The present invention provides various processes for producing polypropylene from an oxygenate-contaminated propylene-containing feedstock, preferably derived from an oxygenate to olefin reaction system. In one embodiment, the process includes providing a propylene-containing stream from an oxygenate to olefin reaction system, wherein the propylene-containing stream comprises propylene and an oxygenate. The propylene in the propylene-containing stream contacts a polymerization catalyst in a polymerization zone under conditions effective to polymerize the propylene to form the polypropylene.