Adding propane or n-butane in low concentrations to a H-2\N-2 feed increases the H-2/N-2 separation selectivity in SAPO-34 membranes by decreasing the N-2 permeance more than the H-2 permeance. More than two clays were required to reach steady state because propane and n-butane diffuse slowly into the zeolite pores, but they adsorb strongly and thus decrease H-2 and N-2 loadings. Although the loading of the more-weakly adsorbed H-2 is expected to decrease inure, the N-2 permeance decreased more than the H-2 permeance apparently because the diffusivity of the larger N-2 molecule decreased more Propane more than doubled the H-2/N-2 selectivity at 298 K, but its effect on selectivity decreased as the temperature increased because the propane loading in the SAPO-34 pores decreased. Ethane also decreased H-2 and N-2 permeances, but it did not change H-2\N-2 selectivity. As with propane, ethane decreased H-2 loadings more than N-2 loadings, and decreased N-2 diffusivity inure than H-2 diffusivity. However, the smaller ethane had less effect on the N-2 diffusivity than did propane, so the net effect was that the selectivity did not change. The effects of alkane adsorption in SAPO-34 membranes were reversed when the alkanes were removed from the feed. (C) 2015 Elsevier B.V. All rights reserved.