| The goal of this dissertation is to study the transport and separation properties of fluid mixtures confined in enclosing media, i.e., by pores. In particular, molecular dynamics simulations are carried out to study the adsorption, transport, permeation and separation properties of fluid mixtures in nanoporous carbon molecular-sieve membranes at the atomic scales. Molecular modeling represents a valuable tool for the study of nanoporous membranes, and of the transport processes that take place in their pore space. My research is intended to provide a better understanding of the effect of confinement on the behavior of the fluids. The result of these studies will allow the chemical and petrochemical industries to improve the design of membrane separation technology.;It is shown that under supercritical conditions, which represent a high pressure and relatively low temperature, the fluids form dynamic molecular clusters that travel the pore space. Their sizes vary with the time in a seemingly oscillatory manner. We study the dynamic behavior, and the size distribution of the clusters as it evolves with the process time. The confined structure of the pores gives rise to adsorption and transport phenomena, as well as dynamic evolution of the fluid clusters, that are completely absent in the same pores under subcritical conditions.;The fluid mixtures we study are the binary mixtures of carbon dioxide and n-alkanes, as well as mixtures of n-alkanes chains. The united atom model, in which CH2 and CH3 groups are considered as one interaction site, are used to model n-alkane chains. Bending and torsion potentials are included, and the bond lengths are kept constant using the RATTLE algorithm. Configurational-bias Monte Carlo technique is used for the efficient generation of molecular model of the n-alkanes.;In addition, the possibility of asymmetry in the permeation properties of fluid mixtures in carbon molecular-sieve membranes is investigated under sub- and supercritical conditions. To do so, we carry out extensive nonequilibrium molecular dynamics simulations of flow and transport of a pure fluid, as well as a binary mixture, through a porous material composed of a macro-, a meso-, and a nanopore, in the presence of an external pressure gradient. We find that under supercritical conditions, unusual phenomena occur that give rise to direction- and pressure-dependent permeabilities for the mixture's components. Hence, the classical models of fluid flow and transport through porous materials that are based on single-valued permeabilities that are independent of the direction of the applied pressure gradient are completely in error. The simulations are in qualitative agreement with the experimental data gathered in our laboratory and provide a rational explanation for them in terms of a non-linear flow regime, coupled with adsorption. (Abstract shortened by UMI.). |
