Center for Neutron Research , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.
Chemical and Biomolecular Engineering , University of Delaware , Newark , Delaware 19716 , United States.
J Am Chem Soc. 2018 Mar 7;140(9):3412-3422. doi: 10.1021/jacs.7b13825. Epub 2018 Feb 21.
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.
对二甲苯、间二甲苯、邻二甲苯和乙苯的 C 烷基芳烃的纯化仍然是最具挑战性的工业分离之一，这是由于这些分子具有相似的形状、沸点和极性。在此，我们报告了金属-有机骨架 Co(dobdc)（dobdc = 2,5-二氧代-1,4-苯二甲酸酯）和 Co( m-dobdc)（ m-dobdc = 4,6-二氧代-1,3-苯二甲酸酯）用于通过单组分吸附等温线和多组分穿透测量分离二甲苯异构体的评估。值得注意的是，Co(dobdc)能够区分所有这四个分子，其结合亲和力遵循对二甲苯>乙苯>间二甲苯>邻二甲苯的趋势。多组分液相吸附测量进一步证明，Co(dobdc)在很宽的浓度范围内保持这种选择性。通过单晶 X 射线衍射进行的结构表征表明，两个骨架都通过每个 C 客体分子与两个相邻的钴(II)中心之间的相互作用程度以及每个异构体在骨架孔内的组装能力来促进分离。此外，与 M(dobdc)结构的假定刚性相反，Co(dobdc)在存在对二甲苯或乙苯时表现出出人意料的结构变形，从而能够容纳额外的客体分子。
