JPH0332562B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for gas phase polymerization of olefins. More specifically, the present invention relates to a method for continuous gas phase polymerization of olefins, which allows continuous and stable operation for a long period of time, and therefore enables the production of olefin polymers of constant quality.

In particular, the present invention relates to a method for gas phase polymerization of olefins, in which gas phase polymerization is carried out continuously while forming a fluidized bed layer under stirring conditions in a gas phase polymerization tank equipped with an agitator. ) carrying out gas phase polymerization while stirring the fluidized bed zone with the upper end of the stirring blade of the stirrer buried in the fluidized bed zone; (ii) in the fluidized bed zone and the stirring; A pressure detection end in the fluidized bed area provided at a position exceeding the upper end of the blade height, and a pressure detection end in the upper space area provided in the upper space area above the fluidized bed area,
Detecting a pressure difference between the two zones, and extracting the olefin polymer from the fluidized bed zone in response to the detected pressure difference such that the height of the fluidized bed zone is maintained substantially constant. This invention relates to a method for continuous gas phase polymerization of olefins.

In a gas phase polymerization tank equipped with a stirrer, olefins are continuously polymerized in gas phase while forming a fluidized bed by blowing gaseous olefin into a layer of olefin polymer particles containing a catalyst. It is known to do so.

At this time, in order to prevent entrainment of fine olefin polymer particles and catalyst particles, the gas flow rate is reduced, and instead, the fluidized bed is stirred by mechanical stirring to obtain a good mixing state. Attempts are also known. However, despite these attempts, it is difficult to make the mixing state uniform in the fluidized bed layer, so lumps of olefin polymer are generated and block the gas inlet and olefin polymer outlet. This often makes long-term operation impossible. In addition, when performing such gas phase polymerization continuously, it is important to extract the olefin polymer while maintaining the height of the fluidized bed zone as constant as possible to obtain a homogeneous polymer and to ensure stable operation. It is necessary for

To this end, it is conceivable to measure the height of the fluidized bed zone and adjust the opening and closing of the polymer discharge valve to keep it constant. Based on this idea, the present inventors provided pressure detection ends at two locations, upper and lower, in the gas phase polymerization tank as a method for measuring the height of the fluidized bed zone, and one of the pressure detection ends was located at the top and bottom of the fluidized bed zone. We tried a method of determining the height of the fluidized bed section by installing one in the upper space section above the fluidized bed section and the other at the upper end of the fluidized bed section or within the fluidized bed section and measuring the differential pressure between the two.

As a result, when the other pressure detection end is provided at the upper end of the fluidized bed area, when the upper end of the fluidized bed area reaches the pressure detection end, a pressure difference with the upper space area is generated. This is detected, and the polymer discharge valve is opened to extract the polymer according to the detected differential pressure, and in response to this extraction, the height of the fluidized bed area is lowered to be lower than the other pressure sensing end. When the level becomes low, the pressure difference with the headspace area disappears, so a control system must be adopted that detects this and closes the polymer discharge valve. , where such control as would allow fine adjustment of the height of the fluidized bed zone is not operationally possible;
It was found that the fluctuation in the height of the fluidized bed zone was quite large, making it difficult to operate stably.

On the other hand, if the other pressure detection end is installed in the fluidized bed area, the pressure may not be detected accurately because the detection end is affected by the stirrer depending on the installation position. It has been found that it is difficult to maintain a constant height of the fluidized bed zone. Furthermore, it has been found that there is a problem in that the detection end is likely to become clogged, even making measurement impossible. There is no risk of this if the measurement is carried out in an area where the agitation is insufficient in the fluidized bed area, but if agitation conditions that cause such a condition are adopted, the formation of a uniform fluidized bed will be inhibited. It was found that there was a problem that stable polymerization did not occur and bulk polymers were produced.

However, as a result of further consideration, the above (i) and
By adopting the above-mentioned method of detecting the differential pressure under conditions that satisfy (ii), it is possible to control the height of the fluidized bed area to be almost constant, and to achieve good mixing in the fluidized bed area. It was discovered that stable polymerization was possible, and troubles such as the formation of bulk polymers and the adhesion of polymers to walls could be prevented. It is therefore an object of the present invention to provide an improved continuous gas phase polymerization process for olefins.

In the olefin polymerization of the present invention, in a steady state, a catalyst is continuously supplied under stirring conditions to a fluidized bed section consisting of an olefin polymer and a catalyst, and a gaseous olefin is transferred to a lower part of the fluidized bed section. By blowing into the solution, a fluid state is maintained and polymerization is carried out. Inside the fluidized bed area,
Stirring is carried out using a stirrer, preferably an anchor-type stirrer, thereby making it possible to obtain a good mixing state even in the lateral direction.

The lower end (bottom) of the fluidized bed section is preferably a perforated plate to aid in uniform dispersion of the gaseous olefin and to prevent falling of polymer particles, etc. Hydrogen can be used for molecular weight control purposes and may be fed from the lower end of the fluidized bed section along with the gaseous olefin, or directly into the fluidized bed section.

The fluidized bed section of the polymerization reactor preferably has a truncated conical or cylindrical shape. The stirrer used in the present invention, preferably a squid-type stirrer, has stirring blades rotating close to the bottom (usually made of a perforated plate) and side wall of the fluidized bed in the shape of a truncated cone, cylinder, etc. It has a structure in which it has a plurality of stirring blades that extend from the rotating shaft along the bottom of the fluidized bed area to the vicinity of the side wall, and further rise and extend from there along the side wall. It is normal for there to be. The heights of the plurality of stirring blades do not necessarily have to be the same. The Ikari type stirrer may also be provided with auxiliary stirring blades or may have other modified designs as long as it has the basic structure as described above.

During the polymerization of olefins, the height of the fluidized bed zone is preferably 1.02 to 1.4 times, more preferably 1.02 to 1.4 times the height of the stirring blades of the stirrer to the upper end.
The olefin polymer is preferably withdrawn continuously or intermittently so that the height of the fluidized bed zone is maintained at 1.02 to 1.2 times, and preferably, the height of the fluidized bed zone is kept almost constant with as little variation as possible. The height to the upper end of the stirring blade of the stirrer is the distance from the bottom of the fluidized bed zone to the upper end of the stirring blade, and when the stirrer has multiple stirring blades and their heights are different. is based on the highest standard.

In the present invention, the stirring blades of the stirrer are operated so as to be buried in the fluidized bed zone.
If a part of the upper part of the stirring blade is exposed from the fluidized bed zone and extends into the head space area, the olefin polymer will adhere or form agglomerates in that part, which will impede stable operation. In addition, if the height of the fluidized bed zone is maintained higher than the above-mentioned preferred range, mixing of the entire fluidized bed zone may become insufficient, which may cause wall adhesion. Good. By using an agitation type stirrer and adjusting the height of the fluidized bed zone to an appropriate position, preferably within the above range, it is possible to prevent the polymer from adhering to the wall or clumping, and to ensure stable operation. It can be performed.

Furthermore, such a configuration also makes it possible to accurately measure the height of the fluidized bed zone using the differential pressure method, and therefore, the height of the fluidized bed zone is kept approximately constant. Automatic control is possible by instructing the olefin polymer extraction valve to open and close depending on the differential pressure. That is, it is possible to measure the height of the fluidized bed by measuring the differential pressure between the fluidized bed area and the upper space area. However, the pressure sensing end in the fluidized bed zone is generally prone to clogging and is susceptible to the effects of agitators.
However, as mentioned above, the height of the fluidized bed zone is preferably maintained at about 1.02 to 1.4 times the height of the stirring blade up to the upper end, and the height of the stirring blade is maintained within the fluidized bed zone and at the height of the stirring blade. If the pressure detection end in the fluidized bed area is installed at a position beyond the upper end, there will be no clogging.
Moreover, it is not affected by the stirrer, so accurate measurements can be carried out over a long period of time. As a result, the fluidized bed area pressure detection end and the upper space area pressure detection end detect the pressure difference between the two areas, and the height of the fluidized bed area is approximately adjusted according to the detected pressure difference. It is possible to draw out the olefin polymer in a constant manner, and continuous operation for a long period of time can be carried out automatically. The position of the pressure detection end on the fluidized bed side is preferably 1.05 to 1.15 times the height of the stirring blade to the upper end.

In the present invention, another pressure detection end is provided slightly above the pressure detection end in the fluidized bed zone, and the pressure difference between this end and the pressure detection end at the upper part of the fluidized bed is measured, and the height of the fluidized bed zone is measured. A mode in which the upper limit is controlled by this differential pressure may be employed in combination with the above-described control.

Olefin polymerization in the present invention includes not only homopolymerization of olefins, but also copolymerization of olefins, copolymerization of olefins and dienes, and the like. Examples of olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene,
Examples include 1-decene. It is particularly suitable for producing crystalline polymers mainly composed of ethylene or propylene, for example containing 90 mol% or more of these monomers.

As the polymerization catalyst, various catalyst systems such as Ziegler type catalyst and Phillips type catalyst can be used. For example, compounds such as titanium, vanadium, chromium, zirconium, etc. can be used as catalyst components. In particular, it is preferable to use a titanium catalyst component supported on a magnesium compound and an organoaluminum compound catalyst component because the catalyst activity is high. These catalyst systems are already widely known. In the polymerization, hydrogen, electron donors, halogen compounds, and other various additives can be used for the purpose of controlling molecular weight, molecular weight distribution, stereoregularity, and the like. These catalyst components and additives can be supplied to any location in the polymerization vessel. In the polymerization, easily volatile inert hydrocarbons may also be present for the purpose of heat removal.
These serve the purpose of heat removal by being vaporized in the polymerization vessel.

The polymerization temperature of olefin varies depending on the type of olefin, but generally a temperature range of about 30°C to about 90°C is adopted. Further, the reaction pressure may be any pressure as long as it is lower than the pressure at which the olefin is liquefied, and is, for example, about 2 to about 30 kg/cm ² ·G.

The olefin is applied from the bottom of the fluidized bed zone at a linear velocity of 1 to 60 cm/sec, particularly about 3 to about 40 cm/sec.
It is preferable to blow in at a rate of cm/sec. In order to remove the polymerization heat, liquid olefin may be supplied to the polymerization vessel. When liquid olefin is supplied, it is preferably supplied above the fluidized bed.

The olefin polymer is removed from the side of the fluidized bed area.
The fluidized bed is extracted continuously or intermittently so that the height of the fluidized bed remains constant. By employing such a method, continuous polymerization can be carried out for a long period of time.

One embodiment of the invention is shown in FIG. After prepolymerizing the olefin using a titanium catalyst component supported on a magnesium compound and an organoaluminum compound component in a prepolymerization tank 1, it is continuously supplied to a fluidized bed zone 3 of a gas phase polymerization tank via a pipe 11. . Additional organoaluminum compound is fed via line 12 to the fluidized bed section 3 of the gas phase polymerization vessel. The fluidized bed zone 3, which is the reaction bed of the gas-phase polymerization tank, is stirred by an agitator type stirrer 4. The gaseous olefin that has not been condensed in the condenser 6 is supplied to the lower part of the polymerization tank through a pipe 13 or through a new pipe 14, and enters the fluidized bed zone 3 through the perforated plate 5, where it is reacted. Used to fluidize the bed and for polymerization. Hydrogen used for molecular weight adjustment is supplied to the polymerization tank through pipe 15. Unreacted olefin discharged from the polymerization tank passes through a pipe 16 and is condensed in a condenser 6, passes through a drum 7 through a pipe 17, and is sprayed from a spraying section 18 onto the reaction bed.

The height of the fluidized bed area 3 is the same as that of the low pressure side line 20 having a detection end in the upper space area 2 and the fluidized bed area 3.
The pressure difference in the high-pressure side line 21, which has a detection end in the middle and beyond the upper end of the stirring blade height (h ₁ ), is measured with a level meter 23, and the height (h ₂ ) of the fluidized bed zone is kept constant. The polymer is extracted from the pipe 19 by instructing the level control valve 24 to open and close. In order to prevent clogging of the high-pressure side line 21, it is preferable to flow purge gas through the pipe 22.

Example 1 <Preparation of titanium catalyst component> 30 g of commercially available anhydrous magnesium chloride, 7.5 ml of ethyl benzoate and methylpolysiloxane (viscosity
(20c.s. (25°C)) was brought into contact for 40 hours using a vibrating pole mill in a nitrogen atmosphere. Obtained solid treated product 20
g was suspended in 200 ml of TiCl ₄ and contacted at 80° C. for 2 hours with stirring. After the reaction was completed, the supernatant was washed with purified hexane by decantation. This operation was repeated until no chlorine was detected in the supernatant hexane. The obtained titanium catalyst component contained 1.9 wt% titanium and 65 wt% chlorine in terms of atoms. By repeating the above operation several times, the following polymerization was carried out.

<Prepolymerization treatment> The titanium catalyst component was added in hexane at 1.5 mmol/
, triethylaluminum (hereinafter abbreviated as TEA)
6 mmol/, methyl p-toluate (MPT)
2 mmol/propylene was added at twice the weight of the titanium catalyst component.

<Gas phase polymerization of polypropylene> Polymerization was carried out according to the flow diagram shown in FIG. 1 using the catalyst prepolymerized as described above.

The inner diameter of the gas phase polymerization tank is 300 mm, and the Ikari type stirrer 4
The height (h ₁ ) of the stirring blade to the upper end of the perforated plate 5
450mm from the high pressure side line 21 is SUS with an inner diameter of 2mm
The pressure detection end in the fluidized bed section is made of
It was inserted 150 mm from the inner wall of the polymerization tank and 30 mm above the top of the stirring blade.

While rotating the Ikari type stirrer at 200 rpm,
The prepolymerized titanium catalyst component
1mmol/hr (titanium atom equivalent), TEA50mmol/
hr, MPT 12 mmol/hr, propylene gas (including circulating gas) in the polymerization tank at a rate of 4 cm/sec,
In addition, propylene liquid was sprayed at the spraying section 18 at a rate of 45 kg/hr.
Sprayed at a polymerization temperature of 70℃ and a polymerization pressure of 18Kg/cm ² G.
Continuous polymerization of propylene was carried out under the following conditions. Further, the polymer was extracted from the pipe 19 at a rate of 10 kg/hr in accordance with the instructions of the level meter so that the height (h ₂ ) of the fluidized bed zone was 490 mm above the perforated plate. In order to prevent clogging of the high-pressure side line, propylene gas was supplied from the pipe 22 at a rate of 100 N/hr.

Polypropylene having an MI of 9.1 and an n-heptane insoluble content of 93.3% by weight could be produced stably for a long period of time.

Comparative Example When the detection end of the high pressure side line 21 was set at the height of the stirring blade and 400 mm below the top end of the stirrer, it was difficult to detect the level and it was not possible to detect an increase or decrease in the level.

[Brief explanation of the drawing]

FIG. 1 of the accompanying drawings is a detailed diagram of an apparatus showing one embodiment of carrying out the method of the present invention.

Claims (1)

[Claims] 1. In a method for gas phase polymerization of olefins, in which gas phase polymerization is carried out continuously while forming a fluidized bed layer under stirring conditions in a gas phase polymerization tank equipped with an agitator, ( i) carrying out the gas phase polymerization while stirring the fluidized bed zone with the upper end of the stirring blade of the stirrer buried in the fluidized bed zone; (ii) performing the gas phase polymerization in the fluidized bed zone; A fluidized bed zone pressure detection end provided at a position exceeding the upper end of the stirring blade height, and an upper space region pressure detection end provided in an upper space region above the fluidized bed bed region,
Detecting a pressure difference between the two zones, and extracting the olefin polymer from the fluidized bed zone in response to the detected pressure difference such that the height of the fluidized bed zone is maintained substantially constant. Continuous gas phase polymerization method for olefins. 2. The method according to claim 1, wherein the height of the fluidized bed zone is within a range of 1.02 to 1.4 times the height of the stirring blade to the upper end. 3. The method according to claim 1 or 2, wherein the gas flow rate in the fluidized bed layer is 1 to 60 cm/sec.