In-Depth Investigation of Chemical Looping Combustion of a Chinese Bituminous Coal with CuFe2O4 Combined Oxygen Carrier

Coal is of heterogeneous nature with a complex chemical structure, which is closely associated with its reactivity. In this research, from the perspective of the chemical structure of coal, reaction characteristics of the as-synthesized CuFe 2 O 4 oxygen carrier (OC) with a typical Chinese bituminous coal (designated as LZ) were deeply investigated using thermogravimetric analysis (TGA). Also, the effect of CuFe 2 O 4 oxygen excess number Φ on the reaction behavior of LZ coal with CuFe 2 O 4 was highlighted. TGA investigation of LZ coal reaction with CuFe 2 O 4 at Φ = 1.0 displayed the enhanced reactivity of CuFe 2 O 4, which was useful to conversion of the aromatic matrix in LZ coal. Furthermore, during LZ coal reaction with CuFe 2 O 4 in the TGA, the gaseous products evolved from the condensed flue gas were in situ analyzed using Fourier transform infrared (FTIR), which indicated that most of the CO 2 resulted from oxidation of CO by CuFe 2 O 4 OC. Meanwhile, the solid product left after LZ coal reaction with CuFe 2 O 4 was analyzed with X-ray photoelectron spectroscopy (XPS), which revealed that oxidation and conversion of the C–C/C–H groups was the limited step at the molecular scale for full conversion of coal. Finally, the effect of CuFe 2 O 4 excess number Φ for LZ coal reaction with CuFe 2 O 4 was investigated by TGA, and the solid product left was analyzed by XPS, which indicated that C–C/C–H was more effectively converted at CuFe 2 O 4 Φ = 1.0 than Φ = 0.5 and 1.5 at the final reaction temperature of 900 °C. In addition, the mechanism of coal oxidation by CuFe 2 O 4 was also explored, and the C–C/C–H involved in LZ coal was preferentially oxidized to form C–O groups and then further converted to O═C–O groups through the formed intermediate C═O groups. Overall, this research was much beneficial for a mechanistic understanding of the conversion of coal in a CLC system and promotion of the efficient utilization of coal.