Understanding the kinetic and thermodynamic origins of xylene separation in UiO-66(Zr) via molecular simulation

Lennox, Matthew J.; D�ren, Tina

Abstract

Xylene isomers are precursors in many important chemical processes, yet their separation via crystallization or distillation is energy intensive. Adsorption presents an attractive, lower-energy alternative and the discovery of adsorbents which outperform the current state-of-the-art zeolitic materials represents one of the key challenges in materials design, with metal-organic frameworks receiving particular attention. One of the most well-studied systems in this context is UiO-66(Zr), which selectively adsorbs ortho-xylene over the other C8 alkylaromatics. The mechanism behind this separation has remained unclear, however. In this work, we employ a wide range of computational techniques to explore both the equilibrium and dynamic behavior of the xylene isomers in UiO-66(Zr). In addition to correctly predicting the experimentally-observed ortho-selectivity, we demonstrate that the equilibrium selectivity is based upon the complete encapsulation of ortho-xylene within the pores of the framework. Furthermore the flexible nature of the adsorbent is crucial in facilitating xylene diffusion and our simulations reveal for the first time significant differences between the intracrystalline diffusion mechanisms of the three isomers resulting in a kinetic contribution to the selectivity. Consequently it is important to include both equilibrium and kinetic effects when screening MOFs for xylene separations.

Citation

Lennox, M. J., & Düren, T. (2016). Understanding the kinetic and thermodynamic origins of xylene separation in UiO-66(Zr) via molecular simulation. Journal of Physical Chemistry C, 120(33), 18651-18658. https://doi.org/10.1021/acs.jpcc.6b06148

• Journal Article Type: Article
• Acceptance Date: Jul 29, 2016
• Online Publication Date: Jul 29, 2016
• Publication Date: Aug 25, 2016
• Deposit Date: Aug 3, 2016
• Publicly Available Date: Jul 30, 2017
• Journal: Journal of Physical Chemistry C
• Print ISSN: 1932-7447
• Electronic ISSN: 1932-7455
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 120
• Issue: 33
• Pages: 18651-18658
• DOI: https://doi.org/10.1021/acs.jpcc.6b06148
• Public URL: https://nottingham-repository.worktribe.com/output/798466
• Publisher URL: http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b06148
• Additional Information: This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry C, copyright © American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b06148