Examination of Perovskite Structure CaMnO3-δ with MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Perovskite structure oxygen carriers with the general formula CaMnxMg1-xO3-δ were spray-dried and examined in a batch fluidized bed reactor. The CLOU behavior, reactivity towards methane, and syngas were investigated at temperature 900°C to 1050°C. All particles showed CLOU behavior at these temperatures. For experiments with methane, a bed mass corresponding to 57？kg/MW was used in the reactor, and the average CH4 to CO2 conversion was above 97% for most materials. Full syngas conversion was achieved for all materials utilizing a bed mass corresponding to 178？kg/MW. SEM/EDX and XRD confirmed the presence of MgO in the fresh and used samples, indicating that the Mg cation is not incorporated into the perovskite structure and the active compound is likely pure CaMnO3-δ. The very high reactivity with fuel gases, comparable to that of baseline oxygen carriers of NiO, makes these perovskite particles highly interesting for commercial CLC application. Contrary to NiO, oxygen carriers based on CaMnO3-δ have no thermodynamic limitations for methane oxidation to CO2 and H2O, not to mention that the materials are environmentally friendly and can utilize much cheaper raw materials for production. The physical properties, crystalline phases, and morphology information were also determined in this work. 1. Introduction Carbon dioxide is the greenhouse gas which contributes most to anthropogenic climate change. A significant amount of CO2 is emitted into the atmosphere each year, of which combustion of fossil fuels was responsible for over 30000 million tons of CO2 in 2010 [1]. The increasing energy demand of a globally growing economy will likely make fossil fuels the main energy source in the foreseeable future. Hence, reducing CO2 emission from combustion of fossil fuels is a key point in reducing the impact of global warming. CO2 capture and storage (CCS) is one important option to reduce CO2 emission. In this concept, CO2 produced from combustion or industrial processes is captured and stored in closed geological formations where it is stored for long periods of time before being converted to carbonate minerals or other stable phases by natural processes. Some of the carbon dioxide may actually leak to the atmosphere, but if the leakage rate is low enough, this may not be of significant importance as natural mechanisms could sequester the carbon. CO2 capture can be achieved by different technologies and the most discussed are postcombustion, precombustion and oxyfuel combustion. Unfortunately, a substantial energy penalty is required for gas separation in these