Properties of coal tar characterized by slight pyrolysis

The behavior of coal tars with different levels of pyrolysis in thermal fractionation is compared in the laboratory. The properties and group composition of the nonboiling residues (medium-temperature pitch) obtained by the distillation of coal tars at different temperatures, in comparable conditions, is investigated. The results indicate that the distillation of tars characterized by slight pyrolysis is accompanied by vigorous destruction processes, also affecting the α₁ fraction (t = 335–350°C), with subsequent reactions among the destruction products, leading to active increase in the α₁ and α₂ fractions (t ≥ 350°C). This is a significant difference between tars characterized by light pyrolysis and considerable pyrolysis.