Review of nanoabsorbents for capture enhancement of CO₂ and its industrial applications with design criteria

Nanoabsorbents manufactured by dispersing nanomaterials in liquid absorbents have attracted considerable attention from researchers and exhibit various promising applications because of their excellent heat- and mass-transfer characteristics. Therefore, many experimental and theoretical studies have been conducted recently to investigate the mass-transfer performance enhancement of nanoabsorbents in different fields. This paper reviews the mass-transfer characteristics and enhancement mechanisms of nanoabsorbents for CO₂ capture. The proposed enhancement mechanisms are discussed in terms of both absorption (bubble breaking, shuttle, and interfacial mixing effects) and regeneration (activation energy, thermal, and surface effects) processes using nanoabsorbents. The results of laboratory-scale experiments and parametrical analysis indicate that the CO₂ absorption performance of nanomaterials is maximized when they exhibit a high surface area, high thermal conductivity, small cluster size, and magnetic properties, which can be explained using the proposed theoretical models. Based on this, the following selection criteria for nanomaterials to maximize the CO₂ absorption/regeneration performance are proposed: thermophysical properties, powder/cluster size, concentration, and addition of nanoabsorbents. In the future, mass-transfer studies need to be conducted for real-life applications and should account for dispersion stability and integrated absorption/regeneration processes. Moreover, optimum geometric conditions and gas–liquid contact modes need to be achieved in the reactor for real-life applications. Finally, this paper suggests future research directions for the absorption and regeneration of CO₂ for industrial applications, including the scale-up method, numerical approach, and life cycle analysis.