FTIR Analysis of the Functional Group Composition of Coal Tar Residue Extracts and Extractive Residues

The extracts and extractive residues were obtained by single-stage extraction with acetone, CS2 and acetone/carbon disulphide solvent (IACDSM) under mild conditions, and they were then characterised by infrared and segmented peak fitting analysis. The results showed that acetone and CS2 solvents could dissolve more aromatic structures containing fatty side chains, while the mixed solvents could extract more phenolic substances. The acetone extracts were mainly asymmetric -CH2 stretching vibrations, while the remaining two extracts were dominated by aliphatic -CH. A comparison of the IR results of the tar residue and the three solvent extracts showed that the main structure of the tar residue was not altered throughout the process, but the aromatic structure was altered more by the extraction. Compared to the original sample, the proportion of tetrasubstituted or trisubstituted benzene rings in the three solvent extracts increased, while the proportion of pentasubstituted benzene rings produced a significant decrease. Comparison of the IR structural parameters showed that the aromatic ring condensation was higher in the as-received CS2 extracts and acetone extracts, with the acetone extracts having longer straight aliphatic chains and fewer branched chains. The analysis of the composition of the extraction results provides a reference basis for the separation and purification technology of coal tar residue, enabling the further development of China’s coal chemical industry.