Kinetics of the reduction of wustite by hydrogen and carbon monoxide for the chemical looping production of hydrogen

Hydrogen of very high purity can be produced via the steam-iron process, in which steam oxidises metallic Fe in 3/4Fe+H2O -> 1/4Fe(3)O(4) + H-2. It is then advantageous to oxidise Fe3O4 in air to Fe2O3, an oxygen-carrier. This higher oxide of Fe is then reduced to regenerate metallic iron by reacting with synthesis gas, producing metallic Fe and possibly some wustite (FexO, 0 < x < 1). In this three-stage process, the reduction of FexO to Fe is the slowest reaction. This paper is concerned with the kinetics of the reduction of wustite (FexO) by reaction with CO, and or H-2. Starting with pure (99 wt%) wustite, the intrinsic kinetics of its reduction to metallic iron were measured in fluidised beds at different temperatures. The reaction was found to have 3 distinct stages, (i) the removal of lattice oxygen in (ii) rate increasing with conversion of solid and (iii) rate decreasing with conversion of solid. A random pore model was used to simulate the latter stages of the reduction of wiistite by either H-2 or CO or a mixture of the two. It was found that the intrinsic rate of reduction in H-2 is substantially faster than with CO, whereas the resistances to diffusion of H-2 and CO through the product layer of Fe are comparable; these factors account for differences in the overall rates observed with these gases. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licensegby/3.03/).