The present invention discloses a process optimizing the yield of propylene from a fluid catalytic cracking unit. The method combines a first catalytic reactor, a fractionation zone, a separation unit and a second catalytic reactor. The separation unit produces a first separation unit stream and a second separation unit stream, the first separation unit stream comprising Cx paraffins, and the second separation unit stream comprising Cx olefins, wherein the second separation unit stream is passed to a second catalytic reactor and the first separation unit stream is removed from the process.