Carbon molecular sieve membranes (CMSM) were successfully prepared from cellophane paper by one single pyrolysis step. The influence of pyrolysis parameters on the membranes' structure, morphology and performance was examined through scanning electron microscopy, X-ray microanalysis, X-ray diffraction and monocomponent permeation experiments towards He, H(2), Ar, N(2), CO(2), O(2), CH(4) and water vapor at 29.5 degrees C. The permeabilities reached a maximum for CMSM heated up to 550 degrees C, without significantly compromising selectivities. The soaking time at this temperature led to pore closing and, consequently, decrease in permeability and an enhancement in selectivity. These membranes were also considerably permeable to water vapor (1000 barrer), and very selective concerning H(2)O/CH(4) (alpha = 921-7518) and H(2)O/N(2) (alpha = 364-9936) separations. No aging effects were observed due to oxygen or water vapor exposure. The permselectivity of CMSM prepared up to 550 degrees C overtook the Robeson bound for polymeric membranes, especially regarding ideal selectivities of pairs O(2)/N(2) (alpha =13-18), H(2)/N(2), H(2)/O(2), H(2)/CH(4) and H(2)/CO(2). Therefore, they might be considered in relevant industrial applications such as separation of nitrogen from air and recovery of hydrogen from synthesis gas. (c) 2010 Elsevier B.V. All rights reserved.