JPH0550526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a process for polymerizing propylene. More specifically, the present invention relates to a method for producing polypropylene of a constant quality with a constant production amount.

Prior Art A method for producing polypropylene by polymerizing propylene using a Ziegler-Natsuta catalyst is well known, and polypropylene has already been produced industrially on a scale of several hundred tons per day. In the production of polypropylene on an industrial scale, it is desirable to produce polypropylene of constant quality at a constant production rate, and it is difficult to remove the heat of polymerization using a large reactor. It is produced continuously using a reactor in which more than one polymerization tank is connected.

Many types of Ziegler-Natsuta catalysts are known for use in the production of polypropylene, and many types are also used in the actual industrial production of polypropylene. However, the performance of the catalyst varies considerably depending on the lot, so simply charging a fixed amount of catalyst into the reactor will cause the production volume to fluctuate. Varying amounts are used.

Problems to be Solved by the Invention However, in the above method, the production amount per catalyst varies depending on the catalyst performance, so the catalyst residue remaining in the polypropylene obtained varies, making it impossible to obtain a constant quality product. Furthermore, there was a problem in that the amount of transition metal catalyst used varied, which was expensive and required relatively complicated equipment due to the manufacturing process and charging.

An object of the present invention is to provide a method for producing polypropylene of constant quality and with a constant production amount.

Means for Solving the Problems As a result of intensive study on methods for solving the above problems, the inventors have found that the above problems can be solved by controlling the production of polypropylene in a specific manner, and have completed the present invention. That is, the present invention provides a method for continuously polymerizing propylene using a transition metal catalyst obtained by supporting titanium tetrachloride on magnesium chloride and a catalyst consisting of an organoaluminium.
Organoaluminium was added to each tank at a ratio of the amount of organoaluminum and the amount of transition metal catalyst within the range that varied the activity without changing the stereoregularity determined by polymerization experiments in which the amount of organoaluminium was varied. A polypropylene polymerization method characterized in that the amount of polypropylene produced is controlled to a desired value by varying the amount added, and when the ratio deviates from the predetermined ratio, the amount of transition metal catalyst charged is varied.

What is important in constituting the present invention is that when the quantitative ratio of organoaluminum/transition metal catalyst is changed, the activity per transition metal catalyst changes significantly, and that within a specific quantitative ratio range, the physical properties of polypropylene are significantly affected. This is based on the discovery that the stereoregularity and molecular weight distribution of the affected polypropylene remain almost unchanged.

A catalyst system that achieves the above characteristics with a wide range of organic aluminum/transition metal catalyst ratios is a catalyst consisting of a transition metal catalyst in which titanium tetrachloride is supported on magnesium chloride and an organic aluminum catalyst.
In particular, as a catalyst system in which the quantitative ratio of organoaluminum/transition metal catalyst can be varied over a wide range that can almost absorb the usual fluctuations in activity between lots,
Examples include catalyst systems that use a catalyst system consisting of a transition metal catalyst in which titanium tetrachloride is supported on magnesium chloride, an organic oxygen-containing compound, a dialkyl aluminum halide, and a trialkyl aluminum, and the ratio of the trialkyl aluminum to the transition metal catalyst is varied.

In the present invention, propylene polymerization is carried out by any of the following methods: solvent polymerization using an inert liquid medium, bulk polymerization using liquid propylene itself as a medium, and gas phase polymerization substantially free of a liquid medium. Moreover, the polymerization of propylene includes not only propylene alone but also copolymerization with ethylene, butene-1, hexene-1, etc.

In the present invention, the predetermined ratio between organoaluminium and transition metal catalyst amount is determined as follows. The relationship between the stereoregularity of polypropylene obtained by varying the amount of organoaluminum in advance is determined.

This relationship is most preferably determined for each reaction tank in an actual polymerization apparatus, but it can also be determined on a laboratory scale and applied in an actual polymerization apparatus if a certain degree of safety margin is considered. 1st
The figure shows the results of determining the above relationships in each tank during continuous polymerization in three tanks (the catalyst shown in the example was used, and only the relationship between triethylaluminum/transition metal catalyst was changed). It can be seen that by changing the quantitative ratio of organoaluminium and transition metal catalyst within the range shown in the upper part of the figure, it is possible to change the activity by about 3 times without changing the molecular weight distribution and stereoregularity. Therefore, it can be understood that the production amount can be controlled by varying within specific upper and lower limit values. It is also clear that even in multi-vessel continuous polymerization, it is possible to maintain the same activity by changing the above ratio (catalytic activity in each vessel decreases in later polymerization vessels due to the deactivation phenomenon of the catalyst itself). ).

Specific embodiments of the present invention will be described below.
That is, according to the present invention, the amount of transition metal catalyst charged in the polymerization reaction system is kept constant. It is detected that the amount of polypropylene produced from the polymerization reaction system is lower than expected (usually this can be known by detecting the amount of polypropylene produced per hour, the amount of propylene consumed, or the amount of heat of the polymerization reaction). and increasing the amount of organoaluminium charged to the polymerization reaction system. The upper limit of the increase is determined by knowing the relationship shown in Figure 1 in advance.
If the planned production volume is not achieved even at the upper limit, this can be dealt with by increasing the amount of transition metal catalyst charged. Similarly, when the planned production amount is exceeded, it is dealt with by reducing the amount of organoaluminum charged, and when the planned production amount is not achieved even at the lower limit, it is dealt with by decreasing the charging amount of transition metal catalyst. .

Effects of the present invention The yield of polypropylene per transition metal catalyst can be controlled without changing the physical properties of the polypropylene obtained by changing the quantitative ratio of organoaluminium and transition metal catalyst within a specific range. It is based on the knowledge of
Organoaluminium is relatively easy to remove as a catalyst residue, and its adverse effect on physical properties is extremely small compared to transition metal catalysts. Therefore, by polymerizing polypropylene using the method of the present invention, it is possible to achieve a constant quality with a constant production amount. It is estimated that it will be possible to provide polypropylene.

Example The present invention will be explained below with reference to Examples.

Example: A transition metal catalyst consisting of titanium tetrachloride supported on magnesium chloride (manufactured according to Example 1 of JP-A-55-102606) using 10 lots with 20 g per lot.
Propylene was polymerized using a bulk polymerization method using propylene itself as a medium using a reactor in which three autoclaves were connected (one tank was used for catalyst depletion). After deactivating the catalyst, the obtained polymer was washed with propylene in a countercurrent washing tower, and unreacted propylene was removed by evaporation to obtain polypropylene powder. For the polymerization reaction, 40 ml of methyl toluate and diethylaluminium chloride were added to 20 g of the above transition metal catalyst.
85 ml mixed with 4 ml based on transition metal catalyst
g/h into the polymerization machine in the first tank, and the polymer slurry in the first tank is continuously transferred to the second tank and then deactivated in the third tank. Triethylaluminum was charged into the first tank and the second tank, varying according to the production amount of polypropylene. Figure 2 shows the relative activity of the 10 lots of catalysts separately evaluated in batch polymerization and the first tank of triethylaluminum.
2 shows changes over time in the amount charged to the second tank and the amount of polypropylene produced. By varying the amount of triethylaluminum, the production amount of polypropylene is 40Kg/h.
(±0.7Kg/h) and stereoregularity (extraction residue after extraction with boiling n-heptane for 6 hours)
was 96.8±0.2% and MW/MN6.4±0.2.

Effects of the Invention By carrying out the method of the present invention, it is possible to produce polypropylene of stable quality at a constant production rate, which is industrially valuable.

[Brief explanation of drawings]

Figure 1 shows the relationship between the organoaluminum/transition metal catalyst quantitative ratio, the amount of polypropylene produced per unit time per transition metal catalyst, and the molecular weight distribution and stereoregularity of the resulting polypropylene. It shows the relationship between the time course of continuous polymerization, the production amount of polypropylene, the amount of triethylaluminum charged (○ first layer x second tank), and the relative activity of each corresponding lot. FIG. 3 is a flow diagram to aid understanding of the present invention.

Claims (1)

[Claims] 1 In a method of continuously polymerizing propylene using a transition metal catalyst obtained by supporting titanium tetrachloride on magnesium chloride and a catalyst consisting of an organoaluminum, it is determined by a polymerization experiment conducted in advance in which the amount of organoaluminum was varied. By varying the amount of organic aluminum added to each tank at the ratio of the amount of organic aluminum to the amount of transition metal catalyst within the range that changes the activity without changing the stereoregularity, the production amount of polypropylene can be adjusted to the desired value. 1. A method for polymerizing polypropylene, which comprises controlling the production amount of polypropylene to a desired value by varying the amount of transition metal catalyst charged when the ratio deviates from the predetermined ratio.