High-temperature CO2 capture cycles for CaO-based pellets with kaolin-based binders

Pellets from natural and acetified Havelock limestone were synthesized and tested for in situ post-combustion CO2 capture in Ca-looping cycles. Natural kaolin and Al(OH)3 obtained from acid leaching of kaolin were used as binders. The results showed that after 30 cycles, pellets prepared from acetified limestone with 10 vol.% acetic acid and CaO/Al(OH)3 mass ratio of 5.5 had a somewhat higher CO2 uptake of 0.13 g/g (g CO2/g sorbent), compared to 0.12 g/g for pellets prepared from natural limestone and Al(OH)3. These uptakes corresponded to 56% and 36.7% of their initial capture capacities, respectively. By contrast, natural sorbent and pellets prepared with kaolin demonstrated a significant decay in their CO2 uptake down to 21% and 21.7% of their initial capacities, respectively. The superiority of acetified sorbents with Al(OH)3 binders appears to be due to the creation of a highly developed porous structure. In particular, α-Al2O3 generated from Al(OH)3 appears to create a stable framework dominated by mesopores, which also inhibits sintering over multiple cycles. However, acetification itself widens pores and alters pore surface area and volume, providing more space for CaCO3 growth. Unfortunately, water addition during pellet synthesis appears to compromise this porous structure, thus reducing the original benefits of acetification.

► Acetification with low acetic acid concentration (10 vol.%) significantly enhanced limestone morphology.
► Acetified limestone pellets with Al(OH)3 binder showed better performance than natural limestone in CO2 capture cycles
► Upon calcination, an Al(OH)3 binder provided a stable mesoporous structure, which inhibited the fast sintering of CaO.
► The sintering associated with the high SiO2 content of kaolin makes it an unsuitable binder for high-temperature CO2 capture.