Simulation of free radical high-pressure copolymerization in a multizone autoclave: Model development and application

A well-mixed model has been formulated to study the steady-state high pressure free-radical homo- and copolymerization of ethylene and vinyl acetate in an industrial multi-feed multi-zone autoclave reactor system. Using a realistic set of kinetic mechanisms and coefficients, the multizone system is modeled as a simple set of well-mixed tank reactors in series. Results from this representation are compared to experimental data in order to estimate apparent initiator efficiencies in each zone. The model is used to calculate monomer conversion and initiator consumption rate, number and weight average molecular weights, and short and long chain branching frequencies at the exit point of each zone and the whole reactor. The effects of zone temperature, feed temperature, and initiator decomposition kinetics on the steady-state reactor performance and polymer properties are considered and simulation results are compared with the industrial data. While estimated initiator efficiencies provide a clear indication of imperfect mixing in the system, the model representation is still able to provide a reasonable estimate of polymer properties.