Templated nanostructure silica membrane versus template-free one: Synthesis, characterization, and performance for hydrogen separation

An experimental study was carried out on synthesis and performance of the MTES (methyltriethoxysilane) templated and template free nanostructure silica membranes for hydrogen separation. The permeance of hydrogen, carbon dioxide and nitrogen pure gases and permselectivity and separation factor of gas mixtures were investigated at 25 °C, 100 °C and 200 °C. Activated molecular sieve with positive and negative sign and Knudsen diffusion were respectively the dominant transport mechanisms in hydrogen, carbon dioxide and nitrogen gas molecules permeances.  Although, the hydrophobic property of templated membrane is a good option for gas separation in hydrothermal conditions, the dense structure of the membrane results in lower permeances and permselectivities in comparison with template free one. Hydrogen permeance at 200 ºC and 3 bar which was measured 30.5×10-8  for template free silica membrane, decreased to 2.37  for MTES templated silica membrane. Permselectivity and separation factor of H2/N2 at the same conditions, which were 31.2 and 21 for template free membrane, reached to 21.5 and 8 for templated membrane. In addition, H2/CO2 permselectivity at the same conditions was measured for template free and templated membranes, 23.4 and 13.9, respectively.