PROCEDIMENTO PER LA POLIMERIZZAZIONE IN FASE GAS DELLE OLEFINE

摘要

Process for the gas-phase polymerization of ethylene and ethylene mixtures with alpha -olefins CH2=CHR in the presence of a high activity catalyst comprising a titanium compound containing at least one Ti-halogen bond supported on magnesium dichloride in active form, said process comprising the steps of: (a) contacting the catalyst component; (b) prepolymerizing ethylene or ethylene mixtures with alpha -olefins in order to produce a polymer amount of from approximately 5 g per g of solid component, up to an amount corresponding to about 10% of the final catalyst yield; (c) polymerizing ethylene or ethylene mixtures with alpha -olefins in the gas-phase, in the presence of the prepolymer-catalyst system obtained in (b) , while maintaining in the gas phase a molar concentration of the alkane comprised between 20 and 90 % with respect to the total gases.