Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Abstract

Purification of the C alkylaromatics o-xylene, m-xylene, p-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal-organic frameworks Co(dobdc) (dobdc = 2,5-dioxido-1,4-benzenedicarboxylate) and Co( m-dobdc) ( m-dobdc = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C guest molecule with two adjacent cobalt(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M(dobdc) structure, Co(dobdc) exhibits an unexpected structural distortion in the presence of either o-xylene or ethylbenzene that enables the accommodation of additional guest molecules.

The Role of Molecular Modeling & Simulation in the Discovery and Deployment of Metal-Organic Frameworks for Gas Storage and Separation

“…276 However, mixtures of C 8 aromatics are very challenging to separate because of their similar shapes, boiling points, and polarities. 278 The two incumbent industrial processes to separate C 8 aromatic mixtures are crystallization and, more often, selective adsorption onto a solid-state material. 276,277,279 MOFs are promising adsorbent materials for separating C 8 aromatics more effectively than zeolites, which are currently used in a simulated moving bed process to obtain high-purity p-xylene.…”

The Role of Molecular Modeling & Simulation in the Discovery and Deployment of Metal-Organic Frameworks for Gas Storage and Separation

“…202 However, mixtures of C 8 aromatics are very challenging to separate because of their similar shapes, boiling points, and polarities. 204 The two incumbent industrial processes to separate C 8 aromatic mixtures are crystallization and, more often, selective adsorption onto a solidstate material. 202,203,205 MOFs are promising adsorbent materials for separating C 8 aromatics more effectively than zeolites, which are currently used in a simulated moving bed process to obtain high-purity p-xylene.…”

Removal of O,m,p-Xylene From Air Samples on Oxidized Carbon Nanotubes Cartridges

“…This results has further strengthened our hypothesis that the CNTs can be used as efficient adsorbent for selective adsorption of three isomers of Xylene. Gonzalez et al [15] proved that the binding affinities of the Xylene isomers with metal-organic frameworks Co2(4,6-dioxido-1,3-benzenedicarboxylate) follow the trend o-Xylene > m-Xylene > p-Xylene. The selectivity of this metal-organic adsorbent was obtained over a wide range of concentrations.…”