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

Abstract

The diffusion coefficients of isopentane (i-C 5H 12), 1-hexene (C 6H 12), cyclohexane (C 6H 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∼ eff) were measured simultaneously. It was found that D∼ eff was about one magnitude smaller than D eff and the logarithmic form of D∼ eff 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. Copyright © 2012 Wiley Periodicals, Inc.