Production of Isotropic Coke from Shale: Microstructure of Coke from the Thermally Oxidized Distillation Residue of Shale Tar

Abstract

Attention focuses on how the thermal oxidation of hydrocarbon mixtures by air injection at elevated temperatures affects the microstructure of the isotropic coke formed on subsequent carbonization. Specifically, the residue from the atmospheric distillation of shale tar is considered; this hydrocarbon mixture serves as the industrial raw material for the production of isotropic coke. In thermal oxidation at high (350°C) and low (250°C) temperatures, samples are taken for fractionation and coking. In the course of thermal oxidation, the γ fraction of the distillation residue is converted to the α + β fraction. The means size of the structural elements in the coke from the thermally oxidized distillation residue declines. However, for coke produced from the γ and α + β fractions, the opposite changes are observed: decrease in mean size for the α + β fraction, and increase for the γ fraction. For the high-temperature samples, this difference is more pronounced. Thus, the formation of isotropic coke microstructure is due to the conversion of the γ fraction to the α + β fraction and also to the changes in properties of the fractions associated with the thermal-oxidation temperature. In this paper the next denotations are made: isooctane-soluble fraction is denoted as γ fraction, isooctane-insoluble-toluene-soluble is denoted as β fraction, toluene-insoluble-quinoline-soluble is denoted as α fraction, the fraction insoluble in quinoline, pyridine and carbon disulfide is denoted as α-1 fraction. Note that in the domestic literature, the designations of the pitch factions were adopted which differ from the designations used in the English-language literature.