JPH0318649B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester. More specifically, when manufacturing polyester,
This invention relates to a method of reusing ethylene glycol obtained by treating an ethylene glycol solution containing a phosphorus compound distilled in a polyester manufacturing process by a specific method as part or all of the ethylene glycol charged. To industrially produce polyesters, such as polyethylene terephthalate, bis-(β
-Hydroxyethyl) terephthalate or its lower polymers are usually polycondensed. Such a biaxially stretched film of polyester, especially polyethylene terephthalate, has a high degree of crystallinity and a high softening point, and has excellent properties in terms of elongation, bending strength, chemical resistance, weather resistance, heat resistance, etc. It is widely used in industry. These polyester films are required to have surface properties suitable for each use, and surface properties are widely imparted by a so-called particle precipitation method. That is, a method in which a phosphorus compound is used together with a metal compound such as an alkali metal compound or an alkaline earth metal compound to precipitate these reaction products as fine particles during the polyester manufacturing process to impart desired properties, for example, JP-A No. Showa 53-
This method is described in Japanese Patent Application Laid-open No. 25694 and Japanese Patent Application Laid-Open No. 54-90294. Although this method is simple and can be easily adopted industrially, in this case, according to the knowledge of the present inventors, it has become clear that repeated polymerizations cause unexpected problems. That is, when a part of the phosphorus compound added in the polyester manufacturing process is distilled out of the system together with ethylene glycol and reused with this ethylene glycol,
The problem is that the phosphorus compound is added again to the polyester manufacturing process. If ethylene glycol containing phosphorus compounds is used as a feed ethylene glycol, the transesterification reaction will not proceed smoothly if the content is large, and even if the amount is relatively small, the transesterification reaction will not proceed smoothly. The particle size of the precipitated particles,
When the amount of particles changes and it is made into a film, polyester that provides the desired surface properties cannot be obtained with good reproducibility. In view of the above circumstances, the present inventors have conducted intensive studies and have determined that ethylene glycol containing a specific phosphorus compound, which is easily distilled out from the polyester manufacturing process, is treated in a specific manner, resulting in substantially no precipitation of particles. If ethylene glycol whose phosphorus compound concentration has been reduced to a level that does not affect ethylene glycol is reused as a charging ethylene glycol, it goes without saying that the reactivity during transesterification will not be impaired, and there will be no impact on the quality of the polymer. The present invention was completed based on the discovery that polyester can be produced economically and without any adverse effects. That is, when producing polyester, the present invention uses a phosphorus compound represented by the following formula distilled from the polyester production process (wherein R ¹ , R ² and R ³ each represent an alkyl group having 1 to 4 carbon atoms). In an ethylene glycol solution containing one or more of
The method of producing polyester is characterized by using ethylene glycol recovered by distillation after adding 10 wt% of water and heat treatment. The present invention will be explained in more detail below. Various phosphorus compounds are added to the polyester manufacturing process depending on the purpose. Among these, phosphorus compounds with acidic hydroxyl groups, such as phosphoric acid, phosphorous acid, and acidic phosphate esters, are used in the reaction system. It quickly reacts with metal compounds present in the system, such as alkali metal compounds or alkaline earth metal compounds, and even if phosphorus compounds are present in excess, their vapor pressure is low and most of them are distilled out of the system. There's nothing wrong with that. Further, in the case of trialkyl phosphites, such as phosphorus compounds such as trimethyl phosphite, triethyl phosphite, and tributyl phosphite, the reaction rate with metal compounds and ethylene glycol is fast, and the amount distilled out of the reaction system is small. Even if a large amount is added and a portion of it is distilled out, it will quickly react with ethylene glycol and turn into a phosphorus compound with a low vapor pressure, so it can be easily removed in the process of purifying the recovered ethylene glycol. Therefore, the effect of the present invention is achieved when trialkyl phosphate,
In particular, phosphorus compounds represented by the following formula (In the formula, R ¹ , R ² and R ³ each have 1 carbon number
-4 alkyl group is shown. ) For example, this is the case when one or more phosphorus compounds selected from the group consisting of trimethyl phosphate, triethyl phosphate, tributyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate, etc. are added. That is, these phosphorus compounds are usually added between the end of the transesterification reaction or the direct esterification reaction and the beginning of the polycondensation reaction, but those with relatively low boiling points, such as trimethyl phosphate and triethyl phosphate, each have It has a boiling point of 215°C and reacts slowly with metal compounds and ethylene glycol, so a considerable portion of it is distilled out of the reaction system along with ethylene glycol until the end of the polycondensation reaction. The concentration of phosphorus compounds in distilled ethylene glycol depends on the amount of phosphorus compounds added and reaction conditions, but
It usually contains ~5000ppm. Generally, the ethylene glycol distilled and recovered from the polyester manufacturing process is subjected to a distillation process to remove coexisting impurities such as small amounts of water, methanol, methyl cellosolve, and ethylene glycol monoacetate, but the vapor of such phosphorus compounds The pressure is often close to that of ethylene glycol, and it is impossible to reduce the phosphorus compound concentration by ordinary distillation operations. The present inventors have attempted various studies on the removal of these phosphorus compounds contained in recovered ethylene glycol, which are difficult to separate from ethylene glycol under normal conditions by distillation. By adding water and distilling after treatment under specific conditions,
It has been found that the concentration of phosphorus compounds in ethylene glycol can be easily reduced. In the present invention, the amount of water added during the heat treatment is 0.2 to 10 wt%, preferably 0.5 to 10 wt%, based on the ethylene glycol solution containing the phosphorus compound.
6.0wt% is good. If it is less than 0.2 wt%, the amount of water is too small and the effects of the present invention are hardly exhibited. Also
If it exceeds 10 wt%, it is not preferable because the thermal energy during subsequent distillation increases. The temperature in this heat treatment is 140℃ or higher under normal pressure,
Preferably it is 160-180°C. At temperatures below 140°C, the effects of the present invention are hardly exhibited. A temperature higher than the boiling point of the ethylene glycol solution under normal pressure is not preferred because not only the yield of diethylene glycol, a by-product, increases, but also the heat treatment must be carried out under pressure, which increases equipment costs. The heat treatment time may be selected depending on the concentration of the phosphorus compound contained in the ethylene glycol, the amount of water added, or the treatment temperature, but according to the present invention, it is preferably 0.5 to 8 hours. is 1 to 5 hours. This heat treatment operation can be carried out either batchwise or continuously. The heat-treated ethylene glycol solution is
Thereafter, it is subjected to a distillation operation, but this distillation may be carried out according to a conventional method, and the distillation conditions are not particularly limited. For example, distillation under reduced pressure or normal pressure may be used, and either a batch method or a continuous method may be employed. By this method, the concentration of phosphorus compounds contained in the ethylene glycol solution can be reduced to, for example, 300 ppm or less, and the obtained ethylene glycol can be used as a charging ethylene glycol.
It does not substantially affect the esterification or transesterification reaction or the quality of the precipitated particles. In addition, in the present invention, when manufacturing polyester, the ethylene glycol used is:
It refers to all ethylene glycols used in the polyester manufacturing process, such as ethylene glycol used in transesterification reactions or direct esterification reactions, and ethylene glycol used to prepare catalysts and various auxiliaries. Of course, it may be used in combination with high-purity ethylene glycol that does not contain ethylene glycol obtained by the method of the present invention. Furthermore, the effects of the present invention are also effectively exhibited when other phosphorus compounds such as phosphoric acid, phosphorous acid, and trialkyl phosphites are used together with trialkyl phosphate. Prior to the present invention, for the same purpose, we published Japanese Patent Application Laid-Open No. 57-14619 as a heat treatment method in the presence of an alkaline compound, and as a method of distillation by adding at least the same volume of water as the ethylene glycol solution. JP-A No. 57-14620 has been filed, but the present invention is more economical than the former because it does not use an alkali compound, or improves the properties of the bottoms liquid because the alkali compound moves to the bottom side of the distillation column. This has the advantage that there are no operational problems due to changes in the energy consumption, and the latter has the advantage of significantly reducing energy costs. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. In addition, in Examples and Comparative Examples, "part" indicates "part by weight". The measurement method used is shown below. Coefficient of friction: Based on the method of ASTM D 1894-63, it has been improved so that it can be measured using a tape-shaped sample.Measurements are carried out in an atmosphere with a temperature of 21 ± 2 °C and a humidity of 65 ± 5%, and the measurement conditions are as follows: Tensioning speed 40mm/
The chart speed was 120 mm/min, and the sample size was 15 mm in width and 150 mm in length. Number of surface protrusions: The number of surface protrusions of 0.05 μ or more per unit length (mm) on the surface of the biaxially stretched film was measured using a stylus type surface roughness measuring machine manufactured by Taylor Bobson. This value is preferably 15 pieces/mm or more. Example 1 (A) 100 parts of dimethyl terephthalate, 68 parts of ethylene glycol, and calcium acetate monohydrate
0.10 part of the mixture was placed in a reactor, heated to raise the temperature, and methanol was distilled off to carry out the transesterification reaction.It took 4.0 hours after the start of the reaction to heat the mixture to 225°C, and the transesterification reaction was substantially completed. Next, a solution of 0.20 part of triethyl phosphate and 0.05 part of triethyl phosphite dissolved in 2 parts of ethylene glycol was added to the transesterification product. Next, a solution of 0.04 part of antimony trioxide dissolved in 2 parts of ethylene glycol was added as a polymerization catalyst, and then polymerization was carried out in accordance with a conventional method. That is, after adding antimony trioxide, the temperature was raised to 280℃ and the pressure reached 10mmHg in 110 minutes, and the pressure was then gradually reduced to a final temperature of 1mmHg.
Hg or less. After 4 hours, return the system to normal pressure.
The polymer was discharged. Next, the obtained polymer was extruded into a sheet form from an extruder at 290°C, rapidly cooled to form an amorphous sheet, then stretched at 93°C to 3.4 times in the longitudinal and transverse directions, and heat treated at 230°C for 3 seconds. Do it
A film with a thickness of 12μ was obtained. On the surface of the obtained film, favorable uniform fine irregularities were observed, and the number of surface protrusions was
It was 20.0 pieces/mm. Furthermore, the film had a coefficient of friction of 0.5 and was excellent in feel and appearance. (B) On the other hand, in order to reuse approximately 40 parts of ethylene glycol distilled during the production of polyester in (A), that is, during transesterification and polycondensation, the concentration of phosphorus compounds in the ethylene glycol was determined by gas chromatography. As a result, 1800 ppm of triethyl phosphate was found, but no triethyl phosphite was detected. Next, 1.2 parts of water was added to this solution and heat treated at 170°C for 3.0 hours, resulting in only 36 ppm of triethyl phosphate remaining, and the residual rate reached 2%. The heat-treated solution was heated under normal pressure.
After removing components on the lower boiling point side than ethylene glycol by distillation, distillation was subsequently performed under reduced pressure of 15 mmHg to obtain 36 parts of regenerated ethylene glycol as the main fraction. Polyester was produced in the same manner as in (A) by mixing 36 parts of this recycled ethylene glycol with 36 parts of separately purified high-purity ethylene glycol that does not contain impurities such as phosphorus compounds, and using this as a charging ethylene glycol. In this case, no difference in transesterification reactivity was observed compared to the case of (A). Further, a polyester film was obtained using the polyester in the same manner as in (A). The surface condition of the polyester film was similar to that of (A), the number of surface protrusions was 19.0/mm, and the coefficient of friction was 0.5, and no difference was observed between them and the film of (A). Comparative Example 1 In (B) of Example 1, the components on the lower boiling side than ethylene glycol were distilled off under normal pressure without adding water and heat treatment, and then distilled under reduced pressure of 15 mmHg to obtain recycled ethylene glycol 36 as the main fraction. I got the department. This recycled ethylene glycol contained 1700 ppm of triethyl phosphate. Next, 36 parts of this recycled ethylene glycol and 36 parts of high-purity ethylene glycol were mixed, and this was used as the charged ethylene glycol, and polyester production was attempted in the same manner as in Example 1 (B). However, the transesterification reaction did not proceed smoothly and polyester could not be obtained, so 15 parts of the recycled ethylene glycol and 57 parts of high-purity ethylene glycol were mixed again, and this was used as the charged ethylene glycol. Polyester and film were produced in the same manner as in case B). In this case, the transesterification reaction rate is the same as in Example 1.
The reaction was slightly slower than in case (A), taking approximately 4.5 hours to complete the reaction. In addition, although many uniform and fine irregularities were observed on the surface of the obtained film, the number of surface protrusions was
The friction coefficient was 10 pieces/mm, and the friction coefficient was 0.8, indicating extremely poor slipperiness. Examples 2 to 4 Table 1 shows the results of heat treatment by adding water in Example 1 (B) by varying the amount of water added, the treatment temperature, and the treatment time. Using the solution heat-treated in this way, Example 1 was prepared.
Polyester and film were produced in the same manner as in case (B). No difference was observed between these films and the film of Example 1 (A) in either the number of surface protrusions or the coefficient of friction. Comparative Example 2 Table 1 shows the results of heat treatment by adding water in (B) of Example 1 by varying the amount of water added and the treatment time. Using the thus heat-treated solution, polyester and film were produced in the same manner as in Example 1 (B). This film has 13 surface protrusions compared to film (A).
pieces/mm, and the friction coefficient was as high as 0.70.

[Table] *Amount of water added to distilled ethylene glycol in (A) of Example 1

Claims (1)

[Scope of Claims] 1. When producing polyester, a phosphorus compound represented by the following formula distilled from the polyester production process (in the formula, R ¹ , R ² and R ³ each represent an alkyl group having 1 to 4 carbon atoms) is used. show.) In an ethylene glycol solution containing one or more of
A method for producing polyester characterized by using ethylene glycol recovered by distillation after adding 10 wt% water and heat treatment. 2. The method for producing polyester according to claim 1, wherein the heat treatment is carried out at a temperature of 140° C. or higher under normal pressure.