2.4. Characterization
The crystallographic properties of the ZSM-5 seeds and tubular zeolite membranes, were examined using an X-ray diffractometer, XRD (Simense D5000 diffractometer using Cu Kα radiation (α=1.54 Å)). The cross-section and surface morphology of ZSM-5 membranes, α-alumina tubular supports, and ZSM-5 seeds were evaluated using scanning electron microscopy, SEM (FESEM, Leo, S430i). The Si/Al ratio of the surface and cross-section of the zeolite layer was measured by energy-dispersive X-ray spectroscopy (EDX, Leo, S430i). The average particle size and the particle size distribution of ZSM-5 nano-seeds were characterized by a laser scattering particle analyzer (Zetasizer, Nano-ZS90, Malvern, UK).
The synthesized ZSM-5 tubular zeolite membranes were then mounted into a sealed stainless-steel dead-end special membrane module in order to perform N2 and SF6 single-gas permeation experiments. The gas permeation tests were performed at 25 ˚C and a transmembrane pressure range of 100 - 300 kPa. The permeate flux was measured using a bubble flow meter during the gas permeation test. The gas permeances (Eq. 1) and ideal selectivity (the ratio of gas permeances obtained in single-gas permeation tests) were used to determine the quality of prepared membranes. The reported gas permeation data were the mean values of multiple measurements in this study.