(291h) Microwave-Assisted Regeneration of Amine-Functionalized Sorbent for Direct Air Capture: Comparative performance of Fluidized and Packed Beds

The mitigation of rising atmospheric CO₂ concentrations demands scalable negative-emission technologies, among which direct air capture (DAC) has emerged as a promising solution [1]. DAC systems complement emission reduction strategies and are essential to achieving the carbon neutrality goals set forth by the IPCC and the Paris Agreement [2]. Because most of the energy in DAC systems is consumed during sorbent regeneration, the development of efficient regeneration methods is critical. Temperature swing adsorption (TSA), temperature–vacuum swing adsorption (TVSA), and pressure swing adsorption (PSA) are common regeneration techniques, with TSA/TVSA being the most widely implemented in DAC processes. Among various heating strategies, including steam heating [3], magnetic induction swing adsorption (MISA) [4], electric swing adsorption (ESA) [5], and microwave swing adsorption (MWSA) [6], the MWSA offers rapid, volumetric, and selective heating through dielectric interaction with the material [7]. This work investigates the applicability and performance of two commercially available amine-functionalized solid sorbents, Purolite A110 and Lewatit VP OC 1065, in a fluidized-bed DAC system using microwave swing adsorption. A sensitivity analysis was conducted to assess the effect of regeneration extent (complete vs. 90% partial regeneration) on key performance indicators (KPIs), and the results were compared to those from packed-bed operation.

Experiments were performed under dry and humid conditions using a custom-built mono-mode microwave system (MicroChem, Sairem Corp.) equipped with a solid-state generator capable of frequency modulation between 2.4–2.5 GHz and adjustable power up to 200 W. This work investigated the feasibility of MWSA-based DAC in fluidized-bed and packed bed configurations using amine-based sorbents. Microwave absorption efficiencies of 41.2% and 37.6% were achieved for Purolite and Lewatit, respectively, with regeneration efficiencies exceeding 83%. Purolite exhibited higher CO₂ uptake and up to 23% lower thermal specific energy consumption (SEC_th) than Lewatit, though with slightly lower CO₂ productivity. The 90% partial regeneration strategy provided an optimal trade-off (CO₂ productivity vs. SEC_th) enhancing CO₂ productivity by up to 8% while reducing SEC_th by 68%, as shown in Fig. 1. Comparing bed configurations, packed beds achieved greater CO₂ uptake, whereas fluidized beds reduced SEC_th by up to 15% and increased CO₂ productivity by 38% for Purolite and 46% for Lewatit. Overall, these results highlight the potential of microwave-assisted regeneration in fluidized-bed DAC systems as an energy-efficient and scalable pathway for carbon removal.

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