JPS6024804B2 - Recovery method of atactic polymer - Google Patents

Description

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

The present invention relates to a method for recovering a polymer (hereinafter abbreviated as atactic polymer) dissolved in liquefied propylene produced as a by-product during polymerization. The present invention is a method of heating an atactic polymer dissolved in liquefied propylene under a pressure of 13 to 40 k9/gauge to vaporize the propylene, separating the atactic polymer and propylene, and recovering the atactic polymer in a molten state. discovered a method of mixing a small amount of solvent with liquefied propylene in order to prevent a decrease in the heat transfer coefficient of the evaporator. The simplest method for recovering atactic polymers is to reduce the pressure of liquefied propylene in which atactic polymers have been 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, but 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 costs equipment and power. Both are disadvantageous.

Further, Japanese Patent Publication No. 47-42379 discloses 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 an aged or foam-type separation tray is used, fine particles of the ysotactic 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. Furthermore, we discovered in Japanese Patent Publication No. 52-Gibu No. 1 that an atactic polymer dissolved in liquefied propylene is heated under a pressure of 13 to 40 k9/young gauge pressure to vaporize the propylene, and the atactic polymer is kept in a molten state. This is a method for recovering atactic polymers, which is characterized by simple equipment and is advantageous in terms of power. The contamination of the heat transfer surface cannot be completely resolved because the heat transfer coefficient may be reduced due to the adhesion of Qian Cheng or a portion of the 6-poison pipe may be blocked.

For this purpose, it is necessary to install two evaporators in parallel and switch between them when dirt occurs to wash or clean the evaporators, or to suspend operation for a moment to wash or clean the evaporators. .

In addition, during operation,
We found that methods such as adopting a relatively low temperature of ~120 qo, and applying pulse-like fluctuations in the amount of liquefied propylene supplied to the evaporator are effective in preventing contamination of the evaporator surface. Again, no complete solution was reached.

The present invention is based on the discovery that a method of removing deposits on a heat transfer surface by mixing a small amount of a solvent with liquefied propylene is effective in preventing staining of the heat transfer surface. That is, in the present invention, an atactic polymer dissolved in liquefied propylene is heated to an evaporation temperature of 45 to 90° C. under a pressure of 13 to 40 k9/distance gauge pressure to vaporize the propylene, and then propylene and the atactic polymer are heated in a molten state. This is a method for recovering atactic polymers, characterized in that a solvent is supplied upstream of an evaporator at a ratio of 1 to 2 weight percent relative to liquefied propylene.

As the solvent, hydrocarbons having 4 or more carbon atoms, alcohol,
One or a mixture of two or more of alkylene oxides and the like is effective.

Hydrocarbons having 4 or more carbon atoms include saturated and unsaturated aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons, and specifically include butane, bentane, hexane, hebutane, 1-butene, cyclohexane, and naphthene. , benzene, toluene, and xylene.

The alcohol has 1 to 8 carbon atoms, specifically methanol, ethanol, isobutanol, and 2-ethylhexanol.

As the alkylene oxide, ethylene oxide, propylene oxaside, etc. are used.

In addition, hydrocarbons with a carbon number of 4 or more used as catalyst carriers used in the polymerization process, as well as deactivators, catalyst decomposers, neutralizing agents, etc. used in the polymer washing process, are recovered and recycled for use. is the most advantageous.

In practice, the amount of solvent in the polypropylene manufacturing process is 1 to 2 weight percent based on liquefied propylene.
Preferably it is 2 to 5 weight percent.

With this method, contamination on the heat transfer surface can be minimized and the heat transfer coefficient can be maintained at a high value at all times.

The present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a flow sheet of an exemplary apparatus used to practice the present invention.

The polymerization step indicates the final step of polymerizing or copolymerizing propylene.

For polymerization, one or several polymerization vessels are used.

In the polymerization step, an isotactic polymer that is insoluble in liquefied propylene and an atactic polymer that is soluble in liquefied propylene are produced.

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,
A method in which the top liquid is taken out, fresh liquefied propylene is added from the propylene introduction line, and the concentration and sedimentation is repeated in a batch manner; ■ A continuous concentration and sedimentation method; and ■ A propylene introduction line that does not contain polymerization slurry and atactic polymer. 3. Method of contacting propylene 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 catalyst decomposer may be added. In either case, liquefied propylene in which an atactic polymer is dissolved is discharged from the upper part of the container 2, and liquefied propylene in which a ysotactic polymer is suspended is discharged from the lower part either batchwise or continuously.

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 fin-tactic 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 atactic polymer is
It is supplied to the evaporator 9.

In the evaporator 9, most of the liquefied propylene is evaporated.

The evaporation temperature is 45 to 90°C, and hot water is used as the heating medium.
Steam and heating oil are used, and the heating medium is 60
~160°C is preferred.

If the temperature exceeds 160 pm, the catalyst residue will decompose and hydrogen chloride will be generated, causing corrosion of the equipment, which is not preferable.

The suitable type of evaporator 9 is a double tube type (inner tube: liquefied propylene, outer tube: heating medium) or a rigid multi-tube type in order to prevent contamination of the evaporation surface and prevention of tube clogging. .

The pressure of the evaporator 9 is generally set at a pressure of 2 to 10 k9/m lower than that of the container 2 within the range of 13 to 40 k9/lump gauge pressure, but in some cases a boost pump may be installed at the outlet of the container 2. It is also possible to make it higher than the container 2.

Now, when the present invention is applied, the liquefied propylene supplied to the evaporator 9 is directly fed to the lower part of the distillation column 14, or the solvent and low molecular weight polymer recovered in the recovery tank 16 are also used to remove the catalyst. Pump 1 the mixed liquid of activator or catalyst decomposer, etc.
7 to the inlet of the vessel 2 or evaporator 9.

Solvent can also be added to the recovery tank 16 via line 18. The circulation flow rate by the pump 17 is between 1 and 2 weight percent relative to the liquefied propylene, and in practice it is 2 percent by weight.
~5 weight percent. With this method, there is almost no need to install evaporators in parallel, but if a method of periodically changing the flow rate of liquefied propylene in a pulsed manner is combined, the prevention of fouling of the evaporator surface can be further ensured.

In this case, the period may be 5 minutes to 1 hour, and the pulse may be 0
．． The flow rate is preferably 1.3 times or more, preferably twice or more, than the average flow rate for 5 to 5 seconds.

Evaporator 9 is directly connected to flash vessel 101 and separates propylene gas and atactic polymer.

In the flash vessel 10, in addition to the atactic polymer, other isotactic polymers, solvents used as catalyst carriers, catalysts such as organoaluminium and titanium compounds, low molecular weight polymers, catalyst deactivators or Decomposition 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 0.9/Funa gauge pressure and the contained propylene is separated in a separator 12.

Separation pressure is used for the atactic polymer, and the atactic polymer is pressurized with a suitable pump (for example, a gear pump or a screw pump) and sent to a combustion process or an oil conversion process. On the other hand, the propylene gas discharged from the flash container 10 excludes entrained or dissolved components with a boiling point higher than that of the propylene (for example, a part of the solvent used as the catalyst carrier, low polymers of propylene, etc.). Mud Crab Tower 1
It is easily liquefied in the condenser 15 with or without passing through the condenser 4.

In addition, the propylene discharged from the separator 6 and the separator 12 is
It is elevated by the pressure machine 13, merges with the propylene that has passed through the flash container 10, and passes through the above steps. The above are application examples of the present invention, but the present invention is not limited to these, and can be appropriately modified within the scope of the present invention.

The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto.

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

Evaporator 9 7.7W (multi-tube type) Supply amount of liquefied propylene 1800kg/day Heating steam temperature 1590 Flash container pressure 19k9/gauge pressure Flash container temperature
At the beginning of the 7th century, the heating medium, steam, was intermittently supplied by temperature control, and the jacket temperature was 10,400 degrees, but after 8 hours it was 110 degrees Celsius, and after 1 hour it was 151 degrees Celsius. showed that. 1 more
It was not possible to maintain the temperature of the flash container at 70° C. after the initial period.

Therefore, when the V supply amount of liquefied propylene was periodically increased in a pulsed manner using the control valve 7 under the following conditions, the temperature returned to 70°C, but the temperature could not be maintained at 70'0 after 4 songs.

Supply amount of liquefied propylene during pulse, approximately 3600k9/
3 second cycle during daily pulse
The pressure was reduced from the three-powder flash container 10 through the control valve 11 to the separator 12 at a pressure of 0.1 k9/equal gauge pressure, and after the propylene in the atactic polymer was evaporated, the atactic polymer was taken out.

The atactic polymer was a pale yellow, grease-like substance. Analysis of the composition of the atactic polymer revealed the following.

Atactic polymer 12k9/H Isotactic polymer 1.4k9/H Volatile substances such as solvents
3.5k9/H ash content (ash content after combustion)
0.6k9/day Intrinsic viscosity of polymer
0.03 Comparative Example 2 Liquefied propylene containing an atactic polymer was supplied to the evaporator 9, and the liquefied propylene was evaporated under the following conditions.

Evaporator 9 3.6 (double tube type, inner tube nominal diameter 11/2B) Supply amount of liquefied propylene 16
00k9/day heating steam temperature 2
10℃Flash vessel pressure 19k9/lump gauge pressureFlash vessel temperature 7pi○In the early days, heating steam was supplied intermittently by a temperature control valve, and the jacket temperature showed 106℃, but 8
After hours, it showed 190 qo.

When the evaporated propylene was collected and checked with litmus paper, it initially showed neutrality, but after 8 hours it showed slightly acidity.

The recovered atactic polymer was greenish-brown in color and had a slightly pungent odor.

Comparative Example 3 Comparative Example 2 was operated under the same conditions except for the heating steam pressure.

Heating steam temperature: 154)0.

The temperature of the jacket was initially 100 qo, but gradually rose to 154 qo and 7000 qo after the paper time.
could not be maintained. The evaporated propylene was neutral and the atactic polymer was a pale yellow grease.

Example 1 The solvent collected in the container 16 in Comparative Example 1 (
2.5w of liquefied propylene (mainly hebutane)
V was supplied to the inlet of the evaporator at a rate of t%.

The temperature of the jacket was initially 104qo, but
After childhood, I couldn't maintain 70 stars. Therefore, when the same pulse as in Comparative Example 1 was applied using the control valve 7,
The temperature of the flash vessel could be maintained at 7000C.
Example 2 The solvent collected in the container 16 in Comparative Example 2 was supplied to the evaporator 9 at a ratio of $% to liquefied propylene.

The temperature of the jacket varied between 106 and 15 ro, but the temperature could be maintained at 70°C.

The evaporated propylene was neutral and the atactic polymer was a pale yellow grease.

Example 3 The solvent collected in the container 16 in Comparative Example 3 was supplied to the evaporator 9 at a ratio of % blur to liquefied propylene.

The jacket temperature varied between 10 and 14 qo, but the temperature could be maintained at 70 qo.

Example 4 In Example 3, the solvent was added to liquefied propylene at 1.5 wt%.
reduced to the proportion of

The temperature of the flash vessel occasionally dropped to 65q0, but was able to maintain approximately 700q0.

However, when the supply amount of liquefied propylene was increased periodically in pulses using the control valve 7 under the following conditions, the amount of liquefied propylene was constantly increased to 7.
I was able to maintain 0qo. Supply amount of liquefied propylene during pulse: Approximately 3,600k9/day During pulse: 3 seconds cycle, 3 powders

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of an example of an apparatus for implementing the present invention. 1... Polymerization step, 2... Container (separator for isotactic polymer and atactic polymer), 3
...Propylene introduction line, 4...Reducing valve, 5...Heating pipe, 6...Separator,
7... Valve, 8, 8'... Hot soot inlet/outlet, 9... Evaporator, 10... Flash container, 11... Valve, 12. ...Separator, 13.
... Compressor, 14 ... Rectification column, 15 ...
... Condenser, 16 ... Recovery tank, 17.
...Pump, 18...line. Traditional drawing 1

Claims (1)

[Scope of Claims] 1. After heating an atactic polymer dissolved in liquefied propylene to an evaporation temperature of 45 to 90°C under a pressure of 13 to 40 kg/cm^2 gauge pressure to vaporize propylene, propylene and an atactic polymer are A method for recovering an atactic polymer in a molten state, the method comprising supplying a solvent upstream of an evaporator at a ratio of 1 to 20 weight percent based on liquefied propylene. 2 Hydrocarbons having 4 or more carbon atoms, alcohol,
The recovery method according to claim 1, which uses one or a mixture of two or more alkylene oxides. 3. The recovery method according to claim 1, wherein a solvent recovered from a polypropylene production process is used as the solvent.