MFI-type zeolite membranes (Na-ZSM-5 and B-ZSM-5) were prepared on gamma-alumina and stainless steel tubular supports and tested for separation of CO2/N-2, mixtures. The effect of pressure on N-2 and CO2 flows and selectivity was investigated. The separation between CO2 and N-2, takes place because of the preferential adsorption of CO2, which hinders the permeation of N-2, through the zeolite pore network. The best results in this work were obtained with a B-ZSM-5 membrane prepared over a porous stainless steel support. In this case, a CO2 permeance of 2.66 x 10(-7) Mol/(M-2 s Pa) with a CO2/N-2 separation factor of 13 was obtained. The results of two characterization methods (N-2/SF6 selectivity and hydrogen permeation in the presence of desorbing butane) are compared, and their relationship with the separation properties of the membranes is examined. The contribution of flow through micropores and intercrystalline pores is discussed. (c) 2007 Elsevier B.V. All rights reserved.