Abstract
High-quality ZSM-5 zeolite membranes were successfully synthesized on
the outer surface of tubular α-alumina substrates by manipulating the
microstructure of the zeolite layer using a new different-sized seeding
(DSSM) in combination with variable-temperature/time (VTT) methodd. In
this method the microcracks/defects in the primary seed layer are filled
by smaller seeds and effectively eliminated using a proper
temperature/time profile, resulting in a significant increase in
selectivity without scarifying permeance. The effects of number and
combination of seed layers, seed size, and synthesis conditions on the
microstructure, N2/SF6 gas permeation, and H2/CO2 separation performance
of membranes are evaluated in detail. The synthesized ZSM-5 membranes
show the microstructure of thin, fully inter-grown, and densified
zeolite layer that is responsible for high selectivity without any
negative effect on the permeance. The best synthesized defect-free
membranes exhibited a very low H2/CO2 selectivity of 0.1 with CO2
permeance of 3×10-5 mol m-2 s-1 Pa-1.