Innovative methods for preparation and testing of Al2O3 supported silicalite-1 membranes

The aim of the present study is to develop a novel type of zeolite membrane and exploit some of the inherent and unique advantages of this membrane in gas separations. The development of inorganic membranes formed from a coherently grown layer of zeolite crystals is a particularly promising approach, since such membranes offer substantially higher permeabilities and selectivities compared with polymeric materials and can perform under extreme conditions, e.g. at elevated temperatures and in aggressive chemical environment. Such zeolite membranes are prepared by in-situ hydrothermal synthesis of zeolite layer within the macropores of alumina ceramic supports (tubes/discs). In this way more stable zeolite membranes are produced, avoiding outer separating layers which are prone to mechanical damage. These membranes have also been shown to have good thermal stability up to 500°C, with no evidence of crack formation. The synthesized materials have been characterized by several techniques such as Hg and N2 porosimetry, scanning electron microscopy (SEM), and X-ray diffraction (XRD). From these measurements it appears that the structure of the zeolite membrane is influenced by several factors, such as structure and size of the pores of the support, chemical composition of the precursor solution from which the crystals will be harvested, reaction conditions, etc. Finally, gas permeabilities and/or selectivities have been measured for several important gas systems. The results of this study indicate the important role of influencing the outcome of the crystal formation by controlling the conditions of the hydrothermal treatment in obtaining optimum gas permeabilities and/or selectivities of these systems.