(174cg) The Self-Reactivation Performance of Nano-CaO-Based CO2 Adsorbents in Calcium Looping Process

The self-reactivation performance including self-reactivation extent and stability of nano-CaO-based CO₂ adsorbents were investigated to obtain the adsorbent with high carbonation conversion and high cyclic stability. The effects of thermal expansibility of dopants, preparation process, heat-treatment of the pre-sintering process and calcium looping process on the self-reactivation performance have been studied in detail. Firstly, nano-CaO-based adsorbents doped with different thermal expansibility materials of MgO, calcium aluminate, CaTiO₃ and CaZrO₃ were prepared by sol-gel method. It was found that the nano-CaO-based adsorbent doped with the lowest thermal expansibility perovskite salt CaTiO₃ or CaZrO₃ had the best self-reactivation performance by generating more cracks. Then, comparing to the sol-gel method, the nano-CaO/CaTiO₃ adsorbent prepared by the adsorption phase reaction method (APCaTi) owned better dispersion of nano-CaO grains leading to a better self-reactivation performance. Also, the APCaTi adsorbent with CaO to CaTiO₃ molar ratio of 16 (APCaTi16) had suitable coating density of CaTiO₃ around CaO, so it had both high carbonation conversion and good self-reactivation performance. As the heat-treatment temperature and time increased to 900^oC-1h, the pre-sintering of APCaTi16 adsorbent was aggravated resulting in closer contact between CaO and CaTiO₃, which strengthened its self-reactivation performance. Moreover, high carbonation temperature and low regeneration temperature corresponding to high carbonation conversion and low sintering degree respectively were favorable for developing the self-reactivation performance. Combining the optimal values of preparation and operation conditions, the carbonation conversion of the nano-CaO/CaTiO₃ adsorbent (with 83.3wt.% CaO) remained 88.2% after 20 cycles of calcium looping process, which was obviously higher than the carbonation conversion of traditional limestone adsorbent (nearly 50%) and nano-CaO/MgO adsorbent (nearly 60% with 85wt.% CaO) after self-reactivation in previous studies. In conclusion, the enhancement effects of thermal expansibility of dopants and calcium looping process on self-reactivation extent and stability were more important. These research findings could not only guide the synthesis of CaO-based adsorbents with high carbonation conversion and high cyclic stability, but also help to figure out the self-reactivation mechanism of nano-CaO-based adsorbents.