Abstract: A process for polymerizing olefins in a gas-phase fluidized-bed reactor comprising a reactor body (1), optionally surmounted by a disengagement chamber (2), in which fine particles entrained by the gas mixture leaving the top of the reactor are separated from the gas and recycled to the upper portion of the reactor body. Polymer is withdrawn from the reactor body (1) via at least two polymer outlets, at least one of which (15) is in the lower portion of the reactor body (1) and at least one of which (16) is in the upper portion of the reactor body at a position below the top of the fluidized bed. The invention includes apparatus for polymerizing olefins and the use of the apparatus.

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 a continuous process for the polymerization of an alpha-olefin having from 2 to 12 carbon atoms, which is carried out in a gas phase polymerization reactor by bringing a gaseous reaction mixture containing the alpha-olefin to be polymerized into contact with a catalyst based on chromium oxide associated with a catalyst based on chromium oxide associated with a granular support and activated by a heat treatment in which the polymerization reactor is fed with (a) alpha-olefin and (b) catalyst at constant rates.

Abstract: A process for controlling the continuous gas-phase polymerization of one or more alpha-olefins in a fluidized and/or mechanically stirred bed reactor using a high activity catalyst based on a transition metal of groups IV, V or VI of the Periodic Table comprises introducing into the reactor, continuously and simultaneously, an activity retarder and an activator, in very small amounts, in a molar ratio and at flow rates which are varied with time in order to maintain substantially constant either the polymerization rate or the transition metal content of the polymer produced.

Abstract: The present invention relates to a process for polymerizing or copolymerizing alpha-olefins comprising, on the one hand, a prepolymerization stage by contacting one or more alpha-olefins with a Ziegler catalyst system consisting of a solid catalyst containing essentially atoms of halogen, magnesium and transition metal, and a co-catalyst consisting of an organometallic compound, and, on the other hand, a polymerization or copolymerization stage in a gas phase process by means of a fluidized bed, by contacting one or more alpha-olefins with the prepolymer produced in the first stage, process characterized in that the alpha-olefin prepolymer and polymer or copolymer are in the form of a powder consisting of particles having specific values for the transition metal content and the mean diameter by mass, and characterized in that the particle size distribution of the prepolymer is narrow and easily controlled.

Abstract: The present invention relates to a process for polymerizing or copolymerizing alpha-olefins comprising, on the one hand, a prepolymerization stage by contacting one or more alpha-olefins with a Ziegler catalyst system consisting of a solid catalyst containing essentially atoms of halogen, magnesium and transition metal, and a co-catalyst consisting of an organomatellic compound, and, on the other hand, a polymerization or copolymerization stage in a gas phase process by means of a fluidized bed, by contacting one or more alpha-olefins with the prepolymer produced in the first stage, process characterized in that the alpha-olefin prepolymer and polymer or copolymer are in the form of a powder consisting of particules having specific values for the transition metal content and the mean diameter by mass, and characterized in that the particle size distribution of the prepolymer is narrow and easily controlled.

Abstract: A process for the continuous polymerization of one or more alpha-olefins with a transition metal catalyst, in a reactor having a fluidized and/or mechanically stirred bed, in which a very small amount of an activity retarder, generally less than 0.1 ppm, is introduced continuously into the reactor at a flow rate which is varied with time so as to keep substantially constant either the polymerization rate or the content of transition metal in the polymer produced. Suitable activity retarders include polymerization inhibitors such as, for example, oxygen, alcohols, carbon monoxide and carbon dioxide and electron donor compounds such as amides and ethers.

Abstract: A process for polymerizing olefins in the presence of a Ziegler-Natta type catalyst or a catalyst based on chromium oxide using a gas-phase fluidized-bed reactor (1) having a recycle line (5) for removing the olefin-containing gas from the top of the reactor and returning it to the bottom of the reactor, the recycle line having at least one heat exchanger (7,10) for cooling the olefin-containing gas, which process comprises introducing an organometallic compound, as a mixture or as a solution in at least one C.sub.3 to C.sub.12 liquid olefin, into the recycle line at a point upstream of a heater exchanger (10).

Abstract: The present invention relates to a process for polymerizing or copolymerizing alpha-olefins comprising, on the one hand, a prepolymerization stage by contacting one or more alpha-olefins with a Ziegler catalyst system consisting of a solid catalyst containing essentially atoms of halogen, magnesium and transition metal, and a co-catalyst consisting of an organomatellic compound, and, on the other hand, a polymerization or copolymerization stage in a gas phase process by means of a fluidized bed, by contacting one or more alpha-olefins with the prepolymer produced in the first stage, process characterized in that the alpha-olefin prepolymer and polymer or copolymer are in the form of a powder consisting of particles having specific values for the transition metal content and the mean diameter by mass, and characterized in that the particle size distribution of the prepolymer is narrow and easily controlled.

Abstract: New catalysts which can be used for the polymerization and copolymerization of ethylene, comprising a support consisting basically of magnesium chloride on which is deposited by precipitation a vanadium compound, obtained by bringing a vanadium compound in which the vanadium is at one of the two maximum valencies 4 and 5 in contact with a support consisting basically of magnesium chloride and optionally of aluminium chloride and comprising products with an Mg--C bond.

Abstract: The invention concerns a process for the production of polyolefins with a wide range of distribution in respect of molecular masses.The process comprises polymerizing ethylene, which is optionally accompanied by one or more other olefins, in contact with a catalytic system comprising:(a) a catalyst comprising a solid compound of titanium, magnesium and a halogen such as chlorine or bormine(b) one or more organometallic compounds of a metal of groups II and III of the periodic table of elements(c) one or more halogenated ethylenic hydrocarbons.The resulting polyolefins are particularly suitable for being shaped by means of extrusion-blowing.

Abstract: The dry polymerization of olefins to produce polymers having a molecular weight above 50,000 in the presence of a catalyst system formed of a compound of a transition metal and a co-catalyst of an organo-metallic compound of a metal of Groups II or III of the periodic table, in which the polymerization reaction is carried out in a series of reaction vessels wherein the formed polymer is transferred from one to the other and in which additional co-catalyst is added to reaction vessels beyond the first, the gaseous effluent from each reaction vessel is recycled back to the reaction vessel and in which the co-catalyst is introduced into the first reaction vessel in an amount such that the atomic ratio of the metal of the co-catalyst to the transition metal is within the range of 0.1 to 10, and in which the co-catalyst is introduced into vessels other than the first in an amount such that the atomic ratio of metal of the co-catalyst to the transition metal is within the range of 0.1 to 20.

Abstract: The polymerization of olefins to form polymers having a molecular weight greater than 50,000 wherein the polymerization is carried out in the presence of a catalyst component formed of a compound of a transition metal of the sub-groups IVa, Va and VIa, and a co-catalyst component of at least one organo-metallic compound of a metal from groups II and III of the periodic table, in which the co-catalyst is in the form of a liquid which is separately introduced into the reaction vessel on a carrier formed of an inert porous powder which is impregnated with the co-catalyst.