Gas permeation through silicalite single crystal membranes

In this dissertation, the Dual Control Volume-Grand Canonical Molecular Dynamics (DCV-GCMD) method has been applied to study dynamics dictating the diffusion of molecules through the Silicalite Single Crystal Membrane (SCM), which has been developed to measure diffusion of gases through a membrane made from a single zeolite crystal. For this purpose, the variation in mass-transfer resistances throughout the diffusion process has been investigated.; In the first part of the work it has been demonstrated that the contribution of resistance at the crystal surface to the overall transport resistance in zeolite membranes is larger and longer range than one might expect. A model was proposed based on the additivity of corresponding mass-transfer resistances acting on entrance, intra-crystalline, and exit steps of the diffusion process. It has been shown that the surface resistance against CH₄ diffusion approaches an asymptote after roughly 200 nm of crystal thickness.; Next, the DCV-GCMD method has been applied to investigate variation of surface resistances to diffusion of molecules through the SCM as a function of permeants. For this purpose three spherical molecules have been selected: CH₄, Ar, and CF₄ that enabled the study of a range of molecular diameters and interaction energies. Simulations results showed that the magnitude and range of surface resistance in zeolite membranes depend on the permeant-crystal interaction size and energy of permeants. Furthermore the range of the surface resistance is primarily a function of molecular size.; To study variations in mass-transfer resistances and diffusivities in further detail, a parametric sensitivity analysis has been performed by varying permeant-crystal interaction size and well-depth, as well as molecular weight in the manner of a factorial design.; In the last part of the research, the DCV-GCMD method has been applied to investigate diffusion of methane + argon and methane + ethane mixtures through the SCM. It has been demonstrated that surface resistance contributes significantly to membrane performance by altering its selectivity and permeance.; The outcome of this research will fill the gap in the present understanding of thermodynamics and transport in micropores to resolve fundamental discrepancies that have hindered progress in the study of zeolites. This study also will permit a detailed understanding of the molecular scale phenomena responsible of competition between transport and thermodynamics of diffusing gas mixtures in the porous media.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation).