Carbon materials with molecular sieve properties (CMS) were prepared by pyrolysis of cotton fabrics by chemical activation procedures. To evaluate the changes in the chemical and textural properties, the impregnants AlCl3, ZnCl2 and H3PO4 were used at 1123 K. The materials were characterized using adsorption of nitrogen and carbon dioxide, TPD, and immersion calorimetry in C6H6. Adsorption kinetics of O-2, N-2, CO2, CH4, C3H8 and C3H6 were measured in all the prepared materials to determine their behaviour as molecular sieves. The results confirm that the chemical used as impregnant has a significant effect on the resulting CMS separation properties. All materials exhibit microporosity and low oxygen surface group contents; however, the sample impregnated with zinc chloride, with an immersion enthalpy value of 66.4 J g(-1) in benzene, exhibits the best performance in the separation of CH4-CO2 and C3H8-C3H6 at 273 K. (C) 2010 Elsevier B.V. All rights reserved.