JPS6024803B2 - Recovery method of atactic polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Processes for polymerizing propylene or copolymerizing propylene and unsaturated hydrocarbon monomers in suspension in liquefied propylene are known.

The present invention uses a polymer dissolved in liquefied propylene produced as a by-product during polymerization (hereinafter abbreviated as "atactic polymer").

) in a method of recovering heat transfer coefficient of an evaporator and maintaining it at a high value. In the present invention, the conditions for recovering the atactic polymer are 13 to 40 k9 under pressure.
/ under gauge pressure, that is, the pressure at which propylene can be liquefied by cooling with industrial water or air.
We have discovered a method that allows operation at temperatures as low as 45 to 90°C, and at even lower heating medium temperatures of 60 to 130°C. Generally, the simplest method for recovering an atactic polymer is to reduce the pressure of liquefied propylene in which the atactic polymer is dissolved to a pressure substantially close to atmospheric pressure.

In this method, propylene is completely vaporized with a small amount of heating, so that the atactic polymer is in a state where it can be easily separated. This method is very simple.The only drawback is that a large amount of liquefied propylene is vaporized under reduced pressure, so a compressor is required to liquefy it again and circulate it to the polymerization process, which is disadvantageous in terms of equipment and power costs. It is.

Furthermore, Japanese Patent Publication No. 47-42379 describes a method for separating atactic polymers under the same pressure and temperature conditions as the method of the present invention, but it has the following drawbacks. (2) Since a separator containing a knot or bubble-type separation tray is used, fine particles of isotactic polymer and catalyst residue mixed into the propylene solution supplied to the separator tend to adhere to the tray.

■ The heat transfer coefficient of the reboiler used to evaporate propylene tends to decrease. In addition, Hakamako No. 50-20046 discloses a method for separating atactic polymers under supercritical conditions of a solvent, but propylene requires a pressure of 45 k9 /
He needs to be boosted even more than Akira.

In addition, a method of recycling the atactic polymer at a high temperature of 160 to 25 degrees, that is, the temperature at which the mixed fin tactical polymer is melted, is often used, but this method requires a large amount of heat or easily decomposes the catalyst residue. It has the following disadvantages.

All of the above-mentioned methods have drawbacks, and we have found the Tokubatsu 1984-Ichiwabura No. 1 publication as a method to solve these problems, but the present invention further improves Samurai Seki 52-Giwabura No. 1. This is an improved version. Tokukan Sho 52-5 Patent No. 1 discloses that an atactic polymer dissolved in liquefied propylene is heated at a pressure of 13 to 40
This is a method for recovering atactic polymers, which is characterized by heating the propylene under k9/d gauge pressure to recover the atactic polymer in a molten state. However, this method has the disadvantage that the traditional thermal coefficient tends to decrease due to the adhesion of static polymers, atactic polymers, or catalyst residues to the refractory surface of the evaporator, or that a part of the transmission pipe tends to become clogged. has.

According to experience, when it comes to reducing the heat transfer coefficient, ■ The lower the propylene evaporation temperature, the better, especially at a temperature below 90°C at which the isotactic polymer does not melt.■ The higher the heating medium, the better. It was found that although the temperature difference between the medium and the evaporated material can be made large, the heat transfer coefficient decreases significantly; rather, when the heating medium is relatively low, from 60 to 130°C, the heat transfer coefficient shows a stable high value. Ta.

However, in any case, it is difficult to maintain the initial high value of the heat transfer coefficient of the evaporator.

The present invention is based on the discovery of a method for solving this drawback through operational operation.

That is, the present invention provides a method for heating an atactic polymer dissolved in liquefied propylene under a pressure of 13 to 14 k9/immersion gauge pressure to vaporize the propylene and recovering the atactic polymer in a molten state. Provided is a method for recovering an atactic polymer, characterized in that a decrease in the phosphorescence coefficient of an evaporator is prevented by periodically increasing the V supply flow rate of propylene in a pulsed manner to 1.3 or more of the average flow rate.

The heat transfer coefficient of the evaporator gradually decreases with time, but the rate of decrease also depends on the amounts of isotactic polymer, atactic polymer, and catalyst residual grooves in propylene, and the rate of decrease is faster as the amount is larger.

It also varies depending on the evaporation temperature of propylene and the temperature of the heating medium.

Therefore, after a certain time, 1/2 of the initial 6 poison heat coefficient ~
It also drops to 1'3.

Therefore, unevaporated liquefied propylene ultimately remains at the outlet of the evaporator. The present invention is an evaporator.
This is to maintain the toxic ripening coefficient at a high value and prevent the adhesion of the fin tactical polymer, atactic polymer and catalyst residue to the heat ring surface and blockage in the poison heat pipe.

In other words, we found a method to constantly maintain the 6 toxic heat coefficient at a high value by instantly increasing the amount of propylene that supplies the evaporator in a pulsed manner and removing deposits from the heat transfer surface. .

The present invention will be explained in more detail with reference to the manufacturing process in FIG. FIG. 1 is an example of a flow sheet for the apparatus used to practice the invention. Polymerization step 1 indicates the final step of polymerizing or copolymerizing propylene. The polymerization uses one or several polymerization vessels.

The polymerization process produces an isotactic polymer that is insoluble in liquefied propylene and an atactic polymer that is soluble in liquefied propylene.

The isotactic polymer is suspended in liquefied propylene to form a polymeric slurry.

The polymerization slurry leaving the polymerization step 1 enters a container 2 to separate isotactic polymer and atactic polymer.

The structure of the container 2 can be various depending on the separation method, but for example, the following method is used:
A method of repeating concentration sedimentation in batches.

■ Continuous concentration and sedimentation method.

■ A method in which a polymerization slurry and propylene 3 containing no atactic polymer are brought into contact with alternating current.

The phase containing the isotactic polymer is separated from the phase in which the atactic polymer is dissolved.

In carrying out this operation, a catalyst deactivator or a scale and soot separating agent may be added.

In either case, liquefied propylene in which an atactic polymer is dissolved is extracted from the upper part of the container 2, and liquefied propylene in which an isotactic polymer is suspended is extracted from the lower part in a batchwise or continuous manner.

The slurry is depressurized to near atmospheric pressure by a pressure reducing valve 4, the propylene is completely vaporized by a heating pipe 5, and the isotactic polymer and propylene are separated by a separator 6 such as a cyclone or flash hopper. This isotactic polymer is in the form of powder, to which additives are added, and is manufactured into a product as it is or through a granulation process.

On the other hand, liquefied propylene containing the atactic polymer is supplied to the evaporator 9. Most of the liquefied propylene is evaporated in the evaporator 9, and separated into a liquid mainly composed of vaporized propylene and an atactic polymer in a directly connected flash vessel 10.

The evaporator 9 is usually a multiple beam evaporator, and liquefied propylene is supplied inside the tube and a heating medium is supplied outside.

In the flash vessel 10, in addition to the atactic polymer, there is also an amount of isotactic polymer, a solvent used as a carrier for the catalyst, a catalyst such as an organoaluminum and a titanium compound, a low molecular weight polymer, a disabling agent for the catalyst, Alternatively, decomposing agents and the like are also separated at the same time.

Atactic polymer is pumped by valve 11 to atmospheric pressure ~1
The pressure is reduced to 0k9/gauge pressure and the contained propylene is separated in a separator 12.

Atactic polymers can be prepared using separation pressure or by using a suitable pump (e.g. gear pump, screw pump).
etc., and then sent to the combustion process or oil conversion process. On the other hand, the propylene gas discharged from the flash container 10 is used to remove entrained or dissolved components with a boiling point higher than that of propylene (for example, a part of the solvent used for the catalyst carrier, low polymers of propylene, etc.). It passes through the crab tower 14, and is easily liquefied in the condenser 15 without passing through the crab tower 14.

Note that the propylene discharged from the separator 6 and the separator 12 is pressurized by the compressor 13, joins with the propylene that has passed through the flash container 10, and passes through the above steps.

The present invention now relates to a method of operating the evaporator 9.
Atactic polymer and catalyst residue adhere to the heat transfer surface of the evaporator 9, so that the heat transfer coefficient gradually decreases.

However, it has been found that it is possible to remove the deposits by instantaneously supplying a large amount of liquefied propylene to the evaporator in a pulsed manner for about 0.5 to 5 seconds.

This allows the heat transfer coefficient to be maintained at a high value.

The frequency of pulses varies depending on the amount and properties of the atactic polymer, isotactic polymer, and catalyst clear in the liquefied propylene, but usually the frequency is 5 minutes to 1 minute.
The supply flow rate may be about once per hour, and the supply flow rate should be at least 1.3 times, preferably at least twice, the average flow rate.

Although it is usually sufficient to set the frequency and the flow rate to constant values, they may be adjusted automatically or manually depending on the condition of the evaporator.

The present invention will be explained in more detail below using Examples and Comparative Examples.

Comparative Example 1 Liquefied propylene containing an atactic polymer was supplied to the evaporator 9, and the liquefied propylene was evaporated.

Evaporator 9 7.7 (multi-tube type) liquefied propylene combined amount 1800k9/day Heating steam pressure 4.5k9/gauge pressure Flash vessel pressure 19k9/gauge When operating under 19k9/gauge temperature of flash vessel. gradually decreases to the initial temperature 1
15oo became 65:00 8 hours later. The heat transfer coefficient of the evaporator in this state is 160 Kcal/hr.

It was ○. The pressure was reduced from the flash vessel 10 through the control valve 11 to the separator 12 at a pressure of 0.1 k9/m gauge pressure, and after the propylene in the atactic polymer was evaporated, the atactic polymer was taken out.

When the atactic polymer was weighed and its composition analyzed, it was found to be as follows.

Atactic polymer 12k9/H Isotactic polymer 1.4kg/day Volatile matter such as solvent 3.5k9/day Ash content (ash content after combustion) 0.6 [9/H In addition, the intrinsic viscosity of the atactic polymer is 0. It was 03.

Since the combined flow rate increases instantaneously, the entire amount of liquefied propylene cannot necessarily be evaporated instantaneously, but by limiting the amount of liquefied propylene to a short period of time, the amount of liquefied propylene stored in the flash container can be reduced. In general operation, it is better to perform the above operation instantaneously after turning off the liquefied propylene supply while leaving the heating medium flowing; This is thought to be due to the rapid evaporation of liquefied propylene due to the amount of heat stored in the container.

The above are application examples of the present invention, but it goes without saying that the present invention can be easily applied even if the manufacturing process is different or the components in the liquefied propylene are different.

Comparative Example 2 Using the same apparatus as in Comparative Example 1, the same liquid was applied to an evaporator.

The supply amount of liquefied propylene was adjusted to a constant condition of 1800k9/H, the pressure of the flash vessel was 19k9 ground gauge pressure, and the temperature was 70°C.

Initially, the heating medium, steam (4.5k9/gauge pressure), was intermittently supplied by the temperature control valve, and the pressure of the heating medium in the evaporator was almost 0, but after 8 hours After 1.5k9/earth 4.0 after 12 hours
k9/ground was shown.

After another 15 hours, I was unable to maintain 70k0. This indicates that the heat transfer coefficient of the evaporator is gradually decreasing. Example 1 Using the same equipment as in Comparative Example 1, the same liquid was fed to an evaporator.

Amount of liquefied propylene to be supplied: 1800 kQ/day Pressure of flash vessel 10: 19 k9/gauge pressure Temperature: O30 adjusted to 70° C. The following pulses were given to the supply amount in one cycle.

Supply v amount: Approximately 2500kQ/h
During the r pulse, the temperature of the flash container was 70℃ even after 24 hours for about 3 seconds.
It became impossible to maintain the temperature at 70 pm after childhood.

Example 2 The pulse in Example 1 was changed as follows.

V supply amount: Approximately 3600kg/hr
After 4 muscle hours for 3 seconds during the pulse, it was no longer possible to maintain the temperature at 70°C.

Example 3 Before applying the same pulse in Example 2, 1
The supply amount was set to 0 for a few seconds, and the heating medium control valve was fully opened. The temperature was maintained at 70° C. even during the 4-hour period, and the pressure of the heating medium in the evaporator was only 0.5 k9/ground.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of an example of an apparatus for implementing the present invention. 1: Polymerization process, 2: Container (separator for isotactic polymer and atactic polymer), 6: Separator, 9: Evaporator, 10: Flash container, 12: Separator, 13: Compressor, 14: Semen crab Tower, 15: condenser. bag, figure

Claims (1)

[Scope of Claims] 1. A method in which an atactic polymer dissolved in liquefied propylene is heated under a pressure of 13 to 40 kg/cm^2 gauge pressure to vaporize the propylene, and the atactic polymer is recovered in a molten state. Recovery of an atactic polymer characterized by preventing a decrease in the heat transfer coefficient of an evaporator by periodically increasing the flow rate of liquefied propylene supplied to the evaporator in a pulsed manner to 1.3 times or more the average flow rate. Method. 2. The recovery method according to claim 1, wherein the temperature of the heating medium is 60° C. or higher. 3. The collection method according to claim 1, wherein the period is 5 minutes to 12 hours. 4. The recovery method according to claim 1, wherein the period is adjusted according to the rate of heat transfer reduction. 5. The recovery method according to claim 1, wherein the above operation is performed after the supply flow rate is once set to zero.