## 2 Coal Samples and Experiments  
### Samples Selection and Basic Coal Analyses  
The twelve block coal samples with different coal ranks (0.46% to 2.79% R\({}_{0,m}\)) were obtained from the active mining areas of the eastern Junggar Basin, eastern Ordos basin and southern Qinshui basin (Table 1). There were four low-rank coals (HDG 6#, BLG 6#, HYC 4#, LHJ 4#), four medium-rank coals (LL-HJG 5#, LL-DP 10#, LL-SL 5#, LL-XM 5#) and four high-rank coals (TY-DY 6#, GJ-DQ 4#, YQ-WK 15#, YQ-YK 15#). The basic coal analysis includes petrographic, proximate analyses and the maximum vitrinite reflectance (R\({}_{0,m}\)) of the coal samples were conducted. The maceral compositions (500 testing points) were acquired by using a Laborlxe 12 POL microscope with the MPS 60 photo system on polished surfaces. In addition, the proximate analysis was operated using a GF-6000 full-automatic proximate analyzer manufactured by Preiser Scientific, USA, with a particle size of \(<\)0.2 mm based on the ISO 17246-2010 test standard as previous research.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample No.**} & \multirow{2}{*}{**R\({}_{\text{a,m}}\) (\%)**} & \multirow{2}{*}{**Coal Rank**} & \multirow{2}{*}{**Porosity (\%)**} & \multirow{2}{*}{**\(d_{a}\) (nm)**} & \multicolumn{4}{c}{**Proximate Analysis (\%)**} & \multicolumn{4}{c}{**Petrographic Analysis (\%)**} \\ \cline{5-10}  & & & & \(\mathbf{M_{\text{add}}}\) & \(\mathbf{A_{\text{add}}}\) & \(\mathbf{V_{\text{add}}}\) & \(\mathbf{FC_{\text{add}}}\) & **V** & **I** & **E** & **M** \\ \hline HDC 66 & 0.68 & high volatile bituminous & 14.7 & 13.80 & 6.38 & 11.30 & 3.50 & 67.30 & 72.30 & 11.00 & 16.20 & 0.50 \\ BLG 68 & 0.68 & high volatile bituminous & 6.4 & 8.70 & 8.63 & 5.38 & 4.10 & 68.06 & 69.90 & 18.30 & 11.60 & 0.20 \\ HYC 49 & 0.65 & high volatile bituminous & 12.3 & 10.60 & 5.78 & 15.82 & 3.94 & 62.20 & 78.00 & 12.20 & 7.00 & 2.80 \\ LHJ 49 & 0.46 & Ligiting & 6.15 & 7.10 & 6.46 & 6.09 & 39.11 & 48.34 & 78.80 & 5.40 & 12.10 & 3.80 \\ LLJ-C1G 5.5 & 1.34 & Medium volatile bituminous & 8.55 & 10.62 & 0.74 & 10.27 & 27.94 & 61.05 & 60.68 & 25.02 & 0 & 14.3 \\ LL-D10 10 & 1.68 & low-volatile bituminous & 8.87 & 10.25 & 0.63 & 11.10 & 21.30 & 66.97 & 59.69 & 34.61 & 0 & 5.70 \\ LL-SL 54 & 1.19 & Medium volatile bituminous & 10.83 & 26.12 & 0.71 & 12.04 & 26.77 & 60.48 & 57.81 & 32.19 & 2.50 & 7.50 \\ LL-V-C49 & 1.44 & Medium volatile bituminous & 12.16 & 10.53 & 0.57 & 9.90 & 26.80 & 62.73 & 40.03 & 56.67 & 0 & 3.30 \\ T-D7 62 & 2.56 & semi-anthracite coal & 8.55 & 11.32 & 0.62 & 38.08 & 35.94 & 25.36 & 49.51 & 7.99 & 0 & 42.50 \\ GJ-D04 48 & 2.05 & semi-anthracite coal & 13.59 & 12.53 & 0.71 & 11.57 & 48.97 & 38.75 & 76.97 & 16.33 & 0 & 6.70 \\ YQQ-V15 24 & 2.54 & semi-anthracite coal & 11.36 & 15.22 & 1.43 & 11.06 & 12.46 & 75.05 & 77.98 & 15.52 & 0 & 6.50 \\ YQ-YQ-Y15 27 & 2.79 & anthracrade coal & 18.12 & 24.60 & 1.20 & 13.30 & 12.49 & 73.01 & 83.55 & 12.15 & 0 & 4.30 \\ \hline \hline \end{tabular} Note: \(d_{a}\) = average pore size; \(\text{M}_{\text{add}}\) = Moisture content (wt %, air dry basis); \(\text{A}_{\text{add}}\) = Ash yield (wt %, air dry basis); \(\text{V}_{\text{add}}\) = Volatile matter (wt %, air dry basis). FCd = Fixed carbon (wt %, air dry basis). V = Vitrinello 1= inerrilite; E = evinlier; M = minerals.  
\end{table}
Table 1: Results of the MIP, petrographic and proximate analysis of the coal samples.