Realistic molecular models of MCM-41 have been developed and used for studying the separation of carbon dioxide from flue gas mixtures using grand canonical Monte Carlo simulations. The simulated X-ray diffraction pattern and surface area of the models are in good agreement with experimental results reported in literature. Adsorption of pure carbon dioxide was studied on the three different models at two different temperatures, 273.2 K and 303.2 K. Isosteric heats of adsorption of CO2 calculated from the simulations were in the range 20-25 kJ/mol, which matches well with reported experimental values. The simulated CO2 adsorption isotherms showed good agreement with experimental isotherms at both the temperatures for two of the models, which were selected for further mixture adsorption studies. Binary CO2/N2 adsorption simulations were performed at different bulk gas compositions, and the selectivities of CO2 over N2 were observed to be in the range 4-10. Further studies on adsorption of ternary and quaternary bulk gas mixtures containing water vapor and O2 in addition to CO2 and N2 did not reveal any significant effect on CO2 adsorption and CO2-N2 selectivity.