Gas permeation properties of ion-exchanged ZSM-5 zeolite membranes

Hydrothermally synthesized, ZSM-5 zeolite membranes (Si/Al = 25 and 600) were ion exchanged with H+, Na+, K+, Cs+, Ca2+ and Ba2+ cations, and the membranes were stable after exchange. Their gas permeation properties were measured over the temperature range of 323-523 K. Both the Si/Al ratio and the exchanged ion size affected the separation performance. For the membrane with a Si/AI ratio of 600, ion exchange only changed the single gas permeances of i-C4H10, apparently because the number of exchange sites was small. For the membrane with Si/Al = 25, single gas permeances increased for the exchanged forms in the order: K+ < Ba2+ similar to Ca2+ < Cs+ < Na+ similar to H+, which coincides with the decrease in ion size and only the Cs ion does not fit this trend. (C) 2000 Elsevier Science B.V. All rights reserved.