Research on adsorption characteristics of H₂S, CH₄, N₂ in coal based on Monte Carlo method

In order to study the adsorption characteristics of H₂S, CH₄ and N₂ by coal under different conditions, the new macromolecular structure model of Dongqu No. 2 was constructed, and the grand canonical Monte Carlo (GCMC) method was used to simulate the adsorption process of three types of gases in coal. The dependence of adsorption capacity of coal on its temperature, pressure and moisture content was analyzed. The results show that with the increase of pressure and temperature, adsorption isotherms of all the three gases follow Langmuir model. For pressure greater than 2 MPa, the influence of temperature on adsorption capacity was greater than that of pressure. With rise in temperature, the decrease in rate of H₂S adsorption was least and drops in the heat of adsorption of H₂S most. This indicates that the adsorption of H₂S on coal is more stable than those of CH₄ and N₂. As the water content of coal increased, its adsorption capacity for the present three gases decreased linearly, and the capacity for H₂S (1.77 mmol/g) changed the most. The reduction of free volume linearly and preferential occupation of adsorption sites by water molecules are the main reasons for the highest change in the adsorbed amount of H₂S gas.