Preparation of a high-silica chabazite-type zeolite membrane with high CO2 permeability using tetraethylammonium hydroxide

High-silica chabazite (CHA)-type zeolite (HS-CHA) crystals and membranes were prepared using tetraethyl ammonium hydroxide (TEAOH) as an organic structure-directing agent. The effect of the hydrothermal synthesis time used for preparation of the HS-CHA crystals on various properties was studied. The crystal structures, Si/Al ratios, amounts of incorporated TEAOH, and morphologies were characterized by X-ray diffractometry, energy dispersive X-ray analysis, thermogravimetry/differential thermal analysis, and scanning electron microscopy, respectively. The results suggested that the CHA-type zeolite crystals were formed after 12 h of hydrothermal synthesis. After 36 h the faujasite (FAU)-type zeolite, which is a precursor of CHA-type zeolite, was transformed completely to HS-CHA crystals. HS-CHA membranes were successfully prepared on an alpha-alumina support by the secondary growth method using TEAOH. This membrane exhibited high CO2 permeance of 3.5 x 10(-6) mol m(-2) s(-1) Pa-1 with an ideal selectivity (CO2/CH4) of 91. This CO2 permeance is twice that of the HS-CHA membrane prepared using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH), which is the conventional organic structure-directing agent for HS-CHA. In addition, TEAOH in the HS-CHA membrane was removed at a temperature 70 degrees C lower than that required to remove TMAdaOH (430 degrees C).