Abstract: The invention relates to a process for the treatment of a gas stream obtained from the production of polyolefins and containing unreacted compounds. According to the process, uncondensed compounds are removed from the gas stream and, when so desired, these compounds are directed to further treatment. According to the invention, the uncondensed compounds are separated from the gas stream by membrane separation. Thus the separation of gases is facilitated, since by coupling the membrane system in conjunction with distillation columns the distillation can be carried out at a substantially higher top temperature. By using the membrane system it is possible effectively to remove the lightest gases, which would otherwise accumulate in the process.

Abstract: The invention relates to a process for the production of polyolefins in a reactor system which comprises at least one gas-phase reactor with at least one monomer is polymerized. According to the process, there is fed into the gas-phase reactor the monomer to be polymerized and possibly a polymer-containing fluid. According to the invention, before being fed into the gas-phase reactor, the fluid is subjected to a phase change in order to separate uncondensed compounds from liquid and possibly solid compounds. The gas including the uncondensed compound is recovered, and hydrogen is separated from the gas by membrane separation. The invention can be applied to the removal of hydrogen from the circulation gas of a gas-phase reactor, for example in order to change the polyolefin grade to be produced.