Engineering self-assembled pellet adsorbents for energy-efficient sub-ambient direct air capture

초록

Direct air capture (DAC) requires sorbents that combine mechanical robustness, scalable manufacturability, and high capture efficiency under ultra-dilute CO2 conditions. However, a persistent gap remains between promising powder chemistries and deployment-ready structured adsorbents capable of translating laboratory-scale material performance into device-level operation under realistic atmospheric conditions-particularly at sub-ambient temperatures, where adsorption thermodynamics and transport behavior fundamentally shift. This study establishes an integrated materials-to-system framework bridging scale-ready pellet fabrication, multiscale transport analysis, and system-level performance evaluation. Integrating carbon nanotubes (CNTs) with silica nanoparticles yields mechanically resilient, mass-producible pellets that convert powder chemistries into fixed-bed-compatible architectures while retaining high CO2 capacity (1.78 mmol g-1 at 25 degrees C, adsorption isotherm), whereas the dynamic uptake reaches 1.279 mmol g-1 after 6 h in 400 ppm CO2 at 38.5 degrees C. Pellet-scale adsorption analysis establishes characteristic length as a governing architectural parameter that regulates effective kinetics in structured sorbents, thereby defining quantitative design criteria for optimizing device-level capture performance rather than merely maximizing intrinsic material uptake rates. Crucially, fixed-bed performance is systematically evaluated across sub-ambient temperatures (-10 to 20 degrees C), where adsorption thermodynamics, diffusional transport, and humidity interactions deviate markedly from room-temperature behavior. Incorporating a humidity-dependent correction, a semi-empirical mass transfer model reproduces breakthrough behavior with high fidelity. System-level analysis reveals a specific energy requirement of 0.334- 0.684 MJ mol-1 and productivity of 4.59-7.21 mol kg-1 day-1, demonstrating competitive throughput with low energy consumption. Collectively, these results provide a framework that integrates scalable material structuring, mass transfer-informed design, and sub-ambient device-level validation, offering guidance for the development of structured adsorbents in DAC applications. (c) 2026 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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