(385d) Materials Design Strategies for Performing ‘Unmixed Reactions’ Using Non-Stoichiometric Solids As Oxygen Carriers
AIChE Annual Meeting
2017
2017 Annual Meeting
Catalysis and Reaction Engineering Division
Reaction Chemistry and Engineering II
Tuesday, October 31, 2017 - 1:36pm to 1:58pm
Chemical looping involves a sequence of cyclically repeated reactions and e.g. a solid carrier material to store and release a reaction intermediate. Theoretically, the carrier at the end of the cycle will remain unchanged whilst the products from the reduction and the oxidation steps are separated. For example, iron oxide can be used as an oxygen carrier material (OCM) for hydrogen production from the water-gas shift reaction. The OCM is reduced in carbon monoxide to produce carbon dioxide and iron or wustite and the iron or wustite are oxidised in water to produce hydrogen and magnetite. However, although iron oxide shows significant usable oxygen capacity for this reaction, it loses its activity rapidly due to sintering and agglomeration. Perovskites, such as La0.7Sr0.3FeO3-δ, have been proposed as alternative oxygen carrier materials due to their high stability and stable productivity under long term redox cycles. They are also oxygen ion-conducting MIECs (mixed ionic and electronic conductors) allowing rapid oxygen permeation through their structure. We will discuss how the particular thermodynamic behaviour of non-stoichiometric oxides can be exploited to develop novel processes. However, the small oxygen capacity of perovskites results in less hydrogen production per cycle than with iron oxide. Here we show how composite OCMs can be designed to achieve high stability and capacity where iron oxide clusters are embedded in an La0.7Sr0.3FeO3-δ perovskite matrix.
Parallels will also be drawn between membrane and chemical looping processes. We will show that any chemical looping process has a membrane analogue and vice versa.