Characteristics of MgO-based sorbents for CO2 capture at elevated temperature and pressure

Abstract

MgO-based sorbents are promising candidates for precombustion CO2 capture performed at elevated temperature and pressure in thermodynamics, where the development of efficient sorbents is of great importance. Herein, we report MgO-Na2CO3-KNO3 sorbents with fast sorption kinetics, high capture capacity and good cyclic stability at elevated conditions. The effects of nitrate species, Na2CO3 doping amounts and sorption conditions on the MgO conversion were investigated during cyclic test. In comparison with LiNO3 and NaNO3, the sample with KNO3 possesses the highest MgO conversion, which increases from 0.78 to 0.86 after 30 cycles with sorption at 400 °C, 2 MPa. For nitrate-promoted MgO, Na2CO3 plays an essential role in the initial fast sorption rate. The sorbent with 60 mol%Na2CO3 possesses the highest MgO conversion of 0.89 after 30 cycles. Moreover, during the operation range of 400 ℃-480 ℃, 2 MPa, the sorbent exhibits an excellent cyclic stability with porous structure. Density functional theory calculations are further conducted to investigate the mechanism of performance improvement brought by Na2CO3. We find dissolved CO32– ions will provide chemisorption sites through the formation of C(CO2)-O(CO32–) bonds and can serve as the CO2 carrier in molten nitrate salts, thus improving both sorption and diffusion rates of CO2.