Patent ID: 7851567

Claim:
A process for the preparation of multimodal ethylene homo- or copolymers in at least two stages, the comonomer being selected from the group consisting of 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, the process comprising (i) preparation of a first ethylene homo- or copolymer fraction in a loop reactor in slurry phase comprising a diluent, (ii) preparation of a second ethylene homo- or copolymer fraction in a gas phase reactor, by using a catalyst not containing an inorganic oxide support, introducing an inert hydrocarbon into the gas phase reactor which is the same as the diluent used in the loop reactor and is selected from propane, butanes, pentanes and hexanes and their mixtures and operating the gas phase reactor in such conditions that at least part of the gas is recycled, and that at least a part of the recycled gas is condensed and the (partially) condensed gas is re-introduced into the gas phase reactor, wherein at least part of the inert hydrocarbon is introduced into the gas phase reactor together with the polymer as a stream and wherein (iii) the stream comprising diluent, polymer and unreacted ethylene, hydrogen and optionally alpha-olefin comonomers withdrawn from the loop reactor is subjected to a flash stage at a pressure between 15 and 30 bar so that at least part of a fluid phase is flashed out to produce a dense stream containing the polymer and a minor part of the fluid phase and a lean stream containing a major part of the fluid phase; (iv) cooling said dense stream comprising the polymer so that at least a substantial part of the diluent contained therein condenses; (v) introducing said cooled dense stream into the gas phase reactor; and (vi) cooling said gas phase reactor by evaporation of said condensed diluent.