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

摘要

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.