Preparation of high performance ZSM-5 zeolite membranes for CO2/H2 separation

Abstract High-quality zeolite 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 a variable-temperature/time (VTT) methods. In this method the defects/microcracks in the bottom seed layer, which are filled by smaller seeds, are effectively eliminated using a designed temperature/time profile, resulting in a significant increase in selectivity without scarifying permeance. The effects of number and combination of seed layers, seed particle size, and the synthesis temperature-time profile on the microstructure, N2/SF6 gas permeation, and H2/CO2 separation performance of membranes are evaluated in detail. The synthesized ZSM-5 zeolite 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 ZSM-5 zeolite membranes on alumina supports exhibited a very low H2/CO2 selectivity of 0.1 with CO2 permeance of 3 × 10−5 mol m−2 s−1 Pa−1.