Ca_xLa_1-xMn_1-yM_yO _3-δ (M = Mg, Ti, Fe, or Cu) as oxygen carriers for chemical-looping with oxygen uncoupling (CLOU)

Perovskite materials of the type Ca_xLa_1-xMn _1-yM_yO_3-δ (M = Mg, Ti, Fe, or Cu) have been investigated as oxygen carriers for the chemical-looping with oxygen uncoupling (CLOU) process. The oxygen carrier particles were produced by mechanical homogenization of primary solids in a rotary evaporator, followed by extrusion and calcination at 1300 C for 6 h. The chemical-looping characteristics of the substituted perovskites developed in this work were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900-1000 C during alternating reducing and oxidizing conditions. The oxygen carriers showed oxygen releasing behavior (CLOU) in an inert atmosphere between 900 and 1000 C. In addition, their reactivity with methane was high, approaching complete gas yield for all of the materials at 950 C, with the exception being the Cu-doped perovskite, which defluidized during reduction. The rates of oxygen release were also investigated using devolatilized wood char as solid fuel and were found to be similar. The required solids inventory in the fuel reactor for the perovskite oxygen carriers is estimated to be 325 kg/MW_th. All of the formulations exhibited high rates of oxidation and a high degree of stability, with no particle fragmentation or agglomeration. The high reactivity and favorable oxygen uncoupling properties make these oxygen carriers promising candidates for the CLOU process.