Organic‐Templating Approach to Synthesis of Nanoporous Silica Composite Membranes (II): MTES‐Templating and CO₂ Separation

Abstract

Nanoporous silica composite membranes for gas separation have been synthesized by the organic‐templating sol‐gel technique and their CO₂/N₂ separation efficiency has been investigated. Stable organic‐templating silica sols capable of coating nanoporous amorphous silica layers on SiO₂/α‐Al₂O₃ composite supports were prepared by the two‐step acid‐catalytic process using the mixture of TEOS and template such as MTES (methyltriethoxysilane) being covalently bonded with TEOS or TPABr (tetrapropylammonium bromide) non‐reacted. The SiO₂/α‐Al₂O₃ composite supports (pore size 1.6 nm) prepared by pressurized coating of the porous α‐alumina tube with a nanoparticulate silica sol were found to be more suitable than pure α‐Al₂O₃ composite supports for synthesizing crack‐free membranes which have the high CO₂/N₂ separation efficiency. The N₂ permeability of organic‐templated silica composite membranes synthesized was about 10⁻⁸ mol/m² · s · Pa and the CO₂/N₂ separation factor of the MTES‐templated silica composite membranes was enhanced up to 19 at room temperature by surface‐modifying the templated silica membrane with the TEOS‐EtOH solution.

Keywords:

• Sol‐gel technique
• Organic‐templating
• SiO₂/α‐Al₂O₃ composite supports
• Nanoporous silica membranes
• CO₂/N₂ permeability and separation factors

Acknowledgment

This work was supported by grant No. R01‐1999‐000‐00198‐0 from the Basic Research Program of the Korea Science & Engineering Foundation.