Insight into Pyrolysis Behavior and Cross-Linking Reactions Mechanism During Coking Coals Pyrolysis

Highlights: The remains of aliphatic structures within the plastic layer promotes cross-linking reactions during the softening–melting stage. (C–C)/(C–H) ratio and H₂ evolution is a key indicator of aromatization cross-linking intensity. Structural densification and aromatic growth after resolidification confirm the intensification of cross-linking, driving the formation of coke. Coke, as an essential metallurgical raw material, is widely used in iron and steel production. To investigate the pyrolysis behavior and cross-linking reactions during the pyrolysis of coking coal, pyrolysis experiments were conducted in a quartz-tube fixed-bed reactor placed in an electric furnace. The yields and compositions of the pyrolysis products were systematically analyzed. Gaseous and tar components generated at different pyrolysis stages were characterized using gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The semi-coke was examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results indicated that the yields of tar from coking coal pyrolysis have a notable impact on the cross-linking reactions occurring during the coal pyrolysis process. The structural differences between Malan coal (ML) and Tunlan coal (TL) coals underlie their distinct behaviors in cross-linking intensity, tar evolution profiles, and coke-forming properties. For high-volatile, highly fluid ML coal, the release of the aliphatic compounds in tar volatiles remains relatively low at the temperature of maximum fluidity, which is beneficial to the cross-linking reactions. In contrast, for TL coal with lower volatility and fluidity, substantial H₂ emission during the early pyrolysis stage promotes cross-linking reactions. This study provides new insights into the temperature-dependent evolution of cross-linking reactions during coking coal pyrolysis.