Mass transfer in olefin polymerization: estimative of macro- and microscale diffusion coefficients through the swollen polymer

Diffusion coefficient of propylene through polypropylene and ethylene through polyethylene, both in toluene and nn-hexane, were estimated taking into account structural parameters of polymer chain and diffusing compound. In order to evaluate the influence of the structural variables considered in the prediction of the diffusivity and the swelling effects of the solvents, dynamic simulations of the metallocene-based slurry polymerization of propylene were performed using the assumptions of the multigrain model. The solvent influence was found to be more pronounced on the MAO diffusion, which is a larger molecule than the monomers propylene and ethylene. For nn-hexane, the screening effects of the polymer chains were shown to hinder the diffusion of large molecules. The monomer concentration along the macro- and microscale particles was found to be quite constant, what can be attributed to the slight influence of the monomer diffusive transport in slurry polymerization of olefins, which is in agreement with the literature.