Presented at the International Congress on Membranes and Membrane Processes (ICOM), Toulouse, France, July 7–12, 2002. 0011-9164/02/$– See front matter © 2002 Elsevier Science B.V. All rights reserved Desalination 149 (2002) 435–440 Adsorption and diffusion properties of zeolite membranes by transient permeation Tracy Q. Gardner*, John L. Falconer, Richard D. Noble University of Colorado; Boulder, CO 80309-0424, USA Tel. +1 (303) 492-7471; Fax +1 (303) 492-4341; email: gardnetq@ucsu.colorado.edu Received 7 February 2002; accepted 21 February 2002 Abstract Adsorption isotherms and diffusion coefficients for light gases and butane isomers were measured for the transport pathways involved in gas permeation through H-ZSM-5 membranes by a transient permeation technique. The permeate responses to step changes in the feed were measured, and the transport was modeled as Maxwell–Stefan diffusion with single-site Langmuir adsorption in the zeolite. Isotherms measured for N 2 , CO 2 , and CH 4 at 295 K were nearly identical to those measured by calorimetry on H-ZSM-5 powders. Isotherms for butane isomers were also similar to isotherms for MFI powders and heats of adsorption and diffusion activation energies were in the ranges reported in the literature. Maxwell–Stefan diffusion coefficients for all gases studied increased slightly with feed partial pressure and were similar to those measured by other macroscopic methods for zeolite membranes and crystals. Effective membrane thicknesses were also determined non-destructively for tubular zeolite membranes by the transient permeation technique. Keywords: Transient permeation; Zeolite membranes; Adsorption isotherms; Maxwell–Stefan diffusion; Transport modeling 1. Introduction Zeolite membranes are inorganic alumino- silicate crystalline films grown on porous supports. Due to their pores of molecular dimen- sions, high chemical and thermal stability, and catalytic nature, zeolite membranes operate as *Corresponding author. molecular sieves and have industrial potential as materials for separators and catalytic membrane reactors. They separate molecules based on differences in adsorptive and diffusive properties as well as molecular size. Diffusing species can travel through the pores of the zeolite crystals and/or between crystal boundaries in the film. Synthesis gels and methods have been modified and refined and zeolite membranes with >99.99%