NaBr promoted CaO for CO2 capture

https://doi.org/10.1016/j.ccst.2021.100015

“The CaCO₃, NaBr were analytical grade reagents purchased from Sinopharm Chemical Reagent Co., Ltd., P. R. China, and the dolomite was sampled from a quarry (Lingshou SHENGFEI mineral products processing factory), Hebei province, P. R. China. The NaBr modified CaO-based sorbents were synthesized by a simultaneous hydration-impregnation method, and the NaBr doping ratio was fixed in 5 wt.%, as reported in our previous work (Xu et al., 2018a, 2016b). Briefly, 10 g of CaCO₃ or dolomite were crashed and calcined at 850 °C for 2 hours in a muffle furnace in air, and 0.5 g of NaBr was dissolved in 50 ml DI water. Then the calcined lime powders were poured into the NaBr solution with constantly stirring (200 rpm) and heating (80 °C) for 1.5 hours. After that, the generated slurry products were moved into an oven (105 °C) for 48 hours to remove the water, which was followed by grinding and sieving into particles in 0.2∼0.3mm. Finally, all the samples were calcined at 850 °C for 2 hours in a horizontal tubular furnace in the air. In this work, the NaBr modified CaO and dolomite were named as “NaBr/CaO” and “NaBr/Domite”, and the benchmark was called “CaO, AR” and “Dolomite”.”

“The cyclic CO₂ capture performance of the NaBr modified sorbents under SO₂-free condition for 50 cycles (Run 1# that listed in Table 1) was evaluated by a TGA (STA-2500 Regulus, Netzsch), and the results were displayed in Figure 1(a) and (b). All the sorbents underwent a rapid decay of CO₂ capture activity over the calcium looping cycles, especially the “CaO, AR” and “Dolomite” lost their CO₂ capture capacity from 0.55 and 0.4 g-CO₂/g-sorbent during the 1^st carbonation to 0.06 and 0.16 g-CO₂/g-sorbent during the 50^th carbonation. However, after NaBr modification, the CaO-based sorbents showed much more promising cyclic CO₂ capture capacity. Even though the NaBr modified sorbents displayed slightly inferior CO₂ capture capacity than the control groups (unmodified sorbents) during the initial several cycles, they showed much more stable CO₂ capture activity over the long runs, especially the “NaBr/Dolomite” showed almost no significant attenuation over the repeated cycles. After 50 cycles, the “NaBr/CaO” and “NaBr/Dolomite” still held CO₂ capture capacity at 0.22 and 0.24 g-CO₂/g-sorbent. The cumulative CO₂ capture capacity of the sorbents is important in the industry. Hence, the cumulative CO₂ capture capacity of the sorbents was calculated by Eq. (9), and the results were shown in Figure 1(b). The “CaO, AR” and “Dolomite” captured 6.8 and 11.2 grams of CO₂ per gram of sorbent over the 50 cycles, while the “NaBr/CaO” captured 15 grams of CO₂ per gram of sorbent over the 50 cycles, which was 2.2 times that of “CaO, AR”. However, the “NaBr/Dolomite” illustrated a just slightly better cumulative CO₂ capture capacity over the 50 cycles than the control group, even though it showed the most stable CO₂ capture activity.”

“Figure 1. (a) Cyclic CO₂ capture performance and (b) Cumulative CO₂ capture capacity of the NaBr modified sorbents under SO₂-free condition.”