CO₂ Permeation through Hybrid Organosilica Membranes in the Presence of Water Vapor

Abstract

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.

Role of Amine Type in CO2 Separation Performance within Amine Functionalized Silica/Organosilica Membranes: A Review

“…adsorption measurement is a typical approach for the determination of the texture microstructure of micro-to-mesoporous materials, which includes silica-based materials. Following the incorporation of alkylamine moieties, however, a possible dual flexible-rigid network can be formed, and therefore an apparently nonporous structure was observed, as evidenced by the N 2 adsorption/desorption isotherms operated at 77 K. This phenomenon was also generally observed in the cases of organic-rich organosilica membranes, as reported elsewhere [21,24,36]. Figure 6 shows the N 2 adsorption/desorption isotherms of several amine-functionalized organosilica materials in our earlier studies.…”

Plasma treatment of hydrophobic sub-layers to prepare uniform multi-layered films and high-performance gas separation membranes

“…Finally, top layers were fabricated by coating BTESE and BTESO sols on Me-SiO 2 films, followed by drying and firing at 300 • C for 30 min. Gas permeance was measured as previously reported [13].…”

“…However, when water vapor is present in the separation processes, this can affect gas separation performance of membranes [11,12]. In our previous work, organosilica membranes showed excellent CO 2 separations under dry conditions, but CO 2 permeance was drastically decreased in the presence of water vapor due to adsorption and/or capillary condensation of water molecules in hydrophilic SiO 2 -ZrO 2 intermediate layers [13]. Many hydrophobic and super-hydrophobic materials have been studied coating on silicon wafers or glass and obtained water-repellent surface and self-cleaning properties [14,15].…”

Organic groups influencing microporosity in organosilicas

“…Si-C-Si bonds are also more rigid because they do not have the impressive freedom of over 40° variation in bond angle that Si-O-Si bonds have [17]. Long and flexible bridges such as hexylene (-C6H12-) and octylene (-C8H16-) groups tend to collapse and fill up the empty space [12,13,[18][19][20].…”