## 1 Introduction  
The coal coking production process produces a large amount of residues, among which coal tar residue is classified as hazardous waste due to the large amount of carcinogenic polycyclic aromatic hydrocarbons (PAHs) [1, 2], which make it a wasted available resource [3]. Although there are many comprehensive utilization methods for tar residue, the lack of in-depth research on the nature of tar residue and the high cost of treatment have prevented the effective treatment and high value-added utilization of tar residue [4].  
Coal tar residue still contains more organic aromatic compounds and fixed carbon. The solvent extraction method uses the \"similar solubility\" principle of the organic components in coal tar residue [5, 6] and the extraction solvent to achieve the separation and recovery of organic components in coal tar residue [7, 8] and improve its utilization rate.  
The extracts are generally determined by gas chromatography-mass spectrometry (GC/MS) [9], Fourier transform infrared spectrometry (FTIR) [10], and pyrolysis gas chromatography-mass spectrometry (PY-GC/MS) [11] techniques to determine their compositional structures. [PERSON] et al. [12] investigated the effect of desabling on the structure of Yimin lignite using FTIR and concluded that the deashing process had a greater effect on the aromatic structure and oxygen-containing functional groups, mainly due to the three effects of substitution, hydrolysis, and ion exchange that occurred during the deashing process. [PERSON] et al. [13] conducted a qualitative and semi-quantitative study of the functional groups of long-flame and anthracite coals based on the FTIR and split-peak fitting techniques. The results showed that the organic matter content of low-degradation coals was less than that of high-degradation coals, and the organic matter maturity of high-degradation coals was higher than that of low-degradation coals. As the degree of coal metamorphism increases, the degree of coal aromatization becomes higher and the degree of coal aromatic ring condensation becomes stronger and more prone to condensation. [PERSON] et al. [14] used acid-washed and Hefeng sub-bituminous coals as research objects, and analysed the molecular structures of the extracted products with the help of FTIR and segmented peak fitting methods. The results showed that the hydroxyl hydrogen bonding structure of all five extraction levels was dominated by self-conjugated hydroxyl hydrogen bonds; CS\({}_{2}\) dissolved a larger proportion of aromatic structures containing fatty side chains in the five extraction levels. The functional groups contained in the extracts were the same at all levels. [PERSON] et al. [15] analyzed the structural characteristics of different chemical components of Yimin lignite using Fourier transform infrared spectroscopy. The results show that humic acid and asphaltene have fewer aromatic rings and are mostly in the form of monocyclic rings, while residual coal has more aromatic rings and is mostly in the form of naphthalene rings; and that humic acid and asphaltene contain a large number of aliphatic hydrocarbons, which are shorter in length and more branched.  
In this paper, single-stage extraction experiments with various solvents were carried out on tar residues using ultrasonic-assisted extraction at room temperature. The extracts and extractive residues were analysed by FTIR detection and segmented peak fitting techniques in order to obtain the structural characteristics of the soluble organic components in the tar residues.