Chemical looping air separation (CLAS) for oxygen production: thermodynamic and economic aspects

a number of conventional and emerging air separation technologies are available today for large-scale oxygen production. These technology platforms are often considered as the energy intensive processes. The increasing demand for the oxygen combined with the need of improved economic performance of such production technologies necessitates the search for alternative methods of oxygen production. Chemical Looping Air Separation (CLAS) is one of these alternatives which can possibly run at relatively lower operating temperature and pressure resulting in lower energy footprints. The present paper describes the results of a comprehensive thermodynamic study conducted on twenty different metal oxides for use in the CLAS process. The study was carried out using Fact-sage and an Ellingham diagram was developed relating the Gibbs free energy of the relevant reactions to temperature for all metal oxide systems. Furthermore, the equilibrium partial pressure of oxygen was calculated at elevated temperatures and the steam/CO₂ requirements were determined for the reduction reactor. Based on this thermodynamic scoping study, oxides of manganese, cobalt, copper, lead and chromium have been found most suitable for the CLAS process. Additionally, other factors such as availability of the metal oxides, their physical properties, reaction kinetics, inventory, mechanical strength, health and safety risks, operating and capital costs have also been qualitatively compared.