# Analysis of the Organic Chemical Fractions of Three Coal Extracts
## 3 Results and Discussion
### Extraction Rate of Three Kinds of Coal Samples  
Solubility parameters are used to measure the ability of an organic solvent to dissolve a solute, but they are not absolutely proportional, and when the optimal solubility parameter is exceeded the dissolution effect may be reduced. Table 4 lists the extraction effect of seven solvents on Pingshuo coal. The total extraction rate of seven solvents on Pingshuo coal is 15.371%, and the extraction rate of each solvent on coal is different. The same solvent dissolves different compounds in the coal with different efficiencies, probably due to the molecular forces between them not being the same. For the Pingshuo coal, the dissolution of CS2, hexane, and acetone is better. CS2 extracted more than 90% of the aromatic hydrocarbons in the coal; n-hexane and CS2 extracted more than 80% of the aliphatic hydrocarbons in the coal; and acetone extracted about 50% of the other compounds in the coal, while the other solvents were generally effective in extracting various compounds. It can be seen from Table 4 above and the following Figure 2 that when the solubility parameter of the solvent is about 9.2, the extraction effect of the solvent on Pingshuo coal is the best, which reaches about 8%; when the solubility parameter is 11.9, the extraction effect of the solvent on Pingshuo coal is the worst, at only 0.2%, which shows that it is not that the higher the solubility parameter is, the better the extraction effect of the solvent on coal. When it is greater than the optimum solubility parameter, the extraction rate will be lower, and it can be seen from the table that for the extraction of Pingshuo coal, between 9 and 10 is better. This shows that the higher the solubility parameter, the better the extraction effect \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Solvent**} & **Extraction Rate/\%** & **Aliphatic** & **Aromatic** & **Content of Other** & **Solubility** \\  & **Rate/\%** & **Hydrocarbon** & **Hydrocarbon** & **Compounds/10\({}^{-4}\) g** & **Parameters/(cal-cm\({}^{-3}\))1/2** \\  & **Content/10\({}^{-4}\) g** & **Content/10\({}^{-4}\) g** & **Content/10\({}^{-4}\) g** & **Content/10\({}^{-4}\) g** & **Content/10\({}^{-4}\) g** \\ \hline CS2 & 2.3159 & 36.33 & 223.28 & 17.56 & 10 \\ n-hexane & 0.3517 & 55.381 & 0 & 1.87 & 7.3 \\ benzene & 0.5333 & 18.922 & 0 & 1.053 & 9.1 \\ methanol & 0.9764 & 0 & 0.2145 & 10.4058 & 14.6 \\ acetone & 2.8124 & 0.36 & 4.524 & 27.224 & 9.9 \\ THF & 8.1693 & 0 & 1.38 & 2.769 & 9.2 \\ methanol/THF & 0.2120 & 0 & 0 & 9.718 & 11.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Extraction rate and extractant composition of Pingshuo coal. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Coal**} & \multicolumn{4}{c}{**Industrial Analysis/W\%**} & \multicolumn{4}{c}{**Elemental Analysis/W\%, daf**} \\ \cline{2-9}  & **M\({}_{\text{ad}}\)** & **A\({}_{\text{ad}}\)** & **V\({}_{\text{daf}}\)** & **FC\({}_{\text{ad}}\)** & **C** & **H** & **N** & **S** & **O\({}^{\star}\)** \\ \hline PS & 2.97 & 18.53 & 29.50 & 49 & 79.77 & 5.60 & 1.41 & 0.63 & 12.59 \\ DT & 2.88 & 16.14 & 23.96 & 57.02 & 82.38 & 4.35 & 0.88 & 2.44 & 9.95 \\ GT & 0.29 & 10.33 & 31.14 & 58.24 & 81.99 & 5.46 & 1.62 & 0.42 & 10.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Industrial and elemental analyses of three coal samples. of the solvent on coal. When the optimal solubility parameter is exceeded, the extraction rate will become lower. As can be seen from the table, for the extraction of Pingshuo coal, a solubility parameter between 9 and 10 has better extraction effects. Table 5 lists the extraction effects of seven solvents on Datong coal. The total extraction rate of the seven solvents from Datong coal is 9.4428%. For Datong coal, the extraction effects of CS\({}_{2}\), n-hexane, and acetone are also better for the coal samples.