Abstract: The present invention relates to a gas phase fluidized bed reactor (1) comprising an upright tubular portion (2) having a fluidization grid (4) in the lower part thereof. According to the invention the upright tubular portion (4) is provided with an external conduit (13) which connects a lower orifice (14) which is above the fluidization grid (4) and an upper orifice (15) which is a height above the lower orifice (14). The invention also relates to a gas phase polymerization process carried out in the reactor.

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 system of the Ziegler-Natta type consisting of a solid catalyst comprising at least one compound of a transition metal belonging to groups IV, V or VI of the Periodic Table, of the elements, and of a cocatalyst comprising at least one organometallic compound of a metal belonging to groups II or III of the Periodic Table in which the polymerization reactor is fed with alpha-olefin at a constant rate.

Abstract: The present invention relates to a gas phase fluidized bed reactor (1) comprising an upright tubular portion (2) having a fluidization grid (4) in the lower part thereof. According to the invention the upright tubular portion (4) is provided with an external conduit (13) which connects a lower orifice (14) which is above the fluidization grid (4) and an upper orifice (15) which is a height above the lower orifice (14). The invention also relates to a gas phase polymerization process carried out in the reactor.

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 Polymer is withdrawn from the reactor body (1) via at least two polymer outlets, at least one of which (15) is in the lower portion of the reactor body (1) and at least one of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: A fluidized bed apparatus (1) having a fluidization grid (2) below which is positioned a tuyere (5) for guiding fluidization gas to the fluidization grid (2). The tuyere (5) comprises a widening pipe the wider end (6) of which is positioned towards the fluidization grid (2) and has an area which is substantially the same as the cross-sectional area of the fluidized bed apparatus (1) and is 2 to 30 times that of the area of the narrower end (7) of the widening pipe. The process for feeding fluidization gas to a fluidized bed using such apparatus enables a good gas distribution across the bed to be achieved with a modest additional pressure drop. The invention is particularly useful for apparatus e.g. greater than 3 m in diameter.

Abstract: The present invention relates to a process for the start up of polymerization or copolymerization in the gas phase by bringing the said alpha-olefins in contact under polymerization or copolymerization conditions in a fluidized bed and/or with mechanical stirring with a charge powder, in the presence of a catalyst system of the Ziegler-Natta type, this process being characterized in that the charge powder used is previously dehydrated and subjected to a treatment by bringing the said charge powder into contact with an organoaluminum compound for a period of at least five minutes, so that the polymerization or copolymerization starts up immediately after the contracting of the alpha-olefins with the charge powder in the presence of the catalyst system.

Abstract: The present invention relates to a process for starting up the polymerization of ethylene or copolymerization of ethylene and at least one other alpha-olefin by bringing ethylene and optionally at least one other alpha-olefin in contact under fluidized-bed polymerization or copolymerization 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 characterized 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 polymerization or copolymerization 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.

Abstract: A process for detecting anomalies in a fluidized bed, e.g. the incidence of agglomeration in gas-fluidized bed polymerization, comprises sensing and converting into electrical signals the pressure at one level, or the pressure difference between two or more levels in the reactor, processing these signals by computer to produce a pressure spectrum and comparing with a reference spectrum obtained in the absence of anomalies. The device comprises one or more pressure sensors 11,12,13, which measure the pressure at various levels in the reactor 1, and a computer 27.

Abstract: The present invention relates to a process for the polymerization of alpha-olefins in the gas phase in the presence of a Ziegler-Natta catalyst system consisting of a catalyst comprising atoms of halogen, magnesium and a transition metal, and cocatalysts based on an organometallic compound of a metal of Groups II or III of the Periodic Table of Elements, this catalyst system being previously converted into a prepolymer or a catalyst supported on a granular substance. This process is characterized in that the polymerization in the gas phase is carried out by contacting one or more alpha-olefins, on the one hand with the prepolymer or the supported catalyst system comprising an organometallic compound (a) which is only slightly volatile as cocatalyst, and on the other hand another cocatalyst consisting of an organometallic compound (b) which is relatively volatile, in such a way that the total quantity of cocatalyst employed is relatively small.