Change in the Molecular Structure of Components of Isotropic Fractions of Petroleum Pitches in the Thermopolycondensation Process

Abstract

The effect of heat-treatment temperature and time on the mesophase formation process in the thermopolycondensation of isotropic petroleum pitch is studied by fluorescence and UV spectroscopy.The molecular structure of the basic components of isotropic petroleum pitch fractions is established. It is shown that UV spectroscopy is ineffective for analysis of multicomponent oil systems, whereas fluorescence spectroscopy allows study of the mechanism of molecular transformations in the mesophase petroleum pitch conversion process.The thorough processing of petroleum entails the effective use of the relatively high-aromatic residual and heavy distillate products. These products are hydrocarbons and heteroatomic compounds, and they are used to make carbon-based materials: carbon fibers, electrocarbon products, metallurgical coke, briquetted coals and cokes, and lacquers. The production of high-modulus carbon fibers (CFs) from anisotropic petroleum pitches also remains an important area of activity.Although technologies for making CFs from petroleum pitch have been introduced on an industrial scale, some very important details of these processes are still not yet understood. This lack of understanding stems from the multicomponent nature of the pitch system and the complexity of the reactions which take place in it during heat treatment. The thermopolycondensation of petroleum residues leads to the formation of a reactive mass of large polycyclic aromatic molecules capable of forming ordered aggregates connected to one another by van der Waals forces; the system subsequently undergoes a phase transformation to the liquid-crystalline state.Without an understanding of the chemical and physico-chemical principles that underlie the complex transformations of the initial compounds into carbon-based materials, it is impossible to control the pyrolytic transformations and develop technologies that are optimum [1][2][3].