Changes in the free radical concentration and carbon structure of coke during the coal coking process

Abstract

Free radical concentration and gas release significantly influence coal's coking behavior and cross-linking structure, warranting dedicated research.Matou coking coal (MT) and Yanzhou West gas coal (YZX) were selected for the coking experiments using coke ovens in this study. Herein, the changes in free radical concentration and contents of gas components in the colloidal layers of the MT and YZX coals were analyzed by gas chromatography (GC) and electron spin magnetic resonance spectroscopy (ESR). Results showed that in the formation of the colloidal layer, the cleavage of fatty side chains and oxygen-containing functional groups produces CH₄ and CO₂. When entering the later stage of the formation of the colloidal layer, the active sites on the aromatic clusters begin to bind to each other and amorphous carbon participates in the polycondensation reaction, producing a large amount of H₂. Some of the pyrolysis products undergo secondary pyrolysis reactions,while some aliphatic strutures containing oxygen-containing heterocycles decompose to form CO. The g-value is a characteristic parameter in ESR spectroscopy that measures the interaction between electron spin and the magnetic field, while ΔHₚ₋ₚ represents the peak-to-peak linewidth of the ESR spectrum, serving as an important parameter to measure spectral broadening.The ESR spectrum shows that the stable free radical concentration of coking coal increased in the colloidal layer stage and the condensation and crosslinking reactions between the aromatic structures in the char region exposed the stable free radicals and transformed them into active free radicals. The characteristic parameters (g value and ΔH_p-p) of the ESR spectrum exhibited good regularity in the glial phase, With a correlation between the g value and the full width at half-maximum of the G peak and ΔH_p-p having a good correlation with the relative content of π→π* transitions in the later stage of the glial phase.