Novel magnetic manganese-iron materials for separation of solids used in high-temperature processes: Application to oxygen carriers for chemical looping combustion

Different chemical looping processes allow burning or gasify solid fuels with inherent CO2 capture because the oxygen is transferred from air to the fuel through a metal oxide based material, which is named oxygen carrier. To improve process efficiency and CO2 capture, highly reactive synthetic materials could be used. One of the challenges of using solid fuels is the oxygen carrier separation from the ash, because loss of oxygen carrier particles is expected during ash drainage. So, their costs would have necessary the recovery of the synthetic oxygen carrier. Mn-Fe based materials show magnetic properties in the spinel phase, which could be used for a magnetic separation. When these Mn-Fe materials are used at high temperature under oxidizing or reducing atmospheres, stability of the spinel phase should be guaranteed in order to take advantage of the magnetic properties. The design of low reactive Mn-Fe based materials with magnetic properties, which can be used as a support material for other highly reactive and active phases, was the main objective of this work. In this sense, the support must have high crushing strength, low reactivity under oxidation and reduction atmospheres at high temperatures and permanent magnetism at low temperature for solids separation. Materials prepared with different Mn/(Mn + Fe) molar ratios and calcination conditions were evaluated regarding mechanical strength, inerticity and magnetic properties. A Cu-based oxygen carrier prepared on the optimal support was prepared and evaluated along 240 oxidation-reduction cycles in thermobalance (25 h experiment), exhibiting suitable mechanical and magnetic characteristics as well as high reactivity.