Effect of Reaction Temperature on the Chemical Looping Combustion of Coal with CuFe2O4 Combined Oxygen Carrier

Reaction temperature is regarded as one of the important factors influencing the efficient utilization of coal in chemical looping combustion (CLC), but research into its effect on the chemical structure of coal in CLC is limited. In the research reported herein, the oxygen-transfer mechanism of CuFe2O4 prepared through the sol gel method combined with combustion synthesis, along with the characteristics of its reaction with a typical coal of high sulfur and high ash contents (abbreviated as LZ), were systematically investigated at different final reaction temperatures, with the research focused on the effect of reaction temperature. H-2-temperature-programmed reduction of CuFe2O4 indicated that the first reduction of the Cu2+ ion in CuFe2O4 was advantageous in the later transmission of atomic oxygen from the Fe3+ reduction, while temperature programmed decomposition of CuFe2O4 under a N-2 atmosphere validated the potential of CuFe2O4 to emit O-2 through its direct decomposition. Furthermore, thermogravimetric analysis and Fourier transform infrared spectroscopy showed better reaction performance between CuFe2O4 and LZ coal than other ferrite oxygen carrier (OC) candidates, such as MnFe2O4, NiFe2O4, and CoFe2O4, which we studied previously. Comprehensive characterization of the solid products from reaction of CuFe2O4 with LZ coal by field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, and Xray photoelectron spectroscopy (XPS) indicated that CuFe2O4 was mainly reduced to Cu and Fe3O4. At the same time, some oxygen-deficient CuFe2O4 was also formed through disintegration of the original CuFe2O4 spinel with more Cu2+ and Fe3+ ions occupying the octahedral sites, which benefited the transmission of the atomic oxygen involved in the CuFe2O4. Finally, XPS analysis of the LZ coal residue after its reaction with CuFe2O4 indicated that the main obstacle to fully utilizing LZ coal at the molecular scale in CLC was the dominance of C-C/C-H groups, with the highest relative content over 62% at the 700 degrees C reaction temperature. Increasing the reaction temperature was quite effective to promote the efficient utilization of LZ coal from the molecular perspective during the reaction between LZ coal and CuFe2O4.