Preparation Of Mesophase Pitch From A Purified Coal Tar Pitch

Carbonaceous mesophase refers to the intermediate liquid crystal state to solid semi-coke. The mesophase pitch is composed of multi flat tray shape condensed polymer aromatic hydrocarbon whose molecular weight varies from 370 to 2000. Because of the low cost, high performance and high carbon yield, mesophase pitch has been successfully applied in high modulus carbon fibers, ultra-high power graphite electrodes, materials for energy storage and high specific surface area activated carbon. These high-grade materials play important role in national defense, industry and daily life. Therefore it is cruial to investigate the thermal polymerization and condensation for excellent mesophase pitch.In this paper, mesophase pitch with high anisotropic content and low softening point was prepared from a purified coal tar pitch. The effects of condensation temperature and soaking time on the yield, anisotropic texture, softening point and insoluble content of derived mesophase pitch were investigated by adding anhydrous aluminium trichloride and direct polymerization without catalyst. The carbonization mechanism and the preparation conditions were investigated systematically and the optimum parameters were obtained. The mesophase pitch prepared from the purified coal tar pitch may possibly be the excellent precursor for the production of high performance carbon materials.The results indicated that:Thermal polycondensation without catalyst:The long-flow mesophase pitch with the softening point of 325℃and yield of 77.9% and bad solubility was obtained at the condensation temperature of 435℃for 5h. By heat-treatment at 400℃for 10h, the prepared mesophase pitch containing large domain texture possesses the lower softening point (305℃) and high yield (81.4%).Catalytic polycondensation:In comparison with the mesophase pitch with the soaking time 5h and reaction temperature 345℃, the mesophase pitch with the lower softening point of 292℃and high yield of 82.9% and better solubility was obtained by AlCl3 at the condensation temperature of 330℃for 10h. It is demonstrated that the high grade mesophase pitch was easier prepared under low thermal temperature and heat-treatment by anhydrous aluminium trichloride as the catalyst.Although high-temperature thermal polymerization could greatly shorten the transformation time of mesophase pitch, at high temperature condensation, it could make the reaction hugely intense and the pitch over dehydrogenate and polymerise, which lead to the rapid formation of mesophase pitch with higher softening point and insolubilityAnalysis indicated that the optimum parameters of thermal polymerization are heat-treatment temperature of 330℃, soaking time of 10h using anhydrous aluminium trichloride as catalyst.