Investigation of manganese-iron oxide materials based on manganese ores as oxygen carrier in chemical-looping with oxygen uncoupling (CLOU)

Artikel i vetenskaplig tidskrift, 2014

Oxygen carrier materials were synthesized using five different types of manganese ores with addition of iron oxide (Fe2O3), and they were investigated for their reactivity and properties in chemical looping with oxygen uncoupling (CLOU). Two different Mn/Fe molar ratios (1:2 and 2:1) were examined. The samples were manufactured by using a lab-scale extrusion method followed by sintering at 950 degrees C for 4 h. To measure their reactivity, the materials were exposed to gaseous CH4 and syngas (50:50 CO/H-2) as well as solid fuel (petroleum coke), in a batch fluidized-bed reactor. With CH4, the materials based on ores from Brazil and Gabon with a Mn/Fe molar ratio 2:1 showed the best reactivity. For reduction using syngas, samples based on Eastern European and South African ores provided higher amounts of oxygen equivalent, up to 3-5% of their mass. To investigate the ability of the samples to release gas-phase oxygen, solid fuel experiments using 0.1 g of petroleum coke in a bed of 10 g oxygen carrier were performed at 950 degrees C with Brazilian, Gabon, and Eastern European ores. In these solid fuel tests samples with a Mn/Fe molar ratio of 1:2 showed higher uncoupling rates. Based on X-ray diffraction analysis, the primary phase detected in all fresh particles was the oxidized form of MnyFe1-yOx, that is, bixbyite [(Mn,Fe)(2)O-3]. All of the particles showed sufficiently high crushing strength (> 2N) and a reasonable attrition resistance (attrition index < 6 wt% h(-1)). This suggests that the materials could be suitable for practical applications. It is concluded that the oxygen carriers made by manganese ores have the potential to be used as oxygen carriers for chemical-looping combustion and chemical looping with oxygen uncoupling.