Diffusivity of Multicomponent Gas Mixtures in Polyethylene

Abstract

A study of the multicomponent diffusion of important processes gases in linear low density polyethylene is presented. It is demonstrated that, much like in the case of multicomponent solubilities, one cannot use pure component diffusivities to predict mass transfer rates in multicomponent systems. It is postulated that interaction between the penetrant species and the polymer modifies the free volume in a concentration-dependent manner, so it is necessary to consider the gas phase composition when calculating realistic diffusion coefficients. In addition, describing the particle morphology as an assembly of normally distributed characteristic length scales is proposed. This allows one to better fit the experimental data, and is a coherent description of experimentally observed particle morphology.

Multiscale modelling of multizone gas phase propylene (co)polymerization reactors—A comprehensive review

“…They also appear to depend on the crystallinity [ 129 ] and eventually the MWD (at least for LLDPE) of the polymer phase. [ 108 ] Care must be taken, in particular, if we need to precisely model quantities such as the MWD or CCD to avoid ‘biasing’ true parameter values with poor estimates of thermodynamic properties.…”

“…For example, in the polyethylene system in the presence of ICA, the diffusivity of both ethylene and ICA is affected by the presence of the other species. [105] Ben Mrad et al [108] recently estimated the diffusion coefficient of different gas species in amorphous PE in multi-component systems using a magnetic suspension balance and observed a codiffusivity effect in most cases. For more details on this topic, the reader may refer to the above-mentioned papers; this is not discussed in the current paper.…”