Estimation of hydrogen mobility of coal tar pitch for carbon fiber using a tritium tracer method

Abstract

Three coal tar pitches for high performance carbon fiber (HPCF) and general performance carbon fiber (GPCF) were hydrogenated by tritium labelled gaseous hydrogen in the absence of both catalyst and vehicle solvent under conditions of temperature 300–400°C, nominal reaction time 0–300 min and initial hydrogen pressure 5.9 MPa. The relative rate constants and apparent activation energies for hydrogen transfer from gas phase to the pitches have been estimated by tracing tritium. The apparent activation energies for hydrogen addition from the gas phase to the three pitches were very close (ca. 9–10 kcal/mol), but apparent activation energies for hydrogen exchange between the gas phase and the three pitches were different from each other (HP, 15.4; GP-A, 2.9; GP-B, 3.7 kcal/mol). Especially, apparent activation energy of hydrogen exchange of the raw pitch for HPCF was significantly larger than those of the raw pitches for GPCF. These results of kinetic parameters for hydrogen transfer can be used to evaluate the distribution and mobility of hydrogens in component molecules of pitches.