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

Hydrothermally synthesized, ZSM-5 zeolite membranes (Si/Al = 25 and 600) we re ion exchanged with H+, Na+, K+, Cs+, Ca2+ and Ba2+ cations, and the memb ranes were stable after exchange. Their gas permeation properties were meas ured 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 wi th a Si/AI ratio of 600, ion exchange only changed the single gas permeance s of i-C4H10, apparently because the number of exchange sites was small. Fo r the membrane with Si/Al = 25, single gas permeances increased for the exc hanged 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.