Regenerable MgO-based sorbents for CO2 capture at elevated temperature and pressure: Experimental and DFT study

MgO-based mixture is a promising candidate for CO2 capture due to its high theoritical capture capacity, noncorrosiveness, low cost and wide availability. In this work, the effects of preparation methods and sorption conditions on the characteristics of MgO-Na2CO3 are studied. A stable MgO conversion of 0.32 for CO2 sorption is obtained during the 30-cycle tests at 400 degrees C, 2 MPa, where the material exhibits a strong skeleton structure with increased specific surface area when prepared by the ball-milling method. A severe sorption condition of 500 degrees C, 3 MPa is also tested, where the material shows a stable MgO conversion of 0.3 after 20 cycles. With the increase of Na2CO3 content in the mixture, a higher MgO conversion can be achieved, but the cyclic stability will be impaired. In addition to the experiments, density function theory calculations are conducted to explore the sorption mechanism of MgO-Na2CO3, where CO2 adsorptions on the pure, the Na-doped, and the Na2CO3-MgO co-adsorption surfaces are compared. The defect is found to help induce electrons from the Na and Mg atoms to the CO2 molecule, thus benefiting the CO2 adsorption process. The presence of Na2CO3 also benefits the adsorption process of MgO due to its electrostatic interaction with CO2 molecules. This work can serve as the guideline for the design of MgO-based CO2 absorbent especially for extreme operating conditions.