JPH11106498A - Continuous production of polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for the continuous production of a polyester capable of producing a polyester having excellent quality and desired carboxyl terminal content in high productivity. SOLUTION: A polyester is continuously produced from terephthalic acid and ethylene glycol by esterification reaction and multi-stage polycondensation reaction. The carboxyl terminal group content of the polyester obtained by the polycondensation reaction is adjusted to a definite value within the range of 15-50 g-eq./t by controlling at least one kind of reaction conditions selected from the temperature, resident time and feeding amount of ethylene glycol in the 1st stage polycondensation or controlling the 1st stage polycondensation reaction conditions together with the esterification conversion of the esterification reaction product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing a polyester having excellent quality and a desired amount of carboxyl terminal groups with good productivity.

[0002]

2. Description of the Related Art Polyethylene terephthalate has various excellent properties, especially excellent mechanical properties.
It is widely used as a material for various molded products such as films, sheets, and bottles.

[0003] Polyethylene terephthalate is generally produced by subjecting an esterification reaction product (oligomer) obtained by esterifying terephthalic acid and ethylene glycol to polycondensation by heating under reduced pressure. There are a batch type and a continuous type in the method for producing this polyester,
In the case of mass-produced products, a continuous system which is advantageous in terms of quality and cost is generally adopted.

[0004] In the case of producing a molded product from polyester obtained by melt polymerization, usually, once formed into chips,
A method of re-melting and molding is adopted. At that time, if the amount of the carboxyl terminal groups of the raw material polyester is large, hydrolysis due to residual moisture of the polyester is likely to occur during remelting. Since the hydrolysis is promoted by the acid catalysis by the carboxyl terminal groups of the polyester, the degree of hydrolysis also changes depending on the fluctuation of the amount of carboxyl terminal groups of the raw material polyester. If hydrolysis occurs during molding by re-melting, not only the inherent desirable characteristics of the molded product, such as insufficient strength of the product or deterioration of color due to a decrease in viscosity, but also the characteristics of the molded product will change if the degree of hydrolysis changes. Spots will result. Therefore, the polyester molded by remelting has a small amount of carboxyl end groups,
It is better to be constant.

In some applications, such as for bottles, it is necessary to further increase the degree of polymerization by further solid-phase polymerization of the polyester obtained by melt polymerization. In this case, as for the polyester after the melt polymerization, the smaller the amount of the carboxyl terminal group is, the better, and it is necessary to control the polyester within a desired range. In general, it is known that the apparent solid-state polymerization reaction rate is slowed down whether the amount of carboxyl end groups is large or small. This is because the apparent rate-limiting step of the solid-state polymerization reaction is mass transfer of water or ethylene glycol. Therefore, in order to keep the solid-state polymerization reaction rate constant, that is, to keep the intrinsic viscosity of the polyester after the solid-state polymerization constant, the amount of carboxyl end groups of the polyester after the melt polymerization is kept constant within a certain range. It is necessary to keep.

[0006] Depending on the intended use of the polyester, a polyester having an appropriate amount of carboxyl end groups is produced in consideration of the required degree of hydrolysis resistance and productivity.
For example, the amount of carboxyl end groups is relatively hydrolysis-resistant polyester such as for clothing fibers,
For polyesters requiring high hydrolysis resistance, such as for films and tire cords, with a level of 35 to 50 g equivalents / t, with a priority on productivity, 15 to 35 g equivalents / t, and solid-phase polymerization for bottles In the polyester attached to 25,
Generally, the level is 35 g equivalent / t.

As a method for adjusting the amount of carboxyl terminal groups of the polyester obtained by melt polycondensation, there is a method of changing the esterification reaction conditions to adjust the esterification reaction rate of the oligomer. However, when trying to obtain a polyester having a small amount of carboxyl end groups by this method, it is necessary to increase the esterification reaction rate. However, when the esterification reaction rate is increased, the content of diethylene glycol bonds increases. However, there is a problem that polyester having predetermined physical properties cannot be obtained. As a production method having high productivity, there is a method in which two or more series of polycondensation reaction are provided for one series of a large-sized esterification reaction to produce polyesters of different brands. It cannot be applied to this method.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous process for producing a polyester having excellent quality and capable of producing a polyester having a desired amount of carboxyl end groups with high productivity. is there.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve this problem, and as a result, when the esterification reaction product is polycondensed in multiple stages into a polyester, an initial polycondensation reaction stage is carried out. The present inventors have found that this object can be achieved by adjusting the conditions of a certain first-stage polycondensation reaction or by adjusting the conditions of the first-stage polycondensation reaction together with the esterification reaction rate of the oligomer. did.

That is, the gist of the present invention is to provide a method for continuously producing a polyester from terephthalic acid and ethylene glycol through an esterification reaction and a multi-stage polycondensation reaction. Adjusting at least one reaction condition selected from the group consisting of time and ethylene glycol supply amount, or adjusting the first-stage polycondensation reaction condition together with the esterification reaction rate of the esterification reactant, A continuous polyester production method characterized in that the amount of carboxyl terminal groups of the polyester is controlled to a constant value within a range of 15 to 50 g equivalent / t.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyesters to be used in the present invention are polyesters from terephthalic acid and ethylene glycol,
That is, although it is polyethylene terephthalate, isophthalic acid, naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid,
Copolymers such as p-hydroxybenzoic acid, 1,4-butanediol, neopentyl glycol, and an ethylene oxide adduct of bisphenol A may be used in combination.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of an embodiment of the present invention.
That is, it is a schematic diagram showing an example in which two series of polycondensation reaction series are provided for one series of esterification reaction. In FIG. 1, reference numeral 1 denotes a first-stage esterification reaction tank, 2 denotes a slurry supply pipe, 3 denotes a second-stage esterification reaction tank, 4 denotes an ethylene glycol supply pipe, 5 denotes a first-stage polycondensation reaction tank, and 6 denotes a first-stage polycondensation reaction tank. A two-stage polycondensation reaction tank, 7 is a third-stage polycondensation reaction tank, 8 is a die head, 9 is a cutter, and 10 is a pellet.

FIG. 1 shows a method for continuously producing a polyester by a two-stage esterification reaction and a three-stage polycondensation reaction. However, the number of steps of the esterification reaction and the polycondensation reaction is not limited thereto. Not something.

In the method for producing polyester as shown in FIG. 1, a slurry of terephthalic acid and ethylene glycol is generally supplied from a slurry supply pipe 2 to a first-stage esterification reaction tank 1 in which oligomers are present in advance. The reaction is carried out by heating and stirring under normal pressure or under slight pressure to obtain an oligomer having an esterification reaction rate of 80 to 90%, more preferably 83 to 87%. Next, this was sequentially transferred to the second-stage esterification reaction tank 3 and heated and stirred at normal pressure or under pressure to raise the esterification reaction rate to a range of 92 to 98%, more preferably 94 to 97%. Oligomer.

If the esterification reaction rate of the oligomer is out of the above range, the rate of the polycondensation reaction in the subsequent step is remarkably reduced, so that the polycondensation reaction tank is extremely depressurized in order to keep the intrinsic viscosity of the product constant. Alternatively, it is necessary to raise the reaction temperature, which is not preferable. That is, if the pressure is too high, the reactants will be scattered from the polycondensation reaction tank, causing process problems.If the reaction temperature is too high, the decomposition of the polymer will be accelerated, and the product color , An increase in by-products, and an increase in the amount of carboxyl end groups.

Furthermore, the esterification reaction rate of the oligomer is
If it is less than 92%, the oligomer has a strong sublimation property, and the oligomer adheres to the gas phase can wall of the reaction tank, etc., and has a high melting point with the passage of time. Clogging filters and degrade polyester quality.

Next, a polycondensation catalyst is added to the oligomer having a predetermined esterification reaction rate, and a first-stage polycondensation reaction tank 5 and a second-stage polycondensation reaction tank 6 under high-temperature and high-pressure conditions are added. It is sequentially passed through the third-stage polycondensation reaction tank 7 and polycondensed to a predetermined degree of polymerization to obtain a polyester having a high degree of polymerization. The polyester having a high polymerization degree is discharged in a strand shape by a die head 8 and granulated by a cutter 9 to form a pellet 10.

In order to set the amount of carboxyl end groups of the polyester to a predetermined target value, the reaction temperature of the first-stage polycondensation reaction tank 5 is maintained while the esterification reaction rate of the oligomer remains at a constant value in the range of 92 to 98%. One or more kinds of reaction conditions among the residence time and the ethylene glycol supply amount are adjusted, or the reaction conditions of the first-stage polycondensation reaction tank 5 are adjusted together with the esterification reaction rate of the oligomer.

As described above, when a polyester having a small amount of carboxyl end groups is to be obtained, if the esterification reaction rate of the oligomer is increased, the content of diethylene glycol bonds increases, and a polyester having predetermined physical properties cannot be obtained. . Therefore, in order to obtain a polyester having a small amount of carboxyl end groups, it is necessary to increase the esterification reaction rate of the oligomer and to adjust the conditions of the first-stage polycondensation reaction.

Next, a range of conditions suitable for adjustment will be described. The temperature of the first-stage polycondensation reaction is preferably from 250 to 290C, more preferably from 260 to 285C, even more preferably from 265 to 280C. If the reaction temperature is too low, the fluidity decreases, stirring becomes poor, the reaction becomes non-uniform, and the stirring power becomes too high. Conversely, if the reaction temperature is too high, problems such as increased sublimation of the oligomer, accelerated thermal decomposition, and deterioration of the color tone of the finally obtained polyester occur. Within this range, the temperature of the first-stage polycondensation is adjusted. When the temperature is increased by 10 ° C., the amount of carboxyl end groups of the polyester decreases by about 3 to 4 g equivalent / t.

The residence time in the first-stage polycondensation reaction tank 5 is preferably 0.3 to 2.5 hours, more preferably 0.5 to 2.0 hours, and even more preferably 0.7 to 1.5 hours. If the residence time is too short, problems on the apparatus such as poor stirring due to insufficient amount of liquid in the reaction tank and poor heat transfer from a coil or the like passing through the heating medium occur.If the residence time is too long, Problems such as an increase in the amount of diethylene glycol produced as a by-product and an increase in stirring power occur. Within this range, the residence time of the first-stage polycondensation tank 5 is adjusted. If the residence time is increased by 0.1 hour, the amount of carboxyl end groups of the polyester is reduced by about 2 g equivalent / t.

When ethylene glycol is added to the first-stage polycondensation reaction tank 5 and the esterification reaction is further advanced, the amount of carboxyl end groups of the polyester can be reduced. When the amount of ethylene glycol added is increased by 0.1 in terms of the molar ratio to the terephthalic acid component, the amount of carboxyl end groups of the polyester decreases by about 6 g equivalent / t. However, if the addition amount of ethylene glycol is too large, the amount of by-products of diethylene glycol increases, or the amount of oligomers and polymers accompanying the distillate gas increases, which is not preferable. It is desirable that the molar ratio to the terephthalic acid component is 0.30 or less, preferably 0.20 or less, more preferably 0.15 or less.

The pressure of the first-stage polycondensation reaction is from 1.3 to
5.3 kPa is preferred, 1.7 to 4.0 kPa is more preferred, and 2.0 kPa is preferred.
~ 3.3 kPa is more preferred. If the reaction pressure is too low, scattering of oligomers increases, and if the reaction pressure is too high, a sufficient polycondensation reaction rate cannot be obtained.

The method of the present invention is applied to a method in which at least one continuous polycondensation reaction series is included in one series of the esterification reaction.
If the polycondensation reaction is carried out in a series of polycondensation reaction series or more, polyesters of different brands can be produced with high productivity.

[0026]

Next, the present invention will be described specifically with reference to examples. In addition, the measuring method is as follows. (a) Esterification reaction rate The total carboxyl end group content A of the oligomer is calculated by the following method.
And the unreacted carboxyl terminal group amount B are calculated and calculated by the following equation. Esterification reaction rate (%) = [(AB) / A] × 100 Total carboxyl end group content A: Determined by hydrolyzing the oligomer with aqueous potassium hydroxide and titrating with 0.5 N hydrochloric acid. Unreacted carboxyl terminal group amount B: Determined by dissolving the oligomer in N, N-dimethylformamide and titrating with 0.1N potassium hydroxide in methanol. (b) Intrinsic viscosity ([η]) Measured at a temperature of 20 ° C. using an equal weight mixture of phenol and tetrachloroethane as a solvent. (c) Carboxyl end group content (COOH)
It is determined by titration with a specified methanol solution of potassium hydroxide. (d) Color tone (b value) Measured with a 300A type color difference meter manufactured by Nippon Denshoku Industries Co., Ltd. (e) Diethylene glycol content (DEG) After polyester is hydrolyzed with an aqueous potassium hydroxide solution, the polyester is measured using a GC-14B gas chromatograph manufactured by Shimadzu Corporation.

EXAMPLE 1 Using the continuous polyester production apparatus shown in FIG. 1, the molar ratio of terephthalic acid to ethylene glycol was 1: 1.
The slurry of 1.5 is discharged from the slurry supply pipe 2 every hour.
At a rate of 366 kg, average residence time 4.5 hours, temperature 261 ° C,
First stage esterification reactor 1 controlled to 34kPa · G pressure
To give an oligomer having an esterification rate of 85%, and then continuously convert the oligomer into an average residence time.
It was supplied to the second-stage esterification reaction tank 3 controlled at a temperature of 255 ° C. and a pressure of 34 kPa · G for 2.0 hours to cause a reaction, and an oligomer having an esterification reaction rate of 94% was obtained at a rate of 9306 kg / h.
Next, a part of the oligomer is continuously supplied to the first polycondensation reaction tank 5 at a rate of 4653 kg / h, and ethylene glycol is supplied from the supply pipe 4 to the reaction tank at a rate equivalent to 0.15 in a molar ratio of terephthalic acid to terephthalic acid. At the same time, antimony trioxide was added as a polycondensation catalyst at a molar ratio of 1.7 × 10 ⁻⁴ to terephthalic acid, and the pressure was adjusted to 2.7 kPa.
After performing the first stage polycondensation reaction at the temperature and residence time shown in
The polycondensation reaction is sequentially performed in the second-stage polycondensation reaction tank 6 and the third-stage polycondensation reaction tank 7, and 4883 kg / hour of polyester (polyethylene terephthalate) pellets (production volume: 110
t) Manufactured. The reaction conditions in the second-stage polycondensation reaction tank 6 were set at a temperature of 275 ° C., a pressure of 0.13 kPa, and a residence time of 1 hour.
C., pressure 0.07 kPa, residence time 1 hour. Table 1 shows the characteristic values of the obtained polyester.

[0028]

[Table 1]

Example 2 4653 per hour which is the remaining amount of the oligomer in Example 1
kg of the oligomer is supplied to the first-stage polycondensation reaction tank of another polycondensation reaction series, and the polycondensation reaction is carried out under the same conditions as in No. 1 of Example 1 without adding ethylene glycol. Manufactured. The obtained polyester was [η] 0.686, COOH 50 geq / t, color tone 5.5, DE
G was 1.40 mol%.

Example 3 A polyester was produced by conducting a polycondensation reaction under the same conditions as in No. 4 of Example 1 except that the esterification reaction conditions were changed so that the esterification reaction rate of the oligomer was 95%. The obtained polyester was [η] 0.686, COOH 15geq /
t, color tone 6.3, DEG 1.57 mol%.

[0031]

According to the method of the present invention, there is provided a continuous method for producing a polyester having excellent quality and capable of producing a polyester having a desired amount of carboxyl terminal groups with high productivity.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of an embodiment of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st stage esterification reaction tank 2 Slurry supply piping 3 2nd stage esterification reaction tank 4 Ethylene glycol supply piping 5 1st stage polycondensation reaction tank 6 2nd stage polycondensation reaction tank 7 3rd stage tree condensation reaction tank 8 Die head 9 Cutter 10 Pellet

Claims (2)

[Claims] 1. A method for continuously producing a polyester from terephthalic acid and ethylene glycol through an esterification reaction and a multi-stage polycondensation reaction, wherein the temperature, residence time, and ethylene glycol supply amount during the first-stage polycondensation reaction Or the first-stage polycondensation reaction condition is adjusted together with the esterification reaction rate of the esterification reaction product, and the amount of carboxyl end groups of the polyester after the polycondensation reaction is adjusted. 15 to 50 g equivalent /
A continuous method for producing polyester, wherein the method is controlled to be a constant value within the range of t. 2. The continuous production method of a polyester according to claim 1, wherein the polycondensation reaction is performed in two or more polycondensation reaction series including at least one continuous polycondensation reaction series with respect to one series of the esterification reaction.