Methane Adsorption Characteristics and Adsorption Model Applicability of Tectonically Deformed Coals in the Huaibei Coalfield

Based on methane isothermal adsorption experiments, the supercritical methane adsorption characteristics of middle-rank tectonically deformed coals (TDCs) screened from the Huaibei coalfield were analyzed. The applicability of different adsorption models to different kinds of TDCs was discussed using the standard deviation method, and the mechanism of methane adsorption in TDCs was explored. The following results were obtained. First, the experimental maximum adsorption capacity of TDCs increases gradually with enhanced tectonic deformation, and the experimental maximum adsorption capacity of ductile TDCs is significantly higher than those of primary coal and brittle TDCs. The adsorption potential of TDCs gradually decreases with increasing adsorption space, and the adsorption potential of ductile TDCs is generally higher than those of primary coal and brittle TDCs. Second, for the applicability of adsorption models to TDCs, the highly applicable models of primary, cataclastic, and scaly coals are the Toth, Langmuir–Freundlich, and Dubinin–Astakhov models; the highly applicable models of schistose coals are the Langmuir, Toth, Langmuir–Freundlich, three-parameter Brunauer–Emmett–Teller, Dubinin–Radushkevich, and Dubinin–Astakhov models; the highly applicable models of wrinkle coals are the Toth, Langmuir–Freundlich, Dubinin–Radushkevich, and Dubinin–Astakhov models; and the highly applicable models of mylonitic coals are the Langmuir, Toth, Langmuir–Freundlich, expand-Langmuir, three-parameter Brunauer–Emmett–Teller, and Dubinin–Astakhov models. Third, the three-parameter Brunauer–Emmett–Teller model is suitable to study the adsorption state of TDCs. As the deformation degree increases, the adsorption state of TDCs transforms from monolayer unsaturated adsorption to multilayer adsorption. TDCs have larger adsorption potential and adsorption space with the enhancement of tectonic deformation, which increases the number of adsorption layers on the coal surface.