Process for (co-)polymerizing ethylene.

摘要

The present invention relates to a process for manufacturing in a gaseous phase a polyolefin, preferably a copolymer of ethylene containing from about 1% to less than 30% by weight of at least one alpha-olefin comprising 3 to 8 carbon atoms, in the presence of a Ziegler-Natta catalyst system comprising (1) a solid catalyst and (2) a cocatalyst based on at least one organometallic compound. The solid catalyst is obtained by contacting (a) a vanadium compound and a titanium compound with (b) at least one organometallic compound capable of reducing the said vanadium and titanium compounds and with (c) a support containing magnesium dichloride free from any Mg-C bond and an electron-donor compound, D1, free from labile hydrogen, the said support consisting of spheroidal particles having given sizes and a narrow particle size distribution. Prior to its contact with (a) and (b), the support is preferably contacted with at least one electron donor compound, D2, containing labile hydrogen. The ethylene (co)polymer is directly obtained in the form of a dry powder consisting of spheroidal non-adhesive particles.