Critical stability evaluations of different types of solid amine sorbents in DAC processes

Direct Air Capture (DAC) technology plays a pivotal role in mitigating climate change by capturing CO 2 directly from the atmosphere. Solid amine adsorbents are highly regarded in the DAC field for their superior CO 2 adsorption capacity and relatively low energy consumption. In practical industrial operations, adsorbents will undergo cyclic adsorption–desorption operations and their stability performances are important concerns. In this study, we carried out a comprehensive stability evaluation for three solid amine adsorbents (SiO 2 -PEI, SiO 2 -APTMS and DRC-I), which were representative of the three typical classes, i.e. impregnation (Class 1), grafting (Class 2), and in-situ polymerization methods (Class 3). All the degradation mechanisms that may encounter in practical DAC operations were included in these tests, i.e. cyclic stability, oxidative stability, water immersion stability, thermal stability, and hydrothermal stability. The experimental results indicate that DRC-I, prepared via in-situ polymerization, exhibits the best stability across all tests, a performance consistent with robust amine-phase stability as indirectly evidenced by non-detectable nitrogen loss in elemental analysis. In the presence of water, a shift in the reaction pathway leads to an increasing trend in CO 2 adsorption capacity, but its working adsorption capacity remains lower than that of the other two adsorbents. Conversely, the impregnated SiO 2 -PEI and grafted SiO 2 -APTMS adsorbents showed much poorer stability performances under aqueous conditions, i.e. in water immersion and hydrothermal stability tests. Overall, considering their CO 2 adsorption capacities and stabilities, all three adsorbents remain inadequate for large-scale industrial CO 2 capture.