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Abstract
Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H2 permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H2/N2 permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H2/N2 permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H2 permeance and the H2/N2 permselectivity of the amorphous silica membrane on the block type were 1.1 × 10−7 mol/m2 · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.
Acknowledgment
This work was carried out as a part of the R & D Project on “Highly Efficient Ceramic Membranes for High-Temperature Separation of Hydrogen” supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.