TGA Study of the Reaction Kinetics of a CuFeMnAlO₄₊ Oxygen Carrier for Methane Chemical Looping Combustion under High Pressure and Atmospheric Pressure Conditions

Reduction and oxidation kinetics of a CuFeMnAlO4+& delta; oxygen carrier for methane were studied using an atmospheric thermogravimetricanalyzer (TGA) and a pressurized TGA. Important parameters such astemperature (500-900 & DEG;C), particle size distribution (150-650 & mu;m), and partial pressures of reactants (methane and oxygen)were evaluated. Results showed that the reduction of the oxygen carrierwas not affected by particle size distribution studied in this work,and that above 750 & DEG;C, the effect of the temperature on oxygencarrier reduction started to diminish. The reaction time approachesan asymptotic limit as methane partial pressure increases. For oxygencarrier oxidation, it was found that the rate of oxidation increasedwith increasing oxygen concentration. The effect of the oxygen concentrationwas more noticeable when the oxygen concentration was below 7.5%.Because of the inherent feature of the oxygen carrier, its chemicallooping with oxygen uncoupling property was also assessed. A phaseboundary-controlled shrinking sphere model was used to model the testdata from the TGAs. Modeling results showed that the oxygen carrierreduction had a reaction order of 1 with an activation energy of & SIM;46kJ/mol. Oxygen carrier oxidation demonstrated a reaction order of1.1 with an activation energy of & SIM;55 kJ/mol. Additionally,the differences of the experimental results between the atmosphericpressure TGA and the pressurized TGA were discussed in detail andthe limitations of the pressurized TGA were highlighted.