(Fe_1-xMn_x)TiyO₃ based oxygen carriers for chemical-looping combustion and chemical-looping with oxygen uncoupling

The manganese based ilmenite analogue pyrophanite (MnTiO₃) and six other combined (Fe_1-xMn_x)TiyO₃ oxides have been examined as oxygen-carrier materials for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). Particles with different compositions were manufactured by spray drying and studied by consecutive reduction and oxidation at 850-1050°C in a batch fluidized-bed reactor using CH₄ as fuel. A fuel conversion of 80-99% could be achieved with most materials, with different formulations being favored at different temperature levels. The exception was pure MnTiO₃ which had very limited reactivity with CH₄. The oxygen uncoupling behavior was examined by exposing the oxygen-carrier particles to an inert atmosphere of N₂. The apparent equilibrium concentration during fluidization with pure N ₂ ranged from zero to 0.9% O₂, depending on temperature and particle composition. One material (Fe_0.50Mn_0.50) TiO₃ was selected and further examined by 12 h of experiments in a small continuously operating circulating fluidized-bed reactor. Up to 80% conversion of natural gas was achieved at 910°C , but defluidization occurred when the temperature was increased to 950°C .