Ilmenite-CO reduction kinetics

摘要

Secondary ilmenite is an inexpensive mineral that is a potential oxygen carrier for the chemical looping process. It has excellent mechanical stability, adequate heat capacity to transfer heat from the air reactor to the fuel reactor, and possesses a modest oxygen transfer capacity. Fresh and preoxidized ilmenite can transfer up to 1.7% and 1.2% oxygen on a mass basis, when reduced for 2 min with CO at 910 degrees C. Preoxidizing ilmenite reduces its tendency to agglomerate but it also reduced its reactivity towards CO. We characterized the kinetics of the reduction of preoxidized secondary ilmenite from South Africa with a mechanistic model. The model assumes CO reacts with surface oxygen atoms, and that bulk oxygen replenishes the surface oxygen. The model accounts for more than 90% of the variance in the data. The activation energies of the surface reduction and reoxidation steps are 51 kJ mol(-1) and 89 kJ mol(-1), respectively. The surface site density decreases with the reduction cycles via the simple power law expression because sintering deactivates the catalyst. (C) 2015 Elsevier Ltd. All rights reserved.