Molecular simulation of multi-component adsorption and diffusion in silicalite zeolite

This work focuses on developing and implementing techniques for simulating multi-component adsorption and diffusion in zeolite silicalite.; A method is described for performing grand canonical Monte Carlo simulations of molecules with internal degrees of freedom. The approach is applied to cyclohexane in the zeolite silicalite. Calculated adsorption isotherms and heats of adsorption compare well with experimental data from the literature. In addition, the simulations provide information on preferential siting of molecules in the different pores of silicalite. Binary adsorption results are also predicted for cyclohexane/methane, benzene/methane and benzene/cyclohexane mixtures. The siting preferences of the single components result in clear segregation effects for these binary systems. The more strongly adsorbing component is found to adsorb in its preferred site regardless of the preferred site of the other component.; Binary systems consisting of large coadsorbed molecules such as n-hexane, cyclohexane and benzene with smaller penetrant molecules such as methane were simulated to investigate the mechanisms of pore blockage in the zeolite silicalite. The larger coadsorbed molecules trap the methane molecules in the zeolite channels on MD time scales. Using the "dragging" and steepest-descent techniques, minimum energy paths in the straight and zig-zag zeolite channels are calculated for the diffusion of methane past the blocking coadsorbed molecules. The passage characteristics were found to depend on both the pore geometry and the nature of the blocking molecule.; Free energy perturbation calculations were carried out along minimum energy paths to get the rate constants of methane hopping past coadsorbed benzene and cyclohexane molecules which adsorb in the channel intersections. Three principal diffusion pathways were found in both the methane/benzene and methane/cyclohexane systems. Kinetic Monte Carlo was then used to obtain the diffusivity of methane with a coadsorbate benzene loading of 4 molecules per unit cell. Unlike with benzene, passage of methane across cyclohexane molecules involved pushing the cyclohexane molecules into the channels from their preferred channel intersection positions.; Finally, object-oriented programming design concepts for the development of molecular simulation code in the context of Fortran 90 are discussed. The salient features of Fortran 90 and the design concepts are illustrated by means of sample code.