EFFECT OF SODA CONCENTRATION ON THE MORPHOLOGY OF MFI-TYPE ZEOLITE MEMBRANES

MFI-type zeolite membranes were hydrothermally synthesized as a thin layer on macroporous α-alumina discs coated with 1µm MFI-type seed crystals as seed. The effect of soda (Na₂O) concentration on the morphology of the membranes was investigated. Soda concentration, and thus the hydroxyl ion concentration, was changed between 0.25 and 6.5 mol/mol gel. At low soda concentrations the crystals forming the layer exhibited mostly (h0h)/c-axis orientation, but at high soda concentrations a membrane layer formed from randomly oriented crystals. The membranes showed high H₂/n-butane ideal selectivity of 476 and 36 at 25°C and 150°C, respectively.