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Fabrication, permeation, and corrosion stability measurements of silica membranes for HI decomposition in the thermochemical iodine-sulfur process

Myagmarjav, O. ; Shibata, Ai*; Tanaka, Nobuyuki ; Noguchi, Hiroki ; Kubo, Shinji ; Nomura, Mikihiro*; Takegami, Hiroaki 

In this study, a corrosion-stable silica ceramic membrane was developed to be used in H$$_{2}$$ purification during the hydrogen iodide decomposition (2HI $$rightarrow$$ H$$_{2}$$ + I$$_{2}$$), which is a new application of the silica membranes. From a practical perspective, the membrane separation length was enlarged up to 400 mm and one end of the membrane tubes was closed to avoid any thermal variation along the membrane length and sealing issues. The silica membranes consisted of a three-layer structure comprising a porous $$alpha$$-Al$$_{2}$$O$$_{3}$$ ceramic support, an intermediate layer, and a top silica layer. The intermediate layer was composed of $$gamma$$-Al$$_{2}$$O$$_{3}$$ or silica, and the top silica layer that is H$$_{2}$$ selective was prepared via counter-diffusion chemical vapor deposition of a hexyltrimethoxysilane. A membrane using a silica intermediate layer exhibited a higher H$$_{2}$$/SF$$_{6}$$ selectivity but lower H$$_{2}$$ permeance with compared with the membrane using a $$gamma$$-Al$$_{2}$$O$$_{3}$$ intermediate layer. The membrane using the silica intermediate layer was more stable in corrosive HI gas than a membrane with a $$gamma$$-Al$$_{2}$$O$$_{3}$$ intermediate layer after 300 h of stability tests. To the best of our knowledge, this is the first report of 400-mm-long closed-end silica membranes supported on Si-formed $$alpha$$-Al$$_{2}$$O$$_{3}$$ tubes produced via chemical vapor deposition method. In conclusion, the developed silica membranes seem suitable for membrane reactors that produce H$$_{2}$$ on large scale using HI decomposition in the thermochemical iodine-sulfur process.

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