JPH0519561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a propylene polymerization method in detail, which is a bulk polymerization method using propylene itself as a medium, continuously using a tank reactor with a constant slurry concentration and slurry liquid level. This invention relates to a method of polymerizing propylene.

Prior Art When polymerizing propylene, a bulk polymerization method using propylene itself as a medium has been known for a long time. Continuous polymerization is also well known.

When carrying out continuous polymerization using a tank reactor, generally a differential pressure level gauge is used or, if necessary, a thermometer inserted at different positions from the top is used to keep the slurry level constant under certain conditions in the gas phase. By knowing where the thermometer inserted is in contact with the slurry based on the reading from the thermometer, the polymerization reaction can be carried out by controlling the amount charged into and discharged from the tank reactor.

Problems to be Solved by the Invention However, the above method using a differential pressure type level meter requires the premise that the slurry concentration is kept constant, and the method of polymerizing at a constant propylene partial pressure using an inert hydrocarbon does not allow polymerization. In order to keep the pressure constant, it is possible to keep the amount of polymerization constant by detecting the amount of propylene charged and varying the amount of catalyst charged so that it remains constant, but in bulk polymerization method Since the medium is propylene, the above control method cannot be adopted. In addition, in the method using a thermometer, the thermometer exposed in the gas phase must be constantly flushed with a low-temperature liquid medium, but in the bulk polymerization method, the liquid medium is propylene, which often polymerizes and causes blockages. It is particularly unsuitable for long-term operation on an industrial scale.

If control is performed to simply keep the apparent liquid level detected by a differential pressure level meter constant without making corrections based on the slurry concentration, depending on the concentration, the detected liquid level may exceed the limit and become full or full. There was a possibility that the liquid level would drop to the point where it would be difficult to drain the slurry, and in some cases, the operation would have to be stopped. Furthermore, when manufacturing a block copolymer in a continuous batch combination as shown in JP-A No. 57-145133, it is difficult to quantitatively transfer the slurry to the polymerization tank that performs the subsequent batch polymerization. Since this process was not carried out, there was a problem in that the physical properties of the obtained block copolymer varied greatly.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for polymerizing propylene using a tank reactor in a bulk polymerization method using propylene itself as a liquid medium while keeping the slurry concentration and liquid level constant.

Means for Solving the Problems The present invention is a method for manufacturing polypropylene by continuously polymerizing propylene using a tank reactor using a bulk polymerization method using propylene itself as a liquid medium, which is detected by a pressure level meter. The amount of slurry withdrawn is controlled so that the amount of slurry in the tank reactor is kept constant, and the amount of propylene charged is controlled so that the slurry concentration in the tank reactor is kept constant based on the amount of polymerization detected by the calorific value. This is a propylene polymerization method characterized by controlling.

In the present invention, the polymerization of propylene refers not only to the homopolymerization of propylene, but also to the polymerization of propylene and butene-1.
Also includes copolymerization with ethylene, hexene-1, etc.

In the present invention, known catalysts can be used for polymerizing the propylene, and there are no particular limitations. In other words, it is a catalyst system consisting of a commonly used reduction metal compound and an organometallic compound. Specifically, a reduction metal is a titanium halide or its support on a carrier such as magnesium halide, silica, or alumina. It can be used as a compound, and organoaluminum, organomagnesium, etc. can be used as the organometallic compound.

Aspects of the present invention will be explained using the drawings. For simplicity, only one tank is shown in the drawing. Polymerization reaction tank 1
If it is the first tank of a reactor in which multiple tanks are connected, line 7-1 is a catalyst charging line. The following explanation will be made assuming that the polymerization tank 1 is the second tank and subsequent polymerizations. Slurry (controlled to a constant slurry concentration) from the polymerization tank in the previous stage is passed from line 7-1 to valve 6-
1 and then charged into the polymerization tank 1. Additional propylene is charged from line 7-4 via valve 6-4. Slurry from polymerization tank 1 is sent to slurry pump 4
One part is returned to the polymerization tank 1 through valve 6-2 and line 7-2, and the other part is transferred to valve 6-3 and line 7-3.
It is sent to a later stage polymerization concentration.

Next, methods for removing polymerization heat and detecting polymerization heat will be explained. The heat of polymerization is removed by a jacket 3 and a propylene vapor cooling condenser 2. The polymerization temperature is controlled by the amount of cooling water introduced into the jacket 33 and into the cooling condenser 2, and the amount of cooling water is introduced according to the internal temperature using a normal control method. At this time, from the viewpoint of controllability, for example, the amount of water introduced into the jacket 3 (or conversely, the amount of water introduced into the cooling condenser 2) is kept constant, and the amount of water introduced into the cooling condenser 2 (or On the contrary, it is preferable to control the amount of water introduced into the jacket 3 according to the internal temperature. In a system where the temperature is controlled to be constant, the heat of polymerization is given as a value correlated to the amount of heat removed by the jacket 3 and cooling condenser 2. That is, all the polymerization heat is absorbed by jacket 3.
The heat is not removed by the cooling condenser 2, but is dissipated by the polymerization tank and piping, and this heat dissipation varies greatly depending on external conditions such as outside temperature, wind, and rain, so it is not affected by external conditions as much as possible. It is advisable to keep them warm. Specifically, the amount of heat removed is expressed as the amount and temperature of the water introduced into the jacket and the amount and temperature of the water discharged, respectively, as g and e.
Detect with. Further, the amount of heat removed by the cooling condenser is detected by b and a, respectively, of the amount and temperature of water introduced into and taken out of the cooling condenser. In addition, the amount of heat removed by the cooling condenser is determined by the amount and temperature of the liquid condensed in the cooling condenser (detected by c), the amount and temperature of non-condensable gas, and the amount and temperature of gas introduced into the cooling condenser (d, respectively). detected by i).

The amount of heat removed by the cooling condenser must be corrected according to the system, since molecular weight is controlled by hydrogen in the polymerization of propylene, and other monomers with different boiling points, specific heats, and latent heats are often used. Once found, it is often possible to accurately determine it by calculating it based on the amount of water introduced into the cooling condenser and the amount of water taken out.

On the other hand, the pressure difference detected by the differential pressure type level meter 5 is given as a value correlated to the liquid level of the slurry in the polymerization tank 1. In the present invention, in order to keep the pressure difference constant, the amount of slurry withdrawn, that is, the valve 6-2, the valve 6-3
This is done by changing the valve opening. At the same time, the slurry concentration is controlled to be constant according to the polymerization amount calculated by the above method.

The simplest case is a case in which all connected polymerization tanks are operated at a constant concentration, and in this case, the amount M of propylene to be introduced per unit time is adjusted to the desired slurry depending on the amount W of polymerization per unit time. If the concentration is C, the monomer density d ₁ and the polymer density d ₂ , then M=W/C.

When polymerizing by changing the slurry concentration in each tank in multi-tank continuous polymerization, it is necessary to change the above formula using the amount and concentration of slurry charged to polymerization reaction tank 1. The amount of slurry introduced into the polymerization reaction tank 1 by performing the same control as
Desired slurry concentration C _-1 and first stage polymerization tank
The value of M is determined using the amount M _-1 of propylene charged from the polymerization tank to the preceding polymerization tank. That is, since it can be expressed as C=M _-1 ×C _-1 +W/M _-1 +M, the amount of monomer charged can be expressed as M=M _-1 ×C _-1 -M _-1 ×C+W/C.

Therefore, whether the slurry concentration in each tank is kept constant or varied, the slurry concentration can be kept constant by controlling the amount of monomer charged in accordance with the polymerization amount calculated from the polymerization heat.

Effects of the Invention By polymerizing propylene using the method of the present invention, propylene can be polymerized at a constant slurry concentration and at a constant slurry liquid level. In particular, by performing batch polymerization after the continuous polymerization section,
In the process of producing a block copolymer, it is possible to feed a slurry with a constant slurry concentration to the batch polymerization section, which makes it possible to keep the quality of the block copolymer constant, which is of high industrial value.

In other words, since the concentration is constant based on the amount of slurry received in the batch polymerization section detected by the level meter, it is possible to accurately know the amount of polymer, and the amount of polymerization to be polymerized in the batch polymerization section can be determined according to the amount of polymer. This is because it can be determined.

[Brief explanation of the drawing]

The drawing shows an example of a polymerization reaction tank for carrying out the method of the present invention.

Claims (1)

[Claims] 1. In a method for producing polypropylene by continuously polymerizing propylene using a tank reactor in a bulk polymerization method using propylene itself as a liquid medium, the tank shape detected by a pressure level meter The amount of slurry withdrawn is controlled so that the amount of slurry in the reactor remains constant, and the amount of liquid propylene charged is controlled so that the slurry concentration in the tank reactor is kept constant based on the amount of polymerization detected by the calorific value. A method for polymerizing propylene, which is characterized in that it is controlled. 2. The method according to claim 1, wherein the continuous polymerization is carried out in a reactor in which one or more tank-type reactors are connected.