Kinetic separation of methane/carbon dioxide by molecular sieve carbons

Abstract

The bulk separation of CH4/CO2 mixture by pressure swing adsorption (PSA) on two different types of carbon molecular sieves (CMS) is analyzed. The two CMS are Bergbau–Forschung (BF) CMS and Takeda 3A CMS. Two different PSA cycles are considered, differing by whether a feed step is used. For a 50/50 feed mixture, it is shown that the separation is feasible with both sorbents to produce a methane product at over 90% purity and at reasonably high product recoveries and sorbent productivities. It is shown in this work that temperature is an important factor to consider for kinetics-based separations, and that a higher temperature is favorable for CH4/CO2 separation on molecular sieve where diffusion is slow. At 25°C, BF CMS yields better separation because the diffusion of both CO2 and CH4 are slow in the Takeda 3A CMS. Increasing the temperature decreases the equilibrium adsorption amounts, but increases the diffusivities. The separation results with Takeda 3A are substantially improved when the temperature ...