DE1135660B - Process for the production of high molecular weight polyethylene or polytetramethylene terephthalates - Google Patents

Description

Process for the production of high molecular weight polyethylene or polytetramethylene terephthalates The production of terephthalic acid glycol esters is known. In the case of polycondensation valuable fiber- or film-forming polyesters are obtained from these esters. In general the terephthalic acid glycol ester is produced by transesterification of a dialkyl terephthalate, especially dimethyl or diethyl terephthalate, with a glycol. While this method supplies suitable esters for the subsequent polycondensation, they naturally have the disadvantage that the terephthalic acid is first converted into the dialkyl ester must before the glycol ester can be made.

Esterification of terephthalic acid with ethylene glycol can also be done by Done refluxing.

However, in order to achieve complete esterification, one must Continue refluxing for several days.

It is also known that the esterification process by catalysts, z. B. mineral acids such as sulfuric acid to accelerate. In the second stage will the obtained terephthalic acid glycol ester polycondenses at a higher temperature, without the terephthalic acid glycol ester being separated off or purified beforehand. the Presence of mineral acids or other dehydrating compounds is therefore very undesirable because their presence causes discoloration or even charring of the polyester. In addition, such catalysts also favor the unwanted glycol ether formation.

In the aggregation of the esterification and polycondensation stages The purity of the terephthalic acid used is of the utmost importance as it is available Impurities are carried through to the final polyester, where they become discolored cause.

In the known esterification of terephthalic acid with a glycol undesired side reactions occur with the formation of polyglycols.

When using ethylene glycol, the side reaction leads to Diethylene glycol, with 1,4-butanediol the ether-forming side reaction leads to tetrahydrofuran.

In the case of the esterification, water must in any case be removed from the reaction mixture removed, the water either from the esterification reaction or from the undesired ether-forming side reaction originates.

The invention relates to a method for the production of high molecular weight Polyethylene or polytetramethylene terephthalates by esterification of terephthalic acid with ethylene glycol or 1,4- Butanediol and immediately following polycondensation the obtained glycol terephthalic acid ester, which is characterized in that one in the case of esterification, a mixture of terephthalic acid and glycol at a molar ratio of terephthalic acid: glycol up to 1: 2.5 at overpressure and a temperature of up to heated to about 2500 C.

The technical progress can be seen in the implementation takes place in a much shorter reaction time and that the polyester produced have a much improved color and a higher softening point, and a contain a smaller amount of polyglycol ether.

Since the esterification takes place with the formation of water, this can progress the reaction can be followed at the pressure developed in the reaction vessel. If no further overpressure occurs, this point can be used as the end point for the esterification can be considered.

The following table compares the vapor pressures of Ethylene glycol and water specified in the temperature range from 200 to 2500 C.

Table I. Temperature vapor pressure vapor pressure of the ethylene glycol of water OC kg / cm2 kg / cm2 200 0.07 14.7 220 1.05 22.4 230 - - 1.61 27.3 240 2.24 32.9 250 2.94 39.2 The excess pressure in excess of the pressure developed by the glycol at the reaction temperature can be released through a suitable relief valve.

The esterification according to the process of the invention is carried out at temperatures carried out up to about 2500 C, since decomposition takes place at higher temperatures.

The transesterification according to the method of German patent specification 818 117 has the disadvantage that both the transesterification and the polycondensation stage the presence of a metallic compound as a catalyst is required. The presence of such metallic compounds has a deleterious influence on the color and heat resistance of the final polyester. On the other hand, the glycol terephthalic acid ester prepared by the process of the invention without the aid of a catalyst and be polycondensed. In order to obtain a high molecular weight quickly, however, preferred a lesser amount of one Add antimony compound, there such compounds are relatively harmless to the color and Stability of the polyester.

The process of the invention can also be semi-continuous or continuous be performed.

A mixture of terephthalic acid and ethylene glycol is continuously used or 1,4-butanediol passed into the reaction vessel. The overpressure is ensured by suitable Valves drained with the removal of water vapor from the reaction vessel, to maintain the optimal working pressure.

The process of the invention is illustrated by the following examples. All parts and percentages are based on weight.

Example 1 Terephthalic acid and ethylene glycol were in one with A stirred autoclave equipped with a steam discharge tube connected to a condenser, implemented. The water formed during the esterification was at a certain pressure blown off together with a small amount of ethylene glycol. The termination of the esterification was recognized by the fact that no further pressure developed above the certain level became. The drain pipe was then opened and the excess ethylene glycol was distilled off. After the addition of the catalyst, the polycondensation was carried out at a temperature of 275 to 2800 C and 0.2 mm Hg up to an intrinsic viscosity of 0.63 to 0.68 performed, the end point being measured by the rotation of the stirrer in the Polyester melt force required was determined.

The table gives details of a number of experiments that were carried out under the above conditions.

Table II Ethy- tere- glycols poly- polyester Acid esterification condensate total duration extension di- len phthalation h glycol Try glycolic acid faucet temperature pressure duration duration point unit \\ color Parts 1 part mol o C kgfom2 minutes minutes hours (minutes ° CI percent; 1 775 830 2.5 / 1.0 220 to 250 2.8 to 3.5 60 115 2 55 252 | 4 1.8 2 620 830 2.0 / 1.0 200 to 250 2.8 to 3.5 100 125 3 45 260 | 2 1.5 3 620 830 2.0 / 1.0 200 to 230 2.1 to 2.45 125 120 4 05 252 1 4 2.5 4 372 830 1.2al, 0 200 to 255 2.8 to 3.5 100 95 3 15 260 1 2 1.5 Note: In the experiments, 0.166 parts of antimony trioxide were added before the polycondensation.

Example 2 830 parts of terephthalic acid (5 moles) and 775 parts of ethylene glycol (12.5 mol) were at 200 to 2500 C in a with a short fractionation column, Condenser and template for the working method equipped with a stirred autoclave under pressure esterified.

The autoclave was closed during the initial heating to 2000C maintained at atmospheric pressure, then with deoxygenated nitrogen the pressure increased to 3.85 kg / cm2. As the esterification proceeds, became water at the top of the column at a temperature of 150 to 1550 C is distilled off and the pressure is kept at 3.85 kg / cm2. The esterification was after Finished 150 minutes; that is 120 minutes subsequent polycondensation process was the same as in Example 1. The polyester obtained had intrinsic viscosity of 0.62, the softening point 2580 C and the color 1.8.

Example 3 A mixture of ethylene glycol and terephthalic acid in a molar ratio 2.5: 1.0 was continuously applied to a cascade reaction vessel at one temperature of 2400 C. At the top of the container were those formed in the reaction volatile constituents through a reflux column and a discharge pipe with such Velocity removed that a constant pressure of 3.5 kg / cm2 is maintained in the container could be. Simultaneously the esters were continuously on Peeled off the bottom of the cascade and at 2750 C and 0.2 mm pressure after adding 0.04 Percent by weight of antimony trioxide polycondensed. A polyester with the softening point 2570 C, the intrinsic viscosity 0.60 and the color 2.0 were obtained.

Example 4 830 parts of terephthalic acid (5 moles) and 1125 parts of 1,4-butanediol (12.5 mol) were esterified in a stirred autoclave at 230 to 2600 C. The pressure was kept at 4.2 kg / cmS by draining off water and tetrahydrofuran. To There was no further increase in pressure for about 1 hour. Then the obtained ester became at 2600 C and 0.2 mm pressure in the presence of 0.03l%, based on the weight of the Terephthalic acid, antimony trifluoride polycondensed in the course of 3 hours. A Polytetramethylene terephthalate with an intrinsic viscosity of 0.40 and the Softening point of 2240 ° C was obtained.

The following comparative examples illustrate the advantages of the process the invention.

Comparative example A To have a comparatively esterifying time 1970 C with the esterification time used in Example 1, it is necessary to 3720 parts of ethylene glycol and 830 parts of terephthalic acid (12/1 mol) to be used, the water formed during the esterification under atmospheric pressure continuously distilled off. The polycondensation of the ester at 2750 C and 0.2 mm Hg in Presence of 0.166 parts of antimony trioxide obtained in the course of 22/2 hours Polyethylene terephthalate had an intrinsic viscosity of 0.62, color 3.0, Softening point 2400 C and a diglycol content estimated by infrared examination of 10 mole percent.

The polyester with a high content of ether compounds and the like A decrease in the softening point shows poor heat and light stability. aside from that is the reproducibility of the intrinsic molar viscosity and the softening point very difficult.

Comparative Example B There was a transesterification between 920 parts Dimethyl terephthalate and 775 parts of ethylene glycol in the presence of 0.184 parts Zinc acetate in the temperature range from 155 to 2000 C in a stirred reaction tion container carried out. The reaction mixture became methanol immediately after its formation separated by distillation over a short fractionating column. The one for transesterification required time was 3½ hours. The glycol ester obtained was after addition polycondensed from 0.166 parts of antimony trioxide at 2750 C and 0.2 mm Hg. The required Time to reach an intrinsic viscosity of 0.65 was 90 minutes, which corresponds to a total of 5 hours.

The polyester obtained had a softening point of 261.50 ° C. and Color 2.6.

The polyester color scale used in the comparative examples was a range from 0 to 3, where 0 = white and 3 = pale amber. The values reported were the mean of four ratings from different ones Edit.

The measurements of the intrinsic viscosity were in 1 / ciger Solution made in o-chlorophenol at 250 C and serve as a measure of the degree of polycondensation.

From the comparative examples it can be seen that according to the method the invention the esterification is very facilitated and that polyester with better Color, higher softening point and lower content of diglycol units will. It can also be seen from Comparative Experiment B that the transesterification takes significantly longer and that the polyester obtained is at the worst end the color scale.

Claims (1)

PATENT CLAIM Process for the production of high molecular weight polyethylene or polytetramethylene terephthalates by esterification of terephthalic acid with ethylene glycol or 1,4-butanediol and immediately subsequent polycondensation of the resulting Glycol terephthalic acid ester, characterized in that the esterification a mixture of terephthalic acid and glycol at a molar ratio of terephthalic acid: Glycol up to 1: 2.5 at overpressure and at a temperature up to about 2500 C heated. Considered publications: German Patent Specifications No. 818 117, 905 736; U.S. Patent No. 2,465,319; British Patent No. 578 079; F. Runge, Introduction to the Chemistry and Technology of Plastics, Scientia Chimica, Monographs, 1952, Vol. 5, p. 15.