JPS6345726B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyolefin, and more particularly, to a method for producing polyolefin by polymerizing olefin in an inert hydrocarbon solvent under pressure. Using an inert hydrocarbon solvent such as hexane,
In the method of producing polyolefin by polymerizing olefin under pressure, the polymerization reaction product in the form of a slurry obtained by polymerization is sent from the polymerization tank to a low-pressure degassing tank, where unreacted olefin and
H ₂ can be degassed under reduced pressure, separated into the produced polymer solvent slurry, unreacted gas, and a gas phase component mainly composed of H ₂ , and the separated gas phase component can be recovered and recycled to the polymerization reactor. This has been done for a long time. The separated gas phase components are pressurized again using a compressor, cooled and liquefied if necessary, and purified if necessary, and then reused for polymerization. In this method, the gas phase components recovered from the degassing tank include unreacted olefin, hydrogen which is a polymerization reaction aid, paraffin which is a hydrogenation product of olefin, as well as low polymerization degree polyolefin, catalyst,
Contains finely divided solid components such as finely divided polyolefin. This fine particulate solid component adheres to the piping leading to the compressor, equipment, and inside the compressor, and adversely affects the operation of the rotating shaft, suction port, discharge port, valve, etc., and impedes stable operation. In order to avoid these problems, conventional techniques have been used to (1) increase the separation performance of gas and solids in the degassing tank, for example by increasing the tank diameter, reducing the linear velocity for extracting gas phase components, and increasing the separation length; By increasing , the amount of entrained solid components is reduced. Alternatively, (2) a method such as installing a filter or demister made of several layers of wire mesh upstream of the compressor has been used. However, in the method (1) above, the capacity of the degassing tank becomes extremely large, which is an industrial problem, and in the method (2) above, the demister and filter installed upstream of the compressor cannot be monitored. Clogging and adhesion occur in a short period of time, requiring demister replacement and filter switching extremely frequently, resulting in a significant drop in productivity and economic efficiency. As a result of extensive research, the inventors of the present invention found that by treating the gas phase components degassed from the slurry using a specific method before sending them to the compressor, the fine powder solid components entrained in the gas phase components can be removed with extremely high efficiency. The present invention was achieved by discovering that it can be removed by using a method that enables stable operation over a long period of time. That is, the present invention polymerizes olefins in an inert hydrocarbon medium under pressure, depressurizes the resulting slurry containing unreacted olefins, degasses and separates the gas phase containing unreacted olefins, and removes the separated gas phase. In a method for producing polyolefin in which the slurry is pressurized again and, if necessary, purified before or after pressurization and then reused for polymerization, the gas phase that has been degassed and separated from the slurry is converted into a liquid before being pressurized again. The present invention relates to a method for producing a polyolefin, which comprises washing with an inert hydrocarbon. Next, the present invention will be explained in more detail. The method of the present invention involves the production of polyolefins using conventionally known inert hydrocarbon solvents such as hexane, heptane, cyclohexane, benzene, toluene, etc., i.e., the production of homopolymers of olefins such as ethylene and propylene, or the production of random polymers. It is applied to a method for producing copolymers such as block copolymers. The catalyst used in the polymerization step of the method of the present invention is not particularly limited as long as it is a conventionally known catalyst for polymerizing olefins, such as a so-called Ziegler catalyst consisting of a combination of a transition metal compound and an organometallic compound,
Catalysts supported on silica, alumina, magnesium compounds, and combinations of these with organometallic compounds are used. Furthermore, the present invention also includes the use of a third component and a fourth component for adjusting crystallinity and molecular weight distribution. The polymerization may be carried out either continuously or batchwise, and the reaction conditions are such that the polymer can be dispersed in the form of particles. Usually 1 to 100 atmospheres, preferably 5 to 30 atmospheres,
The polymerization temperature ranges from room temperature to 100°C. Furthermore, as a method for adjusting the molecular weight of the produced polymer, it is also useful to add an appropriate amount of a known molecular weight regulator such as hydrogen or diethylzinc to the polymerization reaction system. The olefin polymer mixture containing unreacted olefin produced by polymerization is extracted from the polymerization tank in a slurry state and introduced into a degassing tank. The deaeration tank is
Lower pressure in polymerization reactor, usually 0-4Kg/cm ² G
As a result, the gas phase containing unreacted olefin is degassed from the slurry and separated from the polyolefin slurry. The degassing tank may be heated from the outside with a heating medium as the case may be, but heating is usually not necessary. The polyolefin solvent slurry separated in this degassing tank is extracted from the extraction pipe installed in the liquid phase section and sent to the post-treatment system, where the polymer and solvent are separated using a known method. be converted into If necessary, catalyst components remaining in the polymer or solvent are removed by a known method. On the other hand, the gas phase generated in the degassing tank is extracted from an extraction pipe installed in the gas phase section of the tank. This gas phase contains gaseous components such as unreacted olefin and its low polymer, hydrogen as a molecular weight regulator, paraffin (e.g. ethane, propane, butane) as a hydrogenation product of olefin, and a finely powdered catalyst. and polyolefins. In the method of the present invention, the gas phase is introduced into a washing device before the compression step, where it is washed with a separately introduced inert hydrocarbon solvent to remove fine powder and solid components entrained in the gas. . A general gas-liquid contact device can be used as the cleaning device, but considering the efficiency of collecting fine powder solid components, ease of processing the collected fine powder solid components, and cost of the device, , cyclone scrubbers are particularly suitable. The structure of the cyclone scrubber is such that cleaning liquid is blown tangentially into the top of a standard cyclone. It is also effective to spray a cleaning solvent in advance and introduce the slurry or wet fine powder into the above-mentioned type of cyclone scrubber. Since the purpose of cleaning is to obtain clean unreacted olefins and hydrogen, condensation of unreacted olefins and entrainment of the cleaning liquid into the gas phase should be avoided as much as possible. The temperature of the solvent is preferably such that unreacted olefin does not substantially condense under the pressure. The inert hydrocarbon used as the cleaning solvent may be one that is liquid under the cleaning conditions and has a suitable clay to allow spraying. Specifically, for example, aliphatic hydrocarbons such as pentane, hexane, heptane, and octane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, benzene, toluene,
Examples include aromatic hydrocarbons such as xylene. The washing solvent is preferably the same as that used as a medium for the polymerization of polyolefin in the previous step. It is advantageous to use the same solvent as that used in the polymerization reaction because there is no need to add special equipment for subsequent recovery and purification. Although the quality of the solvent does not need to be particularly high purity. When the washed solvent is reused together with the polyolefin inslurry, since it comes into contact with the product resin, it is necessary to remove impurities that may contaminate the product. The amount of solvent used depends on the fine powder content in the gas to be cleaned,
It depends on the type of cleaning equipment used, so it cannot be said with certainty, but when using a cyclone scrubber, the amount of liquid per 1 ^m3 of flow rate of gas to be treated is 0.5 to 1.5.
That's about it. The purified gas phase flow, which is mainly composed of unreacted olefin and hydrogen, is then sent to a compressor.
After pressurizing to 16 to 17 Kg/cm ² G, if necessary, the mixture is cooled to a temperature of 30 to 40°C using a condenser to liquefy unreacted olefin. On the other hand, the solvent that collects the fine powder solids discharged from the cleaning equipment may be subjected to appropriate treatment outside the process, but is usually combined with the polyolefin inslurry from the degassing tank and treated in a subsequent process. do it. Examples will now be given, but the present invention is not limited to these examples. Example 1 Continuous polymerization of propylene was carried out by the process shown in FIG. Polymerization was carried out by supplying a titanium trichloride-containing catalyst as a main catalyst, diethylaluminum monochloride as a co-catalyst, and hydrogen as a molecular weight regulator to a tank-type polymerization reactor 1 equipped with a stirrer, and reacting in n-hexane at 55 to 65°C under pressure. This was carried out continuously by supplying propylene at a constant rate at 10 to 15 Kg/cm ² G. The produced slurry containing the polymer was continuously discharged from line 2 through a flash valve 2' to a degassing tank 3 having a volume of 15 m ³ . The inside of the degassing tank was maintained at approximately 0.2 Kg/cm ² G by suctioning through a gas extraction pipe 6 communicating with the inlet of the compressor 5 via a cyclone scrubber 4 . The temperature of the degassing tank was not particularly heated or cooled, and was maintained at the equilibrium temperature of 20 to 30°C after flashing. 30 to 35% by weight from the extraction pipe 7 at the bottom of the degassing tank
A polypropylene-normal hexane slurry was extracted at a polymer concentration of . The gas led out through the gas extraction pipe 6 is
It is introduced into the cyclone scrubber 4 with a volume of 220 at a speed of 1500 to 2500 m ³ /Hr, where normal hexane is introduced into the cyclone scrubber 4 through the pipe 12 at a gas ratio of 1.3/m ³ and in a countercurrent state at about 20°C. I washed it with. The gas coming out of the gas extraction pipe 8 at the top of the cyclone scrubber is compressed by the compressor 5 to 16 to 17
After pressurizing to Kg/cm ² G, it was subjected to indirect heat exchange with cooling water in a condenser 9, liquefied, and placed in a storage tank 10. The liquefied propylene from which non-condensable components, mainly hydrogen, were separated was reused as a raw material for polymerization reactions. The normal hexane liquid extracted from the lower pipe 11 of the cyclone scrubber 4 is combined with the polypropylene-normal hexane slurry and sent to the subsequent post-treatment process. The gas compositions at the inlet and gas outlet of the cyclone scrubber are as shown in the table below, and when the suction tank 14, compressor 5, and condenser 9 were disassembled and inspected after one year of operation, no solid deposits were found. or,
The frequency of switching filters 15 and 16 is also 1 time.
It was a year ago.

[Table] Example 2 When introducing the cleaning liquid in the previous figure 1,
Cleaning was performed by spraying a cleaning liquid from the pipe 13 in front of the cyclone scrubber 4. The operation was carried out in the same manner as in Example 1, except that the place where the cleaning liquid normal hexane was introduced was changed to the above-mentioned location. When inspected after one year of operation, no adhesion was found on the compressor 5 or condenser 9. Comparative example 1 Next, in the previous figure 1, cyclone scrubber 4
The gas phase components were extracted and the piping 6 was directly connected to the suction tank 14 without installing a gas phase component. Other operating conditions were the same as in Example 1. The frequency of switching filters 15 and 16 is once/
Continuous operation was interrupted after about a month due to fouling and blockage in demister 17.

[Brief explanation of the drawing]

FIG. 1 is a block flow sheet showing an example of the method for producing polypropylene to which the present invention is applied, and the symbols in the figure represent the following. 1... Polymerization reactor, 2... Slurry extraction line, 3
... Deaeration tank, 4... Cyclone scrubber, 5... Compressor, 6... Gas phase extraction line, 7... Polymer extraction line, 8... Gas phase extraction line, 9... Condenser, 10... Storage tank, 11... Cyclone Scrubber return line, 1
2, 13...Solvent supply line, 14...Suction tank, 15
...Filter, 16...Filter.

Claims (1)

[Claims] 1. Polymerizing olefins in an inert hydrocarbon medium under pressure, reducing the pressure of the resulting slurry containing unreacted olefins to degas and separate the gas phase containing unreacted olefins, and pressurizing the separated gas phase again; In a method for producing polyolefin in which purification treatment is performed before and/or after pressurization if necessary and then reused for polymerization, the gas phase degassed and separated from the slurry is converted into liquid using a cyclone scrubber before pressurization again. A method for producing polyolefin, which comprises washing with an inert hydrocarbon.