Effects Of Low-temperature Oxidation Of Lignite On Pyrolysis Behavior Under Microwave Irradiation

China's coal resources are more abundant,of which lignite resources account for about 14 % of coal resources.Lignite easy to be oxidized during transport and storage because of high chemical reactivity,the chemical structure changings thereafter.Lignite pyrolysis technology is an important way to develop and utilize low-grade coal resources clean and high efficiency.Therefore,study of the pyrolysis behavior of low-temperature oxidation is very useful,it can provide a theoretical basis for the development of clean coal utilization and mechanism of the high value-added fine chemical production.The effects of low-temperature oxidation on microwave pyrolysis behavior of lignite were investigated.Lignite sample was pre-oxidized using hydrogen peroxide at 20 °C,40 °C,60 °C and 80 °C.The chemical structure changes in lignite during oxidation were analyzed using Fourier Transform infrared(FT-IR),X-ray photoelectron spectroscopy(XPS)techniques and 13 C Nuclear magnetic resonance(13C NMR),and results showed that the concentration of oxygenated functional group increased after pre-oxidation in expense of aliphatic hydrogen structures.The chemical structure changes in lignite during oxidation led to an increase in weight loss during microwave pyrolysis.Higher concentrations of oxygenated aliphatic compounds and oxygenated aromatic compounds(particularly phenolics)were detected in pyrolysis tar of oxidized coal compared to the raw coal particularly after oxidation at 20 °C.This was attributed to the increase in oxygen functionalities and phenyl ether structure in coal after oxidation.An increase in concentration of CO and CO2 and decrease in concentration of H2 and CH4 in pyrolysis gas was evident after lignite oxidation.The mechanism of phenolics formation during pyrolysis of oxidized coal was also proposed and discussed.Activated carbon aids the yield of CO2 and Fe3O4 promotes the yield of CO were observed.