Embodiments disclosed herein relate to a use of propane contained in a propylene feedstock for setting up impact copolymer polypropylene production in at least two polymerization zones comprising accumulating the propane in a first polymerization zone (2, 5) during a parallel operation mode of the first polymerization zone (2, 5) and a second polymerization zone (7, 10) producing respective propylene polymers. Embodiments disclosed herein also relate to a process and a system for setting up impact copolymer polypropylenes production.