The catalyst is continuously fedin to the multi - zone circulating reactor. In this specially designed loop-reactor, consisting of two reactor zones, the growing polymeric granules are circulated between the two different zones. In the so called “riser” the polymer particles are entrained upwards in a fast fluidization regime by the monomer gas flow from a blower. Then, in the top of the reactor, the polymer particles enter the so - called “down - comer”. In this section there is a downward dense - phase plug - flow regime under gravity. At the bottom of the reactor the polymer particles are again fed back into the “riser” section.

The reactor can be operated with different conditions for hydrogen (as the chain transfer agent) and co - monomer concentration in the two sections, allowing the development of a bimodal (MFR, co - monomer concentration/type) polymer structure at a macro - molecular level. This split between the reaction conditions is achieved by injection of a monomer stream with a different composition than that in the riser section at the barrier between the riser and downcomer sections.