Toward Understanding the Kinetics of CO₂ Capture on Sodium Carbonate

Abstract

Sodium carbonate (Na 2 CO 3 ) has been widely studied as a promising candidate for CO 2 capture from humid flue gas because of its low cost, high abundance, reusability, and moderate operating temperatures. However, the slow kinetics of CO 2 capture on unmodified Na 2 CO 3 make it an unacceptable choice for practical applications. If the reaction kinetics could be dramatically improved, then Na 2 CO 3 could be a viable material for large-scale carbon capture applications. The first step to systematic improvement of kinetics is to understand the rate-limiting steps in the uncatalyzed system. We have therefore investigated the structural, mechanistic, and energetic properties of CO 2 capture on the (001) and (−402) surfaces of Na 2 CO 3 using density functional theory to identify the origin of the slow kinetics observed in experiments. We have identified reaction pathways for co-adsorbed CO 2 and H 2 O that lead to bicarbonate formation on the (001) and (−402) surfaces having activation energies of 0.40 and 0.34 eV, respectively. We modeled surface carbonation reactions under conditions of high surface loading of water by performing ab initio molecular dynamics simulations at typical operating temperatures. Multiple reactions were observed on picosecond time scales. Our results indicate that the Na 2 CO 3 carbonation reaction is not controlled by the kinetics of the reaction at the surface but is likely by diffusion limitations. We propose two possible scenarios that could result in diffusion control of the reaction rate.

Understanding and Improving the Kinetics of Bulk Carbonation on Sodium Carbonate

“…Therefore, we have chosen to study the mechanism of R1 in this work because it is the dominant channel for postcombustion carbon capture. Our previous study revealed that initial surface carbonation on Na 2 CO 3 is facile and suggested that bulk diffusion is kinetically limiting . Here, we elucidate two possible pathways of diffusion-controlled bulk carbonation of Na 2 CO 3 : the molecular interstitial diffusion (MID) mechanism and the ion counter diffusion (ICD) mechanism.…”

“…The climbing image nudged elastic band (CI-NEB) method , was applied to locate the transition state (TS) structures and the reaction pathways. We used the Na 2 CO 3 bulk structure from our previous study and the NaHCO 3 bulk structure from Duan et al…”

“…Our previous study revealed that initial surface carbonation on Na 2 CO 3 is facile and suggested that bulk diffusion is kinetically limiting. 21 Here, we elucidate two possible pathways of diffusioncontrolled bulk carbonation of Na 2 CO 3 : the molecular interstitial diffusion (MID) mechanism and the ion counter diffusion (ICD) mechanism. We use density functional theory (DFT) methods, including Ab initio Molecular Dynamics (AIMD) simulations, to study these proposed mechanisms.…”

“…The climbing image nudged elastic band (CI-NEB) method 38,39 was applied to locate the transition state (TS) structures and the reaction pathways. We used the Na 2 CO 3 bulk structure from our previous study 21 and the NaHCO 3 bulk structure from Duan et al 40 We calculated the formation energy of defect X in bulk Y (E def X ) using the method of Van de Walle and Neugebauer 41…”

Highly efficient and selective CO2 capture of Li2CO3- and (Li–K)2CO3-based porous carbon composites

“…Theoretically, the CO 2 adsorption capacities of commercial Na 2 CO 3 and K 2 CO 3 were 41.5 wt% and 31.8 wt%, respectively. 10 According to the thermogravimetric analysis from 12 basing on density functional theory and molecular dynamics simulation, studied the adsorption process and adsorption types of CO 2 and H 2 O on Na 2 CO 3 crystal surfaces from the atomic scale. Their results showed that the carbonation reaction rate of Na 2 CO 3 was not controlled by the kinetics of the surface reaction, was controlled by the phase diffusion of the adsorbent.…”