Evolution mechanism of functional groups during coal chemical looping combustion

Chemical looping combustion (CLC) plays a vital role in coal combustion which released pure CO2 in the exhaust gas with low energy consumption. Researchers have developed over 1000 oxygen carriers (OCs) to enhance the properties of OCs. This study focus on the microstructural changes of coal during CLC process which could provide the performance improvement direction for OCs. Results showed that the phenolic -OH group can easily be removed by CuO while the free -OH group and the self-associating -OH group are hard to be consumed by the lattice oxygen in CuO at 800 °C, showing good stability in CLC process. Aliphatic hydrocarbons could be consumed in the gas phase rapidly. The functional group of C=O maintains high reactivity with CuO which explains why the addition of CO2 promotes the reaction rate in coal CLC. But C=C group was nonpolar bond and hard to be consumed while the -CH2 and -CH3 group and C-O-C group showed good reactivity with CuO. Higher reaction temperature affords higher reactivity of coal CLC process. But the -OH group changed slowly at higher temperature which could because that higher temperature makes the organic big molecular of the coal char decomposed and produce more -OH group.