Adsorption of CO2 in Flue Gas by Polyethylenimine-Functionalized Adsorbents: Effects of the Support Morphology and Dispersion Mode of Amines

In recent years, the use of polyethylenimine (PEI)-functionalized adsorbents for CO2 capture from flue gas has gained significant attention due to its excellent adsorption capacity. However, the influences of suitable support materials and their morphology on the adsorption and desorption of CO2 have not been adequately explored. In this study, we investigate the impact of three nanostructures of SiO2 support, namely, silica nanospheres (SNPs), silica nanosheets (SNHs), and silica nanotubes (SNTs), on CO2 capture from ultralow emission flue gas, with special emphasis on key parameters such as the adsorption capacity, amine efficiency, kinetics, thermodynamics, cyclic stability, and optimal adsorption temperature to elucidate the crucial role of morphology. Experimental results demonstrated that SNHs facilitate the dispersion of PEI on their surface, thereby effectively utilizing the specific surface area and enhancing the dispersion of the active sites of PEI. This amine dispersion method successfully reduces the mass transfer resistance of CO2 during the adsorption process. Conversely, SNTs lead to PEI dispersion between support particles, resulting in increased diffusion resistance toward CO2 and consequently decreased adsorbent performance. For SNPs, the loading of PEI into the pores effectively prevented the degradation of the adsorption performance caused by PEI leaching during the cyclic use of the adsorbent. In addition, the larger pore volume of SNPs facilitated the loading of a greater number of PEI molecules. Notably, at 60 wt % PEI loading, SNPs exhibited a higher adsorption capacity (3.68 mmol/g), lower adsorption heat (51.91 kJ/mol), and reduced regeneration energy consumption (1.775 GJ/ton). This study sheds light on the role of the support morphology in adsorption processes and presents a novel strategy for designing solid amine adsorbents with favorable cycle stability, high CO2 capture performance, and efficient amine utilization.