Thermal Reduction of Magnetically Stabilized Ferrites Under Reduced Pressure

Oxidation of a metal (or metal oxide) by H₂O and CO₂ followed by a regenerative high temperature thermal reduction of the resulting metal oxide is a promising method for using concentrated solar energy to produce syngas, a precursor for liquid fuels.  For such a process to become viable, the metal oxide material that is formed must have the ability to maintain surface area and retard sintering over thousands of redox cycles.  Previous experiments have already shown that a magnetically stabilized iron-silica porous structure can significantly enhance hydrogen production via oxidation by H₂O and chemical reduction by CO at 800˚C. ¹

Here, the feasibility of thermally reducing the mixed-metal ferrite structure at temperatures up to 1400˚C under vacuum is investigated.  Reducing the reactor pressure effectively decreases the partial pressure of O₂, resulting in a higher extent of reduction than is possible under atmospheric conditions.  Since the need for a diluting inert gas to increase product yield is eliminated, a higher theoretical higher heating value efficiency is possible. 

In addition to laboratory experiments, a reduced pressure solar thermochemical reactor capable of utilizing the novel mixed-metal ferrite structure has been designed.  Results of testing performed using the University of Florida 42 kW solar simulator will be presented. 

[1]Mehdizadeh AM, et al., Enhancement of thermochemical hydrogen production using an iron-silica magnetically stabilized porous structure, International Journal of Hydrogen Energy (2012), doi:10.1016/j.ijhydene.2012.02.189