| Autor: |
Anastasios I. Skoulidas, David S. Sholl, Rajamani Krishna |
| Přispěvatelé: |
Chemical Reactor engineering (HIMS, FNWI) |
| Rok vydání: |
2003 |
| Předmět: |
|
| Zdroj: |
Langmuir, 19, 7977-7988. American Chemical Society |
| ISSN: |
0743-7463 |
| Popis: |
Correlation effects in diffusion of CH 4 and CF 4 in MFI zeolite have been investigated with the help of molecular dynamics (MD) simulations and the Maxwell-Stefan (M-S) formulation. For single-component diffusion, the correlations are captured by the self-exchange coefficient D c o r r ii; in the published literature this coefficient has been assumed to be equal to the single-component M-S diffusivity, D i . A detailed analysis of single-component diffusivity data from MD, along with published kinetic Monte Carlo (KMC) simulations, reveals that D c o r r ii/D i is a decreasing function of the molecular loading, depends on the guest-host combination, and is affected by intermolecular repulsion (attraction) forces. A comparison of published KMC simulations for diffusion of various molecules in MFI, with those of primitive square and cubic lattices, shows that the self-exchange coefficient increases with increasing connectivity. Correlations in CH 4 /CF 4 binary mixtures are described by the binary exchange coefficient D c o r r 12; this exchange coefficient has been examined using Onsager transport coefficients computed from MD simulations. Analysis of the MD data leads to the development of a logarithmic interpolation formula to relate D c o r r 12 with the self-exchange coefficient D c o r r ii of the constituents. The suggested procedure for estimation of D c o r r 12 is validated by comparison with MD simulations of the Onsager and Fick transport coefficients for a variety of loadings and compositions. Our studies show that a combination of the M-S formulation and the ideal adsorbed solution theory allows good predictions of binary mixture transport on the basis of only pure component diffusion and sorption data. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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