Development of Stable Oxygen Carrier Materials for Chemical Looping Processes—A Review

Abstract

This review aims to give more understanding of the selection and development of oxygen carrier materials for chemical looping. Chemical looping, a rising star in chemical technologies, is capable of low CO2 emissions with applications in the production of energy and chemicals. A key issue in the further development of chemical looping processes and its introduction to the industry is the selection and further development of an appropriate oxygen carrier (OC) material. This solid oxygen carrier material supplies the stoichiometric oxygen needed for the various chemical processes. Its reactivity, cost, toxicity, thermal stability, attrition resistance, and chemical stability are critical selection criteria for developing suitable oxygen carrier materials. To develop oxygen carriers with optimal properties and long-term stability, one must consider the employed reactor configuration and the aim of the chemical looping process, as well as the thermodynamic properties of the active phases, their interaction with the used support material, long-term stability, internal ionic migration, and the advantages and limits of the employed synthesis methods. This review, therefore, aims to give more understanding into all aforementioned aspects to facilitate further research and development of chemical looping technology.

Extremely Stable and Durable Mixed Fe–Mn Oxides Supported on ZrO2 for Practical Utilization in CLOU and CLC Processes

“…Additionally, supporting those materials with ZrO 2 have a positive effect on its mechanical strength. The parameter is important for the application of OCs materials in industrial scale CLC plant, and may be tailored by increasing the lifespan of OC [4]. Also, ZrO 2 as an inert material does not negative effect on the reactivity of Fe-Mn based materials [14,20].…”

“…In the first reactor, a material called oxygen carrier (OC) is oxidized at a high temperature by a stream of atmospheric air, and is then transported into the second (fuel) reactor where it is used to oxidize fuel. Oxidation of fuel may take place due to: (1) the releasing of gaseous oxygen from OC, in so-called CLOU-chemical looping with oxygen uncoupling; (2) due to direct reaction between OC and fuel, in so called CLC-chemical looping combustion; or (3) as a result of reaction of gaseous products coming from preliminary gasification of solid fuel particles and OC (ig-CLC-chemical looping combustion with in-situ gasification) [4]. Since fuel in the CLC process is separated from atmospheric air, this is the reason for restricting the production of nitrogen oxides which are usually formed during the conventional combustion process.…”

“…Meanwhile iron oxides, despite their low price and environmental safety, do not exhibit desirable CLOU properties. They are also tending to agglomeration when reacted in high temperatures [4,[9][10][11].…”

“…Similarly, they are relatively resistant to sulphur poisoning, which opens up an opportunity for using them for combustion of a wide range of fuels, such as coal, biomass, or biogas etc. [2,4,[13][14][15][16]. Although in theory OCs based on pure Mn oxides should have decent capacity of oxygen transport, in practice they is exhibit poor CLOU capabilities due to the high equilibrium partial pressure of O 2 in the temperature range in which the fuel combustion process occurs (above 800 • C) [12,13,17].…”

Preventing Agglomeration of CuO-Based Oxygen Carriers for Chemical Looping Applications

“…a single fixed bed reactor with alternating reduction and oxidation steps or dual interconnected continuous fluidized beds. [5] It is worth mentioning here that the latter reactor configuration provides better heat management compared to alternating reactor designs. [6] The solid oxygen carrier is the cornerstone of the CLC process and needs to satisfy certain characteristics.…”