JP2507884B2 - Method for producing polyester - Google Patents

Description

TECHNICAL FIELD The present invention produces poly (ethylene terephthalate) (PET) useful as a material for plastics, films, fibers, etc. by polycondensing terephthalic acid diester and ethylene glycol diacetate. It is about the method.

Prior Art PET is currently manufactured by a method in which EG is distilled off after causing a condensation reaction between terephthalic acid (or its diester) and an excess amount of ethylene glycol (EG). In this method, the latter step of removing EG is the most important, and the higher the efficiency, the higher the PET obtained.
However, since EG is a high-boiling compound, distilling it off requires high agitation under high temperature and high vacuum conditions, and requires a special agitator, and the equipment is expensive.
There was a problem that T tends to decompose.

Means for Solving the Problem The inventors of the present invention have conducted earnest studies for a method capable of producing PET under mild conditions, and as a result, when both terephthalic acid and EG are diesters, they are removed by condensation. Since the substance to be converted becomes an ester with a low boiling point, it can be distilled off under mild conditions, and by using a hydrocarbon as a solvent to cause the condensation reaction in a suspended state, a high reaction rate can be realized. The present invention has been accomplished and the present invention has been completed.

That is, the present invention provides a method for producing PET, which comprises using an alkali metal alkoxide as a catalyst, reacting a terephthalic acid diester and an ethylene glycol diester in a hydrocarbon solvent, and distilling off the resulting ester. Is.

In the present invention, dimethyl ester (or diethyl ester) of terephthalic acid and ethylene glycol diacetate are used as raw materials. Here, in order to increase the degree of polymerization of PET, it is required that the charged mole numbers of terephthalic acid diester and ethylene glycol diacetate be made equal.

In the present invention, an alkali metal alkoxide is used as a catalyst, and a catalyst composed of sodium or potassium and an alkoxide group having 4 or less carbon atoms is suitable. Such an alkali metal alkoxide is usually obtained by allowing an excess amount of anhydrous alcohol to act on an alkali metal to dissolve it, and then distilling off excess alcohol. The amount of the alkali metal alkoxide is appropriately 1/1000 to 1/20 times the molar amount of the raw material.

The hydrocarbon used as a solvent in the method of the present invention is preferably one which dissolves both the raw material and the catalyst and forms a minimum azeotrope with the ester to be distilled off, or one having a boiling point higher than this ester, For example, cyclohexane, isooctane, n-heptane and the like can be mentioned. The hydrocarbon of the solvent is 1 to 1 of the weight of the raw material diester.
100 times the amount used.

To carry out the method of the present invention, terephthalic acid diester as a raw material and ethylene glycol diacetate, an alkali metal alkoxide as a catalyst, and a hydrocarbon as a solvent are charged in a reaction vessel and heated under normal pressure. Heating is usually carried out in an oil bath, which should be above the boiling point of the ester to be distilled or the lowest azeotropic point of the solvent and ester, preferably 5 to 30 ° C higher. If the bath temperature is too high, the reaction rate will not increase because the solvent will distill in the initial stage, and if the bath temperature is too low, the ester will not be distilled out, and the condensation reaction will not proceed easily. , Which leads to a decrease in PET yield. The major feature of this reaction system is that the system does not contain a compound that releases a proton, so that the alkali metal alkoxide of the catalyst exhibits high activity, and the decomposition of PET is suppressed. Therefore, it is necessary to remove as much as possible impurities such as water, alcohol, carboxylic acid, etc. that cause the release of protons from the raw materials and solvent, and care must be taken not to mix water in the air during the reaction. I have to.

Since the PET thus produced is sequentially precipitated from the solvent and becomes a suspension or a cake, it is possible to easily obtain a highly pure PET by taking it out after the completion of the reaction, washing it with the solvent and drying it. .

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 Diethyl terephthalate (20 mmol), ethylene glycol diacetate (16 mmol), and cyclohexane (30 ml) were placed in an eggplant-shaped flask equipped with a condenser for distilling, and the mixture was stirred under normal pressure on an oil bath at 85 ° C. After heating, 0.2 mmol of sodium ethoxide dissolved in 4 mmol of ethylene glycol diacetate was added. Instantly a white precipitate formed,
Distillation started after about 10 minutes, and after about 50 minutes, the whole solidified into a cake. After 2 hours, heating was stopped, and after cooling to room temperature, the product was washed with 20 ml of cyclohexane and dried under reduced pressure to obtain 3.98 g of white fine powder PET having a melting point of 215 to 220 ° C.

Example 2 Using the same procedure as in Example 1, except that potassium ethoxide was used instead of sodium ethoxide, 3.53 g of white fine powder PET having a melting point of 218 to 225 ° C. was obtained.

Example 3 In the same manner as in Example 1, n was used instead of cyclohexane.
-Heptane was used and heated on an oil bath at 105 ° C under normal pressure to obtain 2.91 g of white fine powder PET having a melting point of 205 to 220 ° C.

Example 4 In the same manner as in Example 1, dimethyl terephthalate was used in place of diethyl terephthalate, and cyclohexane was used.
It was heated with 60 ml for 3 hours to obtain 2.51 g of white fine powdery PET having a melting point of 210 to 220 ° C.

According to the method of the present invention, without using a special device,
It is possible to easily obtain white, finely powdered PET under normal conditions and under mild conditions of about 100 ° C.

Claims (1)

(57) [Claims] 1. Dissolving dimethyl terephthalate (or diethyl terephthalate) and ethylene glycol diacetate in a liquid hydrocarbon and heating in the presence of an alkali metal alkoxide to distill off methyl acetate (or ethyl acetate). A method for producing polyethylene terephthalate, comprising: