Role of urea hydrolysis in the sol–gel synthesis of Ca3Al2O6-modified CaO for ultra-stable CO2 capture
Min Jun Hwang, Jong‐Ho Park, Ji Chan Park, Byeong‐Seon An, Sun Hyung Kim, Ki Bong Lee, Hyung Jin Yoon
Abstract
• Ca 3 Al 2 O 6 -modified CaO sorbents were prepared via urea-assisted citrate sol–gel route. • Surface-oriented distribution of Ca 3 Al 2 O 6 could be achieved via urea hydrolysis. • Particle size and porous structure were tailored for enhanced mass transfer. • Outstanding CO 2 sorption of ∼55.6 wt% could be achieved during 10 cycles. CaO-based sorbents are known for their high CO 2 sorption capacity; however, they suffer from gradual deactivation during cyclic usage. To effectively enhance cyclic stability, this study introduced Ca 3 Al 2 O 6 into CaO as a structural stabilizer via the urea-assisted citrate sol–gel method. Gradually controlling the pH through urea hydrolysis resulted in the formation of a more stable colloidal sol, leading to reduced particle size and the development of a porous structure. This enhancement improved CO 2 mass transfer into the CaO particles and significantly boosted the CO 2 sorption kinetics of the CaO-based sorbents. Additionally, urea caused the Ca 3 Al 2 O 6 crystallites to primarily disperse mainly on the surface of the CaO particles, markedly improving cyclic stability even with a small amount of stabilizer. The Ca 3 Al 2 O 6 -modified CaO exhibited perfect cyclic stability without any loss of CO 2 sorption uptake over 10 repeated cycles of sorption and regeneration at 700 °C, exhibiting an average working capacity of ∼55.1 wt%; it is more interesting in that the developed sorbent can capture and release CO 2 at identical temperature just by switching the gas atmosphere. Significant decrease in regeneration temperature is also attributed to enhanced CO 2 mass transfer. Therefore, Ca 3 Al 2 O 6 -modified CaO, exhibiting fast CO 2 sorption/regeneration kinetics and outstanding cyclic stability, could be beneficial for direct CO 2 capture at high temperatures.