Understanding and Improving the Kinetics of Bulk Carbonation on Sodium Carbonate

Abstract

Slow kinetics of CO2 capture on sodium carbonate (Na2CO3) restricts its application in CO2 capture from flue gas despite advantages of low cost, high abundance, and economical retrofitting of extant power plants. Surface carbonation on Na2CO3 is facile; hence, the observed slow kinetics is likely due to diffusion limitations. We present an atomic-level study of the kinetics of Na2CO3 bulk carbonation. We proposal two possible pathways: the molecular interstitial diffusion (MID) mechanism, where CO2 and H2O diffuse through bulk-like sodium bicarbonate (NaHCO3) to react at the NaHCO3/Na2CO3 interface, and the ion counter diffusion (ICD) mechanism, where H+ and HCO3 – are generated at the NaHCO3–gas interface, accompanied by counter-diffusion of H+ and Na+. The MID mechanism is excluded because of the high formation energy of CO2 in NaHCO3 (2.76 eV), computed from density functional theory (DFT). We have identified and studied three main steps in the ICD pathway: (1) H+ and HCO3 – generation at the NaHCO3–gas interface; (2) generation of H+ vacancies (V H –) and interstitial Na+ (I Na +) in the NaHCO3 layer along with Na+ vacancies (V Na –) and interstitial hydrogen (I H +) in the Na2CO3 layer; and (3) V H – and I Na + diffusion through the NaHCO3 layer to the gas–solid interface. Our DFT molecular dynamics simulations confirm facile generation of H+ and HCO3 – on the NaHCO3 surface. We find that the kinetics of Na2CO3 bulk carbonation is controlled by the I H +/V Na – defect pair generation in Na2CO3; we predict that the kinetics can be enhanced by doping lithium into Na2CO3, which decreases the defect formation energy by 0.13 eV. This prediction was confirmed by our fixed-bed experiments, which found a 125% increase in the initial CO2 absorption rate and a 29% increase in CO2 uptake after 36 min exposure in 0.7 wt % (1.0 at. %) Li-doped Na2CO3 compared with undoped Na2CO3.

Sodium Carbonate–Carbon Hybrid Material for Low-Energy-Consuming CO2 Capture

“…After nine regenerations, the reaction rate constant of NaCH-923 was 5.30 × 10 –2 min –1 (Figure S5b). Cai et al reported that this situation may be the result of a series of special diffusion reactions occurring at the interface between sodium carbonate and sodium bicarbonate . The reaction rate is likely to increase with the number of cycles.…”

Direct Evidence of Dynamic Metal Support Interactions in Co/TiO2 Catalysts by Near-Ambient Pressure X-ray Photoelectron Spectroscopy

“…For the sake of convenience, the two species mentioned above are abbreviated as NaO x . The formation of sodium carbonate or hydroxide species is unlikely, since in that case, the Na 1s would appear at a considerably lower BE [39]. When the catalyst is exposed to CO 2 :H 2 (Figure 2d), an evident shoulder appears at the low BE side of the Na 1s peak.…”

CO2 Capture Performance of Na2CO3/γ-Al2O3 Sorbent Modified with Organic Acid

“…They found that the sorbent loaded with γ-Al 2 O 3 as the carrier offers several advantages, such as good dispersion of the active component, easy availability of raw materials, and high adsorption efficiency. Cai et al 21 explored the kinetics of the sodium carbonate intrinsic carbonation reaction and proposed effective improvements. Kazemi et al 22 enhanced the adsorption capacity of the sorbent by modifying the specific surface area and pore volume of γ-Al 2 O 3 carriers.…”