Relationship between the structure of macerals of Ordos lignite and its pyrolysis characteristics
The Ordos lignite was separated into vitrinite-rich group(EL-V)and inertinite-rich group(EL-I)by floating-sinking separation method,and the structures and compositions of the raw coal and its maceral were analyzed by industrial analysis,elemental analysis,X-ray diffraction spectroscopy(XRD),Fourier transform infrared spectroscopy(FTIR)and solid state nuclear magnetic resonance(13C NMR).The pyrolysis characteristics and the escape pattern of gaseous volatiles of the raw coal and its maceral were investigated by powder-particle fluidized bed and TG-FTIR devices,respectively,to further construct the macromolecular structure models of the raw coal and its maceral and quantum chemical calculations were carried out to recognize the law of chemical bonds breaking.The results showed that the vitrinite-rich group had a higher content of volatiles,contained abundant alkyl side chains,and the largest heat weight loss rate,suggesting that the vitrinite-rich group was more reactive in pyrolysis.Compared with the raw coal and inertinite-rich group,the vitrinite-rich group had higher the pyrolysis gas content and tar contend,and its pyrolysis tar contained more aliphatic hydrocarbons and light aromatic hydrocarbons(TXE).The inertinite-rich group had lower H/C ratio,and higher oxygen content and aromatic ring condensation,and its pyrolysis tar contained higher PAHs and phenolics.In addition,the precipitation behaviors of CO2,CO,CH4,aliphatic hydrocarbons and aromatic hydrocarbons were analyzed by TG-FTIR.Based on the breaking of chemical bonds in the macromolecular structure of coal samples and the escape pattern of gaseous volatiles,the possible reaction routes carried out in the coal pyrolysis process were proposed.
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