Synthesis of carbon molecular sieves by benzene pyrolysis over microporous carbon materials

In the present work, an effort has been made to develop suitable process conditions for synthesis of carbon molecular sieves (CMS) from the locally available bituminous and walnut shell char (CH, CW). The process involves modifying a carbon support having a majority of micropores with an effective pore size of about 4–25 Å. The sieves are contacted with different concentration of a volatile carbon-containing organic compound. The char was crushed, milled and agglomerated with starch and pitch as the binders, and then carbonized in nitrogen atmosphere at 650–750 °C for about 60 min. In order to narrow down the pore mouth size, benzene was cracked at 650–800 °C, for 10–60 min to facilitate the deposition of coke on the carbon support. All the products were characterized by analysis of pore size distribution, volume of pores, surface area and adsorption data. The best carbon molecular sieve was obtained for feed benzene entrance in N2 of 3.5 × 10−4 g/ml, cracking time of 30 min and pyrolysis temperature of 800 °C. These carbon molecular sieves are suitable for gas separations. Their performance was judged by the kinetic separation of Ar–O2 mixture. Besides their application to gas separation, these CMS materials are receiving increased attention as catalysts.