1. Field of the Invention
This invention relates to a process for producing polyethylene by the use of a novel catalyst having an extremely high polymerization activity.
Ethylene polymerization or polymer referred to herein includes not only ethylene homopolymerization or homopolymer but copolymerization or copolymer of ethylene with another .alpha.-olefin copolymerizable therewith. Thus ethylene homopolymer and copolymer will be collectively referred to as polyethylene.
2. Description of the Prior Art
In recent years, techniques for producing polyethylene by the use of Ziegler type catalysts supported on a carrier have prevailed, and this is based mainly on the fact that it has become possible by the use of such catalysts to enhance the efficiency of catalyst utilized, to omit the catalyst removal step and to simplify the production process. Nevertheless, a process for polyethylene production being more enhanced in the efficiency of catalyst utilized and more economical has still been pursued.
As for the carrier for supported Ziegler type catalysts, it is known that anhydrous magnesium chloride or its modified substances, organomagnesium halides such as Grignard reagents, organic magnesium compounds such as magnesium ethoxide or compounds other than magnesium compounds such as alumina, silica silica-alumina have already been employed.
On the other hand, the present inventors have developed processes wherein compounds of complicated compositions formed by reacting a trivalent metal halide such as aluminum chloride with a divalent metal compound such as magnesium oxide, which compounds are intrinsically different from the above prior art carriers, are employed as a carrier whereby it is possible to enhance the catalyst efficiency and also omit the step of catalyst removal. For example, the inventions of Japanese patent application laid-open Nos. Sho 54-116078/1979 and Sho 54-113687/1979 (these inventions will hereinafter be referred to as prior inventions) are characterized by employing a solid product prepared by reacting a compound of transition metals of group 4a or group 4b of the Periodic Table, with the above carrier in the presence of a polysiloxane. Nevertheless, a further improved polymer yield has been desired. On the other hand, the inventions of Japanese patent application laid-open Nos. Sho 55-5931/1980 and Sho 55-12165/1980 are characterized by employing a solid product prepared by further successively reacting the final solid product disclosed in the above Japanese patent application laid-open Nos. Sho 54-116078/1979 and Sho 54-113687/1979, with a halogen-containing compound of transition metals of group 4a or group 5a and a halogen-free compound of transition metals of group 4a or group 5a. However the resulting polymers have a very broad molecular weight distribution. The present inventors have made various studies on the improvement in the prior inventions, and have found that the polymer yield is notably improved by devising the choice and combination of the transition metal compounds and their reaction, and have attained the present invention.
The object of the present invention is to obtain a further improved polymer yield as compared with those according to the prior art in the production of polyethylene having a good form and also a narrow molecular weight distribution.