Secondary oxidation of crushed coal based on free radicals and active groups

The secondary oxidation of active groups was studied for crushed coals with various particle sizes. Then, free radicals of these crushed coals were comparatively analyzed after primary and secondary oxidation. The secondary oxidation of active structures on the coal surface was studied by combining the theories of free radicals and functional groups. The coal oxidation reactivity was stronger in Particle 5#. Secondary oxidation had a stronger effect on the reactivity of high-rank coal. A relatively stable aliphatic chain structure was formed during the secondary oxidation of low-rank Coal 1#. The aliphatic hydrocarbon structure was relatively active in high-rank Coals 2# and 3#. Primary oxidation can improve the oxidizability of the aliphatic hydrocarbon structure and facilitate its secondary oxidation process. The OH group in Coal 1# possesses stronger oxidation reactivity and was consumed rapidly during secondary oxidation. In contrast, the consumption and generation rate of the OH group tended to reach a balance in Coal 2# and Coal 3#. CO and CO groups in Coal 1# experienced relatively violent secondary oxidation. The two groups in Coal 2# and Coal 3# experienced relatively gentle secondary oxidation.