Carbon dioxide interaction with perovskite-type oxides and their applications for oxygen separation.

摘要

Perovskite-type oxides are promising materials for air separation with a high selectivity for oxygen. A new perovskite-based high-temperature sorption technology for producing an oxygen enriched carbon dioxide stream is proposed in this thesis. The sorption technology is based on CO2 interaction with perovskite-type sorbents, and is promising for producing oxidants for the oxyfuel combustion process. This work is dedicated to fundamental studies of carbon dioxide reactions with perovskite-type oxides. It is focused on identification of the reaction, study of the equilibrium and modeling of reaction kinetics, and also on development of the novel sorption process with high separation efficiency.; Two types of perovskite-type oxides La0.1Sr0.9Co 0.5Fe0.5O3-delta (LSCF) and Sr0.5Car 0.5Co0.5Fe0.5O3-delta (SCCF) are selected as candidate sorbents for study. XRD shows that perovskite-type oxides react with CO2 at a temperature above 600°C to form carbonates and other metal oxides, and can be recovery in air at above 700°C. The formed carbonates are decomposed to metal oxides at a sufficiently high temperature. A theory of formation of solid solutions between carbonates and the corresponding metal oxides is proposed and can well explain the reaction equilibrium. The sorbent of LSCF possesses a porous structure when sintered at a high temperature of 1250°C, and carries a dense structure when sintered at a relatively low temperature of 900°C. The homogeneous model and the shrinking-core model are applied successfully to describe the carbonation reaction kinetics for samples with porous and dense structures, respectively.; A study of fixed-bed sorption performances demonstrates that perovskite-type oxides are promising sorbents for producing the oxygen enriched carbon dioxide stream. SCCF exhibits much enhanced separation results as compared to LSCF due to the faster reaction kinetics, with the average oxygen concentration of product at 50% and productivity of 0.078 ml/min.g. Effects of sorption conditions, including adsorption time, flow rates of adsorption and desorption feed gases, adsorption and desorption temperatures, on the separation results are investigated. The operation temperature is found to have the most critical effect, and SCCF exhibits the optimal separation performance at adsorption and desorption temperatures of respective 850 and 700°C. The sorption process exhibits quite good reversibility after first few cycles.