Thermodynamic Analysis of CH4/CO2/N2 Adsorption on Anthracite Coal: Investigated by Molecular Simulation

The interpretation of gas adsorption behavior on a coal surface is an important theoretical basis for gas injection to enhance the recovery of coalbed methane. In order to further explore the adsorption properties of different gases (CH4/CO2/N-2) on the coal surface, the thermodynamic parameters of adsorption were revealed using a molecular simulation method. The results show that the Langmuir-Freundlich model is more accurate to represent gas adsorption on anthracite coal than the Langmuir model and Freundlich model, which reveal that the gas adsorption on the coal surface is heterogeneous. Also, thermodynamic parameters indicate that gas adsorption on anthracite coal is a thermodynamically spontaneous (Delta G < 0) and exothermic physisorption (0 <Delta H < 10 kcal/mol) process, and the gas molecules tend to be in an ordered state (Delta S > 0). According to adsorption affinity and thermodynamic parameters, the adsorption capacity of these three gases on a coal surface follows the sequence of CO2 > CH4 > N-2. This research can provide foundational knowledge for further interpretation of gas adsorption behavior on a coal surface.