High-softening-point pitches prepared by the Br2 modification of low-temperature coal tar pitch and their mesophase transformation behavior

High-softening-point pitches were prepared from refined low-temperature coal tar pitch (R-CTP) by thermal bromination, followed by dehydrobromination/polymerization. R-CTP was first brominated in the presence of 5-20 wt.% bromine, and then heat-treated at 250-350℃ for dehydrobromination/polymerization. The structures of the dehydrobrominated pitches were characterized by 1H NMR, LDI-TOF/MS and FT-IR. The introduction of bromine significantly facilitated polycondensation of the component molecules and Br2 modification apparently increased the softening point, coking values and molecular weight of the obtained pitches compared with that formed by direct thermal condensation. The dehydrobrominated pitches showed relatively low melt viscosities and shearing-thinning rheological behavior with obvious plateau regions. An optimized dehydrobrominated pitch produced from R-CTP modified with 15 wt.% bromine (BRC-15%) by heat-treatment at 350℃ for 6 h had a softening point of 232℃ and a carbon yield of 55.2 wt.%. Polarized optical microscopy showed that the semicoke produced by the carbonization of BRC-15% at 410℃ appeared to be the most anisotropic with a large domain texture, and XRD patterns indicated that this sample also had the largest crystallite size (Lc=117 A) of all samples examined.