This paper addresses the feasibility of controlling the entire molecular weight distribution of the produced polymer in gas-phase ethylene polymerization reactors. Nonlinear model predictive controller is used to attain the control objective by utilizing the hydrogen feed rate as the only manipulated variable. The use of other manipulated variables is limited to avoid disturbing the process when influential inputs such catalyst and/or monomer inflows are used. The simulation results indicated successful implementation of the control algorithm to achieve the desired molecular weight distribution. The success depends on the improved hydrogen activities inside the reactor through a modified catalyst that is responsive to hydrogen variation and a wider admissible range of hydrogen feed rates.

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