BTESE-derived Membranes Research Articles

Fabrication of a novel microporous membrane based on ZIF-7 doped 1,2-bis(triethoxysilyl)ethane for H2/CO2 separation

The organosilica membranes for gas separation have been studied for approximately ten years, but the separation performance of the membranes is restricted by the trade-off effect. Therefore, the objective of this work is to design H2-selective mixed matrix membranes by combining the good thermal stability of organosilica and remarkable H2/CO2 selectivity of ZIF-7. Herein, we synthesized ZIF-7 nanoparticles with an average size of 60 nm and investigated the effects of ZIF-7 doping content on the separation performance of organosilica membranes. Interestingly, it absolutely was found that with the doping content of ZIF-7 increased, H2 permeance of ZIF-7/BTESE (1,2-bis(triethoxysilyl)ethane) membranes remained basically unchanged, whereas the permeance of larger molecular gases displayed a dramatically drop. The membrane, when the molar ratio of ZIF-7: BTESE = 0.2, showed the remarkable H2/CO2 (22.7) and H2/N2 (159) selectivity, with a comparatively outstanding H2 permeance at 8.0 × 10−7 mol m−2 s−1·Pa−1. Our results firstly reveal that the doping of ZIFs could be strongly influenced by ZIF-7 doping contents, emphasizing the importance of doping of ZIFs for the further studies on nanoparticles-doped BTESE-derived membranes.

Tuning the microstructure of organosilica membranes with improved gas permselectivity via the co-polymerization of 1,2-bis(triethoxysilyl)ethane and 1,2-bis(triethoxysilyl)methane

1,2-bis(triethoxysilyl)ethane (BTESE)-derived membranes have proven thermal and hydrothermal stability and molecular sieving properties. However, BTESE-derived membranes still have low gas permselectivity due to their loose structure. Herein, we propose a novel strategy of co-polymerization using precursors of both BTESE and 1,2-bis(triethoxysilyl)methane (BTESM) to improve the gas permselectivity of BTESE-derived membranes. BTESM is introduced into BTESE network and the microstructure can be adjusted by different molar ratios of BTESE to BTESM. We find that, as the content of BTESM increase, H2 permeations of BTESE-BTESM membranes remain nearly constant, while the permeations of larger gases (CO2 and N2 etc.) exhibit a greatly decreased. The membrane with a molar ratio of BTESE:BTESM = 3:7 exhibits the highest H2/CO2 (11.3) and H2/N2 (26.8) permselectivity while having a relatively high H2 permeance (1.52 × 10−6 mol m2 s−1⋅Pa−1). Our findings may provide novel insights into preparation of co-polymerization organosilica membranes with excellent H2/CO2 and H2/N2 separation performance.

Selective water vapor permeation from steam/non-condensable gas mixtures via organosilica membranes at moderate-to-high temperatures

The removal of water vapor from humid gas streams is important for steam recovery in power plants and reaction enhancement in a membrane reactor that produces water as a by-product, and so on. The prospect of future applications for organosilica membranes in these fields prompted the present investigation of humid gas separation properties via 1,2-bis(triethoxysilyl)ethane (BTESE)-derived membranes. In this work, binary humid gas separation (H2O/H2 and H2O/N2) was performed on BTESE-derived membranes at temperatures ranging from 80 to 200 °C under feeds of water mole fractions ranging from 0.1 to 0.9. Permeance and the permeance ratios of H2O/H2 and H2O/N2 were confirmed to be dependent on temperature and vapor pressure, and found to be correlated using the water adsorption potential, which accounted for both the temperature and the vapor pressure. The highest levels of water permeate flux, permeance, and permeance ratios of H2O/H2 and H2O/N2 were 37 kg/(m2 h), 5.5 × 10−6 mol/(m2 s Pa)), and 84 and infinity (>6700), respectively, at 150 °C where the partial pressure difference of water across the membrane was 107 kPa. The high performance of BTESE-derived organosilica membranes shows promise for their future applications in humid gas separation at moderate-to-high temperatures.

Improved thermal and oxidation stability of bis(triethoxysilyl)ethane (BTESE)-derived membranes, and their gas-permeation properties

High-temperature treatment (550–700 °C) under N2 increased the thermal stability and oxidizing resistance of BTESE-derived membranes with excellent H2 permeance and selectivity.

Pervaporation of acetic acid aqueous solutions by organosilica membranes

Abstract Organosilica membranes were prepared from bis(triethoxysilyl)ethane (BTESE) by sol–gel processing and applied to the dehydration of aqueous acetic acid (AcOH) solutions in pervaporation. BTESE-derived membranes were found to show high permselectivity with excellent stability. The permeate flux for aqueous AcOH solutions (AcOH: 90 wt%, 75 °C) was 2.0–4.0 kg/(m2 h) with water selectivity of 200–500, corresponding to water permeance of (2.5–5)×10−6 mol/(m2 s Pa). Long-term stability tests in aqueous AcOH solutions revealed that BTESE membranes showed approximately unchanged flux and separation factors, confirming the excellent stability of organosilica membranes. Comparison with gas permeation properties suggests the separation mechanism is dominated by the molecular sieving effect. Concentration dependency was examined for AcOH concentrations ranging from 30 to 90 mol%. An increase in AcOH concentration decreased both water and AcOH permeance, suggesting that adsorbed AcOH on BTESE membranes reduced the effective pore sizes for permeation of the 2 molecules.