Efficient separation of xylene isomers by a guest-responsive metal–organic framework with rotational anionic sites

Abstract

The separation of xylene isomers (para-, meta-, orth-) remains a great challenge in the petrochemical industry due to their similar molecular structure and physical properties. Porous materials with sensitive nanospace and selective binding sites for discriminating the subtle structural difference of isomers are urgently needed. Here, we demonstrate the adaptively molecular discrimination of xylene isomers by employing a NbOF52−-pillared metal–organic framework (NbOFFIVE-bpy-Ni, also referred to as ZU-61) with rotational anionic sites. Single crystal X-ray diffraction studies indicate that ZU-61 with guest-responsive nanospace/sites can adapt the shape of specific isomers through geometric deformation and/or the rotation of fluorine atoms in anionic sites, thereby enabling ZU-61 to effectively differentiate xylene isomers through multiple C–H···F interactions. ZU-61 exhibited both high meta-xylene uptake capacity (3.4 mmol g−1) and meta-xylene/para-xylene separation selectivity (2.9, obtained from breakthrough curves), as well as a favorable separation sequence as confirmed by breakthrough experiments: para-xylene elute first with high-purity (≥99.9%), then meta-xylene, and orth-xylene. Such a remarkable performance of ZU-61 can be attributed to the type anionic binding sites together with its guest-response properties.

Separation and Purification of Hydrocarbons with Porous Materials

“…also reported a ZU-61 MOF with accessible and rotational Lewis basic sites for the adaptive molecular discrimination of xylene isomers (Figure 17). [112] Through the rotation of fluorine atoms, the anionic sites can adapt to the shape specific isomers, therefore jected masses increased from 3 to 30 mg, and only a slight decrease in selectivity was observed as temperature increased from 20 to 32 8C (Figure 18 d-f). Table 6 provides an overview of selected state-of-the-art porous materials for separation of xylene isomers.…”

“…also reported a ZU‐61 MOF with accessible and rotational Lewis basic sites for the adaptive molecular discrimination of xylene isomers (Figure 17). [112] Through the rotation of fluorine atoms, the anionic sites can adapt to the shape specific isomers, therefore enabling ZU‐61 to efficiently separate xylene isomers. ZU‐61 exhibited a preferential adsorption sequence of OX> MX >PX and both high MX uptake capacity (3.4 mmol g −1 , 7.1 mbar) and MX/PX separation selectivity (2.9, obtained from breakthrough curves) were achieved at 333 K. The HTCS method has also been used to investigate the separation of xylene isomers.…”

“…b, c) Structure of ZU-61 with the rotational ligand NbOF 52À anion and bipyridine. d) Breakthrough curves for 1:1:1 PX/MX/OX separations with ZU-61 at 333 K. Adapted from ref [112]…”

Separation of Xylene Isomers in the Anion‐Pillared Square Grid Material SIFSIX‐1‐Cu

“…To date, these novel MOFs have been widely investigated because of their structural diversity and microporous nature for CH 4 adsorption, [12] CO 2 adsorption [14] and separation, [15] acetylene/ethylene separation, [16] propyne/propadiene separation, [17] propane/propylene separation, [18] and water vapor adsorption [19] . More recently, SIFSIX‐1‐Cu and its isomorph ZU‐61 have been proven to have unique m ‐xylene/ p ‐xylene selectivity in xylene gas phase separation [20] . SIFSIX materials can adjust the pore size by changing the organic ligand to separate adsorbate molecules of different sizes, and, on the other hand, they exhibit unique selectivity in the field of adsorption separation due to the SiF 6 2− anions.…”

“…[19] More recently, SIFSIX-1-Cu and its isomorph ZU-61 have been proven to have unique m-xylene/p-xylene selectivity in xylene gas phases eparation. [20] SIFSIX materialsc an adjust the pore size by changing the organic ligand to separatea dsorbate molecules of different sizes, and, on the other hand, they exhibit uniques electivity in the field of adsorption separationd ue to the SiF 6 2À anions. SIFSIX-1-Cu has great potential for xylene separation because of its unique feature of fluorine atoms in SiF 6 2À anions, whichi si nspired by ap reviousc omplexation crystallization method fors eparating m-xylene.…”