TRANSIENT-RESPONSE OF CONTINUOUS-FLOW STIRRED-TANK POLYMERIZATION REACTORS

The transient behavior of polymer properties following a step change in feed conditions during copolymerization in a continuous-flow stirred-tank reactor has been investigated by both modeling and experiment. For kinetics appropriate to Ziegler catalyzed olefin polymerization, the dynamic response of polymer molecular weight and composition is predicted to be relatively slow; four to six reactor turnovers could be required to reach steady state. In addition, response time depends on the direction and magnitude of change and is generally shorter when a property value is decreased. These model predictions were confirmed by measurement of the transient response of copolymer composition and molecular weight for ethylene-propylene-ethylidene norbornene terpolymerization. The model equations also were used to simulate reactor startups, and it was found that steady state following a startup can be reached in about three reactor turnovers. The initial absence of polymer in the reactor causes the dynamic response to be faster for a startup than for reactor control.