Patent ID: 8785572

Claim:
A process comprising: polymerizing (a) propylene, (b) at least one C 4 -C 8 α-olefin, and (c) optionally ethylene, wherein the polymerizing step is carried out in the gas-phase, wherein the process is carried out in a reactor having two interconnected polymerization zones, a riser and a downcomer, wherein polymer particles flow through the riser under fast fluidization conditions, leave said riser and enter the downcomer, wherein the polymer particles in the downcomer flow downward in a densified form, leave said downcomer and are reintroduced into said riser, thus establishing a circulation of polymer between the riser and the downcomer, wherein a gas mixture present in the riser is prevented from entering the downcomer by introducing a liquid barrier into an upper part of said downcomer, thereby creating a recycle gas mixture that flows upward to a separation zone wherein the liquid barrier comprises at least one C 4 -C 8 α-olefin in a total amount of from 0.1% to 35% by mol, and has a composition different from the gas mixture present in the riser, wherein the recycle gas is separated into: (i) a first stream of recycled gas, wherein the first stream of recycled gas is fed into a bottom part of the downcomer, (ii) a second stream of recycled gas, wherein the second stream of recycled gas is fed into a bottom part of the riser; and (iii) a third stream of recycled gas, wherein the third stream of recycled gas is fed into at least one distillation column before being recycled into the downcomer.