To study the adsorption characteristics of CO, CO2, N2, O2, and their binary-components in lignite coal, reveal the influence of CO2 or N2 injection and air leakage on the desorption of CO in goafs, a lignite model (C206H206N2O44) was established, and the supercell structure was optimized under temperatures of 288.15–318.15 K for molecular simulation. Based on molecular dynamics, the Grand Canonical Monte Carlo method was used to simulate the adsorption characteristics and the Langmuir equation was used to fit the adsorption isotherms of gases. The results show that for single-components, the order of adsorption capacity is CO2 > CO > O2 > N2. For binary-components, the competitive adsorption capacities of CO2 and CO are approximate. In the low-pressure zone, the competitive adsorption capacity of CO2 is stronger than that of CO, and the CO is stronger than N2 or O2. From the simulation, it can be seen that CO2, N2 or O2 will occupy adsorption sites, causing CO desorption. Therefore, to prevent the desorption of the original CO in the goaf, it is not suitable to use CO2 or N2 injection for fire prevention, and the air leakage at the working faces need to be controlled.

As an index gas of spontaneous combustion, C2H4 has been used in several coal mines, but its adsorption on residual coal during the process from generation to sampling has an impact on evaluation. The molecular structure models of lignite and anthracite were constructed through molecular mechanics and dynamics, and the Grand Canonical Monte Carlo systems were used to simulate the adsorption of C2H4 and other common gases on lignite and anthracite at temperatures of 288.15–318.15 K. The order of adsorption capacity was CO2 > C2H4 > O2 > N2 in the lignite and anthracite molecular models within the low-pressure zone. When the pressure increases, the adsorption capacity of O2 and N2 exceeded that of C2H4. The C2H4 and CO2 have similar and concentrated adsorption sites, and it is easier to reach the limit adsorption capacity; O2 and N2 have similar adsorption sites, the number of sites is much more than that of C2H4 and CO2, and their limit adsorption capacities are larger than those of C2H4 and CO2. When C2H4 is monitored in a goaf, its concentration is not quite accurate because of the adsorption of residual coal, which is different from the detected temperature of the C2H4 concentration obtained from the experiment. This is of great significance to further experiments and more on-site data statistics to fix the problem for coal mines.

To study the generation rules of organic molecules or fragments and the generation paths of some hydrocarbon gases (C 2 H 2 /C 2 H 4 ) and inorganic gases (CO 2 /H 2 O/H 2 /H 2 S) 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 C 1 –C 4 fragments increase, and the gas molecules generated increase. In the pyrolysis process, the oxygen-containing functional groups and hydrogen groups formed H 2 O and H 2 with the increase of temperature. H 2 S as an intermediate product is always maintained in dynamic equilibrium. CO 2 comes from the decarboxylation of the carboxyl groups. When the temperature is lower than 3000 K, C 2 H 4 and C 2 H 2 are mainly formed by the adjacent carbon structure in coal molecules, and C 2 H 4 is formed from the ethyl side chain, the naphthenic structure, and the unstable aromatic rings. C 2 H 2 is formed from naphthene structures and aromatic rings with multiple side chains. When the temperature is higher than 3000 K, C 2 H 4 and C 2 H 2 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.