Oscillating Boundary Conditions in Supported Olefin Polymerization: Particle-Scale Buffering of Kinetics and Molecular Weight Distribution

In polyolefin reactors, polymer particles move through spatially and temporally varying compositions; it is unclear whether these oscillations materially affect particle-scale kinetics and product microstructure. In this article, we simulate the homopolymerization of olefins in a single heterogeneous catalyst/polymer particle exposed to variable boundary conditions using the polymer flow model. We start by investigating the impact of sinusoidal boundary condition variations on intraparticle monomer concentration profiles using analytical solutions. These simulations show how intraparticle mass transfer resistances and the polymerization itself buffer the interior of the particle from oscillations happening at its surface. The influence of fluctuating monomer and H2 concentrations on polymer molecular weight distribution are also systematically analyzed. Finally, data describing polymer particle trajectories in an industrial reactor are integrated into the model. The simulations show that while oscillatory boundary conditions can affect polymerization rate and polymer molecular weight distribution, they may be safely ignored for most realistic polymerization conditions.