Abstract
Hybrid silica (i.e., bis-triethoxysilylethane: BTESE) membranes doped with B, Ta or Nb were made through a sol–gel process. Triethyl borate, tantalum (V) ethoxide (TPE) and niobium (V) ethoxide (NPE) were selected as doping precursors. The doping concentration was optimized to produce sols, suitable for membrane fabrication. Thermal stability, structural analysis, cross-sectional micrographs and single gas permeation experiments were performed on these membranes, and results are compared with an undoped BTESE membrane. It was observed that the synthesized doped BTESE materials and membranes resulted into a more open (and, in one occurrence, SF6 permeable) pore microstructure, showing high permeances of larger gas molecules, while having a cross-sectional thickness comparable to undoped BTESE membranes.
Highlights
Inorganic membranes have attracted considerable attention for their applicability in gas separation processes in conditions where polymeric membranes cannot be used
We report the incorporation of boron and tantalum in the hybrid silica (BTESE) matrix with the aim to fabricate a defect-free, gas selective membrane film
During the synthesis of hybrid silica sols, containing the ethoxides of niobium or tantalum, the system gelled within minutes when adding these ethoxides at the same time to the reaction mixture as the bis(triethoxysilyl) ethane (BTESE) precursor, while a welldefined sol with a small and homogeneous particle size distribution was obtained for pure BTESE under identical conditions [33]
Summary
Inorganic membranes have attracted considerable attention for their applicability in gas separation processes in conditions where polymeric membranes cannot be used. For hybrid silica (i.e., BTESE), only the incorporation of niobia has been reported to date [24, 25], where it is claimed that the introduction of niobia created surface active sites resulting in a reduced CO2 permeance These authors observed that the H2/CO2 permselectivity at 450 °C was higher (i.e., H2/CO2 = 220) compared to hydrogen selectivity over larger molecule such as nitrogen (H2/N2 = 125) and claiming that CO2 permeance through these Nb-BTESE membranes was determined by size exclusion. We report the incorporation of boron and tantalum in the hybrid silica (BTESE) matrix with the aim to fabricate a defect-free, gas selective membrane film. Tantalum is used as a dopant in hybrid silica, to form a relatively denser microstructure than that of undoped BTESE [33] for improved H2/X gas permselectivities
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