Processes for transitioning between chrome-based and mixed polymerization catalysts

摘要

A process of transitioning from a first polymerization reaction conducted in the presence of a mixed catalyst system to a second polymerization reaction conducted in the presence of a chrome-based catalyst system is disclosed, the polymerization reactions being conducted in one embodiment in a polymerization zone of a gas phase fluidized bed reactor which contains a fluidized bed of polymer particles by the essentially continuous passage of monomer gases through the polymerization zone, comprising:a) discontinuing the introduction of the mixed catalyst system into the reactor;b) maintaining polymerization conditions in the reactor and permitting polymerization to continue for a period of time to allow the components of the mixed catalyst system present in the reactor to produce additional polymer particles;c) introducing a deactivating agent into the fluidized bed in an amount sufficient to deactivate the mixed catalyst system;d) establishing optimal conditions within the reactor for the chrome-based catalyst system; ande) introducing the chrome-based catalyst system into the reactorcharacterized in that the amount of polymer particles in the fluidized bed is substantially maintained in the polymerization zone during the transition steps.