Modeling Low-Density Polyethylene (LDPE) Production in Tubular Reactors: Connecting Polymerization Conditions with Polymer Microstructure and Rheological Behavior

The production of low-density polyethylene (LDPE) in high-pressure tubular reactors is widely studied due to its extensive use worldwide. Reaction conditions have a crucial impact on the polymer molecular architecture, which, in turn, influences the rheological behavior of the polymer in the molten state, a very important variable during subsequent processing. Up to now, the relationships between reactor polymerization conditions, polymer microstructure, and final rheological properties are not completely established, although they could be a very useful tool for rapid process control and optimization. This work presents an integrated model of the high-pressure polymerization of ethylene in tubular reactors, consisting of the combination of a deterministic model of the tubular reactor that calculates molecular properties of the polymer and an empirical rheological model for branched molecules. The integrated model predicts conversion, temperature, and average molecular properties, as well as the bivariate molecular weight-long chain branching distribution, the branching index, and the shear viscosity flow curve for LDPE under different operating conditions. Results compare well with experimental data of an actual industrial reactor. Additionally, the effect of polymerization conditions on molecular and rheological properties is analyzed.