The use of CaO-based adsorbents has a high potential to capture CO2 from various systems due to its high reactivity with CO2, high capacity, and low cost of naturally derived CaO. The application of CaO-based sorbents to remove carbon dioxide is based on a reversible reaction between CaO and CO2. However, multiple carbonation/calcination cycles lead to a rapid reduction in the sorption capacity of natural CaO, and therefore efforts are made to reduce this disadvantage by doping, regenerating, or producing synthetic CaO with stable sorption properties. In this review, the synthesis methods used to obtain CaO-based sorbents were collected, and the latest research on improving their sorption properties was presented. The most commonly used models to describe the CO2 sorption kinetics on CaO-based sorbents were also introduced. The methods of sorbent regeneration and their effectiveness were summarized. In the last part of this review, the current state of advancement of work on the larger scale, possible problems, and opportunities during scale-up of the calcium looping process were presented. Concluding (i) the presented methods of adsorbent synthesis allow for the production of doped CaO adsorbents on a laboratory scale, characterized by high CO2 capture efficiency and good cyclic stability, (ii) the most commonly used in practice models describing CO2 chemisorption are empirical models and the shrinking core model, (iii) the use of sorbent regeneration allows for a significant improvement in sorption capacity, (iv) the scale-up of both the production of new CaO adsorbents and the CO2 capture technology with their use requires further development.

Ammonia solutions are considered to be effective solvents for carbon dioxide absorption. Despite numerous advantages of these solvents, their high volatility is a significant technical and economic problem. Therefore, in this work, silica particles were used as additives to improve CO ₂ absorption and inhibit NH ₃ desorption. SiO ₂ microparticles and colloidal SiO ₂ particles in the concentration range of 0-0.15 wt.% were used in this study. The most favorable mass transport for CO2 absorption was at the concentration of colloidal particles of 0.05 wt.%. Under these conditions, the enhancement in the number of moles of absorbed CO ₂ was above 30%. However, in solvents containing 0.01 wt.% SiO2 microparticles, the increase in CO ₂ absorption was about 20%. At the same time, the addition of SiO2 particles significantly reduced the escape of ammonia from the solution. The best improvement was obtained when colloidal SiO ₂ particles were added, and then NH ₃ escape was decreased by about 60%. This unfavorable phenomenon was also inhibited in ammonia solutions containing SiO2 microparticles at a concentration of 0.01 wt.%.