Synthesis methods of K2CO3 based adsorbents

https://doi.org/10.1016/j.ccst.2021.100011

“Yang et al. prepared carbon aerogels (CAs) using the sol-gel method, and they loaded K₂CO₃ on the mesoporous supports to prepare the CA-potassium carbonate (KC) nanocomposites. The 7CA-KC adsorbent with good textural properties exhibited a high CO₂ uptake of 2.68 mmol CO₂/g and a declined regeneration temperature (Yang et al., 2016). This was because the sol-gel and impregnation method had enabled the K₂CO₃ nanocrystals being embedded in the nanopores of the CAs, and the incorporated K₂CO₃ nanocrystals exhibited higher reactivity than bulk K₂CO₃ (Yang et al., 2016). Guo et al. reported that the sol-gel and impregnation method had benefited the silica-alumina aerogel and silica aerogel supported K₂CO₃ adsorbents developed microstructure and good morphology for enhanced CO₂ uptakes (1.32-1.86 mmol CO₂/g) (Guo, B. et al., 2020a; Guo, B. et al., 2020c; Guo et al., 2018b). For silica aerogel supported K₂CO₃ adsorbents (KSGs), the dispersion of K₂CO₃ would be affected by the different solvents employed in the impregnation process. Instead of deionized water, ethanol as solvent or dispersing agent would bestow the KSGs adsorbents with uniform dispersion of K₂CO₃ (Guo et al., 2015c, d; Guo et al., 2018b). It is well known that K₂CO₃/Al₂O₃ would suffer deactivation in repeated cycles due to the formation of byproduct of KAl(CO₃)(OH)₂. Given this, a novel K₂CO₃/Al₂O₃ adsorbent was synthesized by CO₂ thermal treatment of the impregnated K₂CO₃ on porous δ-Al₂O₃ support. CO₂ thermal treatment played an important role in inhibiting the formation of KAl(CO₃)(OH)₂ byproduct, and therefore had endowed the new K₂CO₃/Al₂O₃ adsorbent with stable CO₂ adsorption capacity (∼3.09 mmol CO₂/g) over multiple cycles (Jo et al., 2016). Efforts had also been made to construct core/shell-structured potassium-based adsorbents by employing γ-alumina and boehmite (γ-AlOOH) as cores and titanium propoxide, tetra ethyl ortho silicate, and zirconium butoxide as shells. By creating a layer between K₂CO₃ and alumina, the core-shell technique had weakened the interactions between the two phases, and the formation of KAl(CO₃)(OH)₂ byproduct could be inhibited. Therefore, the core-shell-structured potassium-based adsorbent retained a high CO₂ uptake (3.31 mmol CO₂/g) and good working stability (Bararpour et al., 2020). It was reported that K₂CO₃/Al₂O₃ prepared by the single-step impregnation (SI) method suffered evident pore structure blockage and limited K₂CO₃ utilization. The multi-step impregnation (MI) method was proposed to promote the dispersion of K₂CO₃ in the broad macropores, and the CO₂ adsorption capacity of the adsorbent prepared via the MI method had been significantly improved from 1.93 to 3.12 mmol CO₂/g (Sengupta et al., 2014a). Bararpour et al. prepared K₂CO₃/alumina adsorbents by the physical mixing method and incipient wetness impregnation method, respectively, and the adsorbent synthesized by the physical mixing method showed a higher CO₂ capture capacity (2.75 mmol CO₂/g) (Bararpour et al., 2018).”