EFFICIENT THEORETICAL SCREENING OF SOLID SORBENTS FOR CO2 CAPTURE APPLICATIONS

Carbon dioxide is a major combustion product of coal, which once released into the air can contribute to global climate change. Current CO2 capture technologies for power generation processes including amine solvents and CaO-based sorbent materials require very energy intensive regeneration steps which result in significantly decreased efficiency. Hence, there is a critical need for new materials that can capture and release CO2 reversibly with acceptable energy costs if CO2 is to be captured and sequestered economically. Inorganic sorbents are one such class of materials which typically capture CO2 through the reversible formation of carbonates. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO2 sorbent candidates from the vast array of possible solid materials has been proposed and validated. The ab initio thermodynamic technique has the advantage of identifying thermodynamic properties of CO2 capture reactions without any experimental input beyond crystallographic structural information of the solid phases involved. For a given solid, the first step is to attempt to extract thermodynamic properties from thermodynamic databases and available literatures. If the thermodynamic properties of the compound of interest are unknown, an ab initio thermodynamic approach is used to calculate them. These properties expressed conveniently as chemical potentials and heat of reactions, either from databases or from calculations, are further used for computing the thermodynamic reaction equilibrium properties of the CO2 absorption/desorption cycle based on the chemical potential and heat of reaction. Only those solid materials for which lower capture energy costs are predicted at the desired process conditions are selected as CO2 sorbent candidates and further considered for experimental validations. Solid sorbents containing alkali and alkaline earth metals have been reported in several previous studies to be good candidates for CO2 sorbent applications due to their high CO2 absorption capacity at moderate working temperatures. In addition to introducing our selection process in this presentation, we will present our results for solid systems of alkali and alkaline metal oxides, hydroxides and carbonates/bicarbonates to validate our methodology. Additionally, applications of our computational method to mixed solid systems of Li2O and SiO2 with different mixing ratios, we showed that increasing the Li2O/SiO2 ratio in lithium silicates increases their corresponding turnover temperatures for CO2 capture reactions. These theoretical predictions are in good agreement with available experimental findings