PROCESS FOR TRANSITIONING FROM THE PRODUCTION OF A FIRST POLYMER TO THE PRODUCTION OF A SECOND POLYMER IN A GAS PHASE FLUIDISED BED OR STIRRED BED REACTOR

摘要

The present invention relates to a process for transitioning from the production of a first polymer to the production of a second polymer in a gas phase fluidised bed or stirred bed reactor, 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 polymer in the reactor, c) Introducing into the reactor a seed-bed comprising at least 50ppm of contaminants, wherein the seedbed has been maintained under at least 50ppm but less than 500ppm of contaminants during storage d) Treating the seed-bed in the reactor to reduce the amount of contaminants, e) Conducting a second polymerisation reaction in the reactor to produce a second polymer.