after heating for 3 hours, alkaline solution light transmittance of 70% or more, 4-CBA amount of 30
In order to purify TPA at 0 ppm or less, a method of performing recrystallization, washing, etc. with acetic acid, water and the like can be mentioned. In this case, it is preferable to recrystallize the reaction product containing TPA oxidized by the high temperature and high pressure by reducing the temperature under reduced pressure in several stages. The slurry containing the recrystallized TPA is separated from the mother liquor by a method such as centrifugation and vacuum filtration while sufficiently washing with acetic acid, water and the like. Other methods for purifying TPA include hydrogenation of terephthalic acid obtained by oxidizing alkylbenzene, particularly paraxylene, in the presence of a catalyst, or reaction with methanol to give dimethyl ester, followed by purification. Then, a method of hydrolyzing is known, but it is not preferable because it is costly and economically disadvantageous as an industrial manufacturing method.

The method for producing the polyester of the present invention will be described below.

The method for producing the polyester of the present invention uses terephthalic acid as a direct starting material and is widely adopted as an industrial production method. TPA and a glycol component are directly esterified, and then polycondensation is directly carried out. It relates to the polymerization method. Either batch polymerization or continuous polymerization may be used.

The polyester of the present invention is not particularly limited, but the main constituent of the dicarboxylic acid unit is a TPA unit, and the main constituent of the glycol unit is an ethylene glycol (hereinafter referred to as EG) unit or 1,4-butanediol (hereinafter referred to as BD).
It is preferable that the TPA unit occupies 45 to 100 mol% of the dicarboxylic acid unit and the EG unit or BD unit occupies 45 to 100 mol% of the glycol unit. In particular, since the TPA unit accounts for 100% in homo-PET and homo-PBT, the effect of the present invention can be remarkably obtained.

The method for producing polyester of the present invention can be applied to polyester elastomer. The applicable polyester elastomer is not particularly limited, but the soft segment may be polyethylene glycol (hereinafter referred to as PEG) or polytetramethylene glycol (hereinafter, referred to as
A PET-based or PBT-based polyester elastomer which is PTMG) is suitable.

The polyester in the present invention may contain one or more dicarboxylic acid units other than the terephthalic acid unit as long as it is about 45 mol% or less of all the structural units, and similarly, the EG unit or the BD unit. It may contain one or more glycol units other than the units.
Examples of dicarboxylic acid units other than TPA include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and diphenoxyethanedicarboxylic acid; dodecanedioic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, Aliphatic carboxylic acids such as; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; hydroxybenzoic acid, glycolic acid,
The units of hydroxycarboxylic acid such as hydroxyethoxybenzoic acid are raised. Examples of glycol units other than EG units or BD units include propylene glycol, diethylene glycol, hexamethylene glycol, p-xylene glycol, 1,4-cyclohexadimethanol and bisphenol. Furthermore, a polyester obtained by copolymerizing a trifunctional or higher polyfunctional compound may be used as long as it does not impair the thermoplasticity.

In the production of the polyester of the present invention,
For the esterification reaction and the polymerization reaction, conventionally known conditions can be used. For example, known catalysts such as antimony compounds and titanium compounds, stabilizers such as phosphorus compounds, lubricants such as silica and titanium dioxide can be used.

[0028]

EXAMPLES The present invention will now be described in more detail by way of examples.

Example 1 Terephthalic acid was synthesized using the equipment shown in the flow sheet of FIG.

From the raw material preparation tank 1 to the first reaction tank 3, 1 part by weight of paraxylene / hour, 3 parts by weight of acetic acid containing 8% by weight of water /
Hour and cobalt acetate tetrahydrate 0.004 parts by weight / hour, manganese acetate tetrahydrate 0.0042 parts by weight / hour, and 47% hydrobromic acid 0.005 parts by weight / hour. It is supplied by the raw material supply pump 2, and the temperature is 195 ° C. and the pressure is 1.
Air was used as the oxidant under the conditions of 5 MPa and a residence time of 60 minutes, and the air was supplied to the first reaction tank 3 by the air compressor 16 so that the oxygen concentration in the exhaust gas of the oxidation reaction was 5.5% by volume, Moreover, the liquid phase oxidation reaction of paraxylene was performed while controlling the water concentration in the first reaction tank 3 to be about 12% by weight.

The reaction product from the first reaction tank 3 is continuously supplied to the second reaction tank 4 at a temperature of 190 ° C. and a pressure of 1.3 MP.
a, under the condition that the residence time was 40 minutes, additional oxidation was performed while supplying air to the second reaction tank 4 by the air compressor 16 so that the oxygen concentration in the exhaust gas was 5.5% by volume.

The reaction product from the second reaction tank 4 is pressurized to 6.2 MPa by the pressure increasing pump 5 and then heated by the heater 6.
And the reaction was heated to 260 ° C. At this time, the oxygen concentration in the exhaust gas from the third reaction tank 7 was 5.5% by volume.
Air was supplied to the heater 6 by the air compressor 16 while controlling so that

The reaction product heated by the heater 6 is the third product.
It is continuously supplied to the reaction tank 7, and the temperature is 260 ° C. and the pressure is 5.5.
Further oxidation was performed under the conditions of MPa and residence time of 40 minutes.

Then, the reaction product from the third reaction tank 7 is supplied to the first crystallization tank 8 at a temperature of 200 ° C. and a pressure of 1.5 MP.
a, air was supplied to the first crystallization tank 8 by the air compressor 16 so that the oxygen concentration in the exhaust gas was 5.5% by volume under the condition of the residence time of 20 minutes.

Further, the reaction product from the first crystallization tank 8 is supplied to the second crystallization tank 9, and the temperature is 150 ° C. and the pressure is 0.45 MP.
It was retained for 20 minutes at a and then cooled and crystallized in the third crystallization tank 10 at a temperature of 107 ° C. and normal pressure.

The slurry in which TPA is crystallized is supplied to the rotating cylindrical filter 12 by the slurry transfer pump 11.
While sufficiently washing with acetic acid as a washing liquid, solid-liquid separation was performed until the liquid content became 15%.

This slurry was sent to a centrifuge 14 via a slurry tank 13 to collect TPA crystals and dried in a dryer 15.

The quality of TPA thus obtained is
FL26 amount 6.3 ppm, alkaline solution (concentration: 7.5
g / dl) light transmittance at 340 nm 89.6%,
Alkaline solution after heating at 280 ° C for 3 hours (concentration: 7.5 g
/ Dl) light transmittance at 340 nm 82.0%, 4
The amount of -CBA was 252 ppm. In addition, F in TPA
The amount of L26 was measured by high performance liquid chromatography (HP
LC).

[Examples 2 to 4, Comparative Examples 1 and 2] PET was polymerized using the continuous polymerization equipment shown in the flow sheet of FIG.

The pure EG content in the mixture of the distilled EG generated from the process, the raw material EG supplied through the control valve 37 and the EG additionally added to the circulating EG storage tank 34 is always 13.8.
TP of the quality shown in Table 1 is controlled so that the weight part / hour is controlled.
A31.1 parts by weight / hour was supplied to the slurry mixer 21 to make a slurry, and then the mixture was supplied to the esterification reaction device 23 via the pump 22. Then, an esterification reaction and a polymerization reaction were performed under the conditions shown in Table 2. As additives, antimony trioxide 0.01 part by weight / hour, phosphoric acid 0.005 part by weight / hour, titanium dioxide 0.15 part by weight /
The time was continuously fed to the esterification reactor 24. The PET quality obtained as a result is shown in Table 1.

[Table 1]

[Table 2] [Example 5 and Comparative Example 3] TPA226 having the quality shown in Table 3
An esterification reaction and then a polymerization reaction were carried out using 4 parts by weight and 1473 parts by weight of BD.

First, 1131 parts by weight of the total required amount of TPA and the above BD amount and 1.5 parts by weight of tetra-n-butyl titanate (hereinafter referred to as TBT) were charged into a reaction vessel equipped with a rectification column, and 190 The esterification reaction was started under reduced pressure at 450 ° C. and 450 mmHg. Then, the temperature was gradually raised and the remaining BD was continuously added. The reaction pressure was changed to 300 mmHg during the reaction. In addition, with the progress of the reaction, the produced water and tetrahydrofuran (hereinafter, THF) were distilled off via the rectification column.

The reaction was completed about 2 hours after starting the esterification reaction (temperature at this time: 239 ° C.). The reaction rate at this time was 98.3%.

TBT was added to this reaction product (temperature: 238 ° C.).
1.5 parts by weight and 116 parts by weight of BD were added. afterwards,
The mixture was transferred to a polymerization reaction vessel, and the pressure was gradually reduced from normal pressure to 1.0 mmHg or less, and at the same time, the temperature was raised to 246 ° C. to carry out a polycondensation reaction. The reaction was completed in about 3 and a half hours. The obtained PBT quality is shown in Table 3.

[0044]

[Table 3]

[0045]

EFFECTS OF THE INVENTION By adopting the method for producing terephthalic acid and polyester of the present invention, a stable color tone (b) with less coloring can be obtained without excessive purification of TPA and without changing the reaction temperature or the addition amount of the catalyst. It is possible to obtain a polyester of (value).

[Brief description of drawings]

FIG. 1 is a schematic view showing an apparatus for producing terephthalic acid of the present invention used in Example 1.

FIG. 2 is a conceptual diagram showing an apparatus for producing polyester used in Example 2.

[Explanation of symbols]

1: Raw material preparation tank 2: Raw material supply pump 3: First reaction tank 4: Second reaction tank 5: Booster pump 6: heater 7: Third reaction tank 8: First crystallization tank 9: Second crystallization tank 10: Third crystallization tank 11: Slurry transfer pump 12: Rotating cylinder type filter 13: Slurry tank 14: Centrifuge 15: Dryer 16: Air compressor 21: Slurry mixer 22: Slurry supply pump 23-24: Esterification reactor 25: Fractionation tower 26: Distillation EG storage tank 27-29: Polycondensation reactor 30-32: Wet condenser 33-34: Circulating EG storage tank 35: Distillation EG extraction pump 36: Distillation EG supply pump 37: Control valve 38: Automatic densitometer 39: Distillation EG filter 40: Distillation EG separation processor

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C07C 63/26 C08G 63/00-63/91

Claims (3)

(57) [Claims] Claims: 1. The amount of 9-fluorenone-2,6-dicarboxylic acid is 10 ppm or less, the amount of 4-carboxybenzaldehyde is 300 ppm or less, and the light transmittance of an alkaline solution (concentration: 7.5 g / dl) at 340 nm. (Quartz cell, optical path length: 10 mm) is 87% or more,
And a light transmittance (quartz cell, optical path length: 10 mm) at 340 nm of an alkaline solution of terephthalic acid (concentration: 7.5 g / dl) after heating at 280 ° C. for 3 hours is 70% or more. . 2. A method for producing a polyester, characterized in that the terephthalic acid according to claim 1 is used in a method for producing a polyester by mainly subjecting terephthalic acid and glycol to an esterification reaction and then polycondensing. 3. The glycol is ethylene glycol or 1,4 butanediol.
A method for producing the described polyester.