A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH
3) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H
2 > NH
3 > N
2. These results suggest that, for permeation through silica membranes, the molecular size of NH
3 is larger than that of H
2, despite previous reports that the kinetic diameter of NH
3 is smaller than that of H
2. At high temperatures, there was no effect of NH
3 adsorption on H
2 permeation characteristics, and silica membranes were highly stable in NH
3 at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH
3 molecules adsorbed on the silica improved NH
3‐permselectivity by blocking permeation of H
2 molecules without decreasing NH
3 permeance. The maximal NH
3/H
2 permeance ratio obtained during binary component separation was ~30 with an NH
3 permeance of ~10
?7 mol m
?2 s
?1 Pa
?1 at an H
2 permeation activation energy of ~6 kJ mol
?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010
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