Optimal-grade transition strategies for multistage polyolefin reactors

Polymer‐producing companies normally produce many polymer grades in each polymerization reactor train according to customer demands; therefore, many grade‐transition operations are necessary. However, the determination of these optimal strategies is difficult. To solve this problem, several sample simulations showing the optimal solutions of grade‐transition strategies for multistage olefin polymerization reactors with bimodal products were performed. The methodology utilized a dynamic process simulator, POLYRED, coupled to a sequential quadratic programming, nonlinear optimization algorithm, by using two different objective functions with and without state constraints. It is shown that the most beneficial case of using the optimization technology is the grade transition where the hydrogen content in a reactor must be decreased and/or constraints are imposed on state variables.