The present disclosure relates to a method for producing a catalyst for use in polymerization of ethylene and copolymerization of ethylene and xcex1-olefin, and more particularly to a method for producing a catalyst containing a transition metal supported on a magnesium-containing carrier whose initial activity is low but slowly increases to an optimal level as the polymerization progresses.
A method was developed some time ago for producing a supported catalyst for polymerization of ethylene and copolymerization of ethylene and xcex1-olefin, by following the way of coating catalysts with a transition metal compound, that is, first reacting an organomagnesium compound having the structure of MgPh2.nMgCl2.mR2O (here, n=0.37xcx9c0.7; mxe2x89xa72; R2O=ether; Ph=phenyl) with an organic halide, and next coating the thus produced carrier with such transition metal compounds as TiCl4, VCl4, or VOCl3 (Application No. 330675/1995 for a Japanese patent).
However, the catalyst produced by the publicly known art above, particularly the catalyst produced by the way of coating the carrier with TiCl4, is found having such problems as a broad molecular weight distribution and high initial activity, though it has the polymerization process partly improved by producing a polymer having a narrow particle size distribution and an increased bulk density.
A way of effectively preventing generation of lumps in the reactor by adjusting the initial polymerization activity to a low point in the process of gaseous fluidized bed polymerization is publicly known. It is also a public knowledge that the quality of products can be improved by decrease of the output of polymers of low molecular weights to be extracted by hexane, if the polymer in use is of a narrow molecular weight distribution, especially in the case of products of linear low-density polyethylene produced by copolymerization of ethylene and xcex1-olefin.
In view of all this, a catalyst is particularly demanded whose activity is low in the initial stage but slowly increases to an optimal activity as the polymerization progresses.
A method for producing a catalyst, which may make it possible to produce a polymer of a narrow particle size distribution and an increased bulk density, has a low activity in the initial stage but slowly increasing to an optimal level accordingly as the ethylene polymerization or ethylene/xcex1-olefin copolymerization by slurry or gaseous process progresses, and is useful in ethylene polymerization or ethylene/xcex1-olefin copolymerization, especially in the gaseous environment, is herein described.
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