Selection of Suitable Oxygen Carriers for Chemical Looping Air Separation: A Thermodynamic Approach

Abstract

The increasing demand for oxygen combined with the need for improved economic performance necessitates the search for alternative methods of oxygen production. Chemical looping air separation (CLAS) is one of these alternatives with a relatively small energy footprint. The present paper describes the results of a comprehensive thermodynamic study conducted by our group to identify suitable oxygen carriers for CLAS at medium to low temperatures. The thermodynamic simulations were carried out using Fact-Sage 6.1 for 20 different metal oxides forming 40 oxygen carrier systems. An Ellingham diagram was developed to relate the Gibbs free energy of the relevant reactions to the temperature for all metal oxide systems. Furthermore, the equilibrium partial pressure of oxygen was calculated at elevated temperatures. The mass balance calculations were also performed for identifying the steam/CO 2 requirements for the reduction reactor. On the basis of the comprehensive thermodynamic study, oxides of manganese, cobalt, and copper have been found most suitable for the CLAS process. Additionally, the possibility of carbonate and hydroxide formation during the reduction with CO 2 and steam, respectively, was calculated. The formation of the mixed oxide phases or the spinel structures between the metal oxides and various supports (such as SiO 2 and Al 2 O 3 ) has also been thermodynamically investigated. Several other important factors were also qualitatively assessed. The Cu oxides with SiO 2 and the Co oxides with Al 2 O 3 were found to be the most suitable oxygen carriers for CLAS.

TGA and kinetic modelling of Co, Mn and Cu oxides for chemical looping gasification (CLG)

“…[7] Moghtaderi considered the application of the chemical looping process for the separation of oxygen from air. Releasing oxygen distinguishes CLOU from chemical looping combustion (CLC).…”

“…Releasing oxygen distinguishes CLOU from chemical looping combustion (CLC). [7] Leion et al combusted coal with Ni based oxygen carriers. [7] Moghtaderi considered the application of the chemical looping process for the separation of oxygen from air.…”

Chemical looping dechlorination through adsorbent-decorated Fe2O3/Al2O3 oxygen carriers

“…3 (a), the G of R1-R2 between 600 and 1000°C is always greater than zero, implying that the corresponding reaction cannot spontaneously proceed in the positive direction [38]. These results indicate that the two oxidation states of Fe cannot react with HCl in thermodynamics, so HCl can always exist in the CLC process when using raw Fe-based OCs.…”

“…4 as the difference between the G of the products minus the G of the reactions. A negative value for G indicates that a reaction can proceed spontaneously without external inputs [38].…”

O2 Release of Mn-Based Oxygen Carrier for Chemical Looping Air Separation (CLAS): An Insight into Kinetic Studies

“…Chemical absorption process may be a rather competitive alternative if the facility corrosion could be reduced. Compared with these technologies, the chemical looping air separation (CLAS), proposed by Mogtaderi et al (Moghtaderi, 2010;Moghtaderi et al, 2011;Shah et al, 2011;Moghtaderi, 2012;Shah et al, 2012), has the advantages of operationsimple, cost-efficient, and energy-saving. The average specific power of CLAS ) is only 26% of that of an advanced cryogenic air separation system (Moghtaderi, 2010).…”