CO 2 capture properties of alkaline earth metal oxides and hydroxides: A combined density functional theory and lattice phonon dynamics study

Abstract

By combining density functional theory and lattice phonon dynamics, the thermodynamic properties of CO(2) absorption/desorption reactions with alkaline earth metal oxides MO and hydroxides M(OH)(2) (where M=Be,Mg,Ca,Sr,Ba) are analyzed. The heats of reaction and the chemical potential changes of these solids upon CO(2) capture reactions have been calculated and used to evaluate the energy costs. Relative to CaO, a widely used system in practical applications, MgO and Mg(OH)(2) systems were found to be better candidates for CO(2) sorbent applications due to their lower operating temperatures (600-700 K). In the presence of H(2)O, MgCO(3) can be regenerated into Mg(OH)(2) at low temperatures or into MgO at high temperatures. This transition temperature depends not only on the CO(2) pressure but also on the H(2)O pressure. Based on our calculated results and by comparing with available experimental data, we propose a general computational search methodology which can be used as a general scheme for screening a large number of solids for use as CO(2) sorbents.

ab initio Thermodynamic Study of the CO2 Capture Properties of M2CO3 (M = Na, K)- and CaCO3-Promoted MgO Sorbents Towards Forming Double Salts

“…The zero-point energy (E ZP ) of each compound and corresponding available experimental measured data are also listed in Table 1. (Duan and Sorescu, 2010;Duan et al, 2011;Duan, 2012). From Table 1, one can see that the calculated entropies of CaMg(CO 3 ) 2 and corresponding carbonates and oxides are in good agreement with the experimentally measured values.…”

“…The calculated entropy of dolomite (159.89 J/mol·K) is between the two experimental values of 155.22 and 166.69 J/mol·K. Along with our previous studies on oxides and carbonates (Duan and Sorescu, 2010;Duan et al, 2011), these results indicate our theoretical approach can predict the reasonable thermodynamic properties of solids. As shown in Fig.…”

“…Compared to calcite (CaCO 3 ), the lower symmetry of dolomite results from the alternating Ca and Mg layers and the slight rotation of the CO groups which move the oxygen atoms off the diad axes that exist in calcite. By applying this double salt crystal structural information into our modeling scheme, the optimized lattice constants and total electronic energies of these three double salts as well as the corresponding carbonates and oxides considered in this work are presented in Table 1 (Duan and Sorescu, 2010;Duan et al, 2011;Duan, 2012), along with experimental structural data. The agreement between the DFT optimized lattice constants and experimental data is generally very good.…”

“…The finite temperature thermodynamic properties were then computed from the calculated phonon density of states by following our previous approach (Duan and Sorescu, 2010). The calculated phonon free energies, entropies, and heat capacities of these solid phase materials involved in this study are plotted as a function of temperature in Fig.…”

“…All calculations have been done using the projector augmented wave (PAW) pseudo-potentials and the PW91 exchange-correlation functional (Perdew and Wang, 1992). This computational level was shown to provide an accurate description of oxide systems (Duan and Sorescu, 2010;Duan, 2011;Duan et al, 2011). Plane wave basis sets were used with a cutoff energy of 500 eV and a kinetic energy cutoff for augmentation charges of 605.4 eV.…”