NaNO₃‐Promoted Mesoporous MgO for High‐Capacity CO₂ Capture from Simulated Flue Gas with Isothermal Regeneration

Abstract

NaNO3‐promoted MgO composite materials have been prepared and their ability to sorb CO2 at a concentration relevant to CO2 capture from flue gas is explored. The uptake kinetics and capacities of sorbents of different NaNO3/MgO ratios are measured at intermediate temperatures of 230–300 °C. The sorbent with a NaNO3/MgO ratio of 0.10 has the highest 12 h sorption capacity among sorbents with different NaNO3 loadings, and the highest sorption capacity of 11.2 mmolCO2 g−1 is observed at 260 °C. Intriguingly, an induction period is observed in the initial stage of CO2 sorption. In situ XRD analysis, in situ FTIR spectroscopy, and a comparison of the CO2 sorption behavior under simulated flue gas conditions in comparison to prior studies employing pure CO2 indicated that the sorption of CO2 occurred through nucleation of MgCO3 crystallites in the material. The data indicate that the concentration of CO2 within the molten medium of NaNO3, which is affected by both the solubility of CO2 in molten NaNO3 and the partial pressure of CO2 in the surrounding atmosphere, has a critical impact on the length of the induction period. A partially desorbed sample after sorption of CO2 displays much‐improved sorption kinetics in the next cycle and was able to sorb and desorb CO2 over multiple cycles at isothermal conditions by simply switching the feed gas from CO2 to inert gas.

Peering into buried interfaces with X-rays and electrons to unveil MgCO 3 formation during CO 2 capture in molten salt-promoted MgO

“…Owing to the impressive effect of molten AMS on the CO2 uptake of bare MgO, the elucidation of the underlying promoting mechanism(s) has been the aim of a series of studies that have led to the postulation of a number of working hypotheses (13,14,17,(19)(20)(21)(22)(23). For example, combining thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD), it has been proposed that the addition of AMS promotes the CO2 uptake of MgO through the following two effects.…”

Assessment of the Effect of Process Conditions and Material Characteristics of Alkali Metal Salt Promoted MgO-Based Sorbents on Their CO2 Capture Performance

“…19,20 Another important parameter to enable fast CO 2 sorption is the solubility and transport of the CO 2 within the AMS. 21,22 However, the majority of the studies dealing with AMSpromoted MgO-based sorbents have investigated only their cyclic performance using different combinations of AMS and have determined the CO 2 uptake (and release) in thermogravimetric analysis (TGA). Moreover, powdery MgO-based sorbents 19−39 and/or high CO 2 concentrations with long durations during the carbonation stage have commonly been used in these studies (Table 1), which may not reflect practically relevant reaction conditions.…”

Assessment of the Effect of Process Conditions and Material Characteristics of Alkali Metal Salt-Promoted MgO-Based Sorbents on Their CO2 Capture Performance

“…Stage I is an induction period (0 < t < 2.5 min), which has been reported previously for MgO-based CO2 sorbents. 22,34,35,39 The duration of the induction period differs significantly in the different works, and it is affected by many parameters such as the types and the weight fractions of the AMS. 22 However, the reason for such an induction period remains unclear thus far.…”

“…22,34,35,39 The duration of the induction period differs significantly in the different works, and it is affected by many parameters such as the types and the weight fractions of the AMS. 22 However, the reason for such an induction period remains unclear thus far. Harada et al 35 hypothesized that within this stage, CO2 is dissolved in the molten AMS coated on the MgO, and then reacts with Mg 2+ and O 2to form MgCO3.…”

“…Here, nucleation and nuclei-growth of MgCO3 are dominating. 22 Finally, with the progress of the carbonation reaction, the formation of the MgCO3 product layer becomes significant, 34 leading to a decrease in the CO2 sorption rate (stage III, t > 8 min).…”