Single Nozzle Flame-Made Highly Durable Metal Doped Ca-Based Sorbents for CO_2 Capture at High Temperature

摘要

The single nozzle flame spray pyrolysis (FSP) method has been employed to synthesize M/Ca (M = La, Y, Hf, W, and Al) sorbents with a 1:10 molar ratio for high temperature multicyclic CO_2 capture. Among the various sorbents, Al-doped CaO sorbent exhibits remarkable adsorption capacity and stability. Further analysis on Al/Ca sorbents with different molar ratios resulted in a highly durable and high uptake capacity sorbent when 3 mol of Al were doped into 10 mol of CaO. Al/Ca (3/10) sorbent was stable up to 100 cycles with CO_2 uptake capacity of 0.40 g/g of sorbent XRD measurements reveal the formation of a solid solution Ca_(12)Al_(14)O_(33) in the case of Al doped CaO and structures like Ca_3WO_6 and CaHfO_3 in the case of W and Hf-doped samples, respectively. On the other hand, Y and La doped sorbents exhibit only peaks due to Y_2O_3 and La_2O_3. The intensity of the peaks due to the Ca_(12)Al_(14)O_(33) increased with increasing the Al doping into the CaO sorbent. The sorbent resistance to sintering-agglomeration has also been increased with increasing Al doping, thus indicating that Ca_(12)Al_(14)O_(33) is responsible for the excellent stability of Al/Ca (3/10) sorbent TEM analysis of the Al-doped CaO sorbents also shows the direct relationship between the amounts of Al doped and sorbent stability. TPD measurements reveal that the addition of foreign metal decreases the decarbonation temperature of CO_2 for CaO. The Al/Ca (3/10) sorbent also shows good resistance to sintering when tested under severe conditions. The increase in the CO_2 uptake capacity in Al/Ca sorbents is attributed to the less number of Ca atoms and more number of Al atoms in the solid solution Ca_(12)Al_(14)O_(33) formation. This leaves excess CaO for the CO_2 capture.