Investigation of Hexane Diffusion in HDPE Particulates for Drying Applications

Diffusion of n-hexane in high-density polyethylene (HDPE) particulates was studied by nitrogen purging of a hexane-permeated HDPE sample in a small glass cell. By monitoring the decrease in hexane concentration in the cell exit gas, the diffusivity of hexane in HDPE was obtained. The method does not require any alteration of the original HDPE specimen and allows both the intrinsic and effective diffusivities to be determined. Intrinsic diffusion data measured for HDPE powder and pellets using this method were compared with those from HDPE sheets to show the unique diffusion characteristics of the powder. Experimental results at various purge flows revealed that the effective hexane diffusivity in the HDPE powder increased with gas purge velocity before reaching a plateau representing the intrinsic diffusivity. The low effective diffusivity values at low purge velocities can be attributed to particle agglomeration in the powder. The effective diffusivity data for unaltered powder samples have great practical significance in characterizing industrial powder dryers.