## 2 Specimens and Experimental Methods
### Experimental  
#### 2.2.1 Adsorption Experiments  
The coal specimens were ground, and the particle size was in the range of 180-250 \(\mu\)m (60-80 mesh). About 100 g for each coal specimen were weighed to put into a thermostat with supersaturated K\({}_{2}\)SO\({}_{4}\) solution for 48 h, in order to make coal specimens containing equilibrium moisture. Then, the isotherm adsorption experiments on the coal specimens were carried out by an ISO-300 isotherm adsorption instrument with the temperature of 35 \({}^{\circ}\)C and pressure varying from 0 to 7 MPa. The experimental principle is shown in Figure 3.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimen No.** & **Tectonic Coal** & **Deformation** & **Deformation** & **Macro Characteristics** & **Micro Characteristics** \\  & **Type** & **Degree** & **Series** & & \\ \hline \multirow{4}{*}{S1} & \multirow{4}{*}{Undeformed coal} & \multirow{4}{*}{No or weak deformation} & Complete coal body structure, well preserved primary band structure, and easily distinguished petrographic constituent (Figure 2a) & & \\  & & & Damaged structure, while visible primary banded structure, and developed fractures (Figure 2c) & A set of structural fractures developed (Figure 2d) & fractures developed \\  & & & & Completely destroyed primary & Extremely developed \\  & & & & structure; broken coal body with the particle size ranging from millimeter to centimeter scale & micro fractures, difficult \\  & & & & (Figure 2e) & (Figure 2f) \\ \hline \multirow{4}{*}{S4} & \multirow{4}{*}{Crumple coal} & \multirow{4}{*}{Strong deformation} & Disappeared primary structure of the coal body, presence of irregular arc or twisting shapes, similar to fold shape, and abnormally developed fractures (Figure 2h) & & \\  & & & & (Figure 2g) & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Macro and micro deformation characteristics of coal specimens.  
Figure 2: Macro and micro photos of coal specimens. (**a**) Undeformed coal (macroscope); (**b**) undeformed coal (microscope); (**c**) cataclastic coal (macroscope); (**d**) cataclastic coal (microscope); (**e**) granulitic coal (macroscope); (**f**) granulitic coal (microscope); (**g**) crumple coal (macroscope); (**h**) crumple coal (microscope).  
Therefore, the adsorption capacity can be calculated by  
\[V_{i}=22.4\times 10^{3}\frac{\eta_{i}^{ex}}{m} \tag{4}\]  
where \(\Delta\eta_{i}^{ex}\) is the adsorption increment after the \(i\)th adsorption equilibrium (mol); \(V_{i}\) is the adsorption capacity after the \(i\)th adsorption equilibrium (cm\({}^{3}\cdot\)g\({}^{-1}\)); \(m\) is the mass of coal specimen (g); \(T\) is the experimental temperature (K); \(R\) is universal constant (\(R\) = 8.314); \(V_{s}\) is the free space volume of the experimental tank (cm\({}^{3}\)); \(V_{r}\) is the free space volume of the reference tank (cm\({}^{3}\)); \(P_{i-1}\) is the gas pressure in the experimental tank (MPa); \(P_{i1}\) is the gas pressure in the reference tank before the \(i\)th adsorption (MPa); \(P_{i2}\) is the gas pressure in the experimental tank after the \(i\)th adsorption equilibrium (MPa); \(P_{i3}\) is the gas pressure in the reference tank after the \(i\)th adsorption equilibrium (MPa); and \(Z_{i-1}\), \(Z_{i1}\), \(Z_{i2}\), and \(Z_{i3}\) are compression factors corresponding to the pressures of \(P_{i-1}\), \(P_{i1}\), \(P_{i2}\), and \(P_{i3}\), respectively.