Mesoporous MgO sorbent promoted with KNO3 for CO2 capture at intermediate temperatures

• Mesoporous MgO-based sorbents were synthesized using an aerogel method.
• MgO·KNO3 composite showed high CO2 sorption rate and capacity in the intermediate temperature range.
• The MgO·KNO3 composite showed higher CO2 capacity among all MgO-akali metal salt composites.
• The amount of salt and its melting temperature influenced the CO2 capacity and stability.

Mesoporous MgO·KNO3 composites were developed using an aerogel method for CO2 sorption in the intermediate temperature range of 250–400 °C. The effects of MgO/KNO3 molar ratio, calcination method and sorption temperature on CO2 sorption rate and capacity were evaluated using a thermogravimetric analyzer. The composite prepared at a MgO/KNO3 molar ratio of 1:0.2 with a four-step calcination had the high CO2 sorption capacity of 13.9 wt% at 325 °C and 120 min, showing about 70% of the total sorption capacity within 10 min and about 7 times higher sorption capacity than pure MgO. In addition, the developed MgO·KNO3 composite showed higher sorption capacity than other MgO composites promoted by alkali metal salts (K2CO3, KOH, NaNO3, Na2CO3, Na2HPO4, LiNO3 and Li2CO3). The sorption rate of CO2 on a MgO·KNO3 composite during the initial 30 min was on the order of 10−4/s. Sorption working capacity was evaluated by 12 cyclic tests at 325 and 375 °C for sorption (20 min) and 450 °C for regeneration (30 min). Sorption working capacity was higher at 325 °C than at 375 °C, but MgO/KNO3 was highly stable at 375 °C, showing 90 wt% of the first cycle.