Diffusion of binary mixtures of CF4 and n-alkanes in faujasite

Using molecular dynamics (MD) simulations, binary mixtures of CF4 and eithe r methane, ethane, butane, hexane, octane, or decane were studied in the ze olite faujasite. The results were analyzed to obtain the structural and tra nsport properties of the system, primarily self-diffusivities and molecule sitings within the zeolite. The scaling of self-diffusivity with mixture co mposition was not pronounced for a given system and may be explained in ter ms of available volume and molecular mobility. Evidence of clustering of si milar molecules was observed in systems with the longer alkane species. For methane-CF4 mixtures, the mutual transport diffusion coefficients were als o calculated for equimolax mixtures. In all cases, the main-term transport diffusivities had larger values than their self-diffusivity counterparts. T he cross-term diffusivities were an order of magnitude smaller than the mai n-term diffusivities. The main-term CF4 diffusivity and both cross-term dif fusivities increased with loading, while the main-term methane diffusivity decreased with loading. The challenges involved in calculating the transpor t diffusivities for binary systems are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.