ETHYLENE POLYMERIZATION OR COPOLYMERIZATION OF ETHYLENE AND ALPHA-OLEFINS IN A FLUIDIZED BASE IN THE PRESENCE OF A CHROMIUM-BASED CATALYST

摘要

The present invention relates to a process for the polymerisation of ethylene or copolymerisation of ethylene and at least one other alpha-olefin, in the gas phase in a fluidised bed reactor, in the presence of a catalyst comprising chromium compounds associated with a granular support comprising a refractory oxide and activated by thermal treatment, which process is characterised in that the catalyst is used in the form of active particles of prepolymer, obtained by bringing the said catalyst in contact with ethylene, alone, or in a mixture with at least one higher alpha-olefin, in such a way that the prepolymer contains from 4x10-5 to 3 milligram atoms of chromium in the catalyst per gram.