Release of Gas‐Phase O2 from Ilmenite during Chemical‐Looping Combustion Experiments

A concentrate of the naturally occurring mineral ilmenite has been found to release small amounts of gas‐phase O2 during chemical‐looping combustion experiments at temperatures in the order of 950 °C. This is unexpected, but the effect has been verified by experiments in two different fluidized‐bed reactor systems. The O2 release is small, resulting in approximately 0.1 vol % O2 in the gas passing through the reactor beds. However, due to the presence of steam as combustion product and as fluidization medium for fuel reactor and loop seals during solid fuel experiments, considerable O2 concentrations could be obtained if analyzed on dry basis. It is suggested that the reason for the experienced O2 release could be the presence of small amounts of manganese in the sample or interactions between said impurities and iron or titanium oxides.