MFI membranes on stainless-steel tubular supports separated mixtures of n-pentane/isoprene; the highest n-pentane/isoprene selectivity was 74, which was obtained at 333 K for a B-ZSM-5 membrane. Separation is due to faster diffusion of the linear alkane. The single-component permeance of n-pentane was higher than its permeance in the mixture because the slower-diffusing isoprene decreases the rate of n-pentane diffusion. No effects due to isoprene polymerization were observed, and the acid sites in B-ZSM-5 did not affect the separations. The separation selectivity for an equimolar mixture of n-hexane and 2,2-dimethylbutane was greater than 300 at 373 K for all membranes, and this was used as an indication of membrane quality. (c) 2005 Elsevier B.V. All rights reserved.