Hydrophobic interface-assisted casting of Al-supported, CaO-based sorbent pellets for high-temperature CO₂ capture

Granulation serves as an effective strategy for mitigating the elutriation of CaO-based sorbents in the fluidized bed-based Calcium Looping system designed for CO2 capture. Here, hydrophobic interface-assisted casted CaO-based sorbent pellets were prepared via a range of hydrophobic materials, i.e., graphite, Nano-titanium dioxide, Nano-silica, and polyethylene powders. The contact Angle values of the composite slurry droplets for the four hydrophobic materials range from 126 to 143 degrees, which can provide enough surface tension to form CaO-based sorbent pellets. Moreover, the Al-based stabilizer precursors in the form of oxide, nitrate and sol, respectively, were incorporated into CaO-based pellets aiming to enhance their cyclic CO2 uptake stability. Soluble aluminum nitrate exhibits the superior performance on enhancing CO2 uptake stability compared to Nano-alumina and alumina sol, whose superiority lies in its ability to disperse more evenly with the active CaO component. Therefore, the Al-supported CaO-based pellet (similar to 30 wt% of Ca12Al14O33) with aluminum nitrate as the precursor of Al-based stabilizer remains excellent CaO carbonation conversion of 50.3 % after 20 cycles, approximately 2 times that of pure CaO pellet. Even under harsh calcination condition (950 degree celsius, 100 vol% CO2), the Al-supported CaO-based pellet is still markedly superior to CaO pellet for cyclic CO2 capture. The freshly calcined Al-supported CaO-based pellet exhibits highly desirable compressive strength (3.4 +/- 0.83 MPa), compared to 0.35 +/- 0.07 MPa for pure CaO pellet. The generated inert Ca12Al14O33 skeleton provides structural stability and strength to the Al-supported, CaO-based pellets, which simultaneously contributes to the enhanced cyclic CO2 uptake capacity and mechanical property.