Modeling Low-Density Polyethylene Polymeryzation in a Multizone-Autoclave Using Coupled Computational Fluid Dynamics and Monte-Carlo Simulation

The industrial production of low-density polyethylene (LDPE) takes place at temperatures of up to 300 °C and pressures of up to 3000 bar. The properties of the polymer are closely linked to the reaction conditions through the reaction rates of the exothermic radical polymerization, which are determined by pressure, temperature and the concentrations of the species in the system which are influenced by the mixing behavior. To model the complex interplay of these factors, Computational Fluid Dynamics (CFD) simulations are a powerful tool. CFD allows for the calculation of flow fields by solving the conservation equations for mass, momentum and energy while incorporating the polymerization kinetics for the LDPE polymerization. Based on the converged CFD simulation, it is possible to divide the reactor into several compartments [1], which are assumed to be perfectly mixed continuously stirred tank reactors (CSTR). With a subsequent Monte-Carlo simulation it is possible to determine the molecular weight distribution (MWD) of the polymer. Building on previous work that focused on modeling continuous polymerization in a 100 mL mini-plant autoclave [2,3], this work focuses on modeling a 300 mL multi-zone autoclave that has recently been commissioned [4]. Based on the experimental conditions, a CFD simulation is carried out to compare the simulated results with the experimental data obtained from the size exclusion chromatography (SEC).