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.
