JPH10324740A - Production of polybutylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the by-production of tetrahydrofuran and obtain the subject polymer improved in whiteness by polycondensing terephthalic acid with 1,4-butanediol in the presence of anhydrous sodium acetate. SOLUTION: This method for producing polybutylene terephthalate comprises esterifying (oligomerizing) (A) terephthalic acid with (B) 1,4-butanediol in the presence of anhydrous sodium acetate in an amount of preferably 0.1-50 ppm, more preferably 1-10 ppm, based on the weight of the component B at 200-250 deg.C at the atmospheric pressure to 100 mmHg for 1-5 hr and subsequently polymerizing the product at a vacuum of 0.1-10 mmHg for 1-5 hr. Known catalysts are preferably used in the esterification reaction and in the subsequent polymerization reaction. The catalysts are preferably a titanium compound, a tin compound, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to terephthalic acid and 1,4
A process for producing polybutylene terephthalate from butanediol.

[0002]

2. Description of the Related Art It is known to produce polybutylene terephthalate by a transesterification reaction of dimethyl terephthalate with 1,4-butanediol or by an esterification reaction of terephthalic acid with 1,4-butanediol. At that time, if 1,4-butanediol having a low temperature of less than 100 ° C. is charged into the reaction vessel, the temperature of the reaction vessel changes greatly, so that distortion occurs in long-term operation. Therefore, 1,4-
It was necessary to preheat butanediol to 100-200 ° C. However, 1,4-butanediol was thermally unstable, and had the problem of cyclizing under heating and converting it to tetrahydrofuran and water. A thermal stabilization method of 1,4-butanediol, which suppresses the formation of tetrahydrofuran by being present, is known (Japanese Patent Publication No. 55-33696).

In this case, alkali (earth) metal hydroxides, alkali (earth) metal acetates, and hexaammine platinum salts are mentioned as alkali metal compounds. In the detailed description of the invention, all alkali metal and alkaline earth metal salts are listed as alkali (earth) metal acetate salts, but in the examples only hydrated salts (lithium acetate dihydrate and acetic acid) Calcium monohydrate) is used.

[0004] Polybutylene terephthalate is produced by an esterification reaction using 1,4-butanediol obtained by hydrolyzing an organic acid ester of 1,4-butanediol in the presence of a cation exchange resin catalyst. In this method, it is known to add an alkali (earth) metal hydroxide to 1,4-butanediol (JP-A-7-10981).

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing polybutylene terephthalate by polymerizing terephthalic acid and 1,4-butanediol, suppressing the by-product of tetrahydrofuran and producing polybutylene terephthalate. It is an object to provide a method where terephthalate is more white.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for producing polybutylene terephthalate by polymerizing terephthalic acid and 1,4-butanediol, wherein the polymerization reaction is carried out in the presence of anhydrous sodium acetate. Characteristic method.

In the present invention, it is essential to use an anhydrous salt of sodium acetate. If an alkali (earth) metal hydroxide is used instead, the effect is small. In particular, when an alkali (earth) metal hydroxide and 1,4-butanediol (or terephthalic acid) are previously mixed and used for a polymerization reaction later, the alkali hydroxide ( It has been found that when the (earth) metal reacts with the carbon dioxide in the air to convert it to, for example, sodium carbonate, the effect is significantly impaired. It was also found that when a hydrate of sodium acetate was used instead, the degree of polymerization of the resulting polybutylene terephthalate was relatively small. By using an anhydrous salt of sodium acetate according to the present invention, by-product of tetrahydrofuran (THF) can be remarkably suppressed during the polymerization reaction of polybutylene terephthalate (PBT), and the obtained PB
T is more white.

Preferably, anhydrous sodium acetate in an amount of 0.1 to 50 ppm, more preferably 1 to 10 ppm, based on the weight of the starting 1,4-butanediol is charged to the polymerization reaction system. If the amount is less than the lower limit, the effect of the invention is insufficient, while if it is more than the upper limit, the effect of the invention is not particularly increased and the PBT tends to be colored.

The polymerization reaction itself can be carried out according to a known method, for example, at a temperature of 200 to 250 ° C. and a normal pressure to 10
Esterification reaction (oligomerization) at 0 mmHg
Time, then 0.1 to 10 mmHg (eg 1 mm
The pressure is reduced to Hg), and the polymerization is further advanced for 1 to 5 hours to obtain the desired PBT.

In the esterification reaction and the subsequent polymerization step, it is preferable to use a catalyst known per se. The catalyst is
For example, a titanium compound and a tin compound.

Hereinafter, the present invention will be further described by way of examples.

[0012]

EXAMPLE Capacity 5 equipped with a cooling pipe, a receiver and a stirring device
Terephthalic acid powder 16 in a 00 ml glass flask
6.2 g (1.0 mol), 1,4-butanediol 1
80 g (2.0 mol), 0.1 g of tetra-n-butyl titanate as a catalyst, and anhydrous sodium acetate in the amount shown in Table 1 (weight ppm based on 1,4-butanediol) were charged. After replacing the inside of the system with nitrogen, the temperature was raised to 210 ° C. in about 25 minutes while stirring at 200 rpm, and the esterification reaction was carried out at normal pressure for 3.5 hours. THF, water, and 1,4-butanediol distilled off during the reaction were cooled in a cooling tube, stored in a receiver, and collected at the end of the esterification reaction.

Thereafter, 0.1 g of tetra-n-butyl titanate was added, and the pressure inside the system was reduced to 1 mmHg or less, and then the temperature was raised to 230 ° C. to allow the polymerization reaction to proceed. The reaction was carried out while distilling off by-produced water and 1,4-butanediol, and was completed in about 2 hours after the temperature reached 230 ° C.

Table 1 shows the by-product THF ratio and the color of the obtained PBT.
Shown in

The THF by-product rate was determined by the following equation.

THF by-product rate = mol number of by-produced THF /
Number of moles of 1,4-butanediol used

[0017]

[Table 1]

Claims (2)

[Claims] 1. A method for producing polybutylene terephthalate by polymerizing terephthalic acid and 1,4-butanediol, wherein the polymerization reaction is carried out in the presence of anhydrous sodium acetate. 2. The process of claim 1 wherein sodium acetate anhydrous in an amount of 1 to 10 ppm based on the weight of the starting 1,4-butanediol is charged to the polymerization reaction system.