The composition and structure of n-hexane insoluble-hot benzene soluble fraction and hot benzene insoluble fraction from low temperature coal tar

Abstract The composition and structure analysis of coal tar is a very important basic issue. In the process of preparing asphaltenes (insoluble in C5-C7 n-alkanes but soluble in hot benzene, HIBS) according to the definition, it was found that hot benzene insoluble (HIBI) components still exist in the coal tar. It is necessary to carry out in-depth analysis and identification of their compositions and structures, in order to obtain detailed information, which provides a certain guiding significance for the deep processing of coal tar. Their compositions and structures were studied by means of physical and thermo-chemical analysis, including Fourier transform infrared spectroscopy (FTIR), Uv-fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), 1H magic angle spinning nuclear magnetic resonance spectroscopy (1H-MAS-NMR), 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR), thermogravimetric analysis (TG) and pyrolysis gas chromatography-mass spectroscopy (PY-GC/MS). The results show that: HIBS and HIBI are mainly composed of aromatic compounds, phenolic compounds and heteroatomic compounds, but the forms of these compounds are different. The ring number of the aromatic structure in HIBI is larger than that in HIBS. The main bonding ways of oxygen in HIBS and HIBI include C O, C–O, C–OH, C–O–C and COO–, but the peak positions of those functional groups are slightly offset. There are more COO– in the structure of the latter. Compared with HIBS, HIBI contains more carboxyl hydrogen and more oxygen-bonded hydrogen, thus inferring that HIBI contains more oxygenated compounds. In addition, HIBI has more shorter alkyl side chains.