JPH10316747A - Process and apparatus for producing polyethylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously produce a high-quality polyester with the least amt. of energy and with a combination of the min. number of necessary reactors by carrying out the steps of esterification, prepolymn., and final polymn., each in one reactor, and by confining the use of a reactor requiring stirring power to the step of final polymn. only. SOLUTION: A polyester is continuously produced with an apparatus comprising the first reactor 3 for reacting an arom. dicarboxylic acid or its deriv. with a glycol compd. to give an oligo- or polyester having an average degree of polynm. of 3-7 ; the second reactor 7 for subjecting the reaction product obtd. at the first reactor 3 to polycondensation to give a low polymer having an average degree of polymn. of 20-40; and the third reactor 11 for subjecting the low polymer supplied from the second reactor 7 to further polycondensation to give a high-mol.-wt. polyester having an average degree of polymn. of 90-180. At least one of the first reactor 3 and the second reactor 7 is not equipped with a stirring function operated by an external power source. The number of revolutions of a stirring blade in the third reactor 11 is set to in the range of 0.5-10 rpm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for continuously producing polyester polymers such as polyethylene terephthalate and polybutylene terephthalate.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a polycondensation polymer such as polyethylene terephthalate, terephthalic acid and ethylene glycol as raw materials are put into a mixing tank at an appropriate ratio for esterification and esterified by a pump. Send to reaction tank. In this esterification step, two or three stirring tanks with stirring blades are arranged in series, and water produced as a by-product is separated by a distillation column. Next, a plurality of vertical stirring tanks and horizontal stirring tanks are installed as a pre-polymerization step, and a horizontal stirring tank is installed as a final polymerization step. A condenser is installed in the tank for these polymerization steps to remove ethylene glycol as a by-product, and the vessel is operated in a reduced pressure atmosphere. In the conventional polyester production process, the number of reaction vessels is 4 to 6 cans, each reaction vessel is equipped with a stirring blade and its power source, and a distillation column and a condenser for separating and removing by-products are installed. ing. Further, since the polymerization process is operated in a reduced-pressure atmosphere, the vacuum means must be operated by another apparatus, and the operation of the production apparatus requires high maintenance costs and equipment costs.

[0003]

SUMMARY OF THE INVENTION The problem of the present invention is an improvement over known processes for the production of high molecular weight polyesters, which increases the efficiency of the entire apparatus and saves energy in plant equipment, thereby operating economically. Is what you do.

An object of the present invention is to improve the above prior art,
An object of the present invention is to provide a continuous polycondensation apparatus and a continuous polycondensation method for efficiently reacting a high-quality polymer with minimum energy by using a minimum necessary reactor configuration.

[0005]

The object of the present invention is to provide an esterification step, a pre-polymerization step, and a final polymerization step as one tank,
A vessel requiring stirring power is achieved by only the final polymerization step.

[0006]

FIG. 1 shows an embodiment of the present invention.
FIG. 1 is an apparatus training diagram of a continuous production process of polyethylene terephthalate according to the present invention. As the industrial polyester production method, the direct esterification method is very economically advantageous, and thus the direct esterification method has recently been widely used. In FIG. 1, reference numeral 1 denotes a raw material adjusting tank for mixing and stirring a predetermined ratio of TPA (terephthalic acid) and EG (ethylene glycol), which are raw materials for polyethylene terephthalate. During the production process, additives such as a polymerization reaction catalyst, a stabilizer, and a color tone adjuster may be added at this stage. Examples of the polymerization reaction catalyst include metal compounds such as antimony, titanium, germanium, tin, and zinc.Depending on the type and combination of the catalysts used, not only the reaction rate differs, but also the hue and thermal stability of the resulting polyester. It is well known that they are different. Furthermore, these reactions are carried out at a high temperature for a long time in the presence of a catalyst, and are accompanied by various side reactions, and the polymer is colored yellow, and the content of diethylene glycol (DEG) and the terminal carboxyl group concentration are more than appropriate values. And physical properties such as a decrease in the melting point and strength of the polyester are reduced. Attempts have been made to develop new catalysts in order to solve such problems, but antimony compounds which are currently most industrially used, especially antimony triacid, are excellent in price and performance. However, even if this catalyst is used, coloring of the produced polyester polymer cannot be avoided. For this reason, phosphorus stabilizers (for example, trimethyl phosphate, triphenyl phosphate) have been used in combination as stabilizers for improvement. In another manufacturing process, the quality is stabilized by devising a position where a polymerization catalyst and a stabilizer are charged. In a typical process, it is preferable to use 200 to 400 ppm of the catalyst and 50 to 200 ppm of the stabilizer. The raw material adjusted as described above passes through the supply line 2 that supplies the raw material to the esterification reaction tank 3. The outer periphery of the esterification reaction tank (first reactor) 3 has a jacket structure (not shown) for keeping the processing liquid at the reaction temperature. An exchanger 4 is provided to heat the processing liquid by a heat source from the outside, and to proceed the reaction while circulating the internal liquid by natural circulation. Here, the most desirable type of reactor is a calandria type in which the processing solution in the reactor is naturally circulated by utilizing the evaporating action of a by-product produced by the self-reaction of the esterification reaction. Since this type of reactor does not require an external stirring power source, there is an advantage that the apparatus configuration is simple, the shaft sealing device for the stirring shaft is not required, and the production cost of the reactor is low. As an example of such a reactor, an apparatus as disclosed in Japanese Patent Application No. 8-249969 is desirable. However, the present invention is not limited to this apparatus, and a reactor having a stirring blade may be used for process reasons. In the first reactor, water generated by the reaction becomes steam, and the vaporized E
A vapor phase 5 is formed with the G vapor. At this time, as the recommended reaction conditions, the temperature is preferably 240 to 280 degrees, and the pressurization condition is desirable. The gas in the gas phase 5 is separated into water and EG by a rectification tower (not shown) provided on the upstream side, the water is removed outside the system, and the EG is returned to the system again. As an advantage of the present invention, it is possible to reduce the number of rectification towers by treating the esterification step in one reactor, and not only the production cost of the rectification tower but also the control of the number of pipes and valves. The number and the like can be reduced, resulting in a significant reduction in equipment cost. The treatment liquid after a predetermined reaction time in the esterification reaction tank 3 reaches a predetermined esterification rate, and is supplied to the initial polymerization tank (second reactor) 7 through the communication pipe 6. At this time, the treatment liquid is heated to a predetermined reaction temperature by the heat exchanger 8 to perform a polycondensation reaction to increase the degree of polymerization. The reaction conditions at this time were 2
70 to 290 degrees and pressure from 266 Pa to 133 Pa
To a degree of polymerization of about 20 to 40. Although the initial polymerization tank shown in this example is described using a reactor having no stirring blade, this reactor is not limited. However, in the initial polymerization stage, the reaction is a stage in which the polymerization reaction rate is governed by the reaction speed, and the reaction proceeds smoothly if a sufficient amount of heat required for the reaction is supplied. From this viewpoint, the processing liquid does not need to be subjected to unnecessary stirring action by the stirring blade, and EG generated by the polycondensation reaction only needs to be released from the system. As an optimum reactor for such an operation, an apparatus as shown in Japanese Patent Application No. 8-233855 is desirable. The EG generated by the reaction is the gas phase 9 maintained in a reduced pressure atmosphere.
And is condensed by a condenser provided on the upstream side and then discharged out of the system. As an advantage of the present invention, it is possible to reduce the number of condensers by processing the initial polymerization process in one reactor, thereby reducing not only the production cost of the condenser but also the number of piping and valves and the number of control devices. As a result, the cost of the apparatus is greatly reduced. After a predetermined reaction time has passed in the initial polymerization tank (second reactor) 7, the processing liquid is supplied to the final polymerization machine (third reactor) 11 through the communication pipe 10. In the final polymerization machine, a stirring blade 1 without a stirring shaft in the center
2, the polycondensation reaction is further promoted while receiving a favorable surface renewal effect, thereby increasing the degree of polymerization to produce a polymer having a desired degree of polymerization. As an apparatus most suitable as a final polymerization machine (third reactor), an apparatus described in Japanese Patent Application No. 8-233857 has the best surface renewal performance and power consumption characteristics. Further, since the viscosity range of the processing liquid is wide, the processing which has been conventionally performed by dividing the processing liquid into two tanks can be performed by one apparatus, and the cost of the apparatus can be greatly reduced.

When polyethylene terephthalate is manufactured in the above-described apparatus configuration, the number of reactors is reduced as compared with the conventional apparatus configuration, so that the cost of the apparatus can be saved. The number of distillation columns and condensers to be used is reduced, and the piping, instrumentation parts, and valves that connect them can be greatly saved, and the running costs are reduced because utility-related costs such as vacuum sources and heat transfer devices are significantly reduced. There are advantages.

[0008]

According to the present invention, the continuous production equipment for polyester is made up of three reactors of an esterification step, a pre-polymerization step and a final polymerization step, so that the efficiency of the whole apparatus is improved and the energy of the factory equipment is improved. It operates more economically with savings.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram of a continuous production process of polyethylene terephthalate showing one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Raw material adjustment tank, 2 ... Raw material supply line, 3 ... Esterification reaction tank, 4 ... Heat exchanger, 5 ... Gas phase part, 6 ... Connecting pipe, 7 ...
Initial polymerization tank, 8 heat exchanger, 9 gas phase, 10 connecting tube, 11 final polymerization machine, 12 stirring blade, 13 polymer, 14 stirring power source.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroo Suzuki 794, Higashi-Toyoi, Kazamatsu, Kudamatsu, Yamaguchi Prefecture Inside the Kasado Plant of Hitachi, Ltd. Inside the Kasado Plant of Hitachi, Ltd.

Claims (6)

[Claims] 1. A first reactor for producing an oligoester or polyester having an average degree of polymerization of 3 to 7 or less by reacting an aromatic dicarboxylic acid or a derivative thereof with a glycol, Average degree of polymerization 20 to 40
A polyester is produced by using a second reactor for producing a low-polymerized product of the above, and a third reactor for further polycondensing the low-polymerized product and polycondensing from an average degree of polymerization of 90 to 180 to produce a high-molecular-weight polyester. In the method, at least one or more of the first and second reactors is a reactor having no stirring function by an external power source, and the method for continuous production of polyester. 2. The third reactor according to claim 1, wherein the reactor has an inlet and an outlet for the liquid to be treated at one lower end and the lower end at the other end in the longitudinal direction of the horizontal cylindrical container main body, respectively. A stirring rotor that has a volatile material outlet and rotates in the longitudinal direction inside the main body and close to the inside of the main body, and the stirring rotor inside the main body has a plurality of stirring blade blocks according to the viscosity of the processing liquid. Wherein the reactor has a stirring blade having no rotating shaft at the center of the stirring rotor. 3. A first reactor for producing an oligoester or polyester having an average degree of polymerization of 3 to 7 or less by reacting an aromatic dicarboxylic acid or a derivative thereof with a glycol, Average degree of polymerization 20 to 40
A polyester is produced by using a second reactor for producing a low-polymerized product of the above, and a third reactor for further polycondensing the low-polymerized product and polycondensing from an average degree of polymerization of 90 to 180 to produce a high-molecular-weight polyester. In the method, the third reactor has an inlet and an outlet for the liquid to be treated at one lower end and the lower end at the other end in the longitudinal direction of the horizontal cylindrical container body, has an outlet for volatiles at the upper part of the main body, A device equipped with a stirring rotor that rotates close to the inside of the main body in the longitudinal direction, and the stirring rotor inside the main body is composed of a plurality of stirring blade blocks according to the viscosity of the processing liquid, and rotates at the center of the stirring rotor. A continuous method for producing polyester, which is a reactor having a stirring blade without a shaft. 4. The continuous production method of a polyester according to claim 1, 2 or 3, wherein the molar ratio of the aromatic dicarboxylic acid or the derivative thereof as a raw material to the glycols is 1: 1.
1.01 to 1: 2.0, the temperature of the first reactor is 240 to 285 ° C, and the pressure is 3 × 10 5 from atmospheric pressure.
Pa, the temperature of the second reactor is 250 to 290 degrees, the pressure is 133 Pa from the atmospheric pressure, and the temperature of the third reactor is 270 degrees to
A method for continuous production of polyester, wherein the method is operated at a pressure of 290 degrees and a pressure of 200 to 13.3 Pa. 5. The continuous polyester production method according to claim 1, wherein the rotation speed of the stirring blade of the third reactor is set to 0.5 rpm to 10 rpm. Production method. 6. The continuous production method of a polyester according to claim 1, 2 or 3, wherein the total reaction time of the first, second and third reactors is operated between 4 and 8 hours. A continuous method for producing polyester.