## 3 Results and Discussion
### Infrared Spectral Split Peak Fitting of Coal Tar Residue and Extractives
#### 3.4.5 Analysis of Structural Parameters of Tar Residues and Extractives  
In addition to the two structural parameters DOC and CH\({}_{2}\)/CH\({}_{3}\), two other structural parameters were used to further characterise the structure of the tar pomace and extractive residues, and the results of the calculated data are shown in Table 11.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Peak \#**} & \multirow{2}{*}{**Position \(\sigma\) (cm\({}^{-1}\))**} & \multirow{2}{*}{**Assignment**} & \multicolumn{4}{c}{**Area Percentage (\%)**} \\ \cline{4-5}  & & & **E** & **ACE** & **CS\({}_{2}\)** & **ACE/CS\({}_{2}\)** \\ \hline
1 & 3600\(-\)3500 & OH -\(\pi\) & 24.55 & 10.89 & 8.38 & 9.25 \\
2 & 3500\(-\)3350 & Self-associated OH & 52.16 & 54.01 & 62.08 & 63.00 \\
3 & 3300\(-\)3150 & Ring hydroxy & 20.84 & 32.16 & 28.98 & 27.75 \\
4 & 3150–3000 & OH-N & 2.44 & 2.95 & 0.56 & 0 \\ \hline \end{tabular}
\end{table}
Table 10: Infrared spectra of four samples 3000–3600 cm\({}^{-1}\) split peak fitting ratio of each absorption peak area.  
Figure 10: Infrared spectra of the original and extractive residues in the 3000–3600 cm\({}^{-1}\) region. (**(a)** is an original tar residue fit, (**b**) is a fit to carbon disulphide, (**c**) is a fit to acetone and (**d**) is a fit to a mixed solvent. The red line is the fit line and the blue line is the sub peak).  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**DOC**} & \multirow{2}{*}{**A(CH\({}_{2}\))/A(CH\({}_{3}\))**} & \multirow{2}{*}{**AR**} & \multirow{2}{*}{**A**} \\ \hline E & 0.87 & 2.54 & 2.11 & 0.33 \\ ACE & 1.80 & 5.05 & 1.09 & 0.21 \\ CS\({}_{2}\) & 0.42 & 3.56 & 1.28 & 0.25 \\ ACE/CS\({}_{2}\) & 0.40 & 1.69 & 0.84 & 0.32 \\ \hline \end{tabular}
\end{table}
Table 11: Structural parameters of coal tar residue and its three extractive residues.  
The aromaticity (AR) is the aromatic C-H bending vibration/fatty C-H, which can be used to determine the degree of aromatisation:  
\[\text{AR}=\text{A}_{700-900}/\text{A}_{2800-3000}, \tag{3}\]  
The A-factor, commonly used to assess the hydrocarbon potential and maturity of cheese roots, is higher for greater A, and lower for greater maturity.  
\[\text{A}=\text{A}_{2800-3000}/(\text{A}_{1490-1600}+\text{A}_{2800-3000}), \tag{4}\]  
Table 11 shows that the aromaticity of the three solvent extracts was less than that of the original tar residue, indicating that the degree of aromatisation was lower than that of the tar residue. The highest A value for tar residue was 0.33, proving that it was the least mature, and the higher CH\({}_{2}\)/CH\({}_{3}\) value indicates the length and branching of the fat side chains in the sample. A comparison of \(\text{A}(\text{CH}_{2})/\text{A}(\text{CH}_{3})\) showed that the acetone extracts had the longest fat chains and the least branched chains. A larger DOC for the acetone residue indicates a higher degree of aromatic ring condensation and the presence of more aromatic hydrocarbons with a large number of aromatic rings, whereas the DOC value for the acetone/CS\({}_{2}\) mixture residue is smaller.