| 摘要 |
A process for producing polyethylene compositions in the presence of polymerizing catalytic system of ethylene catalyst and cocatalyst in a multistage reaction sequence consisting of successive liquid phase and gas phase polymerizations. The process comprises at least one continuous reaction sequence, in which in the first step ethylene and optionally hydrogen and comonomer are polymerized in a loop reactor in a low boiling hydrocarbon medium in the presence of ethylene polymerizing catalyst and cocatalyst, the residence time and reaction temperature being such that the proportion of the ethylene polymer produced in the reactor from the end product of the process is between 1- 20 wt.%, the reaction mixture removed from the step is transferred to second step where polymerization is continued in a loop reactor by adding ethylene, hydrogen and optionally inert hydrocarbon, comonomers and cocatalysts, the residence time being at least 10 minutes, the reaction mixture is removed from the loop reactor, at least an essential part of the reaction medium is removed and the polymer transferred to a third step where polymerizing is carried out in a gas phase reactor in the presence of added ethylene and optionally hydrogen, comonomers and cocatalysts.
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