Molecular Dynamics Simulation and Gas Generation Tracking of Pyrolysis of Bituminous Coal

To study the generation rules of organic molecules or fragments and the generation paths of some hydrocarbon gases (C₂H₂/C₂H₄) and inorganic gases (CO₂/H₂O/H₂/H₂S) in the pyrolysis process of bituminous coal at 1000-5000 K, the ReaxFF molecular dynamics module in AMS software was used to simulate the pyrolysis behavior of the Hongqingliang model, Gaojialiang model, and Wiser model. With the increase of temperature, the system potential energy decreases, the endothermic efficiency increases first and then decreases, the fragments of C₁-C₄ fragments increase, and the gas molecules generated increase. In the pyrolysis process, the oxygen-containing functional groups and hydrogen groups formed H₂O and H₂ with the increase of temperature. H₂S as an intermediate product is always maintained in dynamic equilibrium. CO₂ comes from the decarboxylation of the carboxyl groups. When the temperature is lower than 3000 K, C₂H₄ and C₂H₂ are mainly formed by the adjacent carbon structure in coal molecules, and C₂H₄ is formed from the ethyl side chain, the naphthenic structure, and the unstable aromatic rings. C₂H₂ is formed from naphthene structures and aromatic rings with multiple side chains. When the temperature is higher than 3000 K, C₂H₄ and C₂H₂ are mainly formed by the random combination of free radicals generated by the crushing of coal molecules. The research results are of great significance to coal pyrolysis and clean utilization of coal.