Molecular insights into the influence mechanism of carbon structure in iron coke after gasification on its combustion behavior and kinetics: Experiments, ReaxFF MD, and DFT

Abstract

Iron coke has attracted attention as a low-carbon ironmaking fuel due to its high reactivity and efficient resource utilization. However, the structural characteristics of iron coke after gasification and their effect mechanisms affecting subsequent combustion remain unclear. This study investigated the effects of gasification on the carbon structure of iron coke using XRD and Raman spectroscopy, and revealed the influence mechanism of carbon structure on combustion behavior and kinetics through combined thermogravimetric analysis, ReaxFF MD, and DFT calculations. The results demonstrate that the gasification reaction catalyzed by iron/iron oxides induces more defects in the carbon structure of iron coke. The higher the gasification degree of iron coke, the greater its following combustion reactivity. Increasing the heating rate in the non-isothermal combustion process can markedly enhance the combustion performance of iron coke. ReaxFF MD simulations reveal that oxygen radicals preferentially attack and react with vacancy defects in the carbon structure, which is the primary reason for the increased reactivity of defective structures. Due to the curling effect between carbon layers, the activation energy during combustion initially increases and then decreases with rising carbon conversion. DFT calculations indicate that vacancy defects in the carbon structure play a critical role in enhancing combustion behavior. On one hand, the increased defects provide more active sites, reducing the adsorption energy for O₂ molecules. On the other hand, the synergistic effect of van der Waals interactions and chemical bonds in defective carbon structures effectively reduces activation energy for the combustion reaction.