Selection of oxygen carriers for chemical-looping combustion

Chemical-looping combustion (CLC) has been suggested as an energetically efficient method for capture of carbon dioxide from the combustion of fuel gas. This technique involves the use of an oxygen carrier that transfers oxygen from the air to the fuel, preventing direct contact between them. The oxygen carrier is composed of a metal oxide as an oxygen source, and an inert as a binder for increasing the mechanical strength of the carrier. In this work, 240 samples composed of 40-80% of Cu, Fe, Mn, or Ni oxides on Al2O3, sepiolite, SiO2, TiO2, or ZrO2 were prepared by mechanical mixing as cylindrical extrudates. The samples were sintered at four temperatures between 950 and 1300 degreesC. The effects of the chemical nature and composition of the carrier and the sintering temperature were investigated by reactivity tests in a thermogravimetric analyzer using CH4 as fuel, and the mechanical strength of the solids. On the basis of these properties, the most promising carriers to be used in a CLC system were selected. The best Cu-based oxygen carriers were those prepared using SiO2 or TiO2 as inert, and sintered at 950 degreesC. Among the Fe-based oxygen carriers, those prepared with Al2O3 and ZrO2 as inerts showed the best behavior. ZrO2 was the best inert for those Mn-based oxygen carriers. Finally, TiO2 was the best inert for those Ni-based oxygen carriers.