Effects of added pyrite on apparent kinetic responses and structural evolution during pyrolysis of clarain and durain from tar-rich coal

Abstract

This study investigated how added pyrite affects the stage-dependent pyrolysis behavior and structural evolution of clarain (XJH-L) and durain (XJH-A) from the No. 2 –2 coal seam of the Xiaojihan minefield in the northern Shaanxi Jurassic coalfield, China. Samples containing 0, 3, 6, and 9 wt% added pyrite on a dry-coal basis were characterized by TG–DTG analysis, stage-resolved Doyle fitting at a fixed heating rate of 10 ℃ min −1 , temperature-resolved in situ FTIR and Raman spectroscopy, and low-temperature N 2 adsorption. XJH-L contained more vitrinite and had higher volatile matter and tar yields than XJH-A. Pyrite addition produced a secondary DTG feature near 550 ℃ in both lithotypes, which was more pronounced in XJH-A. Under the fixed heating program, the Doyle-fitted apparent activation-energy values decreased in S 2 and S 3 . At 6 wt% pyrite, the fitted S 3 values decreased from 45.69 to 38.07 kJ mol −1 for XJH-L and from 47.31 to 41.89 kJ mol −1 for XJH-A, while the corresponding values at 9 wt% were similar. FTIR analysis showed greater depletion of O–H, aliphatic C–H, C=O, and C–O structures after pyrite addition, with stronger aliphatic C–H and C=O responses in XJH-A. Aromatic-framework rearrangement began at lower temperatures and extended over a broader interval in XJH-L, whereas the XJH-A response was concentrated at 400–500 ℃. Differences in the measured pore response among pyrite loadings became most evident at 500–600 ℃. Overall, clarain responded earlier and over a broader temperature interval, whereas durain responded mainly at higher temperatures.