Improving the stability of synthetic CaO-based CO2 sorbents by structural promoters

CaO-based materials are promising sorbents for CO2 capture via carbonate looping for high temperature applications, which however suffer from decreasing sorption capacity over multiple sorption/desorption cycles. In this study, we report the development of mixed CaO-based CO2 sorbents with inert structural promoters prepared via sol-gel auto-combustion that exhibit significant stability increase. Different synthesis parameters such as the organic material used as combustion agent, the inert material used as stabilizer and the CaO concentration in the sorbent were investigated. Citric acid was identified as the most suitable combustion agent, resulting in the formation of calcium oxide with the highest initial sorption capacity. Among the four different promoters used to increase the resistance of CaO toward sintering, Al2O3 and ZrO2 resulted in the most stable sorbents due to formation of the mixed phases Ca3Al2O6 and CaZrO3. The two sorbents exhibited a very stable performance with a sorption capacity higher than 9 mol of CO2/kg of sorbent after 100 cycles under mild operating conditions (calcination at 850 degrees C under pure N-2 flow). On the other hand Ca-Mg and Ca-La demonstrated a significant decay of sorption capacity with more than 30% deactivation after 100 and 70 cycles respectively. Under severe but more realistic conditions (calcination at 950 degrees C under pure CO2 flow), the mixed CaO-Al2O3 sorbent still retained similar to 42% of its initial sorption capacity, corresponding to 4.8 mol of CO2/kg of sorbent, while CaO-ZrO2 exhibited a remarkable stability, maintaining sorption capacity of 8.5 mol of CO2/kg of sorbent after 100 cycles. (C) 2015 Elsevier Ltd. All rights reserved.