Adsorption properties of carbon molecular sieves prepared from an activated carbon by pitch pyrolysis

In this study a heat-treatment process using an activated carbon and coal-tar pitch was developed to prepare carbon molecular sieves (CMSs) for CH4/CO2 separation. This process results in a partial blockage of the pores of the activated carbon precursor, so that a reduction in the pore size takes place. Equilibrium CO2 adsorption measurements at different temperatures, and CO2 and CH4 kinetic measurements at different temperatures and feed pressures were carried out using the TEOM technique for a carbon molecular sieve (CMS) prepared by this process (sample CB3) and a commercial CMS (Takeda 3A, sampleT3A). The overall diffusion for CO2 in sample CB3 was faster than that in T3A and a slightly higher CO2 adsorption capacity of CB3 was obtained. The transient uptake profiles in both samples at different temperatures and different CO2 partial pressures were described in some cases by a micropore diffusion model, and in other cases by a dual resistance model. Both equilibrium and kinetic results demonstrate a better CO2/CH4 separation performance for the CMS prepared in the present study (CB3) than for the commercial CMS (Takeda 3A), due to the existence of slightly wider pore-mouth openings in sample CB3. This study demonstrates that the process used in this work is an interesting and reproducible approach to prepare CMS for CO2/CH4 separation.