https://doi.org/10.3390/nano11123188
“The sorbents with the highest and second highest saturated capture amounts, CaTi-3 and CaTi-5, were selected for evaluation of their multicycle stability. The results are shown in Figure 5a,b, respectively. After 20 cycles of repeated use, the capture capacity of CaTi-3 was almost unchanged, whereas that of CaTi-5 decreased by ~17% compared with that in the first cycle (Figure 5c). CaTi-5 showed capacity loss because too much calcium oxide was present in this sorbent. The carbonation behavior of CaTi-3 and CaTi-5 at the twentieth cycle were different than the first cycle (Figure 5d). The two stage carbonation behavior due to more importance of the inner-diffusion mechanism at the twentieth cycle in comparison to the first cycle carbonation reaction revealed that slight sintering occurred in both sorbents during 20 cycles of repeated use. The sintering phenomenon occurred at the CaCO3 phase due to its low Tammann temperature (~530 °C) [13]. Thus, the inner-diffusion controlled mechanism became important as repeated times increased. This result indicated that after 20 cycles of repeated use, calcium species particle sizes increased. Additionally, the capture capacity of CaTi-3 in the twentieth-cycle carbonation was closer to its first cycle than the CaTi-5 case at 10 min, indicating that calcium species particles suffered a greater degree of sintering in CaTi-5 than in CaTi-3.”
“Figure 5. Twenty cyclic repeating experiment results of CaTi-3 (a) and CaTi-5 (b); percentage of capture capacity of each cycle to the first cycle (c), and the carbonation performance of the first and the twentieth experiment of CaTi-3 (up) and CaTi-5 (down) (d).”
“The XRD results of CaTi-3 and CaTi-5 sorbents after 1 and 20 cycles of repeated use are presented in Figure 6a,b, respectively. After 1 cycle, CaTiO3 and Ca(OH)2 diffraction signals could be found in both sorbents. However, several CaCO3 diffraction signals (JCPDS 850849) clearly appeared in CaTi-5 after 20 cycles of repeated use. Given that the cycle experiment involved an initial carbonation part followed by regeneration, the CaCO3 species remaining after the cyclic experiment indicated that decarbonation efficiency decreased. The CaCO3 species could not capture CO2, so CaTi-5-capture capacity loss occurred after 20 cycles. Moreover, one CaCO3 diffraction signal with a very weak peak intensity was found in CaTi-3 after 20 cycles, indicating that cyclic stability started to decrease when the mole ratio of calcium to titanium was greater than 3. The SEM images of CaTi-3 and CaTi-5 after 20 cycles are shown in Figure 7. CaTi-5 presented a denser morphology than CaTi-3, indicating a lower carbonation performance of CaTi-5 compared to CaTi-3, which was consistent with the cyclic-experiment results.”
“Figure 6. XRD results of (a) CaTi-3 and (b) CaTi-5 collected from after 1 cycle and 20 cycle experiments, where the invert triangle symbol represents CaTiO3, the circle symbol represents Ca(OH)2, and the star symbol represents CaCO3.”
“Figure 7. SEM images of CaTi-3 (a) and CaTi-5 (b) after 20 cycle experiment.”