Hydrothermal stability of fluorine‐induced microporous silica membranes: Effect of steam treatment conditions

Abstract

AbstractA fluorine‐SiO2 membrane was prepared using triethoxyfluorosilane (TEFS) as a Si precursor, and its hydrothermal stability was evaluated. The TEFS membrane calcined at 750°C had fewer Si‐OH and Si‐F groups in its network structure and showed H2 permeance that was greater than 10−6 mol m−2 s−1 Pa−1 with H2/N2 and N2/SF6 permeance ratios of 10 and 210, respectively. This membrane performance was relatively stable under the temperature (< 500°C) used for steam treatment, regardless of the steam partial pressure (30, 90 kPa). On the other hand, when the steam treatment temperature was increased beyond 500°C, gas permeance decreased significantly and the membrane became highly selective for He and H2 over smaller molecules (He/N2: > 600, H2/N2: > 100). The relationship between the activation energy of H2 and the permeance ratios (He/H2, He/H2O, H2/H2O) of a TEFS‐derived membrane under steam treatment higher than 600°C resulted in a network pore size that approximated in conventional microporous SiO2 membranes.