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 potential of torrefaction treatment for upgrading low-value tomato peel residues into high-quality solid energy carriers was investigated by using a new bench-scale batch experimental apparatus based on fluidized-bed technology. In particular, the influence of the main process variables (i.e., temperature and time) on both the key performance parameters (i.e., mass and energy yields) and the main properties of the solid product (i.e., elemental composition, ash content, calorific value and equilibrium moisture content) was studied. Fluidized bed experimental runs were performed at 200, 240, and 285 °C by keeping the torrefaction time at 5, 15, and 30 min. Results suggested tomato peels as a good candidate for the torrefaction treatment. In more detail, it was observed that higher temperatures and longer holding times (with a more marked effect of the torrefaction temperature) led to an increase in the calorific value of the torrefied tomato peels, with respect to the parent ones. More specifically, the calorific value increased by a factor of 1.2 for the biomass treated at 285 °C and 30 min. Under the same experimental conditions, a 40% reduction in the O/C elemental ratio and an improved hydrophobicity of the torrefied tomato peels were also observed. These positive effects of the torrefaction treatment occurred while maintaining the mass yield (approximately between ∼75% and ∼94%, daf) and energy yield (∼90% and ∼96%, daf) at satisfactory levels. Fluidized-bed torrefaction experiments were also complemented by TGA-MS investigations and comparative tests carried out in a bench-scale fixed-bed reactor. Outcomes showed that the fluidized-bed technology is more suitable than the fixed bed one to cope with the exothermicity associated with the thermal degradation of nonwoody biomass, which has a tendency to ignite or carbonize easily during torrefaction. Furthermore, the fluidized bed proved to be more effective in ensuring a uniform and consistent quality of the torrefied solids

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