Effect of the Iron Component on Microcrystalline Structure Evolution of Hydrochloric Acid-Demineralized Lignite during the Pyrolysis Process

[Image: see text] Hydrochloric acid-demineralized Shengli lignite (SL(+)) and iron-added lignite (SL(+)-Fe) were thermally degraded using a fixed-bed device to better understand the effect of the iron component on the microcrystalline structure transformation properties of lignite during the pyrolysis process. The primary gaseous products (CO(2), CO, H(2), and CH(4)) were detected by pyrolysis–gas chromatography. X-ray diffraction and Raman spectra were adopted to analyze the microcrystalline structure of lignite and chars. The results indicated that the iron component had a catalysis effect on the pyrolysis of SL(+) below 602.6 °C. The pyrolysis gases released in the order of CO(2), CO, H(2), and CH(4), and the addition of the iron component did not change the sequences. The iron component promoted the generation of CO(2), CO, and H(2) in the low-temperature stage. During the high-temperature stage, the iron component inhibited the formation of CO and H(2). The formation of CH(4) was inhibited by the iron component throughout the pyrolysis process. The evolution characteristics of −OH, C=O, C=C, and C–H functional groups were not significantly affected, and the fracture of aliphatic functional groups and C–O functional groups was inhibited by the iron component during the pyrolysis process. The iron component restricted the spatial regular arrangement tendency of aromatic rings and facilitated the decrease in the small-sized aromatic ring but inhibited the formation of large aromatic rings (≥6 rings) and the content decrease in side chains during the pyrolysis process. Notably, the effects of the iron component on the formation of gaseous products were associated with the microstructure evolution of lignite.