Examining the Cu-Mn-O Spinel System as an Oxygen Carrier in Chemical Looping Combustion

Abstract

Chemical-looping combustion (CLC) and chemical-looping combustion with oxygen uncoupling (CLOU) are attractive alternatives to conventional combustion that provide efficient and direct separation of CO2. Both processes use metaloxides as oxygen carriers to transfer oxygen between two reactor vessels: the air and fuel reactors. Although monometallic oxides (such as Mn3O4, Fe2O3, NiO, and CuO) have been successfully employed as oxygen carriers, double oxides of the general formula CuxMn3_xO4 in the CuO–Mn2O3 system are examined in this work. The carrier was produced by mixing, extruding, and calcining a 1:1 molar (30.8:69.2 mass ratio) mixture of CuO and Mn2O3 at 950 8C for 6 or 12 h in static air. XRD analysis revealed that spinels of the general formula CuxMn3_xO4 were formed with 0.1_x_2.5 in which x=3Cu/(Cu+Mn). The chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor from 800–850 8C over several alternating redox cycles using CH4 as the fuel. The oxygen carrier exhibited reproducible and stable reactivity behavior for both reducing and oxidizing periods in this temperature range. This characteristic makes the system an ideal oxygen-carrier material for CLOU. Moreover, the spinels in the CuxMn3_xO4 series are endowed with favorable physicochemical attributes (such as fast redox processes, high crushing strength, and demonstrated CLOU behavior) and may be viable alternatives to CuO–Cu2O and Mn2O3–Mn3O4 as potential CLOU materials.