Diffusion measurements of isopentane, 1‐hexene, cyclohexane in polyethylene particles by the intelligent gravimetric analyzer

The diffusion coefficients of isopentane ( i ‐C 5 H 12 ), 1‐hexene (C 6 H 12 ), cyclohexane (C 6 H 14 ) in polyethylene particles were measured by a highly sensible microbalance—intelligent gravimetric analyzer, using the desorption method with N 2 as a bypassing gas. Both the effective diffusion coefficients ( D eff ) and dilute diffusion coefficients ( $D_{{\rm{eff}}}^\sim $ ) were measured simultaneously. It was found that $D_{{\rm{eff}}}^\sim $ was about one magnitude smaller than D eff and the logarithmic form of $D_{{\rm{eff}}}^\sim $ was linear with that of D eff . In addition, the effects of particle size and distribution, polymer properties (e.g., the crystallinity and melt index), and operating conditions (e.g., temperature and pressure) on D eff were systematically investigated. The results showed that D eff increased linearly with the increase of the square of particle size. The diffusion behaviors of hydrocarbons in polyethylene are of great importance in the polymerization and purging processes. © 2010 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013