Patent ID: 7582723

Claim:
A process for the polymerizing ethylene or ethylene with further 1-olefins, in which the ethylene is polymerized in the presence of a catalyst in a gas-phase reactor to form polymer particles, the gas-phase reactor comprising a reaction gas comprising propane and unpolymerized ethylene, and the reaction gas being circulated to remove heat of polymerization; the process comprising: the polymer particles are discharged continuously or discontinuously from the reactor; the polymer particles are separated from a major part of concomitantly discharged gas, and the polymer particles are degassed; gas is freed of entrained fine particles; in a first separation stage, gas is separated from a low-boiling fraction comprising ethylene, or from a high boiling fraction comprising further 1-olefins or alkanes, the 1-olefins or alkanes comprising from 4 to 12 carbon atoms; in a second separation stage, a propane fraction is separated off and the propane fraction is used for degassing the polymer particles discharged from the reactor; wherein a partial pressure of ethylene in the propane fraction used for degassing is less than 6000 Pa, and a partial pressure of a sum of further 1-olefins and alkanes comprising from 4 to 12 carbon atoms in the propane fraction is less than 10000 Pa.