Abstract: The present invention relates to a process for stopping an olefin polymerization which is carried out in a low pressure gas phase reactor, which process comprises introducing an effective quantity of deactivating agent into the reactor, characterized in that the olefin polymerisation is carried out using a chromium oxide catalyst and in that the deactivating agent is selected from oxygen, ammonia, water and carbon monoxide and is introduced over a relatively short period of time. The deactivating agent is preferably introduced into the polymerization reactor in a quantity such that in the reactor the weight ratio of the deactivating agent to the catalyst is at least 0.001.

Abstract: The present invention relates to an alpha-olefin prepolymer catalytically active in an alpha-olefin (co-)polymerization comprising a transition metal, an organometallic compound and an antistatic agent. The prepolymer can be prepared by contacting the antistatic agent with a catalyst comprising the transition metal and the organometallic compound before or during an alpha-olefin prepolymerization. It can also be prepared by contacting the antistatic agent with an alpha-olefin prepolymer after a prepolymerization. It can also be prepared by a combination of the two methods. The prepolymer can be introduced into a gas phase (co-)polymerization medium for preparing polyolefin directly in a dry powder form, with a reduced amount of sheeting and agglomerates.

Abstract: The present invention relates to a process for the polymerization of ethylene or copolymerization of ethylene and at least one other alpha-olefin, in the gas phase in a fluidized 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 characterized 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 4.times.10.sup.-5 to 3 milligram atoms of chromium in the catalyst per gram.

Abstract: The present invention relates to a process for (co-)polymerizing ethylene in a gaseous phase, by means of a fluidized and/or mechanically stirred bed reactor, with the help of a catalyst comprising a chromium oxide and a titanium compound, supported on a refractory oxide and activated by a heat treatment. The process is characterized in that the catalyst is introduced into the reactor in the form of a dry powder consisting of particles free from prepolymer and the (co-)polymerization is carried out in the presence of an organoaluminium compound. The (co-)polymer thus obtained has substantially low catalyst residues, and an improved stress cracking resistance.

Abstract: 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 4.times.10.sup.-5 to 3 milligram atoms of chromium in the catalyst per gram.

Abstract: Process for polymerising ethylene, or copolymerising ethylene with an alpha-olefin, in the gas phase in the presence of a prepolymer/catalyst composition, the catalyst being an activated chromium oxide supported on a refractory oxide. The prepolymer is treated to an extraction with a solution comprising inert hydrocarbon and an organometallic compound, for example an alkylaluminum, prior to being dried and introduced into the gas phase (co) polymerisation. Prepolymer thus treated has improved properties in the dry state, for example improved flow.

Abstract: A process and catalyst for polymerizing olefins, especially ethylene or a mixture of ethylene with up to 40 wt % (based on total monomer) or other 1-olefinic monomer, the process comprising (a) supporting a chromium compound on a refractory oxide support material, (b) adding one or more tetravalent titanium compounds, (c) heating the product under such conditions that an active polymerization catalyst in the presence of one or more organometallic compounds wherein the metal is of groups 1A, 2A, 2B or 3A of the Periodic Table (Mendeleef), especially aluminium trialkyls. Step (d) is preferably carried out in the presence of a polyene modifier. The refractory oxide support material is preferably silica. The produced polyolefins are also claimed.

Abstract: A supported Ziegler catalyst prepared by reacting, under substantially anhydrous conditions, a refractory oxide support material having acidic surface hydroxyl groups, e.g. silica, and an organo metallic compound, e.g. a trialkyl aluminium compound, separating any unreacted organo metallic compound and impregnating the solid product with a halogen-containing titanium compound and a halogen-containing vanadium compound. The catalyst, preferably together with a conventional Ziegler catalyst activator, e.g. an aliminium alkyl, is employed to polymerize 1-olefins, for example ethylene.

Abstract: The present invention relates to a process for the polymerization of ethylene or copolymerization of ethylene and at least one other alpha-olefin, in the gas phase in a fluidized 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 characterized 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 4.times.10.sup.-5 to 3 milligram atoms of chromium in the catalyst per gram.

Abstract: 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 4.times.10.sup.-5 to 3 milligram atoms of chromium in the catalyst per gram.