Preparation Of Spinnable Mesophase Pitch From Petroleum Residue

Mesophase pitch, which contains a significant amount of liquid crystals, is formed in petroleum residue, coal-tar, or pure aromatic hydrocarbons during pyrolysis at heat treatment process. Mesophase pitch, with unique physical and chemical properties due to its lamellar structure of oriented polycondensed aromatic hydrocarbons, has been claimed to be excellent raw material for many high performance carbon materials. Mesophase pitch has been widely used in aerospace, military industry, new energy storage devices, transportation, civil construction and other fields. The object of this paper is to study preparation of mesophase pitches from pressure-vacuum two-stage thermal polycondensation of petroleum residue with different process, and study structure and performances of the product. The research also effects on the application of spinnable mesophase pitch prepared by different method for high performance carbon fibers and graphite fibers. And the effect of the spinning conditions and stabilization conditions on the mechanical properties of carbon fibers and graphite fibers was studied. The contents are summarized as follows. (1) Mesophase pitch MP-1with softening point of272℃, anisotropic content of95%and good spinnability, was prepared by direct pressure-vacuum two-stage thermal polycondensation from petroleum residue. Mesophase pitch MP-2, MP-3and MP-4was prepared by pressure-vacuum two-stage thermal polycondensation from toluene-treated petroleum residue. MP-2with softening point of270℃, anisotropic content of90%and good spinnability, was prepared using the same thermal polycondensation conditions as MP-1. With better spinnability, MP-1and MP-2can be used as raw materials for preparation of mesophase pitch based carbon fibers and graphite fibers.(2) According to the FT-IR analysis, the structure of mesophase pitches prepared from petroleum residue is mainly the polycyclic aromatic composition with methyl and methylene side chain structure. And the composition function groups of MP-1are the same with MP-2.(3) Mesophase pitch MP-1and Mesophase pitch MP-2, after melt spinning, stabilization, carbonization and graphitization, turned into the mesophase pitch-based carbon fibers and graphite fibers. The effect of spinning conditions and stabilization conditions on mesophase pitch-based carbon fibers and graphite fibers’ mechanical properties were studied, and the optimal spinning conditions and the optimal stabilization conditions of MP-1and MP-2were found. Treated at these conditions, the mesophase pitch-based carbon fibers got the best mechanical properties with tensile strength2.20GPa, tensile modulus158GPa. And the mesophase pitch-based graphite fibers’ tensile strength is2.68GPa, tensile modulus is496GPa.(4) The composition and structure of mesophase pitch fibers in different processes were studied by FT-IR and XRD analysis. The FT-IR spectrums shows that, as stabilization, carbonization and graphitization processing, the molecular structure of mesophase pitches is becoming more and more structured. According to the XRD analysis, as stabilization, carbonization, graphitization processing, the average accumulation thickness of microcrystallines of mesophase pitch fibers continuously decreased, while the graphitization degree increased, and stabilization treatment has little effect on the fibers’interlayer spacing, while carbonization, graphitization treatments can significantly reduce the fibers’ interlayer spacing.(5) The electrical resistivity of carbon fibers and graphite fibers which were prepared by MP-1and MP-2were tested and analyzed. The results show that graphitization treatment can significantly reduce the fibers’electrical resistivity, thereby enhanced their electrical conductivity, and the electrical conductivity of MP-2carbon fibers and graphite fibers are better than the MP-1carbon fibers and graphite fibers, and this also shows that the MP-1’s praperation is better than the MP-2’s.