Abstract
Molecular Dynamic (MD) simulations were carried out to determine the MaxwellโStefan (MโS) diffusivities, ฤ~i~, and selfโdiffusivities, D~i,self~, of methane (C1), ethane (C2), and propane (C3) for a variety of molecular loadings, q~i~, in three classes of zeolite topologies: (1) intersecting channels (MFI, ISV, BEA), (2) oneโdimensional (1D) channels (AFI, TON, FER, MOR, LTL), and (3) cages separated by windows (FAU, LTA, ERI, CHA, DDR). The ฤ~i~ are strongly dependent on loading, decreasing to zero at saturation loading in all cases. For 1D channels, the decrease of ฤ~i~ with q~i~ is severe. For cages separated by narrow windows (LTA, ERI, DDR, CHA), the ฤ~i~ increase sharply with q~i~ before eventually reducing to zero at saturation loading. Correlation effects are reflected in the ratio of the selfโ to MโS diffusivity, D~i,self~/ฤ~i~; this ratio is seen to be strongly dependent on the topology. Correlation effects are negligibly small in zeolite structures with cages separated by narrow windows. For binary C1โC2 and C1โC3 mixtures in both intersecting channel structures and 1D channels, the D~i,self~ of the more mobile species, C1, is reduced significantly due to the presence of the more tardy C2 or C3. The mobility of the tardy species is enhanced due to the presence of the mobile C1. For cages separated by narrow windows, the interโcage hops are practically independent and there is no accelerating or decelerating effects during mixture diffusion.