Diffusion of Biomass Pyrolysis Products in H-ZSM-5 by Molecular Dynamics Simulations

Seon Ah Kim, Lintao Bu, Mark Nimlos, David Robichaud

Research output: Contribution to journalArticlepeer-review

28 Scopus Citations

Abstract

Diffusion of biomass pyrolysis vapors and their upgraded products is an essential catalytic property of zeolites during catalytic fast pyrolysis and likely plays a critical role in the selectivity of these catalysts. Characterizing the diffusivities of representative biofuel molecules is critical to understand shape selectivity and interpret product distribution. Yet, experimental measurements on the diffusivities of oxygenated biofuel molecules at pyrolysis temperatures are very limited in the literature. As an alternative approach, we conducted MD simulations to measure the diffusion coefficients of several selected molecules that are representative of biomass pyrolysis vapors, namely water, methanol, glycolaldehyde, and toluene in H-ZSM-5 zeolite. The results show the diffusion coefficients calculated via MD simulations are consistent with available NMR measurements at room temperature.1 The effect of molecular weight and molecular critical diameter on the diffusivity among the chosen model compounds is also examined. Furthermore, we have characterized the diffusivities of representative biofuel molecules, namely xylene isomers, in H-ZSM-5. Our calculations determined that the ratio of the diffusion coefficients for xylene isomers is pxylene: o-xylene:m-xylene ≈ 83:3:1 at 700 K. Additionally, our results also demonstrate the different diffusivity between p-xylene and toluene is due to the molecular orientations when the molecules diffuse along the channels in H-ZSM-5 and provide deep insight into the effect of molecular orientation on its diffusivity.

Original languageAmerican English
Pages (from-to)500-510
Number of pages11
JournalJournal of Physical Chemistry C
Volume121
Issue number1
DOIs
StatePublished - 12 Jan 2017

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

NREL Publication Number

  • NREL/JA-5100-67506

Keywords

  • biomass pyrolysis
  • diffusion coefficient
  • molecular dynamics
  • xylene
  • zeolite

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