Integrated Hydrogen and Power Production with CO2 Capture Using Chemical-Looping ReformingRedox Reactivity of Particles of CuO, Mn2O3, NiO, and Fe2O3 Using SiO2 as a Support

A concept for combined hydrogen and power production from natural gas with CO2 capture is presented. The process involves the use of a metal oxide in fluidized bed reactors; the metal oxide is reduced by a mixture of natural gas and steam in a fuel reactor and oxidized by air in the air reactor. The natural gas is partially oxidized in the fuel reactor, resulting in a mixture of CO2, H2, H2O, and CO from the exit. If no hydrocarbons are present in this stream, it can be sent to a water gas shift reactor to get an undiluted stream of CO2 and H2. The product stream from the air reactor contains mostly N2 and some unreacted oxygen. The oxidation reaction is exothermic with resulting heat production in the air reactor; this heat is used to maintain the oxygen carrier particles at the high temperature necessary for the endothermic reaction in the fuel reactor. The hot gases from the air reactor could be used for power production. Metal oxides of Ni, Cu, Mn, and Fe were prepared by impregnation on a SiO2 support and tested in a laboratory fluidized bed reactor using alternating gas flows of CH4/H2O and O2. Among the investigated metal oxides, NiO and CuO showed the highest reduction reactivity in comparison with Mn2O3 and Fe2O3. However, only NiO/SiO2 showed high selectivity toward H2 during the later stages of reduction, while the other metal oxides had large amounts of unreacted CH4 at the exit of the reactor. The reaction rates decreased as a function of the cycle for Ni, Mn, and Fe at high temperatures. This is likely due to the formation of irreversible metal silicates, which do not react at a sufficient rate. Of the investigated carriers, NiO seems to be the most feasible oxygen carrier to be used in the process, although temperatures exceeding 800 °C should be avoided.