(8d) Hydrogen Separation with “Pore-Fill” Type Palladium Membrane

Tianze Zhao, Junya Okazaki, David A. Pacheco Tanaka, Toshishige M. Suzuki, Yoshito Wakui

Since the remarkable permeability and exclusive selectivity for hydrogen, palladium membranes have been expected as promising materials for the continuous separation and purification of hydrogen. In order to attain high hydrogen flux and minimize the material costs, efforts have been made to fabricate ultrathin palladium membrane. However, the significant drawback of thin membranes is their limited durability. They are easily damaged during handling and by thermal process resulting in peeling and generation of cracks and pinholes. Conversely, “Pore-fill” type membrane where palladium metal fills the pores of a supporting matrix is an attractive alternative against the conventional thin film membranes. This “pore-fill” configuration could contribute for easier handling of the membrane since palladium layer is not exposed directly on the surface. We successfully fabricated the pore-fill type palladium membrane by electroless plating technique. The nano-size pores of thin yittria-stabilized zirocina (YSZ) layer formed on the outer surface of the porous YSZ tube was filled by palladium particles. From the cross-sectional observation by SEM-EDX, principal amount of palladium was found on the inner layer of the porous support.

Gas permeability of hydrogen and nitrogen was measured for the pore-fill type palladium membranes to optimize the fabrication conditions. The calcination temperature of the porous YSZ tubes influenced the hydrogen perm-selectivity of the membrane. When the porous tube was calcined at 1350°C, the hydrogen selectivity (H₂/N₂) of the membrane reached the maximum of 6,000 at 600°C. The surfactant in the electroless plating solution was expected to improve the performance of the membrane, since the plating solution could easily penetrate into the nano-size pores of the YSZ layer by lowering the surface tension. The hydrogen selectivity of the membrane reached 20,000 by addition of 0.05 wt.% of Triton X-100. It could be attributed that the densely-embedded palladium particles effectively plugged the nano-size pores, and prevented the nitrogen permeation. After 100 hours of gas permeation test at 600°C, nitrogen leak was not observed. This indicates the pore-fill type palladium membrane could be safely operated at elevated temperature.