Computer Simulation for Adsorption of CO₂, N₂and Flue Gas in a Mimetic MCM-41

Abstract

Adsorption of pure and mixed CO 2 and N 2 is simulated in a mimetic MCM-41. The full-atom MCM-41 model is constructed by caving cylindrical pores from an amorphous silica matrix and energetically optimized. Dreiding force field is used for the dispersive interaction with the atomic charges estimated from the density-functional theory calculations. The optimized MCM-41 maintains a hexagonal array of the mesoscopic pores as evidenced by the three characteristic peaks in the XRD pattern. The pore surface of MCM-41 is corrugated and coated with hydroxyls and defects. The pore size exhibits a Gaussian distribution with an average radius of 14.38 Å close to the experimental value. Simulated adsorption isotherms and isosteric heats of CO 2 match well with the experimental data. CO 2 adsorbs preferentially at the active sites near the pore surface, while N 2 tends to adsorb homogeneously on the pore surface. In CO 2 and N 2 mixture as a flue gas, CO 2 is more adsorbed than N 2 . The selectivity of CO 2 over N 2 drops rapidly with increasing temperature and depends weakly on pressure. At temperatures higher than 400 K, the selectivity approaches a constant and pressure has no discernible effect.