JPS6172007A - Continuous polymerization - Google Patents

Abstract

PURPOSE:In a polymerization system which is composed of a plurality of reactors equipped with slurry circulation lines, the slurry is transferred, at the start of polymerization, by opening and closing valves and, after desired conditions are satisfied, by controlling the degree of valve opening to stabilize the polymerization of alpha-olefin for hours. CONSTITUTION:When continuous bulk polymerization of an alpha-olefin is carried out using the monomer itself as a solvent in a polymerization system consisting of 2 or more reactors 1-3 equipped with slurry circulation lines, only the transfer of the slurry is carried out by opening or closing valves 1-3, 1-4, 2-3, 2-4, 3-3 and 3-4 from the start of the polymerization reactions till the polymerization in individual reactors are reached desired conditions. After the desired conditions are satisfied, the levels of the reaction mixture in the reactors are detected with the level detectors 1-5, 2-5, 3-5 to control the degree of valve opening whereby the transfer rate of the slurry is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a bulk polymerization method using α-olefin itself as a medium. Specifically, the present invention relates to a method for continuous polymerization of α-olefin using a polymerization machine in which two or more reactor tanks 1r (1r) are connected with each other and equipped with a slurry circulation line.

[Conventional technology]

It has been known for a long time that α-olefins are polymerized by bulk polymerization using the α-olefin itself as a liquid medium. In addition, in order to obtain many brands of polymer,
Alternatively, since it is difficult to remove polymerization heat in a large reactor, it is also known to carry out the polymerization reaction using a reactor in which two or more polymerization tanks are connected. However, when polymerizing α-olefins using 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. When increasing the amount of hydrogen, it is difficult to transfer the entire slurry unless the polymerization temperature is lowered in the latter stage. Therefore, for example, Japanese Patent Application Laid-Open No. 53-25585 discloses that the polymerization temperature is lowered in a polymerization tank after washing. I'm here. A method of transferring slurry using a slurry pump is also well known.

[Problem that the invention seeks to solve]

However, the method of transferring gold by pressure difference using a temperature difference has the problem that the polymerization temperature decreases in the subsequent tank, which reduces desolvation activity and makes it difficult to remove heat, and there is no flexibility in determining the polymerization temperature. . Further, in the latter method, although it is not necessary to significantly lower the polymerization temperature, a large back pressure increases the load on the slurry pump, and in some cases, there is a problem that it may become clogged. Furthermore, since the amount of liquid transferred depends on the difference between the increased pressure and the pressure in the next reaction tank, a slurry circulation line is installed to control the amount of slurry transferred, and the slurry is transferred by opening and closing the valve. There are several ways to do this, but valves, especially those for high pressure, often leak if they are opened and closed repeatedly over a long period of time, which is not only dangerous, but also expensive to replace.

[Means for solving problems]

- The inventors of the present invention have conducted intensive studies on methods for solving the above-mentioned problems, and have discovered that the above-mentioned problems can be solved by a specific method, and have completed the present invention. That is, the present invention is a method for continuously polymerizing α-olefins by a bulk polymerization method using α-olefin itself as a medium using a polymerization machine in which two or more reaction vessels equipped with slurry circulation lines are connected. The slurry is only transferred by opening and closing the valves from the start until the various polymerization conditions reach the desired conditions, and after the various polymerization conditions reach the desired conditions, the slurry is transferred by the valve opening degree. The present invention relates to a continuous polymerization method characterized by controlling the amount of liquid transferred.

In the present invention, the α-olefin refers to propylene, butene-11hexene-1 and mixtures thereof or mixtures with ethylene.

In the present invention, any known catalyst can be used to polymerize the α-olefin, and there are no particular limitations. A catalyst system consisting of a transition metal compound and an organometallic compound is used, and specifically, a titanium halide is used. Alternatively, those supported on carriers such as magnesium halides, phosphoric acid, and alumina are used as transition metal compounds, and are preferably used as organometallic compounds such as organoaluminum and organomagnesium.

Embodiments of the present invention will be explained in detail using the drawings.

α-olefin is polymerized by a bulk polymerization method using a polymerization machine consisting of three reactors 1, 2, and 3'i connected together. The slurry from reaction tank 3 is sent to a slurry post-treatment step via valve 3-4. Various liquid level gauges 1-1.2-1.3-
The liquid level height is detected by the controller 1-5.2-5°3-5 according to the signal.
-3.2-4° 3-3.3-4 six valves are operated to control the liquid level to be constant.

What is important in the present invention is that the liquid level is controlled by opening and closing the six valves only until the various conditions are stabilized at the desired conditions, and after the conditions are stabilized, the liquid level is controlled by the valve openings of the six valves. For this purpose, the preferred shape of the valve is one that can quantitatively transfer the slurry at a specific valve opening, such as a v & rut valve, and if necessary, a - It is also possible to prevent the slurry from collapsing by pumping the olefin or inert solvent, or by controlling the liquid level for a short time at specific time intervals by opening and closing six valves.

Control of the cylinder surface by opening and closing the six valves is performed as follows.Reaction tank 1 will be described as an example. The slurry extracted from the reaction tank 1 is pressurized by the pump 1-2, and when the valve 1-4 is closed, the valve 1-3 is opened. When the valve 1-3 is open, the cis slurry is transferred to the reaction tank 2 when the valve 1-3 is closed. By determining the time ratio between when valve 1-3 is open and when valve 1-4 is open, the approximate amount of slurry transferred to reaction tank 1 or reaction tank 2 is determined (in detail, the amount of slurry transferred to reaction tank 1 or reaction tank 2 is determined). and the pressure drop difference on the reaction tank 2 side is added). When valve 1-4 is open, valve 1-3 is closed, so there is no risk of backflow.Since the slurry pressurized by slurry pump 1-2 is transferred to reaction M2, there is a slight back pressure. Even if this occurs, liquid transfer is possible. By opening and closing the valve in small increments, even if the differential pressure between reaction tank 2 and reaction tank 1 is large, a large amount of slurry will not be transferred at once. Even if the pressure fluctuates, the liquid level can be well controlled. After each condition has stabilized to desired conditions, the amount of slurry transferred is controlled by the valve opening degree of the valve. At this time, it is preferable to set a limit value for the valve opening degree of each valve (especially on the close side) and to prevent the valve opening degree from changing beyond that limit value. This is because the slurry is filtered and clogged depending on the valve opening degree. Therefore, when it becomes necessary to change the valve opening beyond the limit value, the controller 1-5.2- is designed to automatically switch to control by opening and closing the valve.
It is preferable to set 5.3-5. Note that the broken line indicates the connection state of the control system.

An example of controlling the opening/closing of the valve and the degree of opening of the valve will be described below.

When controlling by opening and closing valves, the liquid level is detected by a liquid level gauge and compared with a preset liquid level, and if the liquid level is higher than the set value, the slurry control valve 1-3 is opened for a certain amount of time. shorten for a certain period of time. If the liquid level is still higher than the previous measurement level even after the valve 1-3 has been opened a certain number of times, the opening time of the valve 1-4 is increased for a certain period of time. Next, after a certain number of times, the level is compared with the previous measurement level, and if it is lower, the level is further compared with a set value, and the valve opening time is changed.

As a control method after various conditions are almost stabilized, upper and lower limits are first set for the valve openings of the six valves (upper limits are not necessarily required). Next, the six valves are set to preset valve opening degrees based on various pressures, the discharge pressure of the pump, and the discharge amount of the pump. Next, various liquid levels are detected and compared with set values, and if the level is higher than the set value, the valve opening degree 't of the valve on the slurry transfer side is increased by a certain value. In the same way as when draining for a certain period of time, compare the detected height of the liquid level with the set value, and if the liquid level is higher, reduce the valve opening degree of the valve on the slurry return 9 side by a certain value. The liquid level set for each time is compared with the detected liquid level, and the valve opening degree is operated based on the value.

[For production]

By carrying out all the methods of the present invention, it becomes possible to avoid excessive load on the valve, and therefore it becomes possible to stably operate the valve for a long period of time.

〔Example〕

When the control method of the present invention was applied to the gland of polypropylene bulk polymerization, no problems occurred even after 3,000 hours of continuous operation. This test was carried out a total of 5 times, but no leakage was observed from the valve.

On the other hand, when liquid transfer was performed by opening and closing the valves (6 valves were opened and closed every 2.5 minutes once), leakage occurred in one valve after about 1100 hours, so the operation was discontinued.

〔Effect of the invention〕

By carrying out the method of the present invention, it is possible to carry out extremely stable operation for a long period of time without troubles such as damage to valves, which is extremely valuable industrially.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing part of the flow of a plant for carrying out the method of the present invention. 1.2.3... Polymerization tank, l-2, 2-2, 3-2...
・Slurry pump, 1-1.2-1.3-1...Liquid level gauge, 1-3.1-4.2-3-. 2-4.3-3゜3-
4...Valve, 1-5.2-5.3-5...Controller. Procedural amendment document February 6, 1985 Manabu Shiga, Commissioner of the Patent Office1, Indication of the case Patent Application No. 1988-1940352, Title of invention Continuous superposition method 3, Relationship of the person making the amendment with the case Patent applicant name (312) Mitsui Toatsu Chemical Co., Ltd. 4, agent address 40 Toranomon, Mori Building, 5-13-1 Toranomon, Minato-ku, Tokyo Column 6 for claims and detailed description of the invention in the specification; Contents of amendment (1) The scope of claims in the specification is corrected as shown in the attached sheet. (2) Claim characterized by “only” on page 4, line 5 of the specification 1) Slurry circulation line? α-olefin itself using a polymerization machine with two or more reaction tanks connected? In the continuous polymerization of α-olefins using bulk polymerization as a medium, the slurry must be transferred only from the start of the first polymerization reaction until the polymerization conditions in the six tanks reach the desired conditions. This is done by opening and closing the valve. After the polymerization conditions of 6 tanks reach the desired conditions, 4 squares of
A continuous polymerization method in which the main feature is controlling the amount of slurry transferred at one time. 2) 6 tanks of slurry t to control the amount of slurry transferred
# of 4fF claim using Z, Section 1, method of amnesty.

Claims (1)

[Scope of Claims] 1) A method of continuously polymerizing α-olefin by a bulk polymerization method using α-olefin itself as a medium using a polymerization machine in which two or more reaction vessels equipped with a slurry circulation line are connected. From the start of the polymerization reaction until the polymerization conditions in each tank reach the desired conditions, only the slurry is transferred by opening and closing the valves, and after the polymerization conditions in each tank reach the desired conditions, the valves are opened and closed. A continuous polymerization method characterized by controlling the amount of slurry transferred by the valve opening degree. 2) The method according to claim 1, in which the amount of slurry in each tank is used as the control value for the amount of slurry transferred.