JPH0730130B2 - Continuous polymerization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bulk polymerization method using α-olefin itself as a medium. Specifically, it relates to a continuous polymerization method of α-olefin using a polymerization machine in which two or more reaction tanks provided with a slurry circulation line are connected.

[Conventional technology]

It has long been known to polymerize α-olefins by bulk polymerization using α-olefin itself as a liquid medium. . It is also known to carry out the polymerization reaction using a reactor in which two or more polymerization tanks are connected, because it is difficult to remove the heat of polymerization with a large-scale reactor in order to obtain many brands of polymers. ing. However, when polymerizing an α-olefin by the bulk polymerization method, the pressure in the reaction tank is determined by the temperature, and hydrogen is introduced to control the molecular weight of the polypropylene obtained, and in the polymerization tank of a later tank. When the amount of hydrogen is increased, it is difficult to transfer the slurry unless the polymerization temperature is lowered in the latter stage. Therefore, for example, Japanese Patent Publication No. 53-25585 shows that the polymerization pressure is lowered in a later polymerization tank. Further, a method of transferring a slurry by using a slurry pump is also well known.

[Problems to be solved by the invention]

However, in the method of transferring a liquid by making a pressure difference by a temperature difference, the polymerization temperature is lowered in the subsequent tank, so that there is a problem that the catalyst activity is lowered and the heat removal becomes difficult, and there is no degree of freedom regarding the polymerization temperature. In the latter method, the polymerization temperature does not have to be greatly lowered, but there is a problem that a large back pressure increases the load on the slurry pump and in some cases blocks it. Furthermore, the point that the transfer amount depends on the difference between the pressure boosted and the pressure in the next reaction tank does not change, so a slurry circulation line is provided to control the transfer amount of the slurry, and the slurry is transferred by opening / closing the valve. I think there is a way to
In particular, the one for high pressure often causes a leak when the opening / closing operation is repeated for a long time, which is dangerous and the cost required for replacement is also large.

[Means for solving problems]

As a result of earnest studies on a method for solving the above problems, the present inventors have found that the above problems can be solved by a specific method, and completed the present invention.

That is, the continuous polymerization method of the present invention uses a polymerization machine in which two or more reaction tanks provided with a slurry circulation line are connected to form α-
In a method of continuously polymerizing α-olefin by a bulk polymerization method using olefin itself as a medium, at the start of the polymerization reaction or the concentration and reaction ratio of catalyst components in each reaction tank, monomer concentration, polymerization temperature, residence time, slurry Only when the concentration is changed significantly, the height of the liquid surface in each reaction tank is detected to control the amount of slurry transfer by opening and closing the valve, and the concentration and reaction ratio of the catalyst component in each reaction tank, After the monomer concentration, polymerization temperature, residence time, and slurry concentration have reached the desired conditions, detect the liquid level in each reaction tank and control the amount of slurry transfer by the valve opening of the valve. Is characterized by.

In the present invention, the α-olefin means propylene, butene-1, hexene-1 and a mixture thereof or a mixture with ethylene.

In the present invention, the catalyst used for polymerizing the α-olefin is not particularly limited, and known catalysts can be used, for example, a catalyst system composed of a transition metal compound and an organometallic compound is used. Compounds or those obtained by supporting them on a carrier such as magnesium halide, silica or alumina are used as the transition metal compound, and organoaluminum, organomagnesium and the like are preferably used as the organometallic compound.

Embodiments of the present invention will be described in detail with reference to the drawings.

Using a polymerization machine consisting of three tanks in which reaction tanks 1, 2, and 3 are connected,
-Olefins are polymerized in bulk polymerization. The slurry from the reaction tank 3 is sent to the post-treatment step of the slurry through the valve 3-4. The amount of slurry in each reaction tank is liquid level gauge 1-1, 2-1, 3-1
Is detected as the liquid level by the controller and the signal from the controller 1-5, 2-5, 3-5 causes 1-3, 1-4, 2-3, 2-4, 3-3, 3-4 Each valve is operated and controlled so that the liquid level is constant.

What is important in the present invention is that in each reaction tank only when the polymerization reaction is started or when the concentration and reaction ratio of the catalyst component in each reaction tank, the monomer concentration, the polymerization temperature, the residence time, and the slurry concentration are significantly changed. The liquid transfer amount of the slurry is detected by controlling the liquid transfer amount by opening and closing the valve, and the catalyst component concentration and reaction ratio of each reaction tank, monomer concentration, polymerization temperature, residence time, and slurry concentration are desired. After the above condition is met, the liquid transfer amount of the slurry is controlled by detecting the height of the liquid level in each reaction tank and controlling the valve opening of the valve. For this purpose, the shape of the valve is preferably a V-bolt valve or the like that can quantitatively transfer the slurry at a specific valve opening degree. It is also possible to flush the olefin or the inert solvent, or to control the liquid level for a short time at specific time intervals by opening and closing each valve to prevent the clogging of the slurry.

The liquid level is controlled by opening / closing each valve as follows. As an example, the reaction tank 1 will be described. The pressure of the slurry extracted from the reaction tank 1 is increased by the pump 1-2, and when the valve 1-4 is closed, the valve 1-3 is opened and circulated back to the reaction tank 1 to return to the valve 1-4.
When is open, the valves 1-3 are closed and the slurry is transferred to the reaction tank 2. By determining the time ratio when the valve 1-3 is opened and when the valve 1-4 is opened, the approximate amount of the slurry transferred from the reaction tank 1 to the reaction tank 2 is determined (specifically, the reaction tank 1 side). And the pressure loss difference on the reaction tank 2 side is added). When valve 1-4 is open, valve 1-3 is closed and there is no risk of backflow.
Since the slurry whose pressure has been increased in step 3 is transferred to the reaction tank 2, it is possible to transfer it even if a slight reverse pressure is generated. By opening and closing the valve in small steps, a large amount of slurry is not transferred at one time even if the pressure difference between the reaction tank 1 and the reaction tank 2 is large. The liquid level can be well controlled even when the pressure in each reaction tank fluctuates when the component concentration and reaction ratio, the monomer concentration, the polymerization temperature, the residence time, and the slurry concentration are significantly changed. After the catalyst component concentration and reaction ratio in each reaction tank, monomer concentration, polymerization temperature, residence time, and slurry concentration have reached the desired conditions, the valve level is detected by detecting the liquid level in each reaction tank. The amount of slurry transfer is controlled by the opening. At this time, it is preferable to set an upper limit and a lower limit to the valve opening of each valve so that the valve opening is not changed below the lower limit. This is because the slurry is filtered and clogged when the valve opening is equal to or less than the solid particles in the slurry. Therefore, when it is necessary to change the valve opening beyond the lower limit, set the controllers 1-5, 2-5, 3-5 so that the control automatically switches to the control by opening and closing the valve. preferable. The broken line shows the connected state of the control system.

An example of the control of the valve opening and the valve opening of the valve will be described below.

When controlling by opening and closing the valve, the liquid level is detected by a liquid level gauge and compared with a preset liquid level.If the liquid level is higher than the set value, the opening time of the slurry modulo valve 1-3 is set. Shorten for a certain time. If the liquid level is higher than the previous measurement level even after the valves 1-3 have been opened a certain number of times, increase the opening time of the valves 1-4 by a certain amount of time. Next, similarly, after a certain number of times, a method of changing the valve opening time by comparing with the previous measurement level and further comparing with the set value if the level is low can be mentioned.

As a control method after the conditions of each tank are almost stable, first, the upper and lower limits are set for the valve opening of each valve (the upper limit is not always necessary). Next, each valve is set to a valve opening preset according to the pressure of each tank, the discharge pressure of the pump, and the discharge amount of the pump. Next, the liquid level in each tank is detected and compared with a set value. If the liquid level is higher than the set value, the valve opening of the slurry transfer side valve is increased by a certain value. Similarly, after a certain period of time, the detected height of the liquid level is compared with the set value, and if the liquid level becomes higher, the valve opening of the slurry return side valve is reduced by a certain value. Similarly, the liquid level set at regular time intervals is compared with the detected liquid level, and the valve opening is manipulated based on that value.

[Action]

By carrying out the method of the present invention, it becomes possible to avoid an excessive load on the valve, so that it becomes possible to perform stable operation for a long time.

〔Example〕

When the above-mentioned control method of the present invention was applied to a plant of a bulk polymerization method of polypropylene, no problems occurred at all even after continuous operation for 3000 hours. At this time, the operation of significantly changing the conditions of each tank (including the start of polymerization) was carried out 5 times, but no leak from the valve was observed. On the other hand, when liquid transfer was performed by opening and closing the valves (each valve repeatedly opened and closed once every 2.5 minutes), one valve leaked in about 1100 hours, so the operation was interrupted.

〔The invention's effect〕

By carrying out the method of the present invention, extremely stable operation can be performed for a long time without trouble such as valve damage, which is extremely valuable industrially.

[Brief description of drawings]

FIG. 1 is a flow chart showing a part of a flow of a plant for carrying out the method of the present invention. 1,2,3 …… Polymerization tank, 1-2,2-2,3-2 …… Slurry pump, 1-
1,2-1,3-1 …… level gauge, 1-3,1-4,2-3,2-4,3-3,3-4 ……
Valves, 1-5,2-5,3-5 ... Controller.

Continuation of the front page (56) References Japanese Patent Publication Sho 53-25585 (JP, B2) Japanese Patent Publication Sho 59-40841 (JP, B2)

Claims (1)

[Claims] 1. A reaction vessel provided with a slurry circulation line.
In a method of continuously polymerizing α-olefin by a bulk polymerization method using α-olefin itself as a medium by using a polymerization machine connected to more than one tank, the concentration and reaction ratio of the catalyst component at the start of the polymerization reaction or in each reaction tank Only when the monomer concentration, polymerization temperature, residence time, and slurry concentration are significantly changed,
The height of the liquid surface in each reaction tank is detected to control the amount of slurry transferred by opening and closing the valve, and the concentration and reaction ratio of the catalyst component in each reaction tank, the monomer concentration, the polymerization temperature, the residence time, A continuous polymerization method characterized in that after the slurry concentration reaches a desired condition, the liquid level in each reaction vessel is detected and the amount of slurry transferred is controlled by the valve opening of the valve.