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Organosilica membranes for gas separation were prepared by plasma-enhanced chemical vapor deposition (PECVD) using three different types of silicon precursors: hexamethyldisiloxane (HMDSO), trimethylmethoxysilane (TMMOS), and methyltrimethoxysilane (MTMOS). Based on gas permeation measurement, the MTMOS-derived membrane showed the highest He/N 2 selectivity, followed by the TMMOS-derived and HMDSO-derived membranes. FT-IR characterization indicated that the HMDSO-derived membrane had the highest content of methyl group and the lowest Si-O-Si, while the methyl group content for the MTMOS-derived membrane was the lowest and Si-O-Si was the highest. These results suggest that the pore size of organosilica membranes could be tuned by changing the chemical structure of the silicon precursor. The MTMOS-derived membrane was further heat-treated to determine the effect of thermal annealing on gas-permeation properties. The gas permeances were drastically improved by the thermal annealing. After heat-treatment at 500C, the membrane showed a high H 2 permeance of 6.5  10 -7 mol/(m 2 s Pa) with a H 2 /SF 6 selectivity of 410 at 200C, and 5.6  10 -7 mol/(m 2 s Pa) with a H 2 /SF 6 selectivity of 360 at 50C.

Bipolar membrane electrodialysis is applied to CO 2 recovery from alkaline carbonate solution. CO 2 in flue gas is captured by an alkaline hydroxide absorbing solution to form an alkaline carbonate solution. The captured CO 2 is recovered from the alkaline carbonate solution via bipolar membrane electrodialysis, and the alkaline solution is regenerated simultaneously. To reduce the power requirement for CO 2 recovery, this study considers optimal design and operation. Three membrane arrangements were compared, and the results indicate the membrane arrangement comprising a bipolar membrane and cation exchange membrane is the most energy saving. With further optimization of operation conditions, the minimum power requirement for CO 2 recovery was reduced to 2.1 MJ/kg-CO 2 (or 2.1 GJ/t-CO 2 ).

Organosilica membranes were fabricated using bridged organoalkoxysilanes (bis(triethoxysilyl)methane (BTESM), bis(triethoxysilyl)ethane (BTESE), bis(triethoxysilyl)propane (BTESP), bis(trimethoxysilyl)hexane (BTMSH), bis(triethoxysilyl)benzene (BTESB), and bis(triethoxysilyl)octane (BTESO)) to produce highly permeable molecular sieving membranes. The effect of the organoalkoxysilanes on network pore size and microporous structure was evaluated by examining the molecular size and temperature dependence of gas permeance across a wide range of temperatures. Organosilica membranes showed H2/N2 and H2/CH4 permeance ratios that ranged from 10 to 150, corresponding to network pore size, and both H2 selectivity decreased with an increase in the carbon number between 2 Si atoms. Organosilica membranes showed activated diffusion for He and H2, and a slope of temperature dependence that increased approximate to the increase in the carbon number between 2 Si atoms. The relationship between activation energy and He/H2 permeance ratio for SiO2 and organosilica membranes suggested that the molecular sieving can dominate He and H2 permeation properties via the rigid microporous structure, which was constructed by BTESM and BTESE. With increased in the carbon concentration in silica, polymer chain vibration in organic bridges, which is a kind of solution/diffusion mechanism, can dominate the permeation properties. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4491–4498, 2017

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Hybrid organosilica membranes have become attractive for industrial applications because of high performance and long-term stability. This work investigated the influence of water vapor on CO2 gas permeation through the hybrid membranes. Two types of organoalkoxysilanes, bis­(triethoxysilyl)­ethane (BTESE) and bis­(triethoxysilyl)octane (BTESO), were used as precursors to prepare membranes via the sol–gel method. The two membranes showed distinct properties of porosity and water affinity because of the differences in the bridging methylene numbers between the two Si atoms. Under dry conditions, the BTESE and BTESO membranes showed CO2 permeances as high as 7.66 × 10–7 and 6.63 × 10–7 mol m–2 s–1 Pa–1 with CO2/N2 selectivities of 36.1 and 12.6 at 40 °C, respectively. In the presence of water vapor, CO2 permeance was decreased for both membranes, but the effect of water vapor on CO2 permeation was slighter for BTESO membranes than it was for BTESE membranes because of more hydrophobicity and denser structures with a longer linking-bridge group. The hybrid organosilica membranes both showed good reproducibility and stability in water vapor.