| abstract |
A process for preparing an ethylene polymer comprising homopolymerizing ethylene or copolymerizing ethylene with one or more comonomers in a gas-phase polymerization reactor comprising a riser unit, in which growing polymer particles flow upwards under fluidization, fast fluidization or transport conditions, and a downcomer, in which growing polymer particles flow downward in a densified form, wherein the hold-up of polymer particles in the downcomer is from 55 wt.% to 80 wt.% of the total hold-up of polymer particles in the gas-phase polymerization reactor. |