Effect of Iron Component on the Structural Evolution of Carbon Bonds in Hydrochloric Acid-Demineralized Lignite During Pyrolysis

[Image: see text] The pyrolysis characteristics of hydrochloric acid-demineralized Shengli lignite (SL(+)) and iron-added lignite (SL(+)-Fe) were investigated using a fixed-bed reactor. The primary gaseous products (CO(2), CO, H(2), and CH(4)) were detected via gas chromatography. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques were used to study the carbon bonding structures of the lignite and char samples. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to better understand the effect of the iron component on the transformation of the carbon bonding structure of lignite. The results showed that CO(2) was released first during pyrolysis, followed by CO, H(2), and CH(4), and this order was unaffected by the addition of the iron component. However, the iron component promoted the generation of CO(2), CO (<340 °C), and H(2) (<580 °C) at lower temperatures and inhibited the formation of CO and H(2) at higher temperatures while also inhibiting the release of CH(4) throughout the pyrolysis process. The iron component may form an active complex with C=O and a stable complex with C–O, which can promote the fracture of carboxyl functional groups and inhibit the decomposition of ether bonds, phenolic hydroxyl groups, methoxy groups, and other functional groups, thus promoting the decomposition of aromatic structures. At low temperatures, it promotes the decomposition of aliphatic functional groups and finally the bonding and fracture of functional groups in coal, leading to the change of the carbon skeleton, resulting in the change of gas products. However, it did not significantly affect the evolution of −OH, C=O, C=C, and C–H functional groups. According to the above results, a developing reaction mechanism model of Fe-catalyzed lignite pyrolysis was established. Therefore, it is worth doing this work.