Parametric Study of the CaO−Ca12Al14O33 Synthesis with Respect to High CO2 Sorption Capacity and Stability on Multicycle Operation

Abstract

This study focuses on the effect of various parameters of the synthesis procedure of the CO 2 sorbent—CaO−Ca 12 Al 14 O 33 derived from calcium acetate—on the CO 2 sorption ability and lifetime. The synthesis procedure consists of the calcination of the acetate CaO precursor (step 1), the precipitation of the CaO with aluminum nitrates (step 2), followed by calcination at 500 °C for nitrates removal (step 3) and the calcination at 900 °C for the synthesis of Ca 12 Al 14 O 33 (step 4). It has been shown, by employing TGA, that the applied difference in the calcination conditions (900 °C/2 h, 850 °C/1 h, 750 °C/0.5 h,) for the decomposition of the CaO acetate precursor (step 1) is not adequate to affect the sorption fixation and stability results. On the other hand calcination history of the precipitate and the addition of water in between the two calcination steps (nitrates removal and Ca 12 Al 14 O 33 synthesis reaction) are of high importance for ensuring sorption capacities higher than 6.5 mol CO 2 /kg of sorbent in the first cycle. SEM observations showed that the addition of water after calcination at 500 °C (step 3) accounts for the generation of the regular hexagonal crystalloids of Ca(OH) 2 which transforms in a porous network during calcination at 900 °C. It was also demonstrated that the quantity of CO 2 molecules retained increases with decreasing aging time of the precipitate as a result of higher surface area (smaller crystal size) of the as-synthesized samples. The sorbent with the lower binder content (CaO/Ca 12 Al 14 O 33 = 85:15) showed the prospective higher capacity (45% weight increase) in the first cycle but also a fair stability on repetitive sorption−desorption cycles.