Broadening the Polyethylene Molecular Weight Distribution by Periodic Variation of the Hydrogen Feed Rate

摘要

The ability to control the molecular weight distribution of the created polyethylene in gas-phase fluidized-bed reactors is discussed. This objective is achieved via nonlinear model predictive controller utilizing the hydrogen feed rate as the only manipulated variable. The idea for limited usage of manipulated variables is to avoid economically unfavorable operations such as excessive purge and/or reduced production rate. The simulation results indicated successful implementation of the control algorithm to attain the desired molecular weight distribution. The success depends on the improved hydrogen activities inside the reactor by employing a modified catalyst that is responsive to hydrogen variation and allowing a wider range for hydrogen feed rates.