Studying the dynamics of self- and cooperative-diffusion of benzene in sodium compounds by molecular simulations.

摘要

The objective of this dissertation is to employ molecular modeling concepts to investigate benzene transport in NaX type zeolite. Experimentally observed separation performance of NaX faujasite (FAU) membranes can be attributed to the intra-crystalline processes of sorption and diffusion. Membrane permeation occurs by sorption of the guest or sorbate (e.g. benzene) on surface-active host sites of zeolite (e.g. FAU) and simultaneous site-site molecular movement or intra-crystalline diffusion of sorbate. Such processes are controlled by host-guest and guest-guest interactions on the length scales of the pores. In this study, Molecular Dynamics (MD) simulations are performed to evaluate the Self—D_s(T, Θ) and Cooperative (or Maxwell-Stefan)—DMS(T, Θ) diffusivities and the respective energies of activation: $Esact$(Θ) and $EMSact$(Θ) for benzene motion in NaX. The MD simulated D_s and $Esact$ favorably compare with predictions from experimental measurements (PFG-NMR, QENS). Consequently, the predicted DMS is applied in a transport model to predict benzene fluxes through ideal NaX membranes so as to ultimately evaluate and comprehend the experimentally observed fluxes in NaX FAU membranes. This contribution is aimed to be the first step towards understanding the experimentally observed permeation selectivity of benzene over cyclohexane in NaX membranes. Our efforts to understand how molecular interaction phenomena in the pores of the NaX FAU give rise to experimentally observed sorption-diffusion behavior, we believe would have an impact on the approach towards improving zeolite membrane performance and permselectivity in industrially important separations.; In addition, this dissertation discusses two other challenging problems related to the field of microporous and mesoporous materials, namely—(a) Application of techniques such as Transmission electron microscopy (TEM), Electron diffraction (ED) and Energy dispersive X-ray (EDX) analysis in the characterization of the fine structures of porous materials, and (b) Formation of periodic Liesegang patterns of titania by chemical vapor deposition (CVD) in mesoporous glass.