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Published on: September 17, 2021
Diffusion of alkane mixtures in zeolites: validating the maxwell-stefan formulation using MD simulations
1Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands. r.krishna@uva.nl
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Molecular dynamics and Monte Carlo simulations reveal that Maxwell-Stefan diffusivities in zeolites are predictable across mixtures. This simplifies predicting multi-component diffusion in materials like FAU, MFI, and LTA zeolites.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Engineering
Background:
- Understanding gas diffusion in zeolites is crucial for separation and storage applications.
- Accurate prediction of multi-component diffusion coefficients is complex due to strong adsorbate-adsorbent interactions.
Purpose of the Study:
- To investigate the applicability of the Maxwell-Stefan (M-S) diffusion framework for mixtures of light alkanes in FAU zeolite.
- To determine self-diffusivities and M-S diffusivities for pure components and mixtures.
- To validate M-S diffusivity interpolation methods and assess their predictive power for complex mixtures.
Main Methods:
- Molecular dynamics (MD) simulations were performed for pure components and mixtures (methane, ethane, propane, n-butane) in FAU zeolite at 300 K.
- Configurational-bias Monte Carlo (CBMC) simulations were used to obtain sorption isotherms and saturation capacities.
- Maxwell-Stefan (M-S) diffusivities, self-diffusivities, and binary exchange coefficients were calculated.
Main Results:
- The M-S formulation demonstrated a significant advantage: component diffusivities (D(i)) and self-exchange diffusivities (D(ii)) remained nearly constant at a given zeolite occupancy, regardless of mixture composition.
- Binary exchange coefficients (D(ij)) could be accurately interpolated from pure component data using a generalized formula.
- Pure component M-S parameters were sufficient to accurately predict mixture diffusion matrices for up to quaternary mixtures across various loadings.
Conclusions:
- The Maxwell-Stefan framework provides a robust and simplified approach for modeling multi-component diffusion in zeolites.
- Predictive models based on pure component M-S diffusivities can accurately estimate mixture diffusion behavior in FAU, MFI, and LTA zeolites.
- This work offers a valuable tool for designing and optimizing zeolite-based separation and storage processes.
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