Mechanism of steam‐declined sulfation and steam‐enhanced carbonation by DFT calculations

Abstract

Sulfur dioxide (SO2) and carbon dioxide (CO2) removals are of great significance for fossil fuel combustion, where they can be simultaneously captured by calcium‐based absorbents. Nevertheless, the CO2 uptake capacity declines with SO2 partial pressures. This paper aims at explaining the mechanisms of steam‐declined sulfation and steam‐enhanced carbonation by density functional theory calculations. CaO(001) surface is chosen as the absorbent, and the transition state is calculated to obtain the desorption barrier energy of the adsorbates. By analyzing the desorption of the adsorbate on pristine CaO(001) surface and the CaO(001) surface that has adsorbed other adsorbate, it can be concluded that SO2 adsorption inhibits CO2 adsorption since the barrier energy of CO2 desorption on SO2‐CaO(001) surface (24.15 kJ mol–1) is less than CO2 desorption on CaO(001) surface (129.52 kJ mol–1). By comparing the coadsorption energy of the two adsorbates with the sum of the adsorption energy of each adsorbate, it is practical that the H2O adsorption inhibits SO2 adsorption because the calculated coadsorption energy (−221.27 kJ mol–1) is larger than the sum of H2O adsorption energy (–100.00 kJ mol–1) and SO2 adsorption energy (−194.37 kJ mol–1). However, the calculated coadsorption energy of H2O and CO2 adsorption (−254.89 kJ mol–1) is less than the sum of CO2 adsorption energy (−144.23 kJ mol–1) and H2O adsorption energy (−100.00 kJ mol–1), indicating the promotion of CO2 adsorption. Steam in the adsorption process plays the roles of sulfation suppression and carbonation enhancement. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Performance of limestone‐based sorbent for sorption‐enhanced gasification in dual interconnected fluidized bed reactors

“…Moreover, the presence of steam during the carbonation stage exerts a positive influence on the overall performance of the sorbent, as inferred by comparing, respectively, the results for T600W vs. T600D, and T650W vs. T650D. This positive effect can be associated with the enhanced diffusion of CO 2 inside the porous network of the sorbent particle in presence of steam, with the development of a more favorable sorbent morphology and energy related to the CO 2 capture process by CaO, along with the formation of ionic (OH − ) species, in presence of H 2 O, as widely discussed in literature 3,15,39–45 . On the other hand, at higher temperature, H 2 O starts to promote sorbent sintering phenomena, 46,47 and this could explain why T700W ( Ν = 1 ➔ X Ca = 45.4% and N = 10 ➔ X Ca = 12.9%; average 20.8%) did not show the best result among the tests.…”

Density Functional Theory Study on CO2 Adsorption by Ce-Promoted CaO in the Presence of Steam

“…When the atoms exhibit more overlapping electron orbitals, more stable bonds are generated; therefore, the chemisorption of CO 2 is stronger on Ce-promoted CaO. 36,46 As shown in Figure 6b, the peaks of C and O 1 atoms shift toward lower energy after CO 2 adsorption, which indicates the chemisorption of CO 2 and high stability of the generated CO 3 2− structure on Ce-promoted CaO. Besides, more resonance peaks of Ce and O 1 atoms appear, demonstrating that the interaction between the two atoms is responsible for strong CO 2 adsorption on the Ce-promoted CaO surface.…”

A DFT study on the mechanism of HCl and CO2 capture by CaO

“…The influences of different additives on CaO-based sorbents and gas impurities, such as steam and SO 2 , were evaluated using DFT calculations from an atomic viewpoint. [32][33][34] In contrast, the reaction mechanism related to ionic transfer during the chlorination reaction of CaO was not systemically researched in previous studies. Hence, the change in the chlorination reactivity of CaO and the corresponding mechanism are worth understanding for optimization of the HCl removal process.…”