STRUCTURE OF THE PYROBITUMEN OF COAL TAR PITCH
Pyrobitumen species as the side products of oil processing and coal liquefaction are under intense investigation. The data on the structure of macromolecules and on the morphological characteristics of pyrobitumen aggregates were obtained mainly in the area of petrochemical technologies. It is known that the concentration of pyrobitumen in solution and the presence of additives of different chemical nature affect the structure of pyrobitumen associates. The data on the formation of planar pyrobitumen associates and condensed graphite-like structures are of special interest. In connection with the optimization of the graphitization of anode mass, pyrobitumen species of coal tar pitch (β-fraction) were studied previously. Pitch with the high content of fraction proved to be the best efficient binder during the thermal treatment of the anode mass. Structuring processes participated by the macromolecules of pyrobitumen from coal tar pitch have not been studied yet. In the present work, the structural characteristics of the macromolecules of pyrobitumen of the medium-temperature coal tar pitch (CTP) were studied using a complex of physicochemical methods. Pyrobitumen of the fraction of pitch was isolated according to the procedure of selectively soluble groups; toluene and hexane were used as selective solvents. To form pyrobitumen films, 0.01 % solution of pyrobitumen in toluene was chosen. It was demonstrated that the structural fragments of CTP pyrobitumen molecules contain mainly condensed aromatic compounds with 3-7 aromatic rings, while the content of alkyl substituents containing С11 and higher is not determined practically, so the structure of CTP pyrobitumen molecules can be described by Spate's model. According to the XPA data, the coke residue of CTP pyrobitumen is characterized by the presence of crystallites composed of naphthene aromatic layers. These structures are composed of the packs of 7-8 layers, with a size of 20-25 A; they are graphite-like, and the interlayer distance is 3.42 A.