Patent ID: 6867270

Claim:
A process for transitioning from a first polymerization reaction using a first catalyst system to produce a first polymerization product to a second polymerization reaction producing a second polymerization product wherein the second polymerization reaction is incompatible with the first polymerization catalyst system or first polymerization product in a gas-phase reactor, comprising: (a) after the first polymerization reaction, conducting multiple polymerization reactions in the gas-phase reactor using multiple polymerization catalyst systems, multiple reactor conditions and/or multiple feed streams to form multiple polymerization products; (b) forming a substantially contaminant-free seedbed from each polymerization reaction by removing a portion of the polymerization product from each polymerization reaction and stripping or venting reactants and contaminants from each polymerization product; (c) deactivating catalyst species entrained or contained with each polymerization product without contacting the polymerization product with excess deactivator; (d) optionally, after the deactivation step, stripping or venting reactants and contaminants from each polymerization product; (e) storing each substantially contaminant-free seedbed separately in a storage container under dry inert atmosphere to maintain each seed bed as substantially-free of contaminants; (f) stopping each multiple polymerization reaction; (g) removing the contents of each multiple polymerization reaction from the gas-phase reactor while preventing the introduction of additional or substantial contaminants; (h) selecting a stored substantially contaminant-free seedbed that is compatible with the second polymerization reaction in regards to polymerization product or polymerization catalyst system; (i) introducing the selected substantially contaminant-free seedbed into the gas-phase reactor while preventing the introduction of additional or substantial contaminants to the seedbed and reactor; (j) introducing a second feed system into the gas-phase reactor; (k) introducing a second catalyst system into the gas-phase reactor; and (l) conducting the second polymerization reaction.