Moon Hyun June, Heller William T, Osti Naresh C, Song MinGyu, Proaño Laura, Vaghefi Ida, Jones Christopher W
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
Ind Eng Chem Res. 2024 Aug 14;63(34):15100-15112. doi: 10.1021/acs.iecr.4c01595. eCollection 2024 Aug 28.
Solid-supported amines are effective CO adsorbents capable of capturing CO from flue gas streams (10-15 vol % CO) and from ultradilute streams, such as ambient air (∼400 ppm CO). Amine sorbents have demonstrated promising performance (e.g., high CO uptake and uptake rates) with stable characteristics under repeated, idealized thermal swing conditions, enabling multicycle application. Literature studies suggest that solid-supported amines such as PEI/SBA-15 generally exhibit slowly reducing CO uptake rates or capacities over repeated thermal swing capture-regeneration cycles under simulated DAC conditions. While there are experimental reports describing changes in supported amine mass, degradation of amine sites, and changes in support structures over cycling, there is limited knowledge about the structure and mobility of the amine domains in the support pores over extended use. Furthermore, little is known about the effects of HO on cyclic applications of PEI/SBA-15 despite the inevitable presence of HO in ambient air. Here, we present a series of neutron scattering studies exploring the distribution and mobility of PEI in mesoporous silica SBA-15 as a function of thermal cycling and cyclic conditions. Small-angle neutron scattering (SANS) and quasielastic neutron scattering (QENS) are used to study the amine and HO distributions and amine mobility, respectively. Applying repeated thermal swings under dry conditions leads to the thorough removal of water from the sorbent, causing thinner and more rigid wall-coating PEI layers that eventually lead to slower CO uptake rates. On the other hand, wet cyclic conditions led to the sorption of atmospheric water at the wall-PEI interfaces. When PEI remains hydrated, the amine distribution (i.e., wall-coating PEI layer thickness) is retained over cycling, while lubrication effects of water yield improved PEI mobility, in turn leading to faster CO uptake rates.
固体负载胺是有效的CO吸附剂，能够从烟道气流（10 - 15体积% CO）和超稀释气流（如环境空气，约400 ppm CO）中捕获CO。胺吸附剂在重复的理想化变温条件下表现出了有前景的性能（如高CO吸收量和吸收率）以及稳定的特性，能够进行多循环应用。文献研究表明，在模拟直接空气捕获（DAC）条件下，诸如PEI/SBA - 15等固体负载胺在重复的变温捕获 - 再生循环中，通常表现出CO吸收率或吸收量逐渐降低的情况。虽然有实验报告描述了循环过程中负载胺质量的变化、胺位点的降解以及载体结构的变化，但对于长时间使用后载体孔隙中胺域的结构和流动性了解有限。此外，尽管环境空气中不可避免地存在H₂O，但对于H₂O对PEI/SBA - 15循环应用的影响却知之甚少。在此，我们展示了一系列中子散射研究，探索了介孔二氧化硅SBA - 15中PEI的分布和流动性随热循环及循环条件的变化。小角中子散射（SANS）和准弹性中子散射（QENS）分别用于研究胺和H₂O的分布以及胺的流动性。在干燥条件下进行重复的热循环会导致吸附剂中的水被彻底去除，从而使PEI壁涂层变薄且更坚硬，最终导致CO吸收率降低。另一方面，潮湿的循环条件会导致大气中的水在PEI壁界面处吸附。当PEI保持水合状态时，胺的分布（即壁涂层PEI层厚度）在循环过程中得以保留，而水的润滑作用提高了PEI的流动性，进而导致更快的CO吸收率。
