The Heat Effect And Evolution Of Active Groups During Coal Oxidation

Coal plays a strategic role in the development of China's production and construction.The study of the heat effect and evolution of active groups during coal oxidation can provide a theoretical basis for explaining the micro mechanism pf coal spontaneous combustion.In this paper,three kinds of coal samples with different metamorphic degree were selected,and the heat effect and evolution of active groups during coal oxidation were investigated by TG/DSC-FTIR technology,Fourier transform method and electron spin resonance technology.According to results,with increasing metamorphism degree of coal,the temperature of thermal decomposition,ignition point,peak temperature and the temperature of CO,CO2 and H2O(g)produced during coal oxidation were increased correspondingly,while the maximum heat releasing rate decreased,which indicated that the higher degree of coal rank was,the more difficult the oxidation reaction had occurred.The proportions of main functional group of coal is oxygen containing functional group>aromatics>fat hydrocarbon.The lower degree of coal rank has,the more oxygen containing functional groups and the intermolecular association-OH has,with longer side chain and more heterocyclic rings.The-OH of intermolecular association is the most important active group during coal oxidation.It began to take part in the reaction at the initial stage of oxidation and continued to decrease throughout the whole process.Carbonyl bonds is an important transitional group in coal spontaneous combustion,which was oxidized by fatty hydrocarbons to generate a large amount of-OH,then-OH further reacted with oxygen to produce carbonyl group.After the ignition temperature,C=O fractured and generated functional groups such as aldehydes,ketones,carboxylic acids,etc.Therefore,C=O increased firstly and then decreased during coal spontaneous combustion.Fat hydrocarbon is another key group leading to the coal oxygen compound reaction,which continuously fractured during the whole oxidation process and reacted with oxygen to form C=O.The aromatic ring C=C,which is the core structure of coal molecules,does not participate in the reaction at the initial stage of coal oxidation.The electron spin resonance spectroscopy showed that with decreasing metamorphism degree of coal,free radical became unstable,the survival time was relatively shorter and the effect of the electronic exchange of free radicals became weaker.In the low temperature oxidation process of coal,the chemical reaction intensity was smaller and the start time was later.The line width ?H and the change of free radical concentration with temperature showed that the-OH and C=O double bond were the main reactants of coal oxygen reaction and could be converted to each other.The increase of free radical concentration during low temperature oxidation was caused by the reaction of free radicals and oxygen to produce carbonyl radicals.