Kinetics and mechanism of carbonization of QI free products from gas-coking coal hydrogenation—I: The structure and carbonization behavior of pitches produced by the coal hydrogenation at 420°C AND 455°C

Abstract

The structure and carbonization behavior of the pitches from the products of gas-coking coal hydrogenation performed at 420°C and 455°C in a continuous bench scale unit were estimated. The pitches, prepared as residues from vacuum distillation of purified hydrogenation products, were characterized y elemental analysis, solvent fractionation, IR and 1H NMR spectroscopy. The mesophase formation on isothermal carbonization at 450°C and the optical texture of resultant semicokes were studied by polarized-light optical microscopy. The most pronounced effect of hydrogenation temperature rise was an increase in asphaltene content at the expense of preasphaltenes and a decrease of heteroatom content and reactivity of resultant pitch. This alteration of pitch nature resulted in distinctly different carbonization behavior of both materials. The transformation of the low temperature (420°C) hydrogenation pitch occurred at a high rate leading to the coke of small size optical texture. The high temperature (455°C) hydrogenation pitch produced on carbonization large, easily deformable anisotropic units, and the optical texture of resultant semicoke was comparable to that observed in the cokes from petroleum pitch or QI free coal tar pitch.