Experimental investigation of chemical-looping hydrogen generation using Al2O3 or TiO2-supported iron oxides in a batch fluidized bed

Chemical-looping hydrogen generation (CLHG) is a novel technology for hydrogen production with inherent separation of CO2. Three oxygen carriers Fe2O3 using inert materials Al2O3 or TiO2 as support were prepared by mechanical-mixing method, i.e., Fe90Al10 (90%Fe2O3 + 10%Al2O3), Fe60Al40 (60%Fe2O3 + 40%Al2O3) and Fe60Ti40 (60%Fe2O3 + 40%Al2O3). Reactivity of the three oxygen carriers was first determined under CO reduction, steam oxidation and air oxidation atmospheres at 900 °C in a thermogravimetric analyzer. Then experiments to simulate the CLHG process were carried out in a batch fluidized bed. In the fluidized bed, all of the three oxygen carriers showed good reactivity over the multi-cycle experiments at 900 °C, and Fe60Al40 had the highest hydrogen yield. The reactivity of the oxygen carrier supported on Al2O3 was higher than that on TiO2, which interacted with iron oxide forming FeTiO3. The reactivity of Fe60Al40 was better than that of Fe90Al10. No deterioration of the oxygen carrier occurred after the multiple cycles, but for Fe90Al10 some agglomeration was detected. At 600–900 °C, higher temperature favored deeper reduction of iron oxide and increased the hydrogen production, while carbon deposition in the reduction period was suppressed with the rise of temperature. In the reduction, the conversion of fuel gas was constrained by thermodynamics in a single-stage reactor, and a compact fuel reactor was proposed for a full conversion of gaseous fuels.