Granulation of alkaline metal nitrate promoted MgO adsorbents and the low-concentration CO2 capture performance in the fixed bed adsorber

Magnesium-based adsorbents with the modification of alkaline metal salts are considered the competitive candidates for CO2 capture at intermedium temperature. In this article, the NaNO3 promoted MgO adsorbents were prepared and granulated, and the characterization methods were used to detect the microstructure of the granular adsorbents, including NaNO3 distribution, BET specific surface area, micropore size and microcrystal aggregation. The thermogravimetric analyzer (TGA) tests were carried out to investigate the optimal CO2 adsorption and desorption temperatures and the cyclic stability of the NaNO3 promoted MgO granules. Moreover, the pretreatment of carbonization and calcination was adopted to improve the cyclic stability of the granular adsorbents. Furthermore, the fixed bed adsorber with 40 g NaNO3-MgO granules was used to capture CO2 from 50% CO2 mixture gas with N2 and from 20% CO2 mixture gas with N2, respectively, and the CO2 breakthrough behaviors in the fixed bed were investigated. It was found that NaNO3-MgO adsorbents were suitable for the middle and high-concentration CO2 capture (such as 50% CO2 feed gas) in fixed bed adsorber with the higher CO2 recovery efficiency, but the CO2 recovery efficiency was lower for the low-concentration CO2 capture (such as 20% CO2 feed gas) at ordinary pressure. Because about 10 kPa CO2 partial pressure in the gas phase was needed to overcome CO2 mass transfer resistance in the molten salt layer on MgO surface during adsorption, the appropriate pressurization would improve the low-concentration CO2 capture efficiency in the fixed bed adsorber.