Molecular modeling of selectivity of single-walled carbon nanotube and MCM-41 for separation of methane and carbon dioxide

Separation of carbon dioxide and methane in cylindrical geometries materials (including MCM-41 and single-walled carbon nanotube (SWNT)) is investigated systematically using grand canonical Monte Carlo (GCMC) simulations. The selectivities of carbon dioxide with respect to methane (CO2/CH4) in MCM-41 and SWNT at different temperatures and mole fractions are obtained. Simulation results indicate that the selectivity of MCM-41 for CO2/CH4 is insensitive to the bulk mole fraction, while that of the SWNT varies significantly with the bulk mole fraction, although both the MCM-41 and SWNT are described using the cylindrical pore model. By exploring the effects of temperature, pore size and pressure on the selectivity of CO2/CH4, it is found that, to separate CO2 and CH4 efficiently, high pressure, low temperature and small pore size are preferred. In particular, the selectivity of CO2/CH4 in the SWNT can reach 11 at low temperature T = 233 K, high pressure of p = 20 bar and small pore size of 1.52 nm. Compared to the slit-like pores, the cylindrical pores are more efficient for separation of CO2/CH4 at the same temperature and pore size. It is expected that this work can provide useful information for practical application to the separation of CO2/CH4, especially for the determination of operating conditions and geometrical features of porous adsorptive materials. (C) 2010 Elsevier B.V. All rights reserved.