Studies on CO2 uptake by CaO/Ca3Al2O6 sorbent in calcium looping cycles

Abstract

In this work, limestone, aluminum nitrate hydrate, and glycerol water solution by combustion synthesis method were proposed to prepare a synthetic CaO/Ca3Al2O6 sorbent for CO2 capture in calcium looping cycles. The effects of the mass ratio of CaO to Al2O3, cycle number, carbonation conditions, and calcination conditions on the CO2 uptake by the obtained synthetic sorbent in the repeated carbonation/calcination cycles were studied in a dual fixed-bed reactor and a thermogravimetric analyzer. The optimum mass ratio of CaO to Al2O3 was 90:10 in the preparation process of the synthetic sorbent, which exhibited a 0.43 g g−1 of CO2 uptake after 50 cycles. The main compositions of the synthetic sorbent contained the mass ratio of CaO:Al2O3 = 90:10 were CaO and Ca3Al2O6, and the mass ratio of CaO to Ca3Al2O6 was 74:26. The CO2 uptake by CaO/Ca3Al2O6 increases rapidly with the carbonation time in previous 5 min and then rises slowly after 5 min. The carbonation time to reach the maximum CO2 uptake rate of CaO/Ca3Al2O6 was much sooner than that of CaO derived from limestone in each cycle. The optimum carbonation temperature window of CaO/Ca3Al2O6 was 650–700 °C. CaO/Ca3Al2O6 sorbent possessed obviously higher sintering resistance than CaO under the more severe calcination conditions in the cycles. The high CO2 uptake capacity of CaO/Ca3Al2O6 was attributed to its stable porous structure in the multiple carbonation/calcination cycles.