JPS5938966B2 - Polyester polymerization reaction tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical batch polymerization reactor for polyester made of glycol ester of aromatic dicarboxylic acid.

More specifically, the present invention relates to an improvement in the stirring blade of the vertical polymerization reactor. Generally, in the polycondensation reaction of polyesters such as polyethylene terephthalate, ethylene glycol generated under heating and reduced pressure is removed from the reaction system to promote the polymerization. Conventionally, there has been a concern as to how short the polymerization reaction time can be, that is, how quickly the ethylene glycol generated during the reaction can be removed from the reaction system.

For this reason, even in the case of batch-type vertical polymerization tanks, various improvements have been made to the shape of the reaction tank, heating, pressure reduction conditions, etc., and this has now been achieved. By the way, in recent years, for example, Japanese Patent Application Laid-Open No. 51-1262
In 1995, a method was proposed in which a stirring blade was attached to a vertical rotating shaft from the bottom of the reaction tank to the top of the reaction liquid level, but this method has not yet achieved a satisfactory effect.

In other words, if the blade is effective in quickly raising the temperature of the reaction solution in the first half of the polymerization reaction and removing ethylene glycol quickly, the reaction time will be longer in the second half of the polymerization reaction, and vice versa. When the time could be shortened, there was a drawback that the reaction time was longer in the first half of the polymerization reaction.

The present invention overcomes the drawbacks of the prior art described above.

That is, an object of the present invention is to provide a polymerization reaction tank that eliminates the disadvantages of the first half and the second half of the polymerization reaction, and maintains the effect of renewing the reaction liquid level throughout the entire period of the polymerization reaction. In other words, in the present invention, in a batch-type vertical polyester polymerization reaction tank, when the height to the static liquid level is L, the helical angle with respect to the horizontal plane is 500 to 8
00, O, 7L or more, above, the helical angle is 100 to 400
This is a polyester polymerization reaction tank characterized by having stirring blades mounted on a vertical rotating shaft.

The present invention will be explained in detail below.

FIG. 1 is a sectional view of a polymerization reaction tank showing an example of the present invention.

A vertical rotating shaft 2 faces from the top of the reaction tank body 1, and a spiral ribbon-shaped stirring blade 3 is provided on the rotating shaft 2. The reaction liquid is filled up to a predetermined height of L. The helical angle θl at the lower part of the stirring blade 3 is 500-800, and the helical angle θ2 at the upper part is 100-400. The angle of the helical ribbon is different between the upper and lower parts of the stirring blade 3, and the bending point P where the angle changes is when the height of the reaction liquid in the resting state is L.
It is located in the height range of O, 4L-O, 7L. As mentioned above, one of the major features of the present invention is that the angles of the upper and lower parts of the stirring blade are changed. Generally, in the case of polyester, a large amount of ethylene glycol is generated in the first half of the reaction time, so in order to raise the temperature to a specified temperature as quickly as possible, it is important to improve the heat transfer coefficient and to remove the generated ethylene glycol from the reaction liquid. The key points are how to increase the surface renewal rate that causes ethylene glycol to move to the surface, and how to increase the evaporation area of ethylene glycol since the viscosity increases in the latter half of the reaction time and the flow of the reaction liquid becomes poor.

The inventors of the present invention have made extensive studies to solve these problems using a stirring blade, and have obtained the following knowledge regarding the helical angle of the stirring blade. That is, when polyester was polymerized using spiral ribbon stirring blades with spiral angles of (A) 700 and (B) 35 from the top to the bottom with respect to the horizontal plane, heat transfer in the low viscosity region in the first half of polymerization, The surface renewal effect is (support) > (2) The effect of increasing the evaporation area in the high viscosity region in the latter half of polymerization is ^ 〈
We found that (2) has opposite effects in the first half and second half of the reaction.

Therefore, when we investigated the time required for the first half of polymerization (until the intrinsic viscosity is 0.436) under the same conditions by varying the helical angle of the stirring blade, we found that the polymerization rate increased when the helical angle was between 50° and 80°, as shown in Figure 3. I found out it was early.

This is because the temperature of the reaction solution at the initial stage of the reaction rises quickly and the surface renewal rate is good. Similarly, the second half of polymerization (intrinsic viscosity 0.43
5 to 0.640), it was found that the polymerization rate was high when the helical angle was 100 to 40 degrees, as shown in FIG. This is because the reaction liquid was lifted on the top surface of the stirring blade, increasing the evaporation surface area. However, in the first half of the reaction,
The polymerization time when the second half was passed through at the same helical angle was 20° to 70°.
As shown in Figure 5, there was no significant difference in the range up to 100°, and the advantages of the first and second half of the reaction could not be utilized.

In addition, industrially, it is not possible to replace the stirring blades during the application of the reaction, so it is difficult to design equipment that takes advantage of the respective advantages of the stirring blades having the two types of helical angles. Therefore, in order to maintain the effect in the first half of the reaction and increase the effect in the second half of the reaction, a blade with a large helical angle that has a good surface renewal rate is attached to the lower part of the stirring blade, and a blade with a small helical angle that has a good surface area increase effect is attached to the upper part. I thought it might be a good idea to attach wings, so I conducted the following experiment.

That is, using the device shown in Fig. 1, the helical angle of the lower part of the blade 3 is set to 70° and the helical angle of the upper part is set to 20°, and the height of the reaction liquid in the resting state is set relative to the bending angle of the blade. When the time required for polymerization until the intrinsic viscosity reached 0.640 was compared under the same conditions and equipment except that the point P was varied, the results shown in FIG. 6 were obtained. This shows that the polymerization time is the fastest when the bending point P of the helical angle is located within the height range of 0.4L to 0.7L. In other words, the upper end of the stirring blade with a lower part of 70° is 0.4
The lower end of the stirring blade having an angle of 20° at the top is located at a position of 0.7 L or more. When using a spiral ribbon with continuous upper and lower parts as shown in FIG. If the upper and lower parts of the stirring blade are separated as shown in FIG. .4L or above. In other words, 0.4
Below L, the helical angle is 500~80°, while 0.7L
The purpose of the above is to set the helical angle to 10° to 40°. In addition to the spiral ribbon shape as shown in FIG. 1, the stirring blades in the present invention may be anchor-shaped, and can be applied to commonly used shapes such as an "out" shape. However, even in that case, it is necessary to provide the helical angle described above. By implementing the present invention, the polymerization time could be significantly shortened.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a polymerization reaction tank showing an example of the present invention. FIG. 2 is a sectional view showing another example of FIG. 1. 3rd, 4th
, 5 is a graph showing the experimental results that led to the present invention, and FIG. 6 is a graph showing the results of implementing the present invention. 1...
...Reaction tank body, 2...Rotation shaft, 3...
- Stirring blade.

Claims (1)

[Claims] When L is the height to the static liquid level in a 1-batch type vertical polyester polymerization reactor, the helical angle is 50° to 80° with respect to the horizontal plane for 0.4 L or less, and 10° for 0.70 L or more. A polyester polymerization reaction tank characterized in that a stirring blade having an angle of 40° to 40° is provided on a vertical rotating shaft.