(Fe1-xMnx)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 (Fe1-xMnx)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 (Fe0.50Mn0.50) 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 .