Fabrication of pure-phase CHA zeolite membranes with ball-milled seeds at low K⁺ concentration

CHA zeolite membranes were hydrothermally synthesized by secondary growth method. Original and ball-milled seeds were compared for induction of CHA zeolite membranes. The synthetic parameters were investigated extensively in terms of seed size, precursor composition and crystallization temperature. Impurity MER phase was readily generated in membrane layers when using original CHA seeds (average particle size ∼ 3.80 μm) in an individual K⁺-containing synthetic medium. Comparatively, pure phase CHA zeolite membranes could be obtained by induction of ball-milled seeds in a broad SiO₂/Al₂O₃ ratio and at a low K⁺ concentration. The as-synthesized membranes showed better separation performance than those induced with original seeds. Typically, the CHA zeolite membrane synthesized at 433 K for 20 h in a synthesis gel of 11 SiO₂:1 Al₂O₃:1 K₂O:1 Na₂O:550 H₂O showed a water permeation flux of 2.5 kg m^-2 h^-1 and separation factor of 2980 for pervaporation dehydration of 90 wt.% ethanol solution at 348 K. The CHA zeolite membrane synthesized with ball-milled seeds was stable for dehydration of acidic ethanol solution (pH ∼3) at 348 K while the membrane induced with original seeds showed a declined separation behavior.