Solid state reaction kinetics of iron oxide reduction using hydrogen as a reducing agent

• The reaction kinetics of iron oxide reduction within an iron-silica MSPS was investigated using hydrogen as a reducing agent.
• A 1-D isothermal plug flow kinetic model was developed to characterize a step-wise conversion of magnetite to elemental iron.
• The effect of macro- and microscopic mass distribution of iron oxides on the reaction kinetics was investigated.
• Key kinetics parameters, including activation energy, pre-exponent, and order of reaction were determined.

The thermochemical reduction of metal oxides is important for fuel production using chemical looping processes as well as metal extraction from ore. In this study, reaction kinetics for the reduction of iron oxide using hydrogen as a reducing agent is studied. Experiments are conducted with the iron-silica Magnetically Stabilized Porous Structure (MSPS) for different reaction conditions, including reaction temperature, hydrogen inlet molar concentration, and hydrogen inlet flow rate. The reduction reaction is characterized by step-wise conversion of magnetite to elemental iron via wustite. Thus the reaction kinetics is governed by the coexistence of two reactions, magnetite to wustite and wustite to iron conversions. A one-dimensional plug flow isothermal kinetic model is proposed, and a numerical scheme is developed to solve the species transport and substrate conservation equations. The numerical scheme is used as a tool to calibrate the kinetic model, and the critical kinetic parameters, including activation energy, pre-exponent, and order of reaction, are determined for both reactions. The reaction mechanism for both reactions is identified, and a transition in the reaction mechanism is captured with different models. The kinetic model shows good agreement with the experimental data for different operating conditions. This study provides a basis for scaling bench scale hydrogen reduction reactors to an industrial scale.