Aiming at meeting the global goals established for carbon dioxide (CO 2 ) reduction, carbon capture and storage (CCS) plays a key role. In this framework, the adsorption-based CO 2 post-combustion capture is considered one of the most promising approaches because it can provide remarkable energy savings with respect to the standard amine-based absorption capture. To date, most of the research effort has been devoted to the development of novel cutting-edge adsorbent materials with the primary purpose of enhancing the adsorption capacity and lifetime while reducing the heat of adsorption, thus lessening the energetic requirement of the sorbent regeneration. Anyway, other factors, beyond the sorbents, greatly affect the competitiveness of the CO 2 capture based on the adsorption route, namely, the gas−solid contacting system, impacting the sorbent utilization efficiency, and the regeneration strategies, determining most of the global CO 2 capture costs. This review describes the state-of-the-art and most recent progresses of the adsorption-based CO 2 post-combustion capture. In particular, the first section describes the CO 2 adsorption performances of different classes of solid sorbents on the basis of the most important evaluation parameters (equilibrium adsorption capacity, multi-cyclic stability, etc.). In the second section, the two main gas−solid contacting systems, i.e., fixed beds and fluidized beds, have been reviewed, pointing out their strengths and limitations. Finally, the third section provides a review on the different regeneration modes (temperature, pressure, or hybrid swings), with a focus on the possible strategies available to limit the energy penalty.

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The present work is a review presenting the main results obtained by our research group in the field of soundassisted fluidization of fine particles. Our aim is to highlight the role of acoustic fields in enhancing the gas-solid contact efficiency, with specific attention to the phenomenological mechanism upon which this technique is based. In particular, the first section presents the characterization of the fluidization behaviour of four different nanopowders in terms of pressure drops, bed expansion, and minimum fluidization velocity as affected by acoustic fields of different intensity and frequency. The fluidization of binary mixtures comprising two powders is also investigated under the application of different acoustic fields and varying the amounts of the two powders. The second section focuses on the study of the mixing process between two different nanopowders both from a "global/macroscopic" and "local/microscopic" point of view and highlighting the effect of mixture composition, primary particles density and sound intensity. The last section presents a promising application of sound-assisted fluidization, i.e. CO 2 capture by adsorption on a fine activated carbon, pointing out the effect of CO 2 partial pressure, superficial gas velocity, sound intensity and frequency on the adsorption efficiency.

Even though the performances of CO 2 adsorbent materials for temperature swing adsorption (TSA) are typically assessed based on the equilibrium adsorption capacity, the actual feasibility of a sorbent in real applications cannot be reliably inferred from only this parameter. Indeed, more than the maximum CO 2 uptake achievable at equilibrium, it is necessary to know the real quantity of CO 2 that can be captured in a complete adsorption/desorption cycle, namely, the difference between the quantity of CO 2 adsorbed under adsorption and desorption conditions, which is defined as the CO 2 working capacity. In this work, dynamic breakthrough and regeneration tests have been performed using a fine porous activated carbon in a lab-scale TSA sound-assisted fluidized-bed rig to experimentally evaluate the CO 2 working capacity. In particular, the standard sound-assisted fluidized-bed TSA cycle has been modified by applying the heating and purging (H&P) strategy to increase the cycle performances with regard to the CO 2 purity and recovery. Then, the effect of adsorption/desorption temperatures (25−150 °C) and CO 2 partial pressure (0.05−0.20 atm) has been evaluated.

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