Processes for transitioning between chrome-based and mixed polymerization catalysts

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, the polymerization reactions being conducted in a polymerization zone of a gas phase fluidized bed reactor which contains a fluidized bed of polymer particles and monomer gases, the transition comprising the steps of:

• 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 to the reactor a deactivating agent into the fluidized bed;
• d) establishing optimal conditions within the reactor for the chrome-based catalyst system;
• and
• e) introducing the chrome-based catalyst system into the reactor;
• characterized in that the amount of polymer particles in the fluidized bed is substantially maintained in the polymerization zone during the transition steps;
• and wherein the deactivating agent is selected from the group consisting of C1 to C20 carboxylic acids and di-carboxylic acids, C2 to C20 anhydrides, C2 to C20 esters, carbonic acids and esters, carbon dioxide, and mixtures thereof.

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, the polymerization reactions being conducted in a polymerization zone of a gas phase fluidized bed reactor which contains a fluidized bed of polymer particles and monomer gases, the transition comprising the steps of:

• 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 to the reactor a deactivating agent into the fluidized bed;
• d) establishing optimal conditions within the reactor for the chrome-based catalyst system;
• and
• e) introducing the chrome-bed catalyst system into the reactor;
• characterized in that the amount of polymer particles in the fluidized bed is substantially maintained in the polymerization zone during the transition steps;
• and wherein the transition comprises less than or equal to 5 volume turnovers of monomer gases.

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, the polymerization reactions being conducted in a polymerization zone of a gas phase fluidized bed reactor which contains a fluidized bed of polymer particles and monomer gases, the transition comprising the steps of:

• 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 to the reactor a deactivating agent into the fluidized bed;
• d) establishing optimal conditions within the reactor for the chrome-based catalyst system;
• and
• e) introducing the chrome-based catalyst system into the reactor;
• characterized in that the amount of polymer particles in the fluidized bed is substantially maintained in the polymerization zone during the transition steps;
• and wherein the gas phase fluidized bed reactor comprises an inside wall at the polymerization zone, and wherein the temperature of the inside wall is maintained to within 1 to 60° C. below the polymerization temperature.