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

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 13.9wt% at 325°C and 120min, showing about 70% of the total sorption capacity within 10min 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 30min was on the order of 10^-4/s. Sorption working capacity was evaluated by 12 cyclic tests at 325 and 375°C for sorption (20min) and 450°C for regeneration (30min). Sorption working capacity was higher at 325°C than at 375°C, but MgO/KNO₃ was highly stable at 375°C, showing 90wt% of the first cycle.