The study of coal pyrolysis reactions and hydrogen production mechanisms based on the coal macromolecular structure, is crucial for improving energy efficiency and transitioning coal into a clean energy source. This study used the Fourier Transform Infrared Spectroscopy and Mass Spectrometry (TG–FTIR–MS) to analyze the pyrolysis process of Xianfeng (XF) lignite and the generation pattern of the gas products. Lignite and its residual solid samples pyrolyzed at temperatures ranging from 300 °C to 1100° C were analyzed. The variational characteristics of the macromolecular structure during coal pyrolysis were examined. Utilizing molecular dynamics simulations, we analyzed the evolution mechanism of the macromolecular carbon structure of organic matter during the coal pyrolysis process. The results showed that the pyrolysis can be divided into three distinct phases: activation (30–300 °C), pyrolysis (300–650 °C), and condensation (650–1200 °C). During these phases, the coal structure undergoes complex transformations including folding, twisting, shedding of small molecular side chains, and breaking of macromolecular side chains, ultimately leading to the directional arrangement of structural fragments. During the pyrolysis stage, hydrogen generation commenced at a slow rate, primarily driven by the reaction between the C-H bonds of the fatty chains, hydroxyl O-H bond breakage, and the formation of hydrogen radicals. In the condensation stage, both the rate and quantity of H₂ production significantly increased. This phase was characterized by the breaking of hydrogen bonds in carboxyl functional groups and an augmented presence of hydrogen radicals in the aromatic structure. By integrating theoretical insights of molecular dynamics simulations with pyrolysis experiments, this study comprehensively explored the relationship between molecular structures and macroscopic material chemical reactions, shedding light on the pyrolysis and gas production mechanisms of XF coal. These findings provide essential theoretical support for the industrial utilization of coal, including gasification and liquefaction processes.

Coal pyrolysis; Hydrogen; Molecular structure; Molecular dynamics simulation; TG-FTIR-MS