On the effect of morphological features on the properties of MFI zeolite membranes

MFI type zeolite membranes were prepared on alumina and stainless steel tubular supports by different synthesis procedures, giving rise to different zeolite layer structures and distributions of zeolite material with respect to the support. This was used as a base to establish a classification of zeolite membranes. SEM and EPMA analysis showed clear differences among different types of MFI zeolite membranes, concerning the morphology and location of the zeolite deposits. Three types of membranes were identified, namely: type-A membranes, in which the zeolitic material was located mainly inside the support pores; type-B membranes, with a thin layer of randomly oriented crystals on top of the support; and type-C corresponding to MFI c-oriented membranes. These morphological differences translated into diverse qualitative and quantitative behavior of the corresponding membranes, as shown by the evolution of single-gas permeances and separation selectivity with temperature, and by adsorption and temperature-programmed desorption experiments.