Patent ID: 7847036

Claim:
A method for controlling a transition from an initial polymerization reaction to a target polymerization reaction in a fluidized bed reactor, where the initial polymerization reaction is to produce polymer product with properties that meet a first specification set, the target polymerization reaction is to produce polymer product with properties that meet a second specification set including a target density range for the product, and a concentration ratio and a feed ratio for the transition are controllable, said method including the steps of: (a) during the transition, maintaining a first one of the concentration ratio and the feed ratio at an at least substantially constant value while implementing process changes in an effort to bring produced polymer into compliance with the second specification set and monitoring without controlling the other one of the concentration ratio and the feed ratio to generate first data; and (b) during the transition, determining from the first data whether polymer having excessively low density is likely to be produced during the transition, and upon determining from the first data that polymer having excessively low density is likely to be produced during the transition, maintaining during the remaining portion of the transition said other one of the concentration ratio and the feed ratio at a value that is at least substantially constant while allowing the first one of the concentration ratio and the feed ratio to vary.