Refinement of pore size at sub-angstrom precision in robust metal\u2013organic frameworks for separation of xylenes

Xin Li ,Shaojun Xu,Martin Schröder,Sihai Yang,K Mark Thomas,Iván Da Silva ,Damian M Wilary,Haifei Zhang,Leslie W Bolton,Mark D Frogley,Nan-Nan Bai ,Xinran Zhang,Juehua Wang,Tristan Lowe,Yongqiang Cheng,Claire Murray ,Chiu C Tang,Yinyong Sun,Gianfelice Cinque,Xue Han,Christopher G Morris,Anibal J Ramirez‐Cuesta

doi:10.1038/s41467-020-17640-4

Abstract

The demand for xylenes is projected to increase over the coming decades. The separation of xylene isomers, particularly p- and m-xylenes, is vital for the production of numerous polymers and materials. However, current state-of-the-art separation is based upon fractional crystallisation at 220 K which is highly energy intensive. Here, we report the discrimination of xylene isomers via refinement of the pore size in a series of porous metal–organic frameworks, MFM-300, at sub-angstrom precision leading to the optimal kinetic separation of all three xylene isomers at room temperature. The exceptional performance of MFM-300 for xylene separation is confirmed by dynamic ternary breakthrough experiments. In-depth structural and vibrational investigations using synchrotron X-ray diffraction and terahertz spectroscopy define the underlying host–guest interactions that give rise to the observed selectivity (p-xylene < o-xylene < m-xylene) and separation factors of 4.6–18 for p- and m-xylenes.

Highlights

The demand for xylenes is projected to increase over the coming decades
P-xylene is used in the manufacture of poly(ethylene terephthalate) (PET), whereas o-xylene is used to produce phthalic anhydride6,7. m-Xylene can be oxidised to isophthalic acid as PET resin blends, and, more importantly, isomerised into value-added p-xylene[8]
We report the direct observation of binding domains and host–guest interactions for adsorbed xylene molecules in the pores of MFM-300 using a combination of high-resolution synchrotron X-ray powder diffraction, terahertz spectroscopy and molecular dynamic (MD) modelling

Summary

Introduction

The demand for xylenes is projected to increase over the coming decades. The separation of xylene isomers, p- and m-xylenes, is vital for the production of numerous polymers and materials. The full separation of xylenes into three pure isomers is achieved in MFM-300 through both chromatographic and breakthrough experiments at room temperature. We report the direct observation of binding domains and host–guest interactions for adsorbed xylene molecules in the pores of MFM-300 using a combination of high-resolution synchrotron X-ray powder diffraction, terahertz spectroscopy and molecular dynamic (MD) modelling.

Results

Conclusion