Process for starting up the polymerisation of ethylene or copolymerisation of ethylene and at least one other alpha-olefin in the gas phase in the presence of a catalyst based on chromium oxide.

摘要

The present invention relates to a process for starting up the polymerisation of ethylene or copolymerisation of ethylene and at least one other alpha-olefin by bringing ethylene and optionally at least one other alpha-olefin in contact under fluidised-bed polymerisation or copolymerisation conditions and/or stirred mechanically, with a charge powder in the presence of a catalyst comprising a chromium oxide compound associated with a granular support and activated by thermal treatment, this catalyst being used in the form of a prepolymer, this process being characterised in that the charge powder employed is previously subjected to a treatment by contacting the said charge powder with an organo-aluminium compound, in such a way that the polymerisation or copolymerisation starts up immediately after the contacting of the ethylene and optionally one other alpha-olefin with the charge powder in the presence of the prepolymer.