Healing of Microdefects in SSZ-13 Membranes via Filling with Dye Molecules and Its Effect on Dry and Wet CO₂ Separations

It is quite challenging to avoid microdefect formation during hydrothermal growths and/or calcination processes, while manufacturing high-quality zeolite membranes in a reproducible manner. Even less than 1% of defects, which generally provide nonselective pathways, will considerably worsen the intrinsic, high molecular sieving-based separation performance of a continuous zeolite membrane. Herein, we propose a simple and reliable method for blocking defects using water-soluble dye molecules, which were originally used for the visualization of nonzeolitic, defective structures in a zeolite membrane. Because the dye molecules are ∼1 nm in size, they cannot diffuse into the zeolitic pores and selectively access the defects. For the demonstration of dye-based defect healing, we chose a siliceous chabazite type SSZ-13 zeolite membrane (pore size = 0.37 × 0.42 nm²) with some degree of defects and investigated the effect of defect healing on the final CO₂ separation performance. Because the defects were gradually filled by the dye molecules, both CO₂/N₂ and CO₂/CH₄ separation performances were concomitantly increased. Intriguingly, the CO₂ perm-selectivity test with ternary mixtures including H₂O vapor (the third largest component in the flue and natural/shale/bio gas streams) in the feed diminished CO₂ separation performance. This could be ascribed to inhibited transport of the fast permeating species, here CO₂, from the adsorbed H₂O molecules on the dye-treated and water-friendly (relatively hydrophilic) membrane surface. On the contrary, the intact, siliceous (water-repelling or hydrophobic) SSZ-13 membranes showed improved CO₂ perm-selectivities in the presence of H₂O vapor, seemingly due to defect blocking by the physisorbed H₂O molecules.