Stability of BeO doped CaO

https://doi.org/10.1039/D1RA09250B

“Finally, in order to explore the effect of regeneration heat transfer enhancement on sorption durability of the nano-CaO-based adsorbent in CaL process, the evolution of carbonation conversion of CaBe2/Al and Ca/Al adsorbents during 15 CaL cycles were tested in the fixed bed reactor. The results are shown in Fig. 6. The carbonation conditions of two samples were both set as 600 °C-20 vol.% CO₂/80 vol.% N₂-20 min. The regeneration condition of CaBe2/Al adsorbent was set as 750 °C-100 vol.% N₂-50 min, and the regeneration condition of Ca/Al adsorbent was set as 800 °C-100 vol.% N₂-50 min.”

“Fig. 6 Experimental points and calculation fitting curves of cyclic carbonation conversion of CaBe2/Al and Ca/Al adsorbents (EXP: experimental results, CALC: calculated results).”

“It could be found in Fig. 6 that the carbonation conversion (sorption capacity) of CaBe2/Al adsorbent gradually decreased from 81.3% (10.0 mol kg⁻¹) to 48.3% (5.9 mol kg⁻¹) in 15 CaL cycles, which lost 40.6% of initial carbonation conversion. The carbonation conversion (sorption capacity) of Ca/Al adsorbent decreased from 75.5% (11.4 mol kg⁻¹) to 36.9% (5.6 mol kg⁻¹) in 15 CaL cycles, which lost 51.1% of initial carbonation conversion. The deactivation mathematical models of CaBe2/Al and Ca/Al adsorbents were fitted based on the experimental data and eqn (7), as shown in eqn (8) and (9). The average deviation between experimental results and calculated values of carbonation conversion of CaBe2/Al and Ca/Al in 15 CaL cycles were only 2.0% and 0.3% respectively, indicating that the calculated values were consistent with the experimental results. According to the equations, the k_t of CaBe2/Al (0.505) was lower than that of Ca/Al (0.639), while the X_r−t of CaBe2/Al (0.362) was higher than that of Ca/Al (0.285). CaBe2/Al adsorbent with heat transfer enhancement had lower regeneration temperature so that the sintering degree of the adsorbent in regeneration step was reduced, leading to a better sorption durability and a higher residual stable carbonation conversion.”

                                                       Eqn (7)

                                 Eqn (8)

                                Eqn (9)

“Compared with the results of other researches on improving the cyclic durability of CaO-based adsorbents through enhancing decomposition of CaCO₃, the introduction of high thermal conductivity BeO could get more obvious improvement. Li Z. H. et al.³⁷ introduced steam into the regeneration atmosphere of limestone, which would increase the CaCO₃ decomposition rate of 1.3% min⁻¹. The loss ratio of initial carbonation conversion was decreased for 2.4% through 17 CaL cycles. Lu S. Q. et al.²⁰ increased the mean pore diameter of nano-CaO-Al₂O₃ adsorbents from 19 nm to 54 nm, which increased the CaCO₃ decomposition rate by 1% min⁻¹ and decreased the regeneration temperature by 25 °C. The loss ratio of initial carbonation conversion was reduced for 8% through 10 CaL cycles. In contrast, doping high thermal conductivity BeO could reduce the regeneration temperature by 50 °C (from 800 °C to 750 °C), and the loss ratio of initial carbonation conversion was reduced for 10.5% through 15 CaL cycles, which showed best technical advantage.”