Abstract: Process for stopping and restarting a polymerization in a system having a gas phase fluidized bed or stirred bed reactor, a degassing vessel and a seedbed storage silo, by conducting a first polymerization in the reactor using a polymerization catalyst to produce a first polymer, stopping the polymerization and removing the first polymer from the reactor to the degassing vessel, and either: introducing from the seedbed storage silo into the reactor a different seed-bed compatible with a second polymerization, passing to the seedbed storage silo the first polymer from the degassing vessel to form a new seedbed in the storage silo, and conducting the second polymerization in the reactor to produce a second polymer; or passing to the reactor at least a portion of the first polymer from the degassing vessel to thereby form a new seedbed in the reactor, and conducting a polymerization in the reactor to produce polymer.

Abstract: The present invention relates to a process for stopping and restarting polymerisation in a polymerisation system comprising a gas phase fluidised bed or stirred bed reactor, a degassing vessel and a seedbed storage silo, said process comprising the steps of: a) Conducting a first polymerisation reaction in the reactor using a first polymerisation catalyst system to produce a first polymer, b) Stopping the first polymerisation reaction and removing at least the majority of the first polymer in the reactor to the degassing vessel, and either: c1) Introducing from the seedbed storage silo and into the reactor a seed-bed compatible with a second polymerisation reaction, said seed-bed being of a different material to the first polymer, d1) Passing to the seedbed storage silo at least a portion of the first polymer from the degassing vessel to thereby form a new seedbed in the storage silo, and e1) Conducting the second polymerisation reaction in the reactor to produce a second polymer; or c2) Optionally, maintaini