| In this study we investigated Ce modified MnOx/Ce-gammaAl 2O3 oxygen carriers for liquid fuel based chemical looping combustion. The support gammaAl2O3 was modified with 1% Ce to provide thermal stability of the material and to minimize the metal support interaction. On the other hand, MnOx was used as the actual oxygen carrier. Both Ce and Mn were loaded on the support by an incipient wetness technique using a successive metal loading. In order to ensure the desired characteristics, the prepared oxygen carriers were characterized using various physicochemical techniques such as XRF, nitrogen adsorption, TGA, XRD, SEM, TPR, TPO and TPD. TGA and XRD analysis show that Ce modification improves the thermal stability of gammaAl2O3 and hinders the formation of difficult reducing manganese aluminate. TPR result shows excellent reduction and re-oxidation performances of manganese oxide supported on the Ce modified gammaAl2O3. Almost 83% of the loaded MnOx has been reduced during the TPR, which also remained consistent over repeated TPR/TPO cycles. The oxygen carriers were further evaluated in a fluidized CREC Riser Simulator using hexane as a liquid fuel at fluidized conditions as expected in an actual CLC process. Under the studied reaction conditions, CO2 is the main combustion products, which is highly desirable to achieve complete fuel combustion. Over 90 % hexane combustion was achieved at 575 °C. The solid state kinetics of the fuel-oxygen carrier reaction was also conducted using both the TPR and the CREC Riser Simulator data. A nucleation and nuclei growth model describes the solid-state reduction kinetics of the prepared oxygen carrier adequately. The estimated activated energy of MnOx/Ce-gammaAl2O3 reduction were found to be 27 kJ/mole and 59 kJ/mole using hydrogen and hexane, respectively. |
