Effect of mineral extraction on the evolution of nitrogen functionalities during coal pyrolysis

Y The mineral composition of coal has a significant effect on the pyrolysis of coal and the evolution of the nitrogen-containing functional groups. Thermogravimetry-differential thermal analysis-Fourier transform infrared-mass spectrometry (TG-DTA-FTIR-MS), X-ray photoelectron spectroscopy (XPS), and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) were used to study the effects of extraction pretreatment (water-washing, NH4Ac-washing, and HCl-washing) on the pyrolysis characteristics and the three-phase nitrogen transformation mechanism in Xinjiang Hongshaquan coal. The results show that the minerals in each extraction stage can inhibit the transformation of char-N to tar-N/gas-N. The presence of H2O-soluble and HCl-soluble minerals makes the tar-N content of the raw coal (R-coal) 25.5% lower than that of the water-washed coal (W-coal), and the tar-N content of the NH4Ac-washed coal (N-coal) 18.7% lower than that of the HCl-washed coal (H-coal). By contrast, NH4Ac-soluble minerals make the tar-N content of the W-coal 86.3% higher than that of the N-coal. The gas-N was increased by the extraction. The HCl-soluble minerals were the most important factor affecting the gas-N yield, which results in a large amount of char-N being converted into gas-N, while the NH4Ac-soluble minerals inhibit the process. The results of this study will provide data support and theoretical basis for clean coal combustion and improving the quality of coal tar.

Automated summary

The mineral composition of coal significantly affects the pyrolysis of coal and the evolution of nitrogen-containing functional groups. Different extraction pretreatments have varying effects on the nitrogen conversion mechanism in coal, with different minerals playing important roles in the transformation of char-N to tar-N/gas-N. These findings provide valuable data support for clean coal combustion and improving coal tar quality.