Abstract: A process for producing polyethylene compositions in the presence of a catalytic system of ethylene polymerizing catalyst and cocatalyst in a multistage continuous reaction sequence consisting of successive liquid phase and gas phase polymerizations is disclosed. In the first step of the process, ethylene and optionally hydrogen and comonomer are polymerized in a first loop reactor in a low boiling hydrocarbon medium in the presence of ethylene polymerizing catalyst and cocatalyst. The reaction mixture is then removed and then transferred to a second loop reactor where polymerization is continued by addiing ethylene, hydrogen and optionally inert hydrocarbon, comonomers and cocatalysts. Thereafter, the reaction mixture is removed from the second loop reactor along with an essential part of the reaction medium and transferred to a gas phase reactor where polymerizing is continued in the presence of added ethylene and optionally hydrogen, comonomers and cocatalysts to form an end product.

Abstract: The invention relates to a method for homo- or copolymerizing ethene in the presence of a Ziegler-Natta or other catalyst and a possible comonomer and hydrogen for preparing a homo- or copolymer of ethene in particle form in propane. In accordance with the invention, the polymerization is performed in a loop reactor under such supercritical conditions where the temperature is higher than the critical temperature of the mixture formed by ethene, propane and a possible hydrogen and a comonomer, but lower than the melting temperature of the ethene polymer forming in the polymerization, and the pressure is higher than the critical pressure of said mixture.

Abstract: The invention concerns a multi-stage process for producing polyethylene having a bimodal and/or broad molecular weight distribution in the presence of an ethylene polymerizing catalyst system in a multistep reaction sequence, in which the first reaction step is a liquid phase polymerization step and the second reaction step is formed by one or more gas-phase polymerization steps. According to the process of the invention in the first reaction step ethylene is polymerized in a loop reactor (10) in an inert low-boiling hydrocarbon medium the residence time being at least 10 minutes, reaction mixture is discharged from the loop reactor (10) and at least a substantial part of the inert hydrocarbon mixture is separated and the polymer is transferred into one or more gas-phase reactors (30), where the polymerization is completed in the presence of ethylene and optionally hydrogen and a comonomer.

Abstract: The polymerization of certain alpha-olefins in a gas phase involves the problem of agglomeration of the product into particles disadvantageous from the viewpoint of its handling. In the present invention this problem has been solved by means of a new type of process for the homo- or copolymerization of alpha-olefins. In the process the catalyst system is pretreated by contacting and reacting a transition-metal compound which is solid or on a solid carrier with an organoaluminum compound, and possibly an electron donor, in a liquid medium, and by drying the thus formed reaction product to produce a solid catalyst system. The thus pretreated solid and active catalyst system is then fed together with an alpha-olefin in the gaseous state into a gas-phase reactor, and polymerization is carried out by contacting them with each other.