Doped microporous hybrid silica membranes for gas separation

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, crosssectional 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, SF 6 permeable) pore microstructure, showing high permeances of larger gas molecules, while having a crosssectional thickness comparable to undoped BTESE membranes. Graphical Abstract& Louis Winnubst a.j.a.winnubst@utwente.nl;

Structure–property tuning in hydrothermally stable sol–gel-processed hybrid organosilica molecular sieving membranes

“…12. This suggests that densification effects due to thermal degradation of the ethylene bridge may have led to small enough pores for the Nb center to have an appreciable effect on CO 2 transport in the study of Qi, while the same sites did not influence CO 2 permselectivity in an intact BTESE-based matrix as in the study of Qureshi et al [89] Recently, a malonamide-functional membrane with an ability to disperse transition metal ions homogeneously throughout the matrix was reported [17]. Both Ce 4? and Ni 2?…”

“…Qi et al explained these effects by the formation of acidic Nb sites in the matrix structure [20,87], but also by possible densification effects due to the very high thermal annealing temperature for BTESE (400-550°C in N 2 ) [86], temperatures at which thermal degradation of the organic bridges may have occurred [61,86]. Other dopants that have been introduced into BTESE and BTESM matrices by co-condensation are aluminum (Al) [88], boron (B) and tantalum (Ta) [89]. In the latter study, a much lower thermal annealing temperature of 300°C (in N 2 ) was employed.…”

“…Reprinted from Ref. [89] resistant to high temperatures and hydrothermal conditions, they show some degree of performance loss over time. A slow degradation of the flux of 3-4 %/month at 150°C was already reported in the first pervaporation studies [7,19].…”

Hybrid Materials for Molecular Sieves

“…This was explained by the formation of acidic Nb sites in the matrix structure leading to strong gas adsorption. The same approach was also pursued for BTESE-derived silica (Qi et al 2010(Qi et al , 2012Qureshi et al 2015), but in these cases, the phenomenon was either observed or not, depending on the pretreatment of the BTESE membrane. Low CO 2 permeances were observed when the system was annealed at high temperatures (400-550 C in N 2 ) (Qi et al 2012) but not when lower annealing temperatures (300 C in N 2 ) were employed .…”

Metal doped hybrid silica for hydrothermally stable hydrogen separation membranes

“…This lower permeance is an indication for network densification. Qureshi et al [41] investigated Nb doping to BTESE as well, though they were not successful in reproducing the low CO 2 permeance and high H 2 /CO 2 Qureshi et al [41] investigated, besides niobia doping, also boron and tantalum doping. The tantalum doped BTESE membrane showed a similar permeance and selectivity as the niobium doped membrane as described above.…”