Optimal flowsheet configuration and grade transition policy for tandem polymerization processes based on microstructure

Abstract

In response to increasing market volatility and the demand for high-quality products, this study pursues optimal flowsheet configurations and grade transition policies for tandem polymerization processes based on microstructural quality indices. To achieve this, a generalized continuous process model for tandem polymerization of ethylene with integrated molecular weight distributions (MWD) is established. A comprehensive differential–algebraic equations (DAE) model is then developed, in which dynamic MWD is reconstructed using the orthogonal collocation method. A simultaneous collocation approach is adopted to reformulate the DAE model into a large-scale nonlinear programming (NLP) problem, while a generalized initialization method is proposed to effectively solve the NLP problem. The optimized flowsheet configurations demonstrate high economic potential and flexibility, achieving over 80% monomer conversion and multiple polymer grades. The dynamic optimization methodologies efficiently solve MWD-based grade transition formulations, achieving high-performance control profiles that reduce off-spec products and transition time by over 30%. These methodologies demonstrate significant potential for microstructure-oriented optimization in complex polymerization processes.