Typical TGA multi-cycle using CaO based sorbent and general methods for performance improvement

The following content provides a general description of CaO-based adsorbent for CO2 capture regarding the challenges and methods to enhance the performance of CaO adsorbents. They are copied from (, an open access paper:

“A typical TGA multi-cycle run with natural limestone is presented in Figure 2. It can be seen that after only 10 cycles, conversion dropped to 40%, half the conversion in the first cycle. The loss of activity continues, and it has been shown in long series of cycles (>1,000 cycles) that conversions become constant, at the level of 7–8% [20]. It should also be mentioned that most research has been performed under ideal experimental conditions, with calcination stages in N2 at lower temperatures, while the loss of activity occurs much faster under realistic conditions expected in real FBC systems [21,22]. It is typically supposed that during CO2 cycles, the sorbent morphology changes, and the sorbent loses surface area and small pores, which are the main contributors to the rapid carbonation necessary for practical systems.”


Figure 2. Loss of sorbent (Cadomin limestone, 250–425 μm) activity during carbonation/calcination cycles in TGA; 700 °C isothermally: 60 min carbonation in 15% CO2 (N2 balance), 60 min calcination in N2.” (

” The improvement of sorbent activity for extended use is imperative because sorbent replacement costs strongly influence the overall cost of CO2 capture [14]. Reactivation by hydration currently appears to be a promising method for recovery of the sorbent activity [15,23,24]. Another approach is thermal pretreatment of the sorbent at high temperatures [2527]. Here, thermal pretreatment typically causes lower conversions during the early cycles, but conversions in later cycles are higher than those for the original, untreated sorbents. This phenomenon of increasing conversion with an increasing number of reaction cycles has been called self-reactivation [26].

Most doping agents enhance sintering, which is also enhanced by the presence of impurities in the sorbent [22,28]. However, it has been shown that some compounds in the CaO structure prevent sintering. The most investigated are synthetic sorbents with Al2O3 [2931], but recently it has been shown that sorbents containing KMnO4 [32], and TiO2 [33] are also more resistant to sintering. Other attempts include modification by acetic acid [34], and impregnation of CaO on mesoporous supports [35]. Commercial pure lime nano-sized sorbents [36] or flame-made doped nano-particles [37] were also investigated. Nano-sized sorbents were prepared from different precursors [38,39] and procedures [27,40,41]. These modified/synthetic sorbents have superior CO2 carrying capacity, but their practical use is limited due to their high price and difficulties for their use in FBC systems. “



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