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|All Authors / Contributors:||
Frédéric Leroy; Bernard Rousseau, (19..-.... ; chimiste).; Université de Paris-Sud.
|Description:||172 p. : ill. ; 30 cm.|
|Responsibility:||Frédéric Leroy ; sous la dir. de Bernard Rousseau.|
In this work, a study of the mechanisms involved in the transport process of n-alkanes in silicalite using molecular dynamics is presented. A program which permits obtaining equilibrium trajectories in several statistical ensembles has been implemented. A methodology defining the theoretical and practical frame of the self-diffusion coefficient calculation is used. It allows the analysis of the underlying mechanisms and permits to show that the specific time required to reach the diffusion regime defined by Einstein's law depends on the diffusing species, the loading and the direction along which the diffusion is observed. The issues treated here are defined taking available experimental and theoretical work as well as existing simulation data into account. The research axis followed here deal with the effect of the silicalite's symmetry, the introduction of silicalite's flexibility and the choice of the interaction potential on alkanes diffusion process. A unique set of interaction parameters is used in order to ensure the consistency of the presented results for different chain lengths. It is shown that diffusion of methane and n-butane are weakly influenced by the choice between monoclinic and orthorombic. The self-diffusion is enhanced using a flexible silicalite for the lowest loadings and the shortest alkanes, namely methane and n-butane, while no effect is observed for n-hexane and n-octane diffusion. It is shown that standard and optimized united atom force field is not able to improve the description of molecular transport in silicalite, while using an anisotropic united atom model provides simulation results in a better agreement with experimental trends.