(569a) Tuning of Silica Networks for Highly Permeable Hydrogen Separation Membranes Using Bis(triethoxysilyl)Ethane

Inorganic membranes are promising for possible application to high temperature separation systems and membrane reactor systems [1-3]. Metal membranes, which shows 100% selectivity to hydrogen and high permeances at temperatures, have several disadvantages such as expensive cost, degradation with hydrocarbon and acid gases, and hydrogen brittleness at low temperatures. On the other hand, amorphous silica, which can be derived from the sol-gel processing or CVD (Chemical vapor deposition), is a microporous material, consisting of silica network which allows the permeation of small molecules such as helium and hydrogen.

Tetraethoxysilane (TEOS) is a commonly used precursor for preparation of sol-gel derived silica membranes [1-3]. In the process of the hydrolysis and polymerization reaction of TEOS, the Si-O-Si unit can be a minimum unit for amorphous silica networks. The use of an organic-inorganic hybrid alkoxide, which contains at least one organic group such as methyltriethoxysilane (MTES) that can not be hydrolyzed, has been proposed by several research groups for the control of pore size.

In this paper, we propose the use of a new type of organic-inorganic hybrid alkoxide, which contains the organic groups between 2 silicon atoms, such as bis (triethoxysilyl) ethane (BTESE), for the development of a highly permeable hydrogen separation membrane [4, 5]. The concept for improvement of hydrogen permeability of a silica membrane is to design a loose organic-inorganic hybrid silica network using BTESE, i.e., to shift the silica networks to a larger pore size for an increase in H2 permeability.

BTESE silica membranes shows about one order magnitude high H2 permeance (0.57-0.78x10-5 mol m-2 s-1 Pa-1) compared with previously reported silica membranes using TEOS, and a high H2 to SF6 permeance ratio of approximately 1,350-36,300 with a low H2 to N2 selectivity (~10). [5]

BTESE silica membranes were found to show improved hydrothermal stability at 300C under H2O atmosphere (3 kPa).

1. T. Tsuru, Journal of Sol-Gel Science and Technology, 46(2008) 349-361.

2. T.Tsuru, Shintani, H.; Yoshioka, T.; Asaeda, M. App. Cataly. A: General, 302 (2006) 78-85.

3. R. Igi, T. Yoshioka, Y. H. Ikuhara, Y. Iwamoto, T. Tsuru, Journal of American Ceramic Society, 91 (2008) 2975-2981.

4. H. L.Castricum, A.Sah, R. Kreiter, D.H.A, Blank, J.F. Vente,; ten Elshof, J. Mater. Chem. 2008, 18, 2150.

5. M. Kanezashi, K. Yada, T. Yoshioka, T. Tsuru, J Am. Chem. Soc., 131(2009) 414-415.