In Situ FTIR Study of Real-Time Changes of Active Groups during Oxygen-Free Reaction of Coal

The distribution of functional groups in two different rank coal samples and their real-time changes during the oxygen-free reaction of coal were tested. An in situ FTIR system was designed to test the real-time changes of functional groups during coal reaction. The real-time changes of aliphatic hydrocarbon groups and oxygen-containing groups were analyzed using the in situ FTIR method. The results show that the distribution of functional groups and their changes are various for different ranks of coals. The quantity of active groups in low-rank coals is larger than that in high-rank coals. For the anthracite coal sample, the quantities of aliphatic hydrocarbon and oxygen-containing groups increase with the rise of coal temperature. For the lignite coal sample, the quantity of aliphatic carbon groups decreases from 30 to 70 °C, then increases with the temperature rise. The oxygen-containing groups of the lignite coal sample have two different changing trends, that is, an increase with temperature rise, and a decrease at the initial temperature stage, followed by increasing with temperature rise. These phenomena are resulted from the difference of chemical activities of various active groups. This study provides a new method for further study of coal reaction at the level of active groups and explains the generation process of gaseous products during the oxygen-free reaction of coal.