Microporous inorganic membranes for gas separation and purification

The importance of inorganic membranes for gas separation and purification is analyzed. Although the cost of inorganic membranes is higher than that for polymeric membranes, they have higher permeance, selectivity and better resistance to higher pressure and temperature. The main materials used for porous inorganic membranes are alumina (Al2O3), silica (SiO2), zirconia (ZrO2), zeolite and carbon. Ceramics are compounds of metallic and non-metallic elements. They generally have a macroporous support, an intermediate layer and a small porous top layer. Because the Knudsen gas separation regime has a very low selectivity, various membrane surface modification techniques have started to be experimented with at a number of laboratories. The research focuses on materials that exhibit molecular sieving properties, such as silica, zeolites, MOFs (metal-organic frameworks), graphene and carbon. Finally, gas transport mechanisms through porous membranes are summarized.