Single-step process to produce alumina supported hydroxy-sodalite zeolite membranes

Membranes based on zeolites have been extensively studied and used to purify/separate H2 or CO2 or other gases, depending on their composition. The deposition of zeolite films onto porous, chemically and thermally stable, substrates can increase their stability, but the production process may require lengthy two-step procedures. In this work, a single-step method was developed for the production of homogeneous hydroxy-sodalite (HS) zeolite films, without seeding and by direct deposition during hydrothermal treatment on cheap and porous alumina substrates. Alumina substrates have been developed with fine porosity (> 35% porosity, 500–600 nm of mean pore diameter), with low resistance to gas flow but reduced surface porosity to favour the deposition of dense films. The single-step growth of HS films with a thickness ranging from a few to 28 μm on alumina was successfully achieved. These membranes have been tested in hydrogen, methane, carbon dioxide and nitrogen, and good results in terms of hydrogen permeance and separation performance were achieved for 10–12-μm-thick HS films on alumina.