Carbon molecular sieves from carbon cloth: Influence of the chemical impregnant on gas separation properties

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 O₂, N₂, 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.