In-situ analysis of the Al-Fe-Mn-Cu oxide oxygen carrier for chemical looping applications

Abstract

A novel Al-Fe-Mn-Cu oxide oxygen carrier, termed Gen3, was developed by NETL and prepared using natural ore and pigment grade materials. Gen3 was subjected to 10 cycles of reduction-oxidation (redox) through confocal laser scanning microscopy (CLSM) and thermogravimetric analysis (TGA), separately. TGA results indicated that Gen3 shows promise as an oxygen carrier, repeatably lending approximately 6% of its mass to oxygen carrying capacity. CLSM characterization led to the identification of different swelling behaviors among particles of ‘smooth’ (spinel-S) vs. ‘rough’ (spinel-R) surface morphologies, labeled based on appearance before redox cycling. Spinel-R particles exhibited homogeneous chemistry and porosity. Spinel-S particles showed much more localized porosity, specific to high-Cu areas. Gen3 particle volume increased 60% for spinel-S particles and 30% for spinel-R particles over the course of 10 redox cycles. All conditions showed some degree of separation of the complex Al-Fe-Mn-Cu spinel. Primary observed phases included Al-rich spinel, Fe-rich spinel, and Cu/CuO. Al-rich spinel and Cu/CuO in exposed Gen3 at times formed a lamellar structure of alternating Al-rich and Cu-rich layers in exposed Gen3 near areas rich in Cu. An additional Si-O-K-type phase was also observed that likely arose from the impurities involved in pigment grade materials and natural ores. Segregation increased with level of exposure. Si-rich regions and Fe-rich spinels showed extremely low porosity; a more evenly mixed Al-Fe-Mn-Cu spinel showed moderate porosity; Cu and Cu-rich spinel by far showed the highest porosity.

Keywords

• Oxygen carriers
• Spinel
• Chemical looping combustion
• Thermogravimetric analysis
• Confocal laser scanning microscopy
• Porosity