Gas generation mechanisms of bituminous coal under shear stress based on ReaxFF molecular dynamics simulation

Although research on the relationship between coal functional groups and tectonic stress has made great progress in recent years, the evolution of the morphology and chemical structures of coal macromolecules under tectonic stress is still unclear. We used reactive force field molecular dynamics (ReaxFF MD) simulations to explore the gas generation mechanisms of high-volatile bituminous coal model under shear stress. Several interesting results were found. First, in the absence of frictional heat, shear stress can act on the macromolecular structures of coal directly and generate gases, such as CH4, CO2, H2O, H2, and CO. Second, under the action of shear stress, coal macromolecular structures will generate a variety of free radicals, such as center dot OH, center dot H, center dot CH3, and many small free radical fragments or monocyclic radicals. These detached free radicals may combine with each other or attach to other structures to promote further reactions. Third, in the entire macromolecular network, many components may participate in the reactions as "catalysts", providing conditions for the contact of various small free radicals. For the first time, we have obtained direct simulation evidence of the gas generation mechanisms of coal via mechanolysis instead of relying on frictional heat. These results are a beneficial supplement to understand the coalification process.