Amine/oxide hybrid carbon dioxide adsorbents prepared via impregnation of low molecular weight polymeric amines into porous oxide supports are among the most promising solid adsorbents developed for postcombustion CO 2 capture or CO 2 extraction from ambient air. The oxidative stability of adsorbents prepared by impregnation of poly(ethylenimine) (PEI) or poly(allylamine) (PAA) into mesoporous γ-alumina under humid oxidation conditions is evaluated in this work. The PEIbased adsorbents, which contain primary, secondary, and tertiary amines, are shown to degrade drastically at elevated temperatures (110 °C) and in high oxygen concentrations (21%, akin to air), with these effects reduced by both reductions in temperature (70 °C) and oxygen concentration (5%, akin to flue gas). The oxidation behavior of PEI-based adsorbents supported on alumina is qualitatively similar to past work on silica-supported PEI adsorbents. In contrast, the alumina-supported PAA adsorbents that contain only primary amines show significantly improved oxidative stability, losing only 10% or less of their original CO 2 capacity after prolonged oxidative treatment under a variety of conditions. Analysis of the fresh and thermally treated samples by Fourier transform (FT) IR, FT-Raman, and 13 C NMR spectroscopies demonstrates the clear formation of carbonyl functionalities over the oxidized PEI-based adsorbents, whereas no significant changes in the spectra for PAA samples are observed after oxidative treatments. The collected data demonstrate that secondary-amine-free, primary-amine-rich polymers such as PAA may be used to formulate supported amine adsorbents with improved oxidative stability compared to adsorbents based on PEI, which is used ubiquitously in the field today.

Solid oxide-supported amine sorbents for CO2 capture are amongst the most rapidly developing classes of sorbent materials for CO2 capture. Herein, basic γ supports are used as hosts for amine sites through the grafting of 3-aminopropyltrimethoxysilane to the alumina surface under a variety of conditions, yielding the expected surface-grafted alkylamine groups, as demonstrated by FTIR spectroscopy and (29)Si and (13)C cross-polarization magic-angle spinning (CPMAS NMR) spectroscopy. Grafting amine sites on the surface in the presence of water leads to a high density of amine sites on the surface whereas simultaneously creating a unique type of aluminum species on the surface, as demonstrated by both 1D and 2D (27)Al MAS NMR spectroscopy. The thus prepared sorbents result in higher CO2 adsorption capacities and amine efficiencies compared to sorbents prepared in the absence of water or similar amine loading sorbents prepared using silica supports. In situ FTIR spectra of the sorbents exposed to CO2 at various pressures show no distinct difference in the nature of the adsorbed CO2 species on alumina- versus silica-supported amines, whereas water adsorption isotherms show that the improved performance of the amine-grafted alumina support is not a consequence of retained water on the more hydrophobic aminoalumina materials. The findings demonstrate that amine-grafted, basic alumina materials can be tuned to be more efficient than the corresponding silica-supported materials at comparable amine loadings, further demonstrating that the properties of amine sites can be tuned by controlling or adjusting the support surface properties.

Please cite this article as: F. Rezaei, M.A. Sakwa-Novak, S. Bali, D.M. Duncanson, C.W. Jones, Shaping aminebased solid CO 2 adsorbents: effects of pelletization pressure on the physical and chemical properties, Microporous and Mesoporous Materials (2014), doi: http://dx.ABSTRACT: Amine-based solid adsorbents are promising candidates for the separation of CO 2 from dilute gas streams. Here we report the effect of pelletization pressure on the physical and chemical properties of an array of supported amine adsorbents, based on mesoporous silica and γ-alumina supports. The virgin powders based on poly(ethyleneimine) (PEI) and 3-aminopropyltrimethoxysilane (APS) functionalized oxides are pressed at 1000 and 5000 psig pressure to form self-supporting pellets and their physical and chemical properties are compared.No change in chemical structure of the adsorbents is observed after pelletization, though the porosity of each material changes to some degree. Of the three mesoporous supports examined in this study, the commercial porous silica was the most stable support for both class 1 and class 2 adsorbents, whereas lab synthesized mesoporous SBA-15 silica and lab synthesized mesoporous γ-alumina are found to be the least stable supports for class 1 and class 2 adsorbents, respectively. The CO 2 uptake results show a significant drop in equilibrium capacity for the pellets pressed at 5000 psig, regardless of the support used, while the 1000 psig pellets retain their capacity and show comparable performance to their powder counterparts. CO 2 2 breakthrough experiments suggest an increase in mass transfer resistance for the pellet samples as compared with virgin powders, resulting in the dispersion of the concentration fronts during CO 2 breakthrough using a fixed bed. These findings suggest that shaping solid supported amine adsorbents into binderless pellets requires pressing the powders at low to moderate pressures to ensure that these materials retain their performance in processes that require pelletized samples.

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