Many proposals have been made and known for a solid catalyst component comprising a titanium halide compound, a magnesium compound and an electron donor compound as essential components and a process for the polymerization of olefins in the presence of a catalyst comprising said solid catalyst component, an organic aluminum compound and a third component such as a silicon compound.
Further, a solid catalyst component prepared from a dialkoxymagnesium and titanium tetrachloride as main starting materials and a catalyst for polymerization of olefins made of said solid catalyst component, an organic aluminum compound and a third component such as a silicon compound have been known as disclosed in JP-A-63-3010 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-1-221405, JP-A-1-315406, JP-A-3-227309, JP-A-3-70711, JP-A-4-8709, and many other references.
On the other hand, various proposals have been made for a solid catalyst component comprising a halogenated aluminum compound, a magnesium compound and halogenated titanium compound as essential components and a catalyst for polymerization of olefins made of said solid catalyst component, an organic aluminum compound and a third component such as an organic acid ester or silicon compound. For example, JP-A-55-161807 proposes a composition obtained by a process which comprises co-grinding magnesium chloride, an organic acid ester, a halogenated hydrocarbon compound and a halogenated aluminum compound, and then subjecting the mixture to heat treatment with titanium tetrachloride. The above cited publication also proposes a catalyst formed by an organic aluminum compound and an organic acid ester. JP-A-61-31402 discloses a catalyst made of a solid catalyst component obtained by a process which comprises reacting a reaction product of a halogenated aluminum compound and a silicon compound with a magnesium compound, and then reacting the reaction product with a halogenated titanium compound and a phthalic acid ester, an organic aluminum compound and silicon compound.
Moreover, various proposals have been made for a solid catalyst component comprising an alkoxyaluminum compound, a magnesium compound and a halogenated titanium compound as essential constitution components and a catalyst for polymerization of olefins made of said solid catalyst component, an organic aluminum compound and a third component such as an organic acid ester or silicon compound. For example, JP-A-57-145104 proposes a catalyst component obtained by a process which comprises co-grinding magnesium chloride, an organic acid ester and an alkoxyaluminum compound, and then subjecting the mixture to heat treatment with titanium tetrachloride. JP-A-1-245002 discloses a catalyst made of a solid catalyst component obtained by a process which comprises bringing a diethoxymagnesium and titanium tetrachloride into contact with each other, adding a trialkoxyaluminum to the mixture, and then reacting the mixture with phthalic acid dichloride, an organic aluminum compound and an epoxy p-methane compound.
The foregoing various techniques focus on the development of a catalyst component which is active enough to allow the omission of a so-called deashing step, i.e., step of removing catalyst residues such as chlorine and titanium remaining in the polymer produced by the polymerization of propylene in the presence of a catalyst as well as on the enhancement of the yield of stereoregular polymer or the durability of the polymerization activity. These techniques can provide excellent results on these purposes.
However, if the catalysts prepared according to the foregoing prior art techniques are employed for the production of a polymer which requires close control over stereoregularity or crystallinity such as film grade polymer, the stereoregularity or crystallinity must be controlled by changing the ratio of titanium contained in a solid catalyst component and an external electron donor such as organic silicon compound during polymerization. In the polymerization of propylene, the stereoregularity or crystallinity must be controlled by adding a small amount of a comonomer such as ethylene. However, the variation of the ratio of titanium and external electron donor is limited to the critical point within some range, making it difficult to control the stereoregularity or crystallinity of the polymerization product and hence making it very difficult to stably produce a polymer having less varied desired physical properties. On the other hand, if a small amount of a comonomer is added, the content of the comonomer can be hardly controlled. Further, the polymerization of two monomers requires a very intricate process. Moreover, the stereoregularity or crystallinity of the polymerization product can be controlled by lowering the polymerization temperature. However, this approach is disadvantageous in that the yield of polymer produced is reduced.
Thus, the prior art techniques have never made clear any high activity type solid catalyst component and catalyst which can easily and stably provide a polymer having required stereoregularity or crystallinity without any intricate procedures.
If the stereoregularity or crystallinity of the polymer in the polymerization of propylene is controlled in the presence of the foregoing high activity type catalyst, it is difficult to obtain a polymer having the desired stereoregularity or crystallinity stably with little variation. If olefins, particularly propylene, are polymerized by a slurry process in the presence of the foregoing high activity type catalyst, a polymer can be produced in a high yield and with a better stereoregularity than in the polymerization in the presence of the conventional catalyst formed by a titanium trichloride type solid catalyst component, an organic aluminum compound and a third component such as an electron donor compound. At the same time, however, the polymer thus obtained tends to exhibit a higher crystallinity than obtained in the conventional catalyst. This causes some troubles. For example, the polymer thus obtained can be broken when formed at a high speed during working into film or sheet. Further, the formed products thus obtained exhibit an impaired transparency.
In order to solve the foregoing problems, if the foregoing high activity type catalyst is used for the polymerization of olefins, in particular propylene, the lowering of the polymerization temperature or the presence of a small amount of ethylene as a comonomer can be attempted. In this manner, the stereoregularity or crystallinity of the polymer thus produced can be somewhat controlled. However, this induces desirable phenomena. For example, in the case of slurry polymerization, the percent occurrence of a low molecular polymer soluble in the polymerization solvent is raised. In particular, in the polymerization of propylene, the percent occurrence of atactic polypropylene, which has an extremely low stereoregularity, is raised.
If the percent occurrence of atactic polypropylene is raised in slurry polymerization, an extraction step is required after separating the particles of polymer product from the polymerization solvent. This also disadvantageously contaminates the reactor or piping. Thus, this causes problems in production cost and stable operation. Further, if a variety of grades of polymers are produced in one plant, it finds difficulty in controlling the quality of products over the variation of operation conditions in continuous operation, giving undesirable effects on the process operation.
Moreover, if a polymerization catalyst having a composition comprising this kind of a high activity type catalyst component, an organic aluminum compound and an electron donor compound such as silicon compound is employed to polymerize olefins, the polymer thus produced contains much fines derived from fines of solid catalyst component itself or obtained by fragmentation due to reaction heat during polymerization. Thus, the polymer has a broad particle size distribution. As a result, the bulk density of the polymer thus produced tends to drop. If the content of the fine polymer is raised, the continuance of uniform reaction can be inhibited. Further, the pipe in the polymerization process can be blocked. Moreover, some troubles can occur at the separation step and the drying step of the polymer thus produced. It has been desired to solve these problems. In addition, if the particle size distribution is widened, it eventually gives undesirable effects on the molding of the polymer. If the bulk density of the polymer thus produced is lowered, the resulting productivity is extremely lowered. This is the reason why a polymer having as small fine polymer content as possible and a high bulk density has been desired.
In order to solve these problems, JP-A-6-157659 proposes a catalyst for polymerization of olefins made of a solid catalyst component obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixture of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, and then reacting the reaction product with titanium tetrachloride.
Further, JP-A-6-287225 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixture of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, washing the reaction product with an aromatic hydrocarbon, and then again reacting the reaction product with titanium tetrachloride to obtain a solid component which is then dried and freed of fine powder.
On the other hand, JP-A-6-287217 proposes a solid catalyst component for polymerization of olefins obtained by a process which comprises adding a suspension of a spherical particulate dialkoxymagnesium, an aromatic hydrocarbon and a diester of phthalic acid to a mixture of an aromatic hydrocarbon and titanium tetrachloride so that they are reacted, washing the reaction product with an aromatic hydrocarbon, again reacting the reaction product with titanium tetrachloride, drying the solid component thus obtained, removing fine powder from the solid component, and then adding a powdered nonionic surface active agent to the solid component.
The foregoing technique can remove the fine powder derived from the solid catalyst component itself, eventually exerting an effect of reducing the content of fine powder in the polymer thus produced. However, the effect of the foregoing technique does not go so far as to control the generation of fine powder due to fragmentation of particles by the reaction heat during polymerization, in particular in the initial stage of the polymerization reaction. Thus, a fine powder is still present in the polymer thus produced.
Further, the polymer produced according to the foregoing technique has a good morphology but has a low bulk density. In the production of a polyolefin, the amount of a polymer to be produced per unit volume in the polymerization tank is reduced, and the amount of the polymer to be processed during transportation or pelletizing step is limited. As a result, the productivity throughout the entire process for the production of polyolefin is reduced. Further, even if a polymer having a relatively high bulk density can be obtained, the problem of drop of polymerization activity or stereoregularity is left unsolved.
The present invention has been worked out as a result of intensive studies of the solution to the problems of the prior art problems. An object of the present invention is to provide a solid catalyst component for polymerization of olefins and a catalyst which can stably provide a polymer having the desired stereoregularity and crystallinity without changing the polymerization parameter when used in the polymerization of olefins, in particular propylene, can easily control the stereoregularity or crystallinity of the polymer thus produced and can provide a stereoregular polymer in a high yield with a reduced percent occurrence of atactic polypropylene even if a polymer having a relatively low crystallinity is produced, in particular, by subjecting propylene to slurry polymerization. Another object of the present invention is to provide a solid catalyst component for polymerization of olefins and a catalyst which can provide a polymer having a high bulk density and a small content of fine powder while maintaining its high polymerization activity and keeping the yield of highly stereoregular polymer high.