Characteristics of ammonia permeation through porous silica membranes

Abstract 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