Patent ID: 8557932

Claim:
A process for the preparation of a multimodal polyolefin polymer at temperatures of from 40 to 150° C. and pressures of from 0.1 to 20 MPa in the presence of a polymerization catalyst in a first and a second polymerization reactor connected in series, and where optionally further polymerization reactors are connected to said reactors upstream or downstream of said reactors; wherein in the first polymerization reactor a first polyolefin polymer is prepared in suspension in the presence of hydrogen and in the second polymerization reactor a second polyolefin polymer is prepared in the presence of a lower concentration of hydrogen than in the first polymerization reactor, the process comprising: a) withdrawing from the first polymerization reactor a suspension of solid polyolefin particles in a suspension medium comprising hydrogen; b) feeding the suspension to a flash drum of a lower pressure than that of the first polymerization reactor; c) vaporizing a part of the suspension medium; d) withdrawing a hydrogen-depleted suspension from the flash drum and feeding it to the second polymerization reactor; e) withdrawing gas from the gas-phase of the flash drum and feeding it to a heat exchanger; f) condensing a part of the gas withdrawn from the flash drum; and g) returning the liquid obtained in the heat exchanger to the polymerization process at a point where suspension is present.