Study on the effect of NaBr modification on CaO-based sorbent for CO2 capture and SO2 capture

•Competitive adsorption of CO2 and SO2 on CaO-based sorbents was studied•NaBr enhanced the CO2 capture capacity of the CaO-based sorbents•NaBr enhanced the SO2 capture capacity of the CaO-based sorbents•Fractal theory was applied to analyze the mechanism of NaBr promotion•“NaBr/CaO” captured threefold of CO2 than “CaO, AR” over the 50 cycles The calcium looping process has been considered as a promising technology for capturing CO2 from the flue gas, but the decay of CaO-based sorbent, which was caused by the sintering process and the poisoning of SO2, was the major obstacle for its application in industry. In this work, NaBr modification was proposed to enhance the cyclic CO2 capture capacity of the CaO-based sorbents, and the effect of SO2 on the cyclic CO2 capture capacity of the NaBr modified CaO-based sorbents was well studied. The enhancing mechanism of cyclic CO2 capture capacity of the modified CaO-based sorbents was analyzed by X-ray diffraction, field emission scanning electron microscopy, N2 physisorption, and fractal dimensions. The result showed that the SO2 in the flue gas inactivated the CO2 capture activity of the sorbents over the cycles, but the NaBr modification not only enhanced the SO2 capture capacity but also improved the cyclic CO2 capture capacity of the sorbents. The specific surface area and BJH cumulative pore volumes of the sorbents decayed rapidly over the repeated cycles, but the fractal dimensions (D) of the NaBr modified sorbents were still larger than that of unmodified reference sorbent. 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”. Hence, NaBr modification would be a promising strategy to boost the CO2 capture capacity of the CaO-based sorbent in the calcium looping process that contributes to the carbon neutralization scenarios.