Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1994-11-21
2002-01-08
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S124200, C526S128000, C526S142000, C526S127000, C526S348000, C502S103000, C502S119000, C502S125000
Reexamination Certificate
active
06337376
ABSTRACT:
This invention relates to a method for producing a polyolefin by polymerizing at least one olefin in the presence of a novel catalyst system. More particularly, this invention relates to a method whereby a polyolefin having excellent quality can be produced in a single catalyst system at high productivity and high catalytic activity irrespective of the range of density and the method of production.
It is already known to use a catalyst system comprising a transition metal compound and an organometallic compound for low-pressure polymerization of olefins, and such system is widely employed on an industrial scale.
With respect to polyolefins obtainable by the low-pressure polymerization of olefins, it is known that by controlling the density, a wide range of polyolefins can be produced ranging from those having a relatively low density and being excellent in transparency and flexibility, for example, a linear low-density polyethylene, to those having a high density and being excellent in stiffness, for example, a high-density polyethylene and an isotactic polypropylene. For catalyst systems suitable therefore, various studies have been made from various aspects in industry and universities, and many proposals have been made.
On the other hand, as the low-pressure polymerization method using the above catalyst system, there have been known a method, such as a slurry polymerization method, which employes a solvent and thus has an advantage that removal of by-products can be done by the solvent, and a gas-phase polymerization method which employs no solvent and is advantageous from the viewpoint of energy. Industrial productivity in each polymerization method depends substantially on the quality of the resulting polyolefin and the properties of polyolefin particles. More specifically, if the bulk density, average particle size, particle size distribution, proportion of fine particles, and the like of the resulting polyolefin particles are not satisfactory, process troubles are likely to result thereby reducing the productivity. Thus, many proposals have already been made for improving the particle properties with respect to catalyst systems suitable for the respective polymerization methods.
However, conventional proposals are concerned with the technology for the combination of a specific range of density and a specific polymerization method. Therefore, to satisfy the diversification of polyolefins in the market in recent years, polyolefin producers are required to appropriately select and use suitable catalyst systems depending on the respective combinations of the range of density and the polymerization method. That is, in such conventional technology, they must have various catalyst systems to satisfy the diversification of the range of density and the diversification of the polymerization method, such being disadvantageous from the industrial viewpoint.
Under such circumstances, the present inventors have made a further study to make it possible to produce polyolefins of every range of density with a single catalyst system by an optional polymerization method.
For example, in Japanese Examined Patent Publication No. 15110/1977, the present inventors have proposed a catalyst system which exhibits quite high catalytic activities and which comprises a catalyst component (A) obtained by reacting magnesium metal and a hydroxylated organic compound, or an oxygen-containing organic compound of magnesium, an oxygen-containing organic compound of a transition metal and an aluminum halide, and a catalyst component (B) of an organometallic compound. However, when such a catalyst system is applied to a slurry polymerization method or a gas phase polymerization method, polymer particles obtained are still not satisfactory in the powder properties because the average particle size is small, the particle size distribution is broad, and the proportion of fine particles contained in the polymer particles is high.
The present inventors have previously found that the particle size of a polymer can be increased by using a silicon compound in addition to the raw materials for a catalyst component (A) disclosed in Japanese Examined Patent Publication No. 15110/1977, and filed a patent application i.e. Japanese Examined Patent Publication No. 58367/1987, but such a method has not led to an improvement in the particle size distribution.
Further, the present inventors have found that the particle size distribution can be improved by partially reducing raw materials for a catalyst component (A) disclosed in Japanese Examined Patent Publication No. 15110/1977 with an organoaluminum compound, followed by a reaction with a silicon compound and further with an aluminum halide compound, and filed a patent application i.e. Japanese Unexamined Patent Publication No. 262802/1985. However, in this method, the particle size is not sufficiently large and the catalyst particles tend to disintegrate during the step of transportation or polymerization. In addition, in a gas phase polymerization, not only the polymer tends to be fine powder, but also the catalytic activity tends to be low, whereby there still remains a room for improvement.
Under such circumstances, several solutions for improving the particle properties have been proposed. For example, in Japanese Examined Patent Publication No. 49026/1977, it is proposed to conduct a so-called prepolymerization by activating a halide of a trivalent titanium with an organoaluminum compound, followed by treatment with an olefin having from 2 to 6 carbon atoms. However, in this method, the catalytic activity is insufficient and the properties of polyolefin particles are not satisfactory.
Under such circumstances, the present inventors have conducted a gas phase polymerization by applying the technology of this prepolymerization to the catalyst as disclosed in Japanese Unexamined Patent Publication No. 262802/1985. However, as shown in Comparative Examples, both the activity and the powder properties are not satisfactory.
That is, the technique of prepolymerization is not universally effective for any optional catalyst system. In this connection, for example, Japanese Unexamined Patent Publication No. 219311/1984 discloses that when a solid state transition metal catalyst comprising, as essential components, magnesium, a transition metal and a halogen, is prepolymerized with &agr;-olefin, the catalyst tends to be fine particles, and the polymer thereby obtained, accordingly tends to be fine powder. This publication shows that the technology of prepolymerization exhibits a specific effect to a specific catalyst.
An object of the present invention is to make it possible to produce polyolefins of various ranges of density at high productivity by a single catalyst system by an optional polymerization method. More specifically, the object is to provide a method capable of producing polyolefins ranging from a high density to a low density at high catalytic activity by the slurry polymerization method or the gas phase polymerization method, whereby excellent polyolefin particles having a high bulk density, a narrow particle size distribution and a large particle size can be produced.
The present invention have conducted extensitve researches to attain the above-mentioned object, and, as a result, have found it possible to obtain a polymer excellent in powder properties such as bulk density, particle size distribution or particle size by a slurry polymerization method or a gas phase polymerization method by combining an organometallic compound and a solid catalyst component obtained by prepolymerizing at least one &agr;-olefin to a solid composite having a specific composition. The present invention has been accomplished on the basis of this discovery.
The present invention provides a method for producing a polyolefin, which comprises polymerizing at least one &agr;-olefin in the presence of a catalyst system comprising:
(A) a solid catalyst component prepared by prepolymerizing
(vi) at least one &agr;-olefin in the presence of a solid composite obtained by reacting a homogen
Kondo Yozo
Mori Mitsuhiro
Naito Yutaka
Takahashi Fumiharu
Choi Ling-Siu
Tosoh Corporation
Wu David W.
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