Xiangsheng Wang

Pyrolysis mechanism of pitch for carbon fiber using tritium tracer method

Abstract Tritium has been introduced into three coal tar pitches and a naphthalene pitch by two methods, one by isotope exchange with tritiated water using Pt/Al 2 O 3 catalyst, and the other by hydrogenation with tritiated gaseous hydrogen using Ni-Mo/Al 2 O 3 catalyst. The tritium-labelled pitches were carbonized up to 1000°C under nitrogen atmosphere. The release behaviors of hydrogen and tritium during the carbonization of tritiated pitches were investigated by comparing the rates of dehydrogenation and detritiation. The results indicate that the hydrogen introduced into the pitch by the isotope exchange is released more rapidly than the original hydrogen in the pitch while the hydrogen introduced into the pitch by the isotope addition is slightly more difficult to release relative to the original hydrogen in the pitch during the pyrolysis of the pitch. Moreover, it was clarified that the extent of development of optically anisotropic texture of the pitch is related not to the hydrogen exchange ratio but to the rate of hydrogen release during pyrolysis.

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.