| abstract |
A process for the gas-phase polymerization of α-olefÊns CH2=CHR, where R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, carried out in a first and a second interconnected polymerization zones, wherein the growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said riser and enter the second of said polymerization zones (downcomer) through which they flow downward in a densified form, leave said downcomer and are reintroduced into said riser, in which process: (a) the gas mixture present in the riser is totally or partially prevented from entering the downcomer, and (b) the gaseous composition inside a portion of the downcomer is maintained substantially similar to the gaseous composition reacting in the riser. |