Using Ca_xLa_1-xMn_1-yM'_yO _3-δ as oxygen carriers for chemical-looping combustion

Oxygen carriers of the type Ca_xLa_1-xMn _1-yM'_yO_3-δ (CLMM') were investigated as oxygen carrier materials. A matrix of potential substituted Ca _xLa_1-xMn_1-y M'_yO_3-δ (M' = Fe, Ti, Cu, Mg) perovskites were synthesized using mechanical homogenization of primary solids in a rotary evaporator followed by drying and calcination. The resulting powders were subjected to particle fabrication via extrusion followed by crushing and sieving. The oxygen release properties and the reactivity with methane and syngas was investigated using a batch fluidized batch reactor made of quartz. A sample of 15 g of particles and a fuel flow of 450 Nml/min was used for all reactivity experiments. All of the materials showed high rates of oxygen release in gas phase at 900°C, exhibiting so called oxygen uncoupling behavior. In addition, the reactivity with methane was high, approaching 100% gas yield for all of the materials at 950°C, except the Cu-doped material which defluidized during reduction. All materials also exhibited high rate of oxidation. It can be concluded that the CLMM' materials reacted with fuel through both conventional chemical-looping (direct gas-solid reactions) and via chemical-looping with oxygen uncoupling (with the oxygen released from the particles). The stability of the materials was excellent with very little or no attrition. No agglomeration was noticed for most of these materials. High reactivity and very good oxygen uncoupling properties in combination with the low cost of the primary materials, make this system very interesting for chemical-looping combustion of different types of fuel.