The adsorption model of the adsorption process of CH4 on coal and its thermodynamic characteristics

In this study, the adsorption and desorption data of six coal samples with different volatile fraction contents were obtained using a laboratory-made adsorption and desorption system. The experimental temperature was 30 ℃, and the adsorption pressure was 0–3.5 MPa. The fitting effects of four different calculation methods of saturated vapor pressure (P0) (namely Reid method, Antoine method, Astakhov method, and Amankwah method) in applying three adsorption models (namely two-parameter BET model, three-parameter BET model, and D-A equation) were compared and analyzed. The D-A equation was reliable as an adsorption model when the Astakhov method was used to calculate P0. When fitting the adsorption data of six coal samples, R2 values were all greater than 0.99, and the obtained fitting parameters were all within a reasonable range. The Langmuir model and D-A equation were utilized to calculate the surface potential(Ω) and Gibbs free energy change (ΔG) of each coal sample. The D-A equation was more reliable to calculate Ω and ΔG, and it had some advantages in terms of calculation accuracy.