A Molecular Simulation Study Of SC-CO₂ And Coadsorbed Molecule On Porous SiO₂

At present, the molecular simulation research play an important role in many areas, such as chemical engineering, material engineering, biological and pharmaceutical fields, etc. It can not only obtain the microstructure, macroscopic thermodynamics and transport properties of the studied system, but also provide a check for theory development. The objectives of this paper are to explore the properties of the fluid in pores by molecular dynamic and grand canonical Monte Carlo (GCMC) simulation.1. The properties of adsorption and diffusion of a binary mixture of supercritical CO2 and benzene on silicalite (MFI-type) have been studied using the grand canonical Monte Carlo and molecular dynamics (MD) simulations. The adsorption behavior of pure CO2 on silicalite was discussed in detail through the adsorption isotherms, adsorption sites, interaction energies, and isosteric heats of adsorption. For the mixture, the influences of temperature, pressure and composition on the adsorption isotherms have been examined. The adsorption site of the mixture has been analyzed, and benzene molecules get adsorbed preferentially in the more spacious channel intersection positions. These simulation results suggest that SC-CO2 fluid can be used as an efficient desorbent of larger aromatics in the zeolite material. The diffusion characteristic for the pure CO2 and benzene/CO2 mixture was studied using MD simulation. It was found that the large coadsorbed benzene molecule has a pronounced effect on the CO2 diffusion in the mixture, while the mobility of benzene molecules is very small due to geometrical restrictions.2. A classical molecular dynamics (MD) simulation technology is used to investigate the structure and surface properties of amorphous silica. We used the melt-quench procedure to obtain the amorphous SiO2 structure. The obtained radial distribution function and the band angle distributions for the bulk silica are in good agreement with the reported results. Then elevated temperature relaxation was performed to gain the amorphous silica surface. The obtained amorphous surface is thought as a hydrophobic surface basing on the fact that concentration of nb-O in this paper is consistent the dehydroxylated amorphous silica surface of simulation and the hydrophobic surface of dry oxide oxidation experiment.