Synthesis and gas permeation properties of chabazite-type titanosilicate membranes synthesized using nano-sized seed crystals

Chabazite (CHA)-type zeolite membranes have received considerable attention regarding their high permeance and separation performance. A recent report detailing a unique preparation procedure for a CHA-type titanosilicate (Ti-CHA) zeolite-in which titanium heteroatoms were incorporated into the zeolite framework by substitution of aluminum-demonstrates excellent physico-chemical properties when compared with conventional aluminosilicate CHA-type zeolites. In this study, the synthesis of Ti-CHA zeolite membranes (Ti-CHA membrane) was investigated. The Ti-CHA membrane was synthesized on an alumina support via a secondary growth method using Ti-CHA zeolite seed crystals. The Ti-CHA membrane properties were studied as a function of seed crystal size. The average particle diameter was observed to reduce from 2.3 mu m to 450 nm by increasing the loading of Ti-CHA into the synthesis gel. Regardless of the seed crystal particle size, the presence of CHA-type zeolites on the alumina support was confirmed by x-ray diffraction. UV-Vis demonstrated the incorporation of titanium heteroatoms into the zeolite framework. The results indicated the successful synthesis of the Ti-CHA membrane regardless of the seed crystal particle size. Additionally, the membrane thickness decreased by using the seed crystal. Single gas permeation tests showed that the thinnest Ti-CHA membrane prepared in this study exhibited a relatively high CO2 permeance of 1.5 x 10(-6) mol m(-2) S-1 Pa-1, compared with that of previously reported CHA-type zeolite membranes. The influence of moisture on the separation performance of the Ti-CHA membrane was evaluated in the presence of gas mixtures composed of CO2, methane and H2O ranging from 0.1 to 5 vol%. In the presence of 1 vol% H2O, the CO2 permeance and selectivity were only marginally reduced as a result of the highly hydrophobic pore structure.