Exploration of hydrogen-rich gas evolution mechanism during vitrinite pyrolysis: A combined TG-MS and ReaxFF study

Abstract

Understanding the evolution mechanism of hydrogen-rich coke oven gas in vitrinite pyrolysis is crucial for improving the clean utilization of coal. This work focused on the vitrinite extracted from Fangezhuang coal as the sample. Its three-dimensional molecular model was constructed based on elemental analysis, IR spectroscopy, ¹³C NMR, and density functional theory. ReaxFF molecular dynamics simulation, combined with TG-MS, was used to study the vitrinite pyrolysis process and its mechanism of hydrogen-rich gas evolution. Experimental results indicated that H₂ and CH₄, the main hydrogen-rich gases, originated from the aliphatic and partially aromatic moieties of vitrinite, and required the participation of a large number of transferable hydrogen atoms. The reaction network confirmed that the transferable hydrogen atoms included not only the easily-dissociated hydrogen atoms in vitrinite but also the active hydrogen atoms in the gas-phase hydrocarbon radicals. In particular, the latter significantly increased the diffusivity of condensed hydrogen atoms and the collision probability with other components through the gas-phase hydrogen transfer cycle, which favors the generation of gas products. This work provided theoretical support for optimizing the production of coke and coke oven gas in synergy, as well as improving the quality of hydrogen-rich gas in the industry.