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Chemical looping combustion (CLC) is one of the most efficient and advantageous CO2 capture technologies from an economic and energy point of view. An important key factor in this process is the oxygen carriers (OCs) used to transfer oxygen from the air to the fuel. In this work, three natural iron ores from Brazil were selected as interesting oxygen carriers for the CLC process due to their low cost and abundance in nature. Their chemical composition, redox properties, and structural evolution when submitted to a reactivity test in a thermobalance with 15% CH4 and H2 were investigated. The OCs (ItaHP-MG, ItaHP-RN, and ItaLP-RN) revealed good resistance to fracture, and their reactivity increased after the first reaction cycle due to the occurrence of an activation process, leading to a gain in reactivity in the following cycles. The reactivity tests showed that for all OCs, the reactivity with hydrogen was higher when compared to methane, highlighting ItaHP-MG oxygen carrier with relevant rate index values for both fuels (9.60%/min and 3.55%/min for H2 and CH4, respectively). However, OCs performed differently depending on the degree of use of the Fe2O3 phase. Interestingly, ItaHP-MG, with a high Fe2O3 content (96.5%), showed a regeneration of only 60%, while ItaLP-RN, whose Fe2O3 content is 41.5%, presented a degree of use above 85%. This effect is the result of preferential gas–solid interaction on the surface of the OC.

Chemical Looping Combustion (CLC) is considered one of the low cost alternatives for CO2 capture for fossil fuels combustion and to reach negative emissions through biomass CLC. The cornerstone of the CLC process is the oxygen carrier performance that represents the main additional cost with respect to the conventional combustion. Manganese-based oxygen carriers are subjected to a growing interest because they are low cost, not toxic and environmentally friendly. In this work five impregnated oxygen carriers, with manganese oxide Mn3O4 or Mg6MnO8 as their active phase and three commercial supports based on zirconia and synthetic calcium aluminate, were prepared. Their behaviour for CLC was examined by TGA, batch fluidized bed reactor, TPR, SEM-EDX and XRD. After a preliminary screening two carriers (Mn-ZrM and Mn-ZrSG) were subjected to multiple redox cycles by TGA and batch fluidized bed reactor. Both showed high solids conversion by TGA under the tested conditions, appropriated resistance to fracture, rate indexes relatively high, although Mn-ZrM showed agglomeration and deactivation during batch fluidized bed tests. Reactivity in batch fluidized bed reactor of the Mn-ZrSG oxygen carrier with methane increases with temperature although suffered from significant deactivation. This was different to the results found during multiple redox cycles by TGA. There was not a clear reason for this decrease in the reactivity that likely could be due to the uncomplete oxidation in the batch fluidized bed reactor, although further investigations are needed. On the other hand, it presented high and constant reactivity with CO and H2 in all the range of temperatures tested, being suitable for iG-CLC processes of coal or biomass and syngas combustion. Agglomeration problems were not found and the attrition losses were small. Calculated lifetime was around 11,000 h, much higher than any other Mn-based material developed or tested for CLC.

Promising impregnated oxygen carriers, based on copper and iron, have been previously developed for CLC with gaseous fuels (CH4, syngas, LHC). Recently, because of its low cost and environmental compatibility, Mn-based oxygen carriers are now being considered as an attractive option for chemical-looping combustion (CLC) applications. In this work, a screening of different commercial supports in fluidizable particle size for impregnated Mn-based materials has been carried out. Different oxygen carriers have been prepared by incipient impregnation on ZrO2, and CaAl2O4, and evaluated with respect to their mechanical resistance, fuel gas reactivity and fluidization properties such as agglomeration and attrition rate. In a first step, particles showing high enough crushing strength values were selected for the reactivity investigation. The redox reactivity was evaluated through TGA experiments at suitable temperatures for the CLC process (i.e. 850-950 °C) using H2, CO and CH4. Multi cycle redox analysis and full physical and chemical characterization was also performed. In a second step, materials with high enough reactivity were prepared for fluidized bed evaluation. A batch fluidized bed installation with continuous gaseous fuel feed was used to analyze the product gas distribution during reduction and oxidation reactions at different operation temperatures, and agglomeration and attrition behavior of the selected materials. Results showed that an oxygen carrier impregnated using ZrO2 as support, had high enough reactivity and low attrition rate. Therefore, this material can be selected as a candidate for the development of CLC with syngas with promising results.