客体溶剂导向策略构筑异构的金属有机框架材料实现二氧化碳和甲烷的动力学分离

Guest Solvent-Directed Isomeric Metal-Organic Frameworks for the Kinetically Favorable Separation of Carbon Dioxide and Methane

利用吸附分离技术实现二氧化碳和甲烷的分离是提高天然气品质的一种有效手段。然而,基于热力学分离的吸附剂对二氧化碳往往表现出很强的亲和力,因此再生过程会产生巨大的能耗。相较而言,尽管精准调控吸附剂孔径以实现吸附质扩散速率的巨大差异仍具有巨大挑战,动力学分离技术仍是变压吸附(PSA)过程的首选。本文报道了一种用于在亚埃尺度精准调控吸附剂孔径的客体溶剂导向策略,实现了二氧化碳和甲烷的高效动力学分离。基于4,4-(六氟异丙基亚甲基)-双(苯甲酸)和双核铜的轮桨型结构单元,我们构筑了一系列异构的金属有机框架材料。结果表明,得益于周期性扩张和收缩的孔道以及理想的孔径尺寸,CuFMOF·CH_(3)OH(CuFMOF-c)能够有效地捕获二氧化碳并阻碍甲烷的扩散,从而表现出优异的动力学分离性能,其具有极高的动力学选择性(273.5)和平衡-动力学综合选择性(64.2)。分子动力学(MD)模拟阐明了分离机制,固定床穿透实验验证了材料优异的分离性能。

The adsorptive separation of CH4 from CO_(2)is a promising process for upgrading natural gas.However,thermodynamically selective adsorbents exhibit a strong affinity for CO_(2)and thus require a high energy compensation for regeneration.Instead,kinetic separation is preferred for a pressure swing adsorption process,although precise control of the aperture size to achieve a tremendous discrepancy in diffusion rates remains challenging.Here,we report a guest solvent-directed strategy for fine-tuning the pore size at a sub-angstrom precision to realize highly efficient kinetic separation.A series of metal-organic frameworks(MOFs)with isomeric pore surface chemistry were constructed from 4,40-(hexafluoroisopropylidene)-bis(benzoic acid)and dicopper paddlewheel notes.The resultant CuFMOFCH_(3)OH(CuFMOF-c)exhibits an excellent kinetic separation performance thanks to a periodically expanding and contracting aperture with the ideal bottleneck size,which enables the effective trapping of CO_(2)and impedes the diffusion of CH_(4),offering an ultrahigh kinetic selectivity(273.5)and equilibrium-kinetic combined selectivity(64.2).Molecular dynamics calculations elucidate the separation mechanism,and breakthrough experiments validate the separation performance.