Properties of molecular sieve membranes

Abstract: Zeolites are crystalline aluminosilicates with molecular sieving properties and are widely used in industry for catalysis, sorption and ion-exchange applications. Zeolite membranes are commercially interesting since this technology may be employed for continuous separation of molecules under severe conditions. MFI zeolite has suitable pore diameter for many applications and relatively high thermal and chemical stability. Zeolite films in membranes must be thin, to obtain a high flux and free from defects for high selectivity. Many parameters are affecting the properties of zeolite films and in this thesis some of them are investigated. MFI zeolite membranes were prepared using seed crystals and hydrothermal synthesis and characterized with scanning electron microscopy, single gas permeation measurements, porosimetry and separation experiments. Membranes grown in one or several steps with seeding in-between the synthesis steps were compared. It was observed that membranes comprised of small crystals and consequently high concentration of grain boundaries had low separation performance. Grain boundaries could also be opened by extensive rinsing, which reduced membrane quality. The influence of the calcination rate on the performance of zeolite membranes of a particular type was also studied. It was demonstrated that the calcination rate does not affect the membrane quality.